Comprehensive Organic Functional Group Transformations, Volume 6 Elsevier, 2003 Editors-in-Chief: Alan R. Katritzky, Oth...
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Comprehensive Organic Functional Group Transformations, Volume 6 Elsevier, 2003 Editors-in-Chief: Alan R. Katritzky, Otho Meth-Cohn, and Charles W. Rees
Synthesis: Carbon with Three or Four Attached Heteroatoms Part I: Tetracoordinated Carbon with Three Attached Heteroatoms, RCXX′X″ 6.01 Trihalides, Pages 1-33, Richard D. Chambers and John Hutchinson 6.02 Functions Containing Halogens and Any Other Elements, Pages 35-66, Graham B. Jones and Jude E. Matthews 6.03 Functions Containing Three Chalcogens (and No Halogens), Pages 67-102, Glynn Mitchell 6.04 Functions Containing a Chalcogen and Any Other Heteroatoms Other Than a Halogen, Pages 103-136, Martin J. Rice 6.05 Functions Containing at Least One Group 15 Element (and No Halogen or Chalcogen), Pages 137-170, David P. J. Pearson 6.06 Functions Containing at Least One Metalloid (Si, Ge, or B) and No Halogen, Chalcogen or Group 15 Element; Also Functions Containing Three Metals, Pages 171-210, Vadim D. Romanenko, Michel Sanchez and Jean-Marc Sotiropoulos Part II: Tetracoordinated Carbon with Four Attached Heteroatoms, CXX′X″X‴ 6.07 Functions Containing Four Halogens or Three Halogens and One Other Heteroatom Substituent, Pages 211-247, Alex H. Gouliaev and Alexander Senning 6.08 Functions Containing Two Halogens and Two Other Heteroatom Substituents, Pages 249-270, Anastassios Varvoglis
by kmno4
6.09 Functions Containing One Halogen and Three Other Heteroatom Substituents, Pages 271-293, Angela Marinetti and Philippe Savignac 6.10 Functions Containing Four or Three Chalcogens (and No Halogens), Pages 295-318, Alex H. Gouliaev and Alexander Senning 6.11 Functions Containing Two or One Chalcogens (and No Halogens), Pages 319-358, Wolfgang Petz and Frank Weller 6.12 Functions Containing at Least One Group 15 Element (and No Halogen or Chalcogen), Pages 359-375, Duncan Carmichael, Angela Marinetti and Philippe Savignac 6.13 Functions Containing at Least One Metalloid (Si, Ge or B) and No Halogen, Chalcogen or Group 15 Element; Also Functions Containing Four Metals, Pages 377-406, Paul D. Lickiss Part III: Tricoordinated Carbon with Three Attached Heteroatoms, Y=CXX′ 6.14 Functions Containing a Carbonyl Group and at Least One Halogen, Pages 407-457, Geoffrey E. Gymer and Subramaniyan Narayanaswami 6.15 Functions Containing a Carbonyl Group and at Least One Chalcogen (but No Halogen), Pages 459-498, Heiner Eckert and Alfons Nestl 6.16 Functions Containing a Carbonyl Group and Two Heteroatoms Other Than a Halogen or Chalcogen, Pages 499-526, Anthony F. Hegarty and Leo J. Drennan 6.17 Functions Containing a Thiocarbonyl Group and at Least One Halogen; Also at Least One Chalcogen and No Halogen, Pages 527-567, Erich Kleinpeter and Kalevi Pihlaja 6.18 Functions Containing a Thiocarbonyl Group Bearing Two Heteroatoms Other Than a Halogen or Chalcogen, Pages 569-585, José Barluenga, Eduardo Rubio and Miguel Tomás 6.19 Functions Containing a Selenocarbonyl or Tellurocarbonyl Group—SeC(X)X′ and TeC(X)X′, Pages 587-599, Frank S. Guziec and Lynn J. Guziec 6.20 Functions Containing an Iminocarbonyl Group and at Least One Halogen; Also One Chalcogen and No Halogen, Pages 601-637, Thomas L. Gilchrist 6.21 Functions Containing an Iminocarbonyl Group and Any Elements Other Than a Halogen or Chalcogen, Pages 639-675, Ian A. Cliffe 6.22 Functions Containing Doubly Bonded P, As, Sb, Bi, Si, Ge, B or a Metal, Pages 677-724, Vadim D. Romanenko, Michel Sanchez and Lydia Lamandé Part IV: Tricoordinated Stabilized Cations and Radicals, +CXYZ and ·CXYZ 6.23 Tricoordinated Stabilized Cations and Radicals, +CXYZ and ·CXYZ, Pages 725-734, Thomas L. Gilchrist 6.24 References to Volume 6, Pages 735-844
by kmno4
6.01 Trihalides RICHARD D. CHAMBERS University of Durham, UK and JOHN HUTCHINSON BNFL Fluorochemicals Ltd., Durham, UK 5[90[0 GENERAL METHODS
0
5[90[0[0 The Addition of Halo`ens and Interhalo`en Compounds to Fluoroalkenes 5[90[0[1 The Addition of Haloalkanes to Haloalkenes 5[90[0[1[0 Lewis acid!catalysed addition of trihalomethyl cations to haloalkenes*the Prins reaction 5[90[0[1[1 Additions initiated by free radicals\ heat or radiation 5[90[0[1[2 Additions catalysed by salts and complexes of transition metals 5[90[0[1[3 Additions induced electrochemically 5[90[0[2 The Preparation of C1 Chloro~uorohydrocarbons
1 3 3 3 5 6 6
5[90[1 TRIFLUOROMETHYL DERIVATIVES*RCF2 5[90[1[0 General 5[90[1[1 Aryl Derivatives 5[90[1[1[0 Conversion of `roups attached to an aromatic rin` into the tri~uoromethyl `roup 5[90[1[1[1 Substitution by tri~uoromethyl radicals 5[90[1[1[2 Substitution of hydro`en by the tri~uoromethyl `roup actin` as an electrophile 5[90[1[1[3 Substitution of halo`ens by the tri~uoromethyl `roup actin` as a nucleophile 5[90[1[1[4 Substitution of halo`ens by the tri~uoromethyl `roup usin` derivatives of metals 5[90[1[2 Derivatives of Alkanes\ Alkenes\ Alkynes and Other Saturated Compounds 5[90[1[2[0 Halo`en exchan`e 5[90[1[2[1 Conversions of other `roups to the tri~uoromethyl `roup 5[90[1[2[2 Transfer of tri~uoromethyl `roups as radicals 5[90[1[2[3 Reactions involvin` tri~uoromethyl derivatives of metals and metalloids
8 8 8 8 00 01 02 03 05 05 08 19 11
5[90[2 TRICHLOROMETHYL DERIVATIVES*RCCl2 5[90[2[0 Trichloromethyl Groups Attached to an Aliphatic Centre 5[90[2[0[0 Conversion of `roups attached to an aliphatic centre into the trichloromethyl `roup 5[90[2[0[1 Transfer of the trichloromethyl `roup to an aliphatic centre 5[90[2[1 Trichloromethyl Groups Attached to an Aromatic Rin` 5[90[2[1[0 Conversion of `roups attached to an aromatic rin` into the trichloromethyl `roup 5[90[2[1[1 Transfer of the trichloromethyl `roup to an aromatic rin`
12 12 12 12 16 17 18
5[90[3 TRIBROMOMETHYL DERIVATIVES*RBr2
20
5[90[4 MIXED SYSTEMS WITH FLUORINE*RCF1Hal
21
5[90[5 MIXED HALOFORMS*CHXY1 AND CHXYZ
21
5[90[0 GENERAL METHODS There are several general methods which can lead to trihalomethyl compounds where the halogen atoms can be the same or di}erent[ It will be seen that some of these methods lead to compounds 0
1
Trihalides
in which there are two such trihalomethyl groups[ For simplicity\ the general methods are discussed _rst[
5[90[0[0 The Addition of Halogens and Interhalogen Compounds to Fluoroalkenes The addition of halogens and interhalogen compounds to ~uoroalkenes a}ords a valuable method for the preparation of compounds containing the group 0CHal2 where the halogen atoms may be the same or di}erent[ The addition of halogens is conveniently carried out under ultraviolet irradiation "Equations "0# and "1## ð30JA2365\ 57JOC0905Ł\ but the addition of iodine to tetra~uoroethene occurs only at elevated temperatures "Equation "2## ð38JCS1837\ 38JOC636\ 42JCS0437\ 52USP2965930Ł[ Generally the yields of the adducts are high\ but when 0\0!di~uoroethene is treated with iodine a mixture of compounds is obtained\ the most abundant of which is CF2CH1I "Equation "3## ð47JOC211Ł[ F3C
Cl
F
Cl
F3C F Cl
Cl2, UV
Cl Cl Cl
OH
OH F
RF F F F
(1)
F
RF
Br2, UV
F Br
F F
i, ii or iii
F
F
I
I
F
F
(2)
F Br
(3)
F
i, I2, Et2O, 60 °C, 15 h; ii, I2, 150 °C, 24 h; iii, I2, KI, H2O, 100 °C, 5 h F
I2, 185 °C, 16 h
F
F
I
+ F
F
F
F
F
I
+
F
(4) F
F
F
I
+
The addition of the interhalogen compounds ICl and IBr to ~uoroalkenes also can be used to give compounds having the group 0CHal2[ With asymmetric alkenes\ the addition is regioselective\ but the precise composition of the product is in~uenced by the reaction conditions and the presence of catalysts[ The reactions shown in Equations "4#Ð"8# were carried out by several workers and thus under di}erent sets of conditions ð41JCS3312\ 43JCS812\ 50JCS2668\ 50JA1384\ 51JOC0371\ 53JOC141Ł^ the yields and\ where more than one isomer was obtained\ isomer ratios were correspondingly di}erent[ F
F
+ ICl F
Cl
F
F
+ ICl
F
Cl Cl
F
F
F
Cl
F
F
F F
F
F
Br Cl
I
+ IBr
I
Cl
+ IBr F
F
F
Cl
I
F
F
F
I
F
Cl
F
Cl
F
F
F
Cl
Cl
+
(5)
(6)
Cl
+
F
F
F Cl
Cl Cl Cl Cl
F
Cl
+
+ F
+ ICl
F
F
I
F F
F I
Br
I
(7)
I
(8)
I (9)
Br F
The elements bromine and ~uorine\ or iodine and ~uorine\ can be added to ~uoroalkenes by treating the alkene with a mixture of bromine tri~uoride and bromine\ or iodine penta~uoride and iodine "Equations "09#Ð"11##[ Here\ {IF| refers to a stoichiometric mixture of iodine penta~uoride
2
General Methods
and iodine "IF4 ¦1I1 04{IF|#\ and {BrF| to a stoichiometric mixture of bromine tri~uoride and bromine "BrF2 ¦Br1 02{BrF|#[ While the addition of {BrF| to ~uoroalkenes is vigorous and needs to be moderated\ the corresponding reactions of {IF| are carried out at elevated temperatures ð50JCS2668Ł\ and catalysts may be added ð50JA1272\ 73JAP4840114Ł[ The addition of {IF| to tetra! ~uoroethene is particularly important because the product\ penta~uoroiodoethane\ is a starting material in one of the commercial routes to ~uorochemical surfactants and surface treatments ðB! 68MI 590!90Ł[ Additions to hexa~uoropropene and 0\0!di~uoroethene give single isomers\ but additions to chlorotri~uoroethene and 0\0!dichlorodi~uoroethene yield mixtures of isomers whose composition is related to the reaction conditions[ The reaction of {IF| to tetrachloroethene results in ~uorination only "Equation "07##[ For the addition of {IF| to internal alkenes with the formula CF2"CF1#nCF1C"CF2#1\ special procedures are necessary "Equation "11##[ Either potassium ~uoride must be added to the {IF| mixture\ or the alkene may _rst be treated with AgF or AgF:KF in a polar aprotic solvent to make the silver salt\ which in turn is treated with iodine to give the desired product ð76JFC"26#112Ł[ These products are tertiary per~uoroiodoalkanes and are highly toxic\ so special care must be taken during their preparation[ F
F
+ 'IF' F
F
F 3C
+ 'IF'
F
F F
F
+ 'IF' F
Cl
F
Cl
F
F
Cl
F
Cl
Cl
F
Cl
F
F
F Cl
F
Cl
F
I
F
F
F
I
F
I
(14)
(15)
(16)
(17)
+ 'IF'
Cl Cl F
+ 'BrF'
F
Cl Cl
F
F F F
+ 'BrF' F
(13)
F
Cl
F3C
Cl F Cl
(12)
F
F
F
F
F Cl
F
F
Cl
F
F
F
+ 'IF'
F
I
Cl
+ 'IF'
(11)
F I
F
F I Cl
+ 'IF'
F F
+
F F
(10)
F
+
+ 'IF'
F
Cl
I
I F
F
F
I
F
Cl
F
F
F
+ 'IF'
F
F3C I F
F
F
F F
F
Cl Cl F
F
F
F
F Br
F3C F Br
(18)
(19)
F F F
(20)
3
Trihalides F
F
+ 'BrF' F
F
F
F
F Cl
Br
Cl
+ 'IF' CF3
F
F
F
F
Br Cl
F
CF3(CF2)n F F
CF3
CF3(CF2)n
+
CF3 CF3 I
(21)
(22)
5[90[0[1 The Addition of Haloalkanes to Haloalkenes The addition of haloalkanes to haloalkenes can be used to generate alkanes which bear a tri! halomethyl group "Equation "12##[ If the alkene is perhalogenated\ then it can be seen that the adduct will have two trihalomethyl groups[ These addition reactions can be initiated in four main ways\ that is\ by Lewis acids\ by free radical initiators\ by salts and complexes of certain transition metals\ and electrochemically[ RX
+
R
X
(23)
5[90[0[1[0 Lewis acid!catalysed addition of trihalomethyl cations to haloalkenes*the Prins reaction The aluminum chloride!catalysed addition of chloroalkanes to chloroalkenes has been known since the beginning of this century\ and is known as the Prins reaction ð03JPR304\ 24RTC138\ 24RTC296Ł[ More recently\ the reaction has been extended to include the addition of chloro~uoromethanes to ~uoroalkenes and chloro~uoroalkenes[ While most of the activity in this area occurred up to the early 0869s\ and was reviewed by Paleta ð66FCR28Ł and by Paleta and Posta ð61CLY826Ł\ interest has been renewed recently because the adducts may be intermediates in the manufacture of potential replacements for the higher!boiling chloro~uorocarbons "e[g[\ ð80MIP590!90\ 80EUP310211\ 81EUP362094\ 81JAP93053928Ł#[ Most commonly\ the halomethanes used in these reactions are CCl3\ CHCl2\ CFCl2 and CFHCl1\ and these have been added to the alkenes CF11CF1\ CF11CFCl\ CF11CCl1\ CFCl1CCl1\ CCl11CFCl\ C1Cl3\ CHCl1CHCl\ CF11CFH\ CF11CH1 and CF11CHCl "see Table 0#[ The addition of halomethanes to asymmetric perhalogenated ~uoroalkenes proceeds nonregiospeci_cally\ but corresponding additions to the hydrogen!containing alkenes CFCl1CFH\ CF11CFH\ CF11CH1 and CF11CHCl are highly regioselective\ with the electrophilic haloalkyl group becoming attached to the carbon which bears the hydrogen[ This suggests that the preferred isomer is that in which most of the ~uorine atoms on the precursor alkene are attached to the carbon where positive charge develops in the initial stages of the reaction[ In reactions with ~uorotrichloromethane\ both C0F and C0Cl bonds are cleaved\ although cleavage of the C0F bond is preferred due to the greater Al0F bond strength[ In its reaction with the alkenes CFCl1CHF and CF11CHCl the C0F bond is cleaved exclusively[ Some examples of these reactions are given in Table 0\ where it can be seen how the approach can be used to give a variety of propanes with various trihalomethyl groups attached to carbon atoms[ It is probable that the primary products in each of these reactions undergo rearrangement or further reaction\ and therefore the composition and nature of the observed products are dependent upon reaction conditions[
5[90[0[1[1 Additions initiated by free radicals\ heat or radiation When subjected to heat\ light\ or free radical initiators such as peroxides or azo compounds\ haloalkanes add to alkenes and haloalkenes "Scheme 0#[ Whether a simple adduct or a mixture of high molecular!weight telomers is obtained is determined by the relative rates of the propagation\ transfer and termination reactions[ Thus\ compounds with the weakest C0X bond\ that is\ iodides\ give lower molecular!weight products\ as do alkenes which are di.cult to polymerize under the conditions of the reaction[ But if the alkene is easily polymerized\ for example tetra~uoroethene\ or if the telogen is not particularly reactive\ high molecular!weight
4
General Methods Table 0 Lewis acid!catalysed addition of haloalkanes to haloalkenes[
ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Composition Reactants Conditions ")# Products ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * CF1CF1 ½14>C:2 h 69 CF2CF1CCl2\ CF1ClCF1CFCl1 72\ 06 60CCC0756 CFCl2 CHFCl1 CF1CF1 04>C:2[4 h 47 CF2CF1CHCl1\ CF1ClCF1CHFCl 48\ 30 60CCC0756 CF1CCl1 11>C:06 h 31 CF2CCl1CCl2\ CFCl1CF1CCl2\ 34\ 37\ 6 55CCC2473 CFCl2 CF1ClCCl1CFCl1 CHFCl1 CF1CCl1 6>C:01 h 67 CFCl1CF1CHCl1\ 70\ 08 56CCC2777 CF2CCl1CHCl1\ CCl2CF1CHFCl\ CF1ClCCl1CHFCl\ CF1ClCFClCHCl1 CFCl2 CF1CHF 9Ð03>C:6 h 54 CF2CHFCCl2\ CF1ClCHFCFCl1 69\ 29 63CCC0229 CHFCl1 CF1CHF 9>C:6 h 72 CF2CHFCHCl1\ 47\ 31 63CCC0229 CF1ClCHFCHFCl ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Initiation R • + X•
RX
2 In•
or In2 In• + RX
R• + InX •
Propagation R• +
n
R n
Transfer •
+ RX
R
R
n
X
+ R•
n
Termination •
•
+
R
R
R
n
n
X• + X• •
X2
+ X•
R
R 2n
R
n
X n
Scheme 1
material is obtained[ With easily polymerized alkenes\ the telomerization can be controlled by using a large excess of the telogen "preferably an iodide or diiodide# and recycling the lower telomers[ This addition of a haloalkane is often regioselective\ and it is observed that the incoming radical generally attacks the least sterically hindered carbon[ However\ there is still debate on the factors which control the products of these reactions and the relative stability of the potential intermediate radicals\ and polar e}ects "note that trihalomethyl radicals are electrophilic# as well as steric e}ects all play their part[ This approach is used in the manufacture of C7 or C8 per~uoroalkyl iodides\ which are inter! mediates in the preparation of per~uorocarbon surfactants and surface treatments ðB!68MI 590!90Ł[ Illustrative examples of these addition reactions are given in Equations "13#Ð"24# "NB[ Higher telomers are also produced in these reactions# ð36JA0099\ 89JFC"36#150\ 49JA1102\ 42JOC217\ 42JCS811\ 42JCS2650\ 41JCS2389\ 53JOC0087\ 47JA740\ 76IZV797\ 44JA657\ 74T3492Ł "references refer to the respective Equations "13#Ð"24##\ but many more are recorded elsewhere ð52OR"02#80\ B!63MI 590!90\ B!65MI 590! 90Ł[ It is noteworthy that\ unlike other polyhaloalkanes\ trichloromethane adds to alkenes by hydrogen transfer "Equation "15##[
5
Trihalides R
+
CCl4
Cl
Cl
R (24)
Cl F
F
n-C6H13
+
Cl
F
F
F
Cl
Cl
Ph
+
(26) n-C6H13
Cl
Cl
Br (27)
Cl
+
CCl3I
F
F
F
Cl
F
Cl
F
F
Cl
I F
F
F
F
CN
F
F
F
I (30)
F
CF2Br2
OEt
+
F
CN Br
Br (31)
F
F CF2Br2
+
F
OEt
F
Br
F
Br F
F F
F
F CBr4
F
F
(29)
F F
+
F
Br F
F
F
Br
Br
F
F
Br
F F
+ F
CCl3Br
+
EtO2C
Cl
Br
F
(32)
F
(33)
F
F
CF2BrCl
(28)
F
I
F
F
+
CF3I
Ph
F
+
CF3I
(25)
RF
Cl
CCl3Br
Cl
Cl
RF
F
CCl3H
Cl
+
CCl4
Cl
F
(34)
F
EtO2C
CO2Et
Br
Cl Cl
CO2Et Cl
(35)
5[90[0[1[2 Additions catalysed by salts and complexes of transition metals In 0845 ð45CI"M#260Ł\ unexpected results were obtained when the thermal additions of CCl3 and CCl2H to acrylonitrile were carried out using a steel autoclave[ More of the 0 ] 0 adduct was obtained than expected\ and trichloromethane gave the adduct CHCl1CH1CHClCN rather than
6
General Methods
CCl2CH1CH1CN\ which is normally obtained in free radical additions to alkenes "vide supra#[ Later ð52JCS0776Ł\ it was established that copper"II# and iron"III# both catalysed the addition of tetrachloromethane to a variety of vinylic monomers\ and that 0 ] 0 adducts were frequently the sole products\ even with easily polymerized alkenes[ This discovery led to extensive work in the area\ and copper"II# has now been used to catalyse the addition of CCl3\ CCl2Br\ CCl1Br1\ CF2CCl2 and other chloro compounds to a large variety of alkenes and dienes[ It is worth noting that the addition of CF2CCl2 followed by hydrogenation of the adduct can be used to introduce a CF2CH1 group[ While most investigations in this area have used copper! and iron!based catalysts\ other metal salts such as samarium diiodide ð89JCS"P0#1920Ł and vanadium dichloride ð89SL106Ł have been used more recently[ As well as alkenes which contain only hydrogen\ halogenated alkenes and those which contain other groups have also been used[ Generally the 0 ] 0 adduct is the only product\ but higher telomers are produced when the alkene is halogenated[ However\ this method of initation always gives lower molecular!weight material than the corresponding peroxide initiated reaction[ Amines are often added to form complexes and {increase the solubility| of the copper\ and consequently to increase the reaction rate[ The following is not a comprehensive list of references but will serve to lead the reader into the area] ðB!63MI 590!90\ 64ACR054\ 65T1184\ 66TL3204\ 79CCC2377\ 79CCC2491\ 74PAC0716\ 76JPS"A#2914\ 78JFC"34#104\ 89JFC"36#84\ 80MI 590!90\ 81CCC0180\ 81JMOC40\ 82JFC"50#022Ł[ As well as metal oxides\ salts and their complexes with amines\ other transition metal complexes such as carbonyls of iron ð56JCS"C#0049\ 79JOC2846Ł and cobalt ð69JOC1871Ł\ carbonyl complexes of molybdenum ð71JCS"D#1170\ 89JOM"286#40Ł\ iron ð89JOM"275#118Ł and chromium ð73JOM"159#C64Ł\ and phosphine complexes of ruthenium ð62TL4036\ 64TL788\ 67JOC0623\ 74JOM"179#286\ 76JCS"P0#0404\ 81JOM40Ł\ rhodium ð70AG"E#364Ł\ rhenium ð76JCS"P0#0404Ł and palladium ð70CL0058\ 74T282Ł have all been found to be e.cient catalysts in this reaction[ When the chiral Ru2Cl3"diop#2 "diop\ 1\2!O! isopropylidene!1\2!dihydroxy!0\3!bis"diphenylphosphino#butane# was the catalyst\ chiral adducts were obtained ð76BCJ2576Ł[ Clearly the metal!catalysed additions of haloalkanes to haloalkenes proceed by a di}erent mechanism to those promoted by free radical initiators such as peroxides[ Any mechanism needs to be able to explain the {abnormal| addition of trichloromethane\ the suppression of the propagation step "0 ] 0 adducts are the main products#\ and the fact that the addition of tetrachloromethane to cyclohexene is highly stereoselective "with a ruthenium catalyst# compared with the situation which obtains when conventional radical initiators are used[ It is unlikely that the details of the mechanism will be the same for all the catalysts that have been identi_ed\ but it is generally believed that it is not a simple redox process but one in which "e[g[\ for CCl3# a trichloromethyl radical is formed on and bound to the catalyst prior to the addition to the alkene which is itself coordinated to the complex[
5[90[0[1[3 Additions induced electrochemically The free radical chain addition of various polyhalomethanes to alkenes has been initiated by electrochemically in situ generated manganese salts used in a catalytic amount associated with an equimolecular amount of a manganese"III# oxidizable compound such as methyl cyano! or acetoacetate[ In particular\ tetrabromomethane\ bromotrichloromethane\ dibromodi~uoromethane and n!heptadeca~uorooctyl iodide have been added to a variety of alkenes in high yield by this means "Equation "25## ð81TL102Ł[ X X R
+ CX3Y
Mn(II)
Y
X
(36)
anodic oxidation
R CX3 = CBr3, Y = Br; CX3 = CCl3, Y = Br; CX3 = CBrF2, Y = Br; CX3 = C7F15, Y = I
5[90[0[2 The Preparation of C1 Chloro~uorohydrocarbons The manufacture of saturated compounds having the general formula C1HxClyFz represents an important part of the ~uorochemical industry[ These compounds "x O# "chloro~uorocarbons* {CFC|s# have been used as refrigerants\ solvents and foam!blowing agents[ However\ because they
7
Trihalides
have been implicated in the destruction of ozone in the earth|s upper atmosphere\ they are being replaced\ under the terms of the Montreal Protocol\ by hydro~uorocarbons "y O# "{HFC|s# and\ for an interim period\ by hydrochloro~uorocarbons "{HCFC|s#[ The manufacture of these compounds is largely brought about by treating a chlorocarbon with hydrogen ~uoride and sometimes chlorine[ Other reactions in the process may include isomerization and hydrogenation[ The ~uorinations are carried out in either the liquid phase using an antimony"V# catalyst "Swarts| catalyst# or in the gas phase using a chromia!based catalyst[ The main routes to the C1 chloro~uorocarbons and those compounds which are replacing them are outlined in Scheme 1[ 0\0\0\1!Tetra~uoroethane "R023a# is to be the main {high!temperature| refrigerant "e[g[\ mobile air conditioning\ and domestic and industrial refrigeration# while 0\0\0!tri~uoroethane "R032a# and 0\0\0\1\1!penta~uoroethane "R014# will be used in compositions for {low!temperature| refrigeration and static air conditioning "e[g[\ ð82MI 590!90Ł#[ As well as having the uses outlined above\ some of these compounds are intermediates in the manufacture of products such as the anaesthetic halothane "CF2CHClBr#\ and monomers such as 0\0!di~uoroethene and chlorotri~uoroethene[
Cl
Cl
F
Cl
Cl
F
F F
F
F R134a
F R133a
F
Cl
F F Br Halothane Cl
Cl
Cl F Cl
F Cl
Cl
F
Cl
F
Cl
F
F
F
F
Cl R115
R114
Cl Cl F Cl R113a F
F
F F
F F
Cl
R113
F
F
F Cl
Cl R123
F F F
F
F F R125
Cl F Cl
R114a
F
F
F F
F
F
F R134a Cl Cl
F
F
R143a F Cl Cl
+
R141b Scheme 2
F F Cl R142b
F
+
F F R143a
8
Tri~uoromethyl 5[90[1 TRIFLUOROMETHYL DERIVATIVES*RCF2 5[90[1[0 General
There is a very considerable literature relating to the synthesis of organic compounds containing the tri~uoromethyl group\ and this stems principally from the importance of such compounds in the plant protection industry ð80MI 590!91Ł and\ to a lesser extent\ the pharmaceutical industry ðB! 80MI 590!92\ B!71MI 590!90Ł[ Amongst other e}ects\ the introduction of the tri~uoromethyl group increases the lipophilicity of bioactive molecules\ enhancing transport across cell walls\ and can reduce metabolism of a drug[ A major review ð81T5444Ł is focused on the synthesis of tri~uoromethyl derivatives\ and others ð80T2196\ 81T078\ 83TA826Ł include discussions of relevant methodology[ In considering this area\ it is appropriate to draw attention to the fact that processes which involve halogen exchange for ~uorine\ using anhydrous hydrogen ~uoride "AHF# as the source of ~uorine\ will be the most economically favourable for large!scale manufacture by industry\ which is remark! ably adept at handling AHF[ Such procedures are not\ however\ particularly easy on the laboratory scale\ and other approaches described here will frequently be preferred[ Furthermore\ the sensitivity of the molecule under consideration may well dictate the route that is most appropriate[ The considerations described above relate to compounds containing the tri~uoromethyl group as the only halocarbon unit\ but\ of course\ there is a very wide range of applications for more highly ~uorinated systems\ including their use as refrigerants and for other volatile inert ~uid applications\ membranes\ polymers and anaesthetics[
5[90[1[1 Aryl Derivatives 5[90[1[1[0 Conversion of groups attached to an aromatic ring into the tri~uoromethyl group Only the most reactive of organic halides will react with anhydrous hydrogen ~uoride without catalysis "see Section 5[90[0[2#\ but benzotrichloride is converted to the tri~uoride "Equation "26## ð41MI 590!90Ł\ and analogous systems\ including heterocyclic compounds\ may be obtained in this way "Equation "27## ð70AHC"17#0Ł[ More sophisticated techniques have been used in processes to chloro~uorinate side chains in a continuous process "Equation "28## ð79GEP2997970Ł[ Alternatively\ antimony tri~uoride may be used in classical ~uorination processes "Equation "39# ðB!65MI 590!91Ł\ where the product is obtained by simply distilling from the ~uorinating agent\ but the trichloroethyl moiety is much less e.cient for conversion to the tri~uoroethyl group "Equation "30## ð77JOC2526Ł[ A clever {one!pot| methodology is available for acid!induced trichloromethylation accompanied by exchange of chlorine for ~uorine "Equation "31## ð70JFC"07#170Ł[ CCl3
CF3 AHF
(37) 40 °C, autoclave 70%
CF3
CCl3 HF
(38) N
CCl3
204 °C 45%
Cl2, HF
N
300–600 °C 33%
N
CF3
N
Cl
F3C (39)
CF3
CCl3 SbF3 125 °C 58–66%
(40)
09
Trihalides F
Cl
Cl
CF3
CCl3
Cl
Cl
SbF3
+
Cl
+
(41)
SbCl5
NO2
NO2
NO2 48%
NO2
10%
33%
HF, CCl4
(42)
CF3 α:β=2:3
One of the most versatile methods available for introducing the tri~uoromethyl group involves reactions of benzoic acid derivatives and corresponding heterocyclic compounds with sulfur tetra~uoride "Equations "32#\ "33# and "34## ð74OR"23#208\ 70AHC"17#0\ 76JOM"214#02\ 82JFC"59#122Ł\ or the more convenient but less reactive diethylaminosulfur tri~uoride "DAST# ð64USP2803154\ 65USP2865580Ł and related systems "Equation "35## ð77OR"24#402Ł[ CF3
CO2H SF4, 150 °C
(43)
6h
HO2C
F3C
CO2H
CF3
33% conversion
HO2C
CO2H
HO2C
CO2H
SF4, 150–200°C 16 h
F F3C
CF3
F3C
CF3
F3C
+
O F3C F
66–76%
F
F
F
+
F
F
CO2H
F O
O F
8–12%
F 0.8–1.7%
(44)
F
CF3 SF4, HF 80–140 °C autoclave 55–92%
X
F
(45) X
X = OMe, Me, H, Cl, NO2 CO2H
CF3 Et2NSF3
(46)
NaF 50%
Thio derivatives "e[g[\ ortho!thioesters# may also be used for conversion to the tri~uoro! methyl moiety\ using NBS\ or its equivalent\ followed by pyridineÐhydrogen ~uoride "Equation "36## ð75TL3750Ł[ Dithiocarboxylate esters are converted in a similar process "Equation "37## ð81CL716Ł\ and dithiocarboxylate derivatives are also converted in an interesting process that involves xenon di~uoride "Equation "38## ð89TL2246Ł[ A very unusual conversion of a nitrile to the tri~uoromethyl derivative occurs\ using carbonyl ~uoride\ accompanied by other products "Equation "49## ð67IJ018Ł[
00
Tri~uoromethyl C(SMe)3
CF3 i, DBH
(47) ii, HF–pyridine 34%
NO2
NO2
DBH = 1,3-dibromo-5,5-dimethylhydantoin CS2Me
CF3 DBH, Bu4N+H2F3–
(48)
CF3
i, Mg, Et2O ii, CS2
(49)
Ar-X iii, XeF2 40–77%
X Ar = Ph, p-MeC6H4, m-CF3C6H4, α-naphthyl X = halogen (e.g., Br)
HF, NaF
+
(50)
COF2 4 d, 50 °C 20%
CN
CF3
5[90[1[1[1 Substitution by tri~uoromethyl radicals Primary sources of tri~uoromethyl radicals include tri~uoroethanoic acid and tri~uoro! methanesulfonic acid\ but iodo! or bromotri~uoromethanes are important sources that have been used extensively[ Various methods have been applied to generate tri~uoromethyl radicals from these sources ð81T5474\ 80TL6414Ł\ and these radicals are\ of course\ electrophilic in character[ Conse! quently\ a wide range of radical aromatic substitutions occur\ and these probably proceed more e}ectively with the more electron!rich aromatic compounds\ but\ in general\ they are not high! yielding processes "Equations "40#Ð"47## ð70JFC"06#234\ 76CC0690Ł[ hν
+
CF3I
O
N
NH
+
hν
CF3I
F3C
NH
N
(51)
CF3
O
DMF 24%
+ N
CF3 32%
Br
NH
(52)
47%
Br
+
(53)
CF3I CF3 61%, o : m : p = 40 : 30 : 22
NH2
NH2
+
CF3Br
Zn, SO2
(54) CF3
56%, o : p = 1.8 : 1
01
Trihalides OH
OH ButOOH
+
(55)
CF3SO2Na Cu(II)
CF3
45%, o : m : p = 4 : 1 : 6 70 °C
+
C6H6
(56)
C6H5CF3
(CF3CO)2O 54%
[CF3(CO)O]2
X
X = O (53%), NH (65%)
O
O CF3CO2H
HN
CF3
HN
electrolysis 60%
N H
O
(57)
CF3
X
(58) N H
O
Bis"tri~uoroacetyl# peroxide decomposes thermally and can be used to tri~uoromethylate elec! tron!rich aromatic compounds "Equations "48# and "59## ð89JFC"35#312Ł[ An atmosphere of ammonia has been used to promote the reaction of iodotri~uoromethane with pyridine "Equation "50## ð68JAP68172Ł[ Remarkably\ some cross!coupling between hexa~uorobenzene and bromotri~uoro! methane occurs over copper chromite "Equation "51## ð82JFC"50#0Ł\ and\ in other high!temperature chemistry\ polytetra~uoroethylene is used as a source of di~uorocarbene\ which\ under the con! ditions used\ is able to insert into carbonÐ~uorine bonds "Equation "52## ð58IZV085\ 63JCS"P0#097Ł[ 60 °C
+
[CF3(CO)O]2
S
70 °C
[CF3(CO)O]2
+
(59)
CF3
S
72%
(60)
CF3
71%
+
NH3
CF3I
(61)
CF3
180 °C, 24 h 60%
N
N α : β : γ = 46 : 40 : 13
copper chromite
+
C6F6
(62)
C6F5CF3
CF3Br 600 °C, flow 40%
F N
+
(–CF2–)n
CF3
550 °C
N 6%
CF3
F3C
+
F
F
(63)
N 60%
5[90[1[1[2 Substitution of hydrogen by the tri~uoromethyl group acting as an electrophile Nucleophilic attack at a saturated carbon contained in a highly halogenated system is\ in general\ very di.cult\ but Umemoto and co!workers have demonstrated that with superior leaving groups it is possible to e}ect what is\ formally\ nucleophilic attack on the tri~uoromethyl group "Equation "53##[ Very powerful per~uoroalkylating agents are available through so!called {FITS| reagents ""per~uoroalkyl#phenyliodonium iodides# ð73TL70\ 75JFC"20#26Ł[ So far\ the corresponding reagents
02
Tri~uoromethyl
are not available for the introduction of the tri~uoromethyl group\ although this may be a practical di.culty\ rather than a fundamental di}erence in reactivity between tri~uoromethyl and other per~uoroalkyl systems[ However\ a less powerful but e}ective series of salts of tellurium\ selenium and sulfur heterocycles has been developed which will transfer the tri~uoromethyl moiety ð82JA1045Ł\ and it is concluded that the process involves nucleophilic attack on the tri~uoromethyl group[ The overall process is illustrated in Scheme 2\ where the reactivity of the salts "0# varies in the series X Te³Se³S\ while electron!withdrawing substituents in the aromatic ring also increase reac! tivity "1#[ Examples of tri~uoromethyl transfer from the salts "0# are shown "Equations "54#Ð"56##[ The tri~uoromethylation of hydroquinone "Equation "55## e}ectively rules out a free radical process because hydroquinone is known to be an e.cient radical scavenger[ [Ar
H]
+
F3C
[ArHCF3]+ + L–
L
+
ArCF3 + H+ + L–
(64)
F2, CF3SO2OH
CF3I
0 °C
X–
XCF3 O2N
CF3SO2ONO2
NO2
+
+
X CF3 (1)
X
CF3SO2–
CF3 (2)
X = S, Se, Te Scheme 3
CF3
CF3
OH
+
i
(2) (X = S)
OH
OH (65)
+
52% i, DMF (+ 4-dimethylaminopyridine)
6%
OH
OH
+
(2) (X = S)
OH CF3
i
+
(CF3)2
OH 61%
OH
(66)
OH 11%
i, DMF (+ pyridine)
NH2
NH2
+ Reactant (1) (X = S) (2) (X = S)
(1) or (2) Conditions 80 °C, 1 h RT, 0.5 h
CF3
(67)
Products o-CF3 (31%) + p-CF3 (15%) o-CF3 (54%) + p-CF3 (20%)
5[90[1[1[3 Substitution of halogens by the tri~uoromethyl group acting as a nucleophile Tri~uoromethyllithium and !magnesium derivatives are unstable and\ therefore\ a methodology for the transfer of a tri~uoromethyl anion to electrophilic centres via silanes has been developed "Equation "57## ðB!81MI 590!90Ł[ A convenient synthesis of trimethyltri~uoromethylsilane has been
03
Trihalides
reported "Equation "58## ð79ZOB0786\ 73TL1084\ 82RHA121\ 81MI 590!91Ł\ and a process using tetra! kis"dimethylamino#ethene has also been described "Equation "69## ð78JFC"31#318Ł[ The key step involves displacement of the tri~uoromethyl group from silicon\ using tetrabutylammonium ~uoride "which inevitably contains amine#[ Understandably\ reaction only occurs with the more activated aromatic systems "Equations "60# and "61## ðB!81MI 590!92Ł[ CF3–
+
Ar
[ArLCF3]–
L
ArCF3 + L– PhCN
TMS-Cl + CF3Br + (Et3N)3P Me2N
NMe2
TMS-CF3
(69)
PhCN
+ TMS-Cl Me2N
(68)
TMS-CF3
(70)
or CH2Cl2
NMe2
NO2 F
+ TMS-CF3
tbaf, 0 °C, 0.5 h, RT
(71)
C6F5NO2 + CF3C6F4NO2 90%
10%
F NO2
+ TMS-CF3
tbaf, 0 °C, THF
mixture of trifluoromethylated products
(72)
NO2
5[90[1[1[4 Substitution of halogens by the tri~uoromethyl group using derivatives of metals As indicated above\ lithium and magnesium derivatives are unstable and\ therefore\ are not viable reagents for the introduction of the tri~uoromethyl group[ Metals that form weaker bonds to ~uorine generally give more stable tri~uoromethyl derivatives\ and consequently copper\ cadmium and zinc compounds are particularly useful in synthesis ð81T078\ 81T5444Ł[ Therefore\ access to tri~uoromethyl derivatives of these metals is of some importance[ Easily accessible sources for the e}ective use of the tri~uoromethyl moiety include CF2CO1H\ CF2SO1OH\ CF2I "usually made from tri~uoroacetic acid by Hunsdiecker processes#\ CF2Br and CF1Br1[ Tri~uoromethylation of aryl halides occurs using CF2I or CF2Br in the presence of copper powder in aprotic solvents at elevated temperatures "Equation "62## ð79JCS"P0#1644Ł\ but direct reaction of sodium tri~uoroacetate with CuI in N!methyl!1!pyrrolidone "NMP# is also possible ð70CL0608Ł\ and it has been concluded that the reaction proceeds via an intermediate like ðCF2CuIŁ=− rather than ðCF2CuIŁ = "Equations "63#Ð"65## ð77JCS"P0#810Ł[ Tri~uoromethanesulfonyl chloride can be used in an analogous way "Equation "66## ð78JFC"34#75Ł[ NH2
NH2 N
N
HMPA
N
N AcO
N
N
I
+
CF3Cu 46%
O
CF3 N
N AcO
AcO OAc
(73)
O
AcO OAc HMPA = hexamethylphosphoramide I
CF3 CF3CO2Na, Cu, NMP
(74) 160 °C, 4 h 98%
Cl
Cl
04
Tri~uoromethyl CF3
CF3
Br CF3CO2Na, Cu, NMP
+
(75)
160 °C, 4 h
Br
F3C
Br
CF3
CF3
48%
I
F3C
CF3CO2Na, Cu, NMP
N
41%
(76)
160 °C, 4 h 85%
Cl
N
Cl
Cl
CF3 NO2
NO2
Cu, DMF
+
(77)
CF3SO2Cl 100 °C 73%
NO2
NO2
A fascinating route to tri~uoromethylcadmium and !zinc has been developed by Burton and co! workers ð74JA4903Ł in which reaction of dihalodi~uoromethanes with cadmium or zinc powders in DMF gives stable solutions of the corresponding tri~uoromethyl derivatives "Scheme 3#\ which then react further[ Copper reacts in an analogous way but a mixture of homologues is obtained unless ~uoride ion is added\ or other procedures used to prevent the di~uorocarbene generated reacting further with CF2MX "Scheme 3#[ Cadmium derivatives can also be converted to copper reagents ð75JA721Ł\ and these can be stabilized against formation of higher homologues by adding HMPA ð78JA7491Ł "Equations "67# and "68##[ Tri~uoromethylation in dimethylacetamide "DMA# is also e.cient "Equation "79## ð77CC527Ł[ Transfer of the tri~uoromethyl group to amines\ using dibromo! di~uoromethane\ has also been reported ð80JFC"41#118Ł "Equation "70##[ Methyl ~uoro! sulfonyldi~uoroacetate in the presence of copper"I# iodide functions in a similar way ð78JCS"P0#1274Ł\ and the corresponding iodide has also been used "Equations "71# and "72##[ The source of the starting materials in the latter cases is tetra~uoroethene\ via formation and ring opening of a b! sulfone "Scheme 4# ð59JA5070Ł^ this is an attractively direct but\ unfortunately\ potentially hazardous process for laboratory application[
DMF, RT
CF2XY + M
[CF3MX + (CF3)2M] 80–95%
X = Br, Cl; Y = Br, Cl; M = Cd, Zn, Cu
MXY + [CF2]
F
DMF
Me2N
+
+ CO
Me2N
F
F– + [CF2]
CF3–
CF3– + MXY
CF3MX + (CF3)2M
CF3CuX + [CF2]
CF3CF2CuX
[CF2]
CuY
[CF3CdX + (CF3)2Cd]
[CF3Cu] –40 °C
90–100%
Y = I, Br, Cl, CN Scheme 4
etc.
F
F–
05
Trihalides I
CF3 DMF
NO2
+
NO2
CF3Cu
(78)
HMPA 70 °C, 4–6 h 75%
I
F3 C
I
+
CF3Cu
CF3
DMF
I
I
S
(79)
HMPA 70 °C
F3C
Cl
S
CF3
CF3 NO2
NO2
Cu, DMA
+
(80)
CF2Br2 100 °C, 4 h 93%
NO2
CF2Br2
NO2 Me2N
NMe2
Me2N
NMe2
+
+ R2NH
R2NCF3
I
CF3 CuI, DMF
+
FO2SCF2CO2Me
(81)
(82)
60–80 °C, 3 h 80%
NO2
NO2
ICF2SO2F +
Ph
F
Cu, DMF
Br
Ph
80 °C 83%
F
F
< 80 °C
+ F
SO3
F
~3 atm 93%
F F
F
(83)
F
F F
F–
FCOCF2SO2F
O SO2 Scheme 5
5[90[1[2 Derivatives of Alkanes\ Alkenes\ Alkynes and Other Saturated Compounds 5[90[1[2[0 Halogen exchange These reactions ð52AFC"2#070\ B!78MI 590!90\ 30JA2367\ 36JA0719Ł involve\ essentially\ the nucleophilic displacement of other halogens by ~uorine using a metal ~uoride ðB!62MI 590!90\ B!65MI 590!92Ł\ frequently in combination with hydrogen ~uoride[ An important part of the function of the metal ~uoride is to act as a Lewis acid\ to assist the removal of the halogen as a halide ion[ Some of the reactions could involve carbocations "Scheme 5#[ As the number of ~uorine atoms attached to the chlorine!bearing carbon increases\ it becomes progressively more di.cult to e}ect further ~uorination "Equation "73# and "Scheme 6##[ Never! theless\ the inhalation anaesthetic CF2CHBrCl may be obtained by an exchange process "Scheme 7# ð46BRP656668Ł[ For a carbocation!type process\ it is understandable that the introduction of unsaturated sites makes such exchange reactions much easier "Equations "74# ð30JA2367Ł and "75# ð36JA0719Ł#[ Fluorination of hexachlorobutadiene provides an accessible route to hexa~uoro!1! butyne "Equations "75# and "76## ð38JA187Ł[ Functional derivatives are also accessible by these procedures\ for example halo!ethers and !thioethers "Equation "77## ð41JA2483Ł as well as hexa! ~uoroacetone\ which is made commercially by this route "Equation "78## ð53FRP0258673Ł[ Antimony ~uorides and various other ~uorides have been used to promote exchange with hydrogen ~uoride\
06
Tri~uoromethyl [MFxCl]–
+
F– (HF)
Cl + MFx
F + MFx-1Cl
or
δ+
Cl
δ–
MFx-1 F Scheme 6
and very e.cient catalysts have been developed by industry\ including chromia catalysts for use in vapour phase processes^ these are particularly important in the refrigerant industry "see Section 5[90[0[2#[ HF, SbCl3, Cl2
CCl4
CCl3CCl3
CCl3CCl2F
(84)
CCl3F + CCl2F2 + CClF3
110 °C, 3 atm
9%
CCl2FCCl2F
90%
0.5%
CCl2FCClF2
CClF2CClF2
CF3CClF2
Scheme 7
HF, SbF5
CCl3Me
Br2
Cl2
CF3Me
CF3CH2Cl
CF3CHBrCl 425–475 °C
Scheme 8
Cl Cl
F
Cl Cl
SbF3
Cl F
F
F
Cl
+
F Cl
(85)
150 °C
Cl
Cl
Cl
Cl
Cl
43%
Cl
Cl
Cl
Cl Cl
Cl
SbF3Cl2
Cl
Cl Cl
Cl
F
F
F
F Cl
F
Cl
Cl
Cl
F
F
+
F
Cl
28%
Cl
Cl
F
F
F
F Cl
F
(86)
F
F
F
Cl Cl
Zn, Ac2O
F F
F
63%
F
F
F
F
F
F
(87)
07
Trihalides Cl Cl Cl
SbF3, SbCl5
SMe
Cl +
90 °C
F SMe
F
73%
Cl
SMe
(88)
F
O
O
Cl
Cl
Cl
Cl
Cl
Cl
HF, 350 °C Cr (cat.)
F
F
F
F
F
F
(89)
Alkali metal ~uorides\ although easily used\ have limited application for saturated sites "Equation "89## ð52JOC001Ł\ but such systems are extremely e}ective for attack at unsaturated sites "Equation "80##\ where even lithium ~uoride\ normally the least reactive of the alkali metal ~uorides\ can give some ~uorination "Equation "81## ð48JA1967\ 59JA2980Ł[ These reactions probably involve nucleo! philic attack with allylic rearrangement\ and other metal ~uorides will also promote this process "Equation "82## ð59BRP712408Ł[ Terminal ~uorinated alkenes are rearranged to the thermo! dynamically more stable isomers by the ~uoride ion "Equation "83## ðB!62MI 590!91Ł[ Furthermore\ hexa~uorobutadiene is converted into hexa~uoro!1!butyne by ~uoride ion "Equation "84## ð50JA0656Ł and\ more surprising\ hexa~uorocyclobutene also gives hexa~uoro!1!butyne when passed over hot caesium ~uoride or potassium ~uoride "Equation "85## ð68CC853Ł[ An even more remarkable rearrangement induced by hot metal ~uorides involves conversion of per~uorobicyclobutylidene to a product containing three tri~uoromethyl groups "Equation "86##[ Cl
Cl
Cl
Cl Cl
Cl
KF, 190 °C
F
Cl
NMP ~60%
F
Cl
Cl Cl
F
Cl F
F F
F LiF, cellosolve
F
Cl
F
F
90–95%
F
CsF, 100 °C
C4F9
F
no solvent
F
F
F
F
+
C4F9
F–
F–
F
+
F C3F7
F F
(94)
F
F
F
F F
F
F
F
+
F C4F9
F
F–
(93)
F
–
F
F
F
(92)
F
F
F
F
F
F HF, CoF2, 250 °C
Cl
F
F
F
Cl
F– +
(91)
F
F
F
(90)
Cl
F
90%
Cl Cl
F F
F
F
F
Cl
(C2H5)4NF, CHCl3 27 °C, 12 h
F
F
F
CsF, 100 °C, no solvent
F
F
F
F F
F
+ F–
(95)
08
Tri~uoromethyl F
F
i
F
F
F
80–90%
F
F
F
F
F
F
F
F
(96)
i, CsF or KF, 510–590 °C, flow system in N2
F
F F
i
F F
F
(97)
F
F
70%
F
F
F F
F
i, KF, 510 °C, flow system in N2
5[90[1[2[1 Conversions of other groups to the tri~uoromethyl group Use of sulfur tetra~uoride ð59JA432Ł to convert the carboxyl group to the tri~uoromethyl group proceeds well\ except where formation of anhydrides is in competition "Equations "87# and "88## ð67PJC60Ł and in some cases other functional groups present also react preferentially "Scheme 8# ðB! 78MI 590!91Ł[ Treatment of ~uorinated enols with DAST gives tri~uoromethyl derivatives with a high degree of regio! and stereoselectivity "Equation "099## ð80TL4852Ł[ An interesting in situ electrophilic formylation and subsequent reaction with sulfur tetra~uoride has been reported "Equa! tion "090## ð71ZOR117Ł[ HO2C
( )8
CO2H
HO2C
F
F
F ( )3
F
( )3
SF4, 120 °C, 6 h
F
87%
F
F
+
F
+
F
F
F F
O 10%
34%
F ( )8
F
(98)
F
SF4, 5 °C, 48 h
CO2H
F
F
F
F
F
F F
( )3
F
F ( )3
O
F
(99)
F
16% 100 °C
F
50%
F
HF, 20 °C
F
60%
F
F
F
F COF
O
+ SF4
CO2H
HO2C
F
F
F
F
F F
Scheme 9 Ph
F
F
Ph
+ Et2NSF3 OH
F
F
SF4, HCO2H, HF
F
(100)
(101) CF3
Although halogen exchange to form the tri~uoromethyl group proceeds well "see above#\ pro! cedures to convert the methyl group to the tri~uoromethyl moiety directly are limited[ High!valency metal ~uorides\ for example cobalt tri~uoride\ will carry out this conversion at high temperatures\
19
Trihalides
but the rest of the molecule is also ~uorinated in the process\ leading to very useful inert ~uids "Equation "091## ð59AFC"0#055Ł[ Various direct ~uorination procedures can also be used for such transformations "Equation "092## ðB!62MI 590!92Ł[ CF3 CoF3
(102) F
F
CF3 F2
(103) F
Au on Cu
CF3
Electrochemical ~uorination "ECF# is a procedure for converting C0H bonds to C0F bonds at the anode of an electrochemical cell during the electrolysis of hydrogen ~uoride ð56FCR66Ł under conditions that do not generate elemental ~uorine[ The process is operated on an industrial scale and is particularly e}ective for polar systems\ for example the synthesis of tri~uoromethanesulfonic acid "Scheme 09# and other functions "Equation "093# and Scheme 00#[ An interesting conversion of the amino group to the tri~uoromethyl group involves conversion to an azo derivative\ using nitrosotri~uoromethane\ followed by photolytic elimination of nitrogen "Scheme 01# ð66AG"E#743Ł[ ECF
MeSO2F
H2O
CF3SO2F
CF3SO2OH
96%
Scheme 10
ECF
CS2
CF3SF5
(104)
90%
ECF
MeCOF
H2O
CF3COF
CF3CO2H
Scheme 11
CF3 C8H17NH2 + CF3NO
N N C8H17
hν 69%
C8H17CF3
Scheme 12
5[90[1[2[2 Transfer of tri~uoromethyl groups as radicals One of the most e}ective and e.cient procedures for transferring tri~uoromethyl radicals involves the use of iodo! or bromotri~uoromethane for addition to an unsaturated unit "see Section 5[90[0[1#[ These are generally radical chain reactions\ and they proceed with very high e.ciency when a relatively nucleophilic centre is involved\ and a range of catalytic procedures have been developed\ as illustrated in Table 1[ Electrolysis of tri~uoroacetic acid is a very direct and attractive route for generation of tri~uoro! methyl radicals[ Mixed Kolbe processes lead to tri~uoromethyl derivatives by combination of radicals "Equation "094## ð64CJC418Ł\ although the process is not e.cient[ Similarly\ addition of tri~uoromethyl radicals\ generated this way\ to alkenes and derivatives leads to mixtures of products where dimerization of the radical arising from addition of the tri~uoromethyl group can be a signi_cant pathway "Equation "095## ð63CC212\ 67JCS"P0#191Ł[ Products that arise from cyclization of the intermediate radical "Equation "096## ð80T438Ł and from di!addition have been observed "Equa! tions "097# ð68CJC1506Ł and "098# ð78TL098Ł#[ Enzymes have been used to promote radical additions
10
Tri~uoromethyl Table 1 Addition of halo~uoromethanes to alkenes[
ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Reactants Catalyst:conditions Product ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Ru2"CO#01 CF2CH1CHISiMe2 78 73TL292 CH1 CHSiMe2 ¦CF2I CH2CO"CH1#7CH Et2B CH2OCO"CH1#7CHICH1CF2 75 78TL2048 CH1 ¦CF2I CH1 CHC5H02 ¦CF2Br NaSePh CF2CH1CH"SePh#C5H02 ¦ 15\ 23\ 20 80TL264\ 80TL6314 CF2SePh¦PhSeSePh Na1S1O3 NaHCO2 CF2CH1CHIR B!83MI 590!90 CH1 CHR¦CF2I CH1 CHR "R Ph\ Ru"PPh2#2Cl1 CF2CH1CHClR 78CC0448 CO1Et\ alkyl#¦CF2SO1Cl ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
"Equation "009## ð77JOC1249Ł\ and it is probable that these are reacting as electron transfer agents\ in the manner that various other transition metal systems behave[ Reactions of plasma!generated radicals can be very e.cient "Scheme 02# ð68CC017Ł[ F EtO2C
CO2H
electrolysis
F
EtO2C
+ CF3CO2H
electrolysis
+ CF3CO2H F
F
F
+ F
F major
F
F
F
+
F
(105)
F
46%
F
F
+
F
F (106)
F
F
F H N
electrolysis
+ CF3CO2H
F
F
F F
F
(107)
N H O NEt
electrolysis
F
40%
F
O
+ CF3CO2H
NEt F
O
F
electrolysis
CONH2
F
F
+ CF3CO2H
O
F
F
F
F
F (110)
39%
F
Ph F
CI4
plasma
CF3I
F
urease
Ph
(109)
CONH2
F CF3I +
F
F
35%
(108)
CF3• 97%
F3C F3C F3C
CF3 1
Scheme 13
F
+ :
F3C F3C F3C
I 3
11
Trihalides
5[90[1[2[3 Reactions involving tri~uoromethyl derivatives of metals and metalloids Electrophilic tri~uoromethylating agents "see Section 5[90[1[1[2# can be applied to transferring the tri~uoromethyl group to an alkyne "Equation "000## ð89TL2468Ł\ and acidic sites derived from alkyl pyridines may be tri~uoromethylated using tri~ic anhydride\ together with formation of corresponding tri~ates "Equation "001## ð72JOC0665Ł[
Ph
+
Li
+
Se CF3
Ph
46%
CF3SO2O–
(111)
CF3
CF3
+
(112)
+
(CF3SO2)2O N
N
CH2OSO2CF3
N 62%
5%
Nucleophilic tri~uoromethylation has been carried out directly with a system that is highly susceptible to nucleophilic attack "Equation "002## ð89IZV380Ł\ although the nature of the inter! mediate is not clear[ Displacement of the tri~uoromethyl group from trimethyltri~uoromethylsilane\ using the ~uoride ion "see Section 5[90[1[1[3#\ is applicable to a range of systems "Scheme 03# ðB! 81MI 590!90Ł\ and\ used in conjunction with copper"I# salts\ trimethyltri~uoromethylsilane functions as a tri~uoromethylcopper reagent which will tri~uoromethylate aryl\ benzyl and allyl halides "Equation "003## ð80TL80Ł[
F
F
F
F
F
F F
F
F
F F
+ CF3Br/P[NC2H5)2]3
CH2Cl2, –78 °C, argon
F
45%
F
F
F
TMS-O R1 F3C
F– THF
R1 = alkyl, aryl R2 = alkyl
F
F F
HO R1 F3C
HCl
CO2R2
F
F
F
F F
F
R1COCO2R2 + TMS-CF3
F
68–83%
(113)
F
CO2R2
Scheme 14 KF, Cu(I)
R1X + CF3SiR23
R1CF3
(114)
DMF, 60–80 °C 23–94%
Tri~uoromethylcopper reagents\ made by other routes\ react with various substrates "Equations "004# ð81CC42Ł\ "005# ð68TL3960Ł and "006# ð71CL0342Ł#\ and zinc reagents are also useful ð81T078Ł in a variety of contexts[ Cl Ph
Br
+ F
F–, CuI
PhCF3
CO2Me
Ph
Br
+ CuCF3
(115)
84%
F
HMPA (CF3I + Cu)
Ph
F
65%
F
F
(116)
12
Trichloromethyl OH
Zn, CuI
F
61%, (E):(Z) = 3:7
F
+ CF3I
(117)
OH F
5[90[2 TRICHLOROMETHYL DERIVATIVES*RCCl2 5[90[2[0 Trichloromethyl Groups Attached to an Aliphatic Centre Trichloromethyl compounds can be prepared either by converting an existing group into a trichloromethyl group or by introducing a trichloromethyl group on to a carbon atom in an existing molecule "see also Section 5[90[0#[
5[90[2[0[0 Conversion of groups attached to an aliphatic centre into the trichloromethyl group As with chloro~uorocarbons\ the manufacture of many chlorinated solvents is being phased out[ Of these\ only 0\0\0!trichloroethane is relevant to this chapter[ Several routes are available\ and the choice\ which makes use of permutations of chlorination\ hydrochlorination and dehydro! chlorination\ is outlined in Scheme 04[ Hydrochlorination is usually e}ected by Lewis acid catalysis "e[g[\ FeCl2#\ and dehydrochlorination by thermal cracking or by the action of base[ Chlorination is catalysed by free radical sources in the liquid or gas phase[ The route chosen depends in part on how much hydrogen chloride the operator is prepared to make[
H2C
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
CH2
Cl Cl Cl
Cl Cl
C2H6
Cl Scheme 15
5[90[2[0[1 Transfer of the trichloromethyl group to an aliphatic centre "i# Preparation of trichloromethylalkanes Trichloromethyl anions are an unstable species and decompose to give dichlorocarbenes[ However\ the problem of their instability can be minimized by running reactions at low temperature and by generating the trichloromethyl anion in the presence of the substrate[ Trichloro! methyllithium\ which can be made at about −099>C from trichloromethane and butyllithium in THF\ reacts successfully with iodoalkanes at this same temperature to give a series of trichloromethyl alkanes "Equation "007## ð89JOC0170Ł[ Cl R
I
BuLi, CHCl3, THF, –100 °C HMPA
R = –(CH2)nCH=CH2 (n = 2 or 3), –CH2
R
Cl Cl
(118)
13
Trihalides
The trichloromethylation of activated alkyl halides can also be carried out by a cross!coupling reaction with tetrachloromethane in an undivided electrochemical cell with a sacri_cial anode[ The preferred anode is zinc\ with a stainless steel cathode\ and the preferred solvent is a mixture of THF and tetramethyl urea "Scheme 05# ð77TL0588Ł[ Mn+ + ne–
M
Anode
Cathode
CCl4 + 2e–
CCl3– + Cl–
CCl3– + RX
CCl3R + X–
RX = PhCH2Br, MeCHClOCO2Et, BrCH2CO2Me, Me(CH2)9Br Scheme 16
Trichloromethylated compounds can also be prepared by the action of trichloromethyl anions generated by the action of a base on trichloromethane[ Thus\ by using catalytic amounts of electrochemically generated base\ a relatively stable anion is produced which reacts with a\b! unsaturated esters and nitriles to give the corresponding b!trichloromethyl adducts in good yield[ The base is made by the electroreduction of 1!pyrrolidone in DMF using tetraalkylammonium salts as supporting electrolytes "Scheme 06# ð89TL6070Ł[ +e–, 1.8 F mol–1
O
N H
R = Et, X = OTs; R =
CHCl3
–
N
DMF, R4NX Pt cathode
Bun,
–
X = BF4
R4
eg.
R4N+ CCl3–
O
N
2
R4N+
DMF
+
+ –1 H2
O
CO2Me CN
or
N+
Cl Cl
CO2Me
Cl or
Cl
Cl
CN Cl
Scheme 17
b!"Trichloromethyl#nitroalkanes can be prepared in good yield by the reaction between trichloro! methyl anions\ generated from trichloromethyltrimethylsilane and caesium ~uoride "see also 5[90[0[1#\ and nitroalkenes "Equation "008## ð80SC1078Ł[ R3
Cl
i, TMS-CCl3, CsF, THF, 25 °C
R1
NO2 R2
R3
R1
R2
Cl
ii, H+
R1 Bun Ph Me Et Me
Cl
R2 Me H H H Me
NO2
(119)
R3 H H Et H Me
Closely related to the trichloromethyl radical additions outlined in Section 5[90[0[1[2 is the reaction of trichloromethylsufonyl chloride with 0!alkenes in the presence of ruthenium complexes such as dichlorotris"triphenylphosphine#ruthenium"II#[ In this reaction\ the elements of CCl2 and chlorine are added to the double bond in high yield under mild conditions with the extrusion of sulfur dioxide ð72SUL020Ł[ When the chiral Ru2Cl3"diop#2 is the catalyst\ chiral adducts are obtained ð76BCJ2576Ł[
14
Trichloromethyl "ii# Preparation of a!trichloromethyl carbinols
a!Trichloromethyl carbinols are valuable intermediates for making compounds in which the trichloromethyl group is preserved and also for making those in which the trichloromethyl group has been transformed into other functions "e[g[\ ð60S020\ 71TL0598\ 77M0316\ 78S355\ 80RCR0207\ 81TL2324Ł#[ Essentially\ their preparation comprises the formation of a trichloromethyl anion followed by its attack on an aldehyde or ketone "Scheme 07#[ CCl3–
AcCl3 R1
O CCl3– +
R2 R1
R2
–O
Cl Cl Cl
R1 R2 HO
H+
Cl Cl Cl
Scheme 18
Carbonyl compounds have been treated successfully with trichloromethyllithium\ but because the reactions have to be carried out at −099>C\ only the more reactive carbonyls can be used ð53AG"E#402\ 56JOC0106\ 77M0316\ 89JOC0170Ł[ Reactions can be carried out at higher temperatures "−67>C# if lithium dicyclohexylamide is used to generate the trichloromethyllithium from trichloro! methane in the presence of the carbonyl "Equations "019#Ð"012##[ Equation "012# gives equally good results with tribromomethane in place of trichloromethane ð63JA2909Ł[ i
Ph2CO
Ph2COHCCl3
(120)
ii
i, BunLi, CHCl3, –110 °C, THF/Et2O, petroleum ether; ii, H+ i, BunLi, CHCl3, –100 °C, THF
(CF3)2CO
R
( )n
CHO
(CF3)2COHCCl3
ii, H+
i, BunLi, CHCl3, –100 °C, HMPA
R
COHCCl3 ( )n
(121)
(122)
ii, H+
R H H Me O
n 2 3 2 HO
CCl3
i
(123)
i, Lithium dicyclohexylamide, CHCl3, –78 °C, THF, hexane
Trichloromethane and a base have been used extensively to generate the trichloromethyl anion[ The base may be sodium or potassium hydroxide ð33JCS63\ 49JA4901\ 72M702\ 76JOC833Ł\ an alkali metal alkoxide ð47CB1553\ 53JOC0037Ł\ or potassium ~uoride supported on alumina ð75TL2734Ł[ The amount of base\ its nature and also the choice of solvent are particularly important when the carbonyl compound is inclined to undergo an aldol condensation or the Cannizzaro reaction[ Reactions are generally carried out below 9>C to help suppress dichlorocarbene formation[ Phase transfer catalysts have been used in these reactions\ but they were only really successful with higher aldehydes and ketones ð79JOC4103\ 68TL0362Ł[ The thermal decomposition of sodium trichloroacetate in a solvent yields dichlorocarbene ð48PCS118Ł[ However\ the intermediate trichloromethyl anion can be trapped by aldehydes to yield trichloromethyl carbinols[ Under similar conditions\ anhydrides react to give trichloromethyl lactols or their tautomeric keto acids "Equation "013## ð56JOC1055Ł[ Trichloromethyl carbinols are also obtained in high yield when\ in the presence of an aldehyde\ trichloroacetic acid decomposes in DMSO ð72CC172\ 73JCS"P1#0136\ 78JCS"P1#140Ł or HMPA ð89S216Ł\ or a 0 ] 0 mixture of the trichloro!
15
Trihalides
acetic acid and its sodium salt decomposes in DMF ð81TL2324Ł[ These reactions are successful with aliphatic as well as aromatic aldehydes[ They are less successful with ketones unless the ketone is "partially# ~uorinated and therefore more electrophilic\ in which case the yields are high ð81BAU269Ł[ O
O
HO
O
CCl3
CCl3
CCl3CO2Na
O
OH
DME
O
(124)
O
O
Trichloromethyl compounds of silicon and tin have been used as sources of trichloromethyl anions in reactions with carbonyl compounds[ For example\ the reaction of trichloro! methyltrimethylsilane and trimethylsilyl trichloroacetate in the presence of the ~uoride ion with aromatic and aliphatic aldehydes ð74JA3974\ 76SC0936\ 77T3024Ł\ trimethylsilyl trichloroacetate in the presence of potassium carbonate and 07!crown!5 with aromatic aldehydes and ketones ð74TL0064Ł\ and tributyl"trichloromethyl#stannane with aliphatic and aromatic aldehydes ð64JOM"091#312Ł all give the corresponding trichloromethylcarbinols in good yield "Equations "014#Ð"017##[ Equation "017# proceeds with equal success to give tribromomethylcarbinols when tribromomethyltributyltin is used instead of the trichloromethyl tin compound[ R
i, TMS-CCl3, tas-F, THF, 0 °C
Cl Cl Cl
RCHO ii, H+
HO
(125)
R = Ph, n-C10H21, PhCH(Me); tas = tris(diethylamino)sulfonium
R1 O
i, CCl3CO2-TMS, F–, THF
R1
ii, H+
R2
Cl Cl Cl
HO R2
(126)
F = KF or tas-F R1 O = cyclohexanone, benzaldehyde, pivaldehyde, 2-cyclohexenone, crotonaldehyde R2 R1 O
i, CCl3CO2-TMS, K2CO3, 18-crown-6
R1 HO
ii, H+
R2
R2
Cl Cl Cl
(127)
R1 R2
O = e.g. benzaldehyde, 3,5-dichlorobenzaldehyde, 4-hydroxybenzaldehyde, cyclobutanone, cyclopentanone, cyclohexanone
RCHO
i, Bu3SnCCl3, 80 °C ii, H+
R HO
Cl Cl Cl
(128)
R = Me, Et, Pri, Ph, PhCH = CH
The reductive addition of tetrachloromethane to aldehydes using a lead:aluminum bimetal redox system has been reported to give high yields of trihalocarbinols[ While a variety of aliphatic and aromatic aldehydes give good yields\ ketones give less satisfactory results[ The use of bromo! trichloromethane instead of tetrachloromethane gives exclusively the same product "Scheme 08# ð78JOC333Ł[ A variety of aldehydes have been treated with trichloromethyl anions generated by the cathodic reduction of tetrachloromethane in trichloromethane[ Only relatively small amounts of tetra! chloromethane are used in this reaction\ since it is the trichloromethane which supplies the proton to the intermediate anion and thereby generates another trichloromethyl anion*steps "ii# and "iii# in Scheme 19[ The use of vinyl acetate instead of an aldehyde yields the acetate MeCH"OAc#CCl2 ð70TL760\ 71TL0598\ 71TL3790Ł[ These same workers oxidized trichloromethyl carbinols with chromic oxide to give the corresponding trichloromethyl ketones ð71TL0598Ł[
16
Trichloromethyl R
X
HO
X
PbX2 (cat.)/Al, DMF
RCHO + CX4
Pb(0)
Pb(II)
Al(III)
Al(0)
X
X = Cl or Br; R = alkyl, aryl Scheme 19
+2e–
CCl4
CCl3– + Cl– –O
Cl Cl Cl
CCl3– + RCHO R –O
HO
Cl Cl + CHCl3 Cl
R
Cl Cl Cl
R
(i)
(ii)
+ CCl3–
(iii)
Scheme 20
The other approach to making trichloromethyl carbinols is to start with trichloroacetaldehyde "chloral#[ This compound will condense with aromatic hydrocarbons with FriedelÐCraft catalysts "e[g[\ H1SO3\ HCl\ AlCl2\ BF2 and ZnCl1# ð12CB868\ 31JA1404\ 55CJC464\ 57CJC1122\ 79CJC374Ł or under the in~uence of basic catalysts "e[g[\ potassium hydroxide\ potassium carbonate and pyridine# ð45CB1467\ 14JPR014\ 41CB890Ł to yield trichloromethyl carbinols[ Certain Grignard reagents will react with chloral to give trichloromethyl carbinols\ although reduction of the chloral to trichloroethanol can be a problem "Equation "018## ð40M0997\ 45BSF0330Ł[ Finally\ silanes\ R!TMS\ in which the group R is electron!withdrawing\ have been shown to react with chloral in the presence of a Lewis acid to give the corresponding trichloromethyl carbinols "Scheme 10# ð64JOM"82#32Ł[ RMgBr
R-TMS
+
Cl Cl Cl
CHO
+
Cl Cl Cl
R CHO HO R
Al, Ga or InCl3
TMS-O
Cl Cl Cl
Cl Cl Cl MeOH
(129)
R HO
Cl Cl Cl
R = allyl, aryl, vinyl, ethynyl, propargyl Scheme 21
5[90[2[1 Trichloromethyl Groups Attached to an Aromatic Ring The high reactivity of trichloromethylarenes makes them valuable intermediates in the synthesis of acids and their derivatives\ heterocyclic compounds and the tri~uoromethyl group "which we have seen is of great interest to the pharmaceutical and agrochemical industries#[ Similarly to trichloromethyl aliphatic compounds\ trichloromethylarenes may be made by converting a group which is already attached to a ring into a trichloromethyl group or by transferring a trichloromethyl group on to a ring[
17
Trihalides
5[90[2[1[0 Conversion of groups attached to an aromatic ring into the trichloromethyl group Methyl groups in arenes can be trichlorinated using chlorine\ by a free radical mechanism "Equation "029## ð51HOU"4:2#624Ł[ 1! and 3!Methylpyridines and 1! and 3!methylquinolines are also readily trichlorinated\ but here reactions are best carried out by passing the halogen into a solution of the substrate in glacial acetic acid\ optionally acetic anhydride\ and sodium or potassium acetate\ where the reaction is believed to proceed by an ionic process\ with the acetate acting as a base ð12JCS1771\ 28JCS670\ 40JCS0034Ł[ 2!Methylpyridine cannot be trichlorinated by this method\ but when its vapour and chlorine are passed over a chromia catalyst\ pretreated with hydrogen ~uoride\ 2! trichloromethylpyridine is produced ð71EUP54247Ł in reasonable yield[ CCl3 Cl2
(130)
heat or UV
While these methods are fairly general\ there are situations where other methods are necessary^ for example\ in the preparation of methylbenzotrichlorides where chlorination of dimethyl com! pounds leads to chlorination in both side chains\ and in the preparation of compounds such as 3!nitrobenzotrichloride where the electron!withdrawing group inhibits chlorination[ Thus\ car! boxylic acid groups in aromatic and heteroaromatic rings are converted into trichloromethyl groups by treatment with phosphorus pentachloride in thionyl chloride ð66JHC770\ 67JHC782Ł\ or with phosphorus pentachloride alone ð78JCS"P0#172Ł[ This conversion can also be accomplished by treating acids with chlorine in a mixture of phosphorus trichloride and phenylphosphonic dichloride ð72USP3308403Ł or phenyl dichlorophosphorane and phenylphosphonic dichloride ð78USP3722149Ł[ Substituted benzal chlorides\ which can be prepared from the corresponding aldehydes ð67JOC3256Ł\ can be chlorinated further to trichloromethyl compounds by treatment with isobutyl hypochlorite in aqueous sodium hydroxide\ optionally in the presence of an alcohol\ and a phase transfer agent ð67USP3987720Ł[ Substituted benzyl and benzal chlorides are also converted into the corresponding benzotrichlorides when they are treated with tetrachloromethane or hexachloroethane and aqueous sodium hydroxide in the presence of a phase transfer catalyst "PTC# by a process which probably involves nucleophilic attack on chlorine "Equation "020## ð75S113Ł[ Cl
X
CCl3 CCl4 or CCl3CCl3
(131)
50% aqueous , NaOH, PTC, reflux
R R X = H; R = 2-NO2, 2-NO2, 3-Me X = Cl; R = 2-NO2, 2-NO2, 3-Me, 2-Me, 3-Me, 4-Me, 2-Me, 2-Cl, 4-Et
A similar range of compounds is made by treating appropriate dibenzyl sulphides with chlorine or sulfuryl chloride "Equation "021## ð71S840Ł^ or by chlorinating with sulfuryl chloride the product obtained from treating an aldehyde with a dithiol in the presence of acid "Scheme 11# ð75USP3464454Ł[ Dichlorine monoxide can be used to chlorinate methyl groups in methylnitrobenzenes and other methylbenzenes which have electron!withdrawing groups on the aromatic ring "Equation "022## ðB! 71MI 590!91Ł[ While 3!nitrotoluene and highly deactivated compounds such as 1!chloro!3!nitro!\ 2\3! dinitro! and 2\4!dinitrotoluene are converted into the corresponding benzotrichlorides in very high yield\ 1!nitrotoluene is only dichlorinated by dichlorine monoxide to give the benzal chloride[ "NB[ This compound could be chlorinated further by methods outlined above[# In the case of the other substituted toluenes with deactivating groups in the 3 position\ chlorination takes place exclusively in the methyl group with the exception of p!toluenesulfonic acid\ which undergoes chlorination on the ring[ R
R
R
Cl2 or SO2Cl2
2 S
CCl4, POCl3 or o-dichlorobenzene
R = 2-Mea, 3-Meb,c, 4-Mea, 2-Bra, 4-NO2d,e, 2,3-CH=CH–CH=CHa aCl2/CCl4, bCl2, cSO2Cl2/CCl4, dCl2/POCl3, eCl2/o-dichlorobenzene
CCl3
(132)
18
Trichloromethyl R
S ( ) n S
R
CHO
HS
( )n
SH
R SO2Cl2
HCl in CHCl3
CCl3
CCl4
R = 3-Me, 4-NO2, 2-Cl, 4-MeO; n = 2 or 3 Scheme 22 NO2 2
NO2
+ 3Cl2O
CCl4
2
+ 3H2O
(133)
CCl3
5[90[2[1[1 Transfer of the trichloromethyl group to an aromatic ring Aromatic compounds can be trichloromethylated by reaction with tetrachloromethane in the presence of excess Lewis acid\ which is most commonly aluminum trichloride "e[g[\ ð76JPR0020Ł#[ Whilst the trichloromethyl compounds can be the main product\ diaryldichloromethanes are also produced in signi_cant amounts "Equation "023##\ although it is claimed that the addition of mordenite can reduce dimer formation ð81JAP93038032Ł[ The reaction is fairly general\ but there are complications when polymethyl aromatics are trichloromethylated[ Thus\ while m!xylene gives the expected 1\3!dimethyltrichloromethylbenzene\ a Jacobson!type rearrangement occurs in the reaction with p!xylene to give 1\3!dimethyltrichloromethylbenzene as the main product "o!xylene gives no trichloromethyl compounds but yields the dichloromethane\ "2\3!Me1C5H2#1CCl1# ð78CS70Ł[ Similarly\ the trichloromethylation of mesitylene gives the expected product ð50JA3359Ł\ but during the trichloromethylation of pseudocumene ð78CS70Ł both the expected 1\3\4!trimethyltrichloro! methylbenzene and about 04) of the rearranged 1\3\5 isomer are produced "Scheme 12#[ Although mesitylene itself gives only the expected trichloromethylmesitylene\ 0\2\4!trimethylhalobenzenes give signi_cant amounts of the rearranged product "Scheme 13^ in this scheme the products were isolated as the corresponding methyl benzoates# ð69JOC2526Ł[ In the case of the tetramethylbenzenes "Scheme 14#\ durene gives almost exclusively the rearranged product\ 1\2\3\4!tetramethyltrichloromethyl! benzene "a small amount of disproportionation took place under the conditions used#\ whereas isodurene gives predominantly 1\2\3\5!tetramethyltrichloromethylbenzene\ some of the 1\2\3\4 iso! mer and a trace of the 1\2\4\5 isomer ð50JA3359Ł[ It was suggested that rearranged products in these reactions could arise by the trichloromethyl group attacking a ring carbon that is already substituted followed by a 0\1!methyl migration and proton loss\ but rearrangements induced by acid\ HCl:AlCl2\ are also possible[ Cl CCl4, AlCl3
CCl3
+
(134)
CCl3 CCl4, AlCl3 100%
mesitylene
CCl4, AlCl3 15% CCl4, AlCl3 85%
pseudocumene Scheme 23
Cl
CCl3
29
Trihalides X
X
X AlCl3, CCl4
+ CCl3 CCl3
X H F Cl Br
100 70 88 93
: : : :
0 30 12 7
Scheme 24
CCl3 CCl4, AlCl3
durene
CCl4, AlCl3 23%
CCl3
CCl4, AlCl3 2% CCl4, AlCl3
isodurene
73%
CCl3
Scheme 25
Highly chlorinated trichloromethyl and tri~uoromethyl aromatics are quite di.cult to prepare\ but Castaner et al[ ð80JOC092Ł found that treatment of polychlorinated benzenes with aluminum trichloride and ~uorotrichloromethane gives the tri~uoromethyl compound[ Treatment of this with more aluminum trichloride in carbon disul_de yields the corresponding trichloromethyl compound[ This reaction is reversed by treating the trichloromethyl compound with aluminum trichloride and ~uorotrichloromethane[ Bis"trichloromethyl# and bis"tri~uoromethyl# compounds were also made by these methods "Scheme 15#[ CF3 Cl
CCl3F, AlCl3
Cl
Cl3 AlCl3, CS2
Cl
CCl3F, AlCl3
Scheme 26
Trichloromethyl anions can be used to prepare trichloromethylated aromatics ð89TL5720\ In a one!pot reaction sequence\ a cyclopentadieneyliron!complexed arene is added to a solution made from potassium t!butoxide and chloroform in THF at −67>C[ The mixture is allowed to warm to room temperature\ and the intermediate is demetallated in situ with iodine to give the trichloromethylarene in good yield "Scheme 16#[ Aromatic compounds that are susceptible to nucleophilic attack\ such as 0\2\4!trinitrobenzene\ can be trichloromethylated by reaction with trichloromethyl anions generated by the decomposition of trichloroacetic acid in DMSO[ The _rst step is the formation of the Meisenheimer complex\ which is then oxidized to give the trichloromethylated product "Scheme 17# ð72CC039\ 73JCS"P1#0128Ł[ 80JOM"308#246Ł[
20
Tribromomethyl Cl3C R1
R1 HCCl3, ButOK
H
R1
CCl3
I2
–78 °C, THF
R2
R2
FeCpPF6
FeCp
R2
R1 Me Me Me H NO2 H Cl
R2 2-Me 3-Me 4-Me p-TolSO2 4-Me But 4-Cl indane tetralin benzosuberane Scheme 27
Similarly\ hexachloroacetone can be used as the source of trichloromethyl anions[ The decompo! sition of hexachloroacetone in DMSO is slower than that of trichloroacetic acid\ but it is accelerated by the addition of water[ It is believed that it is actually the hexachloroacetone hydrate that decomposes into the trichloromethyl anion\ and trichloroacetic acid which in turn decomposes to generate a second trichloromethyl anion ð75JCS"P1#360Ł CCl3 NO2
O2N
CCl3CO2H
CCl3 NO2
O2N
NO2
O2N
–
DMSO
NO2
NO2
NO2
Scheme 28
5[90[3 TRIBROMOMETHYL DERIVATIVES*RBr2 Considerably less work has been carried out on making compounds bearing a tribromomethyl group than on those bearing a trichloromethyl group[ With few exceptions\ the essentials of the methods for making tribromomethyl compounds are the same as those for making the trichloro! methyl analogues[ Thus\ tribromomethyl carbinols are produced when cyclohexanone is treated with tribromomethyl lithium at −67>C in THF ð63JA2909Ł\ or when various 2!pyridyl ketones are reacted at −099>C ð77M0316Ł[ Corresponding to the decarboxylation of trichloroacetic acid and its sodium salt to give the trichloromethyl anion is the decarboxylation of the analogous tribromo compounds[ The main di}erence between the two systems is that the tribromo compounds are less stable[ Thus\ tribromo! methyl carbinols are obtained when sodium tribromoacetate decomposes in the presence of alde! hydes[ In a similar reaction\ anhydrides react to give tribromolactols or their tautomeric keto acids ð56JOC1055Ł[ Tribromomethyl carbinols are also obtained when\ in the presence of aldehydes\ tribromoacetic acid decarboxylates in DMSO ð72CC172\ 73JCS"P1#0136Ł\ or a mixture of the acid and its sodium salt decarboxylates in DMF ð81TL2324Ł[ Again corresponding to the trichloromethyl case\ the reaction between tributyl"tribromo! methyl#stannane and an aldehyde gives a tribromomethyl carbinol[ The main di}erence between the two reactions is that tribromomethylation is exothermic at room temperature whereas trichloro! methylation requires some heating ð64JOM"091#312Ł[ Finally\ tribromomethyl carbinols can be made by the reductive addition of tetrabromomethane to aldehydes using a lead:aluminum bimetal system ð78JOC333Ł[
21
Trihalides
5[90[4 MIXED SYSTEMS WITH FLUORINE*RCF1Hal Per~uoroalkyl iodides*CnF1n¦0I*are some of the most important intermediates in the prep! aration of compounds which bear the per~uoroalkyl group "e[g[\ ð73JFC"14#58\ 77MI 590!90Ł#[ Some methods for the preparation of these compounds have been described previously "see Sections 5[90[0[0 and 5[90[0[1[1#\ but there are others which need to be noted[ Most of these methods take a per~uorocarboxylic acid as their starting point[ For example\ the thermal decomposition of the acid in the presence of iodine ð42USP1536822Ł\ the decomposition of per~uoroacyl chlorides in the presence of potassium iodide at 199>C ð47JOC1905Ł\ the decomposition of per~uoroacyl anhydrides in the presence of iodine at 249Ð399>C ð46BRP646782Ł and the thermal decomposition of dry metal salts in the presence of iodine all give per~uoroalkyl iodides[ Sodium\ potassium\ barium\ mercury and lead salts have all been used in this last reaction\ but it is silver salts which give the best yields ð40JCS473\ 41JA737\ 41JA738Ł[ This is known as the Hunsdiecker reaction\ and it can also be used to obtain {dihalides| from the corresponding diacid salts\ although lactone formation can be a problem ð41JA737\ 41JA0863Ł[ More recently\ it has been shown that treatment of sodium and potassium salts of per~uorocarboxylic acids with iodine in re~uxing DMF gives per~uoroalkyl iodides in high yield ð56JOC722Ł[ One compound in this class which has attracted a lot of interest of late is per~uorooctyl bromide "PFOB# because of its potential use as a contrast agent for diagnostic imaging[ The telomerization reaction between bromopenta~uoroethane and tetra~uoroethylene does not a}ord a convenient route to PFOB because the propagation step is so much faster than chain transfer\ and a mixture of high telomers is obtained[ Most of the practical routes for the manufacture of PFOB start from per~uorooctyl iodide\ which of course is manufactured on a substantial scale\ and replace the iodine by bromine[ For example\ iodides can be treated with bromine in the vapour phase at 299Ð249>C ð80EUP349473\ 81EUP404147Ł\ or with ultraviolet irradiation for 09 h ð73MI 590!90Ł[ Also\ PFOB can be made by re~uxing per~uorooctyl iodide with tetraalkylphosphonium bromide ð81GEP3914116Ł\ or with sodium bromide ð80GEP2826456Ł in DMF "a certain amount of reduction to the monohydro compound occurs here#\ and by heating with metal "Cs\ Mn"II#\ Fe"II# Fe"III# or Co"II## bromides to 299>C in an autoclave ð80EUP350452Ł[
5[90[5 MIXED HALOFORMS*CHXY1 AND CHXYZ Most methods for the preparation of mixed haloforms take the simple haloforms and replace one or two of the original halogens by others[ Trichloromethane "chloroform# is ~uorinated on an industrial scale in the liquid phase using Swarts| catalyst or in the vapour phase using chromia! based catalysts with hydrogen ~uoride as the ~uorinating agent "see also Section 5[90[0[2#[ The compound of greatest interest to the manufacturer is chlorodi~uoromethane\ since it is used in the manufacture of tetra~uoroethene\ but dichloro~uoromethane can also be made by this method[ Similarly\ tribromomethane "bromoform# can be ~uorinated using antimony tri~uoride and bromine ð54BRP0903141Ł\ or a ~uoride!type ion exchange resin ð51NKZ825Ł\ to give dibromo~uoromethane "Equation "024##[ CHBr3
i, ii
CHBr2F
(135)
i, SbF3, Br2, reflux; ii, amberlite IRA-400 (F type), 80 °C
Chloroform\ bromoform and iodoform can all be treated with an alkali metal halide and a base in the presence of a phase transfer agent to give mixed haloforms "e[g[\ Equations "025#Ð"039## ð78LA076\ 76TL1658Ł\ but satisfactory yields are not always obtained[ A single iodine in iodoform can be replaced by bromine simply by stirring a mixture of iodoform and bromine in tetrachloromethane for some 04 h "Equation "030## ð71CB2783Ł[ NaBr, NaOH, PTC
CHCl3
CHCl3
NaI, NaOH, PTC
CHBrCl2
(136)
CHCl2I + CHClI2
(137)
22
Mixed Haloforms NaCl, NaOH, PTC
CHBr3 NaI, NaOH, PTC
CHBr3
NaCl, NaOH, PTC
CHI3 CHI3
Br2, CCl4
CHBr2Cl
(138)
CHBr2I
(139)
CHClI2 + CHCl2I
(140)
CHBrI2
(141)
Dibromochloromethane reacts with sodium iodide and sodium methoxide in methanol to give bromochloroiodomethane "Equation "031## ð47JA3171Ł\ and with mercuric ~uoride to give bromo! chloro~uoromethane "Equation "032## ð45JA368\ 74JA5882Ł[ Bromochloro~uoromethane having high optical purity has been made by pyrolysing the optically pure strychnine salt of bromochloro! ~uoroacetic acid ð78JA7409Ł[ NaI, NaOH, MeONa
CHBr2Cl
CHBr2Cl
CHBrClI HgF2
CHBrClF
(142)
(143)
The thermal decarboxylation of silver salts of halogenated acetic acids in the presence of a halogen "the Hunsdiecker reaction*see Section 5[90[4# has been used to make the haloforms CHCl1F\ CHClF1\ CHClBrF\ CHClFI\ CHBr1F\ CHBrFI\ CHFI1\ CHBrF1 and CHF1I "e[g[\ Equations "033# and "034## ð41JCS3148Ł[
Copyright
#
CHF2CO2Ag + I2
CHF2I
(144)
CHClFCO2Ag + Br2
CHClBrF
(145)
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.02 Functions Containing Halogens and Any Other Elements GRAHAM B. JONES and JUDE E. MATTHEWS Clemson University, SC, USA 5[91[0 FUNCTIONS CONTAINING HALOGEN AND A CHALCOGEN 5[91[0[0 Halo`en and Oxy`en Derivatives "R0CHal1OR1 and R0CHal"OR1#1# 5[91[0[0[0 Tetracoordinated carbon atoms with two identical halo`en and one oxy`en function attached "R0CHal1OR1# 5[91[0[0[1 Tetracoordinated carbon atoms bearin` mixed halo`ens and one oxy`en function "R0CHal1OR1# 5[91[0[0[2 Tetracoordinated carbon atoms bearin` one halo`en and two oxy`en functions "R0CHal"OR#11# 5[91[0[1 Halo`en and Sulfur Derivatives "R0CHal1SR1 and R0CHal"SR1#1# 5[91[0[1[0 Tetracoordinated carbon atoms with two identical halo`en and one sulfur function attached "R0CHal1SR1# 5[91[0[1[1 Tetracoordinated carbon atoms bearin` mixed halo`ens and one sulfur function "R0CHal1SR1# 5[91[0[1[2 Tetracoordinated carbon atoms bearin` one halo`en and two sulfur functions "R0CHal"SR1#1# 5[91[0[2 Halo`en and Se or Te Derivatives "R0CHal1SeR1 or R0CHal1TeR1# 5[91[0[2[0 Tetracoordinated carbon atoms bearin` two halo`ens and one selenium function "R0CHal1SeR1# 5[91[0[2[1 Tetracoordinated carbon atoms bearin` two halo`en and one tellurium function "R0CHal1TeR1# 5[91[0[3 Halo`en and Mixed Chalco`en Derivatives "R0CHal"OR1#"SR2## 5[91[1 FUNCTIONS CONTAINING HALOGEN AND A GROUP 04 ELEMENT AND POSSIBLY A CHALCOGEN 5[91[1[0 Halo`en and Nitro`en Derivatives] General Considerations 5[91[1[0[0 Tetracoordinate carbon atoms bearin` two halo`ens and one nitro`en function 5[91[1[0[1 Tetracoordinate carbon atoms bearin` one halo`en and two nitro`en functions 5[91[1[0[2 Tetracoordinate carbon atoms bearin` one halo`en\ one nitro`en and one oxy`en function 5[91[1[0[3 Tetracoordinate carbon atoms bearin` one halo`en\ one nitro`en and one sulfur function 5[91[1[1 Halo`en and Phosphorus Derivatives 5[91[1[1[0 Tetracoordinate carbon atoms bearin` two halo`en and one phosphorus function and one halo`en and two phosphorus functions 5[91[1[2 Halo`en and Arsenic Derivatives 5[91[1[2[0 Tetracoordinate carbon atoms bearin` two halo`ens and one arsenic function 5[91[2 FUNCTIONS CONTAINING HALOGEN AND A METALLOID AND POSSIBLY A CHALCOGEN AND:OR GROUP 04 ELEMENT
25 25 25 32 32 33 33 36 37 38 38 38 49 49 49 40 44 46 46 47 47 59 59 59 59 50 51
5[91[2[0 Halo`en and Silicon Derivatives 5[91[2[1 Halo`en and Boron Derivatives 5[91[2[2 Halo`en and Germanium Derivatives 5[91[3 FUNCTIONS CONTAINING HALOGEN AND A METAL AND POSSIBLY A GROUP 04 ELEMENT\ A CHALCOGEN OR A METALLOID
51 51 52 52
5[91[3[0 Halo`en and Lithium Derivatives 5[91[3[1 Halo`en and Ma`nesium Derivatives 5[91[3[2 Halo`en and Copper Derivatives
24
25
Halo`ens and any other Elements 5[91[3[3 5[91[3[4 5[91[3[5 5[91[3[6 5[91[3[7 5[91[3[8
52 53 53 53 54 54
Halo`en and Silver Derivatives Halo`en and Zinc Derivatives Halo`en and Cadmium Derivatives Halo`en and Mercury Derivatives Halo`en and Tin Derivatives Halo`en and Lead Derivatives
5[91[0 FUNCTIONS CONTAINING HALOGEN AND A CHALCOGEN A general review on ortho!ester derivatives covering the literature up to 0873 has been published ð74HOU"E4#Ł and provides a broad overview of several categories of haloalkyl systems relevant to this chapter[
5[91[0[0 Halogen and Oxygen Derivatives "R0CHal1OR1 and R0CHal"OR1#1# 5[91[0[0[0 Tetracoordinated carbon atoms with two identical halogen and one oxygen function attached "R0CHal1OR1# "i# From ethers Direct halogenation of ethers has proved a versatile technique for the synthesis of a variety of perhalogenated compounds of this class[ Novel per~uorinated ethers have been obtained by direct ~uorination of low molecular weight ethers with product ratios a function of the ~ow rate of ~uorine and carrier gas "usually helium# "Scheme 0# ð62JOC2506Ł[ The method has also been applied successfully to the preparation of per~uorinated polymers\ although in these cases the mixtures required heating up to 009>C for e.cient conversion ð66CC148\ 70JCS"P0#0210Ł[ Electrochemical ~uorination has also been investigated\ but it was found that\ under the optimum conditions used\ primary alcohols were converted into cyclic per~uorinated ethers in only moderate yield "Equation "0## ð65BCJ0777Ł[ The electrochemical ~uorination of ethylene glycol ethers has also been reported\ yielding complex mixtures of linear and cyclic per~uorinated compounds ð63ZOR1920Ł[
Me
Me
O
O
O
O
O
Me
F
20 ml/min He, 0.5 ml/min F2, –78 °C, 12 h
F3C
21%
O
F
F3C
16%
CF3
F F
20 ml/min He, 0.5 ml/min F2, –40 °C
Me
F
O
F
FF
O
O
O
F
F
F
CF3
F
Scheme 1
F F OH
HF, 3.5 A/1; 5 °C, 0–10 V
F F
F F
18%
F
O
(1)
CF3
Photochlorination of mixed halogenated ethers has been used in the synthesis of a number of anaesthetic agents "Scheme 1#[ Yields of the chlorinated systems are moderate to good\ reactivity being a function of carbon substitution patterns\ with monochlorinated carbon atoms being more reactive than the corresponding ~uoro!substituted carbons as expected ð41JA1181\ 60JMC406\ 60JMC482Ł[ Fluorination via direct substitution of chloro ethers has been accomplished using either HF or HF in the presence of SbF2 "Equation "1##[ Selectivity can be achieved by controlling HF introduction\ monitoring the progress of the substitution reaction by the HCl liberated ð60JMC482Ł[ Halogenation of heterocycles is a well!studied route to compounds of this class with trisubstituted
26
Halo`en and a Chalco`en
carbon atoms[ Electrochemical ~uorination of a range of oxanes gave the corresponding per! ~uorinated systems in moderate yield "Equation "2## ð68JFC"02#408\ 68JFC"04#242Ł[ F Cl
O
F
F
Cl F
Cl2, hν
F
80%
Cl
F F
O F Cl
Cl2, hν
F3C
O
Cl
Cl
F3C
80%
F O
F
F3C
75%
Cl
Cl F
Cl
Cl2, hν
F 3C
O
O
F Cl
Cl2, hν
F3C
O
Me 60%
F 3C
O
Cl
Scheme 2
CF3 F3C
Cl
O
CF3
HF, SbCl5, 0 °C, 12 min
Cl
or SbF3, SbCl5, 53 °C, 3 h 62%
F3C
O
electrochemical fluorination, HF 5.0–6.2 V, 3.5 A/dm2, 7 h
O
F
(3)
F
R
O
(2) F
Rf
R = Me, 28%; Et, 26%; Prn, 30%; Pri, 23%; Bun, 30%; Amn, 23%
Direct ~uorination of dioxane using elemental ~uorine is reported to give the per~uorinated system in moderate yield "Scheme 2# ð64JOC2160Ł\ whereas treatment with a mixture of sulfur tetra~uoride and hydrogen ~uoride gave the 1\1\2!tri~uorodioxane in high yield "Scheme 2# ð72JFC"11#094Ł[ The same product is also reported using the potassium salt of cobalt tetra~uoride ð60T3422Ł[ Finally\ ~uorination of 3!methylmorpholine using cobalt tri~uoride is reported to give the di~uoromethyl derivative shown in moderate yield "Scheme 2# ð67T086Ł[ O
SF4, 185 °C, 8 h; S2Cl2
O F
89%
O
O O
O
F
KCoF4, 220 °C
F 65%
O
O
F F
N
Me CoF3, 100 °C
F
N
F
31%
Scheme 3
"ii# From mixed trihalomethanes Chlorodi~uoromethane has been used extensively as a source of di~uoromethylene\ which can be intercepted by alkoxide nucleophiles to give alkoxydi~uoromethane adducts[ The conditions used
27
Halo`ens and any other Elements
are similar to those employed in the ReimerÐTiemann reaction\ and give good yields of product di~uoro ethers "Equation "3## ð47JA2991\ 59JOC1998Ł[ A phase transfer method has also been used to generate di~uorocarbene from chlorodi~uoromethane ð77JFC"30#136Ł[
R OH
i, NaOH, H2O, dioxane, 70 °C ii, CHFCl2
R
F (4)
O F
R = Ph, 65%; 4-MeC6H4, 66%; 4-MeOC6H4, 53%; 2,4-Me2C6H3, 56%; 2,4-Cl2C6H3, 44%; 2-naphthyl, 66%; Pri, 60%
The range of functionality tolerated by the reaction includes substituted primary and secondary alkyl halides\ which provides access to heavily functionalized systems "Scheme 3# ð65CB1240Ł[ Trihalomethylmercury compounds have also been used to deliver the dihalomethyl moiety to alcohols and carboxyl groups ð53JA1850\ 63JOM"56#230Ł[ Phenyl"bromodichloromethyl#mercury thus adds to carboxylic acids to yield the dichloromethyl esters shown "Scheme 4#\ and with butanol to give the dichloro ether shown in high yield\ producing phenylmercuric bromide as by!product in both cases[ Di~uorocarbene has also been generated from FSO1CF1CO1H\ and it inserts into alcohols in the presence of CuI ð78JFC"33#322Ł[ Cl
F
Cl
O
Cl
HClCF2
Cl
O
F
97%
F
OH
Cl
F
Cl
Cl
Cl HClCF2
O
O
OH Cl
Cl
F
98%
F F
F
Scheme 4
O PhHgCCl2Br + RCO2H
R
benzene, 60 °C, 45 min
Cl O
+ PhHgBr
Cl R = Ph, 86%; Me, 92%; ClCH2, 86%; But, 81%
PhEt, 80 °C, 30 min
Bu
O
PhHgCCl2Br + BuOH
Cl 85%
+ PhHgBr
Cl
Scheme 5
"iii# From dihalo ethers Treatment of dichloro ethers and bromochloro ethers with antimony tri~uoride results in halogen substitution to yield the corresponding di~uoro ether "Scheme 5# ð52AFC"2#070\ 69ZOR033\ 61JMC593\ 61JMC595Ł[ Alternatively\ anhydrous hydrogen ~uoride can be used in the presence of antimony penta~uoride giving high yields of the di~uoro adducts "Equation "4## ð61JMC593Ł[ Treatment of
28
Halo`en and a Chalco`en
cyclic per~uorinated ethers with aluminum trichloride is reported to give the corresponding a\a\a?! trichloro ether in good yield "Equation "5## ð67JFC"01#248Ł[ Cl Cl
Cl O
Cl
75%
CF3
Cl F
F
SbF3, 60 °C
Cl
F
O F
F
O
F
SbF3, 60 °C
F
70%
CF3
F
F F
O
Cl F Me
Cl
Br
O
Br
F
51%
Br
CF3 Cl
F
SbF3, 117 °C
Me
O
Br
F
F
CF3 F
Cl
SbF3, ∆
O
Br
F O
67%
Cl
C F3Cl Cl
CF3 F SbF3, ∆
Cl
Cl3C
O
Me 84%
F Cl3C
F
F O
Me
Scheme 6
Cl F Cl
F
F F
O
HF, SbCl3, 0 °C 80%
F
F
F F
O
F
F3C
F O
(5)
F
AlCl3, 143 °C, 19 min 53%
Cl F3C
F O
Cl
(6)
Cl
"iv# From carbonyl derivatives Electrochemical ~uorination of acyl chlorides and esters has been used to prepare compounds of this class[ The process gives moderate yields of cyclic per~uorinated ethers\ but often results in formation of mixtures "Scheme 6# ð67JFC"01#0\ 72JFC"12#012Ł[ Sulfur tetra~uoride has been shown to be e}ective for the conversion of the carbonyl group to a di~uoromethylene group[ Thus\ treatment of a variety of anhydrides\ esters\ and formate esters with sulfur tetra~uoride yields the corresponding di~uoromethylene systems\ often in high yield "Scheme 7# ð59JA432\ 53JOC0\ 69ZOR033\ 64ZOR0561\ 65ZOR0176\ 65ZOR0687\ 72JFC"11#196Ł[ Exposure of aryl!ortho! diacid systems to the same conditions results in ring formation in addition to partial per~uorination "Scheme 8# ð69ZOR1387Ł[ Phosphorus pentachloride has been shown to react with a variety of formate esters to yield the corresponding a\a!dichloro ethers "Equation "6## ð52CB0276\ 56OS"36#36\ 60RTC445Ł[ The analogous addition reactions are also applicable to oxalates and other carboxylic esters\ which constitute high! yielding routes to dichloro ethers\ trichloro ethers\ and dichloroacetates "Scheme 09# ð40JA4057\ 45M212\ 64S416Ł[ a!Chlorination of a!chloro!a!alkoxyacyl chlorides has also been employed\ giving the corresponding dichloroalkoxyacyl chloride in good yield "Scheme 09# ð48CB2069Ł[
39
Halo`ens and any other Elements O
C3F7 HF/3.5 A/dm2, 5 °C, 6.4 V, He 100 ml/min
Cl 20%
F O
F3C
C4H9
HF/3.5 A/dm2, 5 °C, 6.4 V, He 100 ml/min
OMe 21%
F O
C2F5
O OMe
CF3
HF/3.5 A/dm2, 5 °C, 6.4 V, He 100 ml/min
O
19%
F
F O
Scheme 7
Cl
Cl
Cl SF4, 300 °C, 10 h
O
O X
F
F
46%
O
O
F CF3
Cl
O
F O
SF4, HF, ∆
X
O
CF3
F
F
X = H, 61%; 4-NO2, 69%; 3-NO2, 83%; 2-Cl, 71%; 4-Cl, 74%; 4-F, 69%; 3-Me, 63%; 4-Me, 46%; 2-MeO, 36%
OCOCF3
OC2F5
OCOCF3
OC2F5
SF4, HF, ∆ 79%
OCOCF3
OC2F5
OCOCF3
OC2F5 Scheme 8
CF3
CO2H CO2H
SF4, ∆
CO2H
SF4, ∆
O
F O
76%
F
CF3 F
CO2H
CF3 F
O
CF3 F
F
Scheme 9
O R
O
Cl
PCl5, ∆
R
+ POCl3 O
(7)
Cl
R = Me, 84%; But, 68%; Ph, 85%
Another versatile route is o}ered using a\a!dichloromethyl methyl ether as a transfer agent\ in the presence of mercuric chloride[ A variety of aryl formate esters have been converted to the corresponding dichloromethyl ethers using this very high!yielding method "Equation "7## ð60RTC445Ł[
30
Halo`en and a Chalco`en O
PCl5, 80 °C
OPh
Cl
Cl
>50%
OPh
O R
O
O
Cl
PCl5, 85–90 °C, 12 h
R
R
O Et
O
Et
O
R
Cl
R = Me, 75%; Et, 85%
O
Cl
O
Cl
PCl5, 110 °C, 15 h
Et
65%
Cl
O
O
O
Et
O Cl Cl
EtO
Cl
Cl2, 150 °C
Cl Cl
EtO
70%
O
O Scheme 10
O
O MeOCHCl2, HgCl2
X
X
O
Cl Cl
(8)
X = H, 85%; 2-Me, 94%; 3-Me, 90%; 4-Me, 90%; 3-Cl, 90%; 4-NO2, 86%; 3-HCl2CO, 90%
"v# From haloalkoxyalkenes Chlorination of chloroalkoxyalkenes has been used successfully to give the corresponding dichloroalkoxyalkanes in good yield "Scheme 00#[ Typical conditions involve exposure of the alkene to a stream of chlorine gas or dry hydrogen chloride "generated in situ# at −4>C followed by distillation of the product ð46RTC858\ 47CB795Ł[ OEt Cl OEt Cl
Cl
Cl
OEt
EtO
Cl
OEt Cl Cl
dry HCl, –5 °C 73%
Cl
OEt Cl Cl
Cl Cl EtO
OEt Cl Cl
dry HCl, 0 °C 88%
dry Cl2, –5 °C 74%
Scheme 11
"vi# From haloalkenes The addition of primary alcohols to halogenated alkenes proceeds rapidly\ giving dihaloalkoxy! alkanes in high yield[ The reactions are often catalyzed by trace amounts of the corresponding metal alkoxide^ this is often required for addition of less reactive secondary and tertiary alcohols\ which usually give mixtures of products "Scheme 01# ð59JOC882\ 54AFC"3#49\ 63BSF1961Ł[ Electron! withdrawing substituents on the alkene also accelerate the reaction^ thus\ methyl tri~uoroacrylate
31
Halo`ens and any other Elements
reacts faster than methyl acrylate ð62CCC55\ 75ZOR0723Ł[ Addition of oximes has also been accomplished\ merely requiring more elevated temperatures "Scheme 01# ð62CCC55Ł[ Addition of alkyl and trihaloalkyl hypohalites to haloalkenes is another useful route to this class[ A variety of primary and tertiary alkyl hypohalites add cleanly at low temperature "Scheme 01# to give high yields of the adducts ð69JOC2629\ 64JA02\ 64JFC"4#14Ł[ Bis"tri~uoromethyl#trioxide has also been employed for this type of addition reaction\ which is applicable both to acyclic and cyclic alkenes "Scheme 01# ð63JOC0187Ł[ Per~uorinated alkenes are reported to react with sulfur trioxide to give cyclic per~uoro! 1!b!sulfones in excellent yield ð75ZOR0731Ł[ Per~uoroalkenes also react with halogen mono~uoro! sulfates to yield both 1!haloalkyl~uoroalkyl ~uorosulfates and vicinal bis"halosulfonyloxy# ~uoroalkanes ð74IZV548Ł[
F
F
F
F
Cl
F
F
BunOH, 10% Na, 0–38%
F
F
F
OBun
81%
OH
F
F
O
, 5% Na, THF, –10 °C
F
75%
F
F Cl
Br
F
Br
F
EtCO2
O
Br
79%
F N
F
F
Br
EtOH, 10% Na, –10 °C–>16 °C
F OH , DME, 10% Na, 25 °C
F
ClOMe, –80 °C
F
96%
F
F
F
O
O F
CF3 CF3 CF3 , –62 °C–>25 °C
F
CF3
F O F
CF3OO2CF3, 67 °C, 8 h
F
F
N
F
F 3C
95%
F
F O
Cl
F3C
F
EtCO2
92%
F
Et
F
F
CF3 CF3 CF3
O2CF3
F
80%
OCF3
F Scheme 12
Epoxidation of ~uoroalkenes is a convenient route to a\a!di~urorooxiranes[ High yields are attainable at low temperature using moderate to high strength hydrogen peroxide "Equation "8## ð55JOC1201\ 69JOC1943\ 61MI 591!90\ 62ZOR1902Ł[ C4F9
F
F
F
60% H2O2, MeOH, –20 °C, 8 h 82%
F
C4F9 F
F
(9)
O
a\a!Dichlorooxiranes have been used by Corey in the enantioselective synthesis of azido and amino acids "Scheme 02#[ The oxiranes\ generated in situ from trichloromethyl carbinols\ are immediately ring!opened by the SN1 attack of aqueous azide\ subsequent oxidation giving a!azido acids in high yield ð81JA0895Ł[
32
Halo`en and a Chalco`en H R
OH
H
NaOH, NaN3
CCl3
O
R
then KH2PO4
Cl Cl
N3
H
R
CO2H
R = n-C5H11, 89%; C6H5(CH2)2, 91%; c-C6H11, 89%; But, 80% Scheme 13
5[91[0[0[1 Tetracoordinated carbon atoms bearing mixed halogens and one oxygen function "R0CHal1OR1# Selective mono~uorination of dichloro ethers has been used to prepare chloro~uoro ethers in moderate to good yield "Scheme 03# ð60JMC482\ 61JMC593\ 64JFC"5#26Ł[ Another useful strategy is addition of tri~uoromethyl hypochlorite to mixed 0\0!dihaloalkenes giving the dihalo ethers in excellent yield "Scheme 03# ð69JOC2629\ 61JMC595Ł[ The ester BrCF"OPh#CO1Et has been prepared by bromination of ethyl~uoro"phenoxy#acetate ð75JOC844Ł[ Cl F Cl
F
F F
O F
F F
anhydrous HF, SbCl5 (cat.), 0 °C
F Cl
Cl
80%
F
F
F F
O F F
ClOCF3, –80 °C 90%
F3C
O F
F
Cl F
Cl
Scheme 14
5[91[0[0[2 Tetracoordinated carbon atoms bearing one halogen and two oxygen functions "R0CHal"OR#11# Numerous examples of compounds of this class exist\ as the corresponding carbenium ion halide salt\ a consequence of stabilizing in~uence of the alkoxy functions ð61CRV246\ 71S0\ 74HOU"E4#Ł[ The following examples described are clear!cut cases where the chemistry is best described by the covalent species[
"i# From 0\2!dioxolanes Direct formation of 1!~uoro!1!tri~uoromethyl!0\2!dioxolanes has been accomplished by treating aryl ortho!bis"tri~uoroacetic# esters with a mixture of sulfur tetra~uoride and hydrogen ~uoride ð65ZOR0176Ł[ Formation of 1!chloro!0\2!dioxolanes has been achieved using a variety of protocols ð56LA"696#24Ł[ Chlorination of derived ortho!esters with phosphorus pentachloride at elevated tem! peratures is a high!yielding process\ as is direct chlorination of unsubstituted 0\2!dioxolanes "Scheme 04# ð50CB433\ 55CB1514\ 56LA"696#24\ 57LA"619#035Ł[ A related procedure used substitutive chlorination of a 1!acetoxy!0\2!dioxolane using dichloromethyl ether ð58TL4992Ł[ Alternatively\ displacement of chloride from 1\1!dichloro!0\2!dioxolanes has been used ð55CB1514Ł[
"ii# From ortho!formates Decomposition of vinyl ortho!formates is a versatile route to dialkoxymethyl halides[ Treatment of dialkoxy vinyl ortho!formates with either hydrogen chloride or hydrogen bromide results in
33
Halo`ens and any other Elements Cl
O
SOCl2, 80 °C
Cl
O
92%
Cl
O
Cl
O
Cl
O
R1
O
OR2
PCl5, 110 °C
R1
O
R1
O
Cl
R2
= Ph, = Me, 88% R1 = CO2Et, R2 = Et, 53% R1 = H, R2 = Et, 87% Scheme 15
liberation of the dialkoxyhalomethane "Scheme 05# ð60RTC0012Ł[ Alternatively\ substitution of triaryl ortho!formates with acetyl chloride has been reported to give good yields of the chloro! diaryloxymethane ð51CB0748Ł[ OR
OR
HCl or HBr, Et2O, 25 °C, 15 min
O
RO
X
RO R = CH=CH2, X = Cl, 50% R = Ph, X = Cl, 60% R = Ph, X = Br, 50% R = p-Tol, X = Cl, 65% R = C(Me)=CH2, X = Cl, 90% OPh
PhO
OPh
MeCOCl
OPh
81%
Cl
PhO
Scheme 16
5[91[0[1 Halogen and Sulfur Derivatives "R0CHal1SR1 and R0CHal"SR1#1# 5[91[0[1[0 Tetracoordinated carbon atoms with two identical halogen and one sulfur function attached "R0CHal1SR1# "i# From sul_des a!Chlorination of sul_des is a popular route to these compounds\ and a variety of di}erent protocols have proved e}ective including photochemical chlorination and use of thionyl chloride "Scheme 06# ð41JA2483\ 42LA"470#022\ 47LA"505#0\ 48LA"510#7\ 54JOC3900Ł[ The ester MeSCH1CO1Me has been converted into the corresponding a\a!dichloro ester using thionyl chloride and into the dibromo ester by reaction with bromine ð70AG"E#474Ł[
Me
SOCl2, 0 °C, 1.5 h then 95 °C, 4 h
Me
S
Cl Me
Cl
Cl2, CCl4, –20 °C
Me
S
Cl
Me 57%
Scheme 17
Cl
S
77%
S
Cl
34
Halo`en and a Chalco`en "ii# From iodo~uoroalkanes
The photochemical reaction of ~uoroiodo alkanes with both methyl sul_de and dimethyl disul_de has been investigated extensively\ and the radical addition process was found to give good yields of the corresponding di~uoro sul_des "Scheme 07#\ the only drawback being the sluggishness of the reaction ð61JCS"P0#044\ 61JCS"P0#048\ 61JCS"P0#0495\ 61JCS"P0#1327Ł[ Metallation of terminal iodo~uoro! alkanes with methyllithium at −67>C\ followed by addition of sulfur dioxide\ results in formation of a lithium di~uoroalkylsul_nate by attack of the intermediate organolithium species ð78S352Ł[ F
F
F3C F I
F F
F Me
48%
I
S F
MeSSMe, UV, 30 d
F
F
F3C
93%
F
F
F
MeSSMe, UV, 21 d
I
Me
F F S
S F
Me
F
Scheme 18
"iii# From a\a!dichloroalkyl sul_des Dichloroalkyl sul_des react smoothly with antimony tri~uoride in the presence of catalytic quantities of antimony penta~uoride to yield the corresponding di~uoro sul_des "Scheme 08# ð41JA2483\ 54JOC3900Ł[ The substitutions are regioselective for the carbons alpha to the sulfur center as shown by control reactions[ F S
Me
Br
Cl
F
SbF3, SbF5 (cat.) 75%
Me
Cl
Cl
Br
F
S Cl
S
Cl Cl
SbF3, SbF5 (cat.)
Cl
46%
F
F
S F
F F
F
Scheme 19
"iv# From chlorodi~uoromethane Substitution of the chloro group of this haloform with thiols has been achieved using a variety of conditions\ typically involving addition of a sodium thiolate followed by thermolysis "Scheme 19# ð46JA4382\ 68JOC0697\ 74S386Ł[ Some debate exists concerning the mechanism of the substitution\ which appears to have both a carbene and SN1 type character[ A phase!transfer method\ which undoubtedly involves di~uorocarbene\ has been described for preparation of sul_des ArSCHF1 from aromatic thiols ð77JFC"30#136Ł[ Cl
F
PhCH2SH, NaOH 50%, DMF, 65 °C
Ph
S
F
75%
F Cl
F F
Na, MeOH then PhSH, 7 h 63%
Scheme 20
F Ph
S
F F
35
Halo`ens and any other Elements
"v# From thioformates Thioformates react cleanly with phosphorus pentachloride in carbon tetrachloride to yield the corresponding a\a!dichloromethyl sul_des in high yield "Scheme 10#[ An alternative but slightly less e.cient route to such compounds is via halomethylene transfer from dichloromethyl methyl ether\ catalyzed by mercuric chloride ð61RTC238Ł[ O R
R
+ POCl3
R
76–87%
S O
Cl
PCl5, CCl4, –40 °C–>25 °C
S Cl
MeOCCl2, HgCl2, reflux 4 h
R
75–93%
S
Cl
+ MeOCHO S
Cl
Scheme 21
"vi# From alkenes "a# Vinyl sul_des[ Chlorination of 0!chlorovinyl sul_des has been used to generate bis"alkylthio#tetrachloroethanes "Scheme 11#[ In this example the alkene is readily available via thiolate!induced substitution and elimination from the corresponding hexachloroethane ð47CB795Ł[
Cl3C
CCl3
NaSEt
EtS Cl
SEt Cl
Cl2 52%
Cl EtS Cl
Cl SEt Cl
Scheme 22
"b# 0\0!Dihaloalkenes[ Addition of thiols and disul_des to halogenated alkenes proceeds rapidly when they are subjected to either ultraviolet or x!ray radiation to give the corresponding addition products "Scheme 12#[ As expected\ addition of thiolates proceeds without photolytic conditions\ but the reaction rates are heavily dependent on the nature of the haloalkene substitutents[ Mixed chloro! and bromo~uoroalkenes are far more reactive than tetra~uoroethylene\ which requires forcing conditions ð59JA4005\ 50JA739\ 54JOC3900\ 55BCJ1080\ 61JCS"P0#23\ 63JFC"3#096\ 65JCS"P0#0067Ł[ Free! radical addition of tri~uoromethanesulfonyl chloride to haloalkenes under UV irradiation has been employed and gives moderate yields of the tri~uoromethylsul_de adducts "Scheme 12# ð51JA2037Ł[ Thermolysis of tetra~uoroethylene with elemental sulfur is reported to produce _ve!\ and six! membered cyclic sul_des bearing a\a!di~uoromethyl groups in yields ranging from 09) to 59) ð51JOC2884Ł[ Addition of thiols to di~uoroalkenes catalyzed by Triton B is also reported to produce a\a!di~uoroalkyl sul_des in high yield ð49JA2531Ł[ Activated haloalkenes\ including penta~uoro! propene!1!sulfonyl ~uoride\ undergo rapid addition of alkyl hydrosul_des\ yielding 0!alkylthio!1H! penta~uoropropane!1!sulfonyl ~uorides "Scheme 12# ð75ZOR0723Ł[
"vii# From carbon disul_de Treatment of carbon disul_de with elemental ~uorine at −019>C is reported to yield octa~uoro! ethyl methyl sul_de in 59) yield ð66IC1863Ł[
"viii# From a!~uoroalkyl sulfoxides The reaction of the sulfoxide of 3!MeOC5H3SOCH1F with "diethylamino#sulfur tri~uoride gives the di~uorosul_de 3!MeOC5H3SCHF1 "57)# by a Pummerer!type reaction ð89JOC3646Ł[ The sul_de
36
Halo`en and a Chalco`en F
Cl
F
Cl
F
RS
RSH, x-rays, 3–4 weeks, 25 °C
Cl
F
F
R = Me, 71%; Et, 61%; Pri, 74%
F
F
S
O
F
F
PhSH, dioxane, 60–80 °C
F
F
91%
F
F
F
S
Me
90%
Cl
F
F
F
F F
S Ph
F
F
ClSCF3, hν, 2 h (R = H)
F F
S F F
R
F
CF3
R = H, 50%; CF3, 63%
CF3
S
C4H9
66%
Cl
R
CF3
C4H9SH, Et2O, –60 °C
SO2F
Me
F
MeSH, 4M NaOMe
Cl
F
F3C
71%
F
F
F
CF3SH, UV irradiation 15 min
OMe F
Cl
SO2F
F
F
Scheme 23
can be oxidized to the corresponding sulfoxide and sulfone[ The reaction is\ however\ unsuccessful with PhSOCH1F[ 5[91[0[1[1 Tetracoordinated carbon atoms bearing mixed halogens and one sulfur function "R0CHal1SR1# Thiolate additions to mixed chloro~uoroalkenes under both radical and ionic conditions have been employed to synthesize mixed dihalo sul_des of this class "see Section 5[91[0[1[0#[ Typical conditions parallel those for identically substituted haloalkenes\ and product yields are comparable "Scheme 13# ð48LA"510#7\ 51JA2037\ 55BCJ1080\ 63JFC"3#096\ 65JCS"P0#0067Ł[ Alternatively\ treatment of dichloro sul_des with antimony tri~uoride results in monosubstitution of chlorine\ giving the mixed "chloro~uoro#sul_de in good yield "Scheme 13# ð48LA"510#7Ł[ The esters BrCF"SR#CO1Et "R Et and Ph# have been prepared by NBS bromination of the corresponding "ethylthio#~uoroacetate or ~uoro"phenylthio#acetate ð75JOC844Ł[ MeS–, MeSSMe
F
F
F
56%
F
Cl
ClSMe, hν, 26 h
Cl
42%
S
Me
F S
S
Cl Cl
SbF3 72%
Scheme 24
F 3C
F F F
Me
F3C
S Me
Cl
F
S
Cl
Cl F
37
Halo`ens and any other Elements
5[91[0[1[2 Tetracoordinated carbon atoms bearing one halogen and two sulfur functions "R0CHal"SR1#1# As in the case of many compounds described in Section 5[91[0[0[2\ much of the chemistry of compounds of this class is represented by the corresponding halothiolium salts ð55AHC"6#28\ 79AHC"16#040Ł[ Cases illustrated below are con_ned to systems where the chemistry is best represented by the covalently bound species[ "i# From thioacetals Chlorination of 0\2!dithianes has been used to generate versatile 1!chloro!0\2!dithianes which are useful for coupling reactions of this masked carbonyl[ Typical conditions involve either sulfuryl chloride or N!chlorosuccinimide\ and recovered yields are high "Scheme 14# ð65BCJ442\ 66TL774\ 68JOC0736Ł[ SO2Cl2, CHCl3
S
S
95%
S
S Cl
S
S NCS, PhH, 20 °C, 30 min
S
S
95%
S
S Cl
Scheme 25
"ii# From thioformates and ortho!thioesters Ortho!thioesters can be monochlorinated successfully using either phosphorus chlorides or acetyl chloride as donors\ giving moderate yields at elevated temperatures "Scheme 15# ð50LA"537#10\ 66JPR06Ł[ An alternative procedure involves treatment of thioesters with a dichloromethyl aryl ether in the presence of mercuric chloride "Scheme 15#[ This procedure\ however\ is less e.cient in that it requires 1 equivalents of thioester ð61RTC238Ł[ SMe SMe
MeS
SMe
MeCOCl, 70 °C 63%
SMe
Cl
O
SEt SEt
EtS
O
PCl3 O CCl4, 78 °C, 1 h 70%
SEt SEt
Cl
SPh
0.5 PhOCHCl2, HgCl2, 90 °C
SPh
80%
SPh
Cl CF3
S
UV irradiation, 3 h, Cl2CF2
Cl
F 3C
Cl
S Cl
S
93%
CF3 CF2Cl S ClF2C
UV irradiation, 3 h, Cl2CF2
F
83%
F
S S
F CF2Cl
Scheme 26
Halo`en and a Chalco`en
38
"iii# Dimerization of thiocarbonyl compounds A variety of substituted thiocarbonyl compounds are reported to undergo rapid dimerization on irradiation with UV light ð54JOC0264Ł[ The corresponding 0\2!dithietanes are formed in high yields\ and are easily puri_ed by distillation "Scheme 15#[
5[91[0[2 Halogen and Se or Te Derivatives "R0CHal1SeR1 or R0CHal1TeR1# 5[91[0[2[0 Tetracoordinated carbon atoms bearing two halogens and one selenium function "R0CHal1SeR1# A variety of examples of compounds from this class have been reported\ and their preparation often involves transmetallation reactions of metal selenyl dihalomethyl derivatives[ Bis"penta~uoroethyl# monoselenide has been prepared by reaction of selenium powder with the corresponding penta~uoroethyl silver salt ð52JCS0157\ 62JCS"D#1203Ł[ Thermolysis of selenium metal with tetra~uoroethylene in the presence of catalytic amounts of iodine\ however\ results in the formation of a mixture of octa~uoroselenolane and octa~uoro!0\3!diselenane "Scheme 16# ð51JOC2473Ł[ Tetra~uoroethylene also reacts with tetraselenium bis"hexa~uoroarsenate"V## over extended periods of time to yield bis"per~uoroethyl# diselenide in good yield "Scheme 16# ð66CJC2025Ł[ Similar reactions have been perfomed using Se7"AsF5#1\ and Se7"Sb1F00#1\ which both react with tetra~uoroethylene to give the bis"per~uoroethyl# diselenide in nearly quantitative yield ð62JCS"D#1203Ł[ Reaction of selenium metal with tri~uoroiodomethane results in the formation of bis"tri~uoromethyl# mono! and diselenide ð47JCS1828Ł[ Similarly\ reaction of silver hepta~uoro! butyrate with selenium metal results in the formation of hepta~uoropropyl mono! and diselenide ð48ZOB831Ł[ Reaction of this diselenide with mercury results in the formation of bis"hepta~uoro! propylseleno#mercury\ which is a versatile alkylseleno transfer agent "Scheme 16# ð52JCS0157Ł[ Treatment of this\ and related mercurials\ with iodine results in near quantitative conversion back to the bis"hepta~uoropropyl# diselenide ð54JCS6400Ł\ whereas combination with 1 equivalents of iodosilane results in good conversion to the corresponding silyl selenide "Scheme 16# ð51JCS1189Ł[ Diselenides also react with manganese pentacarbonyl hydride to yield the corresponding organo! selenium manganese complexes ð54JCS6404Ł[ It has been reported that chlorination of 1\4!dibromo! selenophene results in the formation of 1\4!dibromoselenophene!1\2\3\4!tetrachloride\ although no details of conditions or yield were provided ð25BCJ046Ł[ Diphenyl diselenide reacts under dissolving metal reduction conditions to form an intermediate sodium selenide[ This species can be intercepted with per~uoroalkyl iodides under photolytic conditions to yield per~uoroalkyl selenides in moderate yield "Scheme 16# ð66ZOR1997Ł[ Bis"per~uoroethyl# monoselenide reacts with iodine monochloride to form di~uoro"per~uoroethyl#selenium in quantitative yield ð65JFC"6#150Ł[ Selenocarbonyl di~u! oride is reported to undergo addition with amines to yield an unstable amino di~uoromethyl adduct ð89JOM"275#210Ł[ Tri~uoromethyl selenocarbonyl ~uoride "Se1C"F#CF2#\ produced by thermal 0\1 elimination of trimethyltin ~uoride from trimethylstannylpenta~uoroethylselenane\ is also reported to undergo similar addition reactions ð89JOM"275#210Ł[ Di~uoromethyl selenoethers ArSeCHF1 can be prepared from chlorodi~uoromethane and ArSe− ð74S386Ł[
5[91[0[2[1 Tetracoordinated carbon atoms bearing two halogen and one tellurium function "R0CHal1TeR1# Di~uoromethyl compounds of tellurium were unknown until the mid!0889s[ A general protocol has been reported in which dimethyl telluride is reacted with either a bis"tri~uoromethyl# cadmium or tri~uoromethylzinc bromide in the presence of acetonitrile and boron tri~uoride "Scheme 17# ð83AG"E#212Ł[ The route is reported to be general for all chalcogens\ thus in a similar manner\ methyl "di~uoromethyl# selenide is also formed^ however\ isolated yields were not reported in either case[ Per~uoroalkyl tellurides\ however\ have been prepared by a variety of means ð64JCS"D#377Ł[ One method involves reaction of per~uoroalkyl radicals on a tellurium mirror\ giving low yields of per~uoroalkyl ditelluride ð52AJC611Ł[ A more e.cient method for the preparation of bis~uoroethyl monotelluride is to react tetra~uoroethylene with Te3"AsF5#1 in a Monel reactor "Scheme 17#[ This method is general\ and manipulation of conditions allows formation of varying amounts of the
49
Halo`ens and any other Elements F
F
F
Se
Se, I2, 250 °C, 7 h
F Se
F
+
F Se 5%
10%
F
F
F
F
F
F
OAg
2 SiH3I, 25 °C
H
71%
Ph
Se
Se
Ph
H
H Si
Se
CF3
F
F F
F Se
F3C
ii, Hg, 48 h 99%
Hg(SeC3F7)2
Se
F
i, Se, 280 °C, 2 h
F
F
F3C
87%
O
F3C F
F
Se4(AsF6)2, 14 d, 25 °C
Hg
F
F
F
F
F
Se
C2F5
i, Na, NH3(liq.) ii, C3F7I, hν
Ph 50%
F
Se
CF3 F
+ HgI2
Se
CF3
F
F
Scheme 27
corresponding ditellurides ð64JCS"D#377Ł[ Per~uoroalkyl tellurides have also been prepared from lithium aryl tellurides "obtained by reduction of diaryl ditellurides with LiAlH3# under photo! chemical conditions "Scheme 17# ð68ZOR0450Ł[ Cd(CF3)2, MeCN, BF3, –30 °C
Me2Te
Me
F
Te F
F F
F F
Te4(AsF6)2, 100 °C, 15 atm 87%
F F3C
F
F
F CF3
Te
C3F7I, hν, 30 min
TeLi
Te 44%
C2F5 F
F
Scheme 28
5[91[0[3 Halogen and Mixed Chalcogen Derivatives "R0CHal"OR1#"SR2## Chemistry of these systems is chie~y described by the corresponding oxathiolium salts\ thus excluding their detailed coverage in this section[ The reader is encouraged to consult references describing such systems ð63JHC832Ł[
5[91[1 FUNCTIONS CONTAINING HALOGEN AND A GROUP 04 ELEMENT AND POSSIBLY A CHALCOGEN 5[91[1[0 Halogen and Nitrogen Derivatives] General Considerations Compounds of this general class are somewhat unstable\ with the major contributing isomeric forms being the corresponding haloiminium salts\ for example\ RCHal1NR0R1\ which behaves as
Halo`en and a Group 04 Element
40
RC1N¦R0R1 Hal− ð59AG725Ł[ The degree to which such quaternary salts are formed depends on the overall basicity of the amino "and chalcogen# groups^ thus\ for most compounds of the classes RCHal1NR0R1\ RCHalNR0R1OR2 and RCHalNR0R1SR2 both species must usually be considered whereas\ for compounds of class RCHal"NR0R1#1\ the overriding chemistry is that of the halide salt\ the only exceptions being in cases where "NR0R1#1 1 "NO1#1\ where the electron!withdrawing capacity of the nitro groups diminishes the tendency to ionize[ Several review works discuss this dynamic equilibrium and should be consulted further ðB!65MI 591!90\ B!68MI 591!90\ B!68MI 591!91\ B!68MI 591!92\ B!68MI 591!93\ B!68MI 591!94\ 74HOU"E4#Ł[
5[91[1[0[0 Tetracoordinate carbon atoms bearing two halogens and one nitrogen function Numerous examples exist of compounds in this category[ In many cases\ however\ the chemistry of the product is often described by the corresponding haloiminium salt ð68S130Ł[ All examples described here re~ect cases where product equilibria lie in favour of the covalent species[
"i# From imines Addition of halocarbenes to imines has been successfully used to form 1\1!dihaloaziridines bearing a variety of substituents "Scheme 18# ð48CI"L#0105\ 51JOC2575\ 60JOC2516\ 62ZOR1235\ 63JOC047\ 65JOC2683\ 66ZOR0746\ 67JOC0235\ 68H"01#526Ł[ Methods for formation of the requisite dihalocarbene vary as does the e.ciency of the addition reaction "Scheme 18#[ Addition of ClF to imines takes place at room temperature\ to give N!chloro~uoroalkanes in high yield "Scheme 18# ð64IC0112Ł[ Cl Ph
CHCl3, KOBut, 25 °C, 18 h
N
X
N X = H, 80%; Cl, 68%; OEt, 91%
Ph N
Ph
Cl N
X
Ph Br
HCBr2Cl, KOBut, hexane, 25 °C, 3 h 61%
Ph
Cl
Cl
Cl N
Ph Cl
Ph
Cl
PhHgCCl2F, benzene, 80 °C, 40 h 74%
Cl
N Cl
Ph
Scheme 29
"ii# From amines A variety of halogenation procedures have been applied to tertiary amines\ yielding the cor! responding dihaloaminoalkanes with good conversion[ Yields obtained for di~uoroaminoalkanes using electrochemical ~uorination methods are usually modest\ halogen substitution using sulfur tetra~uoride being a far superior method "Equation "09##[ Perchlorination is also an e}ective route\ giving high yields of a\a!dichloroalkylamines "Scheme 29# ð48CCC3937\ 58LA"629#039\ 66JFC"8#168\ 79JFC"06#54\ 70AG"E#536\ 70ZAAC"363#6Ł[
41
Halo`ens and any other Elements F3C F
CF3 F
F
F3C
98%
F
N
(10)
CF3
Cl
F
Me
N
F
electrochemical
Me
Cl
F
F
ClF, 6 h, 25 °C
N
F
F3C
fluorination 51%
CF3
N
CF3
Cl
F
F
SF4
Cl
N
Cl
F
quantitative
N
Me
F
Me Cl
Cl
N
Cl2
Me
Cl 80%
Me
N Cl
Cl Cl
CCl3 Cl
Scheme 30
"iii# From amides and thioamides Treatment of formamides with chlorinating agents such as thionyl chloride and phosgene often results in formation of dichloroaminoalkanes which exist in equilibrium with the derived chloro! iminium salts "Scheme 20# ð48HCA0542\ 53CB0250\ 68MI 591!91Ł[
+
H
R
R
N
N
Cl– +
COCl2
CHO
H
R
R
N
N
Cl– Cl
H
R = Me, 80%; Ph, 92%
Me
Cl–
Me SOCl2
N
+
Me O
Cl Cl
Me
N 98%
Cl
R N Cl
Cl
Me
R N
Me
Cl
N Cl
Scheme 31
Many such systems of this class have been prepared where electron!withdrawing groups limit the possibility of salt formation[ A wide range of halogenation protocols have been successfully used in these instances\ with a generally high level of conversion to product[ These methods are useful not only for amides but also for thioamides "Scheme 21# ð59JA432\ 51JA3164\ 63JA814\ 64IC0112\ 65ZOR1102\ 67CB810\ 67JOC0616\ 68AG"E#504\ 70JFC"07#82\ 71PJC0258Ł[ Treatment of DMF with carbonyl di~uoride is also reported to give a good "71)# yield of di~uoro"dimethylamino#methane ð51JA3164Ł[
"iv# From acyl halides Treatment of acyl ~uorides with tetra~uorohydrazine under photolytic conditions results in formation of the corresponding N\N!di~uoroaminoalkane "Equation "00##[ One drawback of this radical addition protocol is the requirement that quartz reaction vessels be used ð57JOC2564Ł[
Halo`en and a Group 04 Element CF3
O
Cl CF3
Cl
PCl5, 25 °C, 6 h
CF3
N
F3C
42
O
F N
F15C7
CF3
N
F3C
99%
F
SF4, HF, 150 °C, 18 h
CF3
N
F15C7
78%
CF3
CF3
CF3 O
F N
FCOF, 25 °C, 20 h
Me
F
82%
Me
N
Me
Me
Me N
Me
SF4, KF, 150 °C, 144 h
N Me
90%
F
O O F3C
N
Cl2, CCl4, 20 °C
Et
70%
Cl
Cl
F3C
N
Me
F
Et
Et
Et Scheme 32
O C3F7
N2F4, 40 h, 20 °C, hν
(11)
C3F7NF2
90%
F
"v# From nitriles Chloro~uorination of nitriles is a mild and convenient method for preparation of N\N!dihalo! aminoalkanes[ The reactions have only been reported for nitriles bearing electron!withdrawing groups\ but yields are good to excellent "Scheme 22#[ The intermediate haloimine can be exposed to elemental ~uorine to give N!~uorochloroamines or it can be reacted sequentially with ClF to yield N\N!dichloroamines ð55IC377\ 68JA6539\ 70IC0Ł[ Addition of hydrogen ~uoride to a mixture of HCN and carbonyl ~uoride\ catalyzed by caesium ~uoride\ is reported to yield di~uoromethylcarbamoyl ~uoride\ CHF1NHCOF "69)# ð51JA3164Ł[ Treatment of per~uorinated cycloalkyl nitriles with silver ~uoride at elevated temperature is reported to yield the corresponding per~uorinated cyclo! alkylmethylazo compounds ð73JCS"P0#344Ł[ F
F
R
N
ClF, 0 °C
R
N
ClF, –195 °C
R
Cl
Cl NCl
F F2, –25 °C, 1 h R = CF3, 75%; ClF2C, 70%
F
F
R
N
F
Cl Scheme 33
"vi# From haloiminium salts Treatment of haloiminium salts with hydrogen halides provides a facile route to a!dihaloamines "Equation "01##[ The reactions are typically conducted at or below 9>C in chlorinated solvents\ and
43
Halo`ens and any other Elements
yields of addition products\ which are in equilibrium with their corresponding hydrohalide salts\ are good to excellent ð50CCC2948\ 51CCC1775\ 52CCC1936Ł[ X
+
Me
N
(12)
N
X = Br, 98%; I, 82%; Cl, 77%
Me
Me
X
HX, CHCl3, 0 °C
X–
Me
X
"vii# From haloalkenes and haloalkanes Addition of diethylamine to chlorotri~uoroethene results in the formation of the corresponding diethylaminoalkane in moderate yield "Equation "02## ð70AG"E#536Ł[ The product\ 1!chloro!0\0\1! tri~uorotriethylamine "CTT#\ is a ~uorinating agent ð48JGU1014Ł[ A similar addition reaction has been applied to related secondary amines ð70JFC"07#82Ł[ N!Iodobis"ditri~uoromethyl#amine is reported to add to hexa~uoropropene under photochemical conditions to give "F2C#1NCF1CFICF2 in low yield ð60JCS"C#2722Ł[ ð2¦1Ł Cycloaddition of benzyl azide to hexa~uoropropene gives an intermediate triazoline in 74) yield\ which undergoes thermal decomposition at 149>C to give the corresponding 0!benzyl!1\2\2!tri~uoro!1!"tri~uoromethyl#aziridine "63)# ð55JOC678Ł[ Cyclo! addition of per~uorobutadiene to tri~uoronitrosomethane is reported to give per~uoro!1!methyl! 2\5!dihydro!0\1!oxazine in 59) yield ð54JCS5038\ 55ZOB617\ 56JCS"C#1152Ł[ The azido ester BrCF"N2#CO1Et has been prepared "36)# by reaction of ethyl dibromo~uoroacetate with sodium azide ð75JOC844Ł[ F Cl
F
F
Et2NH 61%
F
Et N
Cl F
(13)
Et
F
CTT
"viii# Routes speci_c to dihalonitroalkanes "a# From nitromethanes[ Di~uoronitromethane reacts with formaldehyde under basic conditions to give 0\0!di~uoro!0!nitroethanol in 77) yield "Scheme 23# ð56ZOB041Ł[ Reactivity of its stabilized anion extends to Michael!type processes\ but only moderate yields of addition products are obtained even for addition to such activated systems as acrylonitrile and ethyl acrylate ð68IZV0800Ł[ Dibromo! nitromethane is reportedly formed when nitromethane is exposed to t!butyl hypobromite ð65JOC0174Ł\ and 0\0!dibromoethane has been prepared from nitroethane by sequential reaction with butyllithium and bromine ð78ZOR1389Ł[ F F
HCHO, K2CO3, H2O
NO2
F
88%
X , NaOEt, K2CO3
F NO2
X = CO2Et, 27%; CN, 13%
F
HO F
NO2
F
X F
NO2
Scheme 34
"b# From haloalkenes[ Fluoroalkenes are reported to react with sodium nitrite in polar aprotic solvents to furnish ~uoronitroalkanes in moderate yield "Scheme 24# ð63IZV1033Ł[ Similar addition reactions can be accomplished using perhaloalkenes and a mixture of concentrated nitric and hydro~uoric acids ð52IZV0835Ł[ 0\1!Dichloro!0\1!di~uoroethylene is converted by nitration followed
Halo`en and a Group 04 Element
44
by reaction with fuming nitric acid into chloro~uoronitrosomethane\ which can then be oxidized to chloro~uoronitromethane ð89MI 591!90Ł[ F
F
F
F3CO
F
F
F
Cl
NaNO2, DMF, 3 d
F
F3CO
50%
F
HNO3 (100%), HF, 20 °C, 7 h
F
F
F
F
Cl
88%
NO2
NO2
F Scheme 35
"c# From nitro alcohols[ 1!Fluoro!1!nitro!0!butanol reacts with aqueous sodium hypobromite to give 0!bromo!0!~uoro!0!nitropropane "Equation "03##[ The reaction is believed to proceed via a transient a!~uoronitronate salt ð69JOC735Ł[ F
NO2 OH
Et
NaOBr, NaOH (aq.), 10 °C, 40 min
F
57%
NO2
Et
(14)
Br
5[91[1[0[1 Tetracoordinate carbon atoms bearing one halogen and two nitrogen functions In all cases in which the nitrogen functions are amino groups\ attempts to prepare compounds of this class results in the formation of the corresponding haloiminium salts[ Examples are widespread\ covering simple amines ð54CB0967\ 62LA39\ 64LA084Ł\ cyclic amines ð50CB1483\ 58RTC178Ł and hydra! zines ð60JOC0044Ł[ One class of compounds within this category which retains stability\ however\ are the halo! diazirines "Scheme 25#[ Typical conditions involve exposure of an acetamidine to bromide saturated DMSO with sodium chlorite] the so!called {Graham conditions| ð54JA3285\ 56JA071\ 57JOC0736\ 70JA5053\ 76TL4790\ 78ACR04Ł or treating N\N!dihaloamidines with base "Scheme 25# ð70JOC4937Ł[ N R
N F3C
H NH2
Cl TRIGLYME, DMSO, 10% NaOH, NaCl, 0 °C
NHCl
NaOCl, NaBr DMSO, LiBr 30%
R = Pri, 49%; MeO, 43%
N N F3C
Br
N N R
tbaf, MeCN 50%
Cl
N N F 3C
F
Scheme 36
"i# Tetracoordinate carbon atoms bearin` one halo`en and two nitro `roups "RCHal"NO1#1# Nearly all compounds in this class have been prepared from the salts of dinitroalkane anions\ reacting with a halogenating agent[ They are grouped according to the nature of the halogenation procedure employed[ "a# Usin` elemental halo`ens[ Typically\ conditions involve formation of the potassium salt of the dinitroalkane\ followed by exposure to the halogen source in situ[ The salts are either prepared by treating the dinitroalkane with the required potassium base or\ in the case of dinitromethane\ via a Ter Meer reaction with chloronitromethane\ itself available by chlorination of nitromethane[ The most commonly used procedure is to pass a ~uorineÐnitrogen mixture into the aqueous solution of the salt at or close to 9>C "Scheme 26# ð57IZV320\ 57IZV1296\ 58IZV0220\ 62IZV0313\ 67JOC2374Ł^ xenon di~uoride is also e}ective as a ~uorinating agent ð76ZOR0546Ł[ Similarly high yields have also
45
Halo`ens and any other Elements
been obtained using the sodium or ammonium salts of dinitroalkanes ð57IZV801Ł and of 1\1! dinitropropane!0\2!diol in which one of the hydroxymethyl groups is cleaved "Scheme 26# ð57JOC2979Ł[ Chlorination of the sodium salts are also reported to give excellent yields of the derived chlorodinitroalkane "Scheme 26# ð58IZV1506\ 76IZV295Ł\ and bromodinitromethane has been prepared by reaction of the sodium salt of dinitromethane with bromine[ ICl has been used to form the corresponding iododinitroalkanes ð66IZV1947Ł[ NO2
NO2
F2, H2O, 0–5 °C
K+
–
NO2
R
F
NO2
R
R = H, 65%; CH2CH2CN, 60%; CH2C(NO2)2, 81%; p-C6H4NO2, 62%; m-diC6H3NO2, 92% NO2 NO2
O2N
76%
NO2
NO2
NO2
NO2
HO
F NO2
84%
Na+
–
NO2
NaOH, H2O, F2, 2.5 h, 0–5 °C
NO2 NO2
F
82%
OH
+ NH4F
NO2
NaOH, H2O, F2, 2 h, 0–5 °C
NO2
HO O2N
F O2N
90%
I
NO2
R
F2, N2, H2O, 1 h, 2–3 °C
NH4+
–
NO2
ICl, CCl4, 10–15 °C
K+
–
NO2
NO2
Cl2, 0–5 °C 99%
Cl
NO2
Scheme 37
"b# Usin` perchloryl ~uoride[ Most work in this category has been conducted using potassium salts of the dinitroalkanes\ providing a generally high yielding approach to the desired ~uoro! dinitroalkanes "Equation "04## ð57JOC2962\ 69IZV276\ 60IZV0376Ł^ similar results "albeit with inferior yields# are obtained using sodium salts ð61JOC041Ł[ For systems where the corresponding salts of dinitroalkanes are unstable\ use of hexamethylphosphoramide "HMPA# and perchloryl ~uoride is reported to allow e.cient ~uorination within 1 hours "Scheme 27# ð58IZV0077Ł[ Interestingly\ exposure of ClOSO1F to cyano!substituted dinitroalkane salts results in formation of the derived N!chloroimidates "Scheme 27# ð65IZV378Ł[ NO2 –
K+
NO2
FClO3, MeOH, 25 °C
F
NO2
R
R
(15)
NO2
R = Ph, 95%; CH2CH2CO2Me, 88%; CH2NHCOPh, 88%; CH2CH2NHCOMe, 93%; CH2CH=CH2, 69%
"c# Usin` hydro`en halides[ Treatment of sulfonium dinitroylides with hydrogen halides results in rapid formation of the corresponding halodinitroalkane "Equation "05##[ The cleavage method is applicable to a range of electrophilic halogen sources including elemental halogens and hypohalites\ with a dialkyl sul_de being the chief by!product ð66IZV028Ł[ NO2 Me
+
S Me
NO2
excess HX, MeCN
+ Me2S
–
NO2
X = Br, 76%; Cl, 89%
X
NO2
(16)
Halo`en and a Group 04 Element NO2
NO2
O2N
FClO3, HMPA, 2 h, 20 °C 88%
NO2
NO2 –
NC
Na+
ClOSO2F, 16 h, 20 °C
NO2 NO2 F
NO2
F O2N
NO2
Cl
N
O2N
66%
NO2
46
Cl
OSO2F Scheme 38
"d# Functional `roup interconversion of dinitrohaloalkanes[ The ~uorodinitromethanide anion undergoes a variety of additional transformations relevant for this section[ Most importantly\ under basic conditions\ 0\ 1 additions to aldehydes are possible to yield secondary alcohols ð69JOC2077Ł\ as are 0\ 3 additions to conjugated alkenes ð68S200Ł\ giving high yields of addition products in both cases[ Related examples of compounds incorporating this functionality where the dinitrohalo group is left intact include acid!catalyzed dimerization of dinitro~uoroalcohols ð58JOC34Ł\ hydrolysis of ~uorodinitroacetonitrile to yield ~uorodinitroacetamide ð57JOC0146Ł and dehydroxymethylation of 1\1!dinitro!1!~uoroethanol ð58JOC34Ł[
"ii# Tetracoordinate carbon atoms bearin` one halo`en\ one nitro `roup and one other nitro`en function An example of this class is the ester BrC"N2#"NO1#CO1Et\ which was obtained in low yield from ethyl dibromonitroacetate by reaction with sodium azide ð75JOC844Ł[
5[91[1[0[2 Tetracoordinate carbon atoms bearing one halogen\ one nitrogen and one oxygen function Based on the previous discussions concerning the stability of ortho!ester halides attached to basic functionality\ salt formation is predominant[ Probably the best studied example of this class is the Vilsmeier reagent and related systems\ formed when formamides are exposed to chlorinating agents "Scheme 28# ð47CCC341\ 48HCA0548Ł[ The equilibrium lies heavily in favour of salt formation\ explain! ing in this case\ and related examples ð58TL1050\ 60CPB1518Ł\ why members of this class have received scant attention[ Other examples can be found describing intermediate formation of this class of compound\ which quickly undergoes rearrangement to give the halide salt ð57JOC0973\ 69CPB673\ 61TL3106\ 62TL3400\ B!68MI 591!92\ 79IZV1245Ł\ and in some cases to give enamines ð54JOC3292\ 57T3106Ł[ R +
R R
R
R POCl3, CH2Cl2
N
R O
N
N
Cl [PO2Cl2]–
Cl OPOCl2
R +
R
N
OPOCl2
Cl–
Scheme 39
5[91[1[0[3 Tetracoordinate carbon atoms bearing one halogen\ one nitrogen and one sulfur function Compounds of this class in which the nitrogen function is an amino group are nearly always found in the form of the corresponding iminium halide salt ðB!68MI 591!94Ł[ The exceptions are nitrohalosul_des[ 0!Chloro!0!chlorosulfenylnitroalkanes have been reported ð74HOU"E4#Ł and the esters PhS"NO1#CXCO1Et "X Br\ and F# have been prepared by halogenation of the ester PhS! "NO1#CHCO1Et ð75JOC844Ł[
47
Halo`ens and any other Elements
5[91[1[1 Halogen and Phosphorus Derivatives 5[91[1[1[0 Tetracoordinate carbon atoms bearing two halogen and one phosphorus function and one halogen and two phosphorus functions "i# From haloalkenes Addition of phosphine to ~uoro and chloro~uoroalkenes is a general route to compounds of this class[ Generally\ the addition reactions are conducted at elevated temperatures\ often in sealed tubes[ Phenylphosphine has also been employed\ with only slight loss of e.ciency resulting "Scheme 39# ð48JA3790\ 54AFC"3#49Ł[ If the reactions are conducted under photolytic conditions\ however\ yields are often substantially improved\ with 73) for the addition to tetra~uoroethylene reported ð52JCS0972Ł[ F
F
X
F F
F
F F
PH3, 150 °C, 8 h
F F
X = F, 53%; Cl, 54%
PPhH2, 150 °C, 8 h 45%
F P
X
H
F
F
F
P F
H
Ph
H
Scheme 40
"ii# From haloalkanes Thermolysis of carbon tetra~uoride with red phosphorus in the presence of iodine results in the formation of a cyclic bis"phosphine# in moderate yield "Scheme 30# ð51JOC2473Ł[ 1\1\1!Trichloro! acetic amidines and imidates react with trialkyl phosphites to yield 1\1!dichloro!1!"dialkoxyphos! phinyl#acetamidines and acetimidates\ respectively "Scheme 30# in good to high levels of conversion ð68ZOB0914Ł[ If the reactions are prolonged\ a second substitution occurs giving a monohalobis"dialkylphosphinyl# derivative[ Addition of chlorodi~uoromethane to sodium diethylphosphonate results in the formation of diethyl di~uoromethylphosphonate ð48JGU0004Ł[ The mechanism of this reaction appears to involve capture of di~uorocarbene rather than an SN1 type process[ Prompted by research on purine nucleoside phosphorylase inhibitors\ it has been shown that diethylphosphinyldi~uoromethyllithium condenses with ortho!a!bromoxylene to give the corresponding di~uorophosphonate in 32) yield "Scheme 30# ð81BMC396Ł[ Interestingly\ other metal dialkylphosphinyldi~uoroalkane derivatives proved vastly inferior in this reaction[ Diisopropylphosphinyldi~uoromethyllithium was shown to give good yields of the 0\1!addition product to o!tolualdehyde at low temperature "Scheme 30#^ the benzylic alcohol was subsequently converted into the tri~uoro derivative using diethylaminosulfur tri~uoride ð81BMC396Ł[ Diethyl "lithiodi~uoromethyl#phosphonate has also been used to introduce the a\a!di~uorophosphonate moiety into phosphate isosteres ð81TL0728\ 83TL2116Ł[ Though alkyl halides are often poor substrates in such coupling reactions\ Martin has reported conditions for addition to aldehydes\ where the resulting product carbinols are deoxygenated using a Barton!type protocol ð81TL0728Ł[ The process is versatile\ tolerant of latent functionality\ and complements existing methods for the introduction of this important moiety ð70JFC"07#086\ 71TL1212\ 78JOC502\ 78TL6902\ 80TL0908Ł[ Dialkyl "iodo~uoro! methyl#phosphonates\ available from dialkyl "bromodi~uoromethyl#phosphonates\ are reported to undergo reductive dimerization to yield tetra~uoroethyl derivatives using cadmium powder\ re~ux! ing in methylene chloride "Scheme 30# ð83JOC1282Ł[ The corresponding dialkyl "bromo! di~uoromethyl#phosphonates fail to undergo this coupling using cadmium\ but this was _nally e}ected using a nickel derivative[ The nickel approach also facilitated dimerization of a dialkyl "iodotetra~uoroethyl#phosphonate\ giving the coupled product in 37) yield ð83JOC1282Ł[ The addition of diethyl trichloromethylphosphonate to alkenes\ catalyzed by copper chloride\ has been reported ð83TL2426Ł[ Ethyl acrylate thus gives the corresponding dichlorophosphonate in moderate yield "Scheme 30#[
Halo`en and a Group 04 Element
48
I F CF4
P(red), I2, 220 °C, 8 h
F
28%
F
F
P
F F
P
F
F
I NH Cl
NH2
Cl
P
RO
R = Et, 84%; Prn, 62%
NH (RO)3P, CH2Cl2, 50 °C, 1.5 h
RO
R = Et, 70%; Prn, 85%
RO
OMe
Cl
Cl NH
Cl
F
P Cl
O
NH
P
OEt P OEt O
F Li
F P O
CHO
F
O
OPri OPri
F
MeO MeO
EtO EtO
O
P
P
Br
F
F
F
F
Zn, NiCl2(PPh3)2 Et4NI, MeCN, 45 °C
EtO EtO
Cl Cl
P Cl
59%
Scheme 41
F
O
OPri OPri
F P
F
O
OEt OEt
F
P
P
OMe OMe
F
F
O
O
F
F F
F
P
P F
OEt OEt , CuCl
F
O
P
48% O
O
MeO
47 %
Zn, NiCl2(PPh3)2 Et4NI, MeCN, 45 °C
O
F
MeO
F
EtO
EtO EtO
Br
F
OH
69%
F
O
P
Cd, CH2Cl2
I
OEt OEt
F
, THF, –78 °C
O
F
F P
80%
EtO
NH2 Cl
43%
Br
P
OMe
Cl
F
Li
EtO
NH
EtO EtO P EtO O
62%
Cl
Cl
O
EtO
(EtO)3P, CH2Cl2, 85%, 2 h
NH2
Cl
NH2
Cl
Cl
Cl
NH
O
RO
(RO)3P, CH2Cl2, 50 °C, 1.5 h
F F
O
F O P
EtO Cl Cl
Cl
O
OEt OEt
OEt OEt
59
Halo`ens and any other Elements
5[91[1[2 Halogen and Arsenic Derivatives 5[91[1[2[0 Tetracoordinate carbon atoms bearing two halogens and one arsenic function Dimethylarsine is reported to add to hexa~uoropropene to give the corresponding dimethylarsenic derivative "Scheme 31# ð54AFC"3#49Ł[ Unfortunately\ no details either of yield or of conditions for this process were reported[ Another report describes the reaction of tetramethyldiarsine "{cacodyl|# with hexa~uoropropene to produce a ~uorodiarsine in 07) yield "Scheme 31# ð53CJC0012Ł[ Me Me
F
F
F
Me2AsH
As
CF3
F
F
F
Me F
Me2AsAsMe2
CF3
As
Me
18%
F3C
F As
Me
F Me
Scheme 42
5[91[2 FUNCTIONS CONTAINING HALOGEN AND A METALLOID AND POSSIBLY A CHALCOGEN AND:OR GROUP 04 ELEMENT 5[91[2[0 Halogen and Silicon Derivatives A variety of a\a!dihaloalkylsilanes are known but few general methods for their preparation exist ð53CB0562Ł[ The following examples cover speci_c cases where conditions have been examined and optimized[
"i# Dichlorocarbene additions Addition of dichlorocarbene "generated from phenyl"bromodichloromethyl#mercury# to a variety of silanes has been reported\ giving good yields of a dichloromethyl silanes "Scheme 32#[ Competition experiments have been carried out in order to determine the kinetics and the precise mechanism of this electrophilic addition process ð56JA0427\ 57JA1833\ 82T7376Ł[ Me Si Me
Cl
PhHgCCl2Br, PhH, 80 °C
Si
58%
Me
Me
Cl Me
Me
Si H
Si
PhHgCCl2Br, PhH, 80 °C
Cl
68%
Me Si R
Me
H Me
Cl
R 34–67%
Me Cl
Si
PhHgCCl2Br, PhH, 80 °C
Cl
Scheme 43
"ii# Other additions to silanes Low temperature metal halogen exchange of bis"trimethylsilyl#dichloromethane followed by protonation has been used to prepare bis"trimethylsilyl#chloromethane "Scheme 33# ð60JOM"18#278\ 89T2748Ł[ Bromination of alkynylsilanes has also been reported\ the major isolated addition product being the tetrabromosilane in nearly quantitative yield "Scheme 33# ð56IZV582Ł[ An alternative
50
Halo`en and a Metalloid
approach to dihalosilanes is cleavage of a bis"trichloromethylsilyl#dichloromethane using hydro! chloric acid "Scheme 33#\ with the a\a!dichloromethylsilane being formed in 76) yield ð53CB0004Ł[ Another report describes alkyl Grignard addition to trichlorosilyldichloromethane\ which yields using methylmagnesium bromide\ trimethylsilyldichloromethane "50)# ð55CB682Ł[ Photochemical addition of silyl radicals to per~uorinated alkenes has also been employed\ UV irradiation of silane in the presence of tetra~uoroethylene giving a 50) yield of 0\0\1\1 tetra~uoroethylsilane in 07 h ð54JCS1090Ł[ Similarly\ photochemical addition of the chlorosilyl radical derived from methyl! dichlorosilane to tetra~uoroethylene results in a 87) yield of the a\a!di~uorosilane adduct ð57ZOB1702Ł[ Lithiation of 0\5!dibromodeca~uorohexane\ followed by addition of trimethylsilyl chloride\ results in formation of 0\5!bis"trimethylsilyl#deca~uorohexane in 55) yield ð58JOM"05#22Ł[ BunLi. –110 °C
Cl
CH2Cl2 + 2 TMS-Cl
TMS
64%
Me Me Si Me
Cl
i, BunLi, –110 °C
Cl TMS
ii, EtOH, –65 °C 73%
Br2, 50 °C, then 80 °C, 12 h
Me
97%
Me
Me
TMS
TMS
Br
Si
Br
Br
Br
HCl
Cl2CHSiCl3 + SiCl4
Cl2(SiCl3 )2 87%
Cl
NCS, CCl4
TMS
SMe OMe
TMS
SMe
TMS
60%
SMe Cl
Cl2, CCl4, Et3N 69%
TMS
OMe
Scheme 44
Preparation of systems containing a metalloid\ halogen and chalcogen have also been reported[ Chlorination of "methylthiomethyl#trimethylsilane has been accomplished\ giving ðchloro! "methylthio#methylŁtrimethylsilane in 59) yield "Scheme 33# ð78T526Ł[ Additionally\ ðmethoxy"methylthio#methylŁtrimethylsilane "itself prepared from ðchloro"methylthio#methylŁ trimethylsilane by addition of sodium methoxide# has been converted to ðchloro"methoxy# methylŁtrimethylsilane "Scheme 33# in 58) yield\ using traditional chlorination conditions ð78T526Ł[ 5[91[2[1 Halogen and Boron Derivatives Compounds of this class are extremely unstable\ which accounts in part for their general lack of utility in synthesis[ The general mechanism for the decomposition of a!bromoalkylboranes "formed from trialkylboranes and bromine# appears to involve HBr!induced cleavage which may proceed via a radical pathway\ rather than by simple rupture of the C0B bond ð69JA6101Ł[ Treatment of a\a!dihaloalkylboranes with nucleophiles such as water also induces rearrangement\ providing a route\ after oxidation\ to secondary alcohols ð60JA1685Ł[ An a\a!dichloroalkylborane was prepared by Seyferth by dichlorocarbene insertion into a trialkylborane "Scheme 34#^ however\ spontaneous rearrangement occurred with subsequent elimination from the chloroborane species ð55JA0723Ł[ It is reported that the stability of the intermediate a\a!dichloroalkylborane is a function of the borane R group\ and that triarylboranes "R Ph# yield the more stable adducts[
R3B
70 °C, 40 min
R=
Prn,
R
PhHgCCl2Br
Bun,
R
R
B
R
Cl
Cl
Ph Scheme 45
Cl
B
R
Cl
R
51
Halo`ens and any other Elements
5[91[2[2 Halogen and Germanium Derivatives Trichlorogermane has been shown to undergo addition to chlorinated alkenes\ and this constitutes an excellent route to a\a!dichloroalkylgermanes "Scheme 35# ð59DOK"020#87Ł[ Photochemical chlori! nation of alkylgermanium compounds has also been reported\ giving moderate yields of the a\a! dichloro species "Scheme 35# ð56ZOB0939Ł[ Bis"per~uoroalkyl#mercury compounds have been shown to react with germanium tetrahalides to produce per~uorogermanium alkyls in good yield "Scheme 35# ð67JA0611Ł[ The trihalo"per~uoroalkyl#germanium compounds produced are versatile synthetic intermediates\ since they react with dialkylcadmium reagents to give alkyl "per~uoro! alkyl#germaniums ð67JA0611Ł[ Bis"triethylgermyl#mercury undergoes exchange with bis"halo! alkyl#mercury compounds\ to yield mixed haloalkyl "triethylgermyl#mercurials ð61JOM"23#188Ł[ These mixed mercurials react with caesium ~uoride to produce haloalkyl germaniums in good yield "Scheme 35# ð61JOM"23#188Ł[ Bis"trialkylgermyl#mercury reacts with bis"haloalkyl#mercury compounds to produce a variety of mixed haloalkyl germanium species ð61IZV74Ł[ The intermediate is presumably a mixed "triethylgermyl#mercury species\ and the isolated yields are good to excellent ð61IZV74Ł[ Cl
Cl
Cl
Cl
F3C
Cl HGeCl3, 80 °C, 2 h 48%
GeCl3
Cl Cl
Cl2, hν
GeCl3
58%
GeCl3
F3C Cl
CsF, THF, 5 min
Et
75%
Et
Et3GeHgC2F5
Et
75%
Et
Et3GeHgCFClCF3
(C2F5)2Hg
GeBr4, 195 °C
Br
45%
Br
Ge
(C2F5)2Hg
I
53%
I
CF3 F
Et Ge
CF3
Cl
F
Br Ge F
GeI4, 135 °C
Cl
Et
F CsF, THF, 5 min
Cl
CF3 F
I Ge F
CF3 F
Scheme 46
5[91[3 FUNCTIONS CONTAINING HALOGEN AND A METAL AND POSSIBLY A GROUP 04 ELEMENT\ A CHALCOGEN OR A METALLOID 5[91[3[0 Halogen and Lithium Derivatives Under the general heading of {lithium carbenoids|\ haloalkyllithium compounds have enjoyed widespread use due to their unusual reactivity and their ability to deliver the versatile halomethylene functional group to suitable acceptors[ A critical aspect of these species is the role of solvent used in their preparation\ THF being the solvent of choice\ owing to its ability to stabilize the carbenoid species[ However\ the increased viscosity of THF at the low temperatures typically employed to generate carbenoids sometimes poses problems\ and often ether or petroleum ethers are used as co! solvents[ Typical conditions involve treating a dilute solution of either a dihaloalkane or a tri! haloalkene at −099>C with an alkyllithium reagent in THF "Scheme 36# ð54JA3036\ 54TL858\ 82T7376Ł[ Since the carbenoids are typically thermally unstable "decomposing completely above −54>C#\ in
52
Halo`en and a Metal
situ reaction with a suitable electrophile is usually carried out\ otherwise intramolecular carbenoid insertions may take place[ Examples of lithiodi~uoroalkanes are common\ available either by metallation of di~uoroiodoalkanes at low temperature ð74TL4132Ł or by metallation of di~uoro! alkanes with lithium amide bases at elevated temperature ð66JOC454Ł[ Terminal lithioper~uoro! alkanes often undergo spontaneous elimination of LiF to yield per~uorinated alkenes ð74TL4132Ł[ The alkoxycarbenoid ClCH1CH1OCHClLi has been generated and used to cyclopropanate cyclo! hexene ð58OS"38#75\ 61JA014Ł[ I
LDA, –78 °C, THF, 30 min
CH2I2
Li
I BuLi, THF, –100 °C
PhCCl3
Cl
Ph
Li
Cl Scheme 47
5[91[3[1 Halogen and Magnesium Derivatives Transmetallation reactions between Grignard reagents and perhalogenated systems is a versatile route to compounds of this class[ Thus phenylmagnesium bromide reacts with 0!iodohepta~uoro! propane at low temperature to produce hepta~uoropropylmagnesium bromide in good yield "Sch! eme 37# ð46JA2240Ł[ Such Grignard reagents are useful for addition of perhaloalkyl functionality to carbonyl compounds ð77BCJ2210Ł[ Other examples of this transmetallation protocol demonstrate its synthetic utility "Scheme 37# including formation of bis"bromomagnesium# compounds ð64JFC"4#364Ł[ F
F
PhMgBr, –78 °C, Et2O
I
F3C F
F
F
F MgBr
F3C
F
F I
F
F
2 RMgBr, –70 °C, Et2O
F
BrMg
F
+ PhI
F
F
I F
F
MgBr
F
F
F
F
Scheme 48
5[91[3[2 Halogen and Copper Derivatives Reaction of copper metal with terminally iodo!substituted per~uoroalkanes at elevated tem! peratures results in formation of a per~uorinated alkylcopper"I# species\ together with copper"I# iodide "Equation "06## ð76JFC"26#060Ł[ Chain polymerization of these species has been reported on thermolysis in DMF ð77DIS"B#1862Ł[ F F3C
I
F
2 Cu, DMSO, 110 °C
F
F3C
Cu
+ CuI
(17)
F
5[91[3[3 Halogen and Silver Derivatives Addition of silver tri~uoroacetate to chlorotri~uoroethene in the presence of metal ~uorides results in the formation of an organosilver compound bearing an a\a!dihalo alkyl group "Equation
53
Halo`ens and any other Elements
"07## ð62JOM"46#312Ł[ Caesium ~uoride is reported to promote this reaction more e.ciently than other alkali metals[ F
F
F
Cl
CF3CO2Ag, MF
Cl
Ag
(18)
F
F3C
5[91[3[4 Halogen and Zinc Derivatives Zinc metal reacts with alkyl iodides\ chlorides and bromides to give the corresponding halozinc reagents "Scheme 38# ð42JCS2596\ 46JA3048\ 73JFC"15#324\ 77JOM"228#06Ł[ Yields of organozinc reagent are heavily dependent on both concentration and temperature of reaction and\ where ethers are not employed as solvents\ solvated products are formed\ for example\ with DMF[ F
F
F3C
I
F
F3C
Cl
F
F3C
75%
F Cl
F
Zn, dioxane
ZnI
F Cl
Zn, DMF
Cl
F3C
F
ZnCl(DMF)2 Cl
Scheme 49
5[91[3[5 Halogen and Cadmium Derivatives Cadmium metal will insert between the carbonÐbromine or carbonÐiodine bond in mixed per! haloalkanes to yield a variety of organocadmium reagents "Scheme 49# ð77JFC"28#314\ 77JFC"30#074Ł[ Alternatively\ transmetallation from dialkylcadmium reagents to dihaloiodoalkanes can be employed to form perhalodialkylcadmium reagents of this class[ F F
2 F5C2I
F
Cd, DMF, 50 °C
X
X = Br, 75%; I, 91%
Me2Cd, MeCN
F F3C
Cd-X
F F
F Cd
F
+ 2 MeI
CF3
Scheme 50
5[91[3[6 Halogen and Mercury Derivatives Mercuric ~uoride will add to haloalkenes quite readily at elevated temperatures to yield per! halodialkylmercury compounds "Scheme 40# ð59JOC094\ 50JCS2714Ł[ Strict regiocontrol in the addition reactions to mixed haloalkenes is usually observed[ It has been reported that per~uoro! propen!1!ol\ the meta!stable enol form of penta~uoroacetone\ reacts with mercury tri~uoroacetate
54
Halo`en and a Metal
to yield tri~uoroacetoxymercuricper~uoroacetone "Scheme 40# ð64DOK"110#0220\ 65ZOR0266Ł[ Care must be taken when handling this species\ as it is reported to undergo rapid hydration to form the corresponding hydrate[ F
F
F
F
F
Cl
HgF2, HF, ∆
Cl
Cl
69%
F3C
F
HgF2, 100 °C
F
56%
F
CF3
(CF3CO2)2Hg, Et2O
F
OH
20 °C, 12 h 79%
F
Hg
F3C
F
F
Cl
CF3 Cl
Cl
Hg
CF3
CF3CO2HgCF2COCF3
Scheme 51
5[91[3[7 Halogen and Tin Derivatives Reaction of dialkyltin hydrides with tetra~uoroethylene is reported to give the 0 ] 1 adducts "Scheme 41# ð54AFC"3#49Ł[ Another route to these compounds is via insertion to iodoper~uoro! alkanes using either tin"II# chloride or tin"II# ~uoride "Scheme 41#[ The resulting organotin com! pounds retain the halogen atoms originally attached in this rapid reaction ð70CL0226Ł[ Reaction of trimethyltin hydride with trialkyl"tri~uoromethyl#stannanes results in reduction to the cor! responding di~uoroalkyltin species "Scheme 41# ð69IC0571Ł[ Bis"per~uoroalkyl#cadmium com! pounds are reported to undergo transmetallation with Me2SnOCOCF2 to yield the corresponding per~uoro organotin derivatives "Scheme 41# ð74JFC"16#298Ł[ Tetrakis"tri~uoromethyl#germanium is reported to react with trimethyltin hydride to produce\ in addition to tris"tri~uoromethyl#germane\ trimethyl"di~uoromethyl#tin in low yield ð83JOM"354#042Ł[ F
F
F
F
Bu2SnH2
F
F
F3C(CF2)5I
SnCl2 (or SnF2), DMF, 25 °C
Me3SnCF3
Me3SnH, 150 °C
F F
F
Sn F Bu Bu F
F
F3C(CF2)5SnCl2I
Me3SnCHF2
63%
(C2F5)2Cd
Me3SnOCOCF3, 70 °C
Me3SnC2F5
64%
Scheme 52
5[91[3[8 Halogen and Lead Derivatives Addition of tetramethyllead to iodopenta~uoroethane at elevated temperature results in for! mation of penta~uoroethyltrimethyllead in moderate yield "Scheme 42# ð59JA5117Ł[ In an analogous manner to the corresponding organotin compounds\ bisper~uoroalkyl cadmium species undergo
55
Halo`ens and any other Elements
transmetallation with Me2PbOCOCF2 to yield per~uoro organolead derivatives "Scheme 42# ð74JFC"16#298Ł[ CF3CF2I
Me4Pb, 150 °C
Me3PbCF2CF3
28%
(C2F5)2Cd
Me3PbOCOCF3, 70 °C
Me3PbC2F5
91%
Scheme 53
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.03 Functions Containing Three Chalcogens (and No Halogens) GLYNN MITCHELL ZENECA Agrochemicals, Bracknell, UK 5[92[0 INTRODUCTION
57
5[92[1 FUNCTIONS BEARING THREE OXYGEN ATOMS 5[92[1[0 Methods for the Preparation of Carboxylic Ortho!esters and Related Compounds 5[92[1[0[0 Ortho!esters from 0\0\0!trihaloalkanes\ a\a!dihalo ethers and a!haloacetals 5[92[1[0[1 Ortho!esters from imidate ester salts 5[92[1[0[2 Ortho!esters from carboxylic acids and derivatives 5[92[1[0[3 Ortho!esters from dioxocarbenium salts 5[92[1[0[4 Ortho!esters from 0\0!dialkoxyalkenes\ 0\0!dihaloalkenes and 0!alkoxyalkynes 5[92[1[0[5 Ortho!esters from 0\0!dialkoxycyclopropanes and related compounds 5[92[1[0[6 Ortho!esters from acetals 5[92[1[0[7 Ortho!esters from ortho!carbonate esters and trialkoxyacetonitriles 5[92[1[1 Preparation of Carboxylic Ortho!Esters from Other Ortho!Esters 5[92[1[1[0 Trans!esteri_cation reactions 5[92[1[1[1 Modi_cation of R0 and R1 of R0C"OR1#2 5[92[2 FUNCTIONS BEARING THREE SULFUR ATOMS 5[92[2[0 Methods for the Preparation of Trithio!ortho!esters and Related Compounds 5[92[2[0[0 Trithio!ortho!esters from RC"X0#"X1#X2 5[92[2[0[1 Trithio!ortho!esters from thioimidate ester salts 5[92[2[0[2 Trithio!ortho!esters from carboxylic acids and derivatives 5[92[2[0[3 Trithio!ortho!esters from dithio! and trithiocarbenium salts 5[92[2[0[4 Trithio!ortho!esters from dithioacetals 5[92[2[0[5 Trithio!ortho!formates from trithiocarbonates 5[92[2[0[6 Trithio!ortho!formates from tetrathio!ortho!carbonates 5[92[2[1 Preparation of Trithio!ortho!esters from other Trithio!ortho!esters 5[92[2[1[0 Hi`her trithio!ortho!esters from trithioformate esters 5[92[2[1[1 Trans!esteri_cation of trithio!ortho!esters 5[92[2[1[2 Modi_cation of R0 and R1 of R0C"SR1#2 5[92[2[2 Methods for the Preparation of Oxidised Derivatives of Trithio!ortho!esters 5[92[2[2[0 Oxidised trithio!ortho!esters containin` at least one sulfoxide `roup 5[92[2[2[1 Oxidised trithio!ortho!esters containin` at least one sulfone `roup 5[92[2[2[2 Oxidised trithio!ortho!esters containin` at least one sulfonate `roup 5[92[3 FUNCTIONS BEARING THREE SELENIUM ATOMS 5[92[3[0 Methods for the Preparation of Triseleno!ortho!esters 5[92[3[0[0 Triseleno!ortho!esters from RC"X0#"X1#X2 5[92[3[0[1 Triseleno!ortho!esters from carboxylic acids 5[92[3[0[2 Triseleno!ortho!esters from triselenocarbenium salts 5[92[3[0[3 Triseleno!ortho!esters from diselenoacetals and related compounds 5[92[3[0[4 Triseleno!ortho!formates from tetraseleno!ortho!carbonates 5[92[3[0[5 Hi`her triseleno!ortho!esters from triseleno!ortho!formate esters
57 57 57 58 60 62 63 65 66 66 67 67 79 70 70 70 72 73 74 74 76 76 77 77 77 78 89 89 89 80 80 81 81 81 82 82 82 83
5[92[4 MIXED CHALCOGEN FUNCTIONS INCLUDING OXYGEN
84
5[92[4[0 Methods for the Preparation of Functions R0C"OR1#"OR2#SR3 5[92[4[0[0 From R0C"X0#"X1#X2
84 84
56
57
Three Chalco`ens 5[92[4[0[1 From monothiocarboxylic esters 5[92[4[0[2 From dioxo! and oxothiocarbenium salts 5[92[4[0[3 From monothioacetals and related compounds 5[92[4[0[4 From 1!alkoxythiophenes 5[92[4[1 Methods for the Preparation of Functions R0C"OR1#"SR2#SR3 5[92[4[1[0 From R0C"X0#"X1#X2 5[92[4[1[1 From dithiocarbenium salts 5[92[4[1[2 From mono! and dithioacetals and related compounds 5[92[4[1[3 Miscellaneous methods 5[92[4[2 Methods for the Preparation of Functions R0C"OR1#"OR2#SeR3 5[92[4[2[0 From 1!alkoxyselenophenes 5[92[4[3 Methods for the Preparation of Functions R0C"OR1#"SeR2#SeR3 5[92[4[3[0 From R0C"X0#"X1#X2 5[92[4[4 Methods for the Preparation of Functions R0C"OR1#"SR2#SeR3 5[92[4[4[0 From monothioacetals and related compounds
5[92[5 MIXED SULFUR AND SELENIUM FUNCTIONS
85 85 86 86 86 86 87 87 88 099 099 099 099 099 099 090
5[92[5[0 Methods for the Preparation of Functions R0C"SR1#"SR2#SeR3 5[92[5[0[0 From R0C"X0#"X1#X2 5[92[5[0[1 From selenodithiocarbenium salts 5[92[5[0[2 From dithioacetals 5[92[5[1 Methods for the Preparation of Functions R0C"SR1#"SeR2#SeR3 5[92[5[1[0 From diseleno!ortho!esters
090 090 090 091 091 091
5[92[0 INTRODUCTION The scope of this chapter is intended to cover the synthesis of compounds bearing the C"X#"Y#Z group in which each of X\ Y and Z are independently linked through O\ S\ Se and Te atoms[ However\ at the time of writing no such compounds containing Te had been reported in the literature\ so the discussion is limited to O\ S and Se containing compounds[
5[92[1 FUNCTIONS BEARING THREE OXYGEN ATOMS Carboxylic ortho!esters contain a carbon atom bearing three alkoxy or aryloxy groups[ Closely related to these are the corresponding acyloxy esters "bearing at least one RCOO group#\ peroxy esters "bearing at least one ROO group# and aminoxy esters "bearing at least one R0R1NO group#[ Ortho!esters which contain one or more hydroxy groups are generally unstable and decompose to carboxylic esters and alcohols\ though a few examples are known in which ortho!hydrogen esters are stabilised by electronic and:or ring strain e}ects ð15BSB301\ 54T1948\ 79JOC1985Ł[ Methods for the preparation of ortho!esters and related compounds have been reviewed by Post ðB!32MI 592!90Ł\ DeWolfe ðB!69MI 592!90\ 63S042Ł\ Sandler and Karo ðB!75MI 592!90Ł and Simchen ð74HOU"E4#2Ł[ Other reviews concentrate on the reactions of ortho!esters ðB!58MI 592!90\ 75UK0792Ł\ and on their use in polymerisation reactions ð74MI 592!90Ł[
5[92[1[0 Methods for the Preparation of Carboxylic Ortho!esters and Related Compounds 5[92[1[0[0 Ortho!esters from 0\0\0!trihaloalkanes\ a\a!dihalo ethers and a!haloacetals Williamson and Kay reported the _rst synthesis of triethyl and tripentyl ortho!formates by reaction of the appropriate sodium alkoxide with chloroform "Equation "0## ð0743LA"81#235\ 0743PRS024Ł[ This procedure has since been used to prepare a number of simple trialkyl ortho!formates ð0768CB004\ 21JA1853\ 22JA2740\ 53RTC008Ł[ The reaction is carried out either by adding chloroform to the alkoxide\ or by adding sodium metal to a mixture of the alcohol and chloroform^ a typical procedure is described in Or`anic Syntheses for the preparation of triethyl ortho!formate ð40OSC"0#147Ł[ Yields are generally low "29Ð34)#\ irrespective of the method used[ CHCl3
NaOR
OR (1)
RO OR
58
Three Oxy`ens
The use of ~uorodichloromethane or di~uorochloromethane in place of chloroform has been reported to give higher yields of ortho!formates ð46JA4382\ 59JA0287Ł[ Carbon tetrachloride and dichlorodi~uoromethane have also been shown to give ortho!formates on reaction with sodium alkoxides ð10JCS0111\ 47USP1742420Ł\ these reactions proceeding via the corresponding haloforms which are generated in situ under the alkaline conditions[ Triaryl ortho!formates are not obtained in appreciable amounts from the reaction of activated phenols with chloroform since the preferred pathway is that of the ReimerÐTiemann reaction^ less activated phenols do give ortho!formates\ but yields are generally poor ð0771CB1574\ 13JA1989\ 44JA5533Ł[ The Williamson synthesis has been extended to the preparation of certain higher ortho!esters^ trialkyl ortho!benzoates "0# ð31JA1414\ 49JA0550Ł and heterocyclic analogues\ for example "1# ð79LA0105Ł\ and trialkyl and triaryl ortho!esters of perhalogenated!acrylates "2# ð56CB1835\ 60ZOR1050Ł and !crotonates "3# ð59IZV120Ł have all been prepared from the appropriate trichloro! methyl compounds[ However\ the general utility of the method for the synthesis of ortho!esters from trihalomethyl compounds bearing a!hydrogen atoms is limited\ since these substrates may also undergo competing elimination reactions under the strongly basic reaction conditions ðB!69MI 592! 90\ 63S042Ł[ Ar
OR OR OR
Cl
N N (MeO)3C
S
C(OMe)3 Cl
(2)
(1)
F
OR
Cl OR
F
Cl
OR
Cl
OR
F (4)
(3)
OR
OR
A variation of the Williamson synthesis was reported by Hill et al[ ð54JOC300Ł\ who obtained ortho!formates "4\ R H# and ortho!benzoates "4\ R Ph# derived from ~uorinated alcohols\ which do not undergo the base promoted reaction\ by the iron"III# chloride catalysed reaction of the alcohol with chloroform and a\a\a!trichlorotoluene respectively "Equation "1##[ Cl Cl Cl
R
Rf
OH
, FeCl3 cat.
R
62–80%
OCH2Rf OCH2Rf OCH2Rf (5)
(2)
Nucleophilic displacement of the halogen atoms of a\a!dihalo ethers and a!haloacetals with alkoxides also gives ortho!esters[ In these cases\ mixed ortho!esters "5#\ in which R1 and R2 are di}erent\ may be obtained "Scheme 0# ð24CB1040\ 47JPR59\ 50CB427Ł[ The cyclic diacyloxy ester "6# was obtained from a\a!dichlorophthalide and 2!hydroxybutanoic acid "Equation "2## ð43LA"476#115Ł[ R1
OR2 Cl Cl
OR2 OR3 OR3 (6) Scheme 1
NaOR3
R1
NaOR2
OR3 OR3 Cl
R1
a\a!Dihalo ethers and a!haloacetals may form as intermediates in the reactions between activated 0\0!dihaloalkenes and alkoxides which yield ortho!esters^ these are discussed in Section 5[92[1[0[4[ O O
OH CO2H , PhNMe , 20 °C 2
O Cl
45%
Cl
O O
(3)
O O
(7)
5[92[1[0[1 Ortho!esters from imidate ester salts Imidate ester salts are transformed into ortho!esters by reaction with alcohols "Equation "3##[ The reaction is normally carried out using imidate ester hydrochloride salts\ which are prepared by the
69
Three Chalco`ens
hydrogen chloride promoted addition of alcohols to nitriles\ and the two!step sequence "nitrile to ortho!ester# is named after Pinner\ who _rst described the preparation of a series of trialkyl ortho! formates using this procedure ð0772CB241\ 0772CB0532Ł[ The method is widely applicable to the synthesis of ortho!formic and higher aliphatic ortho!esters^ yields are generally in the 59Ð79) range\ but are lower "29) or less# for aliphatic ortho!esters bearing two substituents a! and:or b! to the ester function ð31JA0714\ 40JA1122Ł[ Ortho!benzoate esters may be prepared from benzimidate ester hydrochlorides\ but reported yields are low ð63S042Ł[ The procedure is normally used for the preparation of trialkyl ortho!esters "7# in which R1 and R2 are the same\ but is also suitable for the synthesis of mixed ortho!esters in which R1 and R2 are di}erent ð0772CB241\ 0772CB0532\ 22MI 592!90Ł[ OR2 R1
R3OH
OR2 OR3 OR3 (8)
R1
+
NH2 X–
(4)
The simplest procedure for the alcoholysis of an imidate ester is to allow a solution of the imidate ester hydrochloride in an excess of the alcohol to stand at room temperature ð17JA405\ 24JA1379Ł[ However\ reaction times can be long\ and yields are often low[ Improved procedures include heating the imidate ester salt with an excess of the alcohol in diethyl ether ð31JA0714\ 35JA0811Ł\ or petroleum ether ð42JA2876\ 47JA2804Ł[ It is important to maintain strictly anhydrous conditions during these alcoholysis reactions\ since the ortho!ester products are extremely prone to acid!catalysed hydrolysis[ High temperatures also need to be avoided\ as imidate ester hydrochlorides decompose to alkyl chlorides and the corresponding carboxamide at elevated temperatures ð40JA1122Ł[ Ortho!esters may be prepared from nitriles without isolation of the intermediate imidate ester salt[ Erickson synthesised a number of trialkyl ortho!formates in moderate yields "up to 45)# by a one!step process which involved the introduction of hydrogen chloride into a large excess of both hydrogen cyanide and the alcohol ð44JOC0462Ł[ Later workers found that better yields were obtained if the acidity of the reaction medium was reduced to pH 1Ð5 after initial formation of the formimidate ester hydrochloride ð65JAP"K#65097901\ 79JAP"K#7972616\ 73MIP410261Ł[ Other methods for the preparation of ortho!esters which proceed via imidate ester salts have been described[ A variation of the Pinner method involves the alcoholysis of O!methyl imidate salts "8^ Equation "4##\ which are prepared from amides and dimethyl sulfate ð79LA0566Ł[ Ethanolysis of imidoyl chloride salts "09\ R Et\ Ph# produced triethyl ortho!propionate and triethyl ortho! benzoate in yields of 51) and 34) respectively\ via the corresponding O!ethylimidate ester salts ð52CB1560Ł[ Reaction of formamide with benzoyl chloride or ethyl chloroformate in the presence of alcohols gave trialkyl ortho!formates in yields of 39Ð49) "Scheme 1# ð57LA"605#196Ł\ and mixed ortho!esters\ "00# for example\ were similarly obtained by treatment of formamide with benzoyl chloride in the presence of a mixture of a simple alcohol and a diol ð70MI 592!90Ł[ OR2 R1 MeOSO3–
N+
R3OH
R1
OR3 OR3 OR3
(5)
(9)
Cl R N+
Cl–
O EtO O
(10)
O H NH2
R1COCl
O COR1 H
(11)
R2OH
+
NH2 Cl–
OR2 H
+
NH2 Cl– Scheme 2
R2OH
H
OR2 OR2 OR2
60
Three Oxy`ens 5[92[1[0[2 Ortho!esters from carboxylic acids and derivatives "i# From carboxylic acids and esters
Tricyclic ortho!esters are obtained from the reaction of carboxylic acids with 1!alkyl!1!hydroxy! methyl!0\2!dihydroxypropanes "Equation "5## ð46MI 592!90\ 54NEP5301525Ł[ The method works best for carboxylic acids bearing electron withdrawing substituents\ and the reactions are forced to completion by azeotropic removal of water using benzene or xylene[ Ortho!esters derived from diols or simple alcohols are not generally available by this method[ OH HO
O R1
R2 HO
OH
O O
R1
H+
(6)
R2
O
Aliphatic carboxylic esters of 2!methyl!2!hydroxymethyloxetane have been shown to rearrange smoothly to bridged tricyclic ortho!esters in high yield on exposure to boron tri~uoride etherate at temperatures of 9>C or less "Scheme 2# ð72TL4460\ 89JCS"P0#264Ł[ The reaction is postulated to proceed via cyclisation of the zwitterionic species "01#[ O
O
R
BF3•OEt2
O
R
+
66–91%
O – F3B
O
O
R
O O O
(12) Scheme 3
Formate esters react with epoxides in the presence of a catalytic amount of boron tri~uoride to give cyclic ortho!formate esters "Equation "6## ð44AG263Ł[ Acetate esters do not react with epoxides under these conditions[ O H
O
O R2
OR1
R2
R1 O
BF3
(7) O
Ethanolysis of the acetoxy p!toluenesulfonate "02# under basic conditions produced the cyclic ortho!ester "03# ð32JA502Ł[ This product is formed by addition of ethoxide to the intermediate dioxocarbenium ion "04#\ which is itself formed by neighbouring group displacement of tolu! enesulfonate by the acetoxy group "Scheme 3#[ The ortho!ester "05# was formed similarly "Equation "7## ð52PCS263Ł[ Acyloxy ortho!esters were formed by a similar mechanism when acetoxyacyl chlor! ides were treated with alcohols in the presence of triethylamine "Equation "8## ð62JA3905Ł^ the use of alkyl hydroperoxides in place of alcohols produced the analogous peroxy acyloxy ortho!esters in high yields "69Ð099)# ð56AG"E#838Ł[ This method of ortho!ester synthesis has received considerable attention in the _eld of carbohydrate chemistry for the conversion of 0!halo!1!acyloxy carbohydrate derivatives "both furanose and pyranose forms# into the corresponding ortho!esters[ Triethylamine ð89LA388Ł\ 1\5!lutidine ð54CJC0807Ł\ 1\3\5!collidine ð45CB203Ł and silver"I# salts ð60CAR"08#028Ł have been used to catalyse the reactions of 0!halo!1!acyloxy carbohydrate derivatives with alcohols\ and amide acetals ð79MI 592!90Ł and alkoxystannanes ð65CAR"40#C02Ł have been used as alternative sources of the alkoxy group[ The exo!form of the ortho!ester product normally predominates\ and is often formed exclusively[ A representative example is illustrated in Equation "09# ð89LA388Ł[ OTs O
EtOH, KOAc
O
O
+
O
O
(13)
(15) Scheme 4
51%
O (14)
OEt
61
Three Chalco`ens
OTs
O
EtOH, KOAc
(8)
OEt 71%
OAc
O (16)
O
O
O
O Cl
ROH, Et3N
O
42–84%
(9)
O O
OR
Br
O
O
EtOH, Me3N, C6H6
AcO
OAc
37%
(10)
OEt
O
AcO OAc
OAc
Aliphatic O!trimethylsilyl ortho!esters "07\ R alkyl# were obtained from hydroxy esters "06# by deprotonation using a strong base "n!butyllithium or lithium diisopropylamide# followed by reaction with chlorotrimethylsilane "Equation "00## ð80SL059Ł[ This method is not suitable for the preparation of ortho!esters from a!branched carboxylic esters[ O R O
OH Ph Ph Ph
Ph i, BunLi or LiN(Pri)2 ii, TMS-Cl 82–94%
TMS-O R
(17)
O
Ph
O
(11)
Ph
(18)
"ii# From lactones Several examples of the direct formation of ortho!esters from lactones and diols have been reported[ Le Mahieu and Kierstead ð69TL4000Ł described the acid catalysed preparation of the steroid ortho!esters "08\ R H\ Br# from the corresponding lactones and 0\1!dihydroxyethane "Equation "01##\ and Tamaru et al[ ð79BCJ2576Ł prepared the carbohydrate ortho!esters "19#\ "10# and "11# similarly from 1\2\3\5!tetra!O!benzylgluconolactone and the appropriate diol in yields of 66)\ 62) and 32) respectively[ A variation of this method\ which is reported to give higher yields of ortho!esters\ involves the trimethylsilyl tri~uoromethanesulfonate catalysed reaction between lactones and bis!O!trimethylsilyl!0\1!diols[ Yoshimura et al[ ð70CL264Ł prepared the ortho!esters "19#\ "10# and "11# from 1\2\3\5!tetra!O!benzylgluconolactone and the corresponding bis!O!tri! methylsilyl!0\1!diols in yields of 80)\ 78)\ and 53) respectively[ The ortho!ester "12# was obtained in 73) yield from 2\3!dihydrocoumarin and 0\1!bis!O!trimethylsilyloxyethane ð78AJC0124Ł[ HO HO
H H O
O
H
R
HO
H
H
OH , H+, C6H6 56–72%
(12) H
O O
O
H
H
R (19)
Lactones undergo Lewis acid catalysed reaction with epoxides in a similar manner to formate esters to give spirocyclic ortho!esters "Equation "02##[ Lewis acids commonly used are boron tri! ~uoride\ tin"IV# chloride and antimony pentachloride[ The reaction is general\ and has been used to prepare a number of ortho!esters[ Thus\ butyrolactone reacts with 0\1!epoxyethane\ 0\1! epoxypropane\ 0\ 1!epoxy!2!phenoxypropane\ 0\ 1!epoxy!2!"3!methoxyphenoxy#propane\ 0\ 1!epoxy!
62
Three Oxy`ens O
BnO
O O
BnO
O
BnO
O O
OBn BnO
OBn
OBn OBn (21)
(20)
O
O
BnO
O
BnO
O
OBn
O
OBn (22)
O
(23)
0!phenylethane and 0\1!epoxycyclohexane to give the ortho!esters "13\ R H\ Me\ CH1OPh\ CH1OC5H3OMe!p\ Ph# and "14# respectively ð48LA"512#072\ 59GEP0973622\ 71MI 592!90Ł[ O
O
R
O
O
O
Lewis acid
R
O
(13)
O
O O
R
O
O (24)
O (25)
"iii# From dithiocarboxylic esters Dithiocarboxylic esters react with dialkoxystannanes at temperatures of 59Ð84>C to a}ord ortho! esters "Equation "03## ð65CL780Ł[ The method has been used to prepare aliphatic ortho!esters and substituted ortho!benzoate esters\ and reported yields "generally 59) or greater# are favourable compared to some other methods[ S R1 SMe
Bun2Sn(OR2)2, 60–95 °C 45–98%
R1
OR2 OR2 OR2
(14)
5[92[1[0[3 Ortho!esters from dioxocarbenium salts Meerwein et al[ ð45CB1959Ł demonstrated that the O!alkyllactonium tetra~uoroborate salts "15\ R Me\ Et# react with alkoxides to form the cyclic ortho!esters "16\ R Me\ Et# in high yields "Equation "04##[ Ortho!esters derived from the O!ethyl tetra~uoroborate salts of coumarin and 2\3! dihydrocoumarin have been prepared similarly ð54HOU"5#250Ł[ Alkoxides have also been added to dioxolenium tetra~uoroborates "17\ R0 Me\ Ph# and to 1!phenylbenzo!0\2!dioxolium tetra~uo! roborate to give the cyclic ortho!esters "18^ Equation "05## ð59LA"521#27Ł and "29^ Equation "06## ð54AG"E#762Ł respectively[ Several further examples of the addition of alcohols to dioxolenium and dioxenium salts have been described ð56CC02\ 56JOC1529\ 56T3070Ł[
63
Three Chalco`ens +
O
BF4–
NaOR
OR
69–85%
OR OR (27)
(26) O +
O
BF4–
O
NaOR2
R1
+
BF4–
OR2
(16)
O
R1 (29)
(28)
O
(15)
O
NaOR
Ph
O
O
OR
O
Ph
(17)
(30)
5[92[1[0[4 Ortho!esters from 0\0!dialkoxyalkenes\ 0\0!dihaloalkenes and 0!alkoxyalkynes Alcohols and phenols add to 0\0!dialkoxyalkenes "ketene acetals# to give high yields of ortho! esters "Equation "07## ð25JA418Ł[ The reaction is catalysed by acids ð47JA0136Ł\ though ortho!esters are also formed under neutral and basic conditions ð26JA1155\ 31JA0852Ł[ This method is particularly useful for the preparation of hindered ortho!esters\ for example trimethyl ortho!diphenylacetate ð40JA2796Ł\ trimethyl ortho!dimethoxyacetate ð55CB0781Ł and triphenyl ortho!acetate ð34JA549Ł\ which are di.cult to prepare by other methods[ The procedure is also suitable for the synthesis of mixed ortho!esters "20# in which R2 and R3 are di}erent ð25JA418\ 31JA1414\ 53JOC1662Ł^ use of benzaldoximes in place of alcohols or phenols gives rise to aminoxy ortho!ester derivatives "20\ R3 NCHAr# ð50JOC1191Ł[ R1
OR3
R2
OR3
R4OH
R1
OR3 OR3 OR4
R2
(18)
(31)
Activated 0\0!dihaloalkenes undergo reaction with sodium alkoxides\ giving rise to ortho!ester products[ Thus\ ortho!ester "21\ R Me^ X H# was isolated in 68) yield from the reaction between 0\0!dichloro!1!nitroethene with sodium methoxide "Equation "08## ð67BSB582Ł\ "21\ R Et^ X Cl# was obtained in 23) yield from 0\0\1!trichloro!1!nitroethene and sodium ethoxide ð67ZOR1118Ł\ and "22# was prepared from per~uoropropene and sodium methoxide "Equation "19## ð62USP2634119Ł[ It is not known whether these reactions proceed by an additionÐelimination mechanism via a 0\0!dialkoxyalkene intermediate\ or whether they proceed by an additionÐsub! stitution mechanism via a\a!dihaloether and a!haloacetal intermediates[ X
Cl Cl
O2N
NaOR, ROH, 0 °C 34–79%
X O2N
OR OR OR
(19)
OMe OMe OMe
(20)
(32)
F
F
F3C
F
NaOMe, MeOH, 55 °C, 5 h
F F3C (33)
In a reaction related to the addition of alcohols to 0\0!dialkoxyalkenes\ mixed ortho!acetate esters have been prepared by the Lewis acid catalysed addition of alcohols and phenols to 0!ethoxyethyne "Equation "10## ð64RTC198Ł[ Zinc chloride is the preferred catalyst for the reaction with alcohols\ whereas mercury"II# acetate is preferred for phenols[ Triethyl ortho!acetate has also been obtained by treatment of 0!ethoxyethyne with ethanolic sodium ethoxide ð42MI 592!90Ł[ Addition of oximes to 0!ethoxyethyne a}orded the mixed ortho!ester derivatives "23\ R NCR0R1# ð59RTC777Ł[
64
Three Oxy`ens OEt OR (Ar) OR (Ar) (34)
ROH, ZnCl2 or ArOH, Hg(OAc)2
OEt 35–79%
(21)
Tris"b!alkoxyalkyl# ortho!acetates have been obtained by treatment of 0\0!dichloroethene with the appropriate sodium alkoxide ð53JOC1662Ł[ It has been proposed that these reactions proceed through a series of elimination and addition steps via a 0!alkoxyalkyne intermediate "Scheme 4#[ Cl
NaOR
OR
NaOR
Cl
Cl
OR OR OR
NaOR
NaOR
OR 41–57%
Cl Scheme 5
0\0!Dialkoxyalkenes undergo zinc chloride promoted reactions with epoxides to give cyclic ortho! esters "Equation "11## ð68TL1814Ł[ The epoxide generally undergoes attack at the least hindered position\ unless attack at the more substituted position is favoured on electronic grounds[
R1
R1
O
OR2
R3
OR2 R3
ZnCl2 40–60%
OR2
O
(22)
OR2
Triethyl ortho!cinnamate esters have been prepared by addition of ethanol to diethoxyethen! ylidinetriphenylphosphorane "24#\ followed by a Wittig reaction of the resulting phosphorane with aromatic aldehydes ð75S286Ł "Scheme 5#[ A related method for the preparation of a series of unsaturated cyclic ortho!esters "25# involves the addition of an enolised 0\1!diketone to phosphorane "24#\ followed by intramolecular Wittig cyclisation of the intermediate ketophosphorane "Scheme 6# ð72CB0352\ 72CB2371\ 77T4984Ł[ +
–
OEt
Ph3P
OEt (35)
EtOH
+
Ph3P
90%
–
OEt
ArCHO
OEt OEt
42–67%
OEt OEt Ar
OEt
Scheme 6
O
R1
R2
–
(35)
R3
R1 OH
+
O
R1
PPh3 OEt
R2
O R3
46–71%
OEt
OEt
R2 O R3
OEt
(36) Scheme 7
The preparation of cyclic ortho!esters by thermal ð3¦1Ł cycloaddition reactions of 0\0! dialkoxyalkenes and a\b!unsaturated carbonyl compounds was _rst described by McElvain et al[ "Equation "12## ð43JA4625Ł[ Many further examples of ortho!esters "26# have since been prepared by reaction of 0\0!dimethoxyethene\ 0\0!dimethoxy!0!propene\ 0\0!dimethoxy!1!methyl!0!propene\ 0\0\1!trimethoxyethene\ 0\0\1\1!tetramethoxyethene and 1!chloro!0\0!dimethoxyethene with a range of substituted a\b!unsaturated carbonyl compounds ð44JA4590\ 60CC272\ 61CC752\ 70RTC02Ł[ 0\0!Dial! koxyalkenes also undergo ð1¦1Ł cycloaddition reactions with electron de_cient carbonyl compounds\ such as acyl cyanides and aldehydes\ giving rise to the cyclic ortho!esters "27# "Equation "13## ð65JCS"P0#0937\ 66JOC2017Ł[ It has been shown that ð1¦1Ł cycloadducts are the products of the low temperature reaction between 0\0!dialkoxyalkenes and a\b!unsaturated carbonyl compounds\ and that this process is reversible at higher temperature\ when formation of the ð3¦1Ł cycloadducts is favoured on thermodynamic grounds ð70RTC02Ł[
65
Three Chalco`ens R5 R6 R7
R3
R5 R4
R2
heat
R4 R1O
O
OR1
R6
R3 R2
R7
OR1 OR1
O
(23)
(37) O
R2
R3 R1O
OR1
R4
R4
R5
R3 R2
R5
(24)
25–90%
O
OR1 OR1 (38)
A number of _ve!membered ring ortho!esters have been prepared by ð2¦1Ł cycloaddition reac! tions of 0\2!dipoles to 0\0!dialkoxyalkenes[ Some examples are given in Equations "14# ð75JMC442Ł\ "15# ð48G0400Ł and "16# ð55G264Ł[
Ph
Ph
OMe
MeCOCHN2, Cu(acac)3, C6H6, 85 °C, 30 min
OMe 65%
OMe
OMe
Ph
OMe
O But
OMe
N O
(26)
OMe
p-ClC6H4
N+ Ph 125 °C, 16 h 84%
OEt
Ph
O–
Cl
OEt
OMe
ButCNO, 80 °C 30%
(25)
Ph
OEt
N O
(27)
OEt
5[92[1[0[5 Ortho!esters from 0\0!dialkoxycyclopropanes and related compounds Alcohols add to 0\0!dialkoxycyclopropanes which bear an electron withdrawing group "EWG# "carboxylic ester or sulfone# at the 1!position to give ortho!esters "Equation "17## ð62JOC0250\ 74S651Ł[ Mixed ortho!esters "28#\ in which R0 and R3 are di}erent\ have been prepared by this method\ which is analogous to the addition of alcohols to 0\0!dialkoxyalkenes[ Examples of ortho!esters prepared using this procedure are listed in Table 0[ OR1
EWG
OR1 OR1
R4OH, heat
OR1 65–78%
R2
OR4
EWG R2
R3
(28)
R3 (39)
Ring opening of 0\0!dialkoxy!1\1!dichlorocyclopropanes with potassium t!butoxide is accompanied by elimination to produce alkynyl ortho!esters "Equation "18## ð48JA1468Ł[ Addition of alcohols to 0\0!dimethoxycyclopropene produces the unsaturated ortho!esters "39\ R Me\ Et\ Prn\ Pri\ But^ Equation "29## ð66JOC568Ł[ OR1
R2
OR1 Cl
Cl
KOBut
R2
OR1 OR1 OBut
(29)
66
Three Oxy`ens Table 0 Ortho!esters "28# prepared from 0\0!dialkoxypropanes[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R0 R1 R2 R3 EWG ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me H H Me CO1Et 62 74S651 69 74S651 Et H H Et CO1Et 61 74S651 Me Me H Me CO1Et Et Me H Et CO1Et 65 74S651 67 74S651 Me Et H Me CO1Et Me Ph H Me CO1Et 56 74S651 55 74S651 Me Me Me Me CO1Et Me Me Me Me SO1Ph 54 62JOC0250 60 62JOC0250 Et Me Me Et SO1Ph Et Me Me Me SO1Ph 62JOC0250 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
OMe
OMe OMe
ROH
OMe
(30)
OR (40)
Alcohols also add to 1\1!dialkoxyaziridines and 1\1!dialkoxy!1H!azirines to give a!amino!and a! imino!ortho!esters "30^ Equation "20## ð58TL1112\ 62JMC867Ł and "31^ Equation "21## ð56JA4613Ł respectively[ These compounds are di.cult to prepare by other methods[ OR1 OR1
OR1
R2
OR1
R1OH
R2
N H
(31)
NH2 (41) OR1
R2
OR1
PriOH
OR1 N
OR1 OR1
R2
OPri
(32)
NH (42)
5[92[1[0[6 Ortho!esters from acetals Some acetals undergo electrochemical oxidation in the presence of methanol to give ortho!esters in reasonable yields "Equation "22##[ The reaction has been shown to be successful for 1!alkyl! 0\2!dioxolanes ð67S172Ł\ 1!alkyl! and 1!aryl!0\2!benzodioxoles ð74S20Ł and dimethyl acetals of benzaldehydes ð75T442Ł[ Dimethyl acetals of simple aliphatic aldehydes gave lower yields of ortho! esters\ and the reaction failed completely for the corresponding diethyl acetals ð67S172Ł[ Table 1 lists some representative examples of ortho!esters "32# prepared by this method[ OR2 R1
–2e–(anode), MeOH
R1 OR2
OR2 OR3 OMe (43)
(33)
5[92[1[0[7 Ortho!esters from ortho!carbonate esters and trialkoxyacetonitriles Trialkyl ortho!benzoates have been reported to be formed in up to 66) yield by treatment of the appropriate tetraalkyl ortho!carbonate ester with phenylmagnesium bromide "Equation "23## ð94CB450\ B!32MI 592!90Ł\ and similar syntheses of triethyl ortho!phenylpropiolate ð00BSF0297Ł and triethyl ortho!2!butynoate ð69AG"E#345Ł have been described[ However\ the reaction is not always successful\ and other workers have isolated only ketals and ethers from reactions of ortho!carbonate esters with Grignard reagents ð31JA0714\ 38MI 592!90Ł[ No systematic survey of this method has been
67
Three Chalco`ens Table 1 Examples of ortho!esters "32# prepared by electro! chemical oxidation of acetals[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R1 R2 ")# Ref[ R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * H 0"CH1#10 33 67S172 H 0C5H30 38 74S20 53 67S172 Me 0"CH1#10 Me 0C5H30 41 74S20 Pri 0"CH1#10 43 67S172 i 0C5H30 50 74S20 Pr But 0"CH1#10 10 67S172 0C5H30 58 74S20 But 49 74S20 Ph 0C5H30 Ph Me Me 89 75T442 3!ClC5H3 0C5H30 37 74S20 3!ClC5H3 Me Me 73 75T442 0C5H30 33 74S20 3!MeOC5H3 3!MeOC5H3 Me Me 73 75T442 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
carried out\ though DeWolfe ð63S042Ł has suggested that the Grignard reagent needs to bear an electron withdrawing organic moiety for the reaction to work successfully[ RO
OR OR OR
PhMgBr
Ph 77%
OR OR OR
(34)
More recently\ it was reported that trialkyl ortho!benzoate esters are obtained from the reactions of Grignard reagents with trialkoxyacetonitriles "Equation "24## ð70S279Ł[ Trimethyl ortho!benzoate\ trimethyl 1!methyl!ortho!benzoate and triethyl 1!5!di~uoro!ortho!benzoate were prepared in yields of 73)\ 53) and 19) respectively[ Triethyl ortho!phenylpropiolate was prepared in 53) yield from phenylethynyl magnesium bromide and triethoxyacetonitrile using this method ð70S279Ł[ NC
OR OR OR
ArMgX
Ar 20–84%
OR OR OR
(35)
5[92[1[1 Preparation of Carboxylic Ortho!Esters from Other Ortho!Esters 5[92[1[1[0 Trans!esteri_cation reactions Ortho!formate esters undergo exchange reactions on treatment with alcohols "Scheme 7#[ The reaction\ which is acid catalysed\ can be forced to completion by distilling out R0OH "preferably methanol or ethanol# as it is formed\ and a number of trialkyl ortho!formates derived from higher alcohols\ including functionalised alcohols such as 1!chloroethanol and 0!chloro!1!propanol\ have been prepared by this method ð41JA443\ 44JA2790\ 69CB528Ł[ The reaction is subject to steric constraints\ proceeding readily with primary alcohols and less readily with secondary alcohols[ Trans!esteri_cation with tertiary alcohols does not proceed to completion^ treatment of triethyl ortho!formate with t!butanol gave a mixture of t!butyldiethyl and di!t!butylethyl ortho!formates ð52PIA"A#34Ł[ Relatively little has been published on the trans!esteri_cation reactions of higher ortho! esters\ though work that has been reported suggests that these proceed in much the same way as for ortho!formate esters ð49DOK"69#120\ 45ACS0995\ 69CB528Ł[ OR1 R1O OR1
R2OH
OR1 R2O
R2OH
OR1
OR2 R2 O OR1
R2OH
OR2 R2O OR2
Scheme 8
The preparation of mixed ortho!esters by exchange reactions of trialkyl ortho!esters with simple alcohols is not usually feasible since equilibration reactions lead to all possible ortho!ester products
68
Three Oxy`ens
ð22JA2740Ł[ Among the few reported exceptions to this general trend are the reactions of ortho!esters with phenol^ treatment of triethyl ortho!formate and triethyl ortho!acetate with one equivalent of phenol produced good yields of the diethylphenyl ortho!esters "33\ R H\ Me#\ and reaction of triethyl ortho!formate with two equivalents of phenol gave a reasonable yield of the ethyldiphenyl ortho!ester "34^ Scheme 8# ð45ACS0995\ 69CB532Ł[ A recently reported trans!esteri_cation route to mixed ortho!esters\ which is potentially general\ involves the magnesium chloride catalysed exchange reaction with alcohols "Equation "25## ð77TL1912Ł[ Mixed ortho!esters have also been obtained from the O!acyl derivative "35# ð58RTC786Ł\ which was itself prepared by treatment of triethyl ortho! formate with one equivalent of acetic formic anhydride "Scheme 09# ð55RTC682Ł[ In contrast to their reactions with alcohols\ ortho!esters react cleanly with peroxides to form monoperoxy ortho!ester derivatives in high yield ð47CB0831Ł[ OPh
OEt OEt OEt
2 equiv. PhOH, heat
EtO
R (R = H) 51%
OPh (45)
1 equiv. PhOH, heat
R 67–92%
Scheme 9
R1
OEt
OEt OEt OEt
R2OH, MgCl2, CH2Cl2
OR2 OEt OEt
R1
56–96%
OEt
HCO2COMe
EtO 62%
(36)
OEt
ROH, Et3N
RO
AcO OEt
OEt OEt OPh (44)
OEt
48–86%
OEt
(46) Scheme 10
Trans!esteri_cation of simple trialkyl ortho!esters with aliphatic 0\1! and 0\2!diols proceeds cleanly to give mixed cyclic ortho!esters in high yields "Equation "26##[ The reaction is catalysed by acids such as sulfuric acid ð47CB549Ł\ p!toluenesulfonic acid ð69JA473Ł and benzoic acid ð62JA167Ł[ Trans! esteri_cation reactions of trialkyl ortho!benzoates with benzene!0\1!diol proceed in the absence of a catalyst ð54AG"E#762Ł[ Treatment of trialkyl ortho!esters with b!hydroxycarboxylic acids yields cyclic acyloxy ortho!esters "36# ð58TL0936\ 76HCA0219Ł[ In contrast to the equilibration reactions between simple trialkyl ortho!esters and alcohols\ the cyclic ortho!ester "00# reacts moderately cleanly with alcohols to give the exchanged products "37# in yields of 30Ð47) "Equation "27## ð79JCS"P0#645Ł[
R1
OR2 OR2 OR2
HO
OH
R2O
O
R1
O
(37)
R3 R2O
O
R4
R1
O
R4 O
(47)
O OEt O (11)
ROH, H+
O
41–58%
O (48)
OR
(38)
Trialkyl ortho!esters react with conformationally ~exible triols such as glycerol\ 0\2!dihydroxy!1! hydroxymethyl!1!methylpropane and 0\1\3!trihydroxybutane to give good yields of the cor! responding tricyclic ortho!esters "38#\ "49# and "40# respectively ð79MM141\ 79CC196\ 77JA3033Ł\ and exchange with all cis!0\2\4!trihydroxycyclohexane gives high yields of polycyclic ortho!esters "41#
79
Three Chalco`ens
ð42CB689\ 43CB194Ł[ Trans!esteri_cation with conformationally restricted triols normally gives prod! ucts arising from exchange of only two of the alkoxy groups of the ortho!ester[ For example\ exchange with 1\2\4!trihydroxy nucleoside analogues generally leads to exclusive formation of the ortho!ester derived from the 1\2!dihydroxy unit of the triol "Equation "28## ð53CI"L#470\ 56CCC2953\ 74S397Ł[ The trans!esteri_cation method has been used for the preparation of many cyclic\ bicyclic and tricyclic ortho!esters from dihydroxy! and trihydroxy!carbohydrate\ nucleoside and steroid derivatives ðB!69MI 592!90\ 66USP3910348\ 77EUP159868Ł[ R
O R
O
O O
R
O
R
O
(49)
(50)
HO
Het
O O
O O (51)
(52)
O
HOH2C
O
HOH2C
O
O
Het
R1C(OR2)3
(39) O
O
R1
OR2
OH
Ortho!esters have also been prepared by the alcoholysis of amide acetals ð70JOC775Ł and trithio! ortho!esters ð37JA1157\ 79JOC639Ł[
5[92[1[1[1 Modi_cation of R0 and R1 of R0C"OR1#2 Ortho!esters bearing a!hydrogen atoms react with one equivalent of bromine to give a!bromo ortho!esters "42# in up to 79) yield ð26JA0162\ 31JA1414\ 35JA0811Ł^ use of two equivalents of bromine gives a\a!dibromo ortho!esters ð31JA0852Ł[ Dehydrobromination of a!bromo ortho!esters\ "e[g[\ "43##\ to unsaturated ortho!esters\ "e[g[\ "44##\ has been achieved\ but yields are low "08Ð21)# ð62S196\ 74JAP"K#59197872Ł[ Reaction of triethyl ortho!acetate with tri~uoromethylselenenyl chloride gave triethyl a!"tri~uoromethylselenenyl#ortho!acetate\ which was converted to the bis"tri~uoro! methylselenenyl# derivative by deprotonation with sodium hydride\ followed by treatment with a further equivalent of tri~uoromethylselenenyl chloride "Scheme 00# ð81CB460Ł[ Trialkyl ortho! acetates have also been shown to react with perhalogenated aldehydes and ketones\ producing the adducts "45\ R0 H\ CF2\ CClF1^ R1 Me\ Et^ X F\ Cl# in yields of 74Ð83) "Equation "39## ð66ZOR832Ł[
Br R1
OEt OEt OEt
OR3 OR3
Br
OR3 R2 (53)
O O O
O
(54)
(55)
87%
OEt OEt OEt Scheme 11
F X
OR2 OR2 OR2
F3CSeCl, Et2O, –20 °C
F O R1
O O
F3CSe
85–94%
NaH, F3CSeCl
F3CSe
Et2O, –20 °C 97%
F3CSe
F2XC
OH
OR2 OR2
OEt OEt OEt
(40)
OR2
R1 (56)
Dehydrohalogenation of tris"b!chloroalkyl# ortho!esters yielded trialkenyl ortho!esters "Equation
70
Three Sulfurs
"30## ð69CB528Ł[ Ozonolysis of tris"1!propenyl# ortho!formate gave tri!O!acetyl ortho!formate "Equa! tion "31## ð69CB528Ł[ Cl
R2 Cl
R2 R2
O R1
R2
O
KOBut
O
R1
O
O
(41)
O
R2
R2 Cl
O
O3, –78 °C
O
OAc (42)
AcO
60%
O
OAc
5[92[2 FUNCTIONS BEARING THREE SULFUR ATOMS Trithio!ortho!esters contain a carbon atom bearing three alkanethio or arenethio groups[ Related to these are the analogous acylthio esters "containing at least one RCOS group#\ hydrogen esters "containing at least one HS group# and oxidised derivatives bearing sulfoxide\ sulfone and sulfonyl groups[ Methods for the preparation of trithio!ortho!esters and related compounds have been reviewed by Post ðB!32MI 592!90Ł\ DeWolfe ðB!69MI 592!90Ł and Simchen ð74HOU"E4#2Ł[
5[92[2[0 Methods for the Preparation of Trithio!ortho!esters and Related Compounds 5[92[2[0[0 Trithio!ortho!esters from RC"X0#"X1#X2 "i# From 0\0\0!trihaloalkanes and a\a!dihalo ethers Gabriel reported the _rst synthesis of triethyl trithio!ortho!formate and triphenyl trithio!ortho! formate by reaction of the appropriate thiolate salt with chloroform "Equation "32## ð0766CB074Ł[ This method has since been used to prepare a range of trialkyl and triaryl trithio!ortho!formate esters ð0767CB1154\ 22RTC326\ 53CR"148#3940Ł^ yields from reactions with arenethiols are usually high "69) or greater#\ but are lower from reactions with aliphatic thiols[ Bromoform and chloro! di~uoromethane also react with sodium arenethiolate salts to give high yields of triaryl trithio! ortho!esters ð45JA368\ 59JA5007Ł[ Carbon tetrachloride reacts with alkanethiolates to give trialkyl trithio!ortho!esters\ the reactions proceeding via formation of chloroform under the alkaline reaction conditions ð22RTC326Ł[ Tris"tri~uoromethyl# trithio!ortho!formate "46# was prepared by reaction of iodoform with Hg"SCF2#1 "Equation "33## ð56JOC1952Ł[ CHCl3
M+ –SR
SR (43)
RS SR
Hg(SCF3)2, 130 °C
CHI3
SCF3 (44)
F3CS SCF3 (57)
Relatively few reports of the preparation of higher trithio!ortho!esters from 0\0\0!trihaloalkanes have appeared[ 1!Trichloromethylbenzimidazole was converted to the trithio!ortho!esters "47\ R Me\ p!ClC5H3# by reaction with the corresponding thiol ð56JCS"C#29Ł\ and the activated tri! ~uoromethyl group of the thiazole "48# underwent reaction with methanethiol to give the trithio!
71
Three Chalco`ens
ortho!ester "59# ð80JHC0902Ł[ A series of a\a\a!trihalotoluenes have been converted to tris "tri~uoromethyl# trithio!ortho!benzoate esters "50# by treatment with AgSCF2 ð58ZOB0644Ł[ N N H (58)
C(SMe)3 O
CF3
SR SR SR
O
N Cl
S
N
N H (59)
Ar
NEt2
Cl
N H (60)
S
NEt2
SCF3 SCF3 SCF3 (61)
Trithio!ortho!formate esters may also be prepared from dichloromethyl alkyl ethers^ treatment with lead"II# alkanethiolates gives trialkyl trithio!ortho!formates ð50CB427Ł\ whereas reaction with arenethiols in the presence of zinc produces triaryl trithio!ortho!formates ð60ZOR0776Ł "Scheme 01#[ SR2 Pb(SR2)2,
SR2
Et2O
SR2 Cl R1O
ArSH, Zn, Et2O, 35 °C
Cl
SAr
66–92%
ArS SAr
Scheme 12
"ii# From a!halodithioacetals and a!acyloxy! and a!alkoxydithioacetals Treatment of chlorobis"methanethio#methane with methanethiol produced trimethyl trithio! ortho!formate\ though reaction with higher alkanethiols was accompanied by disproportionation\ giving rise to mixtures of trithio!ortho!esters ð50LA"537#10Ł[ Cyclic a!chlorodithioacetals "51\ X S\ CH1# reacted with benzenethiol to give high yields of the trithio!ortho!esters "52\ X S\ CH1^ Equation "34## ð65BCJ442Ł[ Reaction of the benzoyloxytrithiane "53# with a range of alkane! and arene!thiols produced the trithio!ortho!esters "54\ R alkyl\ aryl^ Equation "35## ð63BCJ1346\ 64BCJ1385Ł[ The 1!alkoxybenzodithiole "55# reacted similarly with ethanethiol in the presence of acetic acid to give 1!ethylthio!0\2!benzodithiole "Equation "36## ð64S325Ł[ S
S
PhSH, C6H6, RT
X
Cl
X
S S
S S
S (64)
O S (66)
(45)
S (63)
RSH
OCOPh
S
SPh
80–90%
S (62)
(46)
SR S (65)
EtSH, AcOH, 20 C, 5 h
S
84%
S
SEt
(47)
"iii# From carboxylic ortho!esters and related compounds Carboxylic ortho!formate esters undergo exchange reactions with alkanethiols and arenethiols to give trithio!ortho!esters "Equation "37##[ The reaction may be catalysed using hydrogen chloride ð56AG"E#331Ł\ p!toluenesulfonic acid ð44JA498Ł\ zinc chloride ð53T306Ł\ boron tri~uoride etherate ð61CB2179Ł and montmorillonite KSF ð78SC20Ł\ though it will often proceed in the absence of a
72
Three Sulfurs
catalyst ð59IZV0890Ł[ Exchange of trialkyl ortho!formates with ethanedithiol and propanedithiol gave "56# and "57# respectively ð15JCS1152\ 56AG"E#331Ł\ and exchange of triethyl ortho!formate with 1!methyl!1!thiohydroxymethylpropane!0\2!dithiol produced the tricyclic trithio!ortho!ester "58\ R H# ð44JA498Ł[ Little work has been reported on the exchange of higher ortho!esters with thiols\ though triethyl ortho!acetate does undergo reaction with 1!methyl!1!thiohydroxymethylpropane! 0\2!dithiol to give the tricyclic trithio!ortho!ester "58\ R Me# ð44JA498Ł[ OR1
SR2
R2SH
R1O
(48)
R2S
OR1
S S
S
SR2
S
S
S
S
S
S
S
S
S
(67)
S S
R
S (69)
(68)
5[92[2[0[1 Trithio!ortho!esters from thioimidate ester salts Thioimidate ester hydrochloride salts react with alkanethiols and arenethiols to yield the trithio! ortho!esters "69# ð42JA0557\ 51JOC1747Ł[ Although this method is analogous to the widely used Pinner synthesis of ortho!esters\ relatively few reports of the preparation of trithio!ortho!esters using this procedure have appeared[ Some trithio!ortho!esters prepared by this method are listed in Table 2[ SR2 R1
R3SH
R1
+
NH2 Cl–
SR3 SR3 SR3 (70)
(49)
Table 2 Trithio!ortho!esters "69# pre! pared from thioimidate ester hydro! chloride salts[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R2 Ref[ R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * H Ph 42JA0557 C1F4 Me 51JOC1747 Me 51JOC1747 C2F6 C2F6 Et 51JOC1747 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Other methods for the preparation of trithio!ortho!esters which proceed via thioimidate inter! mediates have been described[ Formamide undergoes an acid catalysed reaction with thiols to give trithio!ortho!esters "Scheme 02# ð96CB0639\ 96LA"242#020Ł\ and the formanilide "60# reacts with phosphorus oxychloride in the presence of thiols to give trithio!ortho!esters in yields of 33Ð58) "Scheme 03# ð59IZV0717Ł[ Acetamide derivatives do not react under similar conditions ð48RTC243Ł[ O
RSH
H NH2
SR
RSH
H NH
SR RS SR
Scheme 13
O H
(71)
H
+
+
N Ph Cl–
N Ph Me
SR
Cl H
N Ph Cl– Me
Me Scheme 14
SR 44–69%
RS SR
73
Three Chalco`ens
5[92[2[0[2 Trithio!ortho!esters from carboxylic acids and derivatives "i# From acyl chlorides and anhydrides A general method for the preparation of trithio!ortho!esters involves the treatment of acyl chlorides with thiols in the presence of zinc chloride or aluminium trichloride "Equation "49##[ This procedure has been used to prepare a range of trithio!ortho!esters derived from aliphatic ð48RTC243Ł and aromatic ð42JA0557\ 79JOC639\ 75TL3750Ł acyl chlorides^ yields are usually greater than 39)[ A limitation of the method is that acyl chlorides containing one or more a!hydrogen atoms give poor yields of trithio!ortho!esters due to competing elimination reactions\ though this problem can be overcome to some extent by using an excess of the thiol reagent ð48RTC243Ł[ Reaction of acetic anhydride with 2!methylbenzenethiol in the presence of boron tri~uoride has been reported to give tris"2!methylphenyl# trithio!ortho!actetate in 29) yield ð42JA0557Ł[ O
SR2 SR2 SR2
R2SH, ZnCl2 or AlCl3, heat
R1
R1 Cl
(50)
"ii# From carboxylic esters and thioesters In 0896\ Holmberg ð96CB0639\ 96LA"242#020Ł discovered that formate esters undergo an acid pro! moted reaction with alkanethiols and arenethiols to give trithio!ortho!esters "Equation "40##[ A range of trialkyl and triaryl trithio!ortho!formates have been prepared using this method ð96CB0639\ 96LA"242#020\ 37JCS576\ 51RTC0998Ł[ These reactions simply involve saturating a mixture of the ester and thiol with hydrogen chloride\ and allowing the mixture to stand^ yields are normally greater than 49)[ Triaryl ortho!formates have also been obtained from the reactions of arenethiomagnesium bromides with ethyl formate ð51ZOB634Ł[ O
SR2
R2SH, HCl
H
(51)
R2S OR1
SR2
The Holmberg method is not suitable for the preparation of trithio!ortho!esters from higher carboxylic esters[ In a modi_cation of the reaction\ triethyl trithio!ortho!acetate has been obtained in low yield from the zinc chloride catalysed reaction of ethanethiol with ethyl acetate ð48RTC243Ł[ More recently\ the synthesis of trialkyl trithio!ortho!benzoate esters by the aluminum trichloride catalysed reaction of methyl benzoates with alkanethiotrimethylsilanes has been reported "Equation "41## ð79JOC639\ 75TL3750Ł[ O Ar
RS-TMS, AlCl3
Ar
OMe
SR SR SR
(52)
Thiocarboxylic esters "61\ R0 H\ alkyl\ aryl# undergo acid or Lewis acid catalysed reactions with thiols to give trithio!ortho!esters ð34USP1278042\ 42JA0557\ 64JOC852Ł[ Mixed trithio!ortho!esters "62#\ in which R1 and R2 are di}erent\ may be prepared by this method "Equation "42## ð34USP1278042\ 42JA0557Ł[ O R1
R3SH
R1 SR2 (72)
HCl or ZnCl2 or BF3
SR2 SR3 SR3 (73)
(53)
"iii# From carboxylic acids Formic acid reacts with alkanethiols and arenethiols to give trithio!ortho!formate esters ð00CB2124\ Higher carboxylic acids do not generally undergo this reaction^ exceptions are the reactions of tri~uoroacetic acid with ethane!0\1!dithiol and propane!0\2!dithiol\ which give the 01CB1831Ł[
74
Three Sulfurs
cyclic bistrithio!ortho!esters "63# and "64# respectively ð56CC0978\ 57JOC1493Ł[ Reaction of formic acid with hydrogen sul_de and acetic anhydride in the presence of zinc chloride a}orded tris "acetylthio#methane "65^ Equation "43## in 39) yield ð65CS011Ł[ This compound may also be prepared by treatment of formic acid with thioacetic acid and acetic anhydride in the presence of zinc chloride ð65CS011Ł[ S
CF3 S S
S
CF3 S
CF3 S
S
S
S
S
S
CF3
S
(75)
(74)
SAc
H2S, (MeCO)2O, ZnCl2, MeCO2H, 20–50 °C, 2 h
HCO2H
(54)
AcS
40%
SAc (76)
5[92[2[0[3 Trithio!ortho!esters from dithio! and trithiocarbenium salts Trithio!ortho!esters and related compounds are obtained from the addition of thiols and other sulfur nucleophiles to dithiocarbenium salts[ Reaction of the dithiolium tetra~uoroborate salt "66# with sodium benzenethiolate produced the 1!phenylthio!0\2!dithiole "67^ Equation "44##\ and reaction with N\N!dialkyldithiocarbamate salts gave 1!dithiocarbamoyldithioles "68# ð58CPB0820Ł[ Treatment of the dithiolium perchlorate salt "79# with one equivalent of potassium ethyl xanthate yielded the analogous ethoxythiocarbonythio derivative "70#\ whereas the use of an excess of potassium ethyl xanthate produced the sul_de "71#\ the reaction being thought to proceed via further reaction of "70# with the xanthate "Scheme 04# ð66JOC0432Ł[ S Ph
+
SCSNR1R2
S
Ph
EtOCS2K
S
Ph S
EtO S
S
Ph S
S ClO4–
Ph
S (80)
S– SCSOEt
(55)
SPh
S (78)
S +
(79)
(81)
Ph
66%
S (77)
S Ph
S
NaSPh, EtOH, 78 °C, 1 h
BF4–
SCSOEt S (81)
Ph S
(80)
S
–EtOCSSCSOEt
S–
S
Ph
S S (82) Scheme 15
1!Methanethio!0\2!dithiolium salts may be reduced to 1!methanethio!0\2!dithioles using sodium borohydride[ The dithiole "73# was prepared in 67) yield from the salt "72# by this method "Equation "45## ð81JOC0585Ł[ MeSe
S +
MeSe
SMe BF4–
MeSe
S
MeSe
S
NaBH4, MeCN, 20 °C, 1 h
S (83)
SMe
(56)
(84)
5[92[2[0[4 Trithio!ortho!esters from dithioacetals Dithioacetals may be converted into trithio!ortho!esters by deprotonation with a strong base\ followed by reaction of the metallated species "74# with a disul_de "Scheme 05#[ The reaction was
75
Three Chalco`ens
_rst described by Frohling and Arens ð51RTC0998Ł\ who prepared triethyl trithio!ortho!benzoate in 65) yield from benzaldehyde diethyl dithioacetal using sodium amide and diethyl disul_de "Equa! tion "46##[ A procedure for the preparation of trithio!ortho!ester "75# from the cyclic dithioacetal "76# using n!butyl lithium and dimethyl disul_de is given in Or`anic Syntheses ð66OS"45#7Ł\ and this method has also been used for the preparation of a range of benzoic\ cinnamic and aliphatic trithio! ortho!esters ð61JOC1646Ł[ However\ the reaction may not be general for the preparation of aliphatic trithio!ortho!esters*trithioacetates and trithiopropionates could not be prepared from the cor! responding dithioacetals using sodium amide and dialkyl disul_des\ presumably because of com! peting elimination reactions ð51RTC0998Ł[ The preparation of trithio!ortho!formate esters by this method appears to be dependent on the nature of the substituents on sulfur\ and on the base used[ Seebach et al[ prepared the mixed trithio!ortho!formate ester "77# in 84) yield from bis"ben! zenethio#methane using n!butyllithium and dimethyl disul_de "Equation "47## ð61CB2179Ł\ whereas Frohling and Arens obtained only tetraethyl tetrathio!ortho!carbonate from the reaction of the bis"ethanethio#methane with sodium amide and diethyl disul_de "Scheme 06# ð51RTC0998Ł[ Doubly 02 C!labelled trimethyl trithio!ortho!formate has been prepared by a related method\ in which the lithiated dithioacetal "78# is treated sequentially with elemental sulfur followed by 02C!labelled methyl iodide "Scheme 07# ð73HCA0969Ł[ SR2
SR2
M+B–
R1
R1
–
SR2
R3SSR3
M+
SR2 SR2 SR3
R1
SR2 (85) Scheme 16
SEt
i, NaNH2
Ph
Ph ii, EtSSEt 76%
SEt
MeS
S
SEt SEt SEt
(57)
S
Ph
Ph S
S
(86)
(87)
SPh
SPh
i, BunLi
(58)
MeS SPh
SEt
NaNH2, EtSSEt
ii, MeSSMe 95%
SEt EtS
SEt
SPh (88)
NaNH2, EtSSEt
EtS
SEt
SEt SEt SEt
Scheme 17
SMe Li+
–
i, BunLi
H
*
SMe (89)
ii, 1/8 S8
*
SMe SMe S– Li+
Scheme 18
Me*I
H 58%
*
SMe SMe * SMe
76
Three Sulfurs
Trithio!ortho!formates have been prepared by reaction of N!p!toluenesulfonylsul_limines "89# derived from dithioacetals of formaldehyde with alkanethiols and arenethiols under alkaline con! ditions "Equation "48## ð65S440Ł[ Mixed trithio!ortho!esters are available by this method[ SR1
SR2
R3SH, KOH
R2
S
(59)
R1S
61–82%
SR3
TosN (90)
5[92[2[0[5 Trithio!ortho!formates from trithiocarbonates Addition of phenyllithium to diphenyl trithiocarbonate at −67>C yields the triphenyl! thiomethylide anion "80^ Equation "59##[ This anion\ when prepared by a di}erent method\ has been quenched with deuterated water to give the deuterated triphenyl trithio!ortho!formate "81# ð61CB376Ł[ Similar addition of methyllithium to the dithiolone "82#\ followed by quenching with acetic acid\ yielded the 1!methanethio!0\2!dithiole "83^ Scheme 08# ð76TL3042Ł[ The use of lithiated trithio!ortho!formates for the preparation of higher trithio!ortho!esters is discussed in Section 5[92[2[1[0[ PhS
PhSLi, THF, –78 °C
Li+
S PhS
D
S
S
MeLi, THF, –60 °C
S
S –
S
(60)
SPh SPh SPh (92)
S S
SPh SPh SPh (91) –
S
S
AcOH
SMe Li+
S
S
S
S
SMe 75%
(93)
(94) Scheme 19
Diphenyl trithiocarbonate undergoes cycloaddition reactions with diaryldiazomethanes to pro! duce the cyclic trithio!ortho!ester derivatives "84^ Equation "50## ð54CB2292Ł[ PhS
Ar2CN2
S PhS
S Ar
SPh Ar
(61)
SPh (95)
5[92[2[0[6 Trithio!ortho!formates from tetrathio!ortho!carbonates Seebach ð56AG"E#331Ł reported the preparation of the trithio!ortho!formate "86# by treatment of the tetrathio!ortho!carbonate "85# with n!butyllithium at −67>C\ followed by quenching the reaction with water "Scheme 19#[ The reaction proceeds via the lithiated trithio!ortho!formate ester "87#[ Similar treatment of tetraphenyl tetrathio!ortho!carbonate with n!butyllithium gave the tri!
77
Three Chalco`ens
phenylthiomethylide anion "80#\ which has been used to prepare the deuterated trithio!ortho!formate "81# ð61CB376Ł[ The use of lithiated trithio!ortho!formates for the preparation of higher trithio! ortho!esters is discussed in Section 5[92[2[1[0[ S S
SMe
S
BunLi, THF, –78 °C
–
SMe
(96)
SMe 70%
Li+
S
S
H2O
SMe
S
(98) Scheme 20
(97)
5[92[2[1 Preparation of Trithio!ortho!esters from other Trithio!ortho!esters 5[92[2[1[0 Higher trithio!ortho!esters from trithioformate esters In 0851\ Hine et al[ ð51JA0640Ł reported the generation of the potassium trithio!ortho!formate salt "88# by deprotonation of trimethyl trithio!ortho!formate with potassium amide\ and the reaction of this with methyl iodide to produce trimethyl trithio!ortho!acetate in 64) yield "Scheme 10#[ Seebach et al[ ð56AG"E#331\ 61CB376\ 61CB2179Ł later described the generation of several lithiated trithio!ortho! formate esters from the appropriate trithio!ortho!formate with n!butyllithium at −67>C\ and the subsequent reactions of these with a range of electrophiles to yield higher trithio!ortho!esters[ This has since developed into a general method for the homologation of trithio!ortho!formates[ Thus\ lithiated trithio!ortho!formates react with alkyl halides to give aliphatic trithio!ortho!esters ð56AG"E#331\ 61CB376\ 61CB2179\ 65CL32\ 71TL2396Ł\ with aldehydes and ketones to give a!hydroxy! trithio!ortho!esters ð56AG"E#331\ 61CB376\ 65CL32\ 70TL3998Ł\ with epoxides to give b!hydroxy trithio! ortho!esters ð56AG"E#331\ 61CB376Ł\ with cyclic a\b!unsaturated ketones to give g!ketotrithio!ortho! esters ð64CC105\ 78TL4370Ł\ with carbon dioxide to give trithiomono!ortho!oxalates ð56M0932Ł\ with carbon disul_de to give trithiomono!ortho!dithiooxalates ð77T1952Ł\ with chloroformate esters to give trithiomono!ortho!oxalate esters ð56AG"E#331\ 61CB376Ł and with iodine to give coupled hexa! thiodi!ortho!oxalates ð61CB2781Ł "Scheme 11#[ An example of the acylation of a lithiated trithio! ortho!formate by reaction with a lactone has been reported "Equation "51##\ but this reaction is not general ð80CJC304Ł[ Since lithiated trithio!ortho!esters may also be obtained from trithiocarbonates "Section 5[92[2[0[5# and tetrathio!ortho!carbonates "Section 5[92[2[0[6#\ these compounds should also be regarded as precursors of higher trithio!ortho!esters[ SMe MeS
KNH2, NH3
SMe
MeI
SMe
75%
–
K+ MeS
SMe
SMe SMe SMe
(99) Scheme 21
S
S Li+
MeS
O
–
O
S
OH O
(62)
S SMe
Triethyl trithio!ortho!heptanoate has been prepared by a radical homologation procedure\ involv! ing treatment of triethyl trithio!ortho!formate with 0!hexene in the presence of t!butyl hydroperoxide "Equation "52## ð77MI 592!90Ł[ SEt
1-hexene, ButO2H, 130 °C
SEt
76%
EtS
SEt SEt
(63)
SEt
5[92[2[1[1 Trans!esteri_cation of trithio!ortho!esters In contrast to the chemistry of ortho!esters\ relatively little work has been published on the preparation of trithio!ortho!esters by trans!esteri_cation reactions of other trithio!ortho!esters with
78
Three Sulfurs SR1 SR2 SR3
R4
SR1 SR2 SR3
HO R4 R5
OH SR1 SR2 SR3
R4
R4X
O
R4COR5
O
R4 O
SR2 R1S
BunLi, THF, –78 °C
Li+ –
SR3
SR1 SR2 SR3
SR1 SR2 SR3
CO2
O CS2
HO
R4OCOCl
SR1 SR2 SR3
I2
SR1 SR2 SR3
S R1S 2 RS R 3S
SR1 SR2 SR3
SR1 SR2 SR3
O R4O
HS
Scheme 22
thiols[ Mixed trithio!ortho!esters undergo rapid acid catalysed disproportionation reactions to yield mixtures of trithio!ortho!esters "Scheme 12# ð50LA"537#10Ł[ The dithiolane "099# and dithiane "090# have been prepared by heating triethyl trithio!ortho!formate with the appropriate dithiol in the presence of zinc chloride ð77URP0310633Ł[ R1
SR2 SR3 SR3
H+
R1
SR2 SR2 + SR2 Scheme 23
R1
SR2 SR2 SR3
+
R1
SR3 SR3 SR3
S
S
SEt
SEt S (100)
S (101)
5[92[2[1[2 Modi_cation of R0 and R1 of R0C"SR1#2 Treatment of triaryl trithio!ortho!acetates with deuterated tri~uoroacetic acid in deutero! chloroform results in a rapid proton exchange reaction to give the deuterated trithio!ortho!acetates "091^ Equation "53## ð64JOC852Ł[ However\ attempts to homologate triaryl trithio!ortho!acetates by reaction with electrophilic acylating agents have not been successful ð64JOC852Ł[ SAr SAr SAr
CF3CO2D, CDCl3, RT, 5 min
D3C ca. 100%
SAr SAr SAr (102)
(64)
Deacetylation of tris"acetylthio#methane using methanolic hydrogen chloride produced meth! anetrithiol "092^ Equation "54## in 49) yield ð65CS011Ł[ This product is stable at −29>C\ although
89
Three Chalco`ens
it polymerises slowly at 19>C[ The hydrolysis proceeds via di! and monoacetyl trithiomethane intermediates\ which can be detected in the 0H NMR spectrum of the reaction mixture[ SAc
SH
2% HCl in MeOH, 6 h
AcS
(65)
HS SAc
50%
SH (103)
5[92[2[2 Methods for the Preparation of Oxidised Derivatives of Trithio!ortho!esters 5[92[2[2[0 Oxidised trithio!ortho!esters containing at least one sulfoxide group Triaryl trithio!ortho!formate esters are oxidised to the triaryl sulfoxide derivatives in high yields on treatment with peroxyacetic acid "Equation "55## ð53CR"148#3940Ł[ The sulfoxide "093# has been prepared by oxidation of the corresponding sul_de with peroxybenzoic acid "Equation "56## ð37RTC773Ł[ SAr
SOAr
MeCO3H, Et2O
ArS
(66)
ArOS SAr
SO2Me MeS
>90%
PhCO3H
SOAr
SO2Me (67)
MeOS
SO2Me
SO2Me (104)
5[92[2[2[1 Oxidised trithio!ortho!esters containing at least one sulfone group Treatment of the sulfone "094# with two equivalents of N!ethanethiophthalimide in the presence of potassium t!butoxide produced the sulfonyldithio!ortho!ester derivative "095# in high yield "Equa! tion "57## ð71CC0072Ł[ Bis"sulfonyl#methanes "096# react with alkyl thioalkyl sulfones and alkane! sulfonyl or arenesulfonyl chlorides in the presence of sodium ethoxide to give disulfonylthiomethanes "097# ð22JCS295Ł and trisulfonylmethanes "098# ð30CB0556Ł respectively "Scheme 13#[ These oxidised trithio!ortho!formate derivatives produce the analogous trithio!ortho!acetate derivatives on treat! ment with methyl iodide in aqueous alkali "Equation "58## ð0781CB236\ 0781CB250Ł[ O 2 equiv.
O Ph
N SEt, KOBut, DMSO O
SO2Me
O Ph
87%
(105)
SO2R1 R3S
R3SSO2R4, NaOEt, EtOH
SO2R2 (108)
SO2R1
R3SO2Cl, NaOEt, EtOH
SO2R2 (107) Scheme 24
SO2R2 R1SO2 SOnR3
MeI, aq. NaOH
SO2Me SEt SEt (106)
(68)
SO2R2 R1SO
2
SO2R3 (109)
SO2R1 SO2R2 SOnR3
(69)
80
Three Seleniums
Trisulfones "009# are the products normally obtained from the oxidation of trialkyl and triaryl trithio!ortho!formates using acidic permanganate ð0781CB236\ 22RTC326Ł\ though Laves ð0789CB0303Ł has reported that controlled oxidation of triphenyl trithio!ortho!formate using this reagent produces the disulfone "000#[ Yields from these permanganate oxidations are often low due to the competing formation of disulfonylmethanes and sulfonic acids ð96CB0639\ 22RTC326Ł[ Trialkyl trisulfones have been obtained from the oxidation of trialkyl trithio!ortho!formates with peroxyacetic and mon! operoxyphthalic acids ð35RTC42\ 42LA"470#022\ 56USP2222996Ł[ The tricyclic trisulfones "001\ R H\ Me# and triaryl sulfones "002# were prepared by oxidation of the corresponding trithio!ortho!esters using hydrogen peroxide in acetic acid ð44JA498\ 53CR"148#3940Ł[ Oxidation of disulfones "003\ R H\ Me# with alkaline permanganate or hydrogen peroxide produced the corresponding trisulfones in high yields "Equation "69## ð0781CB236\ 20JCS1526\ 35RTC42Ł[ SO2
SO2Ph
SO2R
R
PhS
RO2S
SO2Ph (111)
SO2R (110)
R1
SO2R2 SO2R2 SR3 (114)
SO2Ar ArO2S
SO2 SO2 (112)
KMnO4 / HO– or H2O2
SO2Ar (113)
SO2R2 SO2R2 SO2R3
R1
(70)
The disulfonylthiomethane "005# was obtained in 83) yield from the sodium ethanethiolate reduction of the disulfonyldithiomethane "004^ Equation "60## ð71CC0072Ł[ EtS
SO2Et SO2Et SEt (115)
NaSEt, THF 94%
SO2Et (71)
EtS SO2Et (116)
5[92[2[2[2 Oxidised trithio!ortho!esters containing at least one sulfonate group Methanetrisulfonic acid "006# has been prepared by various methods\ including sulfonation of methanedisulfonic acid and oxidation of thiol methanetrisulfonic acid^ these have been reviewed by Backer ð29RTC0096Ł and summarised by DeWolfe ðB!69MI 592!90Ł[ The trimethyl and triethyl esters "008\ R Me\ Et# were obtained by treatment of the silver"I# salt "007# with methyl iodide and ethyl iodide respectively "Equation "61## ð38AK"0#120\ 49ACS286Ł[ SO3H HO3S SO3H (117)
SO3– –O S 3
3Ag+ SO3–
(118)
RI, C6H6
SO3R (72)
RO3S SO3R (119)
5[92[3 FUNCTIONS BEARING THREE SELENIUM ATOMS Triseleno!ortho!esters contain a carbon atom bearing three alkaneseleno or areneseleno groups[ Methods for the preparation of triseleno!ortho!esters have been reviewed brie~y by Krief and Hevesi ð73MI 592!90Ł[
81
Three Chalco`ens
5[92[3[0 Methods for the Preparation of Triseleno!ortho!esters 5[92[3[0[0 Triseleno!ortho!esters from RC"X0#"X1#X2 "i# From 0\0\0!trihaloalkanes Triseleno!ortho!formates "019\ R Me\ Ph# have been obtained from the treatment of bromoform with the appropriate sodium selenolate "Equation "62## ð73HCA0969\ 73S328Ł[ The sodium selenolates were prepared by reduction of diselenides in situ^ sodium methaneselenolate was prepared by the sodium:liquid ammonia reduction of dimethyl diselenide ð73HCA0969Ł\ and sodium benzene! selenolate was prepared by reduction of diphenyl diselenide using hydrazine ð73S328Ł[ Seebach ð73HCA0969Ł prepared 02C!labelled trimethyl triseleno!ortho!formate from 02C!labelled bromoform using this method[ CHBr3
NaSeR
SeR (73)
RSe SeR (120)
"ii# From a\a!dihalo ethers A range of alkane! and areneselenolates were shown to undergo a zinc promoted reaction with dichloromethyl methyl ether to give trialkyl and triaryl triseleno!ortho!formate esters in yields of 39Ð35) "Equation "63## ð60ZOR362Ł[ Cl OMe
RSeH, Zn, Et2O
SeR (74)
RSe
40–46%
Cl
SeR
"iii# From ortho!esters Trans!esteri_cation of ortho!formate esters with methane! or benzeneselenol in the presence of boron tri~uoride etherate produced the triseleno!ortho!formates "010\ R1 Me# and "010\ R1 Ph# in yields of 70) and 53) respectively "Equation "64## ð73JA2673\ 61CB400Ł[ Trimethyl ortho!acetate and methaneselenol gave trimethyl triseleno!ortho!acetate in 55) yield under these conditions ð68JOM"0660#Ł[ Ortho!esters have also been shown to undergo exchange reactions with boron tri! selenides to give triseleno!ortho!esters "Equation "65##\ though these reactions are subject to steric limitations[ Thus\ boron tris"benzeneselenide# and triethyl ortho!formate gave triphenyl triseleno! ortho!formate in 65) yield\ boron tris"methaneselenide# and trimethyl ortho!acetate produced trimethyl triseleno!ortho!acetate in 28) yield\ whereas the reaction between boron tris! "benzeneselenide# and trimethyl ortho!acetate proceeded only very slowly\ a}ording little of the triseleno!ortho!ester product ð68JOC0772\ 68JOC3168Ł[ R1O OR1
R2SeH, BF3•OEt2
SeR2 (75)
R2Se
R 1O
SeR2 (121)
R1
OR2 OR2 OR2
B(SeR3)3, cat. TFA, CHCl3
R1
SeR3 SeR3 SeR3
(76)
5[92[3[0[1 Triseleno!ortho!esters from carboxylic acids 02
C!Labelled triphenyl triseleno!ortho!formate has been prepared in 37) yield by the acid catalysed reaction of 02C!labelled formic acid with benzeneselenol "Equation "66## ð73HCA0969Ł[
82
Three Seleniums
The preparation of triseleno!ortho!esters from other carboxylic acid derivatives has not been reported[ PhSeH, HCl, 0 °C, 1 h
HC*O2H
(77)
HC*(SePh)3
then RT, 30 d 48%
5[92[3[0[2 Triseleno!ortho!esters from triselenocarbenium salts In a manner analogous to the reduction of trithiocarbenium salts discussed in Section 5[92[2[0[3\ 1!alkaneseleno!0\2!diselenoles may be prepared by sodium borohydride reduction of the cor! responding triselenocarbenium salts[ 1!Methaneseleno!0\2!diselenole "011\ R Me# was prepared from the corresponding triselenocarbenium iodide in a yield of greater than 79) using this method "Equation "67## ð64TL0148Ł\ and the 1!ethaneseleno derivative "011\ R Et# was similarly prepared from the analogous tetra~uoroborate salt ð75ZC027Ł[ Se +
Se
NaBH4
SeR X–
Se (78)
SeR Se (122)
5[92[3[0[3 Triseleno!ortho!esters from diselenoacetals and related compounds A few derivatives of triseleno!ortho!esters have been prepared by the direct electrophilic selenation of diselenoacetals and related compounds[ Reaction of a\a!bis"benzeneseleno#acetaldehyde with morpholinobenzeneselenamide produced the triseleno!ortho!ester "012^ Equation "68## ð71TL0446\ 74BSF0108Ł\ and reaction of the selenated enamine "013# with the same reagent gave the addition product "014# ð74BSF0108Ł[ Treatment of acetone with red selenium under basic conditions produced the cyclic selenium salt "015# ð81CC0428Ł[ This reaction proceeds through the diselenoacetal!like intermediates "016# and "017#\ and involves three electrophilic a!selenation steps "Scheme 14#^ it is therefore a counterpart of the haloform reaction[ PhSeN
PhSe CHO PhSe
O
PhSe PhSe CHO PhSe (123)
(79)
O PhSe PhSe PhSe
PhSe PhSe
N
N N O
O (124)
(125)
5[92[3[0[4 Triseleno!ortho!formates from tetraseleno!ortho!carbonates Seebach ð58AG"E#349Ł showed that the lithium triselenomethylide "018# is generated by treatment of tetraphenyl tetraseleno!ortho!carbonate with n!butyllithium at −67>C "Equation "79##\ and that this reacts with deuterated water to give the deuterated triseleno!ortho!formate "029#[ The use of lithiated triseleno!ortho!formates\ for example "018#\ for the preparation of higher triseleno!ortho! esters is discussed in the next section[
83
Three Chalco`ens O O
Se– Se
Red Se, K2CO3, (Ph3P)2NCl, RT, 16 h 26%
Se
Se (126)
Se Se
O
O O
Se
Sex Sex Se
Sey (127) Scheme 25
PhSe
N+(PPh3)2
SePh SePh SePh
BunLi, THF, –78 °C
Se (128)
Li+
–
Se Se
SePh SePh SePh
(80)
(129)
D
SePh SePh SePh (130)
5[92[3[0[5 Higher triseleno!ortho!esters from triseleno!ortho!formate esters Metallated triseleno!ortho!formates "020# are generated on treatment of triseleno!ortho!formate esters with strong bases^ the lithiated triseleno!ortho!formate "020\ R Ph# is obtained from tri! phenyl triseleno!ortho!formate and lithium di!s!butylamide at −67>C ð58AG"E#349Ł\ and "020\ R Me# is generated from trimethyl triseleno!ortho!formate and n!butyllithium at −67>C ð68JOM"0660#Ł[ These lithiated triseleno!ortho!formates react with a range of electrophiles to yield higher triseleno!ortho!esters[ Thus\ lithiated triseleno!ortho!formates react with] alkyl halides to give aliphatic triseleno!ortho!esters ð58AG"E#349\ 68JOM"066#0\ 71TL2396Ł^ aldehydes to give a!hyd! roxytriseleno!ortho!esters ð58AG"E#349\ 70TL3998Ł\ and epoxides to give b!hydroxytriseleno!ortho! esters ð67TL2860Ł "Scheme 15#[ Tris"tri~uoromethyl# triseleno!ortho!formate yielded the cor! responding triseleno!ortho!acetate "021# on metallation with potassium di!i!propylamide\ followed by treatment with methyl iodide "Equation "70## ð73T3852Ł[ Since metallated triseleno!ortho!formates may also be obtained from tetraseleno!ortho!carbonates "Section 5[92[3[0[4#\ these should also be regarded as precursors of higher triseleno!ortho!esters[ SeR1 SeR1 SeR1
R2 R2X
SeR1 R1Se SeR1
Li+ –B, THF, –78 °C
Li+
–
SeR1 SeR1 SeR1
(131)
R2CHO
SeR1 SeR1
R2
SeR1
O
OH
R2
SeR1
R2 OH Scheme 26
SeR1 SeR1
84
Mixed Includin` Oxy`en SeCF3
SeCF3 SeCF3 SeCF3 (132)
i, K+ –N(Pri)2
F3CSe
ii, MeI
SeCF3
(81)
5[92[4 MIXED CHALCOGEN FUNCTIONS INCLUDING OXYGEN Mono! and dithio!ortho!esters are derivatives of carboxylic ortho!esters in which one and two of the oxygen substituents respectively are replaced with sulfur substituents[ Similarly\ mono! and diseleno!ortho!esters are mixed oxygen and selenium functions containing one and two selenium substituents respectively[ Monoselenomonothio!ortho!esters bear one oxygen\ one sulfur and one selenium substituent[ Oxidised derivatives of several mixed functions containing sulfur are known[ Methods for the preparation of mixed oxygen and sulfur functions have been reviewed by Simchen ð74HOU"E4#2Ł[
5[92[4[0 Methods for the Preparation of Functions R0C"OR1#"OR2#SR3 5[92[4[0[0 From R0C"X0#"X1#X2 Triphenyl monothio!ortho!formate has been prepared in 31) yield by reaction of chloro! diphenoxymethane with benzenethiol in the presence of pyridine "Equation "71## ð51CB0748Ł[ OPh
PhSH, pyridine
Cl
OPh
42%
OPh
(82)
PhS OPh
Monothio!ortho!esters have been prepared from the reactions of ortho!ester derivatives with thiols[ Ortho!esters react with one equivalent of n!butanethiol in the presence of aluminum tri! chloride to give monothio!ortho!esters "Equation "72##^ yields are reasonable "54Ð79)# for mono! thio!ortho!formates and !acetates\ but are lower "ca[ 24)# for thio!ortho!benzoates ð57CR"C#0495Ł[ This reaction will also proceed in the absence of a catalyst^ monothio!ortho!formates are obtained in high yields ð58BSF214Ł\ though yields are low for monothio!ortho!acetates and !ortho!benzoates\ which are obtained as mixtures with dithio!ortho!esters ð69MI 592!91Ł[ Treatment of the O!acyl ortho! formate ester "35# with a range of thiols in the presence of triethylamine produced the monothio! ortho!esters "022# in yields of 34Ð64) "Equation "73## ð58RTC786Ł[ The acid catalysed trans!esteri! _cation of ortho!esters with 1!hydroxybenzenethiol produced the cyclic monothio!ortho!esters "023# in good yields "69Ð66)# "Equation "74## ð64S559Ł[ Cyclic monothio!ortho!ester derivatives have also been obtained from the exchange reactions of ortho!esters with 1!hydroxyethanethiol ð66MI 592!90Ł and 1!thiohydroxyacetic acid ð67IZV357Ł[ OR2 OR2 OR2
R1
OEt AcO
1 equiv. BunSH, AlCl3, heat
RSH, Et3N, RT, 20 min 45–75%
OEt (46)
OR2 SBu OR2
R1
(83)
OEt (84)
RS OEt (133)
SH
R1
OR2 OR2 OR2
OH ,H2SO4, 100 °C, 15 min 70–77%
S
OR2 (85)
O (134)
R1
85
Three Chalco`ens
5[92[4[0[1 From monothiocarboxylic esters Monothio!ortho!benzoate esters have been prepared in yields of 55) or more by reaction of a monothiobenzoate ester with a sodium alkoxide\ followed by alkylation of the thiolate intermediate with an alkyl iodide "Scheme 16# ð78S573Ł[ However\ this procedure is not suitable for the preparation of monothio!ortho!esters from simple aliphatic monothio esters\ which may undergo deprotonation under the reaction conditions ð78S573Ł[ Treatment of the hydroxy monothioesters "024\ n 9\ 0# with sodium hydride gave the cyclic thiolate intermediates "025\ n 9\ 0#\ which were methylated in situ to yield monothio!ortho!esters "026\ n 9\ 0# in overall yields of 24Ð67) "Scheme 17# ð75JA5572Ł[ Unlike the reaction of simple monothio!ortho!esters with alkoxides\ this procedure is applicable to the preparation of cyclic monothio!ortho!acetate esters as well as monothio!ortho! benzoates[ S Ar
NaOR1, R1OH or THF
S– OR1 OR1
Ar
OR1
R 2I
Ar
SR2 OR1 OR1
Scheme 27
S
O
S–
NaH, MeCN, 0 °C
R
( )n
( )n O
R
OH
(135)
Me3O+BF4– or MeI 35–78%
O
(136) Scheme 28
MeS
O
R
O
( )n (137)
5[92[4[0[2 From dioxo! and oxothiocarbenium salts Monothio!ortho!esters are obtained from the treatment of dioxocarbenium salts with thiols[ This reaction is analogous to the preparation of ortho!esters from dioxocarbenium salts and alcohols described in Section 5[92[1[0[3[ Reaction of the dimethyl dioxocarbenium salt "027# with meth! anethiol in the presence of triethylamine produced the monothio!ortho!ester "028^ Equation "75## ð76JOC1546Ł\ and the cyclic dioxocarbenium tetra~uoroborate salts "039\ R Me\ Ph^ n 9\ 0# gave monothio!ortho!esters "030\ R Me\ Ph^ n 9\ 0# on treatment with lithium methanethiolate "Equation "76## ð75JA5572Ł[ Alternatively\ the salts "039# could be converted to monothio!ortho! esters "030# by treatment with sodium sul_de\ followed by methylation of the thiolate intermediate with trimethyloxonium tetra~uoroborate or methyl iodide ð75JA5572Ł[ The stable monothio!ortho! hydrogen ester "032# was obtained by treatment of the bicyclic dioxocarbenium tetra~uoroborate "031# with sodium hydrosul_de "Equation "77## ð79JA6468Ł[ OMe MeO
BF4–
+
MeSH, Et3N
SMe OMe OMe
MeO
OMe (138)
(139) O
R
(86)
( )n
+
BF4–
LiSMe
MeS
( )n R
O (140)
O
NaSH
O
+
BF4– (142)
O
(87)
O (141)
(88) O
SH
O
(143)
Monothio!ortho!esters may also be prepared from oxothiocarbenium salts by addition of alk! oxides[ Reaction of 1!ethoxythiolenium tetra~uoroborate with sodium ethoxide gave 1\1!diethoxy!
86
Mixed Includin` Oxy`en
thiolane "Equation "78## ð45CB1959Ł\ and the 1!alkyl! and 1!aryl!1!alkoxy!0\2!benzoxathioles "034# were prepared by treatment of the oxathiolium salts "033# with alcohols in the presence of sodium hydrogen carbonate "Equation "89## ð68S112Ł[ OEt
NaOEt +
S
OEt
S
(89)
OEt
BF4–
S +
O (144)
S
R2OH, NaHCO3, MeCN, 0–5 °C, 10 min
R1 BF4–
R1 (90)
78–97%
O (145)
OR2
5[92[4[0[3 From monothioacetals and related compounds The cyclic monothio!ortho!formate "036# has been prepared in 23) yield by methanolysis of the N!p!toluenesulfonylsul_limine "035^ Equation "80## ð74JOC546Ł[ The alkaline reaction conditions help prevent the product from undergoing disproportionation reactions[ This procedure is analogous to the preparation of trithio!ortho!esters discussed in Section 5[92[2[0[4[ NTos S
S
MeOH, KOH
(91)
OMe 34%
O (146)
O (147)
5[92[4[0[4 From 1!alkoxythiophenes Terrier et al[ demonstrated that the highly electron de_cient 1\3!dinitro!4!methoxythiophene undergoes addition of methanol on treatment with potassium methoxide to produce the stable salt "037#\ which was isolated as a purple solid in virtually quantitative yield "Equation "81## ð64JOC1800Ł[ NO2
NO2 KOMe, MeOH, RT, 15 min
O2N
S
ca. 100%
OMe
–
O2N
S
(92)
OMe K+ OMe
(148)
5[92[4[1 Methods for the Preparation of Functions R0C"OR1#"SR2#SR3 5[92[4[1[0 From R0C"X0#"X1#X2 Cyclic dithio!ortho!esters have been obtained from the reactions of a\a!dichloro ethers with dithiolates[ Treatment of dichloromethyl methyl ether with disodium ethane!0\1!dithiolate "gen! erated from ethanedithiol and sodium# gave 1!methoxy!0\2!dithiolane in 57) yield\ and dilithium propane!0\2!dithiolate "generated from propane!0\2!dithiol and n!butyllithium# reacted with di! chloromethyl methyl ether to produce 1!methoxy!0\2!dithiane in 34) yield "Scheme 18# ð61HCA64Ł[
S
HS(CH2)2SH, Na, MeCN
OMe S
Cl OMe
68%
Cl Scheme 29
HS(CH2)3SH, BunLi, THF
S
45%
S
OMe
87
Three Chalco`ens
Dithio!ortho!esters have also been obtained from exchange reactions of ortho!esters with n! butanethiol ð58BSF214Ł\ though these are normally isolated as side!products from the preparation of monothio!ortho!esters by this method "see Section 5[92[4[0[0# ð69MI 592!91Ł[
5[92[4[1[1 From dithiocarbenium salts Okuyama et al[ ð76JOC1546Ł prepared the dithio!ortho!ester "049# by addition of sodium methoxide to the dithiocarbenium perchlorate "038^ Equation "82##[ This procedure is analogous to the prep! aration of trithio!ortho!esters by the addition of thiols to dithiocarbenium salts discussed in Section 5[92[2[0[3[ SMe ClO4– SMe
MeO
NaOMe, MeOH, MeCN
SMe SMe OMe
MeO
+
(149)
(93)
(150)
5[92[4[1[2 From mono! and dithioacetals and related compounds Dithio!ortho!ester derivatives may be prepared by the reaction of metallated monothioacetals with disul_des[ Deprotonation of 0\2!oxathiane by treatment with n!butyllithium at −67>C\ followed by reaction with dimethyl disul_de produced 1!methanethio!0\2!oxathiane in 71) yield "Scheme 29# ð70TL1994\ 74JOC546Ł[ In a similar manner\ lithiation of a series of sulfonyl oxiranes "040# followed by treatment with diphenyl disul_de gave the oxidised dithio!ortho!ester derivatives "041# in yields of 34Ð89) "Scheme 20# ð80JCS"P0#2980Ł[ S
S
i, BunLi, THF, –100 °C
ii, MeSSMe
S
82%
O
Li+
–
SMe
O
O
Scheme 30
O
R1
SO2Ph
i, BunLi, THF, –100 °C
O
R1
SO2Ph –
R2
R2
ii, PhSSPh
O
R1
Li+
SO2Ph R2
(151)
SPh (152)
Scheme 31
Lithiation of the unsaturated dithioacetal "042# followed by reaction with benzophenone produced the bicyclic dithio!ortho!ester "043# in 87) yield "Scheme 21# ð58S06Ł[ This reaction proceeds via cyclisation of the intermediate ketene dithioacetal "044#[ Selenocyclisation of the related hydroxy ketenedithioacetal "045# gave the spirobicyclic dithio!ortho!ester "046^ Equation "83## ð79JOC1125Ł[
S S
S
i, BunLi
S S
ii, Ph2CO
98%
Li+ –O
Ph
S
Ph
Ph (153)
(155) Scheme 32
Ph
O
(154)
88
Mixed Includin` Oxy`en S
SePh PhSeCl, Et3N, THF, –78 °C
S HO
S
64%
S
Ph (156)
(94) O
Ph
(157)
Some dithioacetals undergo direct oxygenation on treatment with organic peroxides[ Reaction of trithiane with t!butyl peroxybenzoate in the presence of copper"I# chloride gave the benz! oyloxytrithiane "53# and dibenzoyloxytrithiane "047^ Equation "84##^ the yield of "53# was at an optimum "69Ð79) based on recovered trithiane# when 9[6 equivalents of t!butyl peroxybenzoate were used\ and "047# was obtained as the major product when 2[9 equivalents of t!butyl per! oxybenzoate were used ð63BCJ0385Ł[ 1!Benzoyloxydithiane has been generated by an analogous method\ though this product was too unstable to isolate and characterise ð63BCJ0385Ł[ S S
S
S
PhCO3But, CuCl, C6H6, heat
S
S
+
OCOPh
OCOPh
S S
S
(95)
PhOCO (64)
(158)
Cyclic dithio!ortho!formates have been prepared by reaction of N!p!toluenesulfonylsul_limines "89# derived from dithioacetals of formaldehyde with alcohols under alkaline conditions "Equation "85## ð65S440Ł[ SR1
SR1
R3OH, KOH
(96)
R 3O
SR2
56–93%
SR2
TosN (90)
5[92[4[1[3 Miscellaneous methods Generation of benzyne in the presence of carbon disul_de and methanol gave 1!methoxy!0\2! benzodithiole in 67) yield "Scheme 22# ð63CC055Ł[ The reaction proceeds via addition of methanol to the carbene "048#\ which is formed by the cycloaddition of carbon disul_de to benzyne[ A modi_cation of this reaction involves the generation of benzyne by diazotisation of anthranilic acid using an alkyl nitrite^ in this case\ the alkoxy group of the alkyl nitrite is the source of the 1! substituent of the product benzodithiole "Equation "86## ð64S27Ł[ N N
Pb(OAc)4
S
CS2
MeOH
: S
N NH2
S OMe S
(159) Scheme 33
CO2H
RONO, CS2
NH2
S OR
(97)
S
A series of cyclic oxidised derivatives of dithio!ortho!esters "050# has been prepared by the lithium t!butyl peroxide oxidation of alkenes "059^ "Equation "87## ð80JCS"P0#2980Ł[ SO2Ar R1
SR2 (160)
O
LiO2But, THF, –78 °C to –18 °C
SO2Ar R1
SR2 (161)
(98)
099
Three Chalco`ens
5[92[4[2 Methods for the Preparation of Functions R0C"OR1#"OR2#SeR3 5[92[4[2[0 From 1!alkoxyselenophenes In an analogous reaction to that described in Section 5[92[4[0[4\ addition of potassium methoxide to 1\3!dinitro!4!methoxyselenophene produced the stable salt "051#\ which was isolated as a purple solid in virtually quantitative yield "Equation "88## ð64JOC1800Ł[ NO2
NO2 KOMe, MeOH, RT, 15 min
O2N
OMe
Se
–
ca. 100%
O2N
OMe K+
(99)
Se OMe (162)
5[92[4[3 Methods for the Preparation of Functions R0C"OR1#"SeR2#SeR3 5[92[4[3[0 From R0C"X0#"X1#X2 Dihalomethyl methyl ethers react with selenolates to give diseleno!ortho!esters[ Treatment of dichloromethyl methyl ether with sodium benzeneselenolate "generated by the sodium borohydride reduction of diphenyl diselenide# gave the diseleno!ortho!formate ester "052# in 67) yield "Equation "099## ð68JA5527Ł[ Other dichloromethyl alkyl and aryl ethers gave diseleno!ortho!formates "053\ R alkyl\ aryl# in yields of 31Ð65) on treatment with sodium areneselenolates "generated from the selenophenol and metallic sodium# "Equation "090## ð75ZOR096Ł[ Dichloromethyl ethers also react with areneselenomagnesium halides to give diseleno!ortho!formates\ though yields are usually lower than those obtained from reaction with the corresponding sodium selenolates ð75ZOR096Ł[ Reaction of dibromomethyl methyl ether with dilithium benzene!0\1!diselenolate gave 1!methoxy!0\2!di! selenole in 27) yield "Scheme 23# ð77HCA0131Ł[ Cl
NaSePh
OMe 78%
Cl
Cl
PhSe
2 Se, THF/Et2O, –60 °C
Se– Li+
(101)
OR PhSe (164)
42–76%
Cl
(100)
OMe PhSe (163)
ArSeH/Na, MeO(CH2)2OMe
OR
Li
PhSe
Br2CHOMe
Se
38%
Se
OMe Se– Li+ Scheme 34
Li
The cyclic diseleno!ortho!esters "055\ R H\ Me# have been generated from the boron tri~uoride etherate catalysed exchange reactions between triethyl ortho!formate and the 0\2!diselenolates "054\ R H\ Me^ "Equation "091##[ However\ these products were not isolated and characterised\ but were used in situ for the preparation of diselenothio!ortho!esters "see Section 5[92[5[1[0# ð78H"17#278Ł[ Se– Li+
Se
HC(OEt)3, BF3•OEt2
OEt R
Se–
Li+
(165)
R
(102)
Se (166)
5[92[4[4 Methods for the Preparation of Functions R0C"OR1#"SR2#SeR3 5[92[4[4[0 From monothioacetals and related compounds Monoselenomonothio!ortho!ester derivatives have been prepared from the reactions of lithiated monothioacetals with diselenides[ Lithiation of 0\2!oxathiane with n!butyllithium followed by reac!
090
Mixed Sulfur And Selenium
tion with dimethyl diselenide produced 1!methaneseleno!0\2!oxathiane in 49) yield "Scheme 24# ð70TL1994\ 74JOC546Ł[ In a similar manner\ lithiation of the sulfonyl oxiranes "040# followed by treatment with diphenyl diselenide gave the oxidised selenothio!ortho!ester derivatives "056# in yields of 14Ð81) "Scheme 25# ð80JCS"P0#2980Ł[ S
S
i, BunLi, THF, –78 °C
O
ii, MeSeSeMe
S
50%
O
Li+
–
SeMe
O Scheme 35
O
R1
i, BunLi, THF, –100 °C
SO2Ph
O
R1
–
R2
R2
SO2Ph
ii, PhSeSePh
Li+
25–92%
(151)
O
R1
SO2Ph R2
SePh (167)
Scheme 36
5[92[5 MIXED SULFUR AND SELENIUM FUNCTIONS Monoselenodithio! and diselenomonothio!ortho!esters are mixed sulfur and selenium functions which bear one and two selenium substituents respectively[
5[92[5[0 Methods for the Preparation of Functions R0C"SR1#"SR2#SeR3 5[92[5[0[0 From R0C"X0#"X1#X2 1!Chloro!0\2!dithianes react with areneselenolates to give 1!areneseleno!0\2!dithianes[ Thus\ di! thianes "058\ R0 H^ R1 H\ Me\ OMe\ F\ Cl\ NMe1\ CF2# were prepared from 1!chloro!0\2! dithiane and the appropriate sodium areneselenolates "prepared by reduction of the corresponding diaryl diselenide using either sodium borohydride or metallic sodium and ultrasound# ð77JOC2655Ł[ Similar reaction of the 1!chloro!3\5!dimethyl!0\2!dithiane "057\ R0 Me# with sodium "p!methoxy! benzene#selenolate gave the selenodithio!ortho!ester "058\ R0 Me^ R1 OMe#\ which was obtained as a ca[ 4 ] 0 mixture of diastereoisomers "Equation "092## ð77JOC4557Ł[ R1
Na+ –Se
S
R2, C6H6
R1 S
Cl
Se
S R1
R2
(103)
S R1
(168)
(169)
5[92[5[0[1 From selenodithiocarbenium salts 1!Methanethio!0\2!selenothiolium salts are reduced to 1!methanethio!0\2!selenothioles by sodium borohydride[ Reduction of the ~uorosulfonate salt "069# gave the 1!methanethio!0\2!selenothiole "060# in 69) yield "Equation "093## ð79H"03#160Ł\ and similar treatment of the iodide salts "061\ R H\ Me# produced the analogous selenothioles "062\ R H\ Me# ð64TL0148Ł[
091
Three Chalco`ens Se Ph
Se
NaBH4, EtOH
SMe FSO3–
+
SMe
70%
S
Ph
(170)
(171) Se
Se SMe I–
+
R
(104)
S
SMe
S
S
R
(173)
(172)
5[92[5[0[2 From dithioacetals Selenodithio!ortho!esters may be prepared by the selenation of lithiated dithioacetals[ Deprot! onation of 0\2!dithiane using n!butyllithium followed by reaction with p!nitrobenzeneselenyl cyanide produced the 1!seleno!0\2!dithiane "063# in 12) yield "Scheme 26# ð77JOC2655Ł[ However\ treatment of lithiated 0\2!dithiane with the diaryl diselenides "064\ R OMe\ CF2# gave only very low yields of the selenated compounds "065\ R OMe\ CF2# ð75CJC621Ł[ S
O2N
S
BunLi, THF, –20 °C
–
S
Li+
SeCN
S Se
23%
S
NO2
S (174)
Scheme 37 S
R
Se Se
Se
R
R
S (176)
(175)
5[92[5[1 Methods for the Preparation of Functions R0C"SR1#"SeR2#SeR3 5[92[5[1[0 From diseleno!ortho!esters Pinto et al[ ð78H"17#278Ł reported the preparation of the diselenothio!ortho!esters "066\ R H\ Me# from the corresponding O!ethyl diseleno!ortho!esters by treatment with benzenethiol[ The starting diseleno!ortho!esters were generated by the boron tri~uoride etherate catalysed reaction between dilithium diselenides and triethyl ortho!formate "see Section 5[92[4[3[0#\ and were used in situ[ Se OEt R
Copyright
#
Se
1995, Elsevier Ltd. All R ights Reserved
Se
PhSH
SPh R
(105)
Se (177)
Comprehensive Organic Functional Group Transformations
6.04 Functions Containing a Chalcogen and Any Other Heteroatoms Other Than a Halogen MARTIN J. RICE ZENECA Agrochemicals, Bracknell, UK 5[93[0 FUNCTIONS CONTAINING CHALCOGEN AND A GROUP 04 ELEMENT 5[93[0[0 Functions Bearin` Chalco`en and Nitro`en 5[93[0[0[0 Functions bearin` oxy`en and nitro`en 5[93[0[0[1 Functions bearin` sulfur and nitro`en 5[93[0[0[2 Functions bearin` selenium and nitro`en 5[93[0[1 Functions Bearin` Chalco`en and P\ As\ Sb or Bi 5[93[0[1[0 Functions bearin` oxy`en and P\ As\ Sb or Bi 5[93[0[1[1 Functions bearin` sulfur and P\ As\ Sb or Bi 5[93[0[1[2 Functions bearin` selenium and P\ As\ Sb or Bi 5[93[1 FUNCTIONS CONTAINING CHALCOGEN AND A METALLOID AND POSSIBLY A GROUP 04 ELEMENT
093 093 093 000 004 005 005 008 012
013 013 013 013 015 029 029 029 021
5[93[1[0 Functions Bearin` Chalco`en and Boron 5[93[1[1 Functions Bearin` Chalco`en and Silicon 5[93[1[1[0 Functions bearin` oxy`en and silicon 5[93[1[1[1 Functions bearin` sulfur and silicon 5[93[1[1[2 Functions bearin` selenium and silicon 5[93[1[2 Functions Bearin` Chalco`en and Germanium 5[93[1[2[0 Functions bearin` oxy`en and `ermanium 5[93[1[2[1 Functions bearin` sulfur and `ermanium 5[93[2 FUNCTIONS CONTAINING CHALCOGEN AND A METAL AND POSSIBLY A GROUP 04 ELEMENT OR A METALLOID 5[93[2[0 Functions Bearin` Oxy`en and a Metal 5[93[2[0[0 Functions bearin` two oxy`ens and a metal 5[93[2[0[1 Functions bearin` oxy`en\ silicon and a metal 5[93[2[0[2 Functions bearin` oxy`en and two metals 5[93[2[1 Functions Bearin` Sulfur and a Metal 5[93[2[1[0 Functions bearin` sulfur\ oxy`en and a metal 5[93[2[1[1 Functions bearin` two sulfurs and a metal 5[93[2[1[2 Functions bearin` sulfur\ boron and a metal 5[93[2[1[3 Functions bearin` sulfur\ silicon and a metal 5[93[2[1[4 Functions bearin` sulfur and two metals 5[93[2[2 Functions Bearin` Selenium and a Metal 5[93[2[2[0 Functions bearin` selenium\ sulfur and a metal 5[93[2[2[1 Functions bearin` two seleniums and a metal
092
022 022 022 022 022 022 022 023 024 024 024 024 024 024
093
Chalco`en and Any Other Heteroatoms 025 025
5[93[2[2[2 Functions bearin` selenium\ phosphorus and a metal 5[93[2[2[3 Functions bearin` selenium\ silicon and a metal
5[93[0 FUNCTIONS CONTAINING CHALCOGEN AND A GROUP 04 ELEMENT The compounds in this class have been the subject of several reviews ð58ZC190\ B!69MI 593!90\ 60S05\ 66UK574\ B!68MI 593!90\ 68T0564\ 74HOU"E4#2Ł[
5[93[0[0 Functions Bearing Chalcogen and Nitrogen Functional groups bearing chalcogen and nitrogen are available by modi_cation of precursors which contain sp2! or sp1!carbon atoms\ via cycloadditions or by other miscellaneous methods[ This general order is adhered to throughout this section[
5[93[0[0[0 Functions bearing oxygen and nitrogen "i# Functions bearin` two oxy`en and one nitro`en substituent The functional group containing two ether type oxygens and one amine type nitrogen singly bonded to a carbon is most commonly referred to as an amide acetal[ In the majority of cases\ all the heteroatoms are substituted further[ Exceptions are the cyclols which have one unsubstituted oxygen atom[ "a# From sp2!carbon compounds[ Amide acetals can be accessed by transacetalation of other amide acetals ð50LA"530#0\ 52AG185\ 53CCC534\ 54HCA0635\ 57CB30Ł with alcohols[ Typically\ the starting material is N\N!dimethylformamide dimethyl acetal "0#[ The uncatalysed reaction is driven to completion by the removal of generated methanol by distillation[ The use of sterically hindered alcohols can\ however\ lower the reaction yields signi_cantly[ Cyclic amide acetals "1# are available from diols "Scheme 0# ð50LA"530#0\ 53CCC534\ 57CB30Ł[ Transamidation can be achieved with high boiling amines such as morpholine and piperidine ð50LA"530#0\ 55USP2128408Ł[ Simultaneous trans! acetalation and transamidation has also been reported ð53CCC534Ł[ OR
ROH
Me2N
OMe
OR
Me2N HO
OMe
OH
(1)
O Me2N O
Scheme 1
(2)
Cyclols "3# are relatively rare in the literature\ existing as equilibrium mixtures with the cor! responding ring!opened hydroxyamides "2#\ and more commonly they have been proposed as transient reaction intermediates "Equation "0## ð59CRV43\ 52CCC1939\ 52TL328\ 53JOC1658\ 53TL36\ 55UKZ193\ 57TL1602Ł[ O!Alkylation ð51TL690\ 52T0550\ 52T0564\ 54T2426Ł generates fully substituted amide acetals[ O
HO
O (1)
HO
NH (3)
R
R
NH (4)
Symmetrical amide acetals "4# are obtained from ortho!esters with a variety of nitrogen nucleo! philes such as sulfonamides "Equation "1## ð50JOC3204\ 54AJC0856\ 79JOC3927\ 71JCS"P0#1760\ 77JHC896Ł\ ureas ð42JA560\ 52HCA1295Ł\ imidazoles ð79JOC3927Ł and di~uoroamine ð56JA605Ł[
094
Chalco`en and Group 04 OR2 OR2 OR2
R1
R3R4NH
R1
OR2 NR3R4 OR2 (5)
(2)
Under Lewis acid catalysis\ isocyanates will react to give N!carboxy compounds "5# "Equation "2## ð51AG"E#481\ 55GEP0045679Ł[ Cyanide can be displaced from "a!alkoxy!a!alkylamino#acetonitriles "6# ð61CB0239Ł or\ in addition to one of the alkylamino groups\ from a\a!bis"dialkylamino# acetonitriles "7# by alkoxides ð38LA"451#118\ 61CB0239Ł[ Both halogens in a\a!di~uorotrialkylamines "8# have been replaced by alcohols ð52USP2981526\ 53USP2010973\ 54USP2103301\ 72TL0924Ł[ Chloro! diaryloxymethanes have been used to generate diaryloxymethyltriethylammonium chlorides "09# with triethylamine ð47JPR"6#69Ł[ Such reactive compounds give amide acetals on further reaction with amines ð61S21\ 61S307\ 62S312\ 64S161Ł[ OR1
OR1
R2NCO, BF3
R1O
R1O
OR1
NR12
F
NMe2
NC
NMe2 (8)
(7)
OAr NR22
R1
NC OR2
(3) NR2CO2R1 (6)
Cl–
Et3N+
F
OAr (10)
(9)
"b# From sp1!carbon compounds[ The halogen in N\N!dialkyliminium chlorides "00# can be dis! placed on treatment with alkoxides to yield amide acetals "01# "Equation "3## ðB!69MI 593!90\ 61TL3106\ B!68MI 593!90Ł[ In a similar manner\ alkoxide can be displaced from alkoxyiminium salts "02# ð50LA"530#0\ 57PAC408\ B!69MI 593!90\ B!68MI 593!90Ł and thiolate from alkylthioiminium salts "03# ð56BCJ1530Ł[ Lactam acetals are also accessible by this methodology ð52USP2981526\ B!68MI 593!90Ł[ In addition\ pyridine has been demonstrated to react with the oxonium salt "04# to give the pyridinium species "05# ð60S201Ł[ The adduct "06# is formed by capture of the N!acyloxazolium salt with methoxide ð64JCS"P0#0291Ł[ Cl H
OR2
NaOR2
R12N
+
NR12 (11)
(12)
OR2 H
(4) OR2
SEt
+
NR12 (13)
H
+
NMe2 (14) O N
+
+
EtO
OEt BF4– (15)
OEt
N
N O
O
OEt (16)
O
MeO (17)
Formamide acetals are produced by the reaction of N\N\N?\N?!tetrasubstituted formamidium salts with sodium alkoxides ð59AG845\ 51JOC2553\ 52GEP0035781\ 53CCC534Ł[ Tetrakis"dimethylamino#ethene "07# is converted by methanol into a mixture of amide acetals "08# and "19# ð61T0854Ł[ Hexa! ~uoropropene "10# combines with diethanolamine "11# to generate an azadioxabicycloð2[2[9Łoctane
095
Chalco`en and Any Other Heteroatoms
"12# ð61TL2846Ł[ Similar systems\ such as "14#\ are obtained by the reaction of the sodium salts of dialkanolamines such as "13# with nitriles "Scheme 1# ð62AG"E#885Ł[ Me2N
NMe2
Me2N
OMe
MeOH
NMe2
OMe
(18)
HO
Me2N
(19)
H N
F
F
F
CF3
(20) F3C
F
O
O
Et3N
+
OH
OMe NMe2 OMe
MeO
+
Me2N
N (23)
(21)
(22)
i, Na ii, EtCN
H N
HO
O
OH
O N (25)
(24) Scheme 2
"c# Cycloaddition methods[ The unsubstituted ketene acetal "15# reacts with isocyanates to give barbituric acid acetals "16# ð48MI 593!90\ 51AG"E#220\ 55CB2781Ł while the cyclic analogue "17# generates the b!lactam "18# ð77TL1216Ł[ Similarly\ tetramethoxyethene gives the azetidin!1!one "29# "Scheme 2# ð48MI 593!90\ 53AG"E#279Ł[ Ketene acetals will also react with nitrosobenzene\ with dialkyl azo! dicarboxylates ð60CB762Ł and with ketenimines ð65IZV747Ł to give four!membered ring products "20#\ "21# and "22#[ O
O OEt
EtO
PhNCO
Ph
NHPh
PhNCO
N OEt
OEt
EtO
O
N Ph (27)
(26) O
O
PhNCO
O
O
N
(28)
Ph (29)
MeO
OMe
MeO
OMe
OEt
PhNCO
O
MeO MeO
O
N MeO Ph MeO (30) Scheme 3
MeO MeO
O
N MeO Ph MeO (31)
MeO MeO MeO MeO
CF3 CO2Me N
Ph
F3C
N
N
OEt OEt
CO2Me (32)
(33)
Dichloroketene acetals such as "23# react with sulfamyl chlorides to give four!membered ring products "24# "Equation "4## ð56JA1491\ 61JA5024Ł[ a\b!Unsaturated ketones combine with ynamines ð69CR"C#357Ł and with 0!dialkylamino!0!alkylthioethenes ð56BCJ1530Ł to give bicyclic amide acetals "Scheme 3# ð57TL386Ł[
096
Chalco`en and Group 04 O O
O
EtNHSO2Cl
Cl
(34)
(35)
O
2
(5)
SO2
Cl
Cl
Cl
Et N
O
O
2
R2N
R2N O
MeS
O NR2
Scheme 4
An unsymmetrical bicyclic amide acetal "26# has been obtained by treatment of the dihydrooxazole "25# with benzonitrile oxide ð60AG"E#709Ł[ Dialkoxydihydro!0\1\2!triazoles such as "27# are produced by the reaction of azides with some ketene acetals ð52G831\ 57G570\ 61JHC0976\ 65JHC194Ł[ Cyclo! propanone acetals such as "28# undergo ring expansion with aryl isocyanates to give g!lactam acetals "39# "Scheme 4# ð76JCR"S#251Ł[ Ph N
+
O
Ph
N
N+ O– O
(36)
(37) MeO
MeO PhN
N+
N O
N–
N N
MeO
+
N
MeO
Ph (38)
MeO
O
OMe PhNCO
EtO2C
H
EtO2C
N
Ph
OMe H OMe (40)
H (39) Scheme 5
"d# Miscellaneous reactions yieldin` amide acetals[ The imidate "30# has been oxidized by mcpba to the corresponding oxaziridine ð60TL3408\ 62TL0796Ł[ t!Butyl hypochlorite has been used to oxidise a 3!oxa!b!lactam "31# to the amide acetal ð71H"07#190Ł[ Benzoylhydrazones "32# react with lead tetraacetate to give 1\4!dihydro!0\2\3!oxadiazoles ð56TL2490\ 57CB2740Ł[ Reductive conditions are exempli_ed by the reaction of N\N!dimethylformamide and N\N!dimethylacetamide with 0\2!dibro! moketones and a zinc:copper couple to give amide acetals "33# "Scheme 5# ð61JA2190Ł[ The insertion of ethoxycarbonylnitrene\ generated by photolysis of ethyl azidoformate\ into acetals ð56T34Ł and ketene acetals ð61JHC0976Ł leads to N!carboxy amide acetals such as "34#[ Dichlorocarbene reacts with dialkylamines and sodium alkoxides to give the amide acetals HC"OR0#NR11 resulting from insertion and double halogen displacement ð53GEP0050174\ 58LA"614#04\ 58RTC178Ł while the diazo compound "35# on photolysis undergoes cyclisation to the dihydrooxazole "36# ð63JHC418Ł[ Epoxides add to dihydrooxazoles "37# and 4\5!dihydro!3H!0\2!oxazines to give bicyclic amide acetals such as "38# ð55AG"E#764\ 55AG"E#783\ 55LA"587#063Ł[ The bicyclic amide acetal "49# was obtained by the addition of diketene to the C1N bond of a chiral oxazoline "Scheme 6# ð80TL486Ł[ N!Methylpyrrole undergoes anodic oxidation in methanol to generate the symmetrical product "40# ð55JOC3943Ł[ Under basic conditions\ the diazene oxide "41# reacts with methanol to give the azo compound "42# ð67JOC0348Ł[ Ozonides "43# are formed by the reaction of ozone with indoles
097
Chalco`en and Any Other Heteroatoms MeO
N
mcpba, CH2Cl2
But
MeO
(41) Ph
O
Ph
O
HN
OMe O
LiOMe, ButOCl
N
N
O-TMS
O
O
O
Ph (42)
Ph
Ph
Et Pb(OAc)4
Ph
N Et
O-TMS
O
O
O
But
O
HN
O
Ph
N
N H (43)
Et Et
O
N N O
Ph OAc R5
NMe2
O
O
O R1
R3 R4
Br
Br
Zn–Cu
+ R5CONMe2
R2
R1
R4
R2 R3 (44)
Scheme 6
O
O
N2 Ph MeO
N H O (45) Ph
H N
CO2Et OMe
N
OEt N
MeO
OMe (47) O
N
LiCl
+ Et
O
hν
(46)
O
CO2Et
O
hν
+ N3CO2Et
O
Ph
Ph O
Et (49)
(48) H O
O
N But
O (50) Scheme 7
ð41JA2744Ł[ Compounds of this type have also been obtained by cyclisation of hydroperoxides ð41CB838Ł[ The reaction of some cyclic ortho!esters with TMS azide leads to the formation of displacement products such as "44# "Scheme 7# ð68TL402Ł[ "ii# Functions bearin` one oxy`en and two nitro`en substituents Functions bearing two nitrogens and one oxygen are known commonly as ester aminals[ As with the amide acetals\ they are synthetically accessible from sp2! and sp1!carbon compounds\ by cyclisations\ by cycloadditions and by other miscellaneous methods[
098
Chalco`en and Group 04 Me
Me MeO
hν
N
N
OMe
MeO
OMe (51)
Ph
+
–O
Ph
Et3N, MeOH
N N
N N
OPrn
OPrn MeO (53)
(52) Scheme 8
R
O O
N H (54)
N3
O
O
O
Ar (55)
"a# From sp2!carbon compounds[ Some examples of the formation of ester aminals by dis! placement reactions are shown in Scheme 8[ Treatment of bis"dimethylamino#acetonitrile with sodium ethoxide yields the ester aminal "45# ð61CB0239Ł[ The base induced cyclisation of 0!chloro! 4\4\4!trinitropentan!1!ol "46# occurs with the elimination of nitrite ð54AG316Ł[ All three halogens are displaced in the reaction of chloroform with aziridine and sodium methoxide ð58LA"614#04Ł[ Reaction of triethyl ortho!acetate with the 1!aminobenzenecarboxamide "47# leads to the 1! ethoxyquinazolinone "48# ð89JHC0842Ł[ NMe2
NaOEt
NC
NMe2 EtO
NMe2
NMe2 (56)
C(NO2)3 Cl
NO2
Cl O
OH (57)
CHCl3
+
O N H
NaOH
+
H N
NO2
OMe NaOMe
N
OEt OEt OEt
NH2
N
O AcOH
N N H OEt (59)
(58) Scheme 9
"b# From sp1!carbon compounds[ Electron!de_cient heterocycles undergo a range of related additions of water and alcohols ð73CHEC"2#80Ł[ Some examples of these reactions are shown in Scheme 09[ {Covalent hydration| is exempli_ed by the addition of the elements of water to the tetrazoloquinazoline "59# ð54JOC718\ 56KGS0985Ł[ An intramolecular addition occurs when the dini! tropyridine "50# is treated with base ð57TL548Ł[ Diethylamine reacts with 4!phenyl!0\1\3!dioxazolin! 2!one "51# ð61JPR034Ł[ An analogous reaction occurs when 0\2\3!oxadiazolium salts are treated
009
Chalco`en and Any Other Heteroatoms
with secondary amines leading to tertiary products^ primary amines lead to ring!opened products ð60JCS"C#398Ł[
N N
N N
N
2M HCl
N
HN
N N
(60)
OH
NO2
O 2N
N
NO2
O2N NaOMe
N
O (61)
Ph
O
O
OH
N H O Ph
O
Et2NH
N
Et2N
O
O O N H
O
(62) Scheme 10
In a reaction analogous to that with the oxazoline "37#\ epoxides have been demonstrated to react with dihydroimidazoles and tetrahydropyrimidines to give ester aminals ð69LA"631#017Ł[ "c# Cycloaddition methods[ Reaction of p!nitrophenyl isocyanate with O!alkyllactims such as "52# leads to 3!alkoxy!0\2!diazetin!1!ones "Equation "5## ð62TL0108Ł[ O N
OMe
NCO
N
N
+
(6)
OMe
O2N
NO2
(63)
"d# Miscellaneous reactions yieldin` ester aminals[ Addition of a!tetralone to the bisurea "53# in ethanolic hydrogen chloride a}ords a 1!hydroxyhexahydroquinazoline "54# ð55IZV87Ł[ A 2! "dimethylamino#oxaziridine "55# is formed by photocyclisation of the nitrone "56# ð60JA3964Ł[ The reaction of hydrazoic acid with ethoxypropyne gives bisazide "57# "Scheme 00# ð46RTC838Ł[
OH HN
O H2NCONH
Ar
+ Ar
H2NCONH (64) Ph
(65)
NMe2 hν
Me
N+
O Me2N
N Ph (66)
O–
(67)
OEt
NH
+ HN3
Scheme 11
Et
Me
N3 OEt N3 (68)
000
Chalco`en and Group 04 5[93[0[0[1 Functions bearing sulfur and nitrogen "i# Functions bearin` one sulfur\ one nitro`en and one oxy`en substituent
Functional groups bearing oxygen\ sulfur and nitrogen are nonsymmetrical\ and this reduces the number of synthetic routes available for their preparation compared to their symmetrical analogues[ "a# From sp2!carbon compounds[ Two examples of formation of this functional group by dis! placement are shown in Scheme 01[ Triethyl ortho!formate reacts with 1!thiolbenzamide to give a dihydrobenzothiazine "58# ð58T4884Ł[ Displacement of aniline from the 0\2\3!thiadiazoline "69# by ethanol produces the 4!ethoxy analogue "60# ð65ACS"B#726Ł[ O CONH2
OEt
+
EtO
2-Naphthyl-SO3H
NH
OEt
SH
N
Ph
N
Ph
S (69)
EtOH
N
Ph
S
N S
Ph NHPh (70)
OEt
Ph Ph
OEt (71) Scheme 12
1
"b# From sp !carbon compounds[ The N!alkylbenzothiazolium cation "61# reacts with the 1! hydroxybenzaldehyde "62# to give the spiro compound "63# ð61HCA0671Ł^ there are other examples of intramolecular cyclisation of benzothiazolium cations with phenolic ð58T4884Ł and ketonic functions ð89IJC"B#079Ł in the presence of base\ and related reactions of thiazoles ð73H"11#170Ł[ The dime! thylformamide monothioacetal "64# is prepared by O!methylation of N\N!dimethylformamide with dimethyl sulfate\ and subsequent interception of the iminium cation "65# with sodium ethanethiolate ð60BSF2243Ł[ An alternative approach\ the interception of a thioimidate with an alcohol\ has also been reported ð73H"11#02Ł[ Reaction of 1!"1?!thiolphenyl#dihydroimidazole "66# with phthalolyl chloride gave the spiro thioacetal "67#[ In this reaction it may be the cyclic tautomer "68# of phthaloyl chloride which is the reactive species "Scheme 02# ð77LA488Ł[ "c# Cycloaddition methods[ Benzonitrile oxide can undergo 0\2!dipolar cycloadditions to C1S or to C1N bonds which lead to amide thioacetals[ Two examples of such reactions\ leading to the oxathiazole "79# ð68CB0762Ł and to the fused azetidine "70# ð89TL012\ 80JHC370Ł are shown in Scheme 03[ The reaction of keteneÐsulfur dioxide adduct with the 1!aryldihydrooxazoles "71# gives the cycloadduct "72# ð58JHC618Ł[ The dihydroindole "74# was obtained from the reaction of dichloro! ketene with the indole "73# "Scheme 04# ð78JOC0671Ł[ "d# Miscellaneous reactions yieldin` amide monothioacetals[ 3!Thio!b!lactam "75^ R H# under! goes oxidation with lead tetraacetate ð63JCS"P0#11Ł or with t!butyl perbenzoate in benzene ð68CC374Ł to give O!acylated derivatives "75^ R OCOMe or OCOPh#[ Phenacyl bromide reacts with phenyl! propiolic thioanilide "76# in the presence of acetone to produce a 0\2!oxathiole "77# "Scheme 05# ð64LA847Ł[ "ii# Functions bearin` two sulfur and one nitro`en substituent There are many parallels that can be drawn between the preparation of thioamide acetals and their oxa analogues[ It is likely that many of the principles behind the methods for preparation of the latter could be applied to the former[ "a# From sp2!carbon compounds[ Reaction of amide acetals with thiols provides a route to both acyclic and cyclic thioamide acetals "78# and "89# "Scheme 06# ð58BSF221\ 69BSF1902Ł[ Replacement of the alkoxy function of the dithio!ortho!ester "80# has been demonstrated to give the amide dithioacetal "81# ð79PJC034Ł[ a!Chlorothioacetals such as "82# are converted into amide thioacetals "e[g[ "83## by treatment with amines ð50LA"530#10Ł[ "b# From sp1!carbon compounds[ The reaction of alkoxyiminium cations such as "65# with thiolate salts in excess leads to amide thioacetals HC"SR0#1NR11 ð54IZV1068\ 62CB2614Ł[ Chloroiminium salts react with thiols in a similar way ð59MI 593!90Ł and "alkylthio#iminium cations "84# have also been
001
Chalco`en and Any Other Heteroatoms CHO HO
S
piperidine
+ N+
OMe
MeO S
MeO
N
O Me MeO (74)
NO2
Me (72)
(73) OMe
OMe
EtS–
Me2N
N+
SEt
Me (76)
Me
NO2
(75) N
O
N
+
N H
+
S
PhCH2NEt3Cl–
Cl
SH
N
Na2CO3
O
O
Cl
(77)
(79)
(78)
O Cl Cl O Scheme 13
O Ph
Ph S
Ph
N O
N+ O–
Ph
N
N
O
S
CN (80)
CN
SEt
SEt Ph
O
N+ O–
N
N
N
Ph (81) Scheme 14
i, SO2 ii, ketene
N O2N
O
O2S O2N
N
O
O
(82)
(83) Cl O–
S+ N Me SO2Ph (84)
+
Cl3CCOCl
Zn–Cu
Cl O O
N
SMe
SO2Ph (85) Scheme 15
O
002
Chalco`en and Group 04 Br
Ph
R
Br
SMe
NHPh
O N O
CO2Me
+
Br
Ph
O
Ph
S NHPh
S Ph
(86)
(87)
(88)
Scheme 16
SC7H15
HSC7H15
Me2N SC7H15 (89)
OMe Me2N OMe HS
S
SH
S NMe2 (90)
Scheme 17
Ph Ph
Ph
S
Ph
S
S
O
S SMe
SMe
N
O
Me2N
Cl
SMe
SMe
OMe (91)
(93)
(92)
(94)
intercepted with thiols to give thioamide acetals ð54BCJ1096\ 55BCJ1994\ 72CI"L#194Ł[ 0\2!Thiazolium cations "85# undergo reaction with azide anions and with amines to give the addition products "86^ X N2 or NR1# ð54JCS21\ 65BCJ2456\ 65JPR016\ 79JOC1913\ 70JCS"P0#507Ł[ Reduction of the C1N bond of the iminium salt "87# with sodium borohydride yields the corresponding amide thioacetal ð58CPB0813Ł[ A more unusual example is that provided by the reaction of the tris"alkylthio#borane derivatives "88# with amides "Equation "6## ð55IZV253\ 68ZN"B#888Ł[ Ph S S+
SR2
R1
S N+
S
X–
X +NR3
S
2
(95)
S (97)
(96)
SR3
O
+ R1
(98)
R3S
R1
B
NR22
SR3
SR3 NR22 SR3
(7)
(99)
"c# Cycloaddition methods[ The ð1¦1Ł cycloaddition of ketenes to iminodithiocarbonate esters has been used as a route to b!lactams which incorporate the amide dithioacetal function[ Examples with cyclic ð46CB1359\ 62JHC680Ł and acyclic ð65JOC0001\ 76S889Ł iminodithiocarbonates are shown in Scheme 07[ Dihydrothiazoles also react with the keteneÐsulfur dioxide adduct "in a manner
003
Chalco`en and Any Other Heteroatoms
analogous to that shown for the oxazoline "71## to give products which contain this functionality ð58JHC618Ł[ S
MeS
+ ClCOCH2OMe
SMe S
MeO
Et3N
N
N
O
MeS
MeS MeS
SMe Et3N
+ ClCOCH2ON3
N
N3
N O
CO2But
CO2But Scheme 18
"d# Miscellaneous reactions yieldin` amide thioacetals[ Photo!rearrangement of N!"ethoxy! acetyl#tetrahydro!0\2!thiazine!1!thione gives the thiazolidinone "099# "Equation "7## ð75TL0224Ł[ There are several routes to compounds containing methanesulfonyl functions[ The azo compound "090^ R H# has been obtained by the reaction of bis"methanesulfonyl#methane with benzene! diazonium chloride ð40RTC622Ł and from its analogue "090^ R SMe# by reaction with piperidine ð40RTC781Ł[ Reaction of diazomethane with the oxime "091# gave the N!methoxyaziridine "092# ð49RTC0112Ł[ S
O EtO
N
S
S
S
hν
EtO
(8)
N O (100) OMe
R
N NPh SO2Me SO2Me
N
N SO2Me
SO2Me
MeO2S
(101)
OMe
MeO2S (103)
(102)
"iii# Functions bearin` one sulfur and two nitro`en substituents "a# From sp1!carbon compounds[ Addition to alkylthioiminium salts "093# by sodium azide and subsequent cyclisation gives thiatriazoles "094# ð63JCS"P0#439Ł[ Amines will add in a similar manner to the C1N bond of thiazolium cations such as "095# ð60CPB1111\ 76JOC1904Ł and to 2!methylthio! 0\1\3!dithiazolium cations "096# ð63JCS"P0#439Ł[ Phenylmagnesium bromide adds to both the C1C and the C1N bonds of 4!arylidine!1!phenyliminothiazolidin!3!ones "097# ð53T14Ł[ Treatment of hydrazonyl halides with thioamides leads to 1\1!disubstituted dihydro!0\2\3!thiadiazoles "098# ð65ACS"B#726Ł[
+
N O
Ar
N N
SMe Ph
N
S
N
Ph
Me
+
N
S
O
(104)
(105)
(106)
"b# Cycloaddition methods[ Cycloaddition of cyclopentadiene to thiocarbonylbis"0\1\3!triazole# "009# gives the adduct "000# ð79JOC2602Ł[ Diphenylethyne reacts under photochemical conditions to the C1S bond of "001# to give both four! "002# and six! "003# membered ring adducts "Scheme 08# ð65TL2452\ 79LA762Ł depending on the wavelength employed[ Acid chloride derived ketenes undergo
004
Chalco`en and Group 04 O +
S
S
H N N
H N
Ph
SMe
N (107)
Ph
Ph
Ph
S
NPh
S (108)
Ph
NHPh
(109)
ð1¦1Ł cycloaddition with tetrahydro!1!alkylthiopyrimidines to yield thio substituted b!lactams such as "004# ð73TL0738Ł[ Trichloroacetyl isocyanate reacts with mesoionic thiazoles to give cycloadducts such as "005# ð65ACS"B#726\ 65JOC702Ł[ Amide thioacetals react with aryl isocyanates to furnish the imidazolinediones "006# ð62CB2614\ B!68MI 593!91Ł^ a similar reaction occurs with N!alkyl!0\2\3! thiadiazolium salts ð77LA594Ł[ "c# Photoreduction[ The C1S bond of 0\2!diphenyl!1!thioparabonate "007# undergoes photo! reduction in ethanol ð58BCJ1212Ł[ N
N N
N
N
N
N
N
+
N
S N N
S (110)
N
(111) Ph
Ph Me N
S Me
N
Me
N
O
+
Ph
S
hν
Ph
Me
Ph
N
or
Me
N
S
O
N
Me
O O (112)
O
O (113)
(114)
Scheme 19
PhO MeS CBZ N
N
Ph
Ar
O
O
O
N
S
N
RS
COCCl3
Ar (116)
(115)
O
N
Me2N
O Ph
N O (117)
Ar
O
N
N
Ph
S (118)
5[93[0[0[2 Functions bearing selenium and nitrogen "i# Functions bearin` one selenium\ one oxy`en and one nitro`en substituent The 1!methoxydihydroselenazole "008^ Ar 3!PhC5H3# has been obtained from the corresponding N!methylselenazolium cation by reaction with sodium methoxide ð70ZOB0731Ł[ Similarly\ treatment of a N!alkylbenzoselenazolium cation "019# with a 1!hydroxybenzaldehyde derivative generates a 1!spiro derivative "010# ð60BSF445\ 80CL0762\ 82CL02Ł[ R1 N Me N Ph
Ar
Se OMe (119)
R1 N+ Se (120)
Se O R2O (121)
NO2
005
Chalco`en and Any Other Heteroatoms
"ii# Functions bearin` one selenium\ one sulfur and one nitro`en substituent Selenium substituted b!lactams such as "011# have been obtained by cycloaddition of ketenes to 1!alkylselenothiazolines ð75JAP50047875\ 75JOC3626\ 76NKK0336Ł[ SeMe S
MeO
N O
CO2Me (122)
"iii# Functions bearin` one selenium and two nitro`en substituents Two examples of such compounds are provided by the selenide "012# which was obtained from 0\0!dinitroethane and benzeneselenyl chloride ð71IZV050Ł and by the 0\2\3!selenadiazole "013#\ which is formed by addition of a hydrazonyl chloride to the C1Se bond of a selenamide ð89ZOR0018Ł[ Ph
Ph N
N
NO2 SePh NO2
N
Se
O (124)
(123)
5[93[0[1 Functions Bearing Chalcogen and P\ As\ Sb or Bi 5[93[0[1[0 Functions bearing oxygen and P\ As\ Sb or Bi "i# Functions bearin` two oxy`en and one phosphorus substituent Ortho!esters and amide acetals may be converted into phosphorus containing functions by treatment with a phosphorus"III# nucleophile ð75MI 593!90Ł[ A 1!trimethylammonium!0!2!dioxane "014# reacts with isopropyl diphenylphosphinate to give the phosphine oxide "015# "Equation "8## ð77JOC2598Ł[ Similarly\ triethyl phosphite combines with 1!trimethylammonium!0\2!dioxolane a}ording the phosphonate ester ð63JPR802Ł[ Chlorodiphenylphosphine and dichloromethyl! phosphine react with ortho!formate esters to give the phosphine oxides "016# and phosphonate esters "017#\ respectively ð72TL0292\ 78T2676Ł[ Related reactions with hypophosphorous acid ð79AJC176Ł and with diethyl phosphinate ð66TL1876Ł have been reported[ Triethyl phosphite\ in combination with phosphorus trichloride and zinc chloride\ reacts with triethyl ortho!acetate to form the phosphonate diester acetals "018# ð62S436Ł[ The adduct "029# formed from phosphorus trichloride and acetaldehyde reacts with triethyl ortho!formate to give the mixed phosphonate diester acetal "020# ð89CC0022Ł[ O
O N+Me3
+
OPri
Ph2P
PPh2
O (125)
O (126)
O
Me
Ph2P OR (127)
O
OR
OR
P OEt OR (128)
O
O
OEt
EtO P OEt OEt (129)
(9)
006
Chalco`en and Group 04 Cl
O
Cl O (130)
P O MeO
PCl2
OMe
OMe (131)
Dialkyl phosphinates react with the 2!acetylcoumarin to give the hemiacetal "021# ð80PS"46#100Ł[ Hydration of a!phosphono!a!oxo esters "022# proceeds in high yield to give the hydrates "023^ R H#[ Similarly\ alcohols yield the corresponding hemiketals "023^ R alkyl# "Scheme 19#[ The yield is higher for methanol than for t!amyl alcohol as branching leads to steric congestion at the quaternary centre ð78CC135Ł[ 1\1!Dimethylpropylidynylphosphine "024# undergoes a double 0\2! dipolar cycloaddition with 3!chlorobenzonitrile oxide to yield the bicyclic product "025# ð73CC0523Ł[ O
O HOP(OR)2
O
PO(OR)2
O
O
OH (132)
O
O
(Et2O)P
H2O or ROH
CO2Et
(Et2O)P
CO2Et
HO
O (133)
OR
(134) Scheme 20
N
Ar
O But But (135)
P O
Ar N (136) (Ar = 4-ClC6H4)
P
Functions which already contain two oxygens and a phosphorus can be elaborated further at the phosphorus atom by standard methods[ Phosphinite acetals "026# undergo an Arbuzov reaction with alkyl iodides "Equation "09## ð77PS"24#218Ł\ and the trimethylsilyl group of the phosphinites "027# is lost in the Arbuzov reaction with alkyl chloroformates which gives the phosphinates "028# ð75ZOB1316Ł[ Examples of aminoalkylation of phosphorus are also known ð78JCS"P0#0208Ł[ O
OR2
R3I
(R1O)2P
R1O
OR2
OR2 (10)
P R3
OR2
(137) R1O
O
OR2 R1 O
P TMS-O (138)
OR2
OR2
P
R3O2C
OR2
(139)
"ii# Functions bearin` one oxy`en\ one phosphorus and one nitro`en substituent Electrochemical oxidation of the a!acylamino phosphonate "039# in methanol with a carbon anode gives the methoxylated compound "030# "Equation "00## ð78T0580Ł[ In an unexpected reaction\
007
Chalco`en and Any Other Heteroatoms
the phosphonate "031# is generated from the treatment of the tosylate "032# with sodium diethyl! phosphinite ð82HCA1396Ł[ O
O
OMe
MeOH, NaCl
Ph
N H
P(OEt)2
Ph
C anode
N H
O
(140)
P(OEt)2
(11)
O
(141)
O
O N
N (EtO)2P
O
OTs O (143)
O (142)
"iii# Functions bearin` one oxy`en and two phosphorus substituents Double addition of phosphinic acids and phosphites to activated carboxylic acid derivatives such as acid chlorides and anhydrides leads to a\a!diphosphino and a\a!diphosphono alcohols\ respectively ð45JA3349\ 56JCS"C#0436\ 60JOC2732\ 62ZAAC"288#0\ 66TL0954\ 67CC174\ 68S70Ł[ An example of the reaction sequence is shown in Scheme 10[ Carboxylic acids combine with phosphorus trichloride bisphosphonic acids ð61MI 593!90\ 71MI 593!90Ł^ thus\ acetic acid gives MeC"OH#ðPO"OH#1Ł1[ Reaction of chlorodiphenylphosphine with acetic acid and then with acetic anhydride a}ords the bisphosphine oxide "033^ R H# via the intermediate ketone "034# "Scheme 11#[ The acetylated analogue "033^ R Ac# is obtained after prolonged reaction times ð66JCS"P0#0787Ł[ Products analogous to "033^ R H# have also been obtained by hydrolysis of acylphosphine oxides ð67ZN"B#738Ł[ O O Ph
O
(MeO)3P
Cl
Ph
HPO(OMe)2
P(OMe)2
HO
P(OMe)2
Ph
P(OMe)2
O Scheme 21
O
O
O
O
AcOH
Ph2PCl
Ph2PH
O
Ac2O
O
Ph2PH
RO
Ph2P
PPh2 PPh2
O (144)
(145) Scheme 22
The diazophosphonate "035# reacts with cyclohexenol in the presence of rhodium acetate to give the ether "036# "Equation "01## ð81JOC067Ł[ Photochemical oxidation of a!diazophosphonates in methanol leads to the formation of products of an analogous type ð71JOC0173Ł[ Cycloaddition of the silylnitronate "037# to the vinylbis"phosphonate# "038# leads to the formation of the dihy! droisoxazole "049# "Equation "02## ð81PS"58#64Ł[ Oxygen functions can also be introduced by reaction with hydrogen peroxide\ as shown in Scheme 12 ð78JOC3161\ 82JOC3048Ł[ O
O
(MeO)2P
P(OMe)2
OH
O (MeO)2P N2 (146)
O
, Rh2(OAc)4
O
P(OMe)2
(12) (147)
008
Chalco`en and Group 04 Ph O
Ph
TMS-O
N+
+ O–
P(OEt)2 (EtO)2P
P(OEt)2
O (148)
N O
O
(13) P(OEt)2
O (150)
(149)
O
O
P(OH)2
P(OH)2
Na2CO3, H2O2, Na2WO4
P(OH)2
HO
O
HO
O
P(OH)2 O
O
P(OR)2
P(OR)2
H2O2, NaHCO3
P(OR)2
O
O
P(OR)2 O
Scheme 23
"iv# Functions bearin` two oxy`en and one arsenic substituent The cycloaddition of the benzoxarsole "040# to tetrachloro!o!benzoquinone gives a product "041# bearing this array of functional groups "Equation "03## ð72TL4370Ł[
As But O
Cl
Cl
Cl Cl
O
Cl
O
+
Cl
O
(14)
As Cl
O O
(151)
Cl
But (152)
5[93[0[1[1 Functions bearing sulfur and P\ As\ Sb or Bi "i# Functions bearin` one sulfur\ one oxy`en and one phosphorus substituent Removal of an acidic proton from a!oxygen substituted phosphonic acid derivatives gives the opportunity for reaction with electrophilic sulfenylating reagents[ Diethyl a!methoxy phosphonate "042# when treated sequentially with a mixture of n!butyllithium and potassium t!butoxide\ elemental sulfur and iodomethane gives the methylthio product "043# ð65TL366Ł[ The use of n!butyllithium alone gives compounds resulting from transesteri_cation ð68JOC1856Ł[ Similarly\ the a!sily! loxyphosphonate "044# reacts with LDA and diphenyl disul_de a}ording the trisubstituted product "045# ð67TL252Ł[ Activation of the a!carbon atom in a!"alkylthio#phosphonates can be achieved by halogenation[ Treatment of the phosphonate "046# with N!chlorosuccinimide gives the a!chloro derivative "047# which\ in the presence of methanol\ is converted into the a!methoxy compound "048# "Scheme 13# ð74TL2368Ł[ The same substitution can be achieved using electrochemical oxidation in methanol ð76S33Ł\ and a similar halogenationÐsubstitution sequence takes place with sulfoxides analogous to "046# ð67JOC1407Ł[ 1!Lithio!0\2!oxathiane reacts with dimethyl thiophosphonyl chloride to give the substitution product "059# ð74JOC551\ 78JPO238Ł[ The ability of a sulfoxide to activate a neighbouring carbon atom is employed in the Pummerer rearrangement of a!sul_nyl phosphonates such as "050# in the presence of acid anhydrides ð66S070\ 67JOC1407\ 75BCJ2182Ł[ In a reaction analogous to that of the diazo compound "035# the ether "051# is formed from the rhodium catalysed solvolysis of the a! diazophosphonate "052# in 1!propanol "Scheme 14# ð81SL864Ł[ Oxygen substitution can also be achieved by photolysis ð71JOC0173Ł[
019
Chalco`en and Any Other Heteroatoms i, BunLi, ButOK ii, S8 iii, MeI
O (EtO)2P
OMe
O (EtO)2P
SMe (154)
(153) O (EtO)2P
O
i, LDA ii, (PhS)2
Ph
(EtO)2P
O
O
NCS, CCl4
SMe
Ph
O-TMS SPh (156)
O-TMS (155)
(EtO)2P
OMe
(EtO)2P
O
MeOH
SMe
(EtO)2P
OMe (159)
Cl (158)
(157)
SMe
Scheme 24
S
S
S
Me2PSCl, THF
Li
P(OEt)2
O
O (160)
O
O
(EtO)2P
O
Ac2O, MeSO3H
SMe
(EtO)2P
(161)
OAc
O PhO2S
SMe
O Rh2(NHCOCF3)4 PriOH
P(OEt)2
PhO2S
P(OEt)2
OPri (162)
N2 (163) Scheme 25
"ii# Functions bearin` two sulfur and one phosphorus substituent 0\2!Dithianes and 0\2!dithiolanes substituted at the 1!position with leaving groups can react with triphenylphosphine ð66TL774\ 70S42Ł\ to give phosphonium salts such as "053# and "054#[ Similarly\ trialkyl phosphites undergo Arbuzov reactions forming phosphonate diesters such as "055# "Equa! tion "04## ð66TL774\ 67JPR144\ 79S016\ 75MI 593!91Ł[ The alternative approach\ the reaction of 1! lithio!0\2!dithiane with an electrophilic phosphorus species\ chlorodiphenylphosphine ð75T0852\ 80JOC4808Ł or diethyl chlorophosphonate ð67S298Ł\ has also been reported[ Phosphorus substituents can also be introduced by nucleophilic addition\ as with the benzo!0\2!dithiolium salt "056# ð65TL2584\ 89CC369\ 80JCS"P0#046Ł[ Reaction of the dithiocarbonate "057# with trialkyl phosphites generates the phosphonates "058# ð64JOC1466Ł[ S
S
+
PPh3 Cl–
S
S (164)
S Cl S
+
PPh3 BF4– (165)
P(OEt)3, Et3N
S
O P(OEt)2
S (166)
(15)
010
Chalco`en and Group 04 NC
S+
S
–
S
NC
S
O
O
BF4 S (167)
NC
NC
S
P(OR)2
(168)
(169)
Sulfur functionality can be introduced into phosphorus!containing compounds by nucleophilic displacement of chloride by thiols\ in a manner analogous to that in which "047# is formed from "046# ð77SC0500Ł[ More commonly\ sulfur is introduced as an electrophile[ Sulfenylation of phosphorus stabilised carbanions is a useful general method for the formation of compounds containing two sulfurs and phosphorus[ A further sulfur substituent can be introduced into a species containing one sulfur and one phosphorus substituent\ as in sulfenylation of the ylide Ph2P1CHSPh ð89TL3248Ł and of the phosphonate Ph1POCH1SPh ð66JCS"P0#1152\ 79S016Ł[ Alternatively\ both sulfur substituents can be introduced by sequential sulfenylation^ two examples are shown in Scheme 15 ð77S451\ 81SC0248Ł\ and other examples are known ð74JCS"P0#1474Ł[ i, LDA, THF ii, (MeS)2
NPh PPh2
NPh PPh2
i, LDA, THF ii, (MeS)2
(EtO)2P
Al2O3-KF, MeSSO2Me microwave
CO2Et
PPh2 MeS
SMe O
NPh
SMe
O (EtO)2P
CO2Et
MeS
SMe
Scheme 26
S!Methyl "diisopropoxyphosphonyl#dithioformate "069# reacts with carbon nucleophiles on sulfur to give S!alkylated products such as "060# "Equation "05## ð76JCS"P0#070\ 78TL2304Ł[ A similar attack on sulfur occurs with thiols ð81JOC3496Ł[ O
O (PriO)
2P
(PriO)
SMe
SMe O
2P
(EtO)2POCF2Li
S
S
(16)
P(OEt)2
F F (171)
(170)
Trialkylphosphines add to carbon disul_de to give zwitterionic adducts "061#[ These will undergo cycloaddition with acetylenedicarboxylic esters leading to the ylides "062# ð64CC859\ 65BCJ0885\ 68JOC829\ 80JOC0705Ł[ Benzyl thiol reacts with the bisisothiocyanate "063# to give the symmetrical product "064# arising from double cyclisation ð81HAC004Ł[ Similar compounds are obtained by the treatment of compound "065# with acid chlorides with aluminum trichloride catalysis[ The product "066# is a result of a carbon for phosphorus replacement[ Oxidation with hydrogen peroxide gives the phosphine oxide "067# "Scheme 16# ð89JCS"P0#08Ł[ Preformed diethyl a\a!bis"methylthio#phosphonate undergoes lithiation and subsequent 0\1! addition on to a\b!unsaturated aldehydes and ketones to give the alcohols "068# "Equation "06## ð81T7586Ł[ The phosphine sul_de "079# can be methylated with methyl tri~ate to give the S!methyl! phosphonium salt\ which on reaction with HMPA is reduced to the corresponding phosphine ð80TL6218Ł[ R2 O (EtO)2P
SMe Li SMe
+
R1
COR1
O R1
(EtO)2P MeS
OH SMe
(179)
(17)
011
Chalco`en and Any Other Heteroatoms +
PR13
S
+
R2O2C
R13P
R13P + CS2
–
CO2R2
S–
S R2O2C
(172)
Ph
CO2R2 (173)
O N P N
O SCN P NCS
S
SH
S
S
CHCl2 (174)
(175)
RCOCl, AlCl3
P S P S
O
H2O2
P S
P
S
S
(176)
S R (178)
R (177) Scheme 27
S
S
PPh2 S (180)
"iii# Functions bearin` one sulfur\ one phosphorus and one nitro`en substituent This functionality can be produced by reaction of suitably substituted carbanions with elec! trophilic sulfur reagents[ Compounds "070# ð81SC1270Ł and "071# ð74RTC066Ł are examples of compounds formed in this way\ by sulfenylation a! to phosphorus[ The same type of sulfenylation can be achieved starting with a haloalkane and elemental sulfur ð71TL802Ł[ A di}erent method is the addition of a nucleophilic phosphorus reagent to a thioimidate\ as in the conversion of the thioimidate "072# into "073# with sodium diethyl phosphite ð67JCR"S#30Ł[ The same product can be formed by addition of methylmagnesium iodide to the C1N bond of compound "074# "Scheme 17# ð64S674Ł[ O Ph
SMe N H
O (EtO)2P
PPh2 O
SR (182)
(181)
NCO2Et MeS
(EtO)2PO–Na+
O (EtO)2P
O NHCO2Et SMe
(183)
NC
(184)
MeMgI
(EtO)2P NCO2Et MeS (185)
Scheme 28
Diazomethane undergoes cycloaddition with the vinyl sulfone "075# yielding initially the dihy! dropyrazole "076# "Equation "07## ð74CL0988Ł[
012
Chalco`en and Group 04 O
O CH2N2
(EtO)2P
(EtO)2P
N N (18)
Ph MeO2S
SO2Me
Ph
(187)
(186)
"iv# Functions bearin` one sulfur and two phosphorus substituents The sulfenylation of carbanions a! to phosphorus is used to produce this type of compound ð79S016\ 89H"29#744Ł^ an example is the bis"phosphonate# "077# ð79S016Ł[ Trialkyl phosphites react with thiophosgene to give compounds containing this functionality "Scheme 18# ð77PS"39#0Ł[ A related reaction has also been reported ð89TL0040Ł[ O
O
(EtO)2P
P(OEt)2 SPh (188)
O
O P+(OR)3 Cl–
(RO)2P (RO)3P + CSCl2
S
O
(RO)2P
∆
P(OR)2 S
P(OR)2
O Scheme 29
P(OR)2 O
5[93[0[1[2 Functions bearing selenium and P\ As\ Sb or Bi "i# Functions bearin` one selenium\ one sulfur and one phosphorus substituent Selenylation of the anion of the a!sul_nylphosphonate "078# can be accomplished with phenyl! selenyl bromide "Equation "08## ð81TA0404Ł[ Similar selenylations can be achieved using selenium and iodomethane ð70TL2986Ł[ Phenylselenyl chloride also adds to the phosponium ylide Ph2P1 CHSPh ð72CB0844Ł[ Alternatively\ a compound with this functionality is formed by addition of trimethyl phosphite to the heterocyclic cation "089# ð89CC369\ 80JCS"P0#046Ł[ i, BunLi ii, PhSeBr
(EtO)2P O
S
PhSe
(19)
(EtO)2P
S
O
O
O (189) S+ Se (190)
"ii# Functions bearin` two selenium and one phosphorus substituent Reaction of diethyl methylphosphonate with LDA and then with phenylselenyl bromide gives the diselenated product ð81TL4264Ł[ In a similar fashion\ double selenation of the ylide Ph2P1CHMe has been observed ð68CB244Ł[ Trialkyl phosphites add to 0\2!diselenonium cations in a manner
013
Chalco`en and Any Other Heteroatoms
analogous to that with the cation "089# ð77HCA0131\ 81TA0404Ł^ a similar reaction is known with tributylphosphine ð73TL3116Ł[ The a!diazophosphonate "081# undergoes insertion into the diseleno heterocycle "080# in the presence of boron tri~uoride etherate "Equation "19## ð80TL3078Ł[ Se Se
N2
+
Se
BF3•Et2O
P(OMe)2
P(OMe)2
O (192)
(191)
Se
(20)
O
5[93[1 FUNCTIONS CONTAINING CHALCOGEN AND A METALLOID AND POSSIBLY A GROUP 04 ELEMENT 5[93[1[0 Functions Bearing Chalcogen and Boron No compounds in this category have been noted[ It is possible\ however\ that the anion which can be formed from a!phenylthioalkylboronic esters "082# ð67JA0214Ł could react with a range of sulfur\ selenium and phosphorus electrophiles[ R1
O B O
PhS
(193)
5[93[1[1 Functions Bearing Chalcogen and Silicon 5[93[1[1[0 Functions bearing oxygen and silicon "i# Functions bearin` two oxy`en and one silicon substituent Silyl ketals such as "083# are produced from the reaction of alkyl benzoates with TMS!Cl\ magnesium and HMPA ð60JOM"15#072\ 68JOC319Ł[ Silylated hemiketals are also accessible from the TMS!Cl\ magnesium and HMPA reagent combination ð60JOM"15#072Ł[ Acetals with a su.ciently acidic a!hydrogen atom can be deprotonated and silylated using TMS!Cl ð80T2060Ł[ An alternative approach is to form acetals from silyl ketones such as "084# "Scheme 29# ð58CJC3236\ 79TL0246\ 89JA0851Ł[ O
TMS-Cl, Mg, HMPA
OMe
Ph
O Ph
HO
OH
, BF3, Et2O
SiPh3 (195)
Ph
OMe O-TMS TMS (194) O
O
Ph
SiPh3
Scheme 30
Oxidation of compounds containing a vinylsilane moiety provides another route into functions bearing two oxygens and a silicon[ Treatment of a highly strained 0!trimethylsilylcyclopropene derivative "085# with excess mcpba leads to the formation of the epoxide "086# ð75TL4032Ł[ Oxidation of the compound "087# containing two furan rings with singlet oxygen selectively gives the product "088# resulting from cycloaddition to the silylated ring ð89TL6190Ł[ Two other methods starting from vinylsilanes are the rearrangement of the trimethylsilylallene "199# to the dihydrofuran "190# ð71TL298Ł and the addition of dichlorocarbene to 1!trimethylsilyldihydrofuran "191# and sub! sequent reaction with methanol ð73JOM"154#126Ł[ 0!Ethoxy!0!trimethylsilylallene also undergoes
014
Chalco`en and a Metalloid
cycloaddition with enones at the substituted double bond to give products containing this func! tionality "Scheme 20# ð80CB0314Ł[ TMS
mcpba
O TMS
OCHO
TMS
OCHO (197)
(196) 1O 2
O
O
O
O
O TMS
O
TMS (198)
(199) TMS
HO
OMe
•
MeO O
TMS (200)
(201) Cl
Cl TMS
:CCl2
Cl
O
O
(202)
MeOH
OMe O
TMS
TMS
Scheme 31
The disilene "192# and methylfuran!1!carboxylate give a ð1¦1Ł cycloaddition product "193#[ This reaction is particular to the methyl ester\ higher homologues failing to react "Equation "10## ð80OM2355Ł[ Ar
Ar O Si Ar
Ar
+
Si Si Ar
Ar
O
CO2Me
(203)
Si
O
MeO Ar (204)
(21)
Ar
"ii# Functions bearin` one oxy`en\ one phosphorus and one silicon substituent Deprotonation of the a!"trimethylsilyloxy#phosphonate ester "194# with LDA and quenching with TMS!Cl gives the silylated adduct "195# ð70CC858Ł[ Quenching of the lithiated intermediate generated from the a!substituted!a!trimethylsilyloxy phosphonate "196# a}ords some of the alcohol "197# by Wittig rearrangement in addition to recovered starting material ð68TL3364\ 71BCJ113Ł[ The a! diazophosphonamide "198# reacts with aldehydes to yield epoxides "109# "Scheme 21# ð78AG506\ 80NJC282Ł[
"iii# Functions bearin` one oxy`en and two silicon substituents Two silicons can be introduced into a variety of carboxylic acid derivatives by reaction with TMS!Cl and Group 0 or Group 1 metals "Equation "11##[ The addition of HMPA and the use of coordinating solvents often leads to improved yields[ Thus\ primary amides react in the presence of lithium ð68JOM"066#026Ł^ carboxylic acids ð65TL0480Ł\ esters ð67BCJ1280Ł and silyl ketones ð65TL0480Ł utilise sodium while silyl ketones ð78JOC4502Ł and acid chlorides ð61JOM"28#C38Ł are converted with the addition of magnesium[ Other reactions of this type which have been described include the addition of triphenylsilyllithium to ethyl formate ð57CJC1008Ł and the interaction of methyl benzoate with aluminum chloride and tris"trimethylsilyl#aluminum ð70AG"E#470Ł[
015
Chalco`en and Any Other Heteroatoms O TMS-O
O
i, LDA ii, TMS-Cl
P(OEt)2
TMS-O
P(OEt)2
TMS (206)
(205) O TMS-O
O i, LDA ii, H2O
P(OEt)2
TMS Ph
Ph (207)
P(OEt)2 OH
(208)
O
O
(PriNH)2P
TMS
(PriNH)2P
heat, RCHO
N2
TMS
R (210)
(209)
O
Scheme 32
O
TMS-Cl, M
R
X
R
TMS O-TMS TMS
(22)
Triphenylsilylsilyloxirane can be deprotonated with n!butyl lithium at the substituted carbon atom[ Quenching of the intermediate with TMS!Cl a}ords the bis"silyl#oxirane "100#[ 0\0!Bis"tri! methylsilyl#ethene undergoes 0\2!dipolar cycloaddition with benzonitrile oxide giving the dihy! droisoxazole "101# ð72JOC2078Ł[ O
N
Ph
O
Ph3Si TMS (211)
TMS TMS (212)
5[93[1[1[1 Functions bearing sulfur and silicon "i# Functions bearin` one sulfur\ one oxy`en and one silicon substituent The acidity of the proton located on a methylene or methyne unit between a sulfur and an oxygen facilitates deprotonation and subsequent quenching with activated silyl compounds[ Prop! 0!enyloxathiane "102#\ on treatment with s!butyllithium and TMS!Cl gives the a!silylated product "103# "Equation "12## ð81T1490Ł[ The acidity of the proton is increased when the sulfur atom is present at its highest oxidation state\ i[e[\ as a sulfone\ when n!butyllithium will su.ce to cause reaction ð68TL2264\ 77CC534\ 89TL0766\ 80JCS"P0#786Ł[ i, BusLi ii, TMS-Cl
S
S
O (213)
(23) O
TMS (214)
Once formed\ these silylated compounds can undergo further deprotonation and alkylation[ Thus\ 1!trimethylsilyl!0\2!oxathiane "104# is methylated after treatment with s!butyllithium "Equation "13## ð74JOC551Ł[ Other alkylations of this type are known ð74TL1564\ 76JAP5150876\ 76TL1036\ 78JOC4992\ 81JAP3038042Ł[
016
Chalco`en and a Metalloid TMS O
TMS i, BusLi ii, MeI
S
O
S (24)
(215)
Cycloadditions o}er a further route into this trisubstituted functionality[ Phenyl trimethylsilyl thioketone\ which can be generated by the rearrangement of 1!phenyl!1!silylthiirane\ ð56JA320Ł will react with nitrile oxides ð70CC711\ 89H"20#36Ł\ a!nitrosostyrene ð74TL1020\ 76JCS"P0#1536Ł and silyl enones ð80TL1860Ł to a}ord cyclic products "Scheme 22#[ N O PhCNO
Ph
O
S
S
Ph
TMS Ph
Ph
S
Ph TMS
N O
N
Ph
Ph
TMS
TMS
S TMS
S
O
Ph TMS
O
TMS
Scheme 33
"ii# Functions bearin` two sulfur and one silicon substituent Bis"alkylthio#methanes such as "105#\ on treatment with base and on subsequent addition of a silylating agent o}er facile access to both tertiary "106# ð64ZAAC"307#197\ 89CL0300\ 89JOM"277#36\ 80TL5790Ł and quaternary ð66JOC0556\ 74S587\ 75HCA33\ 75JCS"P0#084\ 77ZOB0955Ł bis"alkyl! thio#trialkylsilylmethanes "Equation "14##[ The preferred reagent for deprotonation is n!butyl! lithium\ and trialkylsilyl chlorides are used most often to quench the lithiated intermediate[ These conditions are general enough to allow silylation at hindered positions ð75HCA33Ł[ The presence of TMEDA can lead to higher yields ð77ZOB0955Ł[ Dichlorodimethylsilane has been demonstrated to undergo double substitution of chloride by 1!lithio!1!methyl!0\2!dithiane ð56JA323Ł[ TMS
i, BuLi ii, TMS-Cl
EtS
SEt
EtS
(216)
SEt
(25)
(217)
With 1!allyl substituted 0\2!dithianes\ the lithiated intermediate conceivably could be silylated at either the a! or the g!position of the allyl substitutent[ It is found that silylation usually occurs mainly at the a!position\ even when this leads to the more sterically congested of the two possible products "Scheme 23# ð68TL0716\ 79JCS"P0#1567\ 75HCA0267\ 76JOC744Ł[ In the case of the dithiane derivatives "107#\ deprotonation by LDA and silylation takes place a! to the ring for R Me but at both the a! and the g!positions for R Ph ð77JCS"P0#2256Ł[ S
Ph
i, BuLi ii, TMS-Cl
Ph
S
TMS S
Scheme 34
S S
SR (218)
S
017
Chalco`en and Any Other Heteroatoms
Products which contain sulfur in a higher oxidation state can be accessed by the use of starting materials at the required level of oxidation[ Thus\ the sulfone "108# reacts with trialkylsilyl per! ~uorobutanesulfonates and two equivalents of n!butyllithium to give the products "119# "Equation "15## ð82CB426Ł[ Alternatively\ oxidation can be performed on the silylated compound ð65JOC2864Ł[ O
O
O S
O S
C4F9SO3SiR3
R3Si
(26)
SiR3
S
S
O O (219)
O O (220)
There are many examples of the lithiation of bis"alkylthio#trimethylsilylmethanes and reaction with electrophiles to generate quaternary products "Equation "16##[ Alkylations have been performed with iodoalkanes ð79JA5050\ 80TL1710Ł with the optional addition of HMPA ð73HCA0623Ł[ The sulfone "119^ R Me# is methylated with methyl per~uorobutanesulfonate after deprotonation with two equivalents of n!butyllithium ð80CB0794Ł[ Acetylation of 1!trimethylsilyl!0\2!dithiane has been accomplished by the use of acetyl chloride ð62JCS"P0#1161Ł[ Michael addition of lithiated bis"phen! ylthio#! ð78JOC0189Ł and bis"methylthio#! ð66CB730Ł trimethylsilylmethanes occurs with cyclo! pentenone^ the bis"methylthio# intermediate also adds 0\3! to t!butyl cinnamate ð74TL2920Ł[ 1!Lithio!1!trimethylsilyl!0\2!dithiane undergoes 0\1!addition to cyclohex!1!enone but addition of HMPA to the reaction mixture promotes 0\3!addition ð68CC099Ł[ TMS
Li
R1S
SR1
R2
TMS
R2X
R1S
(27)
SR1
"iii# Functions bearin` one sulfur\ one nitro`en and one silicon substituent The examples of compounds falling into this class in the literature are formed exclusively by cycloaddition[ The thioketone "110# reacts with diazomethane to give the dihydro!0\2\3!thiadiazole "111# ð80MI 593!90Ł[ A dihydro!0\2\3!thiadiazole "112# is obtained from the treatment of thioketone "113# with the hydrazonyl chloride "114# in the presence of triethylamine ð89H"20#36Ł[ The tri! methylsilylallene "115# undergoes a ð1¦1Ł cycloaddition with chlorosulfonyl isocyanate leading to the b!lactam "116# "Scheme 24# ð74TL4990Ł[
But
TMS
CH2N2
N N
But
TMS S (222)
S (221)
Ph Ph
TMS
N N
Ph
PhCH(Cl)=NNHPh (225), Et3N
S
TMS
S (224)
(223) SAr •
SAr
i, CSI ii, Na2SO3
TMS
TMS
NH O
(226) (Ar = 4-ClC6H4)
(227) Scheme 35
Ph
018
Chalco`en and a Metalloid "iv# Functions bearin` one sulfur\ one phosphorus and one silicon substituent
Pairwise combinations of sulfur\ phosphorus and silicon attached to the same carbon atom will all activate the carbon atom towards anion formation or radical halogenation[ The introduction of the remaining element as an electrophile or nucleophile\ as appropriate\ will allow the formation of the complete functional group[ Thus\ deprotonation of diethyl "methylthio#methylphosphonate or diethyl "trimethylsilyl#methylphosphonate with n!butyllithium and quenching with TMS!Cl or with dimethyl disul_de\ respectively\ leads to the same trisubstituted product "Scheme 25#[ The same compound can be prepared by the radical bromination of trimethylsilyl"methylthio#methane and subsequent Arbuzov reaction with triethyl phosphite[ Of these reactions\ the silylation confers the best yield ð78S090Ł[ 0\2!Dipolar cycloaddition of nitrile sul_des to the silylated phosphaalkene "117# and subsequent elimination of a nitrile leads to the formation of the three!membered ring species "118# "Scheme 26# ð78TL3490Ł[ An alternative route to this ring system has been described ð76TL5010Ł[ O (EtO)2P
i, BunLi; ii, TMS-Cl
SMe
O
O (EtO)2P
i, BunLi; ii, Me2S2
TMS
(EtO)2P
SMe TMS
i, NBS
TMS
SMe ii, P(OEt)3
Scheme 36 Ph
TMS P
+
R
N S
N S
Ph
–
R Cl
P
Ph
– RCN
TMS Cl
Cl
(228)
TMS
P
S
(229) Scheme 37
"v# Functions bearin` one sulfur and two silicon substituents Treatment of phenylthio"trimethylsilyl#methane sequentially with n!butyllithium and TMS!Cl gives phenylthiobis"trimethylsilyl#methane[ This can be alkylated by the addition of further n! butyllithium and an alkyl halide ð80T504Ł or it can be oxidised to the sulfone with peroxybenzoic acid ð73JOC4976Ł "Scheme 27#[ Examples of double silylation by TMS!Cl of a carbanion adjacent to a sulfone function are also known ð78LA864Ł[ More bulky silylating agents such as triethylsilyl chloride give selective monosilylation ð78TL1762Ł[ i, BunLi ii, BrC3H6Ph
PhS
TMS
PhS TMS
i, BunLi ii, TMS-Cl
PhS
TMS TMS
Ph TMS
PhSO2
PhCO3H
TMS TMS
Scheme 38
The cycloaddition of the thiocarbonyl ylide "129# to dipolarophiles such as methyl acrylate "Equation 17# ð76CPB0623Ł and acrylonitrile ð75H"13#0460Ł gives bis"trimethylsilyl# substituted tetrahydrothiophenes[ The alkene "120# undergoes thermal isomerisation to the bis"trimethylsilyl# thiirane "121# "Equation "18## ð76CL1066Ł[ TMS
X
X +
S
–
TMS
CH2
S
TMS (230)
X TMS
+
TMS (X = CN, CO2Me)
S
TMS
(28)
029
Chalco`en and Any Other Heteroatoms S
S ∆
Ph
TMS Ph
TMS
TMS
Ph
TMS
(231)
(29)
Ph (232)
5[93[1[1[2 Functions bearing selenium and silicon "i# Functions bearin` one selenium\ one sulfur and one silicon substituent Deprotonation of methyl phenyl sulfone with LDA and reaction of the carbanion with TBDMS! Cl gives the silylated product[ Addition of a further equivalent of LDA and conversion to the cuprate can be followed by reaction with selenocyanogen to give the selenocyanate "122# ð76TL4010\ 77JA7560Ł[ 0!Benzenesulfonyl!0!trimethylsilylalkenes such as "123# undergo Michael addition by alkyllithium reagents and the resultant lithiated species can be quenched with phenylselenyl chloride "Scheme 28# ð70TL3176\ 73TL1910Ł[ PhSO2Me
i, LDA ii, TBDMS-Cl
PhSO2
SiMe2But
i, LDA ii, CuCN
PhSO2
iii, (SeCN)2
SiMe2But SeCN (233)
TMS
PhSe i, MeLi ii, PhSeCl
PhSO2
TMS
PhSO2
O
O OMe
OMe
(234) Scheme 39
"ii# Functions bearin` one selenium and two silicon substituents Reaction of a!trimethylsilyl!a!phenylselenyltoluene "124# with LDA and TMS!Cl gives the product "125# bearing two trimethylsilyl groups "Equation "29## ð66JOC0662Ł[ PhSe
Ph
i, LDA ii, TMS-Cl
TMS SePh TMS
Ph
TMS (235)
(30)
(236)
5[93[1[2 Functions Bearing Chalcogen and Germanium 5[93[1[2[0 Functions bearing oxygen and germanium "i# Functions bearin` two oxy`en and one `ermanium substituent Only one example of this functional group has been reported[ Reaction of the ketal "126# with trimethylgermyl chloride gives the substitution product "127# "Equation "20## ð72CC128\ 72T2962Ł[ O
O Li
TMS
O Me3GeCl
GeMe3 TMS
(237)
O
(238)
(31)
020
Chalco`en and a Metalloid "ii# Functions bearin` one oxy`en\ one nitro`en and one `ermanium substituent
One class of compound has been noted with this grouping[ Treatment of dimethylamides with triethylgermyllithium gives the O!lithiated intermediates "128# resulting from addition to the car! bonyl group[ On workup\ these intermediates are converted into the ketones "139# "Scheme 39# ð72JOM"137#40\ 77JOM"230#182\ 77JOM"237#206Ł[ O R
Et3GeLi
NMe2
LiO
GeEt3
R
NMe2
O R
(239)
GeEt3 (240)
Scheme 40
"iii# Functions bearin` one oxy`en\ one phosphorus and one `ermanium substituent Addition of dimethyl"trimethylgermyl#phosphine to phenyl trimethylsilyl ketone generates the O! silylylated product "131#[ This is believed to be obtained via the O!germyl isomer "130# "Scheme 30# ð66JOM"030#24Ł[ O Me3GePMe2
+
Ph Ph
TMS
PMe2 OGeMe3 TMS
Ph
(241)
PMe2 GeMe3 O-TMS (242)
Scheme 41
"iv# Functions bearin` one oxy`en\ one `ermanium and one silicon substituent Treatment of phenyl triethylgermyl ketone "132# with triethylsilyllithium yields the alcohol "133# ð77MI 593!90Ł[ O!Alkylated functions such as "134# are accessible from the reaction of bromo! trialkylgermanes with lithiated trimethylsilylmethyl methyl ether[ These compounds can be further alkylated at the central carbon atom "Scheme 31# ð81SL732Ł[ O
Et3SiLi
Ph
Et3Ge (243) MeO
TMS
OH SiEt3 GeEt3
Ph
(244) i, BusLi ii, BrGeMe3
MeO
TMS GeMe3
(245) Scheme 42
"v# Functions bearin` one oxy`en and two `ermanium substituents In a reaction analogous to that shown with triethylsilyllithium\ the ketone "132# reacts with triethylgermyllithium to give bis"triethylgermyl# carbinol "135# ð76IZV1761\ 77MI 593!90Ł[ Ethyl for! mate reacts with triphenylgermyllithium to give a mixture of bis"triphenylgermyl#methanol "136# and its formate ester "137#[ The latter can be converted to the former by treatment with lithium aluminum hydride ð57CJC1008Ł[
021
Chalco`en and Any Other Heteroatoms Ph
OCHO
OH
GeEt3 OH GeEt3 (246)
GePh3
Ph3Ge
GePh3
Ph3Ge (248)
(247)
5[93[1[2[1 Functions bearing sulfur and germanium "i# Functions bearin` one sulfur\ one oxy`en and one `ermanium substituent 0\2!Oxathiane\ when reacted with s!butyllithium\ reacts with trimethylgermyl chloride to give the 1!substitution product "138# "Equation "21## ð70TL1994\ 74JOC546\ 74JOC551Ł[ S
i, BusLi ii, Me3GeCl
S GeMe3 O (249)
O
(32)
"ii# Functions bearin` two sulfur and one `ermanium substituent The reported preparations of these compounds are all the results of the formation of a carbanion between two sulfur atoms and quenching with an electrophilic germanium species[ 1!Lithio!0\2! dithiane has been reacted with triethylgermyl chloride ð57CJC1008Ł\ triethylgermyl bromide ð56JA320Ł and triphenylgermyl bromide ð56JA320Ł to give products "149#[ Quaternary systems are also access! ible starting from 1!alkylated dithianes ð56JA320Ł[ Both 0\2\4!trithiane and 0\2\4\6!tetrathiocane can be substituted in the same manner ð64ZAAC"307#197\ 65CB0128Ł[ The difunctional 0!gerana!0\0! dichloro!2!cyclopentene "140# reacts with two equivalents of 1!lithio!0\2!dithiane a}ording the quaternary germanium species "141# ð73JAP48082786Ł[ The bis"sulfone# "108# undergoes substitution at both methylene groups by trimethylgermyl per~uorobutanesulfonate ð82CB426Ł[ S S S
Ge
S
Cl
GeR3
Ge
S Cl
S (250)
(251)
(252)
"iii# Functions bearin` one sulfur and two `ermanium substituents The only example in the literature of compounds containing this grouping "142# is provided by the reaction of methyl alkanesulfonates R0CH1SO2Me with trialkylgermyl halides and sodium hexamethyldisilazide ð73ZOB0731Ł^ the reaction gives a mixture of products including "142#[
R1
GeR23 SO3Me GeR23 (253)
022
Chalco`en and a Metal 5[93[2 FUNCTIONS CONTAINING CHALCOGEN AND A METAL AND POSSIBLY A GROUP 04 ELEMENT OR A METALLOID 5[93[2[0 Functions Bearing Oxygen and a Metal 5[93[2[0[0 Functions bearing two oxygens and a metal
The 0\2!dioxane "143# reacts with n!butyllithium to generate the lithiated species "144# ð72T2962Ł[ Further reaction with trimethyltin chloride a}ords the trimethylstannyl derivative "145# "Scheme 32# ð72CC128\ 72T2962Ł[ TMS O TMS
O
BuLi
(254)
O
Me3SnCl
Li
O
O
TMS
SnMe3
O
(255)
(256)
Scheme 43
5[93[2[0[1 Functions bearing oxygen\ silicon and a metal Trimethylsilylmethyl methyl ether is lithiated at the methylene group by s!butyllithium ð78TL108Ł[ The proton at the 1!position of 1!trimethylsilyloxiranes can be removed with retention of con! _guration by n!butyl! or s!butyllithium ð77JOM"230#182\ 78JOC3931Ł[ Further reaction with trimethyltin bromide gives the trimethylstannyl derivatives "146# "Scheme 33# ð78JOC3931Ł[ O
O TMS
R H
BusLi
O TMS
R
H
H
TMS
R
Me3SnBr
H
Li
SnMe3 (257)
Scheme 44
5[93[2[0[2 Functions bearing oxygen and two metals Reaction of 1!"tributylstannyl#oxirane with n!butyllithium results in the formation of the 1!lithio! 1!"trimethylstannyl#oxirane "147# "Equation "22## ð77JOM"230#182Ł[ O
O BuLi
Bu3Sn
Bu3Sn
(33)
Li (258)
5[93[2[1 Functions Bearing Sulfur and a Metal 5[93[2[1[0 Functions bearing sulfur\ oxygen and a metal Functions bearing oxygen\ sulfur and lithium are generated as intermediates in reactions which involve their subsequent reaction with electrophiles^ examples are provided by the reactions of 0\2! oxathianes "102# and "104# discussed in Section 5[93[1[1[1[ Sulfur can be present in any of its common oxidation states[ Lithiated compounds can also act as precursors to other metalled deriva! tives[ Treatment of 1!lithio!0\2!oxathiane with trimethyllead acetate results in the formation of
023
Chalco`en and Any Other Heteroatoms
compound "148# by metal exchange ð70TL1994\ 74JOC546Ł[ Another approach to compounds with these functional groups is exempli_ed by the reaction of tributylstannyllithium with the thion! olactone "159# and subsequent alkylation with iodomethane "Scheme 34# ð76JA1493\ 89JA2585Ł[ S
MeS
S O
PbMe3
i, LiSnBu3 ii, MeI
SnBu3 O
O (259)
(260) Scheme 45
5[93[2[1[1 Functions bearing two sulfurs and a metal As with functions bearing oxygen\ sulfur and lithium\ lithiated derivatives are often used as intermediates\ generated in situ\ in the derivatisation at the carbon atom between two sulfur atoms[ A range of strong bases such as the butyllithiums\ LDA\ lithium hexamethyldisilazide "LHMDS# and lithium phenylamide can be used in aprotic solvents at low temperatures to lithiate such compounds ð67JOC3124\ 67MI 593!90\ 70JOC0401\ 71JOC0034\ 75S522\ 89MI 593!90Ł[ In the lithiation of the 0\2!dithiane derived from of 1\3!hexadienal\ reaction occurs exclusively at the 1!position ð81MI 593! 90Ł[ Lithiated dithianes "151# are also available from the reaction of the dithioketene acetal "150# with alkyllithium reagents ð58TL062Ł[ Treatment of compounds bearing three phenylthio residues attached to the same carbon atom with s!butyllithium leads to replacement of one of the heteroatoms with lithium ð73JOC594\ 74JOC2155Ł[ Exchange of trimethyltin for lithium has also been used to produce a compound with this functionality "Equation "23## ð77BCJ1036Ł[ S
S
RLi
S
S
(261)
Li
(34) R
(262)
Reaction of a dithioester with ethylmagnesium iodide results in addition to the C1S bond "Scheme 35# ð68JA3621Ł[ S
EtMgI
R R
SEt
SEt MgI SEt
Scheme 46
A variety of metallated 0\2!dithianes and related species can be prepared from the 1!lithio intermediate by metal exchange[ Thus\ the tris"isopropoxy#titanium derivative "152# can be formed by reaction with tris"isopropoxy#titanium chloride ð70HCA246Ł[ In a similar manner\ trialkyltin or triaryltin derivatives can be obtained from 1!lithio!0\2!dithianes and !0\2\4!trithianes by reaction with the appropriate trialkyltin chlorides or triaryltin chlorides ð64ZAAC"307#197\ 68PS"6#192\ 75JOM"292#078Ł[ Alternative routes to functions with two sulfur and one trialkyltin substituent are exempli_ed by the alkylation of 1!lithio!1!tributylstannyl!0\2!dithiane ð78TL04\ 89JA3441\ 81CJC1224Ł
S Ti(OPri)3 S (263)
024
Chalco`en and a Metal
and by the conjugate addition of the intermediate "153# to cyclohexenone with the option of alkylation of the generated lithium enolate "Equation "24## ð64AG26\ 66CB730Ł[ MeS MeS
O
SMe Li SnMe3 SMe (264)
RX
+
Me3Sn
R O
(35)
5[93[2[1[2 Functions bearing sulfur\ boron and a metal a!"Phenylthio#alkylboronate esters such as "154# have been demonstrated to undergo lithiation with LDA "Equation "25## ð67JA0214Ł[
O
O
LDA
B O
B O Li
SPh
(36)
SPh
(265)
5[93[2[1[3 Functions bearing sulfur\ silicon and a metal a!"Trimethylsilyl#methyl sul_des and sulfones are readily metallated at the methylene group by butyllithium ð75JCS"P0#084Ł[ Subsequent exchange reactions have been used to produce trialkyltin derivatives such as "155# ð75JCS"P0#084Ł and copper derivatives ð75JOC2872Ł[ An alternative route to lithiated species is the addition of alkyllithium reagents to vinylsilanes^ thus\ the intermediate "156# is produced from H1C1C"SPh#!TMS and methyllithium ð75JCS"P0#084Ł[ Multinuclear NMR studies have demonstrated the conformational stability of the species "157# in etherÐTHF mixtures due to ion pairing[ Addition of greater than three equivalents of HMPA causes a degree of racemisation to occur ð82AG"E#0358Ł[ SnBu3 Li PhS
TMS (266)
SPh Et TMS (267)
H PhS
Li SiMe2Ph (268)
5[93[2[1[4 Functions bearing sulfur and two metals Two tributyltin functions can be introduced on to a methylene group a! to a sulfone group by lithiation and reaction with tributyltin chloride ð81CC769Ł[
5[93[2[2 Functions Bearing Selenium and a Metal 5[93[2[2[0 Functions bearing selenium\ sulfur and a metal LDA will lithiate "phenylthio#"phenylseleno#methane ð89JA4598Ł[
5[93[2[2[1 Functions bearing two seleniums and a metal Bis"phenylseleno#methane can be lithiated with the hindered base LITMP and HMPA as a cosolvent ð68JOM"066#0Ł[ As an alternative\ reaction of tris"methylseleno#methane with n!butyl! lithium results in replacement of one methylseleno group by lithium ð68TL2264Ł[
025
Chalco`en and Any Other Heteroatoms
5[93[2[2[2 Functions bearing selenium\ phosphorus and a metal Treatment of the a!"phenylseleno#methylphosphonate "EtO#1POCH1SePh with n!butyllithium results in lithiation at the methylene group ð76S058Ł[
5[93[2[2[3 Functions bearing selenium\ silicon and a metal Lithium derivatives can be generated by hydrogenÐlithium exchange\ as in the generation of the species "158# from the corresponding allyl"phenylseleno#silane and lithium diethylamide ð64JOC1469Ł or by exchange of a phenylseleno function for lithium\ as in the generation of the intermediate "169# from "160# and n!butyllithium "Scheme 36# ð67JOM"038#C09Ł[ PhSe
LiNEt2
PhSe Li
TMS
TMS
(269) SePh SePh TMS
BuLi
(271)
SePh Li TMS (270)
Scheme 47
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.05 Functions Containing at Least One Group 15 Element (and No Halogen or Chalcogen) DAVID P. J. PEARSON ZENECA Agrochemicals, Bracknell, UK 5[94[0 FUNCTIONS CONTAINING THREE GROUP 04 ELEMENTS 5[94[0[0 Functions Bearin` Three Nitro`en Atoms 5[94[0[0[0 0\0\0!Triaminoalkanes 5[94[0[0[1 0\0\0!Trinitroalkanes 5[94[0[0[2 Mixed nitro and other functions 5[94[0[1 Functions Bearin` Three Phosphorus Atoms 5[94[0[1[0 Introduction 5[94[0[1[1 Functions bearin` tri! or pentavalent phosphorus 5[94[0[1[2 Functions bearin` heptavalent phosphorus 5[94[0[2 Functions Bearin` Three Arsenic Atoms 5[94[0[3 Functions Bearin` Three Antimony or Bismuth Atoms 5[94[0[4 Functions Bearin` Nitro`en and Other Group 04 Elements 5[94[0[4[0 Functions bearin` two nitro`en atoms and one phosphorus atom 5[94[0[4[1 Functions bearin` two phosphorus atoms and one nitro`en atom 5[94[0[4[2 Functions bearin` nitro`en and other `roup 04 elements 5[94[1 FUNCTIONS CONTAINING GROUP 04 ELEMENTS WITH METALLOIDS 5[94[1[0 Functions Bearin` Group 04 Elements and Silicon 5[94[1[0[0 Functions bearin` nitro`en and silicon 5[94[1[0[1 Functions bearin` phosphorus and silicon 5[94[1[0[2 Functions bearin` nitro`en\ phosphorus and silicon 5[94[1[0[3 Functions bearin` arsenic\ antimony or bismuth 5[94[1[1 Functions Bearin` Group 04 Elements and Boron 5[94[1[2 Functions Bearin` Group 04 Elements and Germanium 5[94[2 FUNCTIONS CONTAINING GROUP 04 AND METAL ELEMENTS\ AND POSSIBLY A METALLOID
026 026 026 032 040 040 040 040 043 044 045 045 045 046 050 051 051 051 052 057 057 058 058 069
5[94[0 FUNCTIONS CONTAINING THREE GROUP 04 ELEMENTS 5[94[0[0 Functions Bearing Three Nitrogen Atoms 5[94[0[0[0 0\0\0!Triaminoalkanes "i# Introduction Methods for the formation of compounds of general structure "0#\ commonly known as ortho! amides\ have been reviewed\ most recently bySimchen\ who has written two accounts ðB!63MI 594!91Ł 026
At Least One Group 04 Element
027
and ð74HOU"E4#2Ł\ but also by deWolfe ðB!69MI 594!92Ł and Kantlehner ðB!68MI 594!90Ł[ Each of these reviews is part of a more general treatment of ortho!acid derivatives but gives extensive references to their preparation[ R2
N
R1
R3 R4 N
R7
N
R5 R6
(1)
As expected\ compounds of this type are moderate to strong bases "unless the nitrogen atoms are acylated# and dissociate to a signi_cant degree in solution as evidenced by the conductivity measurements of Bredereck ð58MI 594!90Ł "quoted in ðB!68MI 594!90Ł#[ This gives rise to their pro! pensity for elimination\ displacement and disproportionation reactions\ as shown in Scheme 0 ð57CB40Ł\ and explains why examples from carboxylic acids higher than formic are relatively rare\ why the amines involved are generally fully substituted and why the most common structural type has three identically substituted nitrogen atoms[ R2
N
R4
R1
N
N+
R1
N
R7 R2
R2
R3
N
R5
R5
R6
N
–NR6R7
R3
R4 R4
R3 R4
N
R1
N R1 R5 N R6 R7
R7
N
R5
+ HNR2R3
R6
Scheme 1
This functional group occurs in some natural products\ e[g[\ oxaline "1# ð65T1514\ 79CPB1876Ł and dibromoagelaspongin "2# ð78T2376Ł[ Br
OMe
Br O N MeO
H N
HN
N
N
HN
N H
O (2)
N
NH
N
O
HO (3)
"ii# Preparation "a# From amidinium salts[ Formamidinium salts are reported by a number of authors to undergo reaction with secondary amines or their metal salts "Scheme 1#[ For example\ the sodium salts of N!methylanilines react with a salt "3# to give the ortho!amides "4# in modest yield ð51JOC2553Ł[ Lithium dialkylamides have been similarly used ð55AG"E#021Ł and this method was applied to the preparation of unsymmetrical examples such as "5# ð57CB0774Ł[ Potassium t!butoxide has been employed as the base in a similar synthesis ð57CB2947Ł^ in this instance the reaction may occur by the initial addition of the alkoxide moiety[ The unusual displacement of cyanide in Structure "6# is presumed to occur via the intermediacy of an amidinium salt "7# ð68S231Ł[ "b# From other amide salts[ The Vilsmeier reagent "8# reacts with the potassium salts of saccharin and phthalimide to give the unsymmetrically substituted adducts "09# ð50CB2098Ł[ Bredereck et al[ report the alkylation of N\N!diethylformamide "00# and its subsequent reaction with diethylamine to give "01# in low yield ð57CB2947Ł[ In previous studies by the same group triformamidomethane "03# was constructed from formamide via similar intermediates "02# "Scheme 2# and a comparison
Three Group 04 Elements Ar Me
N
Ar
+
N
028
ArNHMe, NaH
Me I–
Me
Ar = Ph 44%
(4)
Ar
Ar
N
N N
Me
Me
Ar
(5) Me Me Me Me
N
LiNMe2, Et2O –20 °C
Me
+
N
N
Me Me
N
N
Me
Me
63%
Me Cl–
LiNEt2, Et2O
Et
42%
Me
Et
N
Me
N
N
Me Me (6)
Me
Me
Me
N
N
Me Me
Me Me
N
Me
+
N
N (7)
LiNMe2
Me
–CN
Me
73%
N
Me Me
N
N
Me
Me
(8) Scheme 2
was made of various alkylating and acylating agents ð48CB218Ł[ When dialkyl sulfates were used the yield increased with the bulk of the alkyl group\ perhaps re~ecting the ease of the subsequent displacement step[ O
O
Me
NK
+
Cl
X
N
X
CHCl3, 20 °C
+
Me
Cl–
X = CO, 46% X = SO2, 24%
(9)
X
N
N O
N
Me
Me (10)
Et
Et O
N
Me2SO4
Me
Et
O
N
Et2NH
+
MeSO4–
Et
Et
N
Et
Et
Et
(12) H
NH2
Et N
20 °C
(11)
O
Et N
Me2SO4
Me
O
N
+
H
MeSO4–
HCONH2
O
H
H
N
N N
36%
O
H
O (13)
(14)
Scheme 3
"c# From `uanidines and their salts[ Weingarten ð57T1656Ł described the displacement of a single dimethylamino group from the tetramine "04# by heating it with phenylacetylene[ In the early 0889s\ Kantlehner et al[ used the sodium salt of alkyne to achieve a similar reaction with hexa! methylguanidinium chloride] the monoadduct "05# giving rise to a proportion of the interesting 1 ] 0 adduct "06# on distillation ð89CZ065Ł[ This latter material could be more conveniently prepared
At Least One Group 04 Element
039
directly by bubbling alkyne through a mixture of the other reagents[ The reaction of the same guanidinium salt with phenyllithium gave a reasonable yield of the triamine "07# ð60JOC1774Ł[ Kantlehner et al[ have also published a route to triaminomethanes "08# by mixed hydride reduction of guanidinium salts ð72S894Ł^ in this case the yield steadily declines with the increasing size of substituents on nitrogen\ perhaps re~ecting the stability of the products[ The alkyltitanium complex "19# has been found to insert into tetramethylguanidine "10# to give the cyclic triamine complex "11# in very high yield "Scheme 3# ð77BCJ060Ł[
Ph
C(NMe2)4 88%
(15)
Ph
NMe2 NMe2 NMe2 (18)
NMe2 NMe2 NMe2
heat
+
Ph
PhLi, Et2O
Me2N
NMe2 + NMe
52%
2
NMe2 NMe2 NMe2 (16)
HC CNa , THF 57%
Cl–
NaH,HC CH
∆, distil 20%
76%
NMe2 NMe2 NMe2
Me2N Me2N Me2N (17) R2 N
NR2 + NR
2
NR2
NaH2[Al(OCH2CH2OMe)2]
Cl–
NR2
R2 N
33–55 %
(19) Me2N
Ph
+
Cp2Ti Ph (20)
Me2N
NMe2 NH (21)
NMe2
HN 92%
Cp2Ti
Ph Ph (22)
Scheme 4
"d# From ortho!acid derivatives[ The _rst reported synthesis of this type came from Bredereck et al[ who prepared triformamidomethane "03# by treating triethyl ortho!formate with formamide in the presence of an acid catalyst "Scheme 4# ð48CB218Ł[ Follow!up studies were made in which the nature of the amide was varied and\ by controlling the stoichiometry of the reaction together with the use of toluene as solvent\ the yields were signi_cantly improved ð59CB0287\ 52CB0494Ł[ The formyl groups in "03# could be exchanged for other acyl derivatives to give "12# by reaction with an appropriate acid anhydride ð59CB0287Ł[ Urethane has been used in this context with high yields of the tricarbamate "13# reported ð56ZOR0638Ł[ Triethyl ortho!formate will also react with N!methylaniline to give the product "4# "Scheme 5# in moderate yield ð51JOC2553Ł[ Triethoxyacetonitrile "14# reacts with pyrrolidine among other amines to give the unusual nitrile "15# ð68GEP1713917Ł[ Heating diaminoalkoxymethanes of type "16# gives rise to disproportionation to amide acetals "17# and triaminomethanes "08# "Scheme 6# ð57CB40Ł[ Dithioacetals such as "29# react with suc! cinimide "18# to give the substitution products "20# ð54IZV1068Ł^ phthalimide behaves similarly[ Weisman et al[ synthesised the interesting tricyclic examples "23# by reaction of formamide or acetamide acetal "21# with macrocyclic triamines "22# ð70TL3254Ł[ They found that acetals such as "21# were preferable to simple ortho!esters[ Triazaadamantane "25# was made by condensation of triethyl orthoformate with cyclohexanetriamine "24# "Scheme 7# ð62CB1412Ł[ "e# From alkyl halides[ Clemens et al[ prepared triamines "4# by treating the sodium salts of N! alkylanilines with trihalomethanes ð51JOC2553Ł^ for this conversion di~uorochloromethane was better than either chloroform or dichloro~uoromethane[ This reaction may well proceed through a carbene intermediate and in support of this the pyrolysis of sodium trichloroacetate in the presence of such anilines gave "4# in modest yields "Scheme 8#[ Similar chemistry has been successful using a
Three Group 04 Elements
030
O HN
HCONH2, H+ 32%
EtO
R
O H N
HN
(RCO)2O, ∆
HN
O
NH
O
O
OEt
H N
R O
R
(14)
(23)
OEt OEt
O
H N
HN
H2NCO2Et
OEt
90%
NH
O
O
OEt (24) Scheme 5
EtO
OEt
PhNHMe, ∆
Me
Ph
Ph
N
N
57%
OEt
Me
N
Me
Ph
(5)
OEt OEt OEt
N
N
Et2O, ∆
+
N N H
N
57%
N
(25) (26) Scheme 6
2
R 2N
R 2N
NR2 OR (27)
N H (29)
O
SEt
+ SEt
NR2
+ NR2
OR (28)
Me2N O
R2 N
OR
50%
(19)
O Me2N
O O
N N
(30) O (31) Scheme 7
pyrazole as the amine component ð65S687\ 68LA0345Ł although 0\1\3!triazoles ð58JCS"C#1140Ł and indazoles ð68LA0345Ł gave very poor yields[ "f# From titanium salts[ Tetrakis"dimethylamino#titanium "26# reacts with DMF in ether to give a high yield of triaminomethane "27#\ whereas the corresponding acetamide derivative gave the diaminoethylene "28# ð55JA749\ 55JOC1763Ł[ Similarly\ oxamide "39# gave the same product "27# although no yield was reported "Scheme 09# ð57JOC0135Ł[ "`# Addition to polyaminoethenes[ Tetraaminoethenes "30# react with lactams and imides to give the cyclic triamines "31# ð64CB104Ł^ this type of reaction is covered in a review of similar chemistry ð61AG"E#853Ł[ Exomethylene triazinediones "32# have been shown to combine with some substituted
At Least One Group 04 Element
031
(CH2)p MeO
R
OMe
+
NMe2
(CH2)p
NH HN H N
(CH2)n
(32)
(CH2)m
(CH2)n
(33)
N
N (CH2)m
(34) R
NHR NHR NHR
R
N
43–89%
HC(OEt)3, ∆
R N
N R
N
27–31%
(35)
(36) Scheme 8
CHClF2, NaH Ar = Ph 58%
H Ar
N
Me
Me
Cl3CCO2Na, ∆
Ar
Ar
N
N
Me
N
Me
Ar
(5)
20%
Scheme 9
(Me2NCO)2 (40) Me2NH
Me2N
NMe2
Ti(NMe2)4 (37)
NMe2 (38)
HCONMe2 Et2O 83%
NMe2 Ti(NMe2)4 + MeCONMe2
87%
(37)
NMe2 (39)
Scheme 10
hydrazines by reaction at the ring carbon giving products such as Structure "33# "Scheme 00# ð64CR"C#452Ł[ Ph Ph
Ph
N
N
+
HN
(CH2)n
N 67–91%
N
N
N
toluene, ∆
N
O
Ph Ph
(CH2)n
Ph O (42)
(41) H R O
N
N N
R
R H2NNMe2
O
O
R (43)
N NMe2 R N
N N
O
R (44) Scheme 11
"h# Heterocyclisation reactions[ In an attempt to prepare an oxazoline "35# by pyrolysis of hydroxyethylamide "34#\ Slusarczuk and Joullie obtained the tricyclic compound "36# in modest yield ð69CC358Ł[ The bis"amide# "37# is reported to extrude one molecule of benzimidazole on
Three Group 04 Elements
032
sublimation giving triamine "38# ð66JCS"P0#0051Ł\ and in a similar transformation\ the acylation of diamide "49# with chloroacetyl chloride gave the tetracycle "40# in high yield "Scheme 01# ð70JOC0460Ł[ N
F3 C O (46)
O F3C
∆
OH
N H
N
30%
(45)
CF3
N N (47)
N
N N
O
O
O
N
∆, sublime
H N
N
N
92%
N O (49)
(48)
O H 2N
O
O H N
NH2
Cl
Cl
NH
O 83%
N
Cl NH O
(50)
(51) Scheme 12
"i# Radical methods[ The dimerisation of triarylimidazoles by treatment with potassium fer! ricyanide under appropriate conditions gave the photochromic dimers "41# among other products "Scheme 02# ð55JA2714\ 60JOC1151Ł[ Treatment of acetonitrile with the N!bromosuccinimide complex "42# gave the trisubstituted acetonitrile "43# ð77ACS"B#555Ł^ other aminoacetonitrile derivatives "44# and "45# gave better yields of similar products[ "j# From other triamines[ As part of a wider study\ Katritzky et al[ have trapped the anion of tris"benzotriazolyl#methane "46# with a variety of electrophiles such as alkyl halides and alkyl chloroformates "Scheme 03# ð89S555Ł[ "k# From isocyanates[ Working independently\ two research groups have found that DMF reacts with phenyl isocyanate to give the bicyclic triamine "47# ð57JOC2817\ 57JOC2820Ł[ According to the latter report this product was also obtained from amidine "48#[ Since then a number of similar reactions have been described] among other similar substrates\ lactams ð62JOC1503Ł\ amidines ð57CB2991\ 58CB820Ł\ amidinium salts ð60LA"640#034\ 79HCA0847\ 71CB0610Ł\ tetraaminoethylenes ð60LA"637#0\ 63CB0820Ł and 0\0!diaminoethylenes ð66CR"C#210Ł have all been utilised in place of DMF "Scheme 04#[ Thiocyanates also reacted similarly ð64CB0031Ł[ The cyclic selenourea "59# has been used as a source of the carbene "50# "which can also be formulated as an amidinium ylide# ð72CB1957Ł^ this reacts with phenyl isocyanate to a}ord the product "51#[ Reduction of isocyanates in situ has been used to provide the source of the spiro carbon atom in "52# ð74CB2848Ł[
5[94[0[0[1 0\0\0!Trinitroalkanes "i# Introduction Much work has been done in this area of chemistry but the special advantages o}ered by these materials in the _eld of propellants and explosives represent a signi_cant hazard in the hands of the
At Least One Group 04 Element
033
Ar
K3Fe(CN)6
Ar
N
(52)
Bu4N+
Br N
Ar Ar
N Ar
Ar
N
N
Ar
43–95%
Ar
O
N
Ar
H N
O
O
N–
O
MeCN
O
22%
O
N
O
O N
N CN
O
O (54)
(53) O
O
N
N CN
CN
O (55)
O (56) Scheme 13
N
N
N
N N
N N N N
N N N
(57)
i, ii 58–98%
N N E N
N N N
i, BuLi, THF; ii, EX E = PhCH2, CO2Et, Bun inter alia Scheme 14
unwary[ Several reviews have been published\ the most recent being in the Patai series ðB!69MI 594! 91Ł^ others cover more general aspects of nitroalkane chemistry as well as their synthesis ð48UK373\ 52T"S#044\ 52T"S#066\ 53CRV08\ 55UK0639Ł[ The presence of three strongly electron!withdrawing nitro groups attached to a single carbon atom has a profound in~uence on the chemistry of such compounds and even though not all the nitro groups are coplanar\ they are still prone to elimination and substitution reactions as well as rendering b!heteroatoms virtually non!basic[
"ii# Preparation There are two fundamental approaches to the synthesis of such compounds] the introduction of an intact trinitromethyl group "most commonly as a nucleophile but also as a radical# and the stepwise introduction of the required nitro groups[ "a# Addition of an intact trinitromethyl `roup[ The trinitromethyl anion adds readily to Michael acceptors as shown in Equation "0#[ Such reactions are typically carried out in protic solvents and in the absence of added base which can give rise to complicating by!products[ Kaplan and Kamlet report that for addition to acrylates the optimum pH is around 2[4 ð51JOC679Ł[ Addition occurs to unsaturated ketones ð57JOC0136Ł\ aldehydes ð57JCED326Ł\ phosphonates ð67MI 594!90Ł\ oximes
Three Group 04 Elements
034 O N Ph N Ph N
96%
Ph N
53%
O
N
Me
N
Se
O
(58)
(59) Ph
O Ph
N
Ph
N
Me
Ph
140–150 °C
HCONMe2 + PhCNO
Ph
Ph
Ph O
N
N+
PhNCO
N
47%
N
N
:
–
N
Ph (60)
Ph N
N Ph
Ph
N
O
Ph Ph (62)
(61) R
O N [HRu3(CO)10(SiEt2)]N(PPh3)2, Et3SiH
RNCO
22–69%
R N R N O
N N
O R O
R (63) Scheme 15
ð79MI 594!91Ł\ lactones ð75JHC70Ł and to acrylonitrile ð60ZOR29Ł[ However\ according to Kaplan\ addition to symmetrically disubstituted Michael acceptors does not occur ðB!69MI 594!91Ł[ O2N
NO2
+ NO2
EWG
O2N O2N
NO2 (1) EWG
EWG = CO2R, CHO, COR, PO(OR)2, CHNOH, CN
A detailed study of the alkylation of the silver salt of trinitromethane has been made ð52T"S#066Ł\ and although this method worked well for simple alkyl\ allyl and benzyl groups it failed for other electrophiles such as haloacetates[ One particular complication is the occurrence of competing O! alkylation ð57IZV336\ 66IZV025Ł[ Nevertheless\ variations on this method\ including the use of other salts\ have allowed reactions to occur with diiodomethane ð60ZOR0293Ł\ 0!bromoadamantane ð65KFZ24Ł\ a!chloroamines ð70IZV1035Ł\ ferrocene derivatives ð75ZOR0282Ł\ triazolyl diazonium salts ð61KGS602Ł and a!chloroethers ð89SC2292Ł as illustrated in Scheme 05[ At the beginning of the 0889s\ a study of the phase transfer catalysed methylation of the potassium salt of trinitromethane was published ð89IZV0705Ł in which the addition of a crown ether or polythylene glycols was shown to be advantageous[ This salt has also been used to substitute the pyridinium salt "53# in modest yields ð72IZV1544\ 89TL6268Ł[ Iodotrinitromethane and tetranitromethane are methylated in dipolar aprotic solvents "see Scheme 06# either via intermediate solvent alkylated species or perhaps through preliminary homo! lytic dissociation ð69ZOR078\ 63ZOR1992Ł[ Trinitromethane is methylated by diazomethane ð69IZV837Ł[ Diazo compounds such as "54# insert into bromo! or iodotrinitromethane to give trinitro derivatives "55# ð60ZOR0015\ 66ZOR0448Ł[ Tri! and tetranitromethane react with other nitroalkanes to give trinitromethyl derivatives such as "56# ð62IZV011Ł and "57# ð56USP2205200Ł\ and\ in the presence of a silylating agent\ with "58# to give ethers of "69# "Scheme 07# ð78MI 594!90Ł[ Shechter and Cates\ Jr[ found that trinitromethane reacted with enol ethers "60# at the oxygen! bearing carbon to give "61# ð50JOC40Ł^ this reaction is also reported for enol acetates in alcoholic solvents giving products of type "62# "Scheme 08# ð58IZV1455Ł[ Trinitromethane reacts with formaldehyde to give alcohol "63# ð49JA4218\ 59JOC1958Ł[ In the
At Least One Group 04 Element
035 O2N
NO2
O2N
O2N
NO2
NO2
NO2
O2N
+
O2N
Ag
+
N
O2N
R
R2N
R
OR
O–
R N
O 2N
RX
O2N
Cl
NO2 NO2
RBr, AgO benzene
Et3N
44%
53–75%
NO2 RO
O2N
I
NO2 Ag, salt, CH2I2 Et2O
CH2Cl2/DMF 14–61%
O2N
35%
HetN2+
NO2
O2N
OR
O2N
NO2 I
O2N N N R
NO2 NO2 NO2
N H
NO2 NO2
O2N KC(NO2)3
N
N
+
F X– (64)
H2O MeCN
N
41% 7%
7% 21%
Scheme 16
X
NO2 NO2 NO2
DMSO or DMF MeI X = NO2, 64% X = I, 90%
NO2 NO2 NO2
NO2 O2N NO2 dioxan 51%
CH2N2
NO2 Br
N2
CO2Et
NO2
Br
NO2 NO2 NO2
67%
CO2Et (66)
(65) Scheme 17
NO2 NO2 NO2
Three Group 04 Elements
036
NO2 O2N
NO2
NO2 water, ∆
NO2
O
32%
O
NO2 NO2 NO2 (67)
O2N
NO2 NO2 , base NO2
NO2 NO2 NO2
NO2
(68)
NO2
O
+
TMS-I, Cl –78 °C
Cl
O2N
O2N
O
O2N
65%
NO2
O
OH
NO2
(69)
(70) Scheme 18
NO2 O2N NO2
dioxan
R
OR
OR NO2
R
50–81%
(71)
NO2 NO2 (72)
NO2 O2N
OAc
NO2 ROH, ∆ 28–76%
OR NO2 NO2 NO2 (73)
Scheme 19
presence of amines such as "64# ð51JOC0344Ł and using hydroxymethylamides "65# ð50JOC280Ł\ the Mannich reaction occurs[ In the mid 0879s\ silylaminal "66# has been shown to react with silylated trinitromethane "67# under non!aqueous conditions to give amine "68# ð74IZV1524Ł[ Similar additions to higher aldehydes and ketones are reversible "Scheme 19# ð59JOC1958Ł[ Trinitromethane has also been reported to add to preformed imines such as "79# and "70#\ in these cases in halocarbon solvents ð57IZV1268\ 58IZV1298Ł[ Polynitromethanes have been added to various substrates via a radical mechanism to provide trinitromethane derivatives[ Tetranitromethane is reported to form charge transfer complexes with electron!rich aromatics such as anthracene^ subsequent photolysis can give rise to trinitroarenes "71# "Equation "1## ð74JOC4134Ł[ Other aromatic systems can lead to products such as "72# ð75RTC167Ł and "73# ð79MI 594!90Ł[ Products such as those of direct nitration may also be formed and the exact course of the reaction can be di.cult to predict ð75RTC167Ł[ O2N
NO2 NO2
C(NO2)4 hν >500 nm, CH2Cl2
(2)
16–93%
X
X NO2 (82)
Tetranitromethane will add across alkenes such as "74# ð58ZOR1135Ł and "75# ð75RTC175Ł and in
At Least One Group 04 Element
037 O2N
NO2
CH2O
NO2
O2N
NO2 OH
O2N (74) HC(NO2)3, aq. CH2O
NH2
HO
34%
(75) H N
HO H N
HC(NO2)3, H2O
OH
O2N
H N
NO2
O2N
R
O –O
N
O-TMS
+
R
O2N (77)
NO2
O2N
+
N
O-TMS
R O2N R
NO2 (78)
76%
NO2
NO2 (79)
HC(NO2)3, CHCl3
N
NO2
N
NO2
H N
NO2 NO2
87%
O (76)
NO2
O2N
H N
NO2
N H
O2N
NO2
NO2
(80) O2N
NO2 NO2
HC(NO2)3, CCl4
N
73%
N H
(81) Scheme 20
OMe NO2 NO2
NO2
NO2
NO2 NO2
(84)
(83)
such cases light is not always required "Scheme 10#[ Insertion into a C0H bond of THF a}orded "56# ð62IZV0038Ł^ a similar reaction occured with iodotrinitromethane "Scheme 11# ð61IZV389Ł[ O2N C(NO2)4
MeO
NO2 NO2
MeO
80%
NO2
(85)
C(NO2)4
N
40%
N O2N
(86) Scheme 21
NO2
O 2N NO2
Three Group 04 Elements
C(NO2)4
+ O
35%
THF, ∆ X = H, NO2, I
NO2 O
038
NO2 NO2 (67)
30–50%
+
OR
O
X
NO2 NO2 NO2
Scheme 22
Electrolysis of salts of trinitromethane as shown in Scheme 12 leads to radicals which react with cyclic ethers ð61IZV1592Ł or with toluene ð61IZV0606Ł and other aromatic systems ð71IZV1526Ł[ M+
–
NO2 NO2 NO2
e–, toluene
NO2 NO2
e–, PhR 3–25%
e–, THF
NO2 NO2
NO2
NO2
R
O
NO2
NO2 NO2 (67)
Scheme 23
The mercury salt "76# has been shown to add across the double bonds of allyl alcohol ð51IZV161Ł\ methyl acrylate ð58IZV0734Ł and vinyltrimethylsilane "Scheme 13# ð62RZC0132Ł[ TMS
OH
NO2 NO2
R Hg
Hg(C(NO2)3)2 (87)
NO2
R O2N CO2Me
NO2 NO2
Scheme 24
Trinitroacetonitrile undergoes cycloaddition reactions with TMS azide\ diazo compounds and nitrile oxides to give trinitromethyl!substituted tetrazoles "77# ð70JHC0366Ł\ 0\1\2!triazoles "78# ð76ZOR1513\ 77ZOR533Ł and 0\1\3!oxadiazoles "89# ð75ZOR1507Ł respectively[
O2N O2N
O2N O2N
NO2
NO2 N
N N
R
N
N
N NO2
N O
N H (88)
Ar
N
NO2 NO2
R (89)
(90)
There have been many reports of the cycloaddition of trinitromethane derivatives with alkenes "Equation "2## to give products of type "80#[ Tetranitromethane has been shown to react directly with cyclohexene ð56ACS"C#0281Ł\ ethylene ð55ZOR0891Ł\ vinyl ethers ð58ZOR119Ł and butadiene ð58ZOR0202Ł[ Bromo! and iodotrinitromethane have taken part in similar reactions ð56ZOB0052\ 57IZV510\ 62ZOR158Ł[ Trinitromethane can be O!silylated ð62ZOR785Ł and the resulting adduct reacts with styrene to a}ord "81#[ O!methylation with diazomethane followed by reaction with butadiene yields "82# "Scheme 14# ð57ZOR120Ł[
At Least One Group 04 Element
049 R
XC(NO2)3
R
X
NO2
O2N
N
R
O
O
X = Br, I, NO2
R
(3)
R
R (91)
O2N TMS-Cl
O2N
TMS-O
NO2 NO2
O2N
NO2 N+
styrene
NO2
94%
O–
Ph
CH2N2
O2N MeO
O2N
NO2 N+
N O-TMS O (92)
butadiene
NO2
70%
O–
N O
OMe
(93) Scheme 25
"b# Successive nitration reactions[ The trinitromethyl group has been assembled by successive nitration from various starting materials[ For example\ trinitromethane itself can be made on a commercial scale by treatment of acetylene with concentrated nitric acid in 63) yield ð52T"S#044Ł[ Cyanoacetic acid has been converted to trinitroacetonitrile in good yield using a mixture of nitric acid and sulfur trioxide ð51T68Ł[ Nitrile oxides "83# react with dinitrogen tetroxide to give aryl derivatives "84# "Equation "3## ð89IZV0519\ 89IZV0512Ł[ Oximes have been converted to either di! ð77BCJ1816Ł or trinitromethanes ð59IZV0672\ 69KGS489Ł using nitrogen dioxide[ N2O4, CH2Cl2
+
N O–
Ar
Ar 45–79%
(94)
NO2 NO2 NO2 (95)
(4)
Dinitromethanes may be prepared as precursors to their trinitro counterparts^ Kaplan and Shechter used silver nitrate:sodium nitrite on the silver nitronates "85# ð50JA2424Ł[ Less conveniently\ chloronitromethanes can be nitrated ð53CRV08Ł and tetranitromethane treatment of nitroalkanes has also been used ð50USP1880204\ 56USP2205200Ł[ Other reagents have been used for the further nitration of dinitro analogues\ e[g[\ nitryl ~uoride "86# ð60IZV0483Ł[ Tri~uoroacetic anhydride "TFAA# and nitric acid react with dinitroalkenes such as "87# but less successfully with mononitro analogues such as "88# "Scheme 15# ð81JOC2915Ł[
+
N
O–
O– (96)
Ag+
AgNO3, NaNO2, NaOH Et2O, 0–5 °C
FNO2 (97) MeCN
MeCH(NO2)2 78%
H N
NO2
N H
NO2 (98)
89% TFAA, CH2Cl2 90% HNO3
H N
22%
N H
MeC(NO2)3 43–67%
NO2 (99) Scheme 26
H N N H
NO2 NO2 NO2
Three Group 04 Elements
040
5[94[0[0[2 Mixed nitro and other functions One nitro group in trinitroethane has been displaced by azide in DMF as shown in Scheme 16 ð73BRP1012718Ł[ The same product was obtained by electrolysis of the sodium salt of dinitroethane in dilute sodium azide ð64USP2772266Ł and other examples have been similarly prepared ð89MI 594! 90Ł[ NO2 NO2 NO2
NO2 N3 NO2
NaN3, DMF 28%
aq. NaN3, e–
NO2 NO2
Scheme 27
5[94[0[1 Functions Bearing Three Phosphorus Atoms 5[94[0[1[0 Introduction Functional groups of this type fall into two main classes] those with tri! or pentavalent phosphorus which are predominantly used as ligands in organometallic chemistry "e[g[\ ð81OM15Ł#\ and tris "phosphonato#methanes which have been used as surfactants "e[g[\ ð66USP3919980Ł#[
5[94[0[1[1 Functions bearing tri! or pentavalent phosphorus "i# From functions bearin` two phosphorus `roups The method _rst reported by Issleib and Abicht for the reaction of methylenebisphosphines with a chlorophosphine has been subsequently much utilised to prepare ligands for organometallic complexes "Scheme 17# ð69JPR345Ł[ The original workers described the reaction of lithium salts of bisphosphine "099# and its corresponding bisphosphine oxide "090# with diphenylphosphinyl chloride to form tris"phosphino#methanes in good yields[ Karsch et al[ extended the work to include alkyl substituents\ preparing methylphosphines "091# ð68AG"E#373\ 68ZN"B#0060Ł[ Grim and Walton report phosphine sul_des "092# made by the same basic method ð79PS"8#012Ł^ the paper contains no experimental details even though a report from the same group mentions the preparation of asymmetric tris"phosphino#methane "093# ð75IC1588Ł[ In this case\ the reaction was carried out on transition metal carbonyl complexes of the carbanion of bis"phosphino#methane "094# to improve the chemoselectivity ð71CC175Ł[
"ii# By further reaction of tris"phosphino#methanes Tris"phosphino#methanes have been modi_ed at phosphorus to produce a number of oxides\ sul_des and selenides in various combinations[ The _rst report was by Issleib and Abicht ð69JPR"201#345Ł who converted tris"diphenylphosphino#methane "095# into its trisul_de "096# by heating with sulfur[ This method ð71CB707Ł failed to produce the alkyl analogue "097# which could\ however\ be prepared from a bis"thiophosphinoyl#methane by the standard method "Scheme 18#[ Grim et al[ report the modi_cation of a variety of tris"phosphino#methanes] the mild oxidation of phosphine "095# to phosphine oxide "098# avoids the cleavage of one of the carbonÐphosphorus bonds which occurs under harsher conditions ð75IC1588Ł[ This method was then applied to a number of phosphine sul_des and selenides[ Red selenium was also used to convert phosphine sul_de "009# into "000# although an earlier paper mentions that carbonÐphosphorus bond cleavage occurred in similar reactions ð79PS"8#012Ł[ Grim also reports that salts of phosphines react more readily with selenium because of a reduction in steric crowding ð76PS"27#68Ł[ The functionalisation of phosphorus in metal carbonyl complexes by oxidation using either hydrogen peroxide or sulfur has been claimed although no details are given ð71CC175Ł[ The phosphine imine "001# was prepared in excellent yield by reaction of phosphine "009# with p!tolyl azide "Scheme 29# ð80CC868Ł[ Karsch et al[ describe the methylation of the lithium salt of tris"dimethylphosphino#methane
At Least One Group 04 Element
041
Li
BuLi
Ph2P
PPh2
Ph2P
86%
(100)
PPh2
Ph2PCl
PPh2
Ph2P
61%
PPh2
PPh2 Ph2P
i, BuLi ii, Ph2PCl
PPh2
R12P
Ph2P
73%
O O (101)
i, BuLi ii, R32PCl
PR22
PPh2
O
O
PR32 R12P (102)
S
i, Ph2PSCH2Li ii, Ph2PCl
S Ph2P
Li
PR22
R1, R2, R3 = Ph, Me
Ph2PCl
Ph2P
PPh2
S Ph2P
PPh2 PPh2
(103) O
S
Ph2P
PPh2
O
i, BuLi ii, Ph2PCl
S
Ph2P
PPh2 PPh2 (104)
PPh2 (CO)4M
–
PPh2
M = Cr, W, Mo
(105) Scheme 28
PPh2
S8, C6H6
Ph2P
56%
PPh2
Ph2P
Me2P
PMe2
S PPh2
S S (107)
(106) PMe2
Ph2P
Me2P
S
S8
Me2P
PMe2
i, ButLi ii, Me2PSCl 41%
Me2P S
PMe2 S
S S (108) Scheme 29
"002#] using low temperatures and ether solvents alkylation occurs at carbon to give "003# whereas in pentane with TMEDA alkylation takes place on phosphorus to a}ord the ylide "004# "Scheme 20# ð73ZN"B#0407Ł[
"iii# From phosphaalkynes Phosphaalkynes\ their oligomers and derived metal complexes have been used to prepare complex polycyclic analogues of tris"phosphino#methanes[ This chemistry has been reviewed ð77AG"E#0373\
Three Group 04 Elements PPh2
Ph2P
S
O O (109) PPh2
Se, ∆
PPh2
Ph2P
PPh2
Ph2P
81%
(106)
Se
O
Ph2P
H2O2, acetone, 0 °C
PPh2
Ph2P
042
Ph2P
>95%
S
S (111)
TolN3, ∆
PPh2
Ph2P
S
Ph2P
NTol PPh2
S S (112)
(110) Scheme 30
PMe2 PMe2 PMe2
MeI, Et2O, THF
PMe2 PMe2 PMe2
Li
–115 °C to 20 °C 65%
(114)
MeI, TMEDA, pentane
+
Me3P 80%
PMe2 –
PMe2
(113)
(115)
Scheme 31
89CRV080Ł[ Wettling et al[ report that the prolonged pyrolysis of "005# gave the tetraphosphacubane derivative "006#\ albeit in very low yield ð78AG"E#0902Ł[ Prior reaction of the alkyne to form a zirconium complex "007# greatly improves the conversion ð81AG"E#647Ł[ The phosphacubane "006# has been functionalised at a single phosphorus vertex using a number of reagents ð81AG"E#768\ 82JOC3094Ł[ The zirconium complex "007# has been treated with phosphorus trichloride to form the bicyclic compound "008# "Scheme 21# ð80AG"E#196Ł[
But But
130 °C, 65 h
But
But P P
P 8%
P
P But
(116)
(117)
Cp2ZrCl2 70% BuLi
70%
But
But P
CCl3CCl3, C6H6
Cp2Zr
P
But (118)
P
P But PCl3, hexane 110 °C
But
75%
Cl
P
P
But (119) Scheme 32
P
At Least One Group 04 Element
043
Aluminum chloride catalysed tetramerisation of the phosphaalkyne "005# yielded polycyclic derivatives such as "019# ð81AG"E#0944Ł[ Tungsten ð80CC0294Ł\ manganese ð82AG"E#0313Ł\ iron ð78AG818Ł and vanadium complexes ð76AG"E#897Ł have been converted to related polycyclic systems\ for example "010# "Scheme 22#[
But
P
P
P
i, AlCl3, CH2Cl2, 0–25 °C P ii, But
But
But
But
95%
P
P But (120)
(116)
R2N (CO)5W NR2 (CO)5W
P
P
P
P
30%
P
NR2
But P
NR2
P
But
But
W(CO)5 (121) Scheme 33
Phosphaalkyne "005# reacts with phosphorus ð77AG"E#278Ł and arsenic ð77AG"E#698Ł heterocycles "011#[ In the former case a 1 ] 0 cycloaddition product is obtained whereas in the latter the reaction leads to a 2 ] 0 cycloaddition product minus the elements of benzonitrile "Scheme 23#[ But But
But
Ph
As P But P Ph
X = As P But
Ph
P
P X=P P But
N
P Ph
15%
70%
Ph
X
But P
Ph
Ph
(122)
N
Ph
Scheme 34
"iv# From phosphorus analo`ues of cyclopentadiene Di! and triphosphacyclopentadiene anions oligomerise under the in~uence of transition metals to give complex polycyclic products such as "012# "Equation "4## ð78CC0935\ 81JOM"322#C00\ 82CC200Ł[ But P
But
But
+
–
P Li+
P
–
But
P
P
FeCl3 or CoBr2
P P
24%
Li+
But But
P
But
But
P
P
But
(5)
But
(123)
5[94[0[1[2 Functions bearing heptavalent phosphorus The _rst report of this type of function utilised the reaction of triethyl phosphite with benzoyl peroxide in chloroform to form the tris"phosphonate# "013# ð52JCS0416Ł^ the same product was obtained from the benzoylphosphonate "014#[ The authors report that neither carbon tetrachloride
Three Group 04 Elements
044
nor diethyl ether were satisfactory solvents for this reaction[ Several patents claiming similar compounds as detergents appeared subsequent to this report ð58USP2360395\ 64USP2781565\ 66USP3919980\ 73USP3339535Ł[ More recently\ generation of the quinonoid "015# and subsequent reaction with diethyl phosphite in the presence of a base has been used to prepare the tris"phos! phonate# "016# in good yield "Scheme 24# ð89PS"36#6Ł[ Gross et al[ have developed this basic method further to produce compounds bearing di}erently substituted phosphorus functions\ e[g[\ "017# ð80PS"51#24Ł[ O
Ph P(OEt)3, CHCl3
(PhCO2)2, CHCl3, 48 h
P(OEt)3
PO(OEt) PO(OEt) (124)
(EtO)OP
40%
But
But PO(OEt)2
HO PO(OEt)2
PbO2
PO(OEt)2
O (125) But
HPO(OEt)2 NaOEt
O
PO(OEt)2 PO(OEt)2 PO(OEt)2
HO
80%
PO(OEt)2
But
P(OEt)2
Ph
32%
71%
But
But (126)
(127)
But POPh2 PO(OEt)2 PO(OEt)2
HO But (128)
Scheme 35
5[94[0[2 Functions Bearing Three Arsenic Atoms This author could locate only two reports referring to this functional group[ Tris"diphenyl! arsino#methane "029# was prepared by reaction of the lithium salt of bis"arsine# "018# with chloro! diphenylarsine ð71OM0003Ł[ The product was used in a study of its complexation properties[ In the second report ð82AG"E#092Ł tris"trimethylsilyl#phosphine was desilylated with butyllithium and the resulting lithium salt "020# treated with the arsaalkene "021# in the presence of cobalt"II# chloride to give tetraarsacubane "022# in moderate yield[ The reaction probably proceeds via an intermediate arsaalkyne "Scheme 25#[
Ph2As
AsPh2
i, BuLi, TMEDA ii, Ph2AsCl 60%
AsPh2 Ph2As
(129)
AsPh2 (130) But
O-TMS TMS-As But
(TMS)2PLi
But
As
CoCl2
As
35%
(131)
But
(132) Scheme 36
As As
(133)
As But But
At Least One Group 04 Element
045
5[94[0[3 Functions Bearing Three Antimony or Bismuth Atoms This author was unable to locate any references to the functional groups of either of these types in the literature[
5[94[0[4 Functions Bearing Nitrogen and Other Group 04 Elements 5[94[0[4[0 Functions bearing two nitrogen atoms and one phosphorus atom Gross and Costisella prepared compound "024# from the amidinium salt "023# by reaction with the sodium salt of diethyl phosphite ð58JPR814Ł^ Structure "024# was also made by treating uronium salts "025# with diethyl phosphite "Scheme 26# ð77ZOB1056Ł[ O Me2NH
+
+
Me2N OMe MeSO4–
O
Me2N
(EtO)2PNa
Me2N NMe2 MeSO4–
(EtO)2PH
+
Me2N
PO(OEt)2
OR Me2N
Me2N
(134)
X– (136) R = Me, X = MeSO4– R = Et, X = BF4–
(135)
Scheme 37
The iminium salt "027#\ which was prepared from phosphonate "026# ð60LA"649#33Ł\ reacted readily with a variety of amines to give the phosphonates "028# or with arylsulfonamides to give "039#[ Similarly\ ammonia was added across the imine bond of phosphonates "030# "Scheme 27# ð80PS"52#84Ł[ RO RO
O P
RO
OMe
SOCl2
RO
O Cl–
P +
NMe2 (137)
NMe2 (138)
R2NH 39–95%
EtO EtO
O P
NR2
NMe2 (139)
ArSO2NH2
EtO EtO
O P
NHSO2Ar NMe2 (140)
NCHO Cl3C PO(OR)2
NH4OH/CH2Cl2 R = Et, 85% R = Pri, 73%
Cl3C
NH2 NHCHO PO(OR)2
(141) Scheme 38
The cyclic orthoamide "031# was treated _rst with diethyl phosphite then with benzylamine to yield the bis"amino#methylphosphonate "032# ð89PS"36#150Ł[ The reaction of the tetraaminoalkene "033# with two equivalents of a dialkyl phosphite gave good yields of the imidazolidines "034# as illustrated in Scheme 28 ð67LA05Ł[ Heating a mixture of pyrazolone "035#\ diethanolamine and phosphite "036# gave the heterocycle "037# ð67MIP76757Ł[ Other cyclic examples "049# were prepared by the cycloaddition of an azide to aminophosphenes "038# but these derivatives were unstable above −59>C ð78NJC780Ł[ The reaction of N!phenylbenzohydrazonoyl chloride to 1\4!dimethyl!0\1\2!diazaphosphole "040# occurs by a multistage cycloaddition process involving two equivalents of the derived nitrile imine and the elimination of benzonitrile to give the bicyclic example "041#\ albeit in low yield "Scheme 39# ð72CB438Ł[
Three Group 04 Elements
046
O
O
i, (EtO)2PH, ∆
OEt
ii, Ph
NH
OH
NH2
H N
H N
32%
O
O (142)
Ph
PO(OEt)2 (143)
Ph Ph
Ph
O
N
N
(RO)2PH, ∆
N
N
N
R = Me, 92% R = Et, 93% R = Bun, 82%
N
Ph Ph
O P(OR)2
Ph
(144)
(145) Scheme 39
OH
OH
,∆
HN
O Me
N N
O
+
P
RO
OH
OR
Ph (146)
OH
N
PO(OR)2 Ph (148)
(147) R2
Ph
R2
< –60 °C
+ PhN3
PhP
N
N
Me
H R = CH2CH(Me)Cl
N
N(Me)R1 (149)
N(Me)R1
P
N Ph N (150) Ph
Ph
N
+
MeN P
NNHPh Cl
base
NNHPh
N MeN P
N MeN
Cl
NHPh
P Et3N 21%
(151)
Ph
NHPh N N
Ph
(152) Scheme 40
5[94[0[4[1 Functions bearing two phosphorus atoms and one nitrogen atom "i# Introduction This type of functional group has been most widely prepared in the pharmaceutical industry\ where such compounds are patented as agents for treating abnormal calcium and phosphate metabolism such as the bone disorder Paget|s disease\ "e[g[\ ð78EUP187442Ł#[
"ii# Synthesis from ortho!esters and similar derivatives Gross et al[ have published details of the preparation of aminobis"phosphonato#methanes "042# and the corresponding bis"phosphine# oxides "043# by a method which involves heating ortho!amides either with dialkyl phosphites or with phosphine oxides "Scheme 30# ð57AG"E#280\ 57AG"E#352\ 58JPR466Ł[ Thus\ the cyclic ortho!amide "031# was treated _rst with diethyl phosphite and then diethyl trimethylsilylphosphite to give bis"phosphonato#methane "044# in moderate yield ð89PS"36#150Ł[ The aminopyridine derivative "046# was prepared by the reaction of triethyl ortho! formate with 2!methyl!1!aminopyridine and two equivalents of phosphinite "045# ð70PS"00#200Ł[
At Least One Group 04 Element
047
Similar chemistry using a mixture of phosphorus species resulted in the analogues "047# ð89PS"40:41#12Ł\ which were also made from the diethoxyphosphinyl acetal "048#[ O
O
PO(OR)2
OMe
(RO)2P H, ∆
Me2N
Me2N
60–69%
PO(OR)2
POR2
R2P H, ∆
Me2N
55–70%
OMe
POR2 R = Bun, Ph (154)
R = Me, Et (153) Scheme 41
O
OEt
O
HPO(OEt)2
NH
PO(OEt)2 NH
58%
O
OH
TMS-PO(OEt)2
H N
48%
O
O
(142)
PO(OEt)2
(6)
PO(OEt)2 (155)
O P
150 °C
+ HC(OEt)3 + 2 MeP(OH)OEt N
68%
(156)
NH2
N
N H (157)
O P N
N H
Me OEt
(7)
P Me OEt O
OH R
(EtO)2PCH(OEt)2
P(OEt)2 O (159)
(158)
"iii# Synthesis from amides Amides have been treated with hydrochloric and phosphorous acids to give variable yields of aminobis"phosphonates# "059# ð61ZAAC"278#008Ł^ the reaction of formamides with phosphorus trichloride or tribromide followed by acid hydrolysis resulted in similar compounds ð64BCJ0929Ł[ Using a similar procedure\ chloroacetamide "050# was transformed into the corresponding derivative "051# by a mixture of phosphorus trichloride and phosphorous acid ð68ZAAC"346#103Ł and the same method was used to prepare "052# ð74LA444Ł[ The unusual phosphorous oxide "P3O5# has also been applied to the synthesis of these functions "Scheme 31# ð89PS"40:41#042Ł[ Wet DMF when treated with two equivalents of phosphorus trichloride and then more water\ gave the dimethylamino derivative "053# in good yield\ as shown in Equation "7# ð80PS"45#006Ł[ R1CONR2R3•HCl
H3PO3
R2R3N
21–77%
NH2
Cl O (161)
i, PCl3/H3PO3, dioxan ii, H2O, ∆
PO(OH)2 PO(OH)2 R1 (160) PO(OH)2
Cl
PO(OH)2
42%
2 RCONH2 + P4O6 + 4 H2O
NH2 (162)
70–98%
Scheme 42
R
NH2 PO(OH)2 PO(OH)2
Three Group 04 Elements
048
PO(OH)2 H2N PO(OH)2 (163)
Me2NCHO
i, PCl3 ii, H2O
PO(OH)2 Me2N
70%
(8) PO(OH)2 (164)
"iv# Synthesis from nitriles The earliest report of the preparation of this type of functional group utilised the reaction of nitriles with phosphorus trihalides and water ð46GEP091244Ł[ This method was subsequently used by Worms and Blum to prepare aryl derivatives "054# ð68ZAAC"346#198Ł[ In addition\ these workers used the reaction of cyanocyclohexane with phosphorous acid to obtain the cyclohexyl analogue "055#[ This transformation can be carried out in the presence of a ketone] Blum and Hemman reported that ketone "057# was made from the nitrile "056# and a mixture of phosphorus tribromide and phosphoric acid "Scheme 32# ð77GEP2500411\ 77ZN"B#64Ł[ PO(OH)2 PO(OH)2 NH2
PBr3, H2O
ArCN
Ar Ar = Ph 60%
(165) CN
PO(OH)2 PO(OH)2
H3PO3
NH2
74%
(166) O CN
R
O
H3PO4, PBr3, dioxan R = t-alkyl 38–66%
PO(OH)2 PO(OH)2
R
NH2 (168)
(167) Scheme 43
"v# Synthesis from imidoyl compounds The reaction of imidate "058# with sodium diethyl phosphite in benzene gave tetraethyl bis"phos! phonato#benzylamine "069# ð48LA"512#092Ł[ In a similar way\ diethyl phosphite was added to imidoyl! phosphonate "060# to give aminobis"phosphonato#methane "061# "Scheme 33# ð60LA"649#33Ł[ The treatment of imidoyl halides with phosphorous acid gave rise to the parent acids "062# ð61ZAAC"278#008Ł and similar functions "063# and "064# were obtained using triethyl phosphite ð70PS"00#200\ 71SC304Ł and diethyl phosphinite ð70PS"00#200Ł\ respectively[
"vi# Synthesis from other bisphosphorus species In attempts to prepare aminotris"phosphonato#methanes "066# by addition of diethylphosphite to the imine bond in "065# Gross and Costisella actually obtained the product of reduction "067# via an unexpected carbon to nitrogen phosphorus migration "Scheme 34# ð61JPR858Ł[ This method has since been used to prepare similar derivatives "068# ð63PS"3#130\ 65JPR161Ł[
At Least One Group 04 Element
059
O
NH
(EtO)2P
Ph
H , Na, benzene 63%
OEt
PO(OEt)2 PO(OEt)2 NH2
Ph
(170)
(169) O
O
(EtO)2P
+
NMe2 Cl–
(EtO)2P
PO(OEt)2
H
H2N
39%
PO(OEt)2
(171)
(172)
+
H3PO3
NR2R3 Cl–
R1
PO(OH)2 PO(OH)2 NR2R3
R1
15–78%
Cl
(173) Scheme 44
O PO(OEt)2
P
R2N
Me2N PO(OEt)2
Me OEt Me
P OEt O (175)
(174)
O
PO(OEt)2
(EtO)2P
R 1N PO(OEt)2
H
R1 = Ar, 23–71%
(176)
PO(OEt)2 R1HN PO(OEt)2 (178)
PO(OEt)2 PO(OEt)2 PO(OEt)2
R1HN
(177) Scheme 45
POPh2 R1HN POPh2 (179)
"vii# Miscellaneous syntheses The reaction of aryl isocyanides "079# with dialkyl phosphites and base is reported to give the anilines "070# ð64ZOB0349Ł[ Ferric chloride catalysed displacement of chloride from isocyanate "071# by ~uorophosphite yields the unusual isocyanate "072# ð66ZOB210Ł[ Dehydration of the aminoalcohol "073# by heating with hexamethyldisilazane gave rise to a mixture of bis"phosphonato#pyrrolidine "074# and the product of further loss of phosphite "Scheme 35# ð89PS"43#086Ł[ Diphosphacyclobutanes "076# have been obtained by dimerisation of the phosphorous analogues "075# of amidines ð79ZAAC"351#029\ 71ZAAC"374#12\ 72PS"07#16\ 80PS"50#250Ł[
Three Group 04 Elements
050 R2OP
O R 2P
R1
NC
POR2
H , alkoxide
R1
58–75%
N H
R = alkoxy, alkyl
(180)
(181) O
Cl
+
OCN
P
FeCl3
2 (EtO)2PF
OCN
30%
Cl
P O (183)
(182) PO(OH)2 OH NH2
(TMS)2NH
PO(OH)2
PO(O-TMS)2 N H
(184)
+
N
PO(O-TMS)2
OEt F OEt F
PO(O-TMS)2
(185) NMe2 RP
RP NMe2
PR Me2N
(186)
(187) Scheme 46
5[94[0[4[2 Functions bearing nitrogen and other group 04 elements Kellner et al[ described the reaction of diphenylarsane with tetramethylamidinium chloride in acetonitrile to give bis"dimethylamino#methyldiphenylarsane "077# ð67JOM"038#056Ł[ This reaction proceeds in poorer yield when the sodium salt of the arsane is used in THF[ Imidoyl chloride "089# forms the cyclic derivative "080# by reaction with aminoarsane "078# "Scheme 36# ð67ZC341Ł[ Treatment of arsenadiazole "081# with diphenylnitrile imine gives the bicyclic analogue "082# ð75TL1846Ł[ AsPh2
HAsPh2, MeCN
+
Me2N
Cl–
NMe2
NMe2 Me2N (188)
78%
Et
Et AsH
But
NPh
BuLi, Et2O
+ Cl
NH
Et But
As NH
NH
As
But
N
NHPh
Et
Et
Et (189)
(190)
(191) Ph
MeOC Ph
N MeOC
N
As
NNHPh
N
20 °C
+
N 70%
Cl
N As
N Ph
(192)
(193) Scheme 47
The bis"nitro#methylstibane "083# is formed when the silver salt of 0\0!dinitroethane is treated with diphenylstibyl chloride\ as shown in Equation "8# ð74IZV328Ł[
At Least One Group 04 Element
051
CH2Cl2, <10 °C
MeC(NO2)2Ag + Ph2SbCl
NO2 NO2
Ph2Sb
(9)
90%
(194)
5[94[1 FUNCTIONS CONTAINING GROUP 04 ELEMENTS WITH METALLOIDS 5[94[1[0 Functions Bearing Group 04 Elements and Silicon 5[94[1[0[0 Functions bearing nitrogen and silicon "i# From silyl halides This general method involves deprotonation of the carbon atom attached to a nitrogen function followed by silylation[ Thus\ methyl isocyanide has been successively deprotonated and silylated to a}ord bis"trimethylsilyl#methyl isocyanide "084# ð69JOM"14#274Ł\ the second silylation going in much poorer yield than the _rst[ The product "084# was converted to the corresponding isothiocyanate using sulfur ð71BCJ0052Ł[ Katritzky et al[ prepared bis"trimethylsilyl#methylbenzotriazole "085# by the same method and studied its further alkylation "Scheme 37# ð77RTC530Ł[ More recently\ Snieckus and co!workers showed ð78TL4730Ł that whereas N\N!dimethylbenzamide could be readily silylated using lithium tetramethylpiperidide to yield "086#\ the corresponding diethylamide or piperidide gave O!silyl products[
MeNC
i, BuLi, –78 °C ii, TMS-Cl 80%
i, BuLi ii, TMS-Cl
TMS
i, LDA/THF –78 °C ii, TMS-Cl
N N
90%
N
NC
TMS
40%
N N N
TMS
TMS NC (195) i, BuLi ii, RX
N
R = Me, 90% R = PhCH2, 95%
N
N
TMS
TMS
TMS LDA = lithium diisopropylamide
TMS R
(196) O
O NMe2
i, LiTMP, THF ii, TMS-Cl
TMS N Me
TMS
(197) Scheme 48
"ii# By reductive silylation Amides have been treated with silyl halides in the presence of metals to give bis"tri! methylsilyl#aminomethanes[ Thus\ N\N!dimethylbenzamide\ when added to TMS!Cl and mag! nesium in hexamethylphosphoramide "HMPA#\ gave "087# in modest yield ð60JOM"21#68Ł[ The authors report that the reaction fails using N!methylbenzamide[ Ekouya et al[ studied the same reaction using formamides and lithium metal in THF and found the addition of triethylamine to be advantageous ð68JOM"066#026Ł[ In this case\ the product "088# was formed in only trace amounts in the absence of base "Scheme 38#[ Picard et al[ made bis"trimethylsilyl#aminomethane "199# in good yield by treatment of TMS!CN with TMS!Cl and lithium in HMPA ð80JOM"308#C0Ł[
Group 04 with Metalloid"s#
052
TMS-Cl, Mg, HMPA
Ph
PhCONMe2 32%
TMS
TMS-Cl, Li, THF, Et3N
HCONH2
NMe2 TMS TMS (198)
TMS N
30%
TMS
TMS (199)
i, TMS-Cl, Li, HMPA ii, MeOH
TMS H2N
TMS-CN 65%
TMS (200)
Scheme 49
"iii# Miscellaneous methods Bis"trimethylsilyl#chloromethane has been reported to react with sodium azide in HMPA^ sub! sequent reduction using LAH leads to the amine "199# "Equation "09## "ð80JOM"308#C0\ 81TL2892Ł#[ TMS
TMS
NaN3, HMPA
Cl
(10)
H2N
76%
TMS
TMS
TMS
LAH, Et2O
N3
TMS (200)
Silaneimine "190#\ when treated with dimethylethylamine at elevated temperatures\ inserts into two of the C0H bonds of a methyl group of the amine resulting in the formation of the silaneamine "191# "Scheme 49# ð76CB0246Ł[ +
Me2Si
EtNMe2
NSiBut
3
NMe2Et –
SiMe2NHSiBut3
135°C
Me2Si
67%
MeEtN NSiBut3
39%
SiMe2NHSiBut3 (202)
(201)
TMS
NC
Me2 Si
TMS
TMS
TMS
Me2 Si
TMS
Me2Si TMS Pd(OAc)2
N
LAH, Et2O
56%
(203)
NH HN
N 85%
(204)
(205)
Scheme 50
The aryl isocyanide "192# reacts with octamethyltrisilane in the presence of a palladium catalyst to give the bis"silylimine# "193# which when reduced with LAH results in the formation of the corresponding amine "194# in good yield ð77JA2581Ł[
5[94[1[0[1 Functions bearing phosphorus and silicon "i# From silyl halides In a manner exactly analogous to the nitrogen series\ the quenching of a phosphorus stabilised carbanion by a silylating agent has been widely used to prepare this functional group[ Phosphine
At Least One Group 04 Element
053
sul_de "196# was prepared by reaction of the lithium salt "195# with excess TMS!Cl ð63ZAAC"393#193Ł[ Phosphines "197# have been further silylated in good yields ð70ZAAC"364#07\ 73CB1952Ł and phos! phonates "198# have been similarly treated "Scheme 40# ð76JOM"212#024Ł[ Trimethylphosphine has been doubly deprotonated using t!butyllithium and successively silylated to give "109# ð77ZN"B#0305Ł[ S Li
P
Ph
TMS-Cl
Ph
65%
S TMS
i, BuLi, TMEDA ii, TMS-Cl
R P
Me
P
OR OR
Ph
TMS
P
R = alkyl, Ph, 41–65%
Ph
TMS O
i, LDA, THF ii, TMS-Cl
TMS
R = alkyl, 25–85%
(209)
PMe3
Ph
R
(208) O
Ph
TMS (207)
(206)
TMS
P
P
O
i, LDA ii, MeI
OR OR
TMS
P
91–92%
OR OR
TMS
TMS LDA = lithium diisopropylamide
i, ButLi ii, TMS-Cl
TMS
P
Me
i, ButLi ii, TMS-Cl
Me
TMS
Me
P
Me
TMS (210)
Scheme 51
Bis"phosphino#methanes "100# have been silylated using butyllithium as a base to a}ord bis"phos! phino#trimethylsilylmethanes "101# "Equation "00## ð68CB537\ 77ZN"B#0305Ł[ TMS
i, ButLi ii, TMS-Cl
PR2
R2P (211)
(11)
PR2
R2P (212)
R = Ph, Me
Phosphorus double bonded systems such as "102# and "103# react with nucleophiles at phosphorus "Scheme 41# ð72PS"07#32Ł[ Subsequent silylation in the case of "102# gave "104# whereas protonation at carbon in the case of "103# yielded "105#[ TMS R2NP
i, ButLi ii, TMS-Cl
TMS But2P
TMS
TMS
(213)
(215) i, MeLi ii, MeOH
P
Me P
TMS
TMS
TMS
TMS
(214)
(216) Scheme 52
"ii# From phosphorus halides Sequential replacement of halogens in phosphorus halides using silyl stabilised carbanions is another common method for the synthesis of this group[ Phosphorus trichloride when treated with
Group 04 with Metalloid"s#
054
the lithium salt of bis"trimethylsilyl#methane was converted to either the dichloro compound "106# or its analogous monochloride "107#\ depending on the proportions of the reagents ð79JCS"D#1317Ł[ Dialkyl! ð80AG"E#698Ł and diarylchlorophosphines ð72JCS"D#894Ł produce similar products and Grig! nard reagents have also been used with phosphorus trichloride ð89TL2748Ł and aryldichloro! phosphine "108# ð74OM228Ł "Scheme 42#[ Phosphinylidene chloride "119# was converted to the unsaturated derivative "110# in high yield ð71OM0619Ł[ Cl Li
Et2O, 25 °C
+ 1 PCl3
1
P
73%
TMS
TMS
TMS
Cl
TMS (217) Cl Et2O, ∆
Li
+ 1 PCl3
2
P
TMS
60%
TMS
TMS
TMS
TMS TMS (218) PCl2 Cl
MgCl
THF
+
P
TMS
TMS
TMS TMS (219) Li
TMS
Cl
TMS
P
TMS TMS
TMS
TMS P
79%
TMS
TMS (221)
(220) Scheme 53
The reaction of tris"trimethylsilyl#methyllithium with phosphorus trichloride produced the dichloride "111# ð78JOM"255#28Ł\ which\ after replacement of the halides using sodium methoxide\ gave dimethoxyphosphine "112# which readily desilylated in methanol to give bis"trimethylsilyl#! methane "113#[ This desilylation was previously noted in diphenylphosphine "114#\ which although stable under basic conditions was much less so at lower pH "Scheme 43# ð72JCS"D#894Ł[ TMS TMS TMS
Li
PCl3, Et2O-THF 65%
TMS TMS TMS
Cl
NaOMe
P Cl
95%
(222) TMS TMS TMS
TMS TMS TMS
OMe
TMS
72%
TMS
TMS
OMe P
OMe
(223)
MeOH, RT
MeOH
P 97%
TMS
OMe
(224)
PPh2
PPh2
(225) Scheme 54
"iii# Miscellaneous methods Phosphinylidene derivatives have been reduced under a variety of conditions[ For example\ the phosphine "115# was produced e}ectively by the transfer of hydride from a phosphinyl methyl group ð73ZAAC"400#097Ł[ In another case\ phenylphosphinylidene disilane "116#\ when treated with an equimolar mixture of phenylphosphine and its sodium salt ð76CB0696Ł\ gave the product "117# in
At Least One Group 04 Element
055
high yield and the chloro analogue "118# has been reduced with concomitant disproportionation using LAH "Scheme 44# ð76CC0981Ł[ TMS
TMS
Cl
+ TMS
Me2 P PMe2
TMS-PMe2
Cl
TMS TMS
TMS PHPh TMS (228)
82%
TMS (227)
PMe2 TMS (226)
60%
PhPH2, PhPHNa
PPh
TMS
toluene, 100 °C
H
TMS
LAH
PCl
TMS
TMS (229)
TMS
P
TMS
TMS Scheme 55
The displacement of chloride ion from phosphinylidene chloride "129# with acetylide anions gives rise to the diphosphacyclobutane "120# after dimerisation as a mixture of stereoisomers ð73CB1582Ł[ Interestingly\ the aminophosphinylidene compound "121# dimerises with rearrangement to the unusual small ring compound "122# "Scheme 45# ð89CB0134Ł[ Phosphinylidene compounds also undergo cycloadditions[ For example\ 1\2!dimethylbutadiene gave the phosphorus heterocycle "123# ð74CB703Ł and diphenyldiazomethane the three!membered epiphosphine "124# ð75CB0866Ł[ Ph
TMS TMS
M
+
ClP
TMS
TMS
P
Ph
Ph
(230)
P
TMS
TMS (231)
TMS TMS TMS-NHP TMS
∆
TMS
P
65%
N TMS
P
(TMS)2N
TMS
(233)
(232)
TMS ClP TMS
, C6H6, RT 89%
P Cl
TMS ButP TMS
TMS TMS (234)
But Ph2CN2
P Ph
77%
TMS Ph TMS (235)
Scheme 56
Pentamethylcyclopentadiene groups in the diphosphene "125# have been displaced by the lithium salt of bis"trimethylsilyl#methane to form the new diphosphene "126# as shown in Equation "01# ð75AG"E#808Ł[ TMS Li
P
P
TMS
TMS
TMS P
TMS
TMS (236)
(12)
P
(237)
Group 04 with Metalloid"s#
056
"iv# Modi_cation at phosphorus There have been a number of reports in which previously formed functions have been modi_ed at phosphorus[ Chlorophosphines such as "127# have been reduced using\ for example\ sodium metal or LAH ð71OM0619\ 74OM228Ł[ Alternatively\ the halogen was replaced by a methyl group "Scheme 46# ð73CC0558Ł[ The phosphine oxide "139# has been produced from its parent compound "128# by a mild oxidation which avoids decomposition ð73JOC4976Ł\ and the reaction of bis"phos! phino#methane "130# with sulfur gives the analogous thio compound "131# ð81CB0222Ł[ Cl
H TMS
TMS
P
82%
TMS
TMS
TMS
LAH
Me TMS
P
TMS
Li, MeCl
TMS
TMS
P
TMS TMS
TMS
(238) O
Ph H2O2, acetone, 4 °C
P
TMS
Ph
Me
Ph
89%
TMS (239) Me
Ph
P
TMS
TMS (240) Me P
P
Me
S8, toluene, 50 °C
Me
95%
Me
S
S
P
P
TMS (241)
Me Me
TMS (242) Scheme 57
The bis"trimethylsilyl#methyl group has\ by virtue of its steric bulk\ been used as a stabilising group in the preparation of bisphosphenes "for a review see ð73POL278Ł# e[g[\ the reaction of dichloride "106# with hindered phosphine "132# in the presence of 0\4!diazabicyclo ð4[3[9Ł undec!4! ene "dbu# gives bisphosphene "133# ð72CC417Ł[ The analogue "126#\ prepared by treating di~uoride "134# with lithiophosphine "135#\ had a half!life of one week at 19>C ð76PS"20#70Ł[ The same stabilising e}ect has been utilised in producing phosphinyl radicals "136# ð79JCS"D#1317Ł which were subsequently shown to add to 1\2!dimethylbutadiene to give the corresponding bis"phosphines# "137# "Scheme 47# ð73TL2408Ł[
PH2 Cl
TMS
But
But
But
TMS
THF, dbu
P
P 78%
Cl
TMS
TMS But
But (243)
(217) TMS
(244)
TMS PF2
+
TMS
PHLi TMS
(245)
i, Et2O, pentane ii, dbu
TMS
85%
TMS
P TMS
TMS (237) TMS
TMS
TMS P
(246) • P
But
P
TMS TMS
TMS TMS TMS
P
P
TMS
TMS TMS (248)
(247) Scheme 58
TMS
At Least One Group 04 Element
057
5[94[1[0[2 Functions bearing nitrogen\ phosphorus and silicon The cycloadditions of t!butyl! ð70AG"E#020Ł and trimethylsilyldiazomethane ð72CC0060Ł with phosphinylidenemethylsilane "138# gave the corresponding heterocyclic examples "149# shown in Equation "02#[ TMS TMS
RCHN2, THF
N P TMS
R = But, TMS
TMS
TMS
N
N P
N
TMS
(13)
R (250)
(249)
5[94[1[0[3 Functions bearing arsenic\ antimony or bismuth "i# From trihalides The displacement of one or more halides from the appropriate trihalides has proved the method of choice for the preparation of these functions[ Gynane et al[ ð79JCS"D#1317Ł produced arsenic and antimony derivatives with either one "140# or two bis"trimethylsilyl#methyl groups "141# by the reaction of appropriate trichlorides with the correct proportions of bis"trimethylsilyl#methyllithium[ Bismuth derivatives with three such substituents "142# were similarly prepared ð72IC2310Ł and Grignard reagents have also been used for the synthesis of stibanes "143# ð72POL180\ 73IC1471Ł[ More recently\ the pyridyl derivatives "144# were produced in a similar way ð80CC0459Ł "Scheme 48#[ TMS MCl3 +
Et2O
Li M = As, 70% Sb, 60%
TMS
TMS MCl3 +
2
Et2O
TMS MCl2 TMS (251) TMS MCl
Li M = As, 61% Sb, 65%
TMS
TMS
2
(252) TMS BiCl3 +
Et2O, 0 °C
TMS Bi
Li
3
90%
TMS
TMS
3
(253) TMS SbCl3 +
Et2O, –40 °C
MgCl 74%
TMS
TMS
N Li
TMS SbCl2 TMS (254)
MCl3, Et2O, –80 °C
TMS
M = As, 55% Sb, 70% Bi, 44%
N
TMS TMS MCl2 (255)
Scheme 59
"ii# By modi_cation of the `roup 04 element As in the case of the diphosphenes\ bis"trimethylsilyl#methyl groups have been used to stabilise heteroatomic double bonds[ Diarsenes "147# were prepared ð72JA4495Ł by reaction of aryl arsane
Group 04 with Metalloid"s#
058
"145# with dichloroarsane "146# "Equation "03##\ whereas mixed functions "148# were made by reacting the corresponding phosphine with arsenic and antimony dichlorides ð72CC770Ł[ AsH2 TMS
But But
But
+
AsCl2
THF, dbu
TMS
72%
TMS
As
TMS
But
(14)
But
But (257)
(256)
As
(258)
But TMS But
P
M TMS
But (259) M = As, Sb
The chloroarsane "159# was metallated on treatment with lithium[ Subsequent protonation or methylation produced the arsanes "150# whereas reaction with stannous chloride gave diarsane "151# ð76JOM"219#C16Ł[ Treatment of dichlorostibane "143# with magnesium in THF resulted in the formation of the unusual cyclotetrastibane "152# "Scheme 59# ð81OM034Ł[ TMS As TMS
i, Li ii, SnCl2, Et2O
TMS As TMS
2
TMS AsCl
70%
TMS
2
2
i, Li ii, electrophile
TMS
E = H ex HCl, 90% E = Me ex MeCl, 73%
TMS
(260)
(262)
AsE 2
(261) TMS TMS
TMS
TMS
Mg, THF
Sb
Sb
Sb
Sb
TMS
SbCl2 TMS
TMS
TMS
TMS TMS (263)
(254) Scheme 60
5[94[1[1 Functions Bearing Group 04 Elements and Boron A search of the literature revealed many references to carborane chemistry and readers are referred to specialist texts for further information on this complex subject ðB!69MI 594!90\ 71COMC! I300\ 71COMCI!I432\ 81CRV198Ł[ In the sole report of a simple example uncovered by this author\ Io}e et al[\ disclosed the synthesis of "153# by treatment of dinitromethane salts with chlorodiethylborane "Equation "04## ð63MI 594! 90Ł[ Et2BCl + (NO2)2CH2
base
Et2BCH(NO2)2 (264)
(15)
5[94[1[2 Functions Bearing Group 04 Elements and Germanium Karsch et al[ ð75JOM"201#C0Ł made germanium compounds "154# and analogous lead derivatives by the reaction of the lithium salt of bis"diphenylphosphinyl#methane with germanium"II# chloride "Equation "05##[ GeCl2, –40 °C
(Ph2P)2CHLi 93%
Ge[CH(PPh2)2]2 (265)
(16)
At Least One Group 04 Element
069
5[94[2 FUNCTIONS CONTAINING GROUP 04 AND METAL ELEMENTS\ AND POSSIBLY A METALLOID Many such compounds have been prepared without isolation or characterisation as precursors to the functional groups mentioned earlier in this chapter and hence relevant references can be found above[ The subsequent discussion will refer only to those areas previously uncovered or where the chemistry is signi_cant enough to be considered separately[ Work has been done in the area of organometallic cluster compounds but this falls outside the scope of this chapter[ Many alkali metal salts of dinitromethane derivatives have been made ð46JA3697\ 50JOC3623Ł[ It has been shown by x!ray di}raction that the rubidium salt of cyanodinitromethane exists in a form in which the metal atom is closely associated with one of the oxygens ð61ACS0763Ł[ It seems highly likely that alkali metal salts of other systems\ where delocalisation is possible\ will behave similarly[ The reaction of dinitromethane with triethylthallium gave a compound of Structure "155# in which the metal is reported to coordinate to both carbon and oxygen atoms "Equation "06## ð60IZV0494Ł[ CH2(NO2)2 + TlEt3
Et2O
Et2TlCH(NO2)2 (266)
95%
(17)
The deprotonation of bispyrrole "156# has been achieved using methyllithium and although formal resonance structures are di.cult to write for the lithium salt\ NMR studies indicate extensive delocalisation of charge ð79HCA0089Ł[ Katritzky et al[ have studied the use of benzotriazole as a stabilising group for anionic centres^ among recent publications is one concerning the generation and use of organolithium species "157# ð80JOC1032Ł[ N N N N Li N
N
(267)
(268)
Kau}mann and his group have studied the chemistry of the deprotonation of carbon atoms attached to heavy metals and metalloids\ and a review has appeared ð71AG"E#309Ł[ In some cases the loss of one of the metal substituents is observed[ The preparation of lithium salts of bis"di! phenylstibanyl#methane and bis"diphenylarsanyl#methane and the subsequent deuteration of the products "158# has also been described "Equation "07## ð68TL490Ł[ (Ph2M)2CH2
c-Hex2NLi, HMPA
(269)
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
(Ph2M)2CHLi
D2O M = Sb, 68% M = As, 63%
(Ph2M)CHD
(18)
Comprehensive Organic Functional Group Transformations
6.06 Functions Containing at Least One Metalloid (Si, Ge, or B) and No Halogen, Chalcogen or Group 15 Element; Also Functions Containing Three Metals VADIM D. ROMANENKO Institute of Organic Chemistry, Kiev, Ukraine MICHEL SANCHEZ Universite´ Paul Sabatier, Toulouse, France and JEAN-MARC SOTIROPOULOS Universite´ de Pau et Pays de l’Adour, Pau, France 5[95[0 INTRODUCTION
061
5[95[1 FUNCTIONS CONTAINING AT LEAST ONE METALLOID FUNCTION "AND NO HALOGEN\ CHALCOGEN\ OR GROUP 04 ELEMENT# 5[95[1[0 Functions Containin` Three Metalloids 5[95[1[0[0 Functions bearin` three silicons 5[95[1[0[1 Functions bearin` three borons 5[95[1[0[2 Functions bearin` three `ermaniums 5[95[1[0[3 Functions bearin` mixed metalloids 5[95[1[1 Functions Containin` Metalloids and Metals 5[95[1[1[0 Functions bearin` silicon"s# and metals"s# 5[95[1[1[1 Functions bearin` boron"s# and metal"s# 5[95[1[1[2 Functions bearin` `ermanium"s# and metal"s# 5[95[1[1[3 Functions with mixed metalloid"s# and metal"s# 5[95[2 FUNCTIONS CONTAINING THREE METALS
061 061 061 079 074 075 078 078 087 191 192 193 193 193
5[95[2[0 Three Similar Metals 5[95[2[0[0 Lithium derivatives\ RCLi2
060
061
At Least One Metalloid or Metal
5[95[2[0[1 Mercury derivatives\ RC"H`X#2 5[95[2[0[2 Aluminum derivatives\ RC"AlX1#2 5[95[2[0[3 Tin and lead derivatives\ RC"MX2#2 "M Sn or Pb# 5[95[2[1 Three Dissimilar Metals
195 197 197 198
5[95[0 INTRODUCTION This chapter deals with compounds of the general formula RC"EXm#n"MLk#2−n "E Si\ Ge\ or B^ M metal^ R H or organyl^ X any substituent^ n 9Ð2# having three heteroatoms "E\ M# bonded to the same carbon[ Most of the organoelement species of this type contain classical two! center\ two!electron {{single|| bonds and formally arise through the replacement of hydrogen atoms with the heteroatoms mentioned[ It is the purpose of this chapter to discuss the preparation and some of the chemical transformations of these compounds[ A discussion of carboranes\ metal clusters\ and other electron!de_cient molecules which cannot be portrayed in the same manner and exhibit quite di}erent reactivities\ is not included[ For the same reason\ p!metal complexes containing a C"EXm#n"MLk#2−n fragment are also ignored[ However\ the organometallic compounds of the type RC"EXm#nM2−n "M alkali metal#\ often better described as heteroatom!stabilized carbanions\ are considered[ As will become evident\ the methods of preparation of the above functions are wide and varied[ Some of these methods are discussed in monographs by Colvin ðB!70MI 595!90Ł\ Weber ðB!72MI 595! 90Ł\ Pereyre et al[ ðB!76MI 595!90Ł\ and Negishi ðB!79MI 595!90Ł[ The latter also contains a detailed discussion of standard methods of carbonÐmetalloid and carbonÐmetal bond formation[ Houben! Weyl|s Methoden der Or`anischen Chemie ð63HOU"02:1b#0\ 64HOU"02:6#0\ 67HOU"02:5#070\ 79HOU"02:4#16\ 71HOU"02:2a#0Ł and the appropriate reviews in Comprehensive Or`anometallic Chemistry ð71COMC! I"1#0\ 71COMC!I"6#154\ 71COMC!I"6#404Ł etc[ and Comprehensive Or`anic Chemistry ð68COC"2#576Ł cover parts of the literature up to 0871[ The preparation and properties of some polyborylated compounds are also discussed in a monograph by Pelter et al[ ðB!77MI 595!90Ł and in a book by Pelter ðB!76MI 595!91Ł[ The chemistry of polylithiated aliphatic hydrocarbons has been reviewed by Maercker and Theis ð76TCC"027#0Ł[ Discussion of certain aspects of the topic can also be found in Comprehensive Or`anic Synthesis ð80COS"0#0\ 80COS"0#376Ł and in a number of other references[ ð53AOC"1#146\ B!56MI 595!90\ B!74MI 595!90\ B!74MI 595!91\ 75MI 595!90\ 78MI 595!90\ B!78MI 595!91\ B!81MI 595!90Ł[
5[95[1 FUNCTIONS CONTAINING AT LEAST ONE METALLOID FUNCTION "AND NO HALOGEN\ CHALCOGEN\ OR GROUP 04 ELEMENT# 5[95[1[0 Functions Containing Three Metalloids 5[95[1[0[0 Functions bearing three silicons Trisilylmethyl groups\ especially tris"trimethylsilyl#methyl\ "TMS#2C\ have been widely recognized as versatile building blocks in organic synthesis which have proven their synthetic utility in hundreds of reactions ð71JOM"128#82\ B!74MI 595!90\ 80MI 595!90\ 80MI 595!91Ł[ These burgeoning applications arise from the unique properties of trisilylmethyl derivatives[ Trialkylsilyl groups "R2Si# can be considered {{bulky protons|| and have been widely used for the synthesis of sterically protected molecules[ Due to the acidity of the Si2C0H hydrogen "and hence the availability of the corresponding metal derivatives#\ trisilylmethyl groups can be easily attached to a range of metals and metalloids[ Many of the resulting compounds show enhanced stability compared to the corresponding unsubstituted methyl derivatives and thus are easily handled and studied[ Lastly\ due to the steric as well as to the electronic e}ects trisilylmethyl groups can stabilize an adjacent carbanionic center or an adjacent carbonÐheteroatom double or triple bond[ The main synthetic pathways to 0\0\0!trisilylalkanes are] "a# {{direct synthesis|| in the gas phase involving insertion of silicon into a carbonÐhalogen bond^ "b# reductive silylation of trihalomethanes^ "c# reactions of organometallic carbon nucleophiles with chlorosilanes^
062
At Least One Metalloid
"d# derivatization and rearrangements of the compounds already containing polysilylated C0 units[ A number of other reactions in which an Si2C function is created are known\ but they are more of academic interest[
"i# Trisilylmethanes and their linear C!or`anyl derivatives\ RC"SiX2#2 Compounds of this type are known with R H\ alkyl\ aryl\ hetaryl\ acyl\ and with a variety of substituents on silicon[ The parent tris"silyl#methane "0# is formed in very low yield via LAH reduction of the corresponding chloro derivative "1# ð53CB0888\ 75ZN"B#0416Ł[ This precursor is available\ along with other trisilylated methanes such as structures "2#Ð"5#\ in the {{direct synthesis|| using a copper catalyzed reaction of elemental silicon with chloroform ð47CB11Ł or other halo! hydrocarbons ð74ZC298\ 82ZAAC"508#0383Ł[ SiH3
SiCl3
SiH3
H3Si
SiCl3
Cl3Si
(1)
TMS TMS
TMS
(2)
(3)
HC(SiHCl2)n(SiCl3)3–n (4)-(6); n = 1–3
Attempts were made to obtain tris"silyl#methane by the reaction of silylpotassium\ KSiH2\ with halomethanes ð50JA791\ 56IC0640\ 64JOM"81#052Ł and the pyrolysis of methylchlorosilanes ð56AG"E#566Ł\ but the yields were again in the lower region[ More recently\ tris"silyl#methane was obtained in high yield by a three!step synthesis presented in Scheme 0 ð78CB1004Ł[ An in situ Grignard reaction of easily accessible chlorophenylsilane with bromoform and magnesium gave tris"phenylsilyl#methane "6# in ca[ 49) yield[ The _nal conversion of bromo derivative "7# into tris"silyl#methane "0# has been accomplished through reduction with LAH in a two!phase system employing a phase transfer catalyst[ A similar route is suitable for the preparation of the homologous bis"silyl#methane ð89CB1976Ł and tetrakis"silyl#methane ð89AG"E#190Ł[ Br Br
SiH2Ph
PhSiH2Cl/Mg
Br
THF, reflux 45%
SiH2Ph
PhH2Si
SiH2Br
HBr 84%
SiH2Br
BrH2Si
(7)
(8)
SiH3
LAH 83%
SiH3
H3Si (1)
Scheme 1
Among the methods which can be employed to prepare tris"organosilyl#methanes the most straightforward one involves the MerkerÐScott procedure using magnesium or lithium reduction of halohydrocarbons and halosilanes in a polar solvent ð52JA1132\ 53JOC842\ 54JOM"3#87\ 69JOM"13#536Ł[ The reaction is usually performed by the addition of 0\0\0!trichloro! or tribromoalkane to a haloorganosilane "usually chlorotrimethylsilane# and Mg"Li# in THF[ In principle the synthesis provides a general route to symmetrically substituted tris"organosilyl#methanes\ but the correct choice of reagents and conditions is essential if good yields of pure compounds are to be obtained[ Experimental details for the preparation of tris"TMS#methane "2# from chloroform\ chloro! trimethylsilane and lithium metal are described in Inor`anic Synthesis "Equation "0## ð89IS128Ł[ A related preparation of the compound "Me1PhSi#2CH "69)# has been described starting from the corresponding chlorosilane\ bromoform\ and n!butyllithium ð74JCS"P1#618\ 82JOM"351#34Ł[ The trichloromethyl groups of a\a\a!trichloroethane ð52JA1132Ł\ 0\0\0!trichlorotoluene ð67CB2462Ł\ and a\a\a\a?a?a?!hexachloro!p!xylene ð56AG"E#831Ł can also be transformed into the tris"TMS#methyl groups[ Cl
TMS
TMS-Cl/Li
(1) Cl
Cl
THF, reflux 72%
TMS
TMS (3)
The reductive silylation was shown to tolerate an alkyne function[ Thus hexachlorobutyne!1 and
063
At Least One Metalloid or Metal
chlorotrimethylsilane react with lithium metal to furnish hexa"TMS#butyne!1 "8# in 47) yield "Equation "1## ð82JOM"351#20Ł[ Remarkably\ this compound\ owing to the steric shielding of the central p!system\ resembles trisilylmethanes in reactivity^ its C2C triple bond cannot be hydro! genated at 199>C:49 atm in the presence of a palladiumÐcharcoal catalyst[ Cl Cl Cl
Cl Cl Cl
TMS-Cl/Li THF, 20 °C
TMS TMS TMS
TMS TMS TMS
(2)
(9)
The partially alkylated halosilanes can also be used to obtain trisilylmethanes[ An example is the preparation of tris"dimethylsilyl#methanes "09# from dimethylchlorosilane and bromoform or a\a\a! tribromotoluene "Scheme 1#[ Bromination of silanes "09# and the subsequent reactions of the bromosilanes "00# with AgBF3\ t!butylamine\ and water illustrate the possible synthetic routes to Si!functionalized trisilylated methanes ð72JOM"141#170\ 82IC1297Ł[
Br Br
R
R
R
Me2SiHCl/Mg
Br
Br2
Si(H)Me2 Me2(H)Si Me2(H)Si (10)
THF, reflux
SiBrMe2 Me2BrSi Me2BrSi (11)
benzene, 5 °C
R = H, Ph AgBF4
(BrMe2Si)3CH
ButNH2 H2O
(FMe2Si)3CH (ButNHMe2Si)3CH (HOMe2Si)3CH
Scheme 2
A potentially very promising method for the build up of trisilylated C!0 units is the direct reductive silylation of carboxylic acid derivatives[ However\ whereas a!bis"TMS#alkanols can be readily obtained from esters using TMS!Cl:Na in THF ðB!70MI 595!90Ł\ attempts to realize the direct conversion of esters into trisilylated alkanes has so far had only limited success[ For example\ hexakis"TMS#!1!butene "01# could only be synthesized from dimethyl maleate in 0[4) yield "Equa! tion "2## ð82CB1116Ł[ O
O
TMS OMe
TMS-Cl/Mg/TiCl4
OMe
HMPA
TMS TMS (3)
TMS TMS
TMS (12)
HMPA = hexamethyl phosphoramide
For the synthesis of trisilylmethanes with di}erent silyl groups attached to the carbon atom the major synthetic pathway is a multistep reaction involving the interaction of a suitable Si!func! tionalized organometallic carbon nucleophile with a halosilane[ Scheme 2 illustrates this method! ology ð65JCS"D#1157\ 71CC0212\ 721AAC"386#10\ 74S606Ł[ Other typical examples are given in Schemes 3Ð 5 ð75CB0344\ 76AG"E#473\ 81ZN"B#794Ł[ Direct incorporation of a trisilylmethyl group into organic molecules may be achieved via organo! lithium or organomagnesium derivatives[ The organolithium reagents\ "R2Si#2CLi\ are available by metallation of tris"silyl#methanes with methyllithium in ether:THF ð69JOM"13#418\ 62JOM"44#198\ 72CC716\ 73JOM"158#106\ 75CC858\ 89IS128Ł\ but can also be generated at low temperatures from the tris"silyl#methyl halides and lithium metal or via the halogenÐmetal interconversion with phenyl! lithium "Table 0# ð75CC0932\ 81JCS"D#0904\ 81OM1827Ł[ Tris"TMS#methylmagnesium bromide is formed in 64Ð89) yields from "TMS#2CBr "in turn obtained by photobromination of neat "TMS#2CH at 079Ð089>C# and magnesium metal in diethyl ether ð81OM1827Ł[ Tris"TMS#methyllithium couples normally with methyl iodide to give the 0\0\0!tris"TMS#ethane[ Carbonylation leads to the acid "TMS#2CCO1H in 65) yield ð69JOM"13#418Ł[ The Grignard reagent
064
At Least One Metalloid TMS
i
Me4Si
Li (PMDETA)
iii
TMS
ii
ii
TMS
TMS
MgCl
Cl
TMS v
iv
TMS TMS
TMS
Cl
TMS
vi
Li (HMPA)
TMS
Li (TMEDA)
vii
vii
TMS TMS
TMS
TMS
vii
Li (THF)
TMS
SiR3
Reagents: i, BunLi/PMDETA, hexane, 20 °C; ii, TMS-Cl, hexane/ether; iii, Mg, ether, 20 °C; iv, ButLi/HMPA, THF, –40 °C, 5 h; v, BunLi/TMEDA, hexane, 25 °C, 12 h; vi, Li, ether, reflux, 24 h; vii, Me2PhSiCl, THF, 20 °C. (PMDETA = pentamethyldiethylenetriamine) Scheme 3 TMS Li
i
2 TMS
TMS
TMS
H
TMS
ii
Si TMS
H
I
TMS
TMS
iii
Si
TMS
TMS
I
TMS
TMS
TMS Si
Si
TMS
TMS
TMS TMS
TMS
i, SiH2Cl2, ether/pentane, –78 °C, 66%; ii, I2, 100 °C, 24 h, 37%; iii, C10H8Li, THF, –78 °C, 40% Scheme 4 Br TMS
TMS
Li
BunLi ether, –78 °C
TMS
TMS
TMS
130 °C, 12 h 90%
i, MeLi ii, H2O
SiBrBut2 TMS
Si(H)But2
But2SiHF
THF/ether 97%
TMS
Br2
TMS
CCl4, 0 °C 95%
SiMeBut2 TMS
TMS
Scheme 5 TMS
TMS
TMS
N
ButLi
Si N TMS
Cl
pentane –78 °C
TMS
TMS
N
But Si
N
Li Cl
CF3SO2O-TMS
TMS
N Si N
But TMS Cl
TMS
TMS Scheme 6
a}orded 0\0\0!tris"TMS#!1!phenylethane "63)# when derivatized with benzyl chloride ð81OM1827Ł[ Other carbon electrophiles such as nonenolizable aldehydes\ ketones\ acid chlorides\ and epoxides react with "TMS#2CLi to give the functionalized silanes "Scheme 6# ð70JCS"P0#858Ł[ However\ the method is not completely general^ it is limited by the readiness with which "TMS#2CLi abstracts a proton\ if one is available\ rather than attacks a carbon ð63AG"E#72\ 66CB741\ 70JCS"P0#858Ł[
065
At Least One Metalloid or Metal Table 0 Preparation of trisilylmethyllithium species[
Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Substrate Rea`ent Reaction conditions Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * MeLi Et1O:THF\ re~ux\ 4 h 89IS128 "TMS#2CH MeLi THF\ re~ux\ 5 h 72CC0289 "Me1Ph#2CH "TMS#2CBr Li ether\ 19>C\ 0 h 81OM1827 PhLi ether\ 9>C\ 2 h 81OM1827 "TMS#2CBr "MeOMe1Si#2CCl BunLi THF\ −67>C 75CC0932\ 81JCS"D#0904 "MeOMe1Si#1"TMS#CCl BunLi hexane\ −67>C 81JCS"D#0904 n Bu Li THF:ether\ −099>C\ 0 h 74JCS"P1#0576\ 80JOM"394#038 "MeOMe1Si#"TMS#1CCl ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
MeOCH2Cl or MeOCH2CH2OCH2Cl 78–82%
OR TMS TMS
65%
TMS
TMS Br
Br
NBS
66%
TMS TMS TMS
TMS
BCl3 or ZnBr2
TMS TMS
74%
TMS
TMS TMS
TMS
Li O Ph
PhCOCl
TMS TMS
TMS
TMS
O-TMS
TMS
Ph
OH ethylene oxide
TMS TMS
90%
COR
PCC 95%
TMS
TMS TMS
TMS
R = H or OH Scheme 7
The reaction of tris"TMS#methyllithium with O!ethyl thioformate gave the stable aliphatic thio! aldehyde "02#[ This was reduced with sodium borohydride to give the corresponding thiol "03# "Scheme 7# ð76JA168Ł[
Li
TMS TMS + TMS
S OEt
S THF, –78 °C
NaBH4
16%
TMS
TMS TMS
HS
100%
TMS
(13)
TMS TMS
(14)
Scheme 8
Tris"TMS#methyl!substituted ethene "04# is reported to be obtained by the reaction of 0\1! dilithioðtetrakis"TMS#Łethane with paraformaldehyde[ The formation of the compound implies 0\1! dianionic rearrangement of the silyl group "Equation "3## ð78JA2637Ł[ TMS TMS Li
TMS TMS Li
HCHO THF 73%
TMS TMS TMS (15)
TMS (4)
066
At Least One Metalloid
A quite di}erent route to trisilylated methanes and their derivatives involves the use as substrates of low!coordinate silicon derivatives[ In principle the insertion of unsaturated silicon compounds of the type "X2Si#1C1SiR1 into a polar elementÐhydrogen bond provides a general approach to tris"silyl#methanes[ Since the silaethenes are initially obtained from polysilylated methanes\ this appears to be a circuitous technique[ However\ it does lead to the speci_c polyfunctional compounds which are di.cult to prepare by other reactions ð73JOM"162#030Ł[ Thus alcohols\ phenols\ thiols\ hydrogen halides\ and amines add to the silaethenes "05# and "06# to give the insertion products "Equation "4##[ Ionic reagents like PhSLi and "PhO#1P"O#OLi have been employed in these reactions with equal success ð70CB2407\ 73JOM"162#030Ł[ The 0\0!dimethyl!1\1!bis"TMS#silaethene also inserts into the a!CH bond of pyridine to yield the trisilylmethane "07# "Scheme 8# ð75JOM"204#8Ł[ For all these reactions a nucleophilic attack mechanism can be invoked[ TMS
Me Si X Me (16) X = TMS (17) X = But2MeSi
TMS X H
AH
Me Si Me A
(5)
AH = H2O, ROH, RSH, R2NH, HHal
TMS TMS TMS (16)
Me Si Me
δ–
+
TMS H
Me Si Me N δ+
N
Me
TMS
TMS
Si Me TMS –
Me Si Me
TMS
N+
N
(18) Scheme 9
The formation of trisilylmethane derivatives proceeds equally well when in situ generated sila! ethene is treated with a proton donor reagent ð73JOM"162#030\ 74CRV308\ B!78MI 595!90Ł[ For example\ trisilylated methanes "08# have been isolated in good yield from reacting tris"TMS#methylsilicon halides with methanolic sodium methoxide[ The reaction is believed to proceed through an elim! ination\ analogous to E1 eliminations of alkyl halides\ involving synchronous attack of MeO− at a TMS group\ liberation of X−\ and formation of the transient silaethene followed by addition of methanol across the C1Si bond "Scheme 09#[ The compounds "TMS#2CSiPhMeF and "TMS#2CSi! PhCl1 react analogously to give "TMS#1CHSiPhMe"OMe# and "TMS#1CHSiPhCl"OMe#1 ð67JOM"046#C49\ 79JOM"080#244Ł[ It should be noted that in contrast to the silicon species\ the ger! manium compounds "TMS#2CGeR1X undergo normal "though very slow# direct nucleophilic sub! stitution at germanium ð79JOM"191#046Ł[ TMS TMS TMS
MeOH/NaOH
TMS
SiR2X
R
MeOH
TMS
R
>60%
TMS
SiR2OMe
Si reflux
TMS
(19) R = Me or Ph, X = Cl, Br or I R = Ph, X = F Scheme 10
The ene reactions of silaethenes are also potentially useful for the preparation of functionalized trisilylmethanes[ Thus silaethene "05# reacts with isobutene at −09>C to give compound "19#[ A similar reaction occurs between "05# and other alkenes ð76ZN"B#0951Ł[ The rates of these reactions are sensitive to steric hindrance but even the sterically encumbered silaethene "06# still adds propene
067
At Least One Metalloid or Metal
and isobutene ð75CB0356Ł[ The ene reactions of silaethenes with carbonyl compounds containing a proton in the a!position such as acetone\ cyclohexanone\ or ethyl acetate are also potentially useful for the preparation of functionalized trisilylmethanes "Scheme 00# ð72AG"E#0994\ 75CB0356\ 75JOM"204#8\ 76ZN"B#0951Ł[
R
TMS X
ether –78 to 20 °C X = TMS
Me Si Me
Me TMS Me Si TMS
Me TMS Me Si TMS
(16)
Me
R = Me
Si
R
TMS
Me TMS
(20) O
(16) X = TMS (17) X = TBDMS
R ether, –78 °C
Me TMS Me Si O X R Scheme 11
"ii# Compounds with an Si2C function as part of one or more rin` systems These can be prepared by a variety of methods of which the main ones are] "a# reductive silylation of a halohydrocarbon with a suitable halosilane "the MerkerÐScott procedure#^ "b# metal!induced coupling of chloromethylchlorosilanes^ "c# reaction between a lithiated cyclic carbosilane and a silicon electrophile^ and "d# cycloaddition to multiple carbonÐsilicon bond bearing silicon substituents at the carbon atom[ Synthesis of the tricyclic carbosilane "11# was accomplished by preparing the cyclic carbosilane "10# and reacting it with bromoform and lithium metal "Equation "5## ð61ZAAC"289#046Ł[ A similar reductive silylation route with silane "12# gave the tetrasilabicycloð1[1[1Łoctane "13# "Scheme 01# ð61ZAAC"289#080Ł[ 0\2!Disilabicycloð0[0[9Łbutane "15# has been synthesized by a method involving the low temperature reaction of carbosilane "14# with butyllithium in THF "Scheme 02# ð70ZAAC"364#76\ 73JOM"160#096Ł[ From the trisilylmethane "16# tris"dimethylchlorosilyl#ethene results in a remarkable yield "×74)# presumably via a silacyclopropane intermediate "Scheme 03# ð66ZAAC"329#010Ł[ Me Me Me Si
Me
Si
Si Br Br Br Si
Me Me (21)
Me Me Si Me HCBr3/Li
Si
Me
Me Si
Me
Si
Si
Me Si
Si
Me
Me
Me (6) Si Me Me
(22)
Synthesis of cyclocarbosilanes including an Si2C unit from {{carbon anion|| precursors appears to be a generally applicable method that is primarily limited by the availability of suitable starting materials ð63TCC32Ł[ Typically a lithiated cyclocarbosilane is generated in solution and then treated with the appropriate silylating reagent[ For example\ the conversion of 0\2\4! trisilacyclohexane "17# into trisilylated derivative "18# has been achieved by lithiation with BunLi:TMEDA complex followed by treatment with a chlorosilane "Scheme 04# ð72ZAAC"386#10Ł[ Among the many reactions of unsaturated siliconÐcarbon compounds which lead to cyclo! carbosilanes\ several include photochemical or thermal generation of silaethenes and their sub! sequent conversion into cyclic compounds containing an Si2C unit[ Thus irradiation of a benzene solution of "29# with a high!pressure mercury lamp gave 0\1!disilacyclobutane "20# in 89) yield "Scheme 05# ð68JA0237\ 70JA1213Ł[ Both photolysis and thermolysis of bis"TMS#diazomethane produce a carbene which rearranges
068
At Least One Metalloid Br
Li
SiPhMe2
Li
SiPhMe2 SiPhMe2 Me Si SiPhMe2
MeSiCl3
SiPhMe2
ether, –10 °C
79%
SiMe2Br SiMe2Br Me Si SiMe2Br
Br2 CCl4, 30 °C 95%
Si Si
HCBr3
Me Si
THF, 0 °C 25%
Si
(23)
(24) Scheme 12
Cl TMS
Cl
BunLi
Cl SiMe2Cl
SiMe2Cl
TMS
THF/ether –100 °C
Me Me Cl TMS Si
Li
TMS Cl Si Me Me
(25) Me
Me Si TMS
TMS Si
Me Me (26) Scheme 13
Me2ClSi
SiMe2CHCl
Me2ClSi
Cl
Me BunLi
Me2ClSi
Me
Me2ClSi
Me Si
Me2ClSi
Cl
Me2ClSi
85%
Me2ClSi
Cl
–
ether/pentane –100 °C
(27)
Me Si
Cl
SiMe2Cl
Me2ClSi Scheme 14
Me
Me Si
Me Si Me
Si Me Me
BunLi/TMEDA hexane
Me
Me
Me Si
Si Me
Si Me Me
TMS-Cl
Me
Me Si Me
Me Si Me
Si Me
Li
TMS (29)
(28) Scheme 15
via methyl migration to silaethene Me"TMS#C1SiMe1[ The latter dimerizes to produce as the major products cis! and trans!0\2!disilacyclobutanes\ Me"TMS#C"SiMe1#1C"TMS#Me "35)# ð79JA0473Ł[ Decomposition of compound "21# in the gas phase at 349>C a}ords product "22# via the cor! responding silaethene "Scheme 06# ð79JOM"075#298Ł[ Unsaturated systems of the type a1b\ a0b1c\ and a1b0c1d often combine with the C\C! disilyl!substituted silaethenes to give ð1¦1Ł!\ ð1¦2Ł!\ and ð1¦3Ł!cycloadducts containing Si2C units
079
At Least One Metalloid or Metal Ph Si TMS Ph
TMS
TMS
hν
Ph •
benzene, 20 °C
Si
TMS
Ph
(30) TMS
TMS TMS
TMS 1/2
Ph
TMS
90%
1/2
Ph Si Si Ph
Ph Ph
Si
TMS
Ph Ph
•
Si
TMS
Ph TMS
(31) Scheme 16
Me TMS
SiPh2F
TMS
TMS
450 °C
TMS
Ph
Si
Ph
Si
TMS
Si TMS
Ph
Me (33)
(32)
Me
Scheme 17
ð73JOM"162#030Ł[ However\ practically all such reactions are only useful for speci_c derivatives or speci_c groups of compounds[ Characteristic examples are given in Scheme 07[ The review by Wiberg contains experimental details for the preparation of compounds "23#Ð"25# ð73JOM"162#030Ł[ R
R
R
R
Si Me TMS TMS Me (34)
TMS TMS (16)
N N
Me Si Me
N N TMS
Si Me
TMS Me (35)
Ph Z
Me Me
Si
TMS TMS
Z
Z = O-, N-TMS
Ph
(36)
Scheme 18
5[95[1[0[1 Functions bearing three borons Tri!coordinate boron compounds\ BX2\ have a formally vacant orbital in the valence shell and are isoelectronic with the corresponding carbocations\ ¦CX2[ For triorganoboranes\ BR2\ there is little possibility of populating this orbital by conjugative interaction "apart from hyperconjugation# with the substituents[ It is hardly surprising\ therefore\ that the simple tris"boryl#methanes such as HC"BH2#2 or HC"BMe2#2 are highly reactive\ unstable compounds[ This is also a major reason why
070
At Least One Metalloid
compounds of the type HC"BX1#2 that have actually been isolated\ have X groups in which a heteroatom capable of donating p!electron density is bound to boron[ The preparation and proper! ties of the species containing a B2C function vary a great deal with the structural type and character of substituents\ and they will therefore be discussed under these headings[
"i# Tris"dihaloboryl#methanes\ RC"BHal1#2 The homologous C"BHal1#nHal3−n "n 0Ð3# were observed in the reaction between various boron halides and carbon vapor generated from a carbon arc[ In this manner B1Cl3 a}orded a mixture of C"BCl1#3\ ClC"BCl1#2\ and Cl1C"BCl1#1^ and BCl2 yielded the last two compounds as well as Cl"Cl1B#C1C"BCl1#1[ Compounds ClC"BCl1#2 and Cl1C"BCl1#1 are thermally unstable above −19>C[ From the reaction of B1F3 and carbon vapor\ C"BF1#3 was only isolated in a small amount ð58JCS"A#0771Ł[ The method for synthesizing tris"dichloroboryl#methane "26# is the exchange reaction of tris! "dimethoxyboryl#methane with boron trichloride and a catalytic amount of lithium borohydride "Equation "6##[ Reaction conditions were found to be critical^ it is important that a large excess of boron trichloride be used and that the crude product be distilled rapidly\ since it is particularly unstable to be stored ð62IC1361Ł[ Reaction of structure "26# with boron tribromide failed to lead to pure tris"dibromoboryl#methane\ HC"BBr1#2\ but bromineÐchlorine exchange did occur and the HCB2 signal of HC"BBr1#2 appeared in the NMR spectrum ð61MI 595!90\ 62IC1361Ł[ B(OMe)2
(7)
31%
B(OMe)2
(MeO)2B
BCl2
BCl3/LiBH4(cat.)
BCl2
Cl2B (37)
There are several reports in the literature that the addition of boron halides across multiple bonds leads to 0\0!diboryl!substituted alkanes ð71HOU"02:2a#0\ 80CRV24Ł[ Thus\ diboron tetrachloride adds twice to alkyne giving CH"BCl1#1CH"BCl1#1\ and dehydroboration of alkynes with dichloroborane ethyl etherate "BHCl1=Et1O# in the presence of BCl2 yields `em!diboryl compounds RCH1CH"BCl#1 ð65JA0687Ł[ However\ despite many unique advantages associated with hydroboration and halo! boration\ the synthesis of 0\0\0!tris"dihaloboryl#alkanes via alkynes has not yet been realized[
"ii# Tris"dialkoxyboryl#methanes\ RC"B"OAlk#1#2 These compounds have also been called methanetriboronic esters[ The compound HC"B"OMe#1#2 is named in Chemical Abstracts as methylidynetrisboronic acid hexamethyl ester[ The preparation and properties of tris"dialkoxyboryl#methanes have been reviewed up to 0865 ð64S036\ B!66MI 595!90Ł[ Tris"dimethoxyboryl#methane "27# is readily available on a large scale by direct reaction of chloroform with dimethoxyboron chloride and lithium metal in THF "Equation "7## ð57JA1083\ 58JOM"19#08Ł[ The procedure has been described in detail^ the product is isolated by distillation ð64S036Ł[ 0\0\0!Trichloroethane and a\a\a!trichlorotoluene react analogously\ but attempts to condense polyhalomethanes with bis"dimethylamino#boron chloride\ ClB"NMe1#1\ have failed[ Cl Cl
B(OMe)2
ClB(OMe)2/Li
Cl
THF, –40 °C 25–35%
(8) B(OMe)2
(MeO)2B (38)
Transesteri_cation of structure "27# with ethylene glycol in THF precipitates cyclic boronic ester "28# "74)# ð64JA4597\ 65JOM"009#14Ł[ Similarly the cyclic boronic esters "39# and "30# were formed from the tris"dimethoxyboryl#methane and pinacol or 0\2!propanediol in the presence of a catalytic amount of boron tri~uoride etherate ð69JOM"13#152\ 63JOM"58#34\ 64JOM"82#10Ł[ These compounds
071
At Least One Metalloid or Metal
proved to be more stable than their acyclic analogues and better yields of products have been obtained from them in a wide variety of reactions ð64S036Ł[
O O B O
O B
O
O B
B O
O
O
B
B
O
O
B
O O
O
O
B
B O
(39)
O
O (41)
(40)
The transborylation reaction of tris"dimethoxyboryl#methane "27# with triethylborane in the presence of {{ethylborane|| provides a route to the only known 0\0\0!tris"dialkylboryl#methane "32#[ The initially formed mixed triborylmethane "31# undergoes transformation to the compound "32# on heating at about 099>C "Scheme 08# ð64LA0228Ł[ The full scope of this reaction\ however\ remains to be explored further[ B(OMe)2
BEt3/[>BH]
B(OMe)2
(MeO)2B
B(OMe)Et
BEt3/[>BH]
BEt2
B(OMe)3
Et2B
(38)
BEt2 BEt2
Et2B
(42)
(43)
Scheme 19
The alkylation of the anionic species derived from methanetetraboronic esters ð62JA4985Ł by alkyl halides was found to proceed readily\ but unfortunately the reaction leads to a mixture of monoalkylated and dialkylated derivatives\ as illustrated in Scheme 19 ð69JOM"13#152\ 64S036Ł[ Evi! dently the initially formed 0\0\0!triborylalkane "35# is able to transfer a dimethoxyboryl group to tris"dimethoxyboryl#methide ion "34#\ thus undergoing disproportionation[ Condensation of triborylmethide anions with aldehydes and ketones a}ords alkene!0\0!diboronic esters "37#\ pre! sumably via the unstable cyclic borate anion "36# "Scheme 10# ð69JOM"10#P5\ 63JOM"58#42Ł[ The reaction is a general one and tolerates other functional groups\ including a!chloro\ carbethoxy\ or tertiary amino substituents ð63JOM"58#52\ 64JOM"82#10\ 67JOC849\ 67JOM"041#0Ł[ (MeO)2B
B(OMe)2
(MeO)2B
B(OMe)2
Li
B(OMe)2
(MeO)2B
B(OMe)2
MeLi THF, –70 °C
(44)
R
RI
(MeO)2B
(45) R (MeO)2B
Li
B(OMe)2
(45)
B(OMe)2
–(44)
(46) R
RI
B(OMe)2
(MeO)2B
R B(OMe)2
R = Me, Et Scheme 20
OR Li (RO)2B
B(OR)2 B(OR)2
O B – OR
R1COR2 THF, –70 °C
R1
41–93%
B(OR)2 R2 B(OR)2 (47)
O B(OR)2 = B(OMe)2, B O
O
Scheme 21
,B O
B(OR)2
R2
B(OR)2 (48)
O ,B
R1
O
072
At Least One Metalloid
Finally\ it should be noted that metallation of triborylmethide anions with Ph2ECl\ where E Si\ Ge\ Sn\ or Pb\ provides a useful method for the synthesis of compounds Ph2EC"B"OR#1#2 ð58JA5430\ 62JA4985\ 62JOM"46#114\ 62JOM"46#120\ 63JOM"58#52Ł[
"iii# Boracycloalkanes involvin` a B2C function There are several speci_c methods which are useful for the preparation of boracycloalkanes containing a B2C unit[ Compounds "49# are obtained in up to 49) yield via the isolable 0\0!bis"dialkylboryl#!0!alkenes "38# from dialkyl"0!alkynyl#boranes and dialkylboranes "Scheme 11# ð53TL0556\ 64LA0228\ 73HOU"02:2c#051Ł[ These have been classi_ed as pentaalkyl!0\4!dicarba!closo!pentaboranes"4#\ but the valency requirements of all atoms can be satis_ed without the need to involve electron!de_cient bonding ð69JA3047\ 63JCS"D#554\ 80CB1534Ł[ R2
R12B
R12B
HBR12
R2
5 °C
R2
HBR12
R1
B R1
B B
R1
2B
R1
(49)
R2
R1 = Me, Et, or Pr R2 = H, Me, or C6H13
(50)
Scheme 22
An e.cient synthesis of 1\2\4\5!tetraborabicyclo ð1[0[0Łhexane "40# utilizes the reaction of 0\0\1\1! tetrakis"chloro"diisopropylamino#boryl#ethane with sodium:potassium alloy in benzene "Equation "8## ð89AG"E#181Ł[ R
R R R Cl
B
B Cl H B Cl
H Cl
B
B
R
Na/K
R R
B B
benzene, reflux 73%
B
R = Pri2N
R (51)
(9)
Sealed!tube pyrolysis of BMe2 permits isolation of 1\3\5\7\8\09!hexaboraadamantane "41# in 14) yield ð62CC421\ 64JCS"D#037Ł[ This boronÐcarbon cage compound appears to be unique in having a stoichiometry expected of a carborane and yet not possessing the usual carborane type of structure ð66JCS"D#025Ł[ The ethyl analogue "42# is produced by thermal decomposition of the tris! "diethylboryl#methane or polyboryl compounds\ themselves obtainable by hydroboration of dial! kyl"alkynyl#boranes ð64LA0228Ł[ R
R B
R
B B B R
R
B R
B
(52) R = Me (53) R = Et (54) R = But (55) R = Cl (56) R =Br (57) R = Me2N
Pyrolysis of alkyldichloroboranes such as MeBCl1\ Cl1BCH1CHBCl1 or "Cl1B#2CH at 349>C forms hexachlorohexaboraadamantane "44# "4Ð17)#[ The synthesis of hexabromohexabora! adamantane "45# has been achieved by heating Me1BBr or MeBBr1 to 419>C[ The reactions of structure "44# with t!butyllithium and diethylamine at −59>C lead to the formation of the cor! responding t!butyl! "43# and dimethylamino! "46# derivatives ð78JOM"256#08Ł[ Another route to compounds possessing C3B5Ðadamantane structure uses dimerization of the C1B2!closo!carbaborane "49# by treatment with potassium followed by iodine "Equation "09## ð74AG"E#215Ł[
073
At Least One Metalloid or Metal Et Et
B
Et B
2K/I2
B Et B
B
(10)
B
THF, 20 °C, 4 d 27%
Et
B Et
B
B
Et
Et
(50)
(58)
The formation of compounds C5H8=x"BNPri1# "x 0Ð5# from the reaction of benzene with dich! loro"diisopropylamino#borane and sodium:potassium alloy in 0\1!dimethoxyethane has been con! _rmed by mass spectroscopic studies[ The compound with x 2 was separated from the reaction mixture and identi_ed as 1\7\8!triborabicycloð2[2[0Łnona!2\5!diene!1\7\8!triamine "48# "Equation "00## ð77JOM"236#00Ł[ Similarly\ 0\3\5!triboraspiroð3[3Łnona!1[7!diene "59# has been isolated from the reaction of benzene with subvalent boron species ð89CC630Ł[
Pri2N
B
B
NPri2
B NPri2 (59)
2n Na/K n Cl2BNPri2
(11)
C6H6•xBNPri2
10n –2n MICl (DME)
Pri2N B B
B NPri2
Pri2N (60)
Addition of a mixture of bis"TMS#butadiyne or 1\4!dimethyl!1\3!hexadiene with Pri1NBCl1 to Na:K alloy in hexane gave the 1\3\4!triborabicycloð0[0[0Łpentane "23)# "Equation "01## ð81CB0796Ł[ TMS Pri2N BNPri
Na/K,Cl2
TMS
2
TMS hexane, RT
TMS
B NPri2 B NPri2
(12)
A unique method for the synthesis of compounds containing a B2C function utilizes low!coor! dinate boron derivatives[ 1!Boranediyl!0\2!diboretanes "50# smoothly add ethanol to give com! pounds of structure "51# in quantitative yields "Equation "02## ð78AG"E#670Ł[ Despite considerable synthetic potential\ this method is clearly limited by the availability of the requisite boron substrates[ Ar TMS
Ar
B
EtOH
TMS
B
Ar
100% (NMR)
TMS
B
OEt
(13)
B Ar TMS
B Ar (61)
Ar (62) Ar = 2,4,6-Me3C6H2, 2,3,5,6-Me4C6H
074
At Least One Metalloid 5[95[1[0[2 Functions bearing three germaniums
In contrast to numerous publications dealing with trisilylmethanes\ literature reporting tri! germylmethyl derivatives are sparse[ It is curious that straightforward synthetic routes are known for compounds containing Si2C functions but not for those with functions bearing three germaniums[ It appears that many of the methods suitable for the synthesis of mono! and bisgermylalkanes are ine}ective or not applicable to trigermylmethanes[ For example\ although the compound "Et2Ge#1CH1 was successfully obtained by the reaction of triethylgermylpotassium with dichloromethane\ attempts to prepare "Et2Ge#2CH by a similar route have failed\ because the metalÐhalogen exchange reaction\ followed by conden! sation\ predominated ð56TL0332Ł[ The reaction of Ph2GeNa with chloroform in liquid ammonia was also unsuccessful[ Only one of the three chlorine atoms bonded with a carbon is quantitatively replaced by the Ph2Ge group^ a second chlorine is largely substituted while the third is completely replaced by hydrogen ð21JA0511\ 41JA0307Ł[ The _rst stable compound with a Ge2C function\ 0\4\4\4!tetrakis"trimethylgermyl#!0\2!pentadiyne "53#\ has been synthesized by condensation of the tetralithium compound from 0\2!pentadiyne with chlorotrimethylgermane "Scheme 12# ð62JA2213Ł[ Reaction leads to a mixture of two pergermylated isomers\ "52# "31)# and "53# "06)#\ which were separated by preparative gas chromatography[ The method is only of limited value\ since polylithiated species are not readily available[ BunLi/TMEDA
Me3GeCl
C5Li4
THF
n-butane
GeMe3 GeMe3
+
Me3Ge
GeMe3 GeMe3
Me3Ge
• Me3Ge
GeMe3 (63)
(64) Scheme 23
0\0\0!Tris"triethylgermyl#acetone was reported to form in very low yield from the reaction of triethylgermyldiazoacetone with an equimolar amount of bis"triethylgermyl#mercury in the presence of metallic copper ð66JOM"031#044Ł[ Although this transformation is of some mechanistic interest\ it does not provide a synthetically viable route to trigermylmethyl species[ The more ~exible and useful route to 0\0\0!trigermylalkanes involves stepwise base!assisted introduction of an R2Ge group into compounds containing an activated methyl group[ Sato and co! workers have prepared a series of trigermylacetic acid derivatives using this approach ð77JOM"243#044\ 77OM628\ 89OM0214Ł[ Some of these reactions are outlined in Schemes 13\ 14\ and 15[ The reaction of the lithium salt of trimethylgermylacetonitrile with bromotrimethylgermane is not straight! forward and leads to a mixture of germylated species "Scheme 13#[ Detailed investigation showed that the trimethylgermylacetonitrile anion readily reacts with Me2GeCH1CN via intermolecular anionic rearrangement of the Me2Ge group to give bis"trimethylgermyl#acetonitrile anion and MeCN[ Anion "Me2Ge#1C−CN\ prepared from structure "55# with an equimolar amount of lithium diisopropylamide "LDA#\ is stable enough at low temperature[ However\ treatment of "55# with a 9[4 molar equivalent of LDA gives a mixture of germylated products ð76SC0162Ł[ i, 2 BunLi ii, 2 Me3GeBr
Me3GeBr/Zn
Cl
CN
Me3Ge
benzene/THF 71%
ether, –78 °C
(65)
CN
NC
+ GeMe3
Me3Ge
CN
(66)
Me3Ge
GeMe3 GeMe3
(67) Scheme 24
Trimethylgermylation of ethyl lithioacetate gave a high yield of ethyl"trimethylgermyl#acetate "57#[ The use of excess amounts of LDA and Me2GeCl a}orded ethyl tris"trimethylgermyl#acetate "58# in high yield "Scheme 14# ð77OM628Ł[ Under approximately the same conditions\ the tris! "trimethylgermyl#acetamide "69# has been obtained in 61) yield "Scheme 15# ð77JOM"243#044Ł[
075
At Least One Metalloid or Metal i, LDA ii, Me3GeCl
O
i, 2 LDA ii, 2 Me3GeCl
MeCOOEt
Me3Ge
ether, –78 °C 78%
Me3Ge
COOEt THF –78 °C 82%
Me3Ge
(68) Scheme 25
i, 2 LDA ii, 2 Me3GeCl
O
GeMe3
N
N
Me3Ge
THF –78 °C 82%
i, BunLi ii, Me3GeCl
Me3Ge
0 °C, 72%
Me3Ge
O
OEt GeMe3 (69)
GeMe3 N O (70)
Scheme 26
The LAH reduction of structure "58# gave a 67) yield of 1\1\1!tris"trimethylgermyl#ethanol\ and treatment with n!butyllithium at room temperature a}orded an 75) yield of 0\0\0!tris! "trimethylgermyl#!1!hexanone ð77OM628Ł[
5[95[1[0[3 Functions bearing mixed metalloids Several procedures are available for the synthesis of compounds of the type RC"E0Xm#! "E1Xn#"E2X"m#n#\ where E0\ E1\ and E2 Si\ B\ or Ge\ but two groups of reactions are most important[ The _rst group includes the reactions of organometallics RC"M#"E0Xm#"E1Xn# with inorganic or organoelement halides\ Xm"n#E2Hal\ and the second is the reactions based on unsatu! rated germanium or boron compounds containing elementÐcarbon double bond\ XmE0 C"E1Xn#"E2Xm"n##[
"i# Synthesis based on a!silyl!\ boryl!\ or `ermyl!substituted or`anometallics Three typical examples illustrating this methodology are shown in Equations "03#Ð"05# ð65JOM"009#14\ 67JOM"042#142\ 78AG"E#44Ł[ The requisite organometallics can be obtained by methods which are discussed in Section 5[95[1[1[ MgCl TMS
TMS
ether, 80%
(14) TMS
TMS
TMS
Li
BCl3
TMS
TMS
GeCl3
GeCl4
ether, 20 °C 38%
TMS
TMS B TMS
Cl
Li O
(15)
GePh3
B
B
O
O
O
Ph3GeCl ether, 20 °C 42%
O
B
B
O
O
O
(16)
In principle\ the approach provides a general synthetic pathway to compounds containing mixed metalloid functions\ but the correct choice of the reactants and reaction conditions is very important[ The best results were obtained by the low temperature reaction of a functionalized organolithium or organomagnesium compound with a metalloidal halide in ethereal or THF solution[ The group on metalloid which is usually replaced includes Cl\ F\ RO\ or "TMS#1N ð75CB1855\ 78CB0946\ 80POL0042Ł[ Germanium chlorides react with a!silylated organometallics with retention of the oxidative state of germanium[ For example\ treatment of GeCl1"diox# or Ge"N"TMS#1#1 with an equimolar amount of MgCl"CH"TMS#1# or Mg"CH"TMS#1#1 in ether leads to the bis"bis"TMS#methy#lgermylene "60# in 59Ð69) yield "Equation "06## ð65CC150\ 65JCS"D#1157\ 71CC0396\ 73CC379\ 75JCS"D#0440Ł[ The related preparation of bis"TMS#methyl"pentamethylcyclopentadienyl#germylene "61# has been described
076
At Least One Metalloid
starting from Me4C4GeCl and "TMS#1CHLi "Equation "07## ð75OM0833Ł[ It should be noted that bis"TMS#methyl!substituted germylenes such as structures "60# and "61# and "TMS#2CGeCH"TMS#1 ð80OM0536Ł represent a unique class of compounds\ which can exist as monomers "carbene ana! logues# or dimers "alkene analogues# depending on the structure and phase state ð80CRV200Ł[ If an electrophile such as iodine\ methyl iodide\ acetyl chloride\ a diazoalkane\ or a diazidosilane is added to the germylene "61#\ then high yields of the oxidative addition products containing the Ge"IV#CH"TMS#1 unit are obtained ð75OM629\ 83OM323\ 83OM325Ł[ A reaction of germylene "60# with an alcohol provides the functionalized germane HGe"CH"TMS#1#1OEt ð70JOM"101#C3Ł[ [(TMS)2CH]2Mg
GeCl2(diox)
TMS
(TMS)2CHLi
TMS (17)
ether, 60–70%
Me5C5GeCl
Ge
TMS TMS (71) Me5C5Ge
TMS (18)
benzene/ether –80 °C, 76%
TMS (72)
"ii# Synthesis based on low!coordinate boron and `ermanium derivatives C\C!Disilyl!substituted methyleneboranes\ XB1C"TMS#1 ð82AG"E#874Ł\ and germaethenes\ X1Ge1C"SiR2#1 ð73JOM"162#030\ 89CRV172Ł\ provide access to a variety of compounds containing mixed metalloid functions\ but the scope of the reactions is restricted to the preparation of speci_c polyfunctional compounds[ At a temperature of 499Ð599>C methyleneboranes "62# and "63# undergo rearrangement into cyclic compounds in excellent yield ð89CB636Ł[ In analogous conditions the methyleneborane "64# is transformed to an azasilaboratedine "Scheme 16# ð78CB484Ł[ Me 560 °C
B
R = Ph, 79%
Si
TMS Me
TMS
580 °C
TMS
R = PhCH2, 92%
Me
B
Me
B R
TMS
Si Me
Me
(73) R = Ph (74) R = PhCH2 (75) R = Pri2N Me
Pri 520 °C
N Si Me B
R = Pri2N, 46%
Me
TMS
Scheme 27
Treatment of the trisilyl"germyl#methane "65# with CsF in DIGLYME leads to a compound of structure "67#[ The reaction is believed to take place by initial formation of the unstable germaethene "66#\ which because of steric hindrance\ cannot undergo cyclodimerization and looses a TMS group to give a second transient germaethene "Scheme 17# ð72IZV848Ł[
TMS TMS
GePh2Cl TMS (76)
CsF DIGLYME 48%
TMS TMS
TMS
Ph Ge Ph (77) Scheme 28
Ph Ge Ph
Ph
Ph Ge
TMS
TMS Ge Ph Ph (78)
077
At Least One Metalloid or Metal
A variety of disilyl"boryl#methanes has been prepared by making use of the high reactivity of the B1C double bond towards protic agents and organolithium compounds ð82AG"E#874Ł[ Some of these reactions are outlined in Scheme 18 ð76CB0958\ 78CB484Ł[ Borinanes "79# were obtained from the addition of HCl or HN"TMS#1 to the B1C bonds of boranediylborinanes "68# "Equation "08## ð81AG"E#0273Ł[ A related preparation of the 0\2!diboretane "71# has been described starting from germaethene "70# "Equation "19## ð76AG"E#687Ł[ Pri2N
HX
TMS B
X = Hal, RO, R2N
X
TMS
TMS B Pri2N
TMS
i, MeLi/TMEDA ii, H+
Pri2N
hexane, –78 °C 79%
Me
TMS B TMS
Scheme 29 R B B
R
R
B
HX
TMS
(19)
TMS
TMS (79)
B(X)R
TMS (80) R = But, 2,3,5,6-tetremethylphenyl X = Cl, (TMS)2N R
R TMS
B
TMS
B
X Ge X
HCl
TMS
B
TMS
B
GeX2Cl
(20)
R (82)
R (81) R = But, X = (TMS)2N
Germaethene "72# generated as a reaction intermediate by thermal elimination of LiCl from Me1ClGe0C"Li#"TMS#1\ can be converted into various compounds containing an Si1"Ge#C function and in some cases this provides the best route to the new species "Scheme 29# ð75CB1855\ 75CB1879\ 76CB0192Ł[ Compound "74# has been synthesized by a method involving the low temperature reaction of kinetically stabilized germaethene "73# with methanol "Equation "10## ð80POL0042Ł[ TMS TMS
TMS
OMe TMS
TMS MeOH
Ge
Ge TMS
TMS TMS (84)
TMS TMS
ether, –20 °c 81%
(21) TMS TMS
(85)
"iii# Miscellaneous 0\2!Digermacyclobutane "75# has been found among the products of {{direct synthesis|| from TMS"dichloromethyl#silane "Equation "11## ð61ZOB0410Ł[ The reaction of 0\2!diborete "76# with potassium or lithium in THF leads to compounds 1K¦"76#1− or 1Li¦"76#1−\ which are protonated with "TMS#1NH to yield the 0\2!diboretane "77#[ Reaction of "76#1− with MeI a}ords the 0\2! diboretane "78# "Scheme 20# ð78CB0770Ł[ Cl Cl
Cl Ge
"Ge/Cu"
TMS Cl
TMS
370–390 °C 4%
TMS Ge Cl
Cl (86)
(22)
078
At Least One Metalloid TMS Me2Ge
TMS MeO
TMS OMe
TMS OMe
MeOH
R
TMS Me Ge Me TMS (83)
R
R (R = H, Me, CMe=CH2)
TMS
TMS
Me2Ge
TMS
Me2Ge
TMS
R
R
Scheme 30 R 2N TMS
TMS
B Cl
TMS
2K
B TMS
THF
B Cl R2N
2M+ (87)2–
NR2
R2N (87)
TMS
2M
B THF
TMS
TMS
TMS B
B
(TMS)2NH
(87)2–
2 MeI
NR2
R2 N
B
(88)
B NR2
R2 N (89) Scheme 31
5[95[1[1 Functions Containing Metalloids and Metals 5[95[1[1[0 Functions bearing silicon"s# and metals"s# This section is devoted to methods of preparing a!silylated organometallics having the general structure RC"SiX2#n"MLm#2−n\ where M is a metal\ n 0 or 1\ and R H\ alkyl\ aryl\ or hetaryl[ These compounds are of special interest due mainly to _ndings that silylmethyl groups like "TMS#1CH or "TMS#2C combine bulkiness with the capability to form strong metalÐcarbon bonds and that organometallic compounds bearing the polysilylmethyl group often possess unique proper! ties and have unusual structures ðB!74MI 595!90\ B!80MI 595!90Ł[ Although a!metallated organosilane chemistry has been reviewed extensively since the early 0879s ð79HOU"02:4#16\ B!70MI 595!90\ B!72MI 595!90Ł\ polysilylated organometallics have received only passing comment within reviews with much wider scope ðB!74MI 595!90\ 80COS"0#0Ł[
"i# Alkali metal and ma`nesium derivatives of silylmethanes In the mid 0889s there are four general methods for the production of compounds of this type[ These are] "a# metalÐhydrogen exchange reactions of silylmethanes with basic metal!containing reagents^ "b# oxidative metallation of halo"silyl#methanes^ "c# organometallic addition to vinylsilanes^ and "d# transmetallation of an already a!metallated organosilanes[ Representative examples illustrating the synthesis of alkali metal and magnesium derivatives of
089
At Least One Metalloid or Metal
silylmethanes which have obvious potential synthetic utility are given in Table 1[ A few of the silylmethyl derivatives of the alkali metals display unique aggregate structures and these are discussed by Williard ð80COS"0#0Ł[ Table 1 Preparation of trisilylmethyllithium derivatives of the alkali metals and magnesium[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Compound Method of preparation Reaction conditions Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * t "TMS#1CHLi "TMS#1CH1 ¦Bu Li THF:HMPA "ca[ 3 ] 0#\ 66CB741\ 79JA0473 −67>C "TMS#1CHLi "TMS#1CH1 ¦BunLi¦TMEDA hexane\ 01 h\ 14>C 71CC0212 "TMS#1CH1 ¦BunLi¦PMEDA hexane\ 9[4 h\ 19>C 71CC0212 "TMS#1CHLi "TMS#1CHLi "TMS#1CHCl¦Li ether\ re~ux 65JCS"D#1157\ 79JA0473 "TMS#2CH¦MeOLi HMPA\ 19>C 62TL3082 "TMS#1CHLi "TMS#"MeOMe1Si#CHLi "TMS#"MeOMe1Si#CH1 ¦ButLi pentane\ 19>C 78JOC0673 "TMS#1CHR¦BunLi THF:hexane 75CC561 "TMS#1CRLia a n "TMS#1CRLi "TMS#1CHR¦Bu Li¦TMEDA hexane 73CC0697 "TMS#1CRLia "TMS#1CHR¦BunLi hexane:ether\ 19>C\ 0 h 72CC0308\ 73CC0697 "TMS#1CHR¦BunLi¦TMEDA hexane\ 19>C 73JCS"D#0790 "TMS#1CRLib "TMS#1CHNa "TMS#2CH¦NaOMe HMPA\ 19>C 62TL3082 "TMS#1CHLi¦ButOK hexane\ 19>C\ 05 h 80OM0693 "TMS#1CHK "TMS#1CHCl¦Mg ether\ re~ux\ 3 h 80JOM"310#064 "TMS#1CHMgCl ð"TMS#1CRŁ1Mga "TMS#1CHR¦MgBunBus heptane 75CC561 TMSCHBr1 ¦Mg"Hg# diisopropyl ether 75TL5012 TMS!CH"MgBr#1 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a
R 1!pyridyl[
b
R 3!methylphenyl[
"a# MetalÐhydro`en exchan`e[ The methylene group between two silicon atoms shows enhanced reactivity with respect to proton abstraction by strong bases\ therefore many bis"silyl#methanes undergo metalÐhydrogen exchange on reaction with alkyllithium reagents ð66CB741\ B!72MI 595!90\ 72ZAAC"386#10Ł[ In practice\ these reactions require strongly coordinating solvents or the use of alkyllithiums in the activating presence of TMEDA or potassium t!butoxide[ The successful prep! aration of bis"TMS#methyllithium can be achieved from the bis"TMS#methane using t!butyllithium in hexamethylphosphoramide "HMPA# ð62TL3082\ 63AG"E#72Ł\ t!butyllithium in THF with HMPA at −67>C ð66CB741\ 79JA0473Ł\ BunLi:ButOK reagent in THF solution ð80OM440Ł or the TMEDA complex of n!butyllithium in hexane ð71CC0212Ł[ The last procedure provides one of the simplest routes to "TMS#1CHLi[ In addition\ a feature of the use of TMEDA is that it enables crystalline monomeric lithium derivatives to be isolated[ Silylated product yields for the system TMS! CH1TMS:BunLi:ButOK were in the range 67Ð80) ð80OM440Ł[ Metallation of the carbosilane "TMS#1CHSiMe1CH1TMS gave\ as expected\ "TMS#1C"Li#SiMe1CH1TMS\ since the indicated car! banion is stabilized by three silyl groups[ Only monometallation could be achieved for the carbosilane TMS!CH1SiMe1CH1SiMe2 ð80OM440Ł[ Poly"dimethylsilene#\ "Me1SiCH1#n\ the poly! mer formally derived from dimethylsilaethene\ Me1Si1CH1\ has been shown to be metallated by BunLi:ButOK in THF to give a polycarbosilane in which\ on average\ every fourth CH1 group in an SiCH1Si environment is metallated ð80OM440Ł[ Methoxydimethylsilyl"TMS#methyl lithium\ HC"Li#"TMS#SiMe1OMe\ a reagent useful for the direct conversion of aldehydes and ketones to vinylsilanes\ is readily formed in hydrocarbon solvent from the appropriate silane and t!butyllithium ð78JOC0673Ł[ Access to the p!xylene compound p! MeC5H3CH"TMS#1Li is possible by using BunLi:TMEDA in hexane ð73JCS"D#0790Ł[ However\ organolithium tertiary amines reagents failed to yield the dilithium derivative from 0\3!bis"bis! "TMS#methyl#benzene ð73JCS"D#0790Ł[ Lithium t!butylbis"TMS#acetate\ "TMS#1C"Li#CO1But\ results from the appropriately substituted acetate using LDA in THF at −67>C ð65TL1626\ 66JOC1927Ł[ This organolithium compound is a useful synthetic intermediate in the Peterson alkenation reaction ðB!72MI 595!90Ł[ Reaction of the pyridine functionalized bis"TMS#methane "89# with n!butyllithium in hexane yields complex "80#\ whereas metallation of "89# with BunLi and TMEDA in hexane a}ords lithium derivative "81#[ Both compounds contain unprecedented h2!azaallyl ligand geometries ð73CC0697Ł[ Treatment of 1!bis"TMS#methylpyridine with BunLi in ether or THF yields binuclear complex "82# "Scheme 21# ð72CC0308Ł[ A procedure for the preparation of 1!lithio!0\0\2\2\4\4!hexamethyl!0\2\4!trisilacyclohexane by the metallation of cyclo!ðMe1SiCH1Ł2 with BunLi:TMEDA in hexane has been developed ð72ZAAC"386#10\ 81OM2353Ł[ The yields of monolithium derivative in this synthesis is very good\ but further met! allation did not occur at 19>C even when excess metallation reagent was used[ Similarly 0!TMS! 0\2\4!trisilacyclohexane can be selectively metallated at the more sterically available ring proton^
080
At Least One Metalloid
BunLi in hexane 20 °C
N
TMS
:
N
Li TMS
CH(TMS)2
(TMS)2HC
(90)
BunLi in hexane, 20 °C + TMEDA
(91)
BunLi in ether 20 °C, 1 h
ether, 20 °C
TMS N
TMS
N
TMS
:
Li Li
Me2N
TMS NMe2
Li
TMS
N
TMS
(92)
(93) Scheme 32
however\ if not immediately quenched the kinetic product "83# rearranges to the more stable lithium derivative "84# "Scheme 22# ð72ZAAC"386#10Ł[ In contrast to 0\2\4!trisilacyclohexane\ 0\0\2\2! tetramethyl!0\2!disilacyclobutane "85# reacts with n!butyl\ methyl!\ and phenyllithium to open the Si1C1 ring ð64JCS"D#0323\ 89OM1566Ł[ Even so\ the solutions of 1!lithio!0\2!disilacyclobutane "86# could be prepared by the action of ButLi:TMEDA on "85# in hexane "Scheme 23# ð89OM1566Ł[ In reactions of "86# with TMS!Cl\ Me1HSiCl\ Me2SnCl\ n!PrI\ XCH1CH1X "X Br\ I#\ Me1S1\ and I1\ the disilacyclobutane ring is retained while the methylene carbon atom is functionalized ð89OM1566Ł[ Li Si
BunLi/TMEDA
Si Si
TMS
hexane, 20 °C
Si
Si
Si
Si Li
Si
TMS
Si
(94)
TMS
(95)
Scheme 33
MeLi ether, reflux >74%
Me2Si
TMS Li Si Me Me
SiMe2 Li (96)
ButLi/TMEDA hexane >60%
Me2Si
SiMe2 (97)
Scheme 34
"b# Oxidative metallation of halo"silyl#methanes[ This is a superior method for generating a variety of silyl!substituted organometallics from readily available starting materials[ The synthesis is very simple to carry out in the laboratory and yields are normally excellent[ For example\ chlorobis"TMS#methane reacts with lithium metal in ether to give the corresponding lithium deriva! tive in virtually quantitative yield ð65JCS"D#1157Ł[ The starting functionalized methane may be readily prepared from CH1Cl1\ TMS!Cl\ and BunLi as shown in Scheme 24 ð60JOM"18#278\ 70SRI480Ł[ In the opinion of the present authors\ this route is best for the preparation of "TMS#1CHLi[ One limitation of this scheme is that the synthesis of compounds "TMS#1C"R#Li is di.cult or impossible if group
081
At Least One Metalloid or Metal
R is methyl or primary alkyl[ Thus the reaction of "TMS#1C"Me#Cl with lithium metal leads to "TMS#1C1CH1 and "TMS#1C"H#Me instead of the expected lithium species ð68ZAAC"337#39Ł[ BunLi
Cl
Cl
THF/Et2O/penatne –110 °C
Li
TMS
Cl
Cl
BunLi
+ 2 TMS-Cl
Cl
Cl
EtOH
TMS
TMS
–100 °C 78%
TMS
TMS Li
Li
TMS
ether, reflux
TMS
TMS
Scheme 35
The preparation of bis"TMS#methylmagnesium halides can be performed in ether or THF using halobis"TMS#methane and magnesium powder ð72POL180\ 75JCS"D#0440\ 80JOM"310#064Ł[ The method can be extended to the preparation of bis"metallated# silylmethanes[ Thus\ dili! thio"TMS#methane "87# was obtained by reaction of dichloro"TMS#methane with lithium vapor "Equation "12## ð73CC0553Ł[ It should be noted that an alternative approach to this compound is the thermolysis of TMS!CH1Li ð77POL1912Ł[ The bulky TMS groups seem to prevent extensive polymerization of the dilithium derivative[ In both preparations the only by!products were lithiated methanes and silanes[ No higher polymers such as those observed for "CH1Li1#n were seen ð73CC0553Ł[ Cl
Li
Li (vapour)
(23) TMS
Cl
700–720 °C 10-4 Torr
TMS Li (98)
Bis"bromomagnesio#TMSmethane "88# has been prepared directly from the reaction of TMS! CHBr1 and magnesium amalgam in diisopropyl ether "69)# "Equation "13## ð75TL5012Ł[ In relation to CH1"MgBr#1\ compound "88# is less reactive^ this must be due to the anion!stabilizing e}ect of the TMS group and possibly to steric hindrance[ Br
MgBr
Mg/Br
(24) TMS
Br
Pri2O, 20 °C
TMS MgBr (99)
"c# Or`anometallic addition to vinylsilanes[ While organolithium compounds and Grignard reagents will not\ in general\ add to isolated C1C double bonds\ they will add to the silyl!substituted alkenes to form a!silyllithium or a!silylmagnesium derivatives ð41JA3471\ 43JOC0167\ 69CJC450\ 69TL0026Ł[ The examples provided in Scheme 25 illustrate the application of the method for the synthesis of lithiated bis"silyl#methanes[ Compounds of structure "099# are prepared in more than 89) yield ð63AG"E#72Ł[ The a!lithio derivative "090# can be trapped by trimethylsilyl tri~ate to give compound "091#\ and is a useful silaethene precursor "Scheme 25# ð81ZN"B#794Ł[ Li
TMS
TMS
TMS
CH2O
TMS
RLi
TMS
Li
TMS
TMS
R (100)
R = Bun, Bus, or But TMS TMS
TMS TMS ButLi
Cl TMS
pentane, –78 °C
Li
TMS TMS But
CF3SO2O-TMS
But TMS
Cl
Cl
TMS (101)
TMS (102)
Scheme 36
It has been established\ by analogy to 0\0!bis"TMS#ethenes\ that silaethenes\ germaethenes\ and their analogues add organolithium reagents to form the appropriate polyfunctional derivatives
082
At Least One Metalloid
ð73JOM"162#030\ 74OM228\ 80AG"E#82Ł[ For instance\ the lithium species "093# was generated as shown in Scheme 26 by addition of phenyllithium to a solution of stannaethene "092# ð80AG"E#82Ł[ Me
TMS
PhLi
TMS
hexane, –78 °C
Me2PhSn
Sn Me
TMS
(103)
Li
SnPhMe2
MeOH
TMS
TMS
TMS
(104) Scheme 37
0\1!Dilithio"tetrakis"TMS##ethane "094# results directly from the reaction of tetrakis"TMS# ethylene with excess lithium metal in dry!oxygen!free THF "Equation "14## ð78JA2637Ł[ The structure of "094# has been unequivocally con_rmed by x!ray crystallography and chemical transformations[ Treatment of the dilithium compound with H1O and D1O cleanly produced tetrakis"TMS#ethane "095#[ The reaction with paraformaldehyde a}orded alkene "096# "62)# probably via 0\1!anionic rearrangement of the silyl group "Scheme 27#[ After prolonged standing "8 days#\ quenching the THF solution of "094# with water led to the formation of compounds "097# and "098# together with small amounts of cyclic compounds "009# and "000# "Scheme 28# ð82CL156Ł[ These reactions probably involve intramolecular proton abstraction from a methyl group on silicon followed by subsequent anionic rearrangement[ THF TMS
TMS
TMS
TMS
2Li
TMS
Li
TMS
THF
TMS
Li
TMS
(25) THF (105)
TMS TMS TMS TMS X X (106)
X2O (X = H, D) THF, –78 °C
(105) TMS
TMS
HCOH
TMS TMS (107)
THF, –78 °C
Scheme 38
(105)
i, THF/9 days ii, H2O, –78 °C
TMS
TMS
TMS
+ TMS
TMS
(108), 45%
Me2 Si
TMS
Si Me2 (109), 13%
TMS +
Me2Si TMS (110), 4%
SiMe2
Me2Si
SiMe2
TMS
TMS
+ (111), 1%
Scheme 39
Similarly\ phenyl"tris"TMS#ethylene participates readily in oxidative metallation reaction to give 0\1!dilithiophenyl"tris"TMS##ethane[ Hydrolysis of the dilithio derivative leads to the formation of tris"TMS#phenylethane\ Ph"TMS#CHCH"TMS#1\ in almost quantitative yield ð81CL756Ł[ "d# Transmetallation and related reactions[ There are several useful syntheses using trans! metallation reactions for the preparation of silylmethyl derivatives of alkali and alkaline earth metals[ Bis"bis"TMS#methyl#mercury\ which can be prepared from the Grignard reagent and mercury"II# chloride\ exchanges mercury with lithium and the heavier alkali metals "Equation "15## ð79POL1912Ł[ This procedure has been shown to be a particularly clean method for the generation of a!silyl carbanions[ However\ the dangers inherent in handling volatile mercury compounds make this route somewhat less than attractive[ Bis"TMS#methylpotassium can also be prepared by transmetallation of bis"TMS#methyllithium with potassium t!butoxide in hexane "71)# "Equation "16## ð80OM0693Ł[
083
At Least One Metalloid or Metal TMS
TMS Hg
TMS
M (M = Li, Na, or K) ether, 20 °C
M 2
(26) TMS
TMS
TMS
Li
K
ButOK
(27) TMS
TMS
hexane, 20 °C, 16 h
TMS
TMS
Also included in this category are desilylation of tris"TMS#methane with sodium methoxide in HMPA "Equation "17## ð62TL3082Ł[ The driving force for this reaction may be the formation of a strong Si0O bond of methoxytrimethylsilane[ Similar reactions occur with tetrakis"TMS#methane and bis"TMS#methane ð62TL3082Ł[ TMS TMS
TMS
Na
NaOMe HMPA, 20 °C
(28) TMS
TMS
Dibromo"TMS#methane has been shown to react with a zincÐcopper couple in THF to give the dizinc derivative "TMS#CH"ZnBr#1[ Transmetallation of the compound with magnesium metal a}ords the Grignard reagent "TMS#CH"MgBr#1 ð61JOM"39#C42Ł[
"ii# Bis"TMS#methyl derivatives of transition metals and `roup 02 and 03 metals Practically all compounds of the type RC"SiX2#1"MLm# containing a metal of which the elec! tronegativity is greater than those of lithium and magnesium\ have been prepared by transmetallation reactions starting from a!silyl!substituted organolithiums or Grignard reagents and inorganic or organometallic halides[ A listing of many of these reactions is given in Table 2[ Some speci_c examples are discussed below[ Lithium bis"TMS#methanide reacts with lanthanum aryloxides "Ln La or Sm# under ambient conditions to yield Ln"CH"TMS#1#2*the _rst structurally characterized neutral homoleptic alkyl of the lanthanide metals ð77CC0996Ł[ The conversion of several bis"polymethylcyclopentadienyl#!stabilized lanthanide complexes into bis"TMS#methyl derivatives "001# has been achieved by a low!temperature reaction with bis"TMS#methyllithium[ E}orts to abstract a proton from the a!carbon atom of the lanthanide complex "001^ M Lu# did not yield an alkylidene[ Rather\ a salt "002# was isolated which was assigned a metallacyclobutane structure "Scheme 39# ð74JA7092Ł[ The bis"TMS#methylyttrium complex "003#\ which can be prepared from Cp 1YCl and "TMS#1CHLi\ readily undergoes insertion reactions into the s!yttriumÐcarbon bond to produce new monomeric complexes\ such as "004# and "005#\ stabilized by Cp ligands and "TMS#1CH group "Scheme 30# ð76OM0498Ł[ Compounds "006# have been prepared from the appropriate metallocene dichlorides and an equimolar amount of "TMS#1CHLi in ether[ Sodium amalgam in THF under dinitrogen smoothly reduces the bis"TMS#methylzirconium"IV# metallocenes "006# to complexes of structure "007#\ containing {{side!on|| bonded dinitrogen according to Scheme 31 ð68JOM"070#14Ł[ These results provide a further demonstration that the bulky bis"TMS#methyl ligand may stabilize unusual metal complexes[ The preparation of bis"bis"TMS#methyl#manganese "008# was accomplished by treating anhy! drous manganese"II# chloride with the Grignard reagent in THF as indicated in Scheme 32[ This compound has proved to be a useful agent for transferring the ligand "TMS#1CH from Mn to another metal site[ Thus\ the yield of Pb"CH"TMS#1#1 obtained from structure "008# and PbX1 "X Cl or N"TMS#1# is certainly superior to that achieved in the direct reaction between "TMS#1CHLi and PbX1 ð89JOM"283#46Ł[ Mononuclear cuprate "019# was prepared as its lithium crown ether salt by addition of the organolithium reagent to CuBr in THF[ Its structure consists of a well!separated cation\ "Li"01! crown!3#1#¦\ and a cuprate anion "Equation "18## ð74JA3226Ł[
At Least One Metalloid
084
Table 2 Preparation of bis"TMS#methyl derivatives of transition metals and group 02 and 03 metals[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Silyl rea`ent Yield Metal substratea ðR "TMS#1CHŁ Product ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * ScCl2 RLi ScR2=1THF 63JOM"65#C34 RLi YR2 63JOM"65#C34 YCl2 RLi YCp1 R 58 75OM0615 YCp1 Cl YCp1 "OAr#1 RK YCp1 "OAr#R 61 83OM58 RLi LaR2 77CC0996 La"OAr#2 ðLaCp1 Cl1Ł−Li¦ RLi LaCp1 R 59 74JA7980 RLi CeCp R1 77CC851 CeCp "OAr#1 ðNdCp1 Cl1Ł−Li¦ RLi NdCp1 R 79 74JA7980 RLi SmR2 77CC0996 Sm"OAr#2 ðSmCp1 Cl1Ł−Li¦ RLi SmCp1 R 34 74JA7980 ECl2 RLi ðER2ClŁðLi"THF#3Ł 67CC039 RLi ðYbR2ClŁðLi"THF#3Ł 67CC039 YbCl2 RK LuR2"m!Cl#K"OEt#1 80OM0693 LuCl2 ðLuCp1 Cl1Ł−Li¦ RLi LuCp1 R 53 74JA7980 RLi TiR2 5 67JCS"D#623 TiCl2"Me2N#1 TiCp1Cl1 RLi TiCp1R 52 66JA5534\ 67JCS"D#623 RLi ZrClR2 34 67JCS"D#623 ZrCl3 ZrCp1Cl1 RLi ZrCp1ClR 32 66JA5534 RLi ZrCp1?ClR 32Ð68 68JOM"070#14\ 70JCS"D#703 ZrCp1?Cl1 HfCl3 RLi HfClR2 42 67JCS"D#623 HfCp1Cl1 RLi HfCp1R 26 66JA5534 RLi VR2 03 67JCS"D#623 VCl2"Me2N#1 RLi VCp1R 31 66JA5534 VCp1Cl1 VCp1Br RLi VCp1R 79 66JA5534 CrCl2 RLi CrR2 60 67JCS"D#623 RMgCl MnR1=THF 61 89JOM"283#46 MnCl1 CuBr RLi ðCuBrRŁLi 74JA3226 ZnCl1 RLi ZnR1 67 80JOM"310#064 RLi:TMEDA ðZnR2ŁLi 62 82ZAAC"508#564 ZnCl1 CdCl1 RLi CdR1 23 67JOM"042#142 HgCl1 RLi HgR1 86 67JOM"042#142 "TMS#1CMeLi HgðC"Me#"TMS#1Ł1 23 67JOM"042#142 HgCl1 RMgCl HgR1 66 55JOM"5#340 HgCl1 HgCl1 R1Hg HgClR 61 55JOM"5#340 RLi HgR1 05 69JOM"13#536 HgBr1 HgBr1 R1Hg HgBrR 25 67JOM"042#142 RLi AlClR1 36 67JOM"042#142 AlCl2 AlCl2 RLi AlR2 58 78ZAAC"468#64 RLi AlBut1R 59 81ZAAC"502#56 "AlBrBut1#1 "AlBr1But#1 RLi AlButR1 67 80ZAAC"484#114 "AlCl1#1CH1 RLi "AlR1#1CH1 34 89POL166 RLi GaR2 71 79IC2526 GaCl2 RLi GaR2 31 78JOM"253#178 Ga1Br3 Ga1Br3"diox#1 RLi GaR1Br 43 81CB0436 RLi ðGaR1Ł1 52 78JOM"253#178 Ga1Br3"diox#1 InCl2 RLi InR2 89 79IC2526 InPriCl1 RLi InCl"R#Pri1 50 80ZN"B#0428 RLi ðInR1Ł1 43 78JOM"257#028 In1Br3"TMEDA#1 RLi SnR1 60 75JCS"D#0440\ 65JCS"D#1157 SnCl1 "SnClðN"TMS#1Ł#n RLi SnR1 60 65JCS"D#1157 SnðN"TMS#1Ł1 RLi SnR1 08 65JCS"D#1157 RLi SnCl1R1 73 75JCS"D#0440\ 71CC0396 SnCl3 RLi PbR1 2 65JCS"D#1157 PbCl1 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a
Abbreviations] Ar 1\5!But1C5H2\ Cp h!C4H4\ Cp h!C4Me4\ Cp? h!C4H3X "X H\ Me\ Et\ Pri\ But\ or TMS#[
Studies in the 0879s and early 0889s on the transmetallation reactions of nitrogen!functionalized lithium bis"TMS#methanide "82# have yielded a series of molecules with unusual bonding con! _gurations[ For example\ the reaction of 1!bis"TMS#methylpyridine with butyllithium in THF followed by CuCl\ yields a binuclear complex "010# in which the metal is not involved in electron! de_cient bonding ð72CC0308Ł[ The silver"I# bis"TMS#methyl derivative "011# was prepared by a similar method "Scheme 33# ð73CC501Ł[ The thermally stable N!functionalized bis"TMS# methylcobalt"II# complex has been prepared by reacting the lithium derivative "82# with cobalt"II# chloride in ether ð82JOM"332#C28Ł[ An x!ray structural study has revealed a centrosymmetric molec! ular skeleton in which a pair of pyridine ligands are trans!chelated to the central planar four!
085
At Least One Metalloid or Metal (TMS)2CHLi
[Me2SiCp*2MCl2]–Li(THF)+2
TMS
ButLi/TMEDA
TMS
hexane (M = Lu)
Me2SiCp*2M (112) –
TMS Me Me2SiCp*2Lu
Si
Li(TMEDA)+3
Me (113) M = Nd, Sm, or Lu Scheme 40
TMS
O
TMS
O
YCp*2
CO2
YCp*2
benzene, 20 °C 27%
TMS
(116)
2ButCN toluene, 20 °C 76%
TMS
TMS
N Y(NCBut)Cp*2
TMS
But
(114)
(115)
Scheme 41
(Zr(η-C5H4R)2Cl2)
TMS
(TMS)2CHLi
Zr(η-C5H4R)2Cl
ether, 20 °C
TMS
Na/ –Hg/N2
TMS
THF, 20 °C
TMS
Zr(η-C5H4R)2(N2)
(117) R = H, Me Scheme 42
[Mg(TMS)(µ-Cl)(THF)]2
MnCl2
(118)
Mn[CH(TMS)2]2(THF)
THF, 20 °C, 18 h 72% Sn[N(TMS)2]2
(119) 1/2 Sn2[CH(TMS)2]4
pentane, –10 °C 71%
(119) PbCl2 hexane, 20 °C 64%
Pb[CH(TMS)2]2
Scheme 43 –
CuBr
CuBr
(TMS)2CHLi/12-crown-4 THF/toluene/hexane
Li(12-crown-4)2+ TMS
(29)
TMS
(120)
coordinate cobalt"II# atom[ The complexes "M"NC4H3C"TMS#1!1#1#\ where M Zn\ Cd\ or Hg\ accessible from structure "82# and MCl1\ are mononuclear metal"II# alkyls in which the dative metalÐ nitrogen interactions progressively weaken in the sequence Zn×Cd×Hg ð75CC561\ 82JCS"D#1542Ł[ Monomeric 1!pyridylbis"TMS#methyltin"II# compounds of structures "012#Ð"014# were prepared from "82# and SnCl1 or Sn"N"TMS#1#1 "Scheme 34# ð77CC225Ł[ Bis"1!pyridylbis"TMS#methyl#stannylene "013# upon treatment with aryl azides forms the 0! aza!7!stannabicycloð2[1[9Łocta!1\3\5!triene system "015# via stannaimine intermediate "Scheme 35# ð82CB1136Ł[ The pentacoordinate aluminum derivative "016# is reported to be formed by reaction of lithium bis"TMS#methanide with AlCl2[ Compound "016# rapidly underwent metalÐhalogen cleavage with AlCl2 in benzene yielding the salt!like adduct "017# "Scheme 36# ð76AG"E#570Ł[
086
At Least One Metalloid TMS N
TMS
TMS
Li
N
i, ii
Li
TMS
M THF, 20 °C
N
TMS
TMS
TMS M N
TMS (93)
(121) M = Cu (122) M = Ag i, BuLi, ether, 1 h at 20 °C; ii, CuCl, THF, 1 h, 20 °C or AgBF4, THF, –78 °C Scheme 44
TMS (TMS)2N
TMS
N
Sn
N Sn
TMS
N
TMS
TMS
TMS (124)
(123) 2Sn[N(TMS)2]2 ether
SnCl2, THF or ether
ClSn (93)
N
TMS
2SnCl2 ether
TMS (125)
Scheme 45
TMS TMS (124)
RN3 hexane, RT
TMS
Sn
Nr
TMS
~TMS
N Sn
N
N
TMS R (126)
2
R = 2,6 Pri2C6H3, 68%, 2,4,6-Me3C6H2, 79% Scheme 46
+
TMS
N Li
TMS
AlCl3 ether, 20 °C 54%
N
TMS Cl
TMS
Al N TMS
TMS
benzene, 20 °C 83%
TMS
N
AlCl3
TMS
Al
TMS N
AlCl4–
TMS
(127) (128) Scheme 47
E}orts to generate a carbanionic species by the reaction of Al"CH"TMS#1#2 with t!butyllithium in the presence of TMEDA have led to 0!sila!2!alanatetane "018#[ The reaction probably involves an attack of the strong base to the bis"TMS#methyl substituent followed by intramolecular addition of a carbanionic center to the coordinatively unsaturated aluminum atom "Equation "29## ð78ZAAC"468#64\ 82CB1526Ł[ In contrast to Al"CH"TMS#1#2\ a sterically less crowded compound "029# reacts with t!butyllithium in the presence of N\N?!dimethylpiperazine "DMP# to give lithium "m! hydrido#trialkylalanate "020# "Equation "20## ð80ZAAC"484#114Ł[
087
At Least One Metalloid or Metal –
TMS
TMS
TMS TMS
ButLi/TMEDA
TMS
Me
TMS
Al
Al pentane, –55 °C 60%
TMS TMS
Li(TMEDA)+
Si
(30)
Me
TMS TMS TMS (129) Me
TMS But
TMS
ButLi/DMP
N
TMS
pentane, –60 °C 71%
N
Al
TMS
TMS
H Al But Me
TMS (130)
(31)
TMS
TMS (131)
A rare example of the double transmetallation reaction is shown in Equation "21#[ Bis"bro! momagnesio#TMS!methane reacts with chlorotrimethylstannane in THF to form bis"tri! methylstannyl#TMS!methane "021# in almost quantitative yield ð75TL5012Ł[ MgBr TMS
SnMe3
2Me3SnCl THF, 20 °C 94%
MgBr
TMS
(32)
SnMe3 (132)
5[95[1[1[1 Functions bearing boron"s# and metal"s# The chemistry and preparation of lithium poly"boryl#methides derived from methanetriboronic esters were reviewed in 0864 ð64S036Ł[ Since the late 0879s\ reviews containing information on the preparation of boron!stabilized carbanions "borylmethide salts# have also appeared ðB!76MI 595!91\ B!77MI 595!90\ 80COS"0#376Ł[ The present section considers the preparation of polyheteroatom species of the general formula RC"BX1#n"MLm#2−n\ where n 0 or 1\ M is metal\ and R H\ alkyl\ or aryl[ No methods exist which can be used to prepare all these types of compounds but there are synthetic routes which have some generality[
"i# Synthesis via metalÐhydro`en exchan`e Alkyllithium reagents and other strong bases can abstract a proton from carbon adjacent to a boryl group generating the metallated borylmethane[ In principle\ the reaction could provide a general method of synthesis\ but in certain cases highly nucleophilic bases react predominantly at the boron atom leading to formation of {{ate|| complexes "Scheme 37# ð54TL2318\ 55TL3204\ 62S26Ł[ Successful metalÐhydrogen exchange may be achieved in several ways as follows] "a# the reagent can be a hindered\ nonnucleophilic base^ "b# the groups around boron can be highly branched so that attack on boron is inhibited on steric grounds^ or "c# the electrophilicity of the boron atom may be lowered by the use of heteroatom substituents ð80COS"0#376Ł[ R1
R2M
M
Y
–R2H
BX2
R1 Y
BX2 R1
R 2M
M+ Y
Scheme 48
–
B(R2)X2
088
At Least One Metalloid
The example provided in Scheme 38 illustrates the generation of potassium bis"boryl#methanide "023# from sterically overcrowded bis"dimesitylboryl#methane ð71JCR"S#021Ł[ Interestingly\ while the reaction of structure "022# with lithium dicyclohexylamide gives lithium dimesitylborylmethide\ Mes1BCH1Li\ in preparatively useful yield\ n!butyllithium attacks at boron to give the borate and t!butyllithium gives the hydroborate by b!hydrogen transfer ð72TL512Ł[ i, (c-C6H11)2NLi ii, Mes2BF
Mes2BMe
Mes2B
THF, 20 °C
BMes2
KH
K
THF
Mes2B BMes2 (134)
(133) Scheme 49
The deprotonation of bis"dialkoxyboryl#methanes has been accomplished with lithium 1\1\5\5! tetramethylpiperidine "LITMP# in the presence of TMEDA in THF "Equation "22## ð71OM19Ł[ However\ the reaction is not completely general[ Thus\ the compound "025# undergoes cleavage instead of deprotonation to give lithiated monoborylmethane "026# "Equation "23## ð71OM19Ł[ Li B O O X
O B X O
LITMP/TMEDA
B O O X
O B X O
THF, –78 °C
(33)
(135) O
O
O =
X
B O
O
O
O
B
B
, O
O
,
O
B
B ,
B O
,
Ph O
O
Ph
B
B
O
O
LITMP/TMEDA
O
Li
THF, –78 °C
B
O
(34)
O
(136)
(137)
Diborylmethide salts can be alkylated by alkyl halides to form 0\0!bis"dialkoxyboryl#alkanes\ which in turn can be deprotonated and alkylated with a second alkyl halide to form `em!diboronic esters\ R0R1C"B"OAlk1##1 ð71OM19Ł[ "ii# Synthesis via transmetallation reactions A transmetallation reaction\ for the purposes of this section\ can be de_ned as a reaction in which a borylalkyl group is transferred from boron to a metal atom by the reaction of an organometallic compound with a suitable polyborylated methane[ The method is widely used for the preparation of lithium tris! and bis"boryl#methides starting from the corresponding polyborylated methanes and organolithium reagents "Equations "24# and "25## ð62JA4985\ 63JOM"58#34\ 64JA4597\ 65JOM"009#14\ 65JOM"003#0Ł[ In a typical procedure\ the tris"dialkoxyboryl#methane and methyllithium are stirred at −67>C in a polar solvent "normally THF or a mixture of THF and dichloromethane#[ The reaction time appears to be substrate!dependent\ but the reaction is generally complete after about 1[4 h at −67>C[ A borylmethide salt can be isolated or used in situ for subsequent derivatization[ It should be noted that compounds such as "024# and "027# are very interesting as reagents for conversion of a carbonyl compound to the homologous aldehyde ðB!66MI 595!91\ 67JOC849\ 79JOC0980Ł[ X O
O
Li MeLi
B
THF, –70 °C
B O O X
O B X O
O
O X
B O
=
B
O
O ,
O
O B B O X O O X (135)
, B
B O
O
(35)
199
At Least One Metalloid or Metal O O O B O B
O
B O B O
O B O B
BunLi THF
O O
Li (36)
B O
O O (138)
The reaction of lithium bis"dialkoxyboryl#methides with organoelement halides\ such as Ph2MCl "M Ge\ Sn\ or Pb#\ provides a general route to bis"boryl#"germyl#methanes and their tin and lead analogues "Equation "26## ð65JOM"009#14Ł[ A further extension of this type of chemistry was the successful conversion of the tin compound "028# to the methide salt "039# stabilized by one boron and one tin atom\ and _nally to bis"triphenylstannyl#ethylenedioxyborylmethane "030# "Scheme 49# ð65JOM"009#14Ł[ Tris"dialkoxyboryl#methide salts react with Ph2MCl in a similar fashion to form compound Ph2MC"B"OAlk#1#2 ð58JA5430\ 62JOM"46#114\ 62JOM"46#120\ 63JOM"58#52Ł[ Li
MPh3 Ph3MCl
B O O X
O B X O
X O
SnPh3 O
B
B
=
or B
B
O M = Ge, Sn, or Pb
O
SnPh3
MeLi
O
O
O
O B
O
THF, –78 °C
B
SnPh3
Ph3SnCl
Li
O
B
47%
O (140) Scheme 50
O O (139)
(37)
B O O X
O B X O
THF/ether 36–77%
SnPh3
O (141)
Treatment of tetrakis"dimethoxyboryl#methane with butyllithium or\ preferably\ lithium methox! ide\ followed by triphenyltin chloride yields tris"boryl#stannylmethane "031#\ which on further treatment with butyllithium disproportionates to form bis"boryl#bis"stannyl#methane "032# "Scheme 40#[ Reaction of the monotin compound "031# with ethylene glycol resulted in the loss of one of the three boron atoms to give "triphenylstannyl#bis"ethylenedioxyboryl#methane "028# "Equation "27##[ The tin compound "032# undergoes similar reaction on treatment with lithium methoxide in meth! anol\ providing an alternative route to "boryl#bis"stannyl#!substituted methanes "Equation "28## ð62JOM"46#114Ł[ (MeO)2B
B(OMe)2
(MeO)2B
B(OMe)2
MeOLi or BunLi
(MeO)2B
Li
THF, 20 °C
(MeO)2B
B(OMe)2
(MeO)2B
SnPh3
(MeO)2B
B(OMe)2
(142)
BunLi
Ph3SnCl
Ph3Sn
1/2
SnPh3
(MeO)2B
THF, –78 °C 93%
65%
B(OMe)2
(143) Scheme 51
SnPh3
HO(CH2)2OH
(142)
acetone, 20 °C 90%
O
B
B
O O (139)
O
(38)
190
At Least One Metalloid SnPh3
MeOLi
(143)
(39) Ph3Sn
MeOH, reflux 57%
B(OMe)2
The reaction of benzylbis"boryl#methane "033# with mercuric dichloride and lithium methoxide in anhydrous methanol resulted in the selective replacement of one boron atom by mercury to form the a!metallated borylmethane "034# "Equation "39## ð65JOM"003#0Ł[ Interaction of boryl"stannyl#! alkanes with alkyllithiums generally leads to cleavage of the tin moiety "Equation "30## ð74OM0589Ł[ A useful reaction of dimesitylboryl"TMS#alkanes is that they readily undergo silicon:lithium ex! change with LiF to form lithium borylmethides ð80COS"0#376Ł[ CH2Ph
CH2Ph O
B
B
HgCl2/NaOMe
O
O O (144)
Me3Sn
B
ClHg
MeOH, 25 °C 77%
O
O
(40)
O (145)
MeLi
O
B
Li
O
B
(41)
O
THF, –100 °C
"iii# Synthesis via addition to vinylboranes and methyleneboranes The very low yields of lithium borylmethide salts "ca[ 4)# obtained from the reactions of alkenyldimesitylboranes with organometallic compounds demonstrates that this is not a very useful method for the synthesis of simple a!metallated borylmethanes[ However\ this approach has proved successful for the preparation of a!metallated silyl"boryl#methanes from 0!TMS!0!dimesityl! borylethylenes "see Section 5[95[1[1[3# and several alkali metal polyborylmethides from methylene! boranes ð80COS"0#376Ł[ A speci_c reaction useful for the synthesis of diboriranide "035#\ is shown in Scheme 41[ Treatment of "035# with the very weak acid t!butyl"TMS#amine leads to formation of "036# ð74AG"E#677Ł[ R1
R2 B Cl
R1
B Cl
K/Na
R1
R2 B
R2
THF, 82%
K
R2
R1R2NH
B R2
R1
R2 B
>90%
R2
K (146)
B R2
K (147)
R1 = TMS, R2 = But Scheme 52
C!Borylborataalkyne "037# with t!butyllithium yields 0\2!diborataallene "038#\ which contains a second t!butyl group in place of the "TMS#1CH group[ Upon treatment with one equiv[ of cyclopentadiene\ the 0\2!diborataallene is transformed into the lithium bis"boryl#methide "049# "Scheme 42# ð77AG"E#0269Ł[ Several cyclic compounds\ such as "040# and "041#\ incorporating a C"Li#B1 unit\ have been made by a related 0\1!addition of the C0Li bond to the B1C multiple bond "Equations "31# and "32## ð89AG"E#0929\ 81AG"E#0127Ł[ Readers are referred to a review by Berndt ð82AG"E#874Ł for more detailed information concerning the synthetic potential of meth! yleneboranes in carbometallation reactions[ Mes Mes
B
•
–
ButLi
B TMS
TMS (148)
–
B 50%
Li
Mes
Mes •
–
B But
But (149) Scheme 53
CpH
2Li+
But
B
B
But
Mes Mes (150)
191
At Least One Metalloid or Metal
B
Ar
Ar
Ph
TMS
B
TMS
PhLi
Li
TMS
B
TMS
(42)
B
Ar
Ar (151) Ar = 2,3,5,6-Me4C6H (Dur)
Ar B Ar
Ar
Ar
B
B
TMS
Li
B
TMS
ButLi
TMS
(43)
But
B B
20%
TMS
Ar
Ar (152) Ar = Dur, Mes
A unique reaction leading to the formation of a C"Sn#B1 function has been described by Berndt and co!workers ð76AG"E#435Ł[ The boranediylborirane "042# which\ according to calculations\ has the nonclassical structure shown in Scheme 43\ behaves toward suitable reagents as if it were the carbene[ Reaction of "042# with a stannylene in pentane led to formation of the stannaethene "043# in quantitative yield[ Compound "043# reacts with HCl to give the 0\2!diboretane "044#[ R
R B
B
TMS
B
Sn[CH(TMS)2]2
:
TMS
TMS B R
TMS
pentane, 20 °C
R (153) R
TMS
B
TMS
B
R CH(TMS)2 Sn CH(TMS)2
HCl
TMS
B
~100%
TMS
B
R
TMS Sn Cl TMS
R (154)
(155) R = But Scheme 54
5[95[1[1[2 Functions bearing germanium"s# and metal"s# Isolable examples of compounds of the type RC"GeX2#n"MLm#2−n "n 0 or 1# are virtually unknown[ The signi_cant contribution to this class of compounds was made by Barton and Hockman who reported the preparation and synthetic utilization of lithium bis"tri! methylgermyl#methide "045# ð79JA0473Ł[ This reagent is formed in good yield by methods similar to those described for the analogous silicon compound "Scheme 44#[ The synthetic utility of "045# has been demonstrated by the reaction with tosyl azide leading to the formation of bis"trimethylgermyl#diazomethane[ The triphenylgermyl group seems to have no acidifying e}ect^ lithiation of "Ph2Ge#1CH1 was i, ii
Me3Ge
Cl
Me3Ge iii
iv
Cl Me3Ge
GeMe3
Li
v
GeMe3
Me3Ge
GeMe3 (156)
i, Li, ether, –23 °C; ii, Me3GeCl; iii, ButLi, THF/HMPA, –78 °C; iv, BusLi, THF, –78 °C; v, Li, ether Scheme 55
192
At Least One Metalloid
neither possible with lithium dicyclohexylamide nor with n!butyllithium or t!butyllithium in the presence of HMPA ð79TCC"81#098Ł[ Treatment of "Ph2Pb#1CHLi with Ph2GeCl produced the germylbis"stannyl#methane "046#\ which was converted into functionalized lithium methide "047# by a transmetallation reaction with phe! nyllithium "Equations "33# and "34## ð79TL1796Ł[ GePh3
(Ph3Pb)2CHLi
Ph3GeBr
(44)
THF, 87%
GePh3 Ph3Pb
Ph3Pb PbPh3 (157)
GePh3
PhLi
PbPh3
(45) Ph3Pb Li (158)
>78%
5[95[1[1[3 Functions with mixed metalloid"s# and metal"s# Only a few totally mixed RC"E0Xn#"E1Ym#MLk molecules "E0 and E1 Si\ Ge\ or B^ M metal# have been described[ If unsymmetrical compounds such as XnE0CH1E1Ym or XnE0CH"Hal#E1Ym are available\ then metalÐhydrogen or metalÐhalogen exchange reactions seem to be the most practical routes to metallated derivatives[ Redistribution represents a potential problem and can be avoided by mild reaction conditions and rapid experimental work up procedures[ Several metallating reagents have been examined\ but the most satisfactory method for metallation of TMS"ethylenedioxyboryl#methane "048# involves the use of LITMP:TMEDA in THF "Scheme 45# ð79CC28\ 72OM129Ł[ In contrast to "048#\ substituted TMS"ethylenedioxyboryl#methanes\ TMSCH"R#BO1C1Me3 "R alkyl\ aryl# have proved resistant to the usual deprotonation conditions ð79JOM"073#C30Ł[ Li TMS
B
O
LITMP/TMEDA
TMS
THF, 0 °C
O
R B O
O
RHa1
TMS
53–85%
B
O
O
(159) R = Bu, Am, Hex, PhCH2, PhCH2CH2, PhOCH2CH2 Scheme 56
Lithiation of TMS"trimethylgermyl#methane may be accomplished with t!butyllithium in a mix! ture THF:HMPA at −67>C[ A successful alternative method utilizes the chloro derivative "Scheme 46# ð79JA0473Ł[ ButLi
TMS
GeMe3
THF/HMPA, –78 °C
Li TMS Cl TMS
GeMe3
Li
GeMe3
ether, reflux
Scheme 57
A versatile approach to metallated polyheteroatom!substituted methanes based on the reactions of tris"triphenylplumbyl#methane has been developed by Kau}mann and co!workers ð79TCC098\ 79TL1796Ł[ Germyl"plumbyl#methide "047# undergoes coupling reactions with TMS!Cl to yield the functionalized methane "059# "Equation "35##[ Transmetallation of silylbis"plumbyl#methanes "051# with PhLi gives a new organolithium reagent as shown in Scheme 47 ð79TL1796Ł[ The required
193
At Least One Metalloid or Metal
lithium bis"plumbyl#methide "050# can be obtained by a transmetallation reaction of "Ph2Pb#2CH with PhLi ð79TL1796Ł[ Li
TMS-Cl
Ph3Pb GePh3 (158)
78%
TMS (46)
Li
TMS-Cl
Ph3Pb PbPh3 (161)
89%
Ph3Pb GePh3 (160) TMS
Ph3Pb
PbPh3
TMS
PhLi >70%
Ph3Pb
Li
(162) Scheme 58
5[95[2 FUNCTIONS CONTAINING THREE METALS 5[95[2[0 Three Similar Metals Isolable compounds of the type RC"MLm#2 "M metal# are known with M Li\ Hg\ Al\ Sn\ and Pb[ Methods of synthesizing polylithiated aliphatic hydrocarbons have been reviewed previously ðB!74MI 595!91\ 76TCC0Ł[ The chemistry and preparation of acyclic compounds with functions containing three heavy main group metals have not been surveyed and only passing comments can be found in appropriate sections of Methoden der Or`anischen Chemie ð69HOU"02:3#0\ 63HOU"02:1b#0\ 67HOU"02:5#070Ł\ Comprehensive Or`anometallic Chemistry ð71COMC!I"6#154Ł and in several spe! cialized books ð53AOC"1#146\ 79TCC"81#098\ B!70MI 595!91\ B!76MI 595!90Ł[
5[95[2[0[0 Lithium derivatives\ RCLi2 Polylithium organic compounds can be prepared by a variety of methods and several have been extensively studied ð76TCC"027#0\ 81MI 595!91Ł[ However\ only a few of these methods are readily applicable to the preparation of geminal trilithioalkanes with at least some degree of generality[ These are] "a# reactions of hydrocarbons or halocarbons with lithium vapor^ "b# transmetallation reactions^ "c# metallation of acidic hydrocarbons^ and "d# pyrolysis reactions[ When applicable\ transmetallation\ especially mercuryÐlithium exchange\ is usually the most convenient and is therefore the method of choice[ On the other hand\ reactions of hydrocarbon or halocarbon substrates with lithium vapor probably represent the most general approach[ CarbonÐ lithium bonds in polylithiated alkanes are very susceptible to hydrolysis and the handling of any such compound requires the use of vacuum systems and other specialized techniques[
"i# Reactions with lithium vapor Direct halogenÐmetal exchange in polyhaloalkanes by treatment with lithium metal\ the most popular method for the synthesis of alkyllithium compounds\ is only of limited value for the preparation of polylithiated alkanes due to a!elimination of lithium halide after the _rst step being faster than the halogenÐmetal exchange ð68AG"E#674\ 79HCA1935Ł[ These di.culties can be overcome by high!temperature reaction of polyhaloalkanes with lithium vapor[ Thus\ tetralithiomethane\ CLi3\ and hexalithiomethane\ C1Li5\ the _rst examples of perlithiated alkanes\ were prepared by the reaction of lithium vapor with the appropriate perchlorocarbons under vacuum at high temperatures "649Ð0999>C# ð61CC0967\ 72JOM"138#0Ł[ The reactions are carried out in a stainless steel reactor consisting of a Knudsen cell containing lithium metal heated in a furnace\ an inlet tube\ and a liquid nitrogen cold _nger[ The main advantage of this technique\ besides the high reactivity of lithium vapor\ is the reduction of rearrangements and secondary
194
Three Metals
reactions from rapid quenching of the products onto the cold _nger ð76TCC0Ł[ In both prep! arations\ depicted in Equations "36# and "37#\ the main by!products were C1Li3 and C1Li1[ Further investigations showed that the selectivity can be improved by working at 649>C instead of 749>C ð64CC291\ 68JOC1200\ 71JA6234Ł[ However\ the method although optimized\ still provides a maximum of 39) CLi3 together with 47) C1Li1 ð72JOM"138#0Ł[ When chloroform was used as a substrate\ trilithiomethane was obtained in 04[4) yield "Equation "38##^ the main side products being 28[6) C1Li1\ 19[0) CLi3\ and 08[0) CH1Li1 ð71JA6234\ 72JOM"138#0Ł[ Similarly\ the reaction of dich! loro"TMS#methane with lithium vapor gave TMS!CHLi1 in only 00) yield "Equation "49## ð73CC0553Ł[ CCl4 + 8Li(g) C2Cl6 + 12Li(g) CHCl3 + 6Li(g) TMS-CHCl2 + 4Li(g)
850 °C
850 °C
750 °C
720 °C
CLi4 + 4LiCl
(47)
C2Li6 + 6LiCl
(48)
CHLi3 + 3LiCl
(49)
TMS-CHLi2 + 2LiCl
(50)
The purest perlithiated ethane "C1Li5# was prepared by using diethylmercury instead of hexa! chloroethane as the starting material ð68JA1103Ł[ It was also reported that the vapor phase reaction of carbon with atomic lithium yielded perlithiopropyne "C2Li3# as the main product ð62JA0232Ł[ The major drawback of a technique utilizing reactions between organic substrates and lithium vapor lies in the separation of a mixture of lithium!substituted hydrocarbons[ Unfortunately\ it has not yet been possible to separate the resulting mixtures\ and even separation from the lithium matrix is di.cult ð72JOM"138#0\ 81AG"E#473Ł[
"ii# Transmetallation reactions In many cases of synthesis of substantial amounts of pure polylithiated alkanes there is no practical alternative to transmetallation reactions ð76TCC"027#0Ł[ However\ since the transmetallation route requires the intermediacy of another organometallic compound\ polylithiated alkanes pre! pared by this method share the same limitations and restrictions that the parent organometallic compound encounters[ In practice\ mercuryÐlithium exchange reactions represent one of the most e}ective routes to the di! and trilithiomethanes because the corresponding organopolymercury compounds are comparatively readily available[ Thus\ trilithiomethane "HCLi2# can be prepared in good yield by treating tris"chloromercurio#methane with lithium metal in dry THF "Equation "40## ð71MI 595!90Ł[ Unfortunately\ direct mercuryÐlithium exchange reaction is not suitable for the synthesis of tetralithiomethane "CLi3#[ Treating C"HgCl#3 with lithium metal in diethyl ether resulted in the dimeric products hexalithioethane "C1Li5# and tetralithioethylene "C1Li3#[ The reaction is believed to proceed via radical intermediates ð76TCC"027#0Ł[ HgCl
Li
Li
(51) ClHg
HgCl
THF, 20 °C
Li
Li
A variant of the mercuryÐlithium exchange method is provided by the reaction of organomercury compounds with n!butyllithium[ Many of the polymercury compounds\ including C"HgCl#3 ð73AG"E#884\ 75OS267Ł and CH1"HgCl#1 ð72AG"E#622Ł\ are useful in this reaction[ However\ the pro! cedure has not yet been adequately developed for synthesis of trilithiated hydrocarbons[ Transmetallation reactions with several other elements\ such as boron and tin\ can also be used for the generation of polylithiated organic compounds ð79TCC"81#098\ 71AG"E#309Ł but trilithiated hydrocarbons have not yet been prepared this way[
"iii# Metallation of acidic hydrocarbons Much more easily accessible than the 0\0\0!trilithiated alkanes are certain perlithioalkynes\ since alkyllithium reagents can abstract quantitatively not only the hydrogen atoms on sp!hybridized
195
At Least One Metalloid or Metal
carbon atom\ but also those of the adjacent methyl group ð63MI 595!90\ 71AG"E#309\ 72T1622Ł[ For example\ the conversion of propyne into perlithiated derivative can be achieved by reaction with n! butyllithium in hexane "Equation "41## ð54JA2677\ 58JA5045\ 73AG"E#884Ł[ BunLi
(52)
C3Li4 hexane, 75%
The pattern of reactivity of conjugated diynes closely resembles that of the propyne[ Thus\ reaction of the 0\2!pentadiyne with excess n!butyllithium:TMEDA in hexane gives the perlithiated hydrocarbon C4Li3 "Equation "42## ð62JA2213Ł[ 1\3!Hexadiyne under the same conditions ð65JA7315Ł or even in the absence of TMEDA ð62JCS"P1#488Ł has been converted into the trilithiated product "Equation "43##[ Metallation of 1\3!octadiyne in diethyl ether or THF a}ords another {{lithiocarbon|| "Equation "44## ð62JCS"P1#488Ł[ BunLi
C5Li4
(53)
MeC5Li3
(54)
hexane BunLi hexane BunLi
C3H7C5Li3
C3H7
(55)
ether or THF
Unlike alkynes\ linear and branched alkenes upon treatment with organolithium reagents form only mono! and dilithiated hydrocarbons[ For example\ propene is dilithiated with n!butyl! lithium:TMEDA in hexane to give the corresponding dianion ð64CC766Ł[ Isobutylene under these conditions yields the cross!conjugated trimethylenemethane dianion ð65T0728Ł[ The isomeric 1! butene can be dilithiated to give 0\3!dilithio!1!butene ð63JA4539Ł[
"iv# Pyrolysis reactions The pioneering work in this _eld is due to Ziegler et al[ who reported that pyrolysis of halide! free methyllithium resulted in the formation of dilithiomethane in excellent yield "Equation "45## ð44ZAAC"171#234Ł[ This procedure is still the method of choice for the preparation of CH1Li1\ however\ it is not the best route to 0\0\0!trilithiated hydrocarbons[ Although perlithiopropyne "C2Li3# was detected among the products of the thermal decomposition of CH1Li1 and CLi3 "Equa! tions "46# and "47##\ it could not be separated from the resulting mixtures ð70JA4840\ 71JA1526\ 74JA4202Ł[ MeLi
CH2Li2
225 °C
350 °C 6 min
225 °C
CLi4 8 min
CLi4 + C3Li4 20% 40%
CH4 + CH2Li2
(56)
C3Li4 + C2Li2 80% 20%
(57)
+ C2Li4 + C2Li2
(58)
30%
10%
5[95[2[0[1 Mercury derivatives\ RC"HgX#2 As in many other cases\ transmetallation represents a valuable route to polymercurated methanes[ Thus\ tris"dimethoxyboryl#methane\ readily available via the reaction of chloroform with di! methoxyboron chloride and lithium metal "see Section 5[95[1[0[1#\ undergoes a rapid reaction with mercuric salts to produce trimercurated methanes "Equation "48## ð79JOM"080#6\ 72JOM"132#134Ł[
196
Three Metals B(OMe)2
HgX
HgX2
(59) (MeO)2B
B(OMe)2
THF, RT
XHg
HgX
X = Cl, 62%; AcO, 38%
However\ despite the usefulness of transmetallation reactions\ this route to trimercurated deriva! tives has rarely been used\ because access is easier via direct mercuration of organic compounds containing an activated methyl group ðB!56MI 595!90\ 57MI 595!90\ 60MI 595!90\ 63HOU"02:1b#0\ B!70MI 595! 91Ł[ Treatment of methyl derivatives containing electron!withdrawing groups with a mercuric salt\ HgX1\ results in electrophilic mercuration giving a mercury derivative[ Use of an excess of HgX1 may give rise to trimercurated compounds[ Typical examples from the literature are given in Table 3[ The reactions are normally carried out in aqueous acidic solutions or without solvent at elevated temperatures[ For example\ acetonitrile reacts with anhydrous mercuric acetate at 049>C for 19 h in a bomb tube to give the trimercurated product in 82) yield "Table 3\ entry 7#[ Conditions for preparing the mono! and dimercurated derivatives of acetonitrile have also been described ð63JPR446Ł[ Table 3 Preparation of 0\0\0!trimercurioalkane derivatives[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Entry Compound Method of preparation ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * HCðB"OMe#1Ł2 ¦HgCl1 51 79JOM"080#6 0 HC"HgCl#2 HCðB"OMe#1Ł2 ¦HgBr1 72JOM"132#134 1 HC"HgBr#2 2 HC"HgI#2 HC"HgOAc#2 ¦KI 71 72JOM"132#134 HCðB"OMe#1Ł2 ¦Hg"OAc#1 27 72JOM"132#134 3 HC"HgOAc#2 4 HC"HgSCN#2 HC"HgOAc#2 ¦KSCN 72JOM"145#106 HC"HgOAc#2 ¦KCN 72 72JOM"132#134 5 HC"HgCN#2 6 HC"HgMe#2 HCðB"OMe#1Ł2 ¦MeHgOAc 75JOM"290#0 MeCN¦Hg"OAc#1 82 63JPR446 7 NCC"HgOAc#2 8 NCC"HgMe#2 MeCN¦"MeHg#1O 84 64ZAAC"304#122 EtOH¦HgCl1:NaOAc 71JOM"127#216 09 OHCC"HgCl#2 00 OHCC"HgBr#2 EtOH¦HgBr1:NaOAc 71JOM"127#216 AcH¦Hg"NO2#1 76JOM"208#0 01 OHCC"HgBr#2 02a HO1CC"HgCl#2 {mercuretin|¦HCl 84 73JOM"165#0 a HO1CC"HgOAc#2 {mercuretin|¦AcOH 43 73JOM"165#0 03 04a HO1CC"HgNO2#2 {mercuretin|¦HNO2 75JOM"295#0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a
{{Mercuretin||] AcOðHgC"HgOAc#1CO1ŁnH "n½9#[
Mercuration of C0H bonds a to carbonyl groups also occurs readily[ Thus\ reaction of acetic aldehyde with HgCl1 led to the formation of "ClHg#2CCHO in almost quantitative yield[ Mer! curation of the aldehyde RCH1CHO "R Me\ Et# gave "ClCH1#1CRCHO "74Ð77)# ð73CCA578Ł[ The product obtained by boiling an ethanolic solution of mercuric chloride with sodium acetate ð0788CB769Ł has also been identi_ed as tris"chloromercurio#acetaldehyde "Table 3\ entry 09#[ The bromine analogue was obtained in the same way ð71JOM"127#216Ł[ The crystal structures of solvates "ClHg#2CCHO=DMF and "BrHg#2CCHO=DMSO have been determined by x!ray di}raction methods ð71CSC0460\ 71JOM"127#216Ł[ Mercuration of acetaldehyde with mercuric nitrate in aqueous nitric acid always leads to tri! mercurated acetaldehyde\ which separates from the solution in the form of various nitrates whose type and composition depends upon the acid concentration ð76JOM"208#0Ł[ Addition of an ethanolic solution of acetaldehyde to an aqueous solution of mercuric nitrate gives a hydrated oxonium nitrate of tris"mercurio#acetaldehyde\ "OHg2CCHO#NO2=H1O ð72JOM"142#172Ł[ It has been con_rmed that the compounds obtained by melting mercuric acetate\ named mer! curetin ð16JCS1547Ł\ is identical with the compound prepared by heating mercuric acetate in acetic anhydride ð92LA"218#005Ł[ Mercuretin\ prepared by both routes\ has been identi_ed as the con! densation polymer of tris"acetoxymercurio#acetic acid\ AcO"HgC"HgOAc#1CO1#nH\ with n approxi! mately equal to 09[ Its hydrolysis in dilute HCl gives tris"chloromercurio#acetic acid as the only Hg! containing product "Table 3\ entry 02#[ Two nitrates of trimercurated acetic acid\ obtained from the solution of mercuretin in nitric acid were identi_ed as ð"Hg"H1OHg#"NO2Hg#CCO1#NO2Ł and "1"NO2Hg#2CCO1H=HNO2# ð75JOM"295#0\ 80JOM"300#08Ł[ The reaction of 1!ethyl! and 1\3\3\4\4!pentamethyl!0\2!dioxalanium perchlorate with Hg"OAc#1 and Hg"OCOCF2#1 leads to the formation of mono!\ di!\ and trimercurated carboxylic acids depend!
197
At Least One Metalloid or Metal
ing upon the ratio of reagents ð70ZOB1130Ł[ Mercuration of acetone in acidic aqueous solutions produces at least nine mono!\ poly!\ and permercurated species\ all of which can exist in equilibrium simultaneously ð78OM1535Ł[ 5[95[2[0[2 Aluminum derivatives\ RC"AlX1#2 Geminal trialuminioalkanes are available via bishydroalumination of alkynyldialkylalanes ð69HOU"02:3#0Ł[ In general\ the reaction of terminal alkynes with two molar equiv[ of a dialkyl! aluminum hydride in ether or THF lead to 0\0!dialuminioalkanes "Equation "59## ð59LA"518#111\ 55TL5910\ 60CC0482Ł[ However\ in basic solvents such as triethylamine\ the reaction of alkynes with one molar equiv[ of dialkylaluminum hydride produces metallation rather than hydroalumination ð52AG"E#575\ 57IZV809Ł[ This has been used synthetically to prepare alkynylalanes[ Further treatment of the resultant alkynylalanes with excess dialkylaluminum hydride a}ords trialuminioalkanes "052# "Scheme 48# ð59LA"518#111\ 52BSF0351Ł[ R1
2R22AlH
(60)
R1
ether or THF
R22Al
AlR22
R1 2R2
2AlH
R1
AlR22
2R2
AlR22
R1
Et3N, 20 °C
2AlH
70 °C
R22Al
AlR22 (163)
R1 = Bun, R2 = Et Scheme 59
Related preparation of 0\0\0!trialuminioalkanes involves bishydroalumination of alkynylalanes derived from the reaction of alkali metal acetylides with dialkylaluminum chlorides "Scheme 59# ð59LA"518#111\ 57BSF105Ł[ 2R22AlH
R2AlCl
R
Na
80–90%
R
R
AlR2
R2Al
AlR2 AlR2
R = Me, Et Scheme 60
The chemistry of 0\0\0!trialuminioalkanes is not well developed\ and only the reactions of com! pound "052# with electron!donor molecules\ such as LiH\ KF\ Et1O\ and pyridine have been reported ð72IZV525Ł[ 5[95[2[0[3 Tin and lead derivatives\ RC"MX2#2 "M Sn or Pb# Tris"trimethylstannyl#methane "053# can be readily synthesized via interaction of chloroform with trimethylstannyllithium ð64OMS"09#07Ł or via reaction of bromoform with the Grignard reagent obtained from chlorotrimethylstannane and magnesium turning "Scheme 50# ð73JOM"155#26Ł[ Both procedures give the crude product containing substantial quantities of bis"trimethylstannyl#methane[ Distillation and subsequent crystallization from ethanol a}ord a pure substance in average yield[ Cl Me3SnLi
Cl
Cl THF, 20 °C
SnMe3 Me3Sn SnMe3 (164)
Br Br
Me3SnCl/Mg
Br
THF
Scheme 61
198
Three Metals
A more general route to 0\0\0!tristannylalkanes involves the hydrostannation of 0!stannyl!0! alkynes[ Trimethyltin hydride has been shown to react with 0!stannyl!0!alkynes in the presence of catalytic amounts of azobisisobutyronitrile "AIBN# to form predominantly 0\0!distannyl!0!alkenes "054#[ The latter undergo a second hydrostannation to give the corresponding 0\0\0!tristannylalkanes "Scheme 51# ð72JOM"141#36\ 74OM0933Ł[ R
R
Me3SnH
SnMe3
R
SnMe3
SnMe3
+
70 °C, AlBN 8h
Me3Sn
SnMe3 (165) Bun
(166)
But
R(ratio (165)/(166), %): Me (97/3), (96/4), (98/2), Ph (95/5), MeOCH2 (59/41), PhOCH2 (61/39), PhO (165) R = Me,
Me3SnH
R
SnMe3
52–80%
Me3Sn
SnMe3
Bun,
Ph, PhCH2, MeOCH2, PhOCH2, PhO Scheme 62
0\0!Distannyl!1\1!diorganyl!0!alkenes\ resulting from the coupling reaction of geminal dibro! moalkenes with Me2SnLi\ have also been successfully transformed into the corresponding tri! stannylalkanes "Scheme 52# ð75OM0880Ł[ R1
Br
R2
Br
Me3SnLi THF, –78 °C
R1
SnMe3
Me3SnH
R2
SnMe3
hν
R1 R2
SnMe3 SnMe3 SnMe3
R1 = Me, CH2OMe; R2 = Me, Et, Ph, CH2CH2OMe, CH(Me)OMe, CH2CH2OEt, CH2OMe Scheme 63
Oxymetallation of the alkene derivative "056#\ which is achieved by using Me2SnOMe in hexane\ yields functionalized tristannylalkanes "057# "Equation "50## ð80CB492Ł[ The reaction is believed to involve the formation of adduct at the boryl group followed by intramolecular rearrangements[ R2B
SnMe3
R
SnMe3
R Me3SnOMe
MeO B R R
hexane, 25 °C
(167)
SnMe3 SnMe3 SnMe3
(61)
(168) R = Et
The preparative chemistry of triplumbylmethane derivatives is considerably less rich as compared to the chemistry of tristannylmethanes[ The coupling reaction between chloroform and trior! ganylplumbyllithium is the sole valuable route to tris"triorganylplumbyl#methanes ð69JOM"12#360\ 74CB279\ 80SA"A#738Ł[ The method is especially e.cient for triphenylplumbyl derivatives since the Ph2PbLi is readily available from Ph2PbCl and lithium metal "Equation "51## ð74CB279Ł[ Ph3PbCl
Li
Ph3PbLi
PbPh3
HCCl3 THF, –60 °C 91%
(62) Ph3Pb
PbPh3
The following compounds were made analogously^ "Ph2Pb#3C\ "Ph2Pb#1CCl1\ Ph2PbCHCl1\ and "Ph2Pb#1CH1[ Attempts to prepare "Ph2Pb#2CCl and "Ph2Pb#1CHCl failed\ because of further reac! tion with triphenylplumbyllithium ð69JOM"12#360Ł[
5[95[2[1 Three Dissimilar Metals Trimetallated alkanes with di}erent metals attached to carbon are rare[ Even so\ access to these species is of great interest because it is usually di.cult to reach such structures by classical routes[
109
At Least One Metalloid or Metal
A few of the compounds have been prepared by transmetallation or metallation reactions and examples are described in reviews by Kau}mann ð79TCC098\ 71AG"E#309Ł[ The conversion of 0\0\0!tris"diethylaluminio#hexane "052# into lithiobis"diethylaluminio#hexane has been achieved using reactions with n!butyllithium[ It was noted that only one diethylaluminio group can be replaced by lithium even when an excess lithium reagent was used "Scheme 52# ð72IZV525Ł[ H11C5 Et2Al
AlEt2
BunLi
AlEt2
C6H6, 20 °C
H11C5 Et2Al
Li (63) AlEt2
(163)
Compounds with the grouping Sn0C"Li#0Sn are accessible via the reaction of bis"tri! methylstannyl#methane with lithium dicyclohexylamide "LDCA# in presence of 0 mol HMPA ð68TL490Ł[ The nature of the lithium reagent is critical^ generally\ deprotonation occurs with lithium amides\ while transmetallation occurs with alkyllithiums ð79TCC098\ 89S148Ł[ An alternative method for the preparation of lithium bis"stannyl#methide "058# consists of treating a tristannylated com! pound with phenyllithium in ether "Scheme 53#[ Reaction of lithium derivative "058# with Ph2SnCl gave tris"triphenylstannyl#methane ð79TCC"81#098Ł[ LDCA/HMPA
Ph3Sn
SnPh3
THF, 20 °C
Li Ph3Sn SnPh3 Ph3Sn
SnPh3 (169)
PhLi ether, 20 °C
SnPh3
LDCA = lithium dicyclohexylamide Scheme 64
The lithium bis"triphenylplumbyl#methide "069# has been synthesized via several routes^ met! allation of bis"triphenylstannyl#methane\ transmetallation reaction using "Ph2Pb#2CH and phenyl! lithium\ or by halogenÐmetal exchange starting from bromobis"triphenylplumbyl#methane ð79TL1796Ł[ Lithium derivative "069# reacts smoothly with Me2SnCl to give the expected "stan! nyl#bis"plumbyl#methane "060# "Equation "53##[ Li
Me3SnCl
Ph3Pb PbPh3 (170)
THF, 88%
SnMe3 (64) Ph3Pb PbPh3 (171)
The synthetic potential of compounds of structures "058# and "069# in reactions with other metal halides remains unexplored[
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.07 Functions Containing Four Halogens or Three Halogens and One Other Heteroatom Substituent ALEX H. GOULIAEV Aarhus University, A˚rhus, Denmark and ALEXANDER SENNING Technical University of Denmark, Lyngby, Denmark 5[96[0 TETRAHALOMETHANES*C"Hal#3
101
5[96[0[0 Four Similar Halo`ens 5[96[0[0[0 Tetra~uoromethane\ CF3 5[96[0[0[1 Tetrachloromethane\ CCl3 5[96[0[0[2 Tetrabromomethane\ CBr3 5[96[0[0[3 Tetraiodomethane\ CI3 5[96[0[1 Three Similar and One Different Halo`en 5[96[0[1[0 Tri~uoromethyl halides 5[96[0[1[1 Trichloromethyl halides 5[96[0[1[2 Tribromomethyl halides 5[96[0[1[3 Triiodomethyl halides 5[96[0[2 Two Similar Halo`ens 5[96[0[2[0 Di~uoromethylene dihalides 5[96[0[2[1 Dichloromethylene dihalides 5[96[0[2[2 Dibromomethylene dihalides 5[96[0[2[3 Diiodomethylene dihalides 5[96[0[3 Bromochloro~uoroiodomethane\ CBrClFI
101 101 103 104 105 106 106 119 111 112 112 112 113 115 116 117
5[96[1 METHANES BEARING THREE HALOGENS
117
5[96[1[0 Three Halo`ens and a Chalco`en 5[96[1[0[0 Three halo`ens and an oxy`en function 5[96[1[0[1 Three halo`ens and a sulfur function 5[96[1[0[2 Three halo`ens and an Se or Te function 5[96[1[1 Three Halo`ens and a Group 04 Element 5[96[1[1[0 Three halo`ens and a nitro`en function 5[96[1[1[1 Three halo`ens and a phosphorus function 5[96[1[1[2 Three halo`ens and an As\ Sb\ or Bi function 5[96[1[2 Three Halo`ens and a Metalloid 5[96[1[2[0 Three halo`ens and a silicon function
100
117 117 121 126 126 126 131 132 132 132
101
Four Halo`ens or Three Halo`ens and One Other Heteroatom 132 133 133
5[96[1[2[1 Three halo`ens and a boron function 5[96[1[2[2 Three halo`ens and a `ermanium function 5[96[1[3 Three Halo`ens and a Metal Function
5[96[0 TETRAHALOMETHANES*C"Hal#3 The _rst part of this chapter is con_ned to a limited number of compounds\ they are the 24 possible tetrahalomethanes "Table 0# of which many are commercially available plus a few tri~uoromethyl compounds of hypervalent iodine which have been prepared[ Most of the tetra! halomethanes have been prepared with the exception of the eight iodine!containing tetra! halomethanes\ CClI2\ CFI2\ CBrCl1I\ CBr1ClI\ CBr1I1\ CClFI1\ CBrClI1 and the chiral CBrClFI[ Information on high yielding and selective syntheses of CBrI2\ CCl1I1 "formed as a by!product# and CBrFI1 "04) as a by!product# is\ however\ also rather sparse[ Organic per~uoro compounds have many practical applications\ such as in refrigerants\ as propellants\ as _re extinguishers\ in the plastics industry as well as in the manufacture of phar! maceuticals\ whereas perchloro "apart from CCl3#\ perbromo and periodo compounds are more or less only of academic interest[ Methods for introducing ~uorine into organic compounds are presented elsewhere in this volume and are not discussed in this chapter[ For more information there is a number of excellent books on haloorganic compounds[ Organic ~uorine compounds have been treated by several authors[ The most recent handbook is Hudlicky|s Chemistry of Or`anic Fluorine Compounds ðB!81MI 596!90Ł[ This book covers all _elds of organic ~uorine chemistry\ including methods for introducing ~uorine into organic compounds\ reactions\ properties\ analysis and practical applications of these\ as well as synthetic procedures and the synthesis of ~uorinating agents[ Olah et al[ ðB!81MI 596!91Ł have published a book covering the synthesis of ~uorine compounds\ as have Liebman et al[ ðB!77MI 596!90Ł\ whereas German and Zemskov mainly cover reagents for the synthesis of ~uorine compounds ðB!78MI 596!90Ł[ Older books include Chambers| Fluorine in Or`anic Chemistry ðB!62MI 596!90Ł\ Sheppard and Sharts| Or`anic Fluorine Chemistry ðB!58MI 596!90Ł\ and\ _nally\ Emeleus| The Chemistry of Fluorine and Its Compounds ðB!58MI 596!91Ł\ which covers mainly the inorganic chemistry of ~uorides[ Organic bromine compounds have been described by Jolles in Bromine and its Compounds ðB!55MI 596!90Ł[
5[96[0[0 Four Similar Halogens 5[96[0[0[0 Tetra~uoromethane\ CF3 Treatment of metal carbides with ~uorine at 19>C for 89 min or with CoF2 at 339>C for 8 h leads to mixtures of various ~uorocarbons among which CF3 predominates[ Thus\ Cr1C2 yields 80) CF3\ as do Al3C2 "77)#\ B3C "77)#\ TiC "75)#\ Fe2C "75)#\ CaC1 "64)# and WC "56)# ð48JA795Ł[ Fluorination of silicon carbide with F1 also leads to CF3 "Equation "0## ð49IS060Ł[ MnCm + F2
20 °C, 90 min
CF4 + C2F6 + C3F8 + C4F10
relative yields: 68–91%
6–26%
2–14%
(1)
0–2%
M, n, m: see text for specification.
Tetra~uoromethane is furthermore formed\ in better than 49) yield\ upon ~uorination of acti! vated charcoal with F1 ð28JA1851Ł\ or upon ~uorination of graphite with PF2\ AsF2\ SF5\ CuF1\ FeF2\ VF4 at 899Ð0199>C ð44USP1698075\ 44USP1698077\ 44USP1698089Ł\ PF4 at 1339>C ð47GEP0939900Ł or HgF1 at 459Ð799>C ð44USP1698076Ł[ Fluorination "F1# of tri~uoromethane ð26JA0199\ 25CB188Ł or tetrachloromethane at 69>C in the presence of As gives a relative yield of 63) CF3 with CClF2 as the main by!product ð39JA2366Ł[ Treatment of tetrachloromethane ð20USP0850511Ł or tetraiodomethane ð37JCS1077Ł\ under readily available laboratory conditions\ with BrF2 as ~uorinating agent also leads to tetra~uoromethane "Equation "1#\ Table 1#[
102
Tetrahalomethanes
Table 0 Bibliographic information on the preparation\ melting points and boiling points of the tetra! halomethanes[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Formula CA Re`[ no[ Beilsteins Handbuch der Gmelin Handbuch der M[p[ B[p[ Or`anischen Chemiea Anor`anischen Chemieb ">C# ">C# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * CX3 CF3 64!62!9 H 48\ I 7\ II 00\ III 24\ IV 15 81:82 −073c −029c CCl3 45!12!4 H 53\ I 01\ II 11\ III 53\ IV 45 028:039 −12c 66c CBr3 447!02!3 H 57\ I 06\ II 24\ III 81\ IV 74 143 77Ð89c 089c Cl3 496!14!4 H 63\ I 08\ II 28\ III 093\ IV 87 162:172 057c 029Ð039 "0!1 torr# CF2X CClF2 CBrF2 CF2I
64!61!8 64!52!7 1203!86!7
III 31\ IV 23 III 72\ IV 62 III 87\ IV 81
181:182 295:296 203
−070c −057c
−79c −46 to −47c −11[4c
CCl2X CCl2F CBrCl2 CCl2I
64!58!3 64!51!6 483!11!8
H 53\ III 52\ IV 43 H 56\ II 20\ III 74\ IV 66 H 60\ III 88\ IV 84
212 228 172:181\ 186:187\ 238
−000 to −009c −5c −08a
12[6c 094c 031a
CBr2X CBr2F CBr2Cl CBr2I
242!43!7 483!04!9 03238!79!4
I 06\ III 80\ IV 74 H 57\ II 24\ III 80\ IV 74 H 60\ IV 85
173:181\ 186\ 226:228 172:181\ 186\ 238:240 186:187\ 240
−62[5c 44a 24d"dec[#
095Ð096c 059a
CI2X CFI2 CClI2 CBrI2
0384!38!3 03238!71!6 447!05!6
H 63
186::187 186:187\ 240 186:187\ 240
002a
CF1X1 CBrClF1 CClF1I CBrF1I
242!48!2 319!38!4 642!55!1
IV 64 IV 83
241:243\ 271:274 272\ 274 272\ 274
−048[4b\e
−3f 22f 53[4Ð54[4g "635 mmHg#
CCl1X1 CCl1F1 CBrCl1F CCl1FI CBrCl1I
64!60!7 242!47!1 319!37!3 39798!80!3
H 50\ III 37\ IV 39 IV 65 IV 84
243\ 272\ 274 243\ 272\ 274 272\ 275 272\ 275
−047c −095b −096b
−18[7c 40Ð41f 89b
CBr1X1 CBr1F1 CBr1Cl1 CBr1ClF CBr1FI CBr1ClI
64!50!5 483!07!2 242!44!8 0367!93!1 39798!82!5
I 05\ III 76\ IV 79 H 57\ III 77\ IV 71 III 76\ IV 71
241:243\ 264:267 242:243\ 268:271 243\ 272\ 275 272\ 275 272\ 275
−039h 11a
12[7b\e 024a 68Ð79c
CI1X1 CF1I1 CCl1I1 CBr1I1 CClFI1 CBrFI1 CBrClI1
0073!65!4 483!12!9 03948!89!5 242!38!0 642!56!2 39798!83!6
243\ 267:268 271 271 272\ 275 272\ 275 272\ 275
79[4b\e 74i
CBrClFI CBrClFI "R# CBrClFI "S# CBrClFI "2# CBrClFI " # 642!54!0 275 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a Beilsteins Handbuch der Or`anischen Chemie ðB!07MI 596!90\ B!17MI 596!90\ B!30MI 596!90\ B!48MI 596!90\ B!61MI 596!91Ł[ Gmelin Handbuch der Anor`anischen Chemie ðB!63MI 596!91Ł[ c From Aldrich|s catalog of chemicals ðB!82MI 596!90Ł[ d From Dehn ð98JA0119Ł[ e Calculated value[ f From Haszeldine ð41JCS3148Ł[ g From Burton et al[ ð71JFC"19#78Ł[ h From Miller and Smyth ð46JA19Ł[ i From Holand ð0776LA"139#114Ł[ b
103
Four Halo`ens or Three Halo`ens and One Other Heteroatom
Table 1 Synthesis of ~uorotrihalo!\ di~uorodihalo!\ tri~uorohalo! and tetra~uoromethanes with BrF2 and IF4[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Tetrahalomethane Relative Relative Temp[ Reaction Total Productsa "relative amount 0# amount amount ">C# time yield ")# "ratio# of IF4 of BrF2 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 9[22 RT 50 CCl1F1 "4# CCl2F "84# CCl3 9[5 9[73Ð0[95c
−67 to RTb RT
78 54Ð69
CCl1F1 "74# CCl2F "04# CCl1F1"04Ð32# CClF2 "46Ð74#
CCl2F
9[7
RT
85
CCl1F1
CBr3
9[22 9[55
−9 9
83 75
CBr2F "½099# CBr1F1 "trace# CBr2F "½11# CBr1F1 "½77# CBrF2 "trace# CBrF2 CBr2F "trace# CBr1F1 "¼099# CBrF2 "trace# CF3 "trace#
0d
9 89
9[52 CI3e
83 72
2h
0[81
RT 37 CBr1F1 "22# CF3 "56# 9[77 RT to 89Ð099 29 min 54 CIF2 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Source] Banks et al[ ð37JCS1077Ł[ a Volatile products were collected in cold traps[ b Tetrachloromethane was added to solid BrF2 in carbon dioxide[ c The reaction was conducted in an autoclave[ d Bromine tri~uoride was added dropwise[ e Tetraiodomethane was added dropwise over 1 h[
CI4 + BrF3 (1:2)
RT
CBr2F2 + CF4 48% (33:67)
(2)
Tetra~uoromethane can furthermore be made by electrochemical means with HF as the ~uorine donor[ Thus\ electrochemical ~uorination of trimethylamine yields mainly tris"tri~uoromethyl#! amine\ but also some tetra~uoromethane "Equation "2## ð41USP1505816Ł\ whereas electro! chemical ~uorination of dimethyl sul_de "Equation "3## yields CF3 as well as sulfur hexa~uoride and tri~uoromethylsulfur penta~uoride ð42JCS1261Ł[ Electrochemical ~uorination of acetic acid\ acetyl chloride\ acetone\ trimethylacetic acid\ acetonitrile or methanol in HF with nickel anodes and iron cathodes as well as acetic acid with a KF¦2 HF melt have also been applied in the synthesis of tetra~uoromethane ð38MI 596!90Ł as has the electrolysis of concentrated tri! ~uoroacetic acid solutions with platinum electrodes "Equation "4## ð22BSB091Ł[ HF, electrolysis
NMe3
N(CF3)3 + CHF3 + CF4 + NF3
(3)
(CF3)2SF4 + CF3SF5 + CF4 + SF6
(4)
HF, electrolysis
SMe2 97%
2% electrolysis
21%
60%
17%
CF4 + C2F6 + CO2 + O2
CF3CO2H
(5)
Other possibilities involve bond breaking in per~uoroalkenes\ for example oxidation of tetra! ~uoroethylene with dioxygen which yields carbon dioxide and tetra~uoromethane "Equation "5## ð33USP1240289Ł[ F
F
F
F
O2
CF4 + CO2
(6)
5[96[0[0[1 Tetrachloromethane\ CCl3 An old review on the preparation of tetrachloromethane exists ðB!37MI 596!90Ł[ A major technical preparation uses chlorination of carbon disul_de at 29>C in the presence of an iron catalyst with formation of tetrachloromethane and disulfur dichloride[ The actual chlorinating agent is S1Cl1 and the sulfur formed is rechlorinated to S1Cl1 "Scheme 0# ð63MI 596!90\ B!82MI 596!92Ł[
104
Tetrahalomethanes
Tetrachloromethane and disulfur dichloride can be separated by careful distillation in an inert gas stream ð64USP2773874Ł[ iron catalyst 30 °C
CS2 + 3Cl2
CCl4 + S2Cl2
CS2 + 2S2Cl2
CCl4 + 6S
2Cl2 + 4S
2S2Cl2
2CS2 + 5Cl2
2CCl4 + S2Cl2
+ 2S
Scheme 1
Tetrachloromethane is also commercially prepared by chlorination of chloromethane\ formed by chlorination of methane or\ more commonly\ by treatment of methanol with hydrogen chloride ð56MI 596!90\ 63MI 596!90\ 70MI 596!90\ B!80MI 596!91\ B!82MI 596!91Ł[ Another industrial procedure for the manufacture of chloromethanes uses a CuCl1:KCl melt as catalyst and chlorine source[ This melt is regenerated by an oxychlorination procedure which uses the HCl produced in the chlorination reaction[ The overall reaction is presented in Equation "6# ðB!82MI 596!91Ł[ CH4
CuCl2/KCl melt
+ HCl + O2
MeCl + higher chloromethanes + H2O
(7)
Other processes involve heating of animal charcoal\ CO\ Cl1 and PCl2 at 399>C at 09 atm in an autoclave with AlCl2 and FeCl2 as catalyst\ which gives an 74) conversion to CCl3 ð56MI 596!90Ł[ Pyrolysis of hexachloroethane at 299Ð319>C yields a mixture of CCl3 and CCl1CCl1 ð49TFS184Ł[ Increasing the temperature to 699Ð799>C causes further degradation of tetrachloroethylene to tetrachloromethane "Scheme 1# ð26GEP57954\ 45BRP638397Ł\ and subjecting propene to chlorinolysis at 349Ð449>C produces a mixture of tetrachloroethylene and CCl3 the ratio of which ranges from 24 ] 54 to 54 ] 24 depending on the exact conditions used "Equation "7## ðB!82MI 596!91Ł[ Cl3C
CCl3
300–420 °C
Cl
Cl
Cl Scheme 2
Cl
CCl4
Cl
Cl2
CCl4 450–500 °C
700–800 °C
+
Cl
+
Cl (35:65 to 65:35)
CCl4
(8) Cl
Thermal decomposition at 599>C of trichloroacetyl chloride gave a low yield "16)# of tetra! chloromethane in admixture with hexachloroethane "Table 2# ð28JA324Ł[ Under severe conditions "499>C\ in the presence of FeCl2# it is also possible to chlorinate benzene and naphthalene to CCl3 in high yields "83)# ð56MI 596!90Ł[ Finally\ yields of 89) or more have been achieved by passing thiophosgene with gaseous MoCl4 or WCl5 at 7 atm over activated charcoal at 329>C ð56MI 596!90Ł[
5[96[0[0[2 Tetrabromomethane\ CBr3 Tetrabromomethane is formed in a relative yield of 83) with an admixture of 5) CClBr2 upon treatment of CCl3 with HBr:AlBr2^ overall yield 76) "Equation "8## ð40USP1442407Ł[ It can be made\ furthermore\ from tribromomethane "or acetone# by oxidation with a sodium hypobromite solution containing excess bromine ð21JA1914Ł[ This reaction is probably catalyzed by antimony"III# chloride ð0769LA"045#59Ł[ CCl4
HBr/AlBr3
CBr4
+ CClBr3
(9)
87% (94:6)
Tetrabromomethane can also be made in a manner similar to the method used in the manu! facturing of CCl3\ but with CS1 and Br1 ðB!82MI 596!91Ł[
105
Four Halo`ens or Three Halo`ens and One Other Heteroatom
Table 2 Synthesis of tetrahalomethanes by thermal decomposition of trihaloacetyl halides or metal halo! acetates in the presence of halogen[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Temp[ Yield Products Ref[ Startin` material X1 ">C# ")# "ratio# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 599 29 CCl3"78# CCl2CCl2"00# 28JA324 CCl2COCl CCl2COBr 399 04 CBrCl2"56# CCl2CCl2"22# 28JA324 039 79 CBrCl2"83# CCl2CCl2"5# 28JA324 CCl2COI CF2CO1Na I1a 179 50 CF2Ib 40JCS473 CF2CO1K I1a 179 44 CF2Ib 40JCS473 I1a 179 21 CF2Ib 40JCS473 "CF2CO1#1Bag "CF2CO1#1Hgg I1a 149 24 CF2Ib 40JCS473 I1a 149 15 CF2Ib 40JCS473 "CF2CO1#1Pbg Cl1a RT 89 CClF2b 40JCS473 CF2CO1Ag a b Br1 49 77 CBrF2 40JCS473 78Ð83 CF2Ib 40JCS473 I1a CCl2CO1K Cl1 009Ð019 "trace# CCl3 0766CB567 009Ð019 ×69 CBrCl2 0766CB567 Br1 I1 009Ð019 "trace# CCl2I 0766CB567 ClI 009Ð019 "trace# CCl3 0766CB567 Cl1a 079Ð159 77 CCl1F1b 41JCS3148 CClF1CO1Agc Br1a 079Ð159 80 CBrClF1b 41JCS3148 079Ð159 67 CClF1Ib 41JCS3148 I1a Br1a 079Ð159 70 CBr1F1b 41JCS3148 CBrF1CO1Agd I1a 079Ð159 4 CBrF1Ib 41JCS3148 CCl1FCO1Age Cl1a 079Ð159 52 CCl2Fb 41JCS3148 079Ð159 47 CBrCl1Fb 41JCS3148 Br1a a b 079Ð159 09 CCl1FI 41JCS3148 I1 CBrClFCO1Agf Cl1a 079Ð159 52 CBrCl1Fb 41JCS3148 079Ð159 60 CBr1ClFb 41JCS3148 Br1a ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a Excess X1 "0[4 times the amount of metal haloacetate# was used[ b The products were continously removed by pumping through a cold trap cooled with liquid air[ c Silver chlorodi~uoroacetate was prepared in 54) yield by permanganate oxidation of 0\0\1\2!tetrachloro!2\2! di~uoropropene\ followed by Ag1O:P1O4 treatment[ d Bromodi~uoroacetic acid was prepared "7) yield# by Swarts| method 92MI 596!90 and converted to the silver salt by Ag1O:P1O4 treatment[ e Prepared as a mixture of CCl1FCO1Ag and CHClFCO1Ag "22 ] 56# by treatment of chloro~uoroacetic acid with 19) excess Cl1\ followed by hydrolysis of the intermediate acid chloride[ The silver salts were prepared by treatment of the corresponding acids with Ag1O:P1O4 "46)#[ f Silver bromochloro~uoroacetate was prepared in an overall yield of 12) by treatment of bromo~uoroacetic acid with 19) excess Cl1\ followed by hydrolysis of the intermediate acid chloride[ The silver salt was prepared by treatment of the corresponding acids with Ag1O:P1O4[ g Barium tri~uoroacetate was prepared from tri~uoroacetic acid and Ba"OH#1[ Mercury and lead salts were made similarly from tri~uoroacetic acid and mercury"II# and lead"II# oxide\ respectively[
5[96[0[0[3 Tetraiodomethane\ CI3 Tetraiodomethane may be made in the laboratory by heating CCl3 with CaI1 ¦1 H1O or LiI¦0[4 H1O for 4 days at 89Ð81>C in an evacuated reaction vessel "yield 49Ð44)# ð04CR"045#541\ B!82MI 596! 93Ł\ by treatment of acetone with KI:NaOCl "sat[# ð04CR"045#541Ł or by treating triiodomethane with potassium hypoiodite under exclusion of light at 79Ð89>C ð16BSF0140Ł[ The synthesis of tetraiodomethane from acetone or triiodomethane su}ers from the fact that only small quantities are preparable and that puri_cation is di.cult[ On the other hand\ the synthesis from tetrachloromethane and lower alkyl iodides allows the preparation of larger quantities of tetraiodomethane\ giving nearly quantitative yields and a high! purity product\ for example starting from CCl3 in the presence of AlCl2 and iodoethane "0 ] 9[1 ] 3[9# ð49IS26Ł or iodomethane "0 ] 9[91 ] 3[1# ð34JA0531Ł as the iodine donor[ The chloromethane or chloroethane formed during the reaction is distilled o} from the reaction vessel "Equations "09# and "00##[ + MeI
CCl4
(1:4)
CCl4
+ EtI (1:4)
AlCl3 (cat.) 40 °C, 2 h
AlCl3 (cat.) RT, 45 min
CI4
+ MeCl
(10)
92% (purity 99%)
CI4 + quant.
EtCl
(11)
Crystalline CI3 can be prepared by irradiation of a mixture of CF2I and CO1 at 29 torr[ Carbon dioxide seems\ under these conditions\ important for the formation of CI3 ð75MI 596!90Ł[
106
Tetrahalomethanes
Tetraiodomethane may be puri_ed by recrystallization from chloroform or benzene in vacuo ð34JA0531\ 26JOC65Ł[ When stored\ tetraiodomethane should\ like other iodine containing tetra! halomethanes\ be protected from oxygen\ water and light ð26JOC65Ł[
5[96[0[1 Three Similar and One Different Halogen 5[96[0[1[0 Tri~uoromethyl halides "i# Chlorotri~uoromethane\ CClF2 Chlorotri~uoromethane also known as Freon 02\ is formed in 84) yield upon treatment of tetra~uoromethane with SbF2Cl1 = 1HF at 059>C and 69 atm ð36CI"L#316Ł\ and furthermore as a by! product "06)# in the preparation of CF3 from CCl3 with F1:As\ as mentioned previously ð39JA2366Ł[ Chlorotri~uoromethane has\ however\ been prepared in numerous ways such as by treatment of CCl3 with ~uorine in the presence of iodine or CoF2 ð20ZAAC"190#134Ł\ as well as with HF and di}erent oxometal ~uoride or metal ~uoride catalysts "Equation "01## ð45USP1633036\ 45USP1633037\ 45USP1634775\ 45USP1637066Ł and with antimony"V# chloride as catalyst at 79Ð059>C ð42USP1547816Ł[ Chlorotri~uoromethane is also formed when CCl1F1 is kept in contact with oxoaluminum chloride ð43USP1583628Ł or\ under more severe conditions\ upon treatment of CCl1F1 with F1 in the presence of Hg at 239Ð269>C ð39JA2366Ł[ AlF3
CCl4 + HF (1:1.25)
CCl2F2 + CCl3F + CClF3 90% (35:60:5)
300 °C
(12)
Chlorotri~uoromethane also constitutes the main product of the chlorination of graphite in the presence of HF "Equation "02##[ This reaction has been optimized and found to be most e.cient when conducted at 499>C[ The e}ects of di}erent catalysts have also been investigated ð44USP1698073Ł[ C
Cl2, HF
CCl3F +
CCl2F2 + CClF3
500 °C, 3 h
+ CF4 + haloethanes
(13)
89% (7:21:53:14:5)
By use of BrF2 as ~uorinating agent chlorotri~uoromethane may be prepared in the laboratory ð37JCS1077Ł[ Banks et al[ ð37JCS1077Ł found that slow addition of the ~uorinating agent "BrF2 or IF4#\ lowering of the ratio of tetrahalomethane to ~uorinating agent as well as low temperature and an e.cient condensing system "in order to keep the more volatile intermediates in contact with BrF2 or IF4# favors the formation of tri~uorohalomethanes and tetra~uoromethane[ Bromine tri~uoride reacts smoothly\ but vigorously with CCl3 "Equation "03## and CBr3 whereas the reaction is violent in the case of CI3[ These reactions can be conducted at 9>C[ Iodine penta~uoride\ on the other hand\ is less reactive and the reactions were conducted at 89Ð099>C "vide infra# "Table 1#[ CCl4 + BrF3 (1:0.84–1)
RT
CCl2F2 + CClF3
(14)
65–70% (15–43 to 57–85)
Other possibilities include ~uorination of CHCl2 by the versatile ~uorinating agent CF2OF which yields a mixture of CCl1F1 "5)#\ CClF2 "72)# and CF3 "00)# ð48JA0978Ł[ Carbonyl di~uoride may by PCl4 treatment at 154Ð249>C be converted to a mixture of ~uorochloromethanes "Equation "04## as may phosgene by treatment with HF:Cl1:FeCl2 at 314>C for 06 h "Equation "05## ð46JA4790Ł[ Calcium ~uoride:antimony penta~uoride treatment of phosgene at 499>C for 5 h ð45USP1646103Ł leads to a mixture with CClF2 as the main product "Equation "06##[ COF2 + PCl5
autoclave
(1:1.25)
265 °C, 16 h
(1:2.7)
350 °C, 12 h
CCl2F2 + CClF3 + CCl4 + 15% (67:33:0:–:–) 35% (14:0:86:–:–) X, Y = Cl, F
COXY + CO2
(15)
107
Four Halo`ens or Three Halo`ens and One Other Heteroatom FeCl3/C
COCl2 + HF + Cl2
COCl2
CCl2F2 + CClF3 + CF4
425 °C, 17 h autoclave
(6:6:1) CaF2/SbCl5
CClF3 +
CCl2F2 + CClF3 + CF4 + CCl4
500 °C, 6 h
(16)
72% (19:75:6)
(17)
(65:30:5:trace:trace)
Silver tri~uoroacetate when treated with chlorine also forms chlorotri~uoromethane ð40JCS473Ł\ as does photochlorination of tri~uoromethane ð26JA0199Ł and cleavage of hexa~uoroethane with Cl1 at 899>C ð38JA1388Ł[ Isotopically labeled CClF107F has been prepared by irradiation of a mixture of CClF2 and 07F08F[ CF207F was the main by!product ð68MI 596!90Ł[
"ii# Bromotri~uoromethane\ CBrF2 Bromotri~uoromethane may be synthesized in 89) yield under severe conditions "544Ð579>C# by treatment of tri~uoromethane with bromine ð35JA857\ 48USP1764143Ł or in 83) yield under milder conditions by ~uorination of tetrabromomethane at 9>C with BrF2 being added dropwise "Equation "07#\ Table 1# ð37JCS1077Ł[ Furthermore\ it can be made from tetrabromomethane with SbF2:Br1 at 199>C ð49USP1420261Ł or in low yield with TiF3 at 019>C ð47JCS3134Ł[ Individual products are separated from the reaction mixture by condensation in cold traps[ CBr4
BrF3, 0 °C
CF3Br
(18)
94%
Hofmann rearrangement of tri~uoroacetamide with sodium hypobromite does not yield tri! ~uoromethylamine\ but instead bromotri~uoromethane "Equation "08## ð46JCS29Ł[ This reaction is only useful for the generation of CBrF2 and cannot be used for CClF2 and CF2I ð43JA4030Ł[ Other degradative processes involve the Hunsdiecker reaction\ for example the heating of silver tri~uoroacetate and bromine at 54Ð029>C with formation of bromotri~uoromethane in 77) yield "Equation "19#^ Table 2# ð40JCS473\ 41JA0236Ł\ and the heating of tri~uoroacetyl bromide to 549>C causing elimination of carbon monoxide and formation of CBrF2 "Equation "10## ð44USP1693665Ł[ Bromination\ with elemental bromine\ of tri~uoroacetic acid at 439>C "Equation "11## or tri! ~uoroacetic acid anhydride at 299>C "Equation "12## in contact with activated carbon also leads to bromotri~uoromethane ð42USP1536822Ł[ NaOBr
CF3CONH2
CF3Br
(19)
CF3Br + CO2
(20)
CF3Br + CO
(21)
–NaNCO
CF3CO2Ag CF3COBr
65–130 °C
650 °C
Br2, activated charcoal
CF3CO2H
CF3Br + CO2
(22)
+ CO2
(23)
540 °C Br2, activated charcoal
(CF3CO)2O
CF3Br 300 °C
Bromotri~uoromethane has also been made by plasma chemical means[ The reaction conditions were applied for 3Ð4 min[ Thus\ treatment of hexa~uoroethane with bromine under the in~uence of high!frequency electrical discharges "01 MHz\ 0 kV# at 3Ð19 torr gave 62) conversion and a 66) yield of CBrF2[ Treatment of CF2Cl under the same conditions gave only 12) conversion and a yield of 50) ð64ZAAC"307#098Ł[ As was the case with chlorotri~uoromethane\ bromotri~uoromethane is also formed upon bromination of hexa~uoroethane at 899>C ð38JA1388Ł[
108
Tetrahalomethanes
Bromotri~uoromethane may\ furthermore\ be prepared by Cl:Br exchange[ Thus\ treatment of CClF2 with HBr at 399>C in the presence of a ZnBr1:C catalyst leads to CBrF2 in 16) yield ð66BEP745122Ł[
"iii# Iodotri~uoromethane\ CF2I The preparation and reactions of per~uoroiodoalkanes have recently been reviewed by Deev et al[ ð81RCR64Ł[ Synthesis in high yield "80)#\ of iodotri~uoromethane is possible by the Hunsdiecker reaction\ for example from silver tri~uoroacetate and iodine\ and is used industrially "Equation "13## ð40JA1350\ 40JCS473Ł[ Sodium\ potassium\ barium\ mercury"II# and lead"II# tri~uoroacetate give in general lower yields of CF2I\ but the yield can be improved "79)# when sodium tri~uoroacetate is treated with excess iodine in the presence of CuI at 049>C in DMF ð56JOC722Ł or DMSO ð78MI 596!91Ł[ Other decomposition reactions have also been applied\ such as the heating of tri~uoroacetyl chloride with KI at 199>C for 5 h "Equation "14## giving 30) conversion and a yield of 58) iodo! tri~uoromethane under elimination of CO ð47JOC1905Ł\ or a procedure where tri~uoroacetyl ~uoride and lithium iodide at high temperature give CF2I in 69) yield "Equation "15## ð89CL702Ł[ CF3CO2Ag
I2
CF3I + AgI + CO2 91%
(24)
KI, 200 °C
CF3COCl
CF3I + KCl + CO 69%
6h
CF3COF
LiI
(25)
CF3I + LiF + CO 70%
(26)
In the laboratory\ iodotri~uoromethane may also be conveniently made from the commercially available methyl chlorodi~uoroacetate "Equation "16## which\ on the other hand\ can be prepared from CF1CF1 "Scheme 2#[ Thus\ treatment of CClF1CO1Me with equimolar potassium ~uoride and iodine at 099Ð019>C in DMF and in the presence of catalytic amounts of CuI gives a yield of 69Ð 79)[ CuI is essential for the high yield which in its absence drops to about 09)[ Omission of potassium ~uoride results in the formation of chlorodi~uoroacetamide in 03) yield as the only identi_ed product[ Furthermore\ substitution of methyl chlorodi~uoroacetate with the bromo ana! logue gives a yield of 69) upon heating to 79>C in DMF for 4 h ð81CC796Ł[ CuI (cat.) 100–120 °C, 2–3 h
CF3I + CF2I2 + CH3I + CO2 + KCl 80–90% (88:12)
ClCF2CO2Me + KF + I2 DMF
F F
F F
ICl
ClCF2CF2I
fuming H2SO4
ClCF2COF
MeOH
(27)
ClCF2CO2Me
Scheme 3
Other reactions include the reaction of tri~uoronitrosomethane with iodine at 49Ð69>C\ with a yield of 79Ð84) ð54IZV0762Ł\ and\ in low yield\ the ~uorination of CI3 with TiF3 ð47JCS3134Ł\ or with IF4 "Table 1# in a yield of 54) ð37JCS1077\ 38JCS1745Ł[ Due to the inferior reactivity of iodine penta~uoride compared to bromine tri~uoride\ the reaction requires heating at 89Ð099>C for 29 min[ Furthermore\ prolonged UV irradiation of methyl tri~uoromethyl sul_de or bis"tri~uoromethyl# sul_de in the presence of sources of iodine radicals yields 29Ð53) iodotri~uoromethane ð61JCS"P0#0495\ 63JCS"P0#0695Ł[ Iodotri~uoromethane can\ like bromotri~uoromethane\ be made by plasma chemical means "see the previous section#\ but only in modest yields[ Thus\ treatment of hexa~uoroethane with iodine
119
Four Halo`ens or Three Halo`ens and One Other Heteroatom
under the in~uence of high frequency electrical discharges "01 MHz\ 0 kV# at 3Ð19 torr gave 29) conversion\ but only a yield of 4) CF2I[ Treatment of CF2Cl under the same conditions gave only 03) conversion but a yield of 17) ð64ZAAC"307#098Ł[
"iv# Tri~uoromethyliodine"III# compounds\ "CF2#nIZ2 −n "n 0\ 1# The preparation and isolation of CF2IF1 ð48AG413Ł\ CF2ICl1 ð78JFC"34#390Ł\ CF2I"ONO1#1 ð63IC1700Ł and CF2I"OCOCF2#1 ð65JFC"7#066Ł have been reported in the literature[ Tri~uoromethyliodine"III# di~uoride\ for instance\ is prepared by oxidative ~uorination "F1# at −79>C of tri~uoroiodomethane with trichloro~uoromethane as solvent ð48AG413Ł[ Bis"tri~uoromethyl#iodine derivatives "n 1\ Z ONO1\ OCOCF2\ F\ Cl# have been prepared by Tyrra and Naumann ð80CJC216Ł by tri~uoromethylation of tri~uoromethyliodine"III# dichloride\ dinitrate\ di~uoride or bis"tri~uoroacetate# with either Cd"CF2#1 = 1 glyme or Bi"CF2#2[ None of these were\ however\ isolated\ but only detected and investigated by NMR[
5[96[0[1[1 Trichloromethyl halides "i# Trichloro~uoromethane\ CCl2F Trichloro~uoromethane has been widely used as refrigerant and propellant and is known as Freon 00[ Industrial preparations include Cl:F exchange of HF with CCl3\ in a gas phase reaction at 049>C with catalysis from aluminum\ chromium\ nickel or calcium ~uoride[ The main by!product is Freon 01\ CCl1F1[ Alternatively\ the reaction may be conducted in the liquid phase under pressure at 099>C and with antimony ~uoride catalysis ð45USP1628878\ B!82MI 596!91Ł[ The product of the reaction between tetrachloromethane and HF is highly dependent on the relative amounts of CCl3 and HF as well as on the temperature[ At an HF ] CCl3 ratio of 0 ] 8\ a temperature of 324>C and a pressure of 69 atm\ the total yield is 84)\ consisting of 66) CCl2F\ 07) CCl3 and 4) CCl1F1 "Equation "17## ð36IEC393Ł[ In liquid phase reactions antimony chlorides\ such as SbCl2\ together with a certain amount of chlorine or even better\ SbCl4 have been used ð36JA836Ł[
CCl4 + HF
cat. 435 °C, 70 atm
CCl3F + CCl4 + CCl2F2
(28)
95% (77:18:5)
Trichloro~uoromethane is also formed as one of the minor products in the reaction of graphite with Cl1 and HF at 499>C as described above ð44USP1698073Ł[ Sodium hexa~uorosilicate under pressure at 169>C "Equation "18## ð48AG163Ł\ titanium tetra! ~uoride ð47JCS3134Ł\ chlorine tri~uoride:cobalt tri~uoride at 14>C ð42JCS0952Ł\ iodine penta~uoride at 29Ð24>C ð20ZAAC"190#134Ł and bromine tri~uoride "Table 1\ Equation "29## ð37JCS1077Ł are also useful as ~uorinating agents for tetrachloromethane[
CCl4 + Na2SiF6
autoclave 270 °C, 2 h
CCl3F + CCl2F2 + CClF3 + NaCl + SiF4
(29)
~100% (33:66:trace)
CCl4 + BrF3 (1:0.33)
RT
CCl2F2 + CCl3F
(30)
61% (5:95)
In the laboratory the Hunsdiecker reaction may be applied for the synthesis of trichloro! ~uoromethane "in 52) yield# from silver dichloro~uoroacetate and chlorine "Table 2\ Equation "20## ð41JCS3148Ł[
110
Tetrahalomethanes CCl2FCO2Ag + Cl2
180–260 °C
CCl3F + CO2 + AgCl
(1:1.5)
(31)
63%
"ii# Bromotrichloromethane\ CBrCl2 Treatment of tetrachloromethane with HBr:AlBr2 leads to bromotrichloromethane ð23JA0344Ł[ Bromotrichloromethane is formed by treatment of trichloromethane with bromine at 114Ð349>C ð26CR"193#0816\ 36JCS563Ł\ or in 79Ð74) yield at 319Ð349>C by recycling the material with b[p[ below 64>C ð41MI 596!90Ł\ and\ furthermore\ under the in~uence of light ð31JA0231Ł[ Older methods involve heating potassium trichloroacetate with bromine at 019>C "Equation "21#\ Table 2# ð0766CB567Ł or heating trichloromethanesulfonyl bromide with ethanol at 099>C ð0758ZC513Ł[ Low yields "09)# of bromotrichloromethane have been achieved by heating tri! chloroacetyl bromide to 399>C[ Most of the trichloroacetyl bromide was recovered "Table 2# ð28JA324Ł[ Cl3CCO2K + Br2
110–120 °C >70%
CBrCl3 + CO2 + KBr
(32)
The less easily available tetrahalomethanes may\ however\ also be prepared by base!catalyzed {{halogen dance|| "Scheme 3# ð81MI 596!92\ 82BSF488Ł[ Heating chloroform with tetrabromomethane and dibenzoyl peroxide ð40USP1442799Ł or N! bromosuccinimide ð41MI 596!91Ł also yields bromotrichloromethane[ base
CBrCl3
CCl4 + CBr2Cl2 + CBr3Cl + CBr4 base/solvent
F3CCCl3 + CBr4 RT, 0.5–11 h
F3CCBrCl2 + F3CCBr2Cl + F3CCBr3 + CBrCl3 + CBr2Cl2 + CBr3Cl solvent: DMF, CH2Cl2 base: TBAF, NaOPh, NaOH, KOH, NaOEt, NaNH2 Scheme 4
"iii# Trichloroiodomethane\ CCl2I Good yields "64)# of trichloroiodomethane in admixture with hexachloroethane "05)# are achieved by distillation "039>C# at atmospheric pressure of trichloroacetyl iodide "Scheme 4\ Table 2# ð28JA324Ł\ prepared from hydrogen iodide and trichloroacetyl chloride[ Treatment of bromotrichloromethane with aluminum iodide leads to trichloroiodomethane ð42JCS811Ł[
Cl3CCOCl
HI
Cl3CCOI
distillation 140 °C
Cl3CCCl3 + CCl3I 80% (6:94)
Scheme 5
Trichloromethane treated with iodine and sodium hydroxide at 9>C for 04 h\ gave 09) di! chloroiodomethane as well as 0) trichloroiodomethane[ The iodinating agent in this medium is sodium hypoiodite generated in situ[ Use of tetrachloromethane\ excess iodine and sodium hydroxide at 9>C for _ve days gave trichloroiodomethane in less than 4) yield[ An attempt to iodinate tetrachloromethane with NaI in acetone failed ð68JCED140Ł[
111
Four Halo`ens or Three Halo`ens and One Other Heteroatom
5[96[0[1[2 Tribromomethyl halides "i# Tribromo~uoromethane\ CBr2F Tribromo~uoromethane is formed as a coproduct "20)# in the reaction of "dibromo! ~uoromethyl#triphenylphosphonium bromide\ formed from triphenylphosphine and CFBr2 in THF\ with iodine monobromide in tetraglyme "Scheme 5# ð71JFC"19#78Ł\ and under controlled reaction conditions\ in high yield "83)# upon ~uorination of tetrabromomethane with bromine tri~uoride "Equation "22#\ Table 1# ð37JCS1077Ł[ R3P + CFXYZ
solvent
[R3PCFXY]+ Z– + X'Y' + KF
[R3PCFXY]+ Z– solvent'
CFXYX'
solvent = THF, diethyl ether or triglyme solvent' = triglyme, tetraglyme or DMF R = Ph or (NMe2) X, Y, Z = F, Cl or Br X', Y' = Cl, Br, I Scheme 6
CBr4
+ BrF3
~0 °C
(1:0.33)
CBr3F + CBr2F2 94% (100:trace)
(33)
Furthermore\ it is available by ~uorination of tetrabromomethane with antimony tri~uoride "08Ð81) yield# ð07CB558\ 46JA4543\ 47BSB565\ 48JCS02Ł[ Birchall and Haszeldine heated tetrabromo! methane with antimony tri~uoride and bromine "1 ] 0 ] 9[0# 0 h at 019Ð029>C\ followed by 29 min at 049Ð059>C\ with a yield of 54Ð69) after distillation "Equation "23## ð48JCS02Ł[ Silver ~uoride has also been applied as ~uorinating agent in a distillation apparatus*allowing bromotri~uoromethane to distil out of the reaction mixture ð07CB558Ł[ CBr4 + Br2 + SbF3 (2:0.1:1)
i, 120–130 °C, 1 h ii, 150–160 °C, 0.5 h
CBr3F 65–70%
(34)
"ii# Tribromochloromethane\ CBr2Cl Tribromochloromethane is formed as the main product "relative yield 31)# after base!catalyzed {{halogen dance|| reactions "Scheme 3# ð81MI 596!92\ 82BSF488Ł[ Thus\ after treatment of CF2CCl2:CBr3 with KOH in DMF at RT for 3 h\ tribromochloromethane is formed with the following by!products] CF2CCl1Br "relative yield 21)#\ CF2CClBr1 "10)# and CBr1Cl1 "08)# ð81MI 596!92Ł[ Dibromochloronitrosomethane may be re~uxed with bromine for 2 h giving a 84) yield of tribromochloromethane[ Dibromochloronitrosomethane is in turn accessible from Br1C1NOH "Scheme 6# ð21CB435Ł[ Br
OH N
Br
i, HgCl2 (aq.) ii, Br2, NaOAc
ClBr2CNO 75–80%
Br2, reflux, 3 h
CBr3Cl 95%
Scheme 7
Treatment of CCl3 with an equimolar amount of Br1 for 1 h at 114>C leads to tri! bromochloromethane in admixture with bromotrichloromethane and dibromodichloromethane ð0781CB077Ł[ Trichloromethane heated with bromine for 03 h at 114Ð164>C ð26CR"193#0816Ł as well as HBr:AlCl2 treatment of tetrachloromethane gives tribromochloromethane[ In the latter reaction\ HBr is bubbled into a solution of CCl3 and AlCl2 and the temperature raised to 89>C[ The product contains 5) tribromochloromethane and 83) tetrabromomethane with an 76) conversion of tetrachloromethane[
Tetrahalomethanes
112
"iii# Tribromoiodomethane\ CBr2I Treatment of CHBr2 with KI\ NaOCl and NaOH for 13 h gave mainly CHBr1I "09)# and only traces "9[0)# of tribromoiodomethane could be detected[ The same reaction conditions were also applied to CBr3 for six days\ but again only a very low yield "³0)# of CBr2I was obtained[ On the other hand\ when CBr3 was treated with NaI in acetone for 4 min a yield of more than 29) CBr2I was observed\ although the product was contaminated with CBrI2 and brominated acetone "Equation "24## ð68JCED140Ł[ According to an old procedure by Dehn ð98JA0119Ł it should\ however\ be possible to prepare tribromoiodomethane from tribromomethane and nitrosyl iodide[ Dehn reported the product as a solid darkening at 24>C[ NaI, acetone
CBr4 5 min
CBr3I + CBrI3 + brominated acetone ~30%
(35)
5[96[0[1[3 Triiodomethyl halides "i# Fluorotriiodomethane\ CFI2 and chlorotriiodomethane\ CClI2 Fluorotriiodomethane and chlorotriiodomethane still await preparation\ but theoretical dis! cussions of their physical properties are on record ð47MI 596!90\ 48MI 596!92\ 55ZOB0244\ 61MI 596!90\ 65ZC266\ 66MI 596!90\ 68JMR448\ 72MI 596!90\ 80MI 596!90Ł[
"ii# Bromotriiodomethane\ CBrI2 Bromotriiodomethane has been prepared by Dehn ð98JA0119Ł by treatment of triiodomethane with NaOBr[ It is an unstable solid which liberates iodine upon exposure to light or upon dissolution[ Bromotriiodomethane has also been reported as a by!product in the Finkelstein reaction mentioned above\ that is the treatment of tetrabromomethane with sodium iodide in acetone "Equation "24## ð68JCED140Ł[
5[96[0[2 Two Similar Halogens 5[96[0[2[0 Di~uoromethylene dihalides "i# Bromochlorodi~uoromethane\ CBrClF1 Bromochlorodi~uoromethane may be prepared in 80) yield by the heating of silver chloro! di~uoroacetate with bromine "Equation "25#\ Table 2# ð41JCS3148Ł[ CClF2CO2Ag + Br2 (1:1.5)
180–260 °C
CBrClF2 + CO2 + AgBr
(36)
91%
Bromochlorodi~uoromethane is formed\ but only in very low yield "4)#\ in the reaction of tris"dimethylamino#"chlorodi~uoromethyl#phosphonium chloride\ formed from tris"dimethyl! amino#phosphine and CF1Cl1 in triglyme\ with bromine in triglyme "Scheme 5# ð71JFC"19#78Ł[ Trabalka et al[ describe in a patent ð70MIP57244Ł the formation of bromochlorodi~uoromethane by heating of chlorodi~uoromethane with bromine and chlorine at 499Ð799>C[ Other synthetic methods include the preparation from chlorodi~uoromethane\ bromine and oxygen with catalysis from chromium trioxide at 499>C[ The yield was 75) and the reaction product consisted of CBrClF1\ CBr1F1 and CHClF1 "47 ] 6 ] 24^ Equation "26## ð48USP1760163Ł[ Other sources are bro! modi~uoromethane by vapor phase chlorination ð42USP1528291Ł or UV irradiation of a mixture of
113
Four Halo`ens or Three Halo`ens and One Other Heteroatom
chlorodi~uoroiodomethane and bromine ð41JCS3148Ł[ Finally\ treatment of 0\2!dichloro!0\0\2\2! tetra~uoroacetone with bromine at 479Ð549>C yields bromochlorodi~uoromethane ð48USP1774349Ł[ CHClF2 + Br2 + O2
CrO3 500 °C
CBrClF2 + CBr2F2 + CHClF2
(37)
86% (58:7:35)
"ii# Chlorodi~uoroiodomethane\ CClF1I Chlorodi~uoroiodomethane has been prepared by Haszeldine "Equation "27#\ Table 2# ð41JCS3148Ł in 67) yield by heating silver chlorodi~uoroacetate with iodine[ This halomethane is\ however\ unstable and liberates iodine on exposure to O1 or light ð41JCS3148Ł[ CClF2CO2Ag + I2 (1:1.5)
180–260 °C
CClF2I + CO2 + AgBr 78%
(38)
Di~uorocarbene is generated from methyl chlorodi~uoroacetate by treatment with LiCl:HMPA and may\ when formed in the presence of I1 or IBr\ be used to prepare chlorodi~uoroiodomethane in 04) yield "contaminated with 4) CF1I1# and 29) "contaminated with 09) CBrF1I#\ as shown in Equations "28# and "39#\ respectively ð67JOC1532Ł[
CClF2CO2Me + LiCl/HMPA + I2
90–95 °C, 48 h triglyme
CClF2I + CF2I2
(39)
20% (75:25)
CClF2CO2Me + LiCl/HMPA + IBr
90–95 °C, 48 h triglyme
CClF2I + CBrF2I 40% (75:25)
(40)
Another method is the reaction of ð"Me1N#2P"CF1Cl#ŁCl\ formed from tris"dimethylamino#! phosphine and CF1Cl1 in triglyme\ with dry potassium ~uoride and iodine at 9>C for 1 h and then overnight at room temperature[ The isolated yield of CClF1I is 23) "Scheme 5# ð71JFC"19#78Ł[ Chlorodi~uoroiodomethane can\ like bromo! and iodotri~uoromethane\ be made by plasma chemical means\ but only in modest yields[ Thus\ treatment of chlorotri~uoromethane with iodine under the in~uence of high!frequency electrical discharges "01 MHz\ 0 kV# at 3Ð19 torr gave 6) conversion\ and a relative yield of 10) ð64ZAAC"307#098Ł[
"iii# Bromodi~uoroiodomethane\ CBrF1I When di~uorocarbene is generated in the presence of IBr\ bromodi~uoroiodomethane is formed as a by!product "09)# "Equation "39## ð67JOC1532Ł[ Another method is the reaction of "bromo! di~uoromethyl#triphenylphosphonium bromide\ formed from triphenylphosphine and CF1Br1 in triglyme\ with dry potassium ~uoride and iodine in triglyme[ The isolated yield of CBrF1I is 30) "Scheme 5# ð72JFC"12#228\ 71JFC"19#78Ł[ Bromodi~uoroiodomethane is one of the few tetrahalomethanes which could not be prepared except in poor yield "³4)# by the Hunsdiecker method "Table 2#[
5[96[0[2[1 Dichloromethylene dihalides "i# Dichlorodi~uoromethane\ CCl1F1 The industrial preparation of dichlorodi~uoromethane\ known as Freon 01\ involves halogen exchange of CCl3 with HF\ as described above for CFCl2 ðB!82MI 596!91Ł[ At a HF ] CCl3 ratio of 3 ] 8\ a temperature of 389>C and a pressure of 69 atm\ the total yield in the reaction between CCl3 and HF has been reported to be 48)\ consisting of 68) CCl1F1 and
114
Tetrahalomethanes
10) CCl2F "Equation "30## ð36IEC393Ł\ whereas in the presence of SbCl2 and Cl1 at 009>C and 29 atm\ CCl1F1 constitutes 89) of the product ðB!81MI 596!93Ł[ Furthermore\ treatment of phosgene with chlorine and anhydrous hydrogen ~uoride at 314>C in the presence of FeCl2:C also yields a mixture consisting of CCl1F1\ CClF2 and CF3 "Equation "06## ð46JA4790Ł[ Trichloromethane does\ as mentioned above\ also form a CClmFn mixture when treated with CF2OF ð48JA0978Ł\ and dichlorodi~uoromethane is formed as one of the minor products in the reaction of graphite with Cl1 and HF at 499>C as described above ð44USP1698073Ł[ 490 °C, 70 atm
CCl4 + HF (9:4)
CCl2F2 + CCl3F 59% (79:21)
(41)
In the laboratory\ dichlorodi~uoromethane may be prepared in high yield "85)# by ~uorination of CCl2F with BrF2\ or as the main product of the ~uorination of CCl3 with BrF2 at −67>C:RT in a total yield of 78) "Scheme 7\ Table 1#[ Trichloro~uoromethane is the only by!product ð20USP0850511\ 37JCS1077Ł[ CCl4 + BrF3
–78 °C to RT
(1:0.6) RT
CCl4 + BrF3 (1:0.8)
CCl2F2 + CCl3F 89% (85:15) CCl2F2 96%
Scheme 8
Treatment of tetrachloromethane with sodium hexa~uorosilicate under pressure at 169>C in an autoclave yields a mixture of CClnF3−n with dichlorodi~uoromethane as the major product "Equa! tion "18## ð48AG163Ł[ Degradative reactions forming CCl1F1 include the chlorinolysis at 449>C of 0\0!di~uoroethane\ formed by treatment of acetylene with HF ðB!48MI 596!91Ł and the heating of silver chloro! di~uoroacetate with chlorine "Equation "31#\ Table 2# ð41JCS3148Ł[ CClF2CO2Ag + Cl2
180–260 °C
(1:1.5)
CCl2F2 + CO2 + AgCl 88%
(42)
Dichlorodi~uoromethane may _nally also be made by electrolysis of chlorodi~uoroacetic acid ð22BSB091Ł[
"ii# Bromodichloro~uoromethane\ CBrCl1F Bromodichloro~uoromethane has been prepared by Haszeldine ð41JCS3148Ł by use of the Hunsdiecker reaction\ in 47) yield by heating silver dichloro~uoroacetate with bromine "Equation "32## and in 52) yield by heating silver bromochloro~uoroacetate with chlorine "Equation "33#\ Table 2#\ and also by bromination of dichloro~uoromethane at 364>C "30) conversion\ yield 67)# ð45USP1644203\ 46JA3048\ 48JA1967Ł[ CCl2FCO2Ag + Br2
180–260 °C
(1:1.5) CBrClFCO2Ag + Cl2 (1:1.5)
180–260 °C
CBrCl2F + CO2 + AgBr 58%
(43)
CBrCl2F + CO2 + AgCl 63%
(44)
"iii# Dichloro~uoroiodomethane\ CCl1FI Dichloro~uoroiodomethane has been prepared in poor yield by heating silver dichloro! ~uoroacetate with iodine[ Dichloro~uoroiodomethane turned out to be unstable to storage at RT[ It forms di}erent haloethanes with liberation of iodine ð41JCS3148Ł "Table 2#[ It has been prepared in 33) yield "52Ð62) yield according to Fried and Miller ð48JA1967Ł# by a
115
Four Halo`ens or Three Halo`ens and One Other Heteroatom
Finkelstein reaction from bromodichloro~uoromethane:NaI:acetone in a closed vessel for 2 h at 019>C "Equation "34## ð46JA3048Ł[ CBrCl2F + NaI
acetone 120 °C, 3 h
CCl2FI + NaBr 44–73%
(45)
"iv# Bromodichloroiodomethane\ CBrCl1I Bromodichloroiodomethane has not been prepared yet\ but theoretical discussions of its physical properties are on record ð61MI 596!90\ 68JMR448\ 80MI 596!90Ł[
5[96[0[2[2 Dibromomethylene dihalides "i# Dibromodi~uoromethane\ CBr1F1 Dibromodi~uoromethane may be prepared in 72) as the only product by ~uorination of tetra! bromomethane with IF4 "Equation "35##\ as the major product "relative yield 65)# by ~uorination with BrF2\ and as a minor product "relative yield 05)# by ~uorination of tetraiodomethane with IF4 "Table 1# ð37JCS1077Ł[ Fluorination of tetrabromomethane with TiF3 forms dibromo! di~uoromethane in low yield as a mixture with bromotri~uoromethane ð47JCS3134Ł[ Furthermore\ CBr1F1 is formed in high yield "70)# by the heating of silver bromodi~uoroacetate with bromine "Equation "36#\ Table 2# ð41JCS3148Ł[ CBr4 + IF5 (1:0.6)
90 °C, 3 h
CBrF2CO2Ag + Br2 (1:1.5)
CBr2F2 + CBr3F + CBrF3 + CF4 83% (100:trace:trace:trace) 180–260 °C
CBr2F2 + CO2 + AgBr 81%
(46)
(47)
Other methods involve vapor phase bromination of di~uoromethane at 499>C "50) conversion^ the product is a mixture of CHBrF1 and CBr1F1 ð42USP1528290Ł# and treatment of di~uoromethane with a mixture of bromine and chlorine at 249>C ð42USP1547975Ł[ Furthermore\ a low yield is obtained from bromochlorodi~uoromethane and HBr:Br1 at 599>C "55) conversion^ the product is a 83 ] 5 mixture of CHBrF1 and CBr1F1 ð45USP1618576Ł#\ or from tribromo~uoromethane\ HF and a chromium oxo~uoride catalyst at 149>C ð45USP1634775Ł[ Reaction between tetrabromomethane\ HF and an aluminum oxo~uoride catalyst at 129Ð149>C\ 0\2!dichloro!0\0\2\2!tetra~uoroacetone and bromine at 479Ð549>C ð48USP1774349Ł or the heating of tetrabromomethane with AgF "0 ] 1#\ allowing distillation from the reaction mixture to occur ð07CB558Ł\ all lead to dibromodi~uoro! methane[ Dibromodi~uoromethane is formed\ but only in a very low yield "2)#\ in the reaction of tris! "dimethylamino#"chlorodi~uoromethyl#phosphonium chloride\ formed from tris"dimethylamino#! phosphine and CF1Cl1 in triglyme\ with bromine in triglyme "Scheme 5# ð71JFC"19#78Ł[
"ii# Dibromodichloromethane\ CBr1Cl1 Bromotrichloromethane disproportionates in the presence of tetrabutylammonium ~uoride to a mixture of tetrachloromethane\ dibromodichloromethane\ tribromochloromethane and tetra! bromomethane ð82BSF488Ł[ Other bases and solvent systems have also been tried in such base! catalyzed {{halogen dance|| reactions[ The individual halomethanes were obtained by fractional distillation "Scheme 3# ð81MI 596!92Ł[ It is also obtained\ in admixture with other halomethanes\ from tetrachloromethane treated with bromine tri~uoride in the presence of AlCl2 or BBr2[ Dichloromethane and bromine react under formation of dibromodichloromethane on illumi! nation ð31JA0231Ł or after heating in a sealed vessel at 119Ð149>C for more than a week
116
Tetrahalomethanes
ð0776LA"139#081Ł[ Furthermore\ impure CBr1Cl1 is obtained upon treatment of trichloromethane with bromine in a closed reaction vessel at 114Ð164>C ð26CR"193#0816Ł or by heating dichloro! bromonitrosomethane with bromine "vide supra# ð21CB435Ł[
"iii# Dibromochloro~uoromethane\ CBr1ClF Dibromochloro~uoromethane is formed in 60) yield upon heating of silver bromo! chloro~uoroacetate with bromine "Equation "37#\ Table 2# ð41JCS3148Ł and by vapor phase bro! mination of dichloro~uoromethane at 549>C ð45USP1644203Ł[ CBrClFCO2Ag + Br2 (1:1.5)
180–260 °C
CBr2ClF + CO2 + AgBr 71%
(48)
"iv# Dibromo~uoroiodomethane\ CBr1FI Dibromo~uoroiodomethane is formed as the major product "46)# in the reaction of "dibromo! ~uoromethyl#triphenylphosphonium bromide\ formed from triphenylphosphine and CBr2F in THF\ with iodine in tetraglyme[ The crude product is\ however\ contaminated with substantial amounts of other halomethanes "Scheme 5# ð71JFC"19#78Ł[
"v# Dibromochloroiodomethane\ CBr1ClI Dibromochloroiodomethane still awaits preparation\ but theoretical discussions of its physical properties are on record ð61MI 596!90\ 68JMR448\ 80MI 596!90Ł[
5[96[0[2[3 Diiodomethylene dihalides "i# Di~uorodiiodomethane\ CF1I1 Di~uorodiiodomethane has been prepared in low yield "16)# by ~uorination of CI3 with HgF1 in 0\1!dichlorobenzene[ Excessive ~uorination is minimized by distillation of the CF1I1 formed in the reaction ð73JOC194\ 74DIS"B#739Ł[ A better method has\ however\ been reported by Su et al[ ð81CC796Ł who discovered a convenient method for obtaining pure CF1I1 in fair yield "49Ð59) isolated yield^ 79) by 08F NMR#[ Treatment of methyl bromodi~uoro! or chlorodi~uoroacetate with equimolar amounts of KI\ I1 and a catalytic amount of CuI leads to the formation of CF1I1 "Equation "16##[ This method is\ however\ somewhat compromized by di.culties in the separation of CH2I and CF1I1[ Pure di~uorodiiodomethane is obtained from potassium bromodi~uoroacetate by heating with equimolar amounts of KI\ CuI and I1 in DMF at 39>C for 09 h[ The use of only a catalytic amount of CuI causes the yield to drop to 09) "Equation "38## ð81CC796Ł[
CBrF2CO2K + KI + CuI + I2
DMF 40 °C, 10 h
CF2I2 + KBr + CO2 90% (50–60% isolated)
(49)
"ii# Dichlorodiiodomethane\ CCl1I1 Dichlorodiiodomethane has been prepared by Holand in 0776 ð0776LA"139#114Ł by treatment of CH1Cl1 with Br1:I1 "0 ] 3:3# at 099Ð199>C for several weeks[ Distillation of the crude product gave dichloroiodomethane and dichlorodiiodomethane[ Dichlorodiiodomethane melts at 74>C under liberation of iodine and is probably unstable in solution ð0776LA"139#114Ł[
117
Four Halo`ens or Three Halo`ens and One Other Heteroatom
"iii# Bromo~uorodiiodomethane\ CBrFI1 Bromo~uorodiiodomethane is formed as a minor by!product "04)# in the reaction of "dibromo! ~uoromethyl#triphenylphosphonium bromide\ formed from triphenylphosphine and CBr2F in THF\ with iodine in DMF "Scheme 15# ð71JFC"19#78Ł[
"iv# Dibromodiiodomethane\ CBr1I1^ chloro~uorodiiodomethane\ CClFI1^ and bromochlorodiiodomethane\ CBrClI1 Dibromodiiodomethane\ chloro~uorodiiodomethane and bromochlorodiiodomethane still await preparation\ but theoretical discussions of their physical properties are on record ð47MI 596!90\ 48MI 596!92\ 55ZOB0244\ 61MI 596!90\ 65ZC266\ 66MI 596!90\ 68JMR448\ 72MI 596!90\ 80MI 596!92Ł[
5[96[0[3 Bromochloro~uoroiodomethane\ CBrClFI Bromochloro~uoroiodomethane\ although often mentioned as the prototype of a chiral compound\ has not been prepared yet[ MO calculations indicate that it is the second least stable chiral halomethane judged from the enthalpies of formation ð89BCJ0167Ł[ The only chiral halo! methane which has been prepared is CHBrClF\ and it has been shown that this derivative hydrolyzes much faster than other mixed halomethanes ð45JA368Ł^ this may also be the case with bromo! chloro~uoroiodomethane[ It would be interesting to try the Hunsdiecker reaction on silver bromochloro~uoroacetate which reacts with both chlorine and bromine as mentioned above[ It may\ however\ turn out to be a very low yielding reaction\ as was the case with the treatment of silver bromodi~uoroacetate with iodine "Table 2# ð41JCS3148Ł[ Theoretical discussions of the physical properties of so far unsynthesized tetrahalomethanes are on record ð47MI 596!90\ 48MI 596!90\ 55ZOB0244\ 61MI 596!90\ 65ZC266\ 66MI 596!90\ 68JMR448\ 72MI 596!90\ 80MI 596!90Ł[
5[96[1 METHANES BEARING THREE HALOGENS 5[96[1[0 Three Halogens and a Chalcogen Trihalomethoxy as well as trihalomethylthio groups may be regarded as superhalo`ens and behave as such[ They are\ for example deactivating and ortho!\ para!directing substituents in electrophilic aromatic substitution[ As superhalo`ens\ they have been used as alternative substituents to cir! cumvent existing patents and to impart increased lipophilicity to compounds relative to their halogen substituted counterparts[ For more information see a comparison and discussion on trihalomethyl "and other pseudohalogens# vs[ halogen by Haas\ who has made a large contribution to this synthetic _eld ð71CZ128\ 73MI 596!90Ł[ The subject of trihalomethoxy and trihalomethylthio containing compounds has previously been reviewed by Marhold ð72HOU"E3#514\ 72HOU"E3#0192Ł\ Hocker ð72HOU"E3#0257Ł and McClinton and McClinton ð81T5444Ł[
5[96[1[0[0 Three halogens and an oxygen function "i# Trihalomethanols\ CHal2OH Tri~uoromethanol is a rather unstable compound which\ above −19>C\ eliminates hydrogen ~uoride under formation of carbonyl ~uoride[ It was therefore not synthesized until 0866\ when Seppelt prepared tri~uoromethanol by treating tri~uoromethyl hypochlorite with HCl at −019>C ð66AG214Ł[
Three Halo`ens
118
"ii# Trihalomethyl ethers\ CHal2OR Aryl tri~uoromethyl ethers may be prepared from the corresponding phenols by treatment with tetrachloromethane and hydrogen ~uoride\ with the exception of phenols with ortho!substituents capable of hydrogen bonding to the hydroxy group[ The yields are generally best when electron! withdrawing substituents are present ð68JOC1896Ł[ Chlorine may be used as such and later removed by hydrogenation ð76JA2697Ł[ The reaction is catalyzed by antimony trichloride and probably passes through the trichloro derivative ð68JOC1896Ł[ Trichloromethyl ethers "aryl and alkyl# can in turn be transformed to tri~uoromethyl ethers by treatment with F1:SnF1 ð80CL0310Ł\ HF ð75BSF814Ł\ HF:SbCl4 ð61GEP1018199Ł\ SbF2 ð44DOK"094#099Ł or even better SbF2:SbCl4 ð47JGU1428Ł[ Mixed trihalomethyl ethers may be prepared by decreasing the reaction temperature and the amount of HF "HF:SbCl2# used ð61GEP1018199\ 68JOC1896\ 75BSF814Ł[ Rico and Wakselman made mixed trihalomethyl ethers from potassium phenoxides\ CBr1F1 or CBrClF1 and a catalytic amount of 0!propanethiol kept in DMF at RT for 3 h[ Unfortunately\ low yields "5Ð49)# were obtained with aryl di~uoromethyl ethers as the major and aryl bromo! di~uoromethyl ethers as the minor product ð70T3198Ł[ Synthesis of aryl trichloromethyl ethers from the corresponding nonhalogenated ether is achieved by photochlorination "69) yield# or by use of Cl1:PCl4 "60) yield# ð66CI"L#016\ 75BSF814Ł[ A carbonyl function can be regarded as a latent CF1 function[ The corresponding transformation is e}ected by SF3\ sometimes in the presence of HF[ Other reagents include the more easily handled alkylsulfur tri~uorides\ MoF5:BF2\ COF1 or the more reactive SeF3 ðB!81MI 596!90Ł[ According to Hudlicky ðB!81MI 596!90Ł the following order of reactivity is observed with SF3 as ~uorinating agent] alcohols×aldehydes\ ketones×acids\ amides×esters\ acid anhydrides×alkyl halides[ This has been exploited in the synthesis of tri~uoromethyl ethers[ Thus\ treatment of ~uoroformic acid esters "FC"1O#OR# with sulfur tetra~uoride leads to tri~uoromethyl ethers[ This reaction is especially convenient for the synthesis of aryl tri~uoromethyl ethers\ and only when electron! withdrawing groups are present in the b!position can the aliphatic counterparts be synthesized in satisfactory yields ð50JA3759\ 53JOC0\ 53JOC00Ł[ Analogous to this O!alkyl chlorothioformic acid esters "ClC"1S#OR# can also be transformed to tri~uoromethyl ethers by treatment with MoF5\ in 39Ð89) yield ð62TL1142Ł[ Trichloromethyl ethers are prepared similarly by chlorination with Cl1 of ZC"1S#OR "Z Cl\ SMe# and ðROC"1S#SŁ1 ð44JA0788\ 45JA5969\ 47JGU1428\ 47ZOB1495\ 53ZOB0868\ 61JOC1540Ł[ A very mild method for the transformation of xanthates or "di~uoro"methylthio#methyl# ethers into tri~uoromethyl ethers was introduced by Kuroboshi et al[ They made use of "HF#8: pyridine:0\2!dibromo!4\4!dimethylhydantoin "DBH# as oxidative desulfurization!~uorinating agent and achieved yields of 37Ð79) ð81TL3062Ł[ Electrophilic addition of halogens to alkenes is a standard reaction in organic chemistry\ and addition of trihalomethyl hypohalites\ which may be considered as a halogen bound to a super! halogen\ should therefore be expected to constitute a similar reaction\ which is exactly the case[ Thus\ b!~uoro! or b!chloroalkyl tri~uoromethyl ethers may be prepared by addition of tri~uoromethyl hypo~uorite or hypochlorite to alkenes[ The reaction of tri~uoromethyl hypochlorite with unsubstituted alkenes can be controlled at temperatures below −000>C\ whereas the reaction with electron!poor alkenes only proceeds at a signi_cantly higher temperature "½49>C#[ The addition is most probably polar in nature\ with Markovnikov regiochemistry\ and gives syn!addition products[ Tri~uoromethyl hypo~uorite\ on the other hand\ is more reactive and its reactions have to be conducted at much lower temperature[ They are most probably of free!radical nature\ that is anti!Markovnikov and lack stereoselectivity[ The yields are in most cases quantitative ð72JOC131\ 75IC265\ 80CL0310Ł[ Bis"tri~uoromethyl# and bis"trichloromethyl# ether are prepared from dimethyl ether by electro! ~uorination "HF# ð49USP1499277Ł and photochlorination "Cl1# ð47CT404Ł\ respectively[ Tri~uoromethoxide is a rather poor nucleophile but\ with tris"dimethylamino#sulfonium ""Me1N#2S¦^ TAS¦# as counterion\ nucleophilic substitution is possible[ Fluorination instead of tri~uoromethoxylation may\ however\ be expected at secondary substitution sites due to the elevated reaction temperature required ð74JA3454\ 74MI 596!90Ł[ Transformation of an enol group into a di~uorohalomethoxy group has been accomplished by reaction with di~uorocarbene[ Thus\ 5!substituted 1!quinoxalones upon treatment with dibromo! di~uoromethane gave 5!substituted 1!"bromodi~uoromethoxy#quinoxalines[ Further treatment with poly"hydrogen ~uoride#:pyridine yields the corresponding tri~uoromethyl ethers "Scheme 8# ð81JFC"48#306Ł[ A summary of selected methods for the synthesis of trihalomethyl ethers is found in Table 3[
129
Four Halo`ens or Three Halo`ens and One Other Heteroatom
R
N
N
R
R
CBr2F2
N H
N
poly (HF)/pyridine
O
N
OCBrF2
N
OCF3
+ N
R
N
OCHF2
R = H, OMe, CF3, Cl Scheme 9
Table 3 Selected methods for the formation of trihalomethyl ethers[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Startin` material Rea`ent"s# Reaction conditions Product"s# Ref[ "yield# ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Ar0OH CCl3:HF 049>C\ 7 h Ar0OCF2 "09Ð62# 68JOC1896 R0OCCl2 R aryl or alkyl
HF:SbCl4
039>C\
R0OCF2 "64Ð75#
61GEP1018199
Cl1:hn Cl1:PCl4
79>C\ 089Ð199>C\
Ar0OCCl2 "69# "60#
66CI"L#016 75BSF814
SF3
099Ð064>C\ 5 h
R0OCF2 "07Ð61#
53JOC0 53JOC00
Cl1
9:49>Ca
R0OCCl2 "14Ð89#
"see text#
−14Ð029Ð089>C
"39Ð89#
62TL1142
Ar0OMe
R0OC"1O#F R aryl or alkyl R0OC"1S#Z Z Cl\ SMe\ SSC"1S#OR R aryl or alkyl
MoF5 b
R0OC"1S#SMe R aryl or alkyl
Poly!HF:pyridine:DBH
−67Ð9>C\ 0 h
R0OCF2 "49Ð79#
81TL3062
CR11CR1
CF2OF CF2OCl
varying
CF2O0CR10CR10F CF2O0CR10CR10Cl "½quant[#
80CL0310 75IC265 72JOC131
R0OCF2 ] R0F 74MI 596!90 R0OTf CF2O−TAS¦c R alkyl "77\ 61 ] 17#d 74JA3454 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a Depending on the actual compound type[ b DBH\ 0\2!dibromo!4\4!dimethylhydantoin[ c TAS¦\ tris"dimethylamino#sulfonium[ d This ratio "tri~uoromethoxylation vs[ ~uorination# was achieved at a secondary site[ Milder conditions may be used at primary sites which favor tri~uoromethoxylation[
"iii# Trihalomethyl esters\ CHal2OC"1O#R Trihalomethyl esters may be considered as carboxylic acid superhalides and therefore expected to be very reactive[ They may\ furthermore\ be expected to be thermally unstable and to release carbonyl dihalide with formation of the corresponding carboxylic acid halide\ as is the case with trichloromethyl perhalobutanoic acid esters ð58CB2016Ł[ Only very few compounds containing a CHal2ZC"1Z?#R "Z\ Z? O\ S\ Se\ Te# substructure are known[ They are in general formed by halogenation of the corresponding methyl esters[ Thus\ aerosol ~uorination of methyl per~uoroadamantaneacetate yields the tri~uoromethyl ester plus the acid ~uoride in 00) yield ð81JOC3638Ł and low yields were also obtained after electro~uorination of methyl esters ð89JFC"49#062Ł\ whereas photochlorination of methyl perchloro!2!butenoate at RT gave the corresponding trichloromethyl ester in more than 82) yield ð58CB2016Ł\ and pho! tochlorination of dimethyl carbonate yields bis"trichloromethyl# carbonate in quantitative yield ð72HOU"E3#0257Ł[ Trichloromethyl esters are\ furthermore\ formed by the reaction between an alcohol and diphosgene "CCl2C"1O#Cl# in 51Ð64) yield ð29JPR109\ 29JPR70Ł and obtained in 71Ð80) yield by photochlorination of methyl chloroformate ð79OS"48#084Ł[ Bis"tri~uoromethyl# oxalate has been obtained in 80) yield by irradiation of a mixture of "CF2#1O1 and CO with a low! pressure Hg!lamp ð56MI 596!91\ 57MI 596!90Ł[ Other methods include thermal decomposition of methyl"tri~uoromethyl#dioxirane which yields tri~uoromethyl acetate "Equation "49## ð80JA6543Ł
120
Three Halo`ens
and cleavage of amides with CF2OF at RT which gives N\N!dihaloamines and tri~uoromethyl esters "Scheme 09# ð63JCS"P0#621\ 79JFC"04#190Ł[ O F3C
∆
MeCO2CF3 + F3CCO2Me
O
(50)
R O
R N
F3COF (excess)
R
F3COCR2CR2NF2 +
R R = H, Me
O2N
CO2CF3
NO2 O R1
N H
O
F3COF
R2
R1
+ F2NR2 OCF3
Scheme 10
"iv# Trihalomethyl hypohalites\ CHal02OHal 1 The ~uorinating agent tri~uoromethyl hypo~uorite may be prepared in good yields from CO ð37JA2875Ł\ CO1 ð55IS054Ł and COF1 ð58JA3321Ł by treatment with elemental ~uorine in the presence of silver"II# ~uoride[ The hypo~uorite is quite thermostable and does not eliminate ~uorine unless heated above 164>C[ Tri~uoromethyl hypochlorite is prepared in 88) yield from carbonyl ~uoride by treatment with chlorine mono~uoride:cesium ~uoride ð58JA1891Ł[
"v# O!Trihalomethyl peroxides\ CHal2OOR and trihalomethyl sulfonates\ CHal2OSO1R Tri~uoromethyl hydroperoxide "CF2OOH# is prepared in 79) yield by hydrolysis of CF2OOCOF ð60JA2771Ł or by thermal decomposition of 0!hydroxy!1\1\1!tri~uoro!0!"tri~uoromethyl#ethyl hydroperoxide "0#\ which is prepared by oxidation of hexa~uoroacetone with 89) H1O1 ð60CC673Ł[ Bis"tri~uoromethyl# peroxide is prepared in 81) yield from carbonyl ~uoride and chlorine tri~uoride "4 h at 149>C# ð54USP2191607Ł or tri~uoromethyl hypo~uorite ð46JA4517Ł[ Chloro tri! ~uoromethyl peroxide adds to alkenes "−000>C:RT\ 1:26 h "depending on the alkene type## in analogy with tri~uoromethyl hypochlorite^ b!chloroalkyl tri~uoromethyl peroxides are formed "09Ð 64) yield# "Equation "40## ð64JA02Ł[ F3C F3C
O OH OH (1)
R1
R3
–111 °C
F3COOCl + R2
R1 F3COO R2 34–75%
R4
R3 Cl R4
(51)
Trichloromethyl hydroperoxide has also been prepared by photoperoxidation of trichloromethane at RT "Equation "41## ð74AG37Ł[ O2, hν
CHCl3 20 °C
Cl3COOH
(52)
Acylation of tri~uoromethyl hydroperoxide is achieved by treatment with an acyl ~uoride under dry conditions[ Tri~uoroacetyl tri~uoromethyl peroxide has been prepared in this way "07 h\
121
Four Halo`ens or Three Halo`ens and One Other Heteroatom
RT# in 84) yield ð60JA2771Ł[ Acetyl trichloromethyl peroxide has been prepared similarly from trichloromethyl hydroperoxide and acetyl chloride ð74AG37Ł[ Tri~uoromethyl tri~uoromethanesulfonate may be prepared from the silver"I# sulfonate and tri~uoroiodomethane "199>C\ 13 h# in 75) yield ð68TL2754Ł or from tri~uoromethanesulfonyl hypochlorite and tri~uorobromomethane "−000>C\ 0 h# in 84) yield ð79JA1570Ł[ Trichloromethyl tri~uoromethanesulfonate has been prepared from mercury"II# tri~uoromethanesulfonate and bromotrichloromethane "9>C\ 01 h# in 67) yield ð58CB1049Ł[
"vi# N!Trihalomethoxy compounds\ CHal2ON"1O#nR A general review of the synthesis of O!alkylated hydroxylamines has recently been given by Andree and Kluth ð89HOU"E05a#103\ 89HOU"E05a#160Ł[ O!"Tri~uoromethyl#di~uoroformaldehyde oxime has been prepared in excellent yield by de! hydro~uorination of CF2ONHCF2 with KF[ It is thermally stable at RT but dimerizes at RT in the presence of CsF to CF2N"OCF2#CF1NOCF2 ð70JFC"07#330Ł[ Treatment of trichloromethyl hydroperoxide with N1O4:NaHCO2 at −14>C leads to trichloro! methyl pernitrate "CCl2COONO1# ð74AG37Ł[
"vii# Metal trihalomethoxides\ CHal2OM Potassium tri~uoromethoxide may be prepared from carbonyl ~uoride and potassium ~uoride in acetonitrile at 19>C[ This salt is more stable than the corresponding alcohol and can be heated in solution to 79>C without formation of carbonyl ~uoride ð54CJC0782Ł[
5[96[1[0[1 Three halogens and a sulfur function "i# Trihalomethanethiols\ CHal2SH Tri~uoromethanethiol is a stable compound whereas the other trihalomethanethiols may be expected to be rather unstable ð72HOU"E3#514\ 82TL1862Ł[ The former has been prepared from mer! cury"II# tri~uoromethanethiolate in 88) yield by treatment with hydrogen chloride ð42JCS2108Ł or in 89) yield by treating "tri~uoromethylthio#silane with hydrogen iodide ð59JCS2405Ł[ The synthesis of trichloromethanethiol has previously been claimed by Connolly and Dyson ð23JCS711Ł\ but a recent investigation showed this to be in error ð82TL1862Ł[
"ii# Trihalomethyl sul_des\ CHal2SR The synthesis of sul_des has previously been reviewed by Gundermann and Humke ð74HOU"E00#047Ł[ Photochlorination of aryl methyl sul_des leads to aryl trichloromethyl sul_des which may be transformed to the corresponding tri~uoromethyl analogues by treatment with SbF2 ð26FRP719684\ 27BRP368663\ 41ZOB1105\ 43JGU774\ 59JOC59Ł[ In the presence of electron!withdrawing groups in the aromatic moiety BF2 catalysis and higher reaction temperatures are required for the ~uorination step ð64S610Ł[ Aryl tri~uoromethyl sul_des have\ furthermore\ been prepared from the corresponding aryl halides by direct tri~uoromethylthiolation with methyl ~uorosulfonyldi~uoroacetate "FSO1CF1! CO1Me#\ CuI and S7[ The choice of solvent and of aryl halide as well as of the metal iodide is of great importance[ Yields ranging from 30) to 63) have been reported in HMPA and N! methylpyrrolidone whereas no reaction is observed in DMF[ Aryl iodides were found to be most reactive and aryl chlorides inactive ð82CC807Ł[ Replacement of CuI by KI results in the formation of tri~uoromethane after work!up ð78CC694Ł[ Replacement of aryl bound halogen by a tri~uoromethylthio group can also be accomplished with di}erent soft metal tri~uoromethanethiolates\ CF2SM\ M being Cu"I#\ Ag"I# or Hg"II#[ Thus\ CF2SCu "74Ð029>C\ 0[4Ð5 h in DMF\ HMPA or N!methylpyrrolidone#\ tri~uoro! methanethiolates aryl iodides in yields of approximately 64) ð74S556Ł[ This method is also
122
Three Halo`ens
available for the synthesis of tri~uoromethylthio substituted heteroaromatics\ and the best yields are achieved with electron!poor systems ð64S610Ł[ Yields may\ furthermore\ be improved by use of copper"I# tri~uoromethanethiolate on alumina support ð89JFC"37#138Ł[ Mercury"II# bis"tri~uoromethanethiolate#\ "CF2S#1Hg\ reacts with alkyl and allyl chlorides with formation of the corresponding tri~uoromethyl sul_des ð48JA2464\ 56JOC1952\ 70TL2936Ł[ Silver"I# tri~uoromethanethiolate\ CF2SAg\ reacts with alkyl halides under formation of alkyl tri~uoromethyl sul_des with an insoluble silver halide as a convenient by!product ð50JCS1486\ 54ZOB0517Ł[ Other sources of tri~uoromethanethiolate ions which have been used in nucleophilic aromatic substitution include the in situ formation of tri~uoromethanethiolate from thiocarbonyl ~uoride or bis"tri~uoromethyl# trithiocarbonate ""CF2S#1C1S# and calcium\ potassium or caesium ~uoride ð41JCS1087\ 74C074\ 76JCS"P0#1008\ 77JCS"P0#0068Ł[ Electron!rich aromatic systems undergo substitution with tri~uoromethanesulfenyl chloride ð49JA2418\ 42CB446\ 53JOC787\ 66CB56\ 67JFC"00#498Ł and trichloromethanesulfenyl chloride ð52ACS1469Ł\ in some cases under free radical conditions\ yielding aryl tri~uoromethyl sul_des in good yields "generally in excess of 59)# and aryl trichloromethyl sul_des\ respectively[ Tri~uoromethanesulfenyl chloride as well as tri~uoromethanesulfenyl ~uoride reacts with nucleophiles^ with alkenes they form b!halo"tri~uoromethylthio#alkanes ð51JA2037\ 56JOC1952\ 76JFC"23#364Ł\ and with aryl Grignard reagents\ tri~uoromethanesulfenyl chloride "at 9>C# forms aryl tri~uoromethyl sul_des\ which are\ however\ contaminated with the corresponding aryl chlorides ð53JOC784Ł[ Tri~uoromethanethiol also reacts with alkenes under UV irradiation with formation of the corresponding alkyl tri! ~uoromethyl sul_des ð50JA739Ł[ Aromatic potassium thiolates react with bromotri~uoromethane under pressure "1Ð2 atm\ RT\ DMF# to give the corresponding tri~uoromethyl sul_des "6Ð64) yield# ð73CC682\ 74JOC3936Ł[ The use of mixed tetrahalomethanes such as dibromodi~uoromethane or bromochlorodi~uoromethane leads to mixed halomethyl sul_des ð70TL0886\ 70TL212Ł[ Alkylation of aliphatic and aromatic disul_des may be conducted in DMF:H1O at RT under radical conditions by treatment of bromotri~uoromethane with sulfur dioxide radical anion "derived from Na1S1O3:NaO1SCH1OH# and Na1HPO3 to neutralize the sulfur dioxide formed during the reaction "20Ð82) yield# ð80CC882Ł[ Tri~uoroiodomethane reacts similarly with sul_des under UV irradiation\ but more slowly\ for example\ the reaction with dimethyl sul_de "hn\ 10 days# gives a 81) yield of tri~uoromethyl methyl sul_de ð61JCS"P0#1079Ł[ This reaction has been extended to alkane!\ arene! and heteroarenethiols as well ð68ZOR285\ 68ZOR0134Ł and may\ furthermore\ be conducted under phase transfer conditions "41Ð74) yield# ð71JFC"10#254Ł[ N!"Tri~uoromethyl#!N!nitrosobenzenesulfonamide "CF2N"NO#SO1Ph\ TNS!B#\ N!"tri~uoro! methyl#!N!nitrosotri~uoromethanesulfonamide "CF2N"NO#SO1CF2\ TNS!Tf#\ S!"tri~uoromethyl#! dibenzothiophenium tri~ate "TBT!Tf# and its seleno analogue "TBSe!Tf# "1#\ and "3!chlorophenyl#! "1\5!dimethylphenyl#tri~uoromethylsulfonium hexa~uoroantimonate "2# have been developed as e.cient tri~uoromethylating agents and are more easily handled than tri~uoroiodomethane gas[ Thus\ TNS!B reacts with dialkyl sul_des to give the corresponding tri~uoromethyl alkyl sul_des in 44Ð53) yield ð71TL2818Ł[ TNS!Tf gives generally higher yields of tri~uoromethyl sul_des from thiols and dialkyl sul_des after shorter reaction times ð75BCJ336Ł[ The reaction of sodium alkane! thiolates with "1# ð89TL2468Ł produces the corresponding tri~uoromethyl sul_des in 36Ð76) yield\ as does treatment with "2# ð73ZOR004Ł[
Cl Z+ CF3
+
TfO–
S
Z = S, Se, Te
SbF6– CF3
(2)
(3)
Direct chlorination of methyl sul_des leads to trichloromethyl sul_des in yields ranging from 45Ð099)\ as does chlorination of alkyl halodithioformates a reaction which also may be used for the formation of dichlorohalomethyl sul_des ð28AG346\ 48ZOB2675\ 59ACS1129\ 51ACS006Ł[ Trichloromethyl sul_des have\ furthermore\ been prepared in 59Ð65) yield from thiocyanates by treatment with trichloromethyl anions "derived from CHCl2:NaOH# under phase transfer conditions ð63S163Ł[ Finally\ trihalomethyl sul_des can be interconverted] CF2SR:CCl2SR "with AlCl2#^ CF2SR:
123
Four Halo`ens or Three Halo`ens and One Other Heteroatom
CBr2SR "with BBr2 or AlBr2#^ CCl2SR:CF2SR "with KF:07!crown!5\ SbF2 or HF#^ CCl2SR: CBr2SR "with HBr#[ Other ~uorinating agents include AgBF3\ Hg1F1 and ðBnNMe2Ł¦F− ð27USP1097595\ 41JA2483\ 45CB0059\ 56ZOB0669\ 60GEP1992032\ 66JOC1913\ 70TL0886Ł[ Kolomeitsev et al[ have developed a method for the synthesis of tri~uoromethyl sul_des from the corresponding alcohols[ The alcohol is treated with bis"diethylamino# chloro phosphite which gives the intermediate diethylamino alkyl phosphite "ROP"NEt1#1# in 79Ð89) yield[ Further treatment with bis"tri~uoromethyl# disul_de gives the tri~uoromethyl alkyl sul_de in 89Ð84) yield[ The overall yields in this two step procedure are excellent "61Ð75)# ð83S034Ł[ Table 4 presents a summary of selected methods for the formation of trihalomethyl sul_des[ Table 4 Selected methods for the formation of trihalomethyl sul_des[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Startin` material Rea`ent"s# Reaction Product Ref[ conditions "yield# ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Ar0SCCl2 "45Ð099# "see text# Ar0SMe Cl1\ hn R0SC"1S#X R aryl or alkyl X Cl\ F
Cl1
½39>C\
R0SCCl2 "04Ð79#
48ZOB2675
Ar0X\ X Br or I Ar Ph or heteroaromatics
FSO1CF1CO1Me\ S7\ CuI
099Ð019>C\ 4Ð7 h
Ar0SCF2 "30Ð63#
82CC807\ 78CC694
Ar0I\ Ar Ph or pyridine
CF2YCu Y S\ Se
74Ð029>C\ 4Ð5 h
Ar0SCF2 "30Ð84#
89JFC"37#138\ 74S556\ 64S610
ArH\ ArH elec[ rich aromatics
CF2SCl\ Lewis cat[
59>C\ 19 h
Ar0SCF2 "39Ð67#
"see text#
R1C1CR1
CF2SCl\ hn
CF2S0CR1CR10Cl "40Ð72#
56JOC1952\ 51JA2037
Ar0MgX
CF2SCl
R1C1CR1
CF2SH\ hn
Ar0SK
CF2Br
R0SNa
9>C
Ar0SCF2 "½49)#
53JOC784
CF2S0CR1CR10H "45Ð71#
50JA739
Ar0SCF2 "6Ð64#
74JOC3936\ 73CC682
"1# or "2#
R0SCF2 "36Ð76#
89TL2468\ 73ZOR004
R1S
TNS!B or TNS!Tfa
R0SCF2 "44Ð53#
75BCJ336\ 71TL2818
R1S\ R aryl or alkyl
CF2Br\ Na1S1O3\ NaO1SCH1OH\ Na1HPO3
R0SCF2
80CC882
Ph0SCCl2
SbF2\ "BF2#
Ph0SCF2 "69#
"see text#
R0SCX2\ X F\ Cl\ Br
"see text#
R0SCY2 Y F\ Cl\ Br
"see text#
1Ð2 atm\ RT\ 2 h
RT
i\ −39>C\ 1 h^ R0SCF2 83S034 R0OH\ R alkyl i\ "Et1N#1PCl:NEt2^ or benzyl ii\ CF2SSCF2 ii\ −49Ð19>C\ 4 min[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a N!"Tri~uoromethyl#!N!nitrosobenzenesulfonamide "CF2N"NO#SO1Ph\ TNS!B#\ N!"tri~uoromethyl#!N!nitrosotri~uoromethanesulfon! amide "CF2N"NO#SO1CF2\ TNS!Tf#[
"iii# Trihalomethyl sulfoxides and trihalomethyl sulfones\ CHal2S"1O#nR The synthesis of sulfoxides and sulfones has previously been reviewed by Gundermann and Humke ð74HOU"E00#554Ł and by Schank ð74HOU"E00#0018Ł[ Partial oxidation of alkyl:aryl tri~uoromethyl sul_des with 16) hydrogen peroxide in acetic acid "1 h re~ux# yields the corresponding sulfoxides ð54ZOB0517Ł[ More drastic oxidation with nitric acid\ hydrogen peroxide or chromium trioxide in glacial acetic acid gives the corresponding sulfones ð41JA2483\ 54ZOB0517\ 56JOC1952\ 76JCS"P0#1008\ 82CC807Ł[ The transfer of CX2SO1 groups is possible by reactions of nucleophiles such as BuLi with electrophilic species like "CF2SO1#1O\ "CF2SO1#1NPh and CF2SO1Cl[ In the case of primary or
124
Three Halo`ens
secondary organometallics ditri~ation is possible due to the presence of acidic a!protons in the monotri~ated products ð66JOC2764Ł[ Alkynyl tri~uoromethyl sulfones have been prepared from sodium alkynides and tri~ic anhydride in 06Ð64) yield ð81T078Ł[ Monotri~ation of aromatic compounds can be carried out as FriedelÐCrafts tri~ation with "CF2SO1#1O:AlCl2\ but only aromatic compounds of at least intermediate reactivity such as xylene\ toluene\ and benzene are tri~ated ð66JOC2764Ł[ Aryl tri~uoromethyl sulfones have been prepared in high yields "69Ð88)# by di~uorocarbene insertion into arenesulfonyl ~uorides[ The reagent mixture used is Me2SiCF2 or Me2SnCF2 and "Me1N#2S¦Me2SiF1−"TASF#[ The yield is una}ected by electronic e}ects of arene substituents "Equation "42## ð89S0040Ł[ ArSO2F
2Me3MCF3, TASF
ArSO2CF2F 70–99% TASF = (Me2N)3S+ Me3SiF2– M = Sn, Si
(53)
THF, 20 °C
Transformation of an arenesulfonamide into an N!"tri~uoromethyl#azosulfonylarene is e}ected by treatment of the amide with tri~uoronitrosomethane in base "70Ð81) yield#[ This intermediate eliminates N1 on heating to form the corresponding tri~uoromethyl phenyl sulfone "½39) yield# "Scheme 00# ð71CL0408Ł[ F3CNO + H2NSO2Ar
base
∆
F3CN=NSO2Ar
F3CSO2Ar –N2
81–92% Scheme 11
~40%
"iv# S!Trihalomethyl thio! and dithioesters\ CHal2SC"1Z#R "Z O or S# Tri~uoromethyl thioesters have been prepared by the reaction of mercury"II# bis"tri~uoro! methanethiolate#\ "CF2S#1Hg\ with acyl chlorides "39Ð49>C\ 12Ð40) yield# ð48JA2464Ł[ Bis"tri! ~uoromethyl# trithiocarbonate is formed in ½099) yield by CsF treatment at 9>C of thiocarbonyl di~uoride ð55AG895\ 57CB1598Ł[ FriedelÐCrafts "tri~uoromethyl#thiothioacylations have been achieved with HF:SbF4 and FC"1S#SCF2 ð76CB318Ł with the latter formed from thiocarbonyl ~uoride and potassium ~uoride ð57CB1598Ł "Scheme 01#[ The corresponding "trichloromethyl#thiothioacylation "69>C\ 3 h^ RT 05 h# has been achieved in 15) yield by treating anthracene with trichloromethyl chlorodithioformate formed in 64) yield from trichloromethanesulfenyl chloride and CS ð73JOC2743Ł[ Condensation of bis"tri~uoromethyl# trithiocarbonate ""CF2S#1C1S# with "CF2S#1C1C"SCF2#1 in the presence of a catalytic amount of HgCl1 "2 d at 069>C# gives 0\0!bis"tri~uoromethylthio#!1\1!bisð"tri~uoro! methylthio#thiocarbonylŁethene in 09) yield\ with bis"tri~uoromethyl# disul_de as the main product ð66CB805Ł[
S
S F M=K M = Cs
+ F
F 3 1
1 1
S
(SCF2)x +
+ MF
–20–0 °C, 1 h –78 °C, 18 h
10–15%
F3CS
SCF3 58%
100% R
S
S HF/SbF5 +
SCF3 F
SCF3
SCF3
Et2O –50 °C–RT
Scheme 12
R
R Yield (%) H 65 4-MeO 54 3-CF3 27 2,5-F2 35
125
Four Halo`ens or Three Halo`ens and One Other Heteroatom
"v# Trihalomethanesulfenyl\ !sul_nyl and !sulfonyl halides^ CHal 02S"1O#n"Hal 1# The synthesis of sulfenyl\ sul_nyl and sulfonyl halides has previously been reviewed by Schubart ð74HOU"E00#52Ł\ Krauthausen ð74HOU"E00#503Ł and Pawlenko ð74HOU"E00#0956Ł[ See also the review by Sizov et al[ on the formation of poly~uoroalkanesulfenyl chlorides ð81RCR406Ł[ In this section only sulfenyl halides are treated\ due to their synthetic importance in the synthesis of trihalomethyl sul_des[ Umpolun` of metal trihalomethanethiolates can be achieved by chlorination to the corresponding trihalomethanesulfenyl chlorides ð50JCS1486Ł[ Bromine and iodine\ however\ oxidize silver"I# tri! ~uoromethanethiolate to bis"tri~uoromethyl# disul_de ð50JCS1486Ł[ The industrial preparation of trichloromethanesulfenyl chloride takes place by chlorination of carbon disul_de under conditions which suppress the formation of bis"trichloromethyl# disul_de ð60S367\ 55FRP0326897Ł[ A general method for the synthesis of trihalomethanesulfenyl halides is to halogenate "Hal1# thiocarbonyl halides and this method can therefore also be used to prepare mixed tri! halomethanesulfenyl halides ð48ZOB2681\ 51JCS3250\ 53AG796\ 65CB2321Ł^ furthermore\ by halogen exchange in trihalomethanesulfenyl halides with SbF2:SbCl4 "Br:F#\ HF "Cl:F#\ NaF "Cl:F#\ HF:CrOF "Cl:F# or HBr "Cl:Br# ð47USP1710443\ 48ZOB2390\ 48ZOB2673\ 59JOC1905\ 56GEP0121843Ł[ Still other methods include chlorination of disul_des\ for example chlorination of dimethyl disul_de leads to trichloromethanesulfenyl chloride in 79) yield and high purity while photo! chlorination at RT of bis"tri~uoromethyl# disul_de leads to tri~uoromethanesulfenyl chloride in 44) yield ð42JCS2108\ 50USP2903960Ł[
"vi# Trihalomethanesulfenic\ !sul_nic and !sulfonic derivatives^ CHal2S"1O#nZR The trihalomethanesulfenyl\ !sul_nyl\ and !sulfonyl halides are important starting materials for the synthesis of other trihalomethanesulfenyl\ !sul_nyl\ and sulfonyl derivatives[ For example mercury"II# bis"tri~uoromethanethiolate# ð"CF2S#1HgŁ\ reacts with sulfenyl chlorides with formation of the corresponding tri~uoromethyl disul_des ð48JA2464Ł[ Other methods which allow the formation of mixed trihalomethyl disul_des are the photoreaction between thiocarbonyl halides and trihalo! methanesulfenyl halides ð57CB1506Ł and the photoreductive dimerization of trihalomethanesulfenyl chlorides with\ for example\ CO as reductant ð56JINC1708Ł[ Trihalomethanesulfenic acids are\ as most other sulfenic acids\ unstable[ Trichloro! methanesulfenic acid for instance eliminates HCl with formation of dichlorosul_ne "Cl1C1S1O# ð58CC767Ł\ whereas the sul_nic and sulfonic acids are stable compounds[ A preparative method which gives access to halodi~uoromethanesulfonic acid derivatives in high yields is the decarbonylative photolysis of HalC"1O#CF1SO1F "the reaction is conducted at 79Ð89>C for Hal Cl\ 49>C for Hal Br\ RT for Hal I# ð68S861Ł[ The synthesis of sulfenic\ sul_nic and sulfonic acid derivatives has been reviewed previously by Schubart ð74HOU"E00#52Ł\ Krauthausen ð74HOU503Ł\ Pawlenko ð74HOU"E00#0944\ 74HOU"E00#0973Ł and Jager ð74HOU"E00#0962Ł and is not discussed here[ See\ however\ the review by Sizov et al[ on transformation of poly~uoroalkanesulfenyl chlorides ð81RCR406Ł[ The CF2SO1 group "in CF2SO1Ar# was found by NMR measurements to be even more electron! attracting than the NMe2 group "in ArNMe2¦# ð57ZOB1480Ł[
"vii# Metal trihalomethanethiolates^ CHal2SM Metal trihalomethanethiolates are important as precursors of aryl trihalomethyl sul_des "vide supra# and their synthesis is therefore mentioned here[ Copper"I# tri~uoromethanethiolate\ CF2SCu\ is obtained in nearly quantitative yield by heating "49Ð59>C# CF2SSCF2 with copper powder in DMF\ HMPA or N!methylpyrrolidone for 0Ð2 h\ depending on the activity of the copper powder ð74S556Ł[ The thiolate can be used in situ\ but also isolated and stored until needed[ The copper"I# thiolate can also be prepared by reaction of mercury"II# bis"tri~uoromethanethiolate# with copper powder ð48JA2464Ł or by reaction of AgSCF2 with Cu:CuBr ð74S556Ł[ Mercury"II# bis"tri~uoromethanethiolate#\ "CF2S#1Hg\ may be prepared from HgF1 and carbon disul_de in 61) yield after heating 3 h at 149>C in a steel autoclave ð48JA2464Ł or photochemically in 89) yield from bis"tri~uoromethyl# disul_de and metallic mercury ð42JCS2108Ł[
126
Three Halo`ens
Silver"I# tri~uoromethanethiolate\ CF2SAg\ is formed in 68) yield by the reaction of dry silver"I# ~uoride with dry carbon disul_de after heating 01 h at 039>C in a steel autoclave ð50JCS1486Ł^ it reacts with alkyl halides with formation of alkyl tri~uoromethyl sul_des and an insoluble silver halide as a convenient by!product ð50JCS1486\ 54ZOB0517Ł[
5[96[1[0[2 Three halogens and a Se or Te function "i# Tri~uoromethylselenium compounds^ CF2SeR The chemistry of tri~uoromethylselenium compounds has been reviewed and compared with that of the corresponding sulfur compounds ð75JFC"21#304Ł[ Aryl tri~uoromethyl selenides can be prepared from aryl halides and "CF2#SeCu in analogy with the synthesis of the corresponding tri~uoromethyl sul_des "Equation "43## ð74S556Ł[ Se!"Tri! ~uoromethyl#dibenzoselenophenium tri~uoromethanesulfonate "1^ Z Se# can be obtained by ~uo! rination of a mixture of 1!ð"tri~uoromethyl#selenoŁbiphenyl with CF2SO2H and by treatment of the corresponding sulfoxide with "CF2SO1#1O[ Compound "1# can be used as an electrophilic tri~uoromethylation reagent "vide supra# ð82JA1045Ł[ Bis"tri~uoromethylseleno#ketene is available by dehydration of bis"tri~uoromethylseleno#acetic acid or by dehydrochlorination of the corresponding acid chloride ð81CB460Ł[ Z X
I
+ F3CYCu
85–130 °C 1.5–6 h
Z
YCF3
X
+ CuI
(54)
41–95%
X = H, Me, NO2; Y = S, Se; Z = CH, N
Mercury"II# tri~uoromethaneselenolate reacts with S!tri~uoromethyl bromothioformate ð"CF2#SC"1O#BrŁ "029>C for 05 h# with formation of "CF2S#C"1O#Se"CF2# ð67CB1780Ł[ Run overnight at 9>C the same reaction gives a yield of 75) ð65CB2321Ł[ Oxidation of an aryl tri~uoromethyl selenide with chlorine yields the corresponding aryl! dichloro"tri~uoromethyl#selenane\ ArSeCl1"CF2# ð74S556Ł[ Aryl tri~uoromethyl selenides can be oxidized with chlorine:water to the corresponding selenoxides and with tri~uoroperacetic acid to the corresponding selenones ð57ZOB1498Ł[ Tri~uoromethaneselenonic acid\ CF2SeO2H was prepared for the _rst time by Haas and Weiler in 0874 by oxidation of CF2SeO1H with KMnO3 under neutral aqueous conditions[ Upon attempted puri_cation it decomposes "at concentrations higher than 89)# to CF3\ COF1\ SeO1 and H1O ð74CB832Ł[
"ii# Tri~uoromethyltellurium compounds^ CF2TeR Mixtures of bis"tri~uoromethyl# telluride and dialkyl tellurides are subject to ligand exchange and form alkyl tri~uoromethyl tellurides such as BnTe"CF2# and ButTe"CF2# ð81C67\ 81OM1836Ł[ Mixtures of "CF2#1Te and "C5F4#1Te as well as of "CF2#1Te1 and "C5F4#1Te1 undergo scrambling under irradiation to give "CF2#Te"C5F4# and "CF2#TeTe"C5F4#\ respectively ð89JFC"37#196\ 82CM0210Ł[ An 75) yield of dimethyl"tri~uoromethyl#telluronium iodide is obtained in the photoreaction "at −67>C# of Me1Te and CF2I ð78ZAAC"465#114Ł[ Te!"Tri~uoromethyl#dibenzotellurophenium tri~uoromethanesulfonate "1^ Z Te# can be obtained by treatment of 1!ð"tri~uoromethyl# telluroŁbiphenyl with "CF2SO1#1O and DMSO[ Compound "1# can be used as an electrophilic tri~uoromethylation reagent ð82JA1045Ł[ Tetrakis"tri~uoromethyl#tellurane "CF2#3Te\ which has been obtained from dichlorobis"tri~uoromethyl#tellurane and "CF2#1Cd\ reacts with ~uoride ions to form ð"CF2#3TeFŁ−\ with ~uoride ion acceptors to form ð"CF2#2TeŁ¦\ and with XeF1 to form the hypervalent tellurium compound "CF2#3TeF1 ð81ZAAC"597#58Ł[
5[96[1[1 Three Halogens and a Group 04 Element 5[96[1[1[0 Three halogens and a nitrogen function This subject has previously been reviewed by Marhold ð72HOU"E3#514Ł[
127
Four Halo`ens or Three Halo`ens and One Other Heteroatom
"i# Trihalomethylamines\ CHal2NR1 The unsubstituted and monosubstituted trihalomethylamines possess more or less salt character and are quite unstable[ The phosgeneiminium character makes them prone to hydrolysis "Equation "44##[ X
X
X
NH2+ X–
NH2 X
(55)
X
"a# Primary trihalomethylamines\ CHal2NH1[ Tri~uoromethylamine has been prepared by treat! ing N\N!dichloro!N!"tri~uoromethyl#amine with HCl at −67>C which gives the hydrochloride[ The free base is stable below ½−29>C\ above which it eliminates HF with formation of di~uoro! phosgeneimine "Scheme 02# ð68JA236Ł[ Synthesis of trichloromethylamine is achieved by treating ClCN with HCl[ The intermediate hydrochloride is unstable\ but addition of antimony"V# chloride converts it into the stable hexachloroantimonate salt ð53CB0175\ 62BSB12Ł[ –Cl2
F3CNCl2 + 3HCl
F3CNH3+ Cl– Scheme 13
amine base
F3CNH2
"b# Secondary trihalomethylamines\ CHal2NHR[ Secondary tri~uoromethylamines have been prepared from N!substituted isocyanide dichlorides "CCl11NR# by reaction with HF[ Yields of 58Ð87) have been achieved with N!aryl substituted compounds\ whereas the aliphatic counterparts dimerize and:or polymerize "Equation "45## ð52BEP521254Ł[ Bis"tri~uoromethyl#amine may be syn! thesized by addition of HF to tri~uoromethyl isocyanide di~uoride "CF2N1CF1# in 78) yield ð48ZOB1048Ł or by HF treatment of trichloromethyl isocyanide dichloride in 34) yield ð44JCS1421\ 47JA2593Ł[ Cl
R N
HF
Cl R = aryl
F3CNHR
(56)
69–98%
"c# Tertiary trihalomethylamines\ CHal2NR1[ Tertiary tri~uoromethylamines are stable com! pounds which have been prepared by ~uorination of R1NC"1S#SSC"1S#NR1 with either SF3 or COF1\ or by ~uorination of N\N!disubstituted ~uorothioformamides "FC"1S#NR1# with SF3[ These methods may be applied to both aryl and alkyl tri~uoromethylamines "Equation "46## ð50JA2311\ 51JA3164\ 60ZOR1999Ł[ S R2N
S
S
NR2 S
SF4
R2NCF3 58–73%
(57)
Tertiary trichloromethylamines have been made similarly by chlorination of N\N!disubstituted chlorothioformamides with Cl1 or PCl4 "½65) yield# ð48ZOB2675\ 60ZOR1973Ł\ by chlorination of R1NC"1S#SC"1S#NR1 with COCl1 "82) for R Me# ð72HOU"E3#514Ł\ by chlorination of N\N! diarylthioformamides "HC"1S#NAr1# and of alkanesulfonylthioformamides "RSO1C"1S#NR1# ð71GEP2933105\ 61CB1743Ł[ N!"1\3\5!Trichlorophenyl#!N\N!bis"trichloromethyl#amine has been pre! pared by chlorination at 039>C of the corresponding N\N!dimethylamine ð58LA"629#039Ł[ Alkylation of N!substituted phosgeneimines with strong alkylating agents such as RO2SF\ followed by Cl−:FSO2−!anion exchange\ gives the corresponding dichlorophosgeneiminium chlorides ð62AG726Ł[ Dimethyl"tribromomethyl#amine has been prepared similarly to the trichloromethyl and tri~uoromethyl analogues\ for example\ by bromination with Br1 of Me1NC"1S#SS"C1S#NMe1 ð61LA"644#034Ł[ Tertiary tri~uoromethylamines may alternatively be synthesized from the corresponding tri! chloromethylamines by treatment with HF or SbF2 under anhydrous conditions in 47Ð68) yield ð55ZOB0298\ 71GEP2933105Ł[ Bis"tri~uoromethyl#alkylamines are formed by alkylation of metal "K¦\ Cs¦\ Hg1¦# bis"tri! ~uoromethyl#amides in 33Ð73) yield ð79JCS"P0#1143\ 64IZV1168Ł[ N!Bromo! and N!iodo!N\N!bis"tri~uoromethyl#amines add to double bonds with formation
128
Three Halo`ens
of b!bromo! and b!iodoalkyl bis"tri~uoromethyl#amines\ respectively\ in 61Ð87) yield ð47JA2593\ 54JCS5030\ 57JCS"C#685\ 79JCS"P0#0433Ł[ Tris"tri~uoromethyl#amine has been prepared by treatment of tri~uoromethyl isocyanide di! ~uoride with CF2SF4 ð46JA58Ł and as a by!product "11) yield# of the reaction between O\N\N! tris"tri~uoromethyl#hydroxylamine and tri~uoromethyl isocyanide di~uoride where N\N\N?\N?! tetrakis"tri~uoromethyl#hydrazine is the main product ð56JCS"C#0130Ł[ Mixed N\N!dihalo"trihalomethyl#amines "halo equals chlorine or ~uorine# have been prepared in 59Ð64) yield from the corresponding imines by treatment "−19>C for 2Ð3 h# with chlorine mono~uoride ð60IC0524Ł[
"ii# N!Trihalomethylamides\ CHal2NRC"1O#R Isocyanates are used as starting materials for the synthesis of N!alkyl!N!"tri~uoromethyl#! carbamoyl ~uorides and of O!alkyl!N!"tri~uoromethyl#carbamates[ Thus\ tri~uoromethyl iso! cyanate reacts with CsF and subsequently with an alkyl halide\ with formation of N!alkyl!N! "tri~uoromethyl#carbamoyl ~uorides "Scheme 03# ð65IZV198Ł while the reaction of tri~uoromethyl isocyanate with alcohols yields O!alkyl!N!"tri~uoromethyl#carbamates in 55Ð73) yield "Equation "47## ð48ZOB1046Ł[ Aryl isothiocyanates are converted into N!aryl!N!"tri~uoromethyl#carbamoyl ~uorides in 32Ð72) yield by treatment with HgF1\ followed by COF1:CsF "Equation "48## ð54JA3227Ł[ F
F F3CN
•
CsF
O
RBr
O Cs+
–
N
O NCF3
CF3
R
Scheme 14
O F3CN
•
O
+ ROH
F 3C
(58)
OR N H 66–84% F
N
•
S
i, HgF2 ii, COF2/CsF
O
N
CF3 (59) R
R 43–83%
Hydrolysis of ð56JCS"C#1291Ł[
N\N!bis"tri~uoromethyl#carbodiimide
gives
N\N?!bis"tri~uoromethyl#urea
"iii# Trihalomethyl isocyanates\ CHal2N1C1O^ trihalomethyl isocyanide dihalides\ CHal2N1CHal1 and N!"trihalomethyl#carbodiimides CHal2N1C1NR Key starting materials in the synthesis of bis"tri~uoromethyl#amines are\ as mentioned above\ tri~uoromethyl isocyanide di~uoride "CF2N1CF1# and trichloromethyl isocyanide dichloride "CCl2N1CCl1#[ One high yielding method for the synthesis of these is the chlorination of N\N! dimethylcarbamoyl chloride which gives trichloromethyl isocyanide dichloride in 76) yield ð52GEP0111806\ 69GEP0815548Ł^ further treatment with sodium ~uoride yields tri~uoromethyl iso!
139
Four Halo`ens or Three Halo`ens and One Other Heteroatom
cyanide di~uoride which distills o} from the reaction mixture "67) yield\ Scheme 04# ð61CA"66#014841Ł[ Other methods of preparation of these compounds are described in Section 5[19[0[ Me
O
Cl2
Cl3C
N
Cl N
Me
Cl
250–300 °C
Cl
NaF
F3C
F N
150 °C
F
87%
78%
Scheme 15
Other key starting materials in the synthesis of "trihalomethyl#amines are the trihalomethyl isocyanates "CHal2N1C1O#[ Tri~uoromethyl isocyanate is formed in 64) yield from tri! ~uoroacetyl chloride by treatment with azidotrimethylsilane and thermolysis of the intermediary tri~uoroacetyl azide by Curtius amide degradation "Scheme 05# ð68CB1047Ł[ Tri~uoromethyl iso! thiocyanate is formed in 59) yield upon H1S treatment of tri~uoromethyl isocyanide di~uoride\ followed by distillation from NaF ð58ZOB088Ł[ Trichloromethyl isocyanate is unstable and rearranges quantitatively to chloroformyl isocyanide dichloride[ The same product is obtained in 78) yield by photochlorination of methyl isocyanate "Scheme 05# ð65CA"74#031557Ł[ Tribromomethyl isocyanate is formed in 58) yield by NBS bromination of methyl isocyanate "Scheme 05# ð71CB759Ł[ N!"Tri~uoromethyl#carbodiimides are formed in 35Ð79) yield by the reaction between tri! ~uoromethyl isocyanide di~uoride and an alkyl! or arylamine in the presence of KF:Et2N ð79JFC"04#058Ł[ TMS-N3 autoclave
O F3C
MeN
Cl
•
O
20 °C, 2 h hν, Cl2 autoclave
∆, –N2
O F3C
N3
Cl3CN
•
60 °C, 12 h
F3CN
•
O
NBS 16 h
Cl
N Cl
Br Br3CN
•
Cl O
N
Br
O Br
69%
O
O
70 °C, 15 h 89%
MeN
•
75%
O
Scheme 16
"iv# N!Halo"trihalomethyl#amines\ CHal02NRHal1 N!Bromo! and N!iodo!N\N!bis"tri~uoromethyl#amine are to be considered as umpoled amines and thus as key intermediates for the introduction of the bis"tri~uoromethyl#amine functionality by reaction with nucleophiles such as alkenes "vide supra#[ They are formed by bromination and iodination of mercury"II# bis"tri~uoromethyl#amide in 89) and 56) yield\ respectively ð47JA2593\ 55JCS"A#256Ł[ N!Chloro!N\N!bis"tri~uoromethyl#amine is similarly formed in 69) yield by chlori! nation of potassium bis"tri~uoromethyl#amide and N!~uoro!N\N!bis"tri~uoromethyl#amine is obtained by ~uorination of tri~uoromethyl isocyanide di~uoride with elemental ~uorine ð70JFC"06#352Ł[ Addition of halogen to N!halo isocyanide dihalides "Hal1C1NHal# or cyanogen chloride leads to N\N!dihalo!N!"trihalomethyl#amines in 59Ð86) yield ð69CC284\ 61LA"644#034\ 70JFC"06#352Ł[
"v# N!"Trihalomethyl#hydroxylamines\ CHal2NR0OR1^ trihalonitrosomethanes\ CHal2NO and trihalonitromethanes\ CHal2NO1 Photodimerization of tri~uoronitrosomethane\ followed by acid hydrolysis and oxidation with silver oxide\ lead to bis"tri~uoromethyl#aminoxyl radical ð46JCS0630Ł which reacts with alkyl halides with formation of O!alkyl!N\N!bis"tri~uoromethyl#hydroxylamines[ The O!methyl compound was prepared in this way by reaction with iodomethane at RT "Scheme 06# ð58JCS"A#320Ł[ The bis"tri! ~uoromethyl#aminoxyl radical also reacts with activated positions of alkanes with formation of N\N!
130
Three Halo`ens
bis"tri~uoromethyl#hydroxylamine and O!alkyl!N\N!bis"tri~uoromethyl#hydroxylamines "Scheme 07# ð62JCS"P0#0981\ 64JCS"D#1114\ 64JCS"P0#1922\ 79JFC"05#280\ 70JCS"P0#344\ 70JFC"06#220Ł[
F3CNO
F 3C
hν
HCl/H2O
N O NO
F 3C N OH
F 3C
Ag2O
N O•
F3C Scheme 17
F3C
F 3C N OH
F3C
Ag2O
RH
N O•
F 3C
F3C
F3C N OMe
96%
F3C
F3C
F 3C N OR
+
F3C
F3C
MeI
N OH F 3C
9–98% R = CMe2, CH2TMS, CH(Ph)CN, CH2SMe, CH2Ar Scheme 18
N!"Tri~uoromethyl#hydroxylamine "as its diethyl ether adduct# is formed in 37) yield when tri~uoronitrosomethane is treated with potassium hydrogen sul_te in H1O:Et1O\ followed by hydrolysis "Scheme 08# ð71JCS"P0#574Ł[ Tri~uoronitrosomethane reacts as an ene reaction compon! ent\ for instance with propene with formation of N!"tri~uoromethyl#!N!allylhydroxylamine in 89) yield "Equation "59## ð79JCS"P0#0859Ł[ O!Aryl!N\N!bis"tri~uoromethyl#hydroxylamines are prepared in high yield "×79)# from the sodium salt of N\N!bis"tri~uoromethyl#hydroxylamine and an aryl chloride ð70JFC"06#74\ 70JFC"06#480Ł[ O!Benzylated derivatives have been prepared in high yield "×79)# from benzyl chlorides and mercury"II# bisðbis"tri~uoromethyl#aminoxideŁ ð62JCS"P0#0981Ł[
F3CN
O
HO
KHSO3
N SO3– K+
H2O/Et2O –196–20 °C, 2h
HO
H3O+
NH•OEt2
F3C
F3C 48%
Scheme 19
OH F3CN
O
+
F3C
N
(60)
Tri~uoronitrosomethane may be prepared by di}erent methods\ for example by free radical substitution of iodotri~uoromethane with NO:Hg:hn "78) yield# ð43JCS801Ł or by the heating of CF2C"1O#ONO "089>C\ 45) yield# ð51JOC0953Ł or CF2C"1O#NHOH "52) yield# ð59DOK"021#591Ł[ Trichloronitrosomethane has been prepared similarly by the heating of CCl2C"1O#NHOH "89Ð84>C\ 51) yield# ð42JCS1964Ł and by treatment of CCl2SO1Na with HNO2 "45) yield# ð59DOK"021#591Ł[ Nitrotri~uoromethane is available in 38) yield by oxidation of the corresponding nitroso com! pound with Mn1O6 ð42JCS1964Ł[ Trichloronitromethane "chloropicrin# which is commercially avail! able and useful as an insecticide and as a synthetic building block\ can be prepared in a number of ways including the chlorination of nitromethane with strongly alkaline aqueous sodium hypochlorite "89) yield# ð33USP1254870Ł[
"vi# N!"Trihalomethyl#sulfenamides\ CHal2NR0SR1 N\N!Bis"tri~uoromethyl#alkanesulfenamides may be prepared by the reaction of mercury"II# bis"tri~uoromethyl#amide with an alkanesulfenyl chloride[ N\N!Bis"tri~uoromethyl#methane! sulfenamide has been prepared in 85) yield by this method ð55JINC0712Ł[ Another method is the addition of N\N!bis"tri~uoromethyl#!S!"chloro#thiohydroxylamine\ formed by the reaction of N! chloro!N\N!bis"tri~uoromethyl#amine with elemental sulfur ð53USP2010001Ł\ to alkenes which leads to N\N!bis"tri~uoromethyl#!1!chloroalkanesulfenamides "Scheme 19# ð70JFC"08#80Ł[
131
Four Halo`ens or Three Halo`ens and One Other Heteroatom F F3CN F
i, KF ii, Cl2
F 3C N Cl
S 225 °C
F3C
F 3C
N S
N SCl
F 3C 70%
F3C
CClMe2
F3C 81%
Scheme 20
"vii# Metal "trihalomethyl#amides\ CHal2NRM "Trihalomethyl#amines are poor nucleophiles\ but may be converted into stronger nucleophiles by conversion to metal "trihalomethyl#amides[ The starting material for metal "tri~uoromethyl#! amides is tri~uoromethyl isocyanide di~uoride "CF2N1CF1# which by reaction with HgF1 or KF forms the corresponding metal amides ð47JA2593\ 64IZV1168Ł[
"viii# Miscellaneous compounds Tri~uoronitrosomethane reacts with amines with formation of N!tri~uoromethyldiazenes "CF2N1NR# ð50DOK"030#246\ 57ZOB698Ł[ N\N!Bis"dibromomethylene#hydrazine "Br1C1NN1CBr1# reacts with silver"II# ~uoride with formation of N\N!bis"tri~uoromethyl#diazene "CF2N1NCF2# in 81) yield\ which may be further transformed into the corresponding hydrazine "CF2NHNHCF2# by treatment with H1S\ HI or PH2 ð51DOK"031#243\ 51JA1226\ 55JOC2722Ł[
5[96[1[1[1 Three halogens and a phosphorus function Dialkyl! and diarylphosphines react with tetrachloromethane in the presence of triethylamine to yield the corresponding phosphines "CCl2#PR1 in 76Ð84) yield ð80PS"44#074Ł and dichloro! methylenephosphines CCl11PR react with CCl3 in ether in the presence of "Et1N#2P to form bis"trichloromethyl#phosphines "CCl2#1PR in 67Ð70) yield ð81ZOB837Ł[ Tri~uoromethylphos! phaalkenes "CF2#P1CFOR have been prepared from the corresponding di~uoromethylene compounds ð82ZN"B#47Ł[ The iminomethylenephosphine "CF2#P1C1NBut has been prepared from "CF2#P1CF1 and t!butylamine and the cyclic diphosphane "3# is available from "CF2#P1CF1 and 1\2!dimethyl!1\3!butadiene ð80ZN"B#867Ł[ Per~uoro!1!phosphapropene upon addition of an alcohol and subsequent treatment with a secondary amine yields the derivative "CF2#P1C"OR#NR1 "R Me\ Et# in 47) yield ð80HAC274Ł[ P P
CF3 CF3
(4)
Tri~uoromethanephosphonic acid can be obtained by hydrolysis of diiodo"tri~uoromethyl#! phosphine ð43JCS2487Ł[ With alcohols diiodo"tri~uoromethyl#phosphine forms tri~uoromethane! phosphonic acid monoalkyl esters in 17Ð48) yield ð77ZOB0414Ł[ Trimethyl phosphite reacts upon re~ux with tetrachloromethane to form dimethyl trichloromethanephosphonate in 80) yield ð35ZOB0410Ł[ This ester\ when re~uxed with concentrated hydrochloric acid\ is quantitatively converted to trichloromethanephosphonic acid dihydrate ð44JA1758Ł[ Azidobis"tri~uoromethyl#phosphine reacts with "CF2#1P0N1PPh2 to form "CF2#1P0N1P! "CF2#10N1PPh2 ð82JOM"337#108Ł[ Aminobis"trichloromethyl#phosphines such as Me1NP"CCl2#1 can be oxidized with hydrogen peroxide to the corresponding phosphine oxides and with S7 to the corresponding phosphine sul_des[ With chlorine the corresponding chlorophosphonium chlorides are formed which are dealkylated upon heating to MeN1P"CCl2#1[ Aminobis"tri! chloromethyl#phosphines can be cleaved with HCl to form ClP"CCl2#1 ð82ZOB0139Ł[ Dibromo"tri! ~uoromethyl#phosphine "CF2#PBr1 can be converted to the corresponding "tri~uoromethyl#! phosphinylbistriazolide which is useful for the tri~uoromethylphosphonation of carbohydrates ð82TL038Ł[
132
Three Halo`ens 5[96[1[1[2 Three halogens and an As\ Sb\ or Bi function
Mixed di~uorohalomethylarsines are accessible by treatment of arsenic"III# chloride\ bromide or iodide\ respectively\ with di~uorocarbene\ generated from "CF2#1Cd = 1MeCN[ Arsenic"III# ~uoride reacts with the same cadmium reagent with tri~uoromethylation ð89ZAAC"477#15Ł[ Tris"tri~uoro! methyl#stilbine ð89JFC"35#154Ł and tris"tri~uoromethyl#bismuthine ð76JOM"223#212Ł are accessible from the appropriate element halides and "CF2#1Cd[ Diphenyl"tri~uoromethyl#bismuthine and phenylbis"tri~uoromethyl#bismuthine have been prepared from the corresponding phenyl! halobismuthines and "CF2#1Cd ð80JOM"306#C36Ł[ Bis"tri~uoromethyl#chloroarsine yields the cor! responding azide when treated with sodium azide ð81JST"157#278Ł and azidobis"tri~uoromethyl#arsine reacts with triphenylphosphine to give "CF2#1As0N1PPh2 ð82JCS"D#552Ł[
5[96[1[2 Three Halogens and a Metalloid 5[96[1[2[0 Three halogens and a silicon function Compounds with an "a! or b!~uoroalkyl#silane structure are prone to rearrangement with elim! ination of a ~uorosilane R2SiF ð48QR122\ 53AOC"0#032Ł[ The construction of the CF2SiR2 moiety requires several steps such as insertion of di~uorosilylene into the C0I bond of tri~uoroiodomethane\ metathesis of CF2SiFI with SbF2 to yield CF2SiF1\ and subsequent reduction with LAH to tri~uoromethylsilane ð75JOM"205#30Ł^ also bis"tri~uoromethyl#! silane has been prepared ð89JOM"274#196Ł[ A more convenient procedure starts from bromo! tri~uoromethane\ tris"diethylamino#phosphine\ and an appropriate silicon halide ð82OM3829Ł[ Tetra! kis"trichloromethyl#silane has been prepared in 53) yield by photochlorination of "CH1Cl#Me2Si[ The corresponding chlorination of TMS leads to destruction of the reaction mixture ð78ZOB1517Ł[ A reagent prepared from tetrakis"dimethylamino#ethylene and CBr2F reacts with organo! chlorosilanes RnSiCl3−n to give dibromo~uoromethylsilanes "CBr1F#SiRnCl2−n in 16Ð43) yield ð82OM3829Ł[
5[96[1[2[1 Three halogens and a boron function Many tri~uoromethyl boranes are unstable due to the vacant orbital on boron\ which causes halide migration from carbon to boron with formation of di~uorocarbene[ Oxygen or nitrogen"III# ligands as well as tetracoordination of the boron atom increase stability[ Dibutyl"tri~uoromethyl#borane\ "CF2#BBu1\ is formed in the reaction between potassium di! butylborate"I# and tri~uoroiodomethane[ The former reacts with boron tri~uoride to yield di~uo! ro"tri~uoromethyl#borane\ CF2BF1\ ð56JA2335Ł[ Tris"tri~uoromethyl#borane\ "CF2#2B\ is an extremely strong Lewis acid and can only be isolated in the shape of adducts with Lewis bases[ For example\ "CF2#2B = NR0R1R2 can be obtained from "dialkylamino#dichloroboranes "R0R1N#BCl1 and bromotri~uoromethane:tris"diethylamino#phosphine or tri~uoroiodomethane:tetrakis"di! methylamino#ethylene and subsequent alkylation of the secondary amine adducts so formed ð82JOM"335#14Ł[ In dichloromethane solution aminohaloboranes such as Et1NBCl1 and Et1NBBr1 react with CF2Br:P"NEt1#2 to yield the corresponding "CF2#BClNR1\ "CF2#BBrNR1\ and "CF2#1BNR1 ð78JOM"267#014Ł[ Dimethylaminobis"tri~uoromethyl#borane "CF2#1BNMe1 "4# inserts into oxiranes to form the corresponding oxaazoniaboratacyclopentanes "5# ð82ZN"B#824Ł[ Compound "4# also undergoes ene reactions with alkenes ð82JOM"345#08Ł[ With diazoalkanes "4# forms the corresponding three! membered rings "6# ð82AG318Ł[ R
R1 +
+
F3C Me
B N (5)
CF3
Me2N
–
CF3
NMe2
R2
B
F3C Me
O
F3C
B– CF3
R = Me, CH2F, CF3, Et, Bn
R1, R2 = H, Bn, TMS
(6)
(7)
133
Four Halo`ens or Three Halo`ens and One Other Heteroatom
Hexamethyldistannane reacts metathetically with tri~uoroiodomethane to form "tri~uoro! methyl#trimethylstannane[ The latter reacts further with boron tri~uoride to generate ðMe2SnŁ¦ ð"CF2#BF2Ł− which in turn can be converted to the corresponding potassium salt ð59JA4187Ł[
5[96[1[2[2 Three halogens and a germanium function Germanium"II# iodide has been treated with tri~uoroiodomethane in an autoclave at 029Ð024>C and found to give triiodo"tri~uoromethyl#germane\ "CF2#GeI2\ and diiodobis"tri~uoromethyl# germane\ "CF2#1GeI1[ The iodine atoms of the former can be exchanged for chlorine by treatment with silver"I# chloride with formation of "CF2#GeCl2 ð51JA787Ł[ The compounds "CF2#GeF2 and K1ð"CF2#GeF4Ł have been similarly prepared ð59JA5117Ł[ Atomic germanium in a solvent slurry reacts with tetrachloromethane to form "CCl2#GeCl2 and with bromotrichloromethane to form "CCl2#GeBr2 in low yield ð77BCJ2991Ł[
5[96[1[3 Three Halogens and a Metal Function The chemistry of "tri~uoroalkyl#metal compounds has previously been presented in a textbook by Emeleus ðB!58MI 596!91Ł and in reviews by Trichel and Stone ð53AOC"0#032Ł[ The synthetic methods for the preparation of "per~uoroorgano#metallic compounds have been reviewed by Chambers ðB!62MI 596!90Ł\ and tri~uoromethyl!containing transition metal complexes by Morrison ð82AOC"24#100Ł[ Of the di}erent "tri~uoromethyl#metal complexes prepared to date\ donor ð0\1!dimethoxy! ethanel"glyme# or DMFŁ stabilized bis"tri~uoromethyl#cadmium seems to be the most reliable and e.cient tri~uoromethylating agent[ Other "tri~uoromethyl#metal complexes have been prepared\ for which some application in the electronic industry may be found\ such as the stable gold complexes[
"i# Trihalomethyl alkali and earth alkali metals\ CHal2M "M Li\ Na\ K\ Cs\ M`# The preparation of a!haloalkyl Grignard reagents has been reviewed by Villieras ð60MI 596!90Ł[ The trihalomethyl alkali and earth alkali metals are very di.cult to isolate due to the dihalocarbene character of the carbon[ They are therefore most often prepared in situ and used without isolation[ In the case of "trichloromethyl#lithium the position of the equilibrium at −099>C "Equation "50## lies to the side of "trichloromethyl#lithium ð64JA076Ł[ Cl3CLi
:CCl2
+ LiCl
(61)
Ligand exchange has been attempted in the synthesis of "tri~uoromethyl#lithium and !magnesium[ When tri~uoroiodomethane is treated with methyllithium in diethyl ether\ "tri~uoromethyl#lithium is formed initially\ but this complex decomposes into lithium ~uoride and di~uorocarbene which dimerizes[ This is also the case with magnesium ð43JA363\ 53AOC"0#032Ł[ According to Kobrich\ lithiation of 1\1!diphenyl!0!bromoethene with "dichloromethyl#lithium and subsequent treatment with tetrachloromethane gives "trichloromethyl#lithium and 1\1!diphenyl!0\0! dichloroethene[ "Trichloromethyl#lithium has also been prepared in situ from butyllithium and tetrachloromethane or trichloromethane and then treated with a number of electrophiles by Hoeg et al[ ð54JA3036Ł[ "Trichloromethyl#lithium\ !sodium\ !potassium and !caesium have\ furthermore\ been prepared and investigated by IR in an Ar:CCl3 matrix at 04 K ð64JA076Ł[ "Tribromomethyl#lithium should be available by the reaction of butyllithium with tetra! bromomethane[ No data have\ however\ been presented ð56AG04Ł[ "Trichloromethyl#magnesium chloride has been prepared from isopropylmagnesium chloride and CCl3 at −004>C in THF or with CHCl2 at −67>C in THF:hexamethylphosphoric triamide "HMPT# "79:19# in 59) and 69) yield\ respectively[ "Tribromomethyl#magnesium chloride was prepared similarly with CBr3 at −004>C in THF or with CHBr2 at −84>C in THF:HMPT "79:19# in 49) yield ð56BSF0419Ł[
134
Three Halo`ens "ii# Trihalomethylaluminum\ !`allium\ !indium and !thallium\ CHal2MRn\ "M Al\ Ga\ In\ Tl# compounds
Tris"tri~uoromethyl#gallane has been prepared in 25) yield by Guerra et al[ by treating gallium tribromide with a slight excess of Cd"CF2#1 = glyme in CH1Cl1[ Further treatment with tri! methylphosphine or trimethylarsine leads to ð"CF2#2GaPMe2Ł and ð"CF2#2GaAsMe2Ł in quan! titative yields ð89JOM"289#C62Ł[ Naumann et al[ were able to prepare the following tri~uoromethyl group 02 metal complexes ðGa"CF2#1Cl = DMFŁ "in 28) yield#\ ðGa"CF2#2 = DMFŁ "31)#\ ðCd"NCMe#1ŁðGa"CF2#3Ł "38)#\ ðIn"CF2#1Cl = DMFŁ "21)#\ ðIn"CF2#2 = 1NCMeŁ "25)# and ðTl"CF2#2 = 1DMFŁ "34)# from ðCd"CF2#1 = D\ D glyme\ diglyme\ MeCNŁ and GaCl2\ InCl2 or TlCl2[ The reactions were conducted in CH1Cl1\ MeCN or DMF at −29 to 39>C ð80JOM"396#0Ł[ "iii# Trihalomethyltin and !lead\ CHal2MRn "M Sn"II#\ Sn"IV#\ Pb"IV## compounds Tri~uoromethyl"trimethyl#stannane has been prepared in 70) yield by heating at 79>C for 19 h or irradiation of a mixture of tri~uoroiodomethane and hexamethyldistannane "Me2SnSnMe2#[ Chlorination of "tri~uoromethyl#trimethylstannane leads to "tri~uoromethyl#dimethyltin chloride "Scheme 10# ð47JOC0454\ 59JA0777Ł[ SnCl4 + MeMgI
dibutyl ether reflux
SnMe4
SnBr4
Me3SnBr
Na/NH3 (l)
Me3SnSnMe3
120 °C, 3 h
89%
89%
CF3I 80 °C, 20 h
Me3SnSnMe3
Me3SnCF3
Cl2
71%
Me2(CF3)SnCl + MeCl
closed vessel –Me3SnI
Scheme 21
The "tri~uoromethyl#tin halides have been prepared[ Thus\ when tin tetrabromide is heated for 1×04 h at 009>C in an ampoule with Hg"CF2#1\ "CF2#2SnBr "7)#\ "CF2#1SnBr1 "05)#\ and CF2SnBr2 "44)# are formed\ whereas when "CF2#1Cd = diglyme is used as tri~uoromethylating reagent "CF2#3Sn "34)# and CF2SnBr2 "09Ð14)# are collected ð81JOM"322#52Ł[ Tris"tri~uoromethyl#tin iod! ide may be prepared from tetrakis"tri~uoromethyl#stannane^ either by treatment with HI or BrI2 "giving 49Ð79) yield of "CF2#2SnI and 19Ð49) yield of "CF2#1SnI1#[ "Tri~uoromethyl#tin triiodide is formed similarly by HI treatment of tri~uoromethyltin tribromide in 83) yield[ When these products are treated with AgCl for 2 h at 49>C\ the corresponding chlorides are formed in 84) yield[ Tris"tri~uoromethyl#tin ~uoride is formed upon heating "2 h at 099>C# of tetrakis! "tri~uoromethyl#stannane ð81JOM"322#52Ł[ Mixed "tri~uoromethyl#methylstannanes ð"CF2#nSnMe3−nŁ have been prepared by ligand exchange between tetramethylstannane and tetrakis"tri~uoromethyl#stannane ð81JOM"322#52Ł[ Mono!\ bis! and tris"tri~uoromethyl#stannane may be prepared by reduction of "CF2#nSnX3−n with tributylstannane at −49>C for 1 h[ The yields were 78)\ 81) and 34)\ respectively ð81JOM"323#048Ł[ A number of "tri~uoromethyl#lead complexes have been prepared in a stepwise manner by Eujen and Patorra ð81JOM"327#46Ł[ Bis"tri~uoromethyl#cadmium reacts with trimethyl! and triethyllead bromide in sulfolane at 69>C to give "CF2#PbMe2 "40) yield# and "CF2#PbEt2 "45)#[ Bromination "Br1# at 9>C or iodination "I1# at RT gave the corresponding "tri~uoromethyl#dialkyllead halides "alkyl methyl or ethyl# in quantitative yields[ The "tri~uoromethyl#dialkyllead bromides may be transformed into the bis"tri~uoromethyl#dialkyllead complexes ""CF2#1PbMe1 "36) yield# and "CF2#1PbEt1 "49)## by treatment with Cd"CF2#1[ Bis"tri~uoromethyl#methyllead bromide was then prepared in 64) yield\ by bromination at −14>C "61 h# of bis"tri~uoromethyl#dimethyllead\ which by further reaction with Cd"CF2#1 gave tris"tri~uoromethyl#methyllead in 18) yield[ Tetrakis"tri~uoromethyl#lead has not been prepared and must be expected to be rather unstable like the analogous tetrahalolead complexes ð81JOM"327#46Ł[ "iv# Trihalomethylzinc\ !cadmium and !mercury\ CHal2MR "M Zn\ Cd\ H`"II## compounds Miller et al[ failed to prepare trihalomethylzinc iodides or bromides from zinc and tri! haloiodomethanes or trihalobromomethanes in glyme ð46JA3048Ł whereas Burton and Wiemers
135
Four Halo`ens or Three Halo`ens and One Other Heteroatom
did so by treating activated "acid washed# zinc or cadmium with dibromodi~uoromethane or bromochlorodi~uoromethane in DMF for 1 h at RT[ When dichlorodi~uoromethane was used\ the reaction had to be carried out at 79>C in a sealed ampoule[ A yield of 79Ð84) of "tri! ~uoromethyl#cadmium halide and a yield of 79Ð74) of "tri~uoromethyl#zinc halide was achieved[ The "tri~uoromethyl#metal halides were not isolated but stored for later use as 0 M solutions in DMF ð74JA4903Ł[ Bis"tri~uoromethyl#cadmium "00) yield\ 88) purity# and bis"tri~uoromethyl#zinc "7) yield# were prepared at low temperature "³34>C# by the reaction of the metal with hexa~uoroethane in a radio frequency discharge[ The {{naked||\ that is nondonor stabilized\ compounds Cd"CF2#1 and Zn"CF2#1 decompose at 9>C and −39>C\ respectively\ but may be stabilized with glyme ðCd"CF2#1 = glymeŁ and pyridine ðZn"CF2#1 = 1pyridineŁ ð75JA3092\ 80CJC216Ł[ The bis"tri~uoro! methyl#cadmium glyme adduct may also be prepared from dimethylcadmium and bis"tri~uoro! methyl#mercury in glyme ð79CC560\ 70JA1884\ 75JA721Ł[ Alkali metal tetrakis"tri~uoromethyl#cadmates have been prepared and investigated by NMR\ but not puri_ed ð78JOM"257#020Ł[ The formation of "tri~uoromethyl#mercury iodide is accomplished photochemically in 79) yield by treatment of tri~uoroiodomethane with mercury at 049>C ð37JCS1077Ł[ Further treatment of this isolatable intermediate with cadmium amalgam at 019Ð029>C causes the formation of bis"tri! ~uoromethyl#mercury in 79Ð89) yield ð38JCS1842Ł[ Bis"tri~uoromethyl#mercury is also formed from mercury"II# oxide and tris"tri~uoromethyl#phosphine upon 11 h heating at 099>C in a sealed tube "73) yield# ð59JA4648Ł[ "Trichloromethyl#mercury"II# chloride and bis"trichloro! methyl#mercury have been prepared\ by halide substitution\ from mercury"II# chloride or mercuric bromide with sodium trichloroacetate[ The intermediate mercury"II# trichloroacetate decomposes into the trichloromethyl derivative with elimination of carbon dioxide[ The reaction is conducted in diglyme at re~ux temperature for 0 h with yields of 58Ð66)[ The actual ratio of sodium trichloroacetate to mercury"II# chloride determines whether the product is bis"trichloro! methyl#mercury or the "trichloromethyl# mercury"II# halide ð52JOC0018Ł[
"v# Trihalomethylcopper\ !silver and !`old\ CHal2MRn "M Cu"I#\ A`"I#\ Au"I#\ Au"III## compounds The tri~uoromethyl complexes of group 00 may be arranged into the following order of stability according to Nair and Morrison] AuCF2 ×AgCF2 ×CuCF2 ð78JOM"265#038Ł[ "Tri~uoromethyl#copper"I# is probably formed initially in some coupling reactions\ for example\ when tri~uoroiodomethane is heated "029Ð039>C# with metallic copper in DMF[ This intermediate is trapped by aryl iodides with formation of the corresponding tri~uoromethylarenes ð58TL3984\ 69CPB1223Ł[ This method has later been improved by Kobayashi et al[ to include the corresponding reaction with aliphatic halides[ They shook tri~uoroiodomethane and copper powder in HMPA at 019>C for 1[4 h[ After removal of excess copper powder the aliphatic halide was added and the mixture stirred at RT or 69>C under N1 atmosphere[ They were able to tri~uoromethylate aliphatic and vinylic halides in 02Ð70) yield by the "tri~uoromethyl#copper"II# iodide formed in situ ð68TL3960Ł[ The "tri~uoromethyl#silver"I# trimethylphosphine complex has been prepared from silver acetate and Cd"CF2#1 = glyme in Et1O^ after 09 min trimethylphosphine was condensed into the reaction vessel[ The "tri~uoromethyl#silver"I# trimethylphosphine complex\ ð"CF2#AgPMe2Ł was isolated in 25) yield ð78JOM"265#038Ł[ "Tri~uoromethyl#gold"I# complexes stabilized "air and moisture insensitive# by trimethyl!\ triethyl! or triphenylphosphine ""CF2#AuL\ L PMe2\ PEt2 or PPh2# have been prepared in 54Ð64) yield from ClAuL "L PMe2\ PEt2 or PPh2# and Cd"CF2#1 = glyme in CH1Cl1[ Bis"tri~uoromethyl#mercury was ine}ective as a tri~uoromethylating agent\ even at 049>C ð78JOM"265#038\ 78OM0387Ł[ These gold"I# complexes are oxidized by elemental bromine or iodine with formation of phosphine stabil! ized "tri~uoromethyl#gold"III# dihalides in ½24) yield ""CF2#AuX1L\ L PMe2\ PEt2 or PPh2#[ The analogous addition of tri~uoroiodomethane to "CF2#AuL "L PMe2 or PEt2# in CH1Cl1 leads to bis"tri~uoromethyl#gold"III# iodide in 79) yield "87) cis\ 1) trans# ð78JOM"265#038\ 78OM0387Ł[ The unstable tris"tri~uoromethyl#gold"III# complex has been prepared by Guerra et al[\ from gold vapors and plasma!generated tri~uoromethyl radicals at −085>C ð75JOM"296#C47Ł\ and may also be obtained as the trimethylphosphine stabilized analog ð"CF2#2Au"PMe2#Ł by reaction of "CF2#1! AuI"PMe2# with Cd"CF2#1 = glyme in the presence of excess tri~uoroiodomethane in 79) yield
Three Halo`ens
136
ð78OM0387Ł[ The organogold"I# complex ð"CF2#Au"−C2N¦0Me#Ł was prepared similarly by Dryden et al[ in 67) yield ð81CM868Ł[ Nair and Morrison made ð"CF2#2Au"PEt2#Ł in 19Ð49) yield from CF2I and ð"CF2#Au"PEt2#Ł ð78JOM"265#038Ł[ Bis"tri~uoromethyl#gold"III# m!halide dimers ðAu"CF2#1"m!X#Ł1 have also been prepared\ by a vapor deposition technique\ from gold treated with excess "0 ] 099# of either bromotri~uoromethane or tri~uoroiodomethane[ The products may be recrystallized from pentane and are moderately air and light sensitive[ The m!bromide was isolated in 05) yield wheras the m!iodide was isolated in 7) yield ð89IC2141Ł[
"vi# Miscellaneous trihalomethyl transition metal\ CHal2MRn "M transition metal# compounds A number of platinum complexes containing tri~uoromethyl as a ligand have been prepared by ligand exchange from Pt"CF2#nMe1−nNBD "NBD\ norbornadiene# ð82JOM"342#296Ł[ This complex is itself made from PtMe1NBD by tri~uoromethyl:methyl exchange with CF2I ð77JOM"231#288\ 82JOM"342#188Ł[ Tri~uoromethyl:methyl exchange has also been used to prepare other platinum complexes containing tri~uoromethyl as a ligand ð89IC1385Ł[ Tri~uoroiodomethane adds to cis!PtMe1L1 "L PMe1Ph# at 079>C under vacuum to give PtMe1L1"CF2#I with CF2 and I in axial positions ð69IC1445Ł[ Hydrido tri~uoromethyl complexes of platinum"II# have been prepared by Michelin et al[ ð89OM0338\ 78JCS"D#0038Ł[ Other transition metal complexes with tri~uoromethyl as ligand have been prepared[ These include rhodium ð89JOM"277#280\ 80CC054Ł\ ruthenium ð89JOM"284#216\ 89JOM"286#198Ł\ osmium ð89JOM"284#216Ł\ iridium ð89JOM"283#504Ł\ manganese ð50JA0487Ł and cobalt complexes ð50JA2482Ł[
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.08 Functions Containing Two Halogens and Two Other Heteroatom Substituents ANASTASSIOS VARVOGLIS University of Thessaloniki, Greece 5[97[0 INTRODUCTION
149
5[97[1 TWO HALOGENS AND TWO CHALCOGEN FUNCTIONS 5[97[1[0 Two Halo`ens and Two Oxy`en Functions 5[97[1[0[0 Di~uoro compounds 5[97[1[0[1 Dichloro and dibromo compounds 5[97[1[1 Two Halo`ens and Two Sulfur Functions 5[97[1[1[0 Di~uoro compounds 5[97[1[1[1 Dichloro\ dibromo\ and diiodo compounds 5[97[1[2 Two Halo`ens\ an Oxy`en\ and a Sulfur Function 5[97[1[3 Two Halo`ens and Other Chalco`en Functions 5[97[2 TWO HALOGENS AND ONE CHALCOGEN FUNCTION 5[97[2[0 Two Halo`ens\ a Chalco`en\ and a Nitro`en Function 5[97[2[0[0 Oxy`en compounds 5[97[2[0[1 Sulfur compounds 5[97[2[1 Two Halo`ens\ a Chalco`en\ and Other Functions 5[97[3 TWO HALOGENS AND TWO GROUP 04 ELEMENT FUNCTIONS 5[97[3[0 Two Halo`ens and Two Nitro`en Functions 5[97[3[0[0 Diamines and their derivatives 5[97[3[0[1 Dinitro compounds 5[97[3[0[2 Cyclic compounds 5[97[3[1 Two Halo`ens and Two Phosphorus Functions 5[97[3[1[0 Bis"phosphonates# 5[97[3[1[1 Cyclic compounds 5[97[3[1[2 Miscellaneous compounds 5[97[3[2 Two Halo`ens and Two Other Group 04 Element Functions
149 149 149 140 141 141 143 144 145 145 145 145 146 147 147 147 147 159 150 152 152 153 154 155
5[97[4 TWO HALOGENS AND ONE GROUP 04 ELEMENT FUNCTION
155
5[97[4[0 Two Halo`ens\ a Phosphorus\ and a Metalloid or Metal Function
155
5[97[5 TWO HALOGENS AND TWO METALLOID FUNCTIONS 5[97[5[0 Two Halo`ens and Two Silicon Functions 5[97[5[0[0 Linear carbosilanes 5[97[5[0[1 Cyclic carbosilanes 5[97[5[1 Two Halo`ens and Two Boron or Other Metalloid Functions 5[97[6 TWO HALOGENS AND ONE METALLOID FUNCTION 5[97[6[0 Two Halo`ens\ a Silicon\ and a Metal Function 5[97[7 TWO HALOGENS AND TWO METAL FUNCTIONS
138
156 156 156 157 158 158 158 169
149
Two Halo`ens and Two Other Heteroatoms
5[97[0 INTRODUCTION A great variety of functionalities characterize the family of compounds containing functions with two halogens and two other heteroatom substituents^ however\ the family has few representatives[ Heteroatom substituents include O\ S\ Se\ Te\ B\ N\ P\ As\ Si\ Ge\ and some metals\ and the halogen atoms are F and Cl in most cases[ Several members of the family stand on the verge of organic and inorganic chemistry\ particularly when relatively small molecules are involved without hydrogen atoms[ It is emphasized that the experimental work with elemental ~uorine requires special con! ditions and considerable expertise[
5[97[1 TWO HALOGENS AND TWO CHALCOGEN FUNCTIONS 5[97[1[0 Two Halogens and Two Oxygen Functions 5[97[1[0[0 Di~uoro compounds Addition of ~uorine to the carbonyl bond of simple per~uorooxo compounds leads to the formation of either stable adducts "`em!~uorohypo~uorites# or to products of further trans! formation[ In the case of FC"O#OF "0#\ both types of product may be formed[ Thus\ the simplest compound of this class\ di~uorodioxirane "3#\ has been obtained from "0# and either ~uorine or chlorine ~uoride in a ~ow system using a pelletized caesium ~uoride catalyst[ After the initial attack of ~uoride on carbon\ an electron transfer follows between "1# and the halogen^ the free radical intermediate "2# cyclizes to "3#\ or may produce "4# when ClF is used "Scheme 0# ð82AG"E#894Ł[ Bis"~uoroxy#di~uoromethane was the unique product obtained from the reaction between FC"O#OF and ~uorine\ again in the presence of caesium ~uoride\ in a Monel bomb "Equation "0## ð56JA4050Ł[ The same product was also formed from the double addition of ~uorine to CO1\ catalyzed by caesium ~uoride ð56JA0798\ 56JA0851Ł[ A variation involves the action of ~uorine upon sodium tri~uoroacetate or sodium oxalate ð56JA0700Ł[ Another hypo~uorite\ the peroxide "6#\ was produced by the addition of ~uorine to the carbonyl bonds of "5# "Equation "1## ð56CC769Ł[ In some esters of thionocarbonic acid the C1S group was directly transformed into CF1 upon treatment with ~uorine^ in this way\ compounds of the type "RCH1O#1CF1 were formed "where R is a polynitromethyl group# ð78IZV002\ 82IZV1402Ł[ Similar compounds were obtained by substitution from the cor! responding CCl1 analogues and SbF4 in SO1Cl1[ O F
O–
F
CsF, RT
F
OF (1)
O•
F
F2 or ClF
F
OF (2)
F
O O
F
OF (3)
(4) 20–50%
F
OCl
F
OF
+ (5) 0–70%
Scheme 1
O + F2
F
CsF, RT
OF
F
(1) F
OF
OF
O F
O
O
O (6)
OF F
+ 2F2
KF, –95 °C
F F
O
O
F F
(2)
FO (7)
Bis"~uoroxy#di~uoromethane reacts with halogenated alkenes\ probably through the free radical "2# which transfers its OCF1O group to the double bond[ The products are either halogenated acetals of methanal\ for example "7#\ or 0\2!dioxolanes\ for example "8# "Scheme 1#[ Upon treatment of the latter with Zn and K1CO2 in DMF\ chlorine was eliminated and per~uoro!0\2!dioxole was produced ð57IC513\ 81EUP388046\ 81EUP388047\ 81JFC"47#032\ 81JFC"47#189Ł[ Photochemically\ F1C"OF#1 also adds its OCF1O group to the double bond of per~uoro Dewar benzene^ the reaction is complex and the major product "5) yield# "09# rearranges thermally to "00# "Scheme 2#[ ð68JOC1702Ł[ Cyclic
140
Two Chalco`ens
thionocarbonates have been converted into 1\1!di~uoro!0\2!dioxolanes by ~uorinolysis of the C1S function using Bu3NH1F2 and N!iodosuccinimide ð83SL140Ł[ F
F3CF2CO
OCF2CF3
F
F
Cl
F , –180 °C
F
F
F
OF
F
OF
Cl Cl
Cl
F
F
F
F O
O
F
F (9)
(8) 90% Scheme 2
F
F F
F
F
OF
+ F
F
F
hν
F
F F
O
OF
F
F O
F
F
∆
F F O
F
O
F
O
O F
F
F (10)
F F (11)
Scheme 3
Some di~uorodialkoxymethanes are produced in a di}erent way\ after halogenolysis of the double bond of either F2CN1C"OR#1 or F4SN1C"OR#1 by chlorine ~uoride "Equation "2## ð89JFC"37#284Ł[ In some cases ~uorine can substitute for hydrogen attached to an sp2 carbon[ Per~uorodi! methoxymethane and per~uoro!0\2!dioxane*as well as other products*have been reported to result from electrochemical ~uorination of methyl 2!methoxypropionate ð65ZOR656Ł[ The physical properties of such compounds have been described but their preparation has not yet been docu! mented ð81MI 597!90\ 82MI 597!90Ł[ Chemical and electrochemical methods have been used to ~uorinate the methanal derivative "01# to "02# "Equation "3## ð80JFC"44#202Ł[ OCH2CF3 N F3C
F
OCH2CF3
F
OCH2CF3
F
OCF2CF2SO2F
F
OCF2CF2SO2F
+ F3CNCl2
+ 2ClF OCH2CF3
OCF2CF2SO2F OCF2CF2SO2F (12)
F2, NaF
(3)
(4)
(13)
The action of ~uorine on polymethylene oxide gives mainly a per~uoropolymer\ but it also brings about ~uorinolysis\ with partial ~uorination and depolymerization^ among the products identi_ed were F2COCF1OCF1H and HF1COCF1OCF1H ð70JCS"P0#0210Ł[ Chlorine in F1CCl1 is substituted by two ~uorosulfato groups in its reaction with ClOSO1F^ F1CBr1 reacts similarly with the peroxy compound FO1SOOSO1F[ In both cases the product is F1C"OSO1F#1 ð54IC0717\ 63IZV224Ł[ Ozonation of tetra~uoroethylene gave rise to an apparently stable moleozonide ð57CI"M#086Ł[ Singlet oxygen reacted with tetra~uoroethylene at −49>C to produce peroxidic per~uoroethers\ which upon strong and prolonged heating were converted into a mixture containing\ inter alia\ per~uoro!0\2!dioxetane\ per~uoro!0\2\4!trioxane\ and per~uoro!0\2\4\6!tetraoxocane ð61GEP1000585Ł[ In another patent\ the reaction of the adduct from the reaction between "F1N#1C1NF and KCN with F1C"OF#1 is claimed to give a mixture of products\ including the peroxide F2COOCF1OF ð60USP2474107Ł[ The unusual compound F2COOCF1OOOCF2\ bearing both peroxide and trioxide functions\ was formed among other products from a complex reaction between F1C"OF#1 and CsOCF2 ð60IC1068Ł[
5[97[1[0[1 Dichloro and dibromo compounds The number of compounds in this category is few[ The compounds can be obtained either by carbonyl "or thiocarbonyl# transformation or by chlorination of a methylene group[ Dichloro! diphenoxymethane "03# was produced upon heating diphenyl carbonate with PCl4^ similarly\ phenylene carbonate gave 1\1!dichloro!benzo!0\2!dioxole "04# ð50CB433\ 71JHC0194Ł[ Some diethyl
141
Two Halo`ens and Two Other Heteroatoms
thionocarbonates of the general formula "RCH1O#1C1S "where R is CF2\ CF1NO1 or CF"NO1#1# were converted into the corresponding CCl1 compounds using either SO1Cl1 or Cl1 ð78IZV002Ł[ Photochemical chlorination of 0\2!dioxolane converted it into its perchloro analogue "05# ð61JOC0347Ł[ Some dichlorobis"aryloxy#methanes were similarly prepared via radical!induced chlori! nation of the formaldehyde diaryl acetals with SO1Cl1 or Cl1 ð77S850Ł[ Dibromomethylal\ CBr1"OMe#1\ was obtained by simply dropping Br1 into cooled methylal ð11AG378Ł[
Cl
OPh
O
Cl
Cl
OPh (14)
O
Cl
Cl
Cl
O
O
Cl
Cl Cl Cl (16)
(15)
5[97[1[1 Two Halogens and Two Sulfur Functions 5[97[1[1[0 Di~uoro compounds The reaction of ~uorine with thiocarbonyl compounds usually gives addition products in which sulfur has also been oxidized[ Carbon disul_de is thus converted into the isolable compound "06# and subsequently into "07# "Scheme 3# ð66IC1863Ł[ The yield of "07# increased when caesium ~uoride was used as a catalyst^ chlorine ~uoride reacts in a similar way\ leading to the formation of "trans! ClSF3#1CF1 ð72JFC"12#214Ł[ The pseudohalogen CF2SF was also added to carbon disul_de^ no oxidation occurred and the double adduct "CF2SS#1CF1 was obtained in high yield ð81ZN"B#258Ł[ The related reaction of F1C1S with CF2SCl gave the adduct "F2CS#CF1SCl ð57CB1506Ł[ The same product was formed upon addition of ClF to F2CSC"S#F\ while a related addition of ClF occurred to the C1S bond of FC"S#SCN ð63CZ098Ł[ Compound "06# reacts with metal ~uorides\ a}ording relatively stable anions or cations[ For example\ with CsF a symmetrically bridged anion was formed\ while with AsF4 in liquid SO1 the stable sulfonium salt F1C"SF2#SF1¦AsF5− resulted ð80CB0242\ 81CC0906Ł[ When BF2 in SO1 was used\ "06# a}orded the solvolysis product "08#\ as a mixture of two diastereoisomers[ With silylated amines\ "08# was converted into sul_nimides\ for example "19# or "10# "Scheme 4#[ From the reaction between "08# and HCl\ the rather unstable F1C"S"O#Cl#1 was produced\ which upon hydrolysis gave the bis"sul_nic acid# F1C"SO1H#1[ Direct ~uorination at an sp2 carbon has been e}ected in some cases\ for example with "11# which was converted into "12#^ this was hydrolyzed to the sulfonic acid "14# through its salt "13# "Scheme 5# ð89IC3477Ł[
CS2
F2/He, –120 °C
F
SF3
F
SF3
F2/He, –80 °C
F
(17) Scheme 4
O
O
F
S NMe2
F
S NMe2
Me2N-TMS
O
SF5 F SO2F (22)
F2, NaF
F F
SF5
SF5 (18)
O
F
F
S
F
S
F F
MeN(TMS)2
F
S
F
S
NMe
F
O
(19) Scheme 5
(21)
O (20)
SF5
F
Ba(OH)2
(F5SCF2SO3)2Ba
H+
F F
SO2F (24)
(23) Scheme 6
SF5 SO3H (25)
142
Two Chalco`ens
Electrochemical methods have been used for the preparation of "07# and F1C"SO1F#1 ð48JA463\ While the latter was formed from CH1"SO1F#1 in 79) yield\ the former was one of many products into which 0\2\4!trithiane was transformed\ for example\ F2CSF3CF1SF4\ and the trithianic derivative "CF1SF3#2[ A di}erent approach was used for the preparation of the sulfone\ PhSO1CF1SPh\ which was obtained from the reaction of PhSO1CHF1 and aqueous NaOH in a two! phase system "CH1Cl1 with Aliquat 225#^ the sulfone was oxidized with H1O1 to F1C"SO1Ph#1 ð78JFC"32#42Ł[ A fairly large family of perhalogenated 0\2!dithietanes and their sulfur derivatives is known[ Photochemical dimerization of thiophosgene leads in a straightforward way to the formation of "15# ð22CB456Ł[ Upon treatment with SbF4\ this gives rise mainly to compound "16#\ along with some mono! and dichloroper~uoro!0\2!dithietanes "Scheme 6# ð54JOC0264Ł[ A related method started with compound "17#\ which was converted by strong acids into the isolable salt "18#^ treatment with caesium ~uoride a}orded the tri~uorodithietane "29# "Scheme 7# ð76CB318Ł[ A similar compound to "18# is the salt "20#\ which can undergo a variety of transformations at its carbocationic center\ as shown in Scheme 8 ð89CB0524Ł[ 75JFC"21#78Ł[
Cl
hν
2
Cl
S
Cl
SbF5
F
S
F
Cl
S
Cl
60%
F
S
F
S Cl
(26)
(27)
Scheme 7
F S
2
F
HF/SbF5 or FSO3H/SbF5
X
X
S
+
F SbF6–
F–
S
(28) X = Cl or SCF3
F
S
F
X
S
F
(30)
(29) Scheme 8
F
S
F
S
+
F AsF6– F
(31) X–,
F
S
S
SO2, RT
F Na2S2O3
BaCS3
F
F X S X = F, Cl, Br, I
F
S
F
S
F
S
S F
F
S
F
S
+
SCF3 AsF6–
O
S
Scheme 9
The majority of the reactions of per~uoro!0\2!dithietane involve oxidation at the sulfur[ Depend! ing on the oxidant and the conditions\ several products can be obtained using ~uorine or xenon di~uoride ð73JFC"15#248\ 78JFC"34#114Ł^ chlorine ~uoride ð62JFC"2#06\ 81CB424Ł^ chromium trioxide ð79AG"E#192Ł^ tri~uoromethyl hypochlorite or per~uoro!t!butyl hypochlorite ð66JA3083\ 67IC1062\ 68JA4838\ 70JA395\ 75IC164Ł^ and tri~uoromethaneperoxysulfonic acid ð72CB0512Ł[ Examples of the oxidation products are the structures "21#Ð"24#[ When "24# was heated with chlorine ~uoride\ it was transformed into the open chain compound F2CSO1CF1SF3Cl ð81CB424Ł[
F F
O2 S S O2 (32)
F
F
F
F
F4 S S F4 (33)
F F
OCF3 F3CO S F F F F S OCF3 F3CO (34)
F F
F4 S S O2 (35)
F F
143
Two Halo`ens and Two Other Heteroatoms
5[97[1[1[1 Dichloro\ dibromo\ and diiodo compounds Halogenated 0\2!dithietanes result from the photochemical dimerization of chloro! ~uorothiophosgene\ chlorobromothiophosgene\ and dibromothiophosgene ð65CB2321\ 66CB805\ 76CB0388Ł[ Tetrabromo!0\2!dithietane was also obtained from its tetrachloro analogue by sub! stitution using BBr2\ in 67) yield ð66CB805Ł[ These compounds\ along with tetrachloro!0\2!dithi! etane undergo various reactions at either carbon or sulfur\ in much the same way as tetra~uoro! 0\2!dithietane ð22CB456\ 66CB805\ 72CB0512\ 76SUL48\ 77JFC"28#218Ł[ Some transformations of the parent disulfone 0\0\2\2!tetraoxo!0\2!dithietane "25# are of interest] it can be halogenated by aqueous chlorine or bromine\ a}ording tetrachloro or tetrabromo disulfones in high yields "an analogous iodination does not occur#[ Chlorination was also e}ected using C3F8SO1Cl and Et2N[ The tetra! chlorodisulfone "26#\ upon mild hydrolysis\ was converted quantitatively into the sulfonic acid "27# "Scheme 09#[ Trichloro disulfone "39# was obtained from the silylated disulfone "28# upon treatment with butyllithium and C3F8SO1Cl:Et2N "Equation "4## ð72CB0174\ 74CB1197Ł[ Treatment of dibro! mothiophosgene "Br1C1S# with ozone at −79>C resulted in its partial trimerization^ hexabromo! 0\2\4!trithiane was formed in 4) yield ð66CB805Ł[ O2 S
Cl2/H2O, RT
Cl
88%
Cl
S O2
O2 S S O2
(36)
Cl
O2 S
Cl
H2O, 40 °C
Cl
SO3H
Cl Cl
(37)
Cl
(38)
Scheme 10
O2 S TMS
i, BuLi ii, C4F9SO2Cl/Et3N
TMS
Cl
(39)
(5)
Cl Cl
S O2
O2 S S O2 (40)
Bis"halogenated# open chain `em!disulfones exist for all four halogens^ some have been known since the end of the nineteenth century\ for example Br1C"SO1Et#1 ð0789CB2115Ł[ They may be produced by direct chlorination or bromination of `em!disulfones using aqueous halogen^ sulfuryl chloride or sulfuryl bromide may also be used ð24JA106\ 62JOC2247\ 64CJC1553\ 64JOC0167\ 79CJC0885\ 77ZOR0216Ł[ The trisulfone of 0\2\4!trithiane has been fully chlorinated photochemically\ while trithiane itself can be converted directly into the same product\ that is\ hexachloro!0\0\2\2\4\4! hexaoxo!0\2\4!trithiane "30#\ when heated with aqueous chlorine and MoO2 ð52JPR0\ 53ZC346Ł[ An interesting transformation of this trisulfone occurred when it was heated with SbF2 and catalytic amounts of SbCl4 in sulfolane\ resulting in the isolation of "31#[ The hexabromo analogue of "30# gave the tetrabromo analogue of "31# under milder conditions\ in dioxaneÐwater[ With tertiary amines or phosphines\ these trisulfones a}orded stable salts such as "32# "Scheme 00# ð75CB2520Ł[ Under certain conditions*when 0\2\4!trithiane is treated with sodium hypochlorite in an alkaline environment*chlorination occurs\ but oxidation stops at the disulfone stage and "33# is produced ð45JCS497Ł[ When treated with a tertiary amine\ the monosulfone of hexachloro!0\2\4!trithiane was converted to "34# ð57USP2265203Ł[ Cl
O2 S
Cl O2S
–
SO2
Cl
Cl (43)
O2 Cl S
Cl
Cl Et3NH+
Et3N
Cl SO2
Cl O2S Cl
Cl (41)
Cl
Cl
O 2S
SO2
SbF3/SbCl5, sulfolane, 190 °C
Cl Cl (42) 62%
Scheme 11
The potassium salts of monohalogenated `em!disulfones have also been halogenated "Equation "5## ð62JOC2247Ł[ Phenyliodonium ylides undergo brominolysis\ a}ording dibromo!`em!disulfones ð89CC0348\ 80CC369Ł[ Alternatively\ the halosuccinimides NCS\ NBS and NIS give the corresponding dihalodisulfones "Equation "6## ð77JCR"S#295Ł[ Chlorination of a methylene group in some sulfones bearing another sulfur!containing group has been e}ected by aqueous chlorine in acetic acid^ in
144
Two Chalco`ens O2 Cl S
Cl
Cl S
Cl
Cl O2S
SO2
Cl
Cl
Cl (44)
Cl
S Cl O2 (45)
some cases further transformations led to the isolation of interesting products\ as depicted in Scheme 01 ð45JCS497\ 64CJC1553\ 79CJC0885\ 72CJC509\ 80CJC1016Ł[ N!Chlorosuccinimide and sulfuryl chloride were used in order to convert H1C"SO1Cl#1 into Cl1C"SO1Cl#1 ð65CZ280Ł[ F3CSO2 –
X2, CCl4
Y K+
F3CSO2
X
F3CSO2
Y
(6)
F3CSO2 X = Y = Br X = Y = Cl O SO2Ph PhI
+
CH2Cl2, RT
NI
2
I
SO2Ph
I
SO2Ph 79%
(7)
SO2Ph O Cl2, AcOH
MeSO2CH2SH or MeSO2CH2SO2OPh
MeSO2CCl2SO2OPh
Cl2/H2O
MeSO2CCl2SO2Cl
MeSO2CH2SCH2Ph AcOH NaOCl
4-ClC6H4SCH2SO3Na
4-ClC6H4SO2CCl2SO3Na
Scheme 12
The transformation of a thiocarbonyl group into CCl1 can be achieved by chlorination[ One example involved photochemical addition of chlorine to carbon disul_de^ the dichloromethane bis"sulfuryl chloride#\ Cl1C"SCl#1\ formed initially was used for the preparation of the heterocycle "35# "Scheme 02# ð89JCS"P0#498Ł[ In another example\ the heterocycle "36# was heated in a sealed tube with PCl4 and was converted directly into "37# "Equation "7## ð80CB1914Ł[ Cl2
CS2
hν
ClS Cl
SCl
N
TMS-N=S=N-TMS
S
56%
Cl
S
N S
Cl
Cl (46)
Scheme 13 F 3C
S S
F3C
S
PCl5 ∆
F3C
S
Cl
F3C
S
Cl
(8)
(47)
(48)
5[97[1[2 Two Halogens\ an Oxygen\ and a Sulfur Function Only one compound of this type is known[ It was obtained from the addition of chlorine to either MeOC"S#SMe or MeOC"S#SSC"S#OMe\ both of which a}orded the same product\ MeOCCl1SCl ð42JA3471\ 45JA5969Ł[
145
Two Halo`ens and Two Other Heteroatoms
5[97[1[3 Two Halogens and Other Chalcogen Functions Tetra~uoro!\ tetrachloro!\ and tetrabromo!0\2!diselenetanes are known[ The ~uoro compound "49# was obtained by heating polymeric F1C1Se\ which in turn was formed from the boron compound "38# "Scheme 03# ð65ZAAC"316#003Ł[ Treatment of "49# with BCl2 or BBr2 gave its tetra! chloro or tetrabromo analogues[ 0!Tri~uoromethyl!0\2\2!tri~uoro!0\2!diselenetane was formed from the interaction of "CF2CF1Se#1Hg and "CF2Se#1Hg\ followed by treatment with Et1AlI ð80CB40Ł[ Two cyclic ethers*oxetane and tetrahydropyran "40#*were converted into "42# when treated with the selenoxide "41# and acetic anhydride\ in a Pummerer!type reaction "Equation "8## ð82TL0200Ł[ Tetra~uoro!0\2!ditelluretane was obtained by thermolysis of Me2SnTeCF2\ which initially "at −085>C# gave the monomer F1C1Te ð81C67Ł[ The same compound "43# was produced from the reaction of Hg"TeCF2#1 with two equivalents of Et1AlI^ when the monomer F1C1Te was allowed to react with F1C1Se\ tetra~uoro!0\2!selenatelluretane "44# was formed[ Compound "43# was converted into its tetrachloro analogue with BCl2 ð82JCS"D#1436Ł[ F
KF
B(SeCF3)3
∆
Se
∆
F polymeric
(49)
F
Se
F
F
Se
F
(50)
Scheme 14 O O
F
+
Ac2O, CH2Cl2
Se
X
Ph
AcOCH2XOCF2SePh
(9)
F
(51) X = CH2 or (CH2)3
(52)
(53)
F
Te
F
F
Se
F
F
Te (54)
F
F
Te (55)
F
5[97[2 TWO HALOGENS AND ONE CHALCOGEN FUNCTION 5[97[2[0 Two Halogens\ a Chalcogen\ and a Nitrogen Function 5[97[2[0[0 Oxygen compounds Per~uoromethyleneimine "N!~uorocarbonimidic di~uoride# "45# is a good precursor for the prep! aration of several compounds in this category\ especially compound "47#\ through the addition of FSO1OX "46# to its double bond "Equation "09##[ The related compound FSO1OCF1N"OSO1F#F was also obtained from "45# and the peroxide FO1SOOSO1F ð72IC794Ł[ However\ the reaction between F1C1NCl and FSO1OX led to the formation of a di}erent product\ that is\ the azo compound FSO1OCF1N1NCF1OSO1F ð73JOC2489Ł[ Other additions to the double bond of per! halogenated imines include the reactions in Scheme 04 ð65JA2418\ 72JOC3733\ 76AG"E#203\ 89JFC"37#284Ł[ Some of these compounds were cyclized to form oxaziridines\ upon reaction with metal ~uorides at a low temperature "Scheme 05# ð65JA2418\ 68IC808\ 79IC0229\ 72JOC3733Ł[ Direct epoxidation of per~uoroazaalkenes is not normally possible\ except with F1C1NCF2 which\ with mcpba\ gave the corresponding oxaziridine in 49) yield ð82JOC3643Ł[ F NF
+
FSO2OX
FSO2OCF2NFX
(10)
F (56)
(57)
(58) X = F, Cl, Br
Oxaziridine "48# underwent cycloaddition reactions with tetrahalogenated ethylenes and also with methyl ketones\ a}ording _ve!membered heterocycles such as "59# and "50# "Scheme 06# ð71JA3923\
146
One Chalco`en Cl
+
NCl
F5SOCCl2NCl2
F5SOCl
Cl F NCF3
+
F3COOH
F3COOCF2NHCF3
NCF2CFClX
+
F3COOH
F3COOCF2NHCF2CFClX
F F F
X = F, Cl or Br (CF3)2N NCF3
+
–F3CNCl2
2 ClF
(CF3)2NCF2OCH2CF3
F3CCH2O Scheme 15 F
O F
KHF2, –196 °C
F3COOCF2NHCF2CFClX
F NaF, –196 °C
F3COOCF2NHCF3
Cl
N
X F
F
F
O
F
N CF3
i, F3CO2H ii, NaF
F NSF5
F
O
F
N
F
SF5 Scheme 16
75JOC3355Ł[
The per~uoro oxazolidine "59# was also formed in low yield upon pyrolysis of per! ~uoromorpholine ð54JCS5966Ł[ The same compound and some related per~uoro!0\2!oxazolidines "51#Ð"53# were produced electrochemically from various precursors ð45JA4526\ 47JA0778\ 89JFC"37#146Ł[ The potassium and caesium salts of F1NCF1OH have been formed upon reaction of di~uo! roaminocarbonyl ~uoride "F1NCOF# with KF or CsF ð56IC0600Ł[ F
F
O
F
N CF3
F
X
F
Y
F
O
F
N
F Y
X (60)
X, Y = halogens
F3C
RCOMe
F
(59) F
O N O
R
F3C (61) Scheme 17 F F F3C
O N F (62)
F F CF3
F F F 3C
O
F N(CF3)2 F
N F (63)
F F F5C2
O N
F F F
F (64)
5[97[2[0[1 Sulfur compounds Some unusual reactions have been reported with thiocyanates and ~uorine[ Methyl thiocyanate was converted into F4SCF1NF1 when heated with elemental ~uorine ð48JA2488Ł[ Potassium or silver
147
Two Halo`ens and Two Other Heteroatoms
thiocyanate in the presence of catalytic amounts of CaF1 gave\ among several other products\ FSCF1NF1 ð54ZOB0301Ł[ An interesting conversion of compound "54# occurred upon its treatment with triethylamine\ when the zwitterion "55# was obtained "Equation "00## ð89AG"E#59Ł[ The anal! ogous reaction between "56# and quinuclidine "57# resulted in the formation of another zwitterion\ "58# "Equation "01## ð78AG"E#110Ł[ O2 S
F
F
THF, –70 °C
+ 2 Et3N F
S
F
S O2 (67)
(11)
(66) F
+ F
2 Et3N+CF2SO2–
F
S O2 (65)
+
N CF2SCF2SO2–
N
(12)
F (68)
(69)
Addition of chlorine to "69# gave "60#[ Upon heating this was converted into a mixture of heterocycles "61# and "62# "Scheme 07# ð60CB1621Ł[ Compound "61# was converted by Hg"SCF2#1 into F2CSSCF1NCS\ while "69# added photochemically F2CSCl to a}ord F2CSSCFCl "NCS#[ S
F
Cl2
F
Cl
NCS (70)
Cl
F
SCl
70 °C
F
N S
NCS
S (72)
(71)
+
Cl
N S
Cl
S (73)
Cl
Scheme 18
5[97[2[1 Two Halogens\ a Chalcogen\ and Other Functions Per~uoro!1!phosphapropene\ F2CP1CF1\ when added to methanol forms F2CPHCF1OMe^ C1F4P1CF1 reacts similarly ð75ZN"B#038\ 89ZN"B#037Ł[ The sul_nic salt "64# was obtained from "63# and sodium sul_te or sodium dithionite^ its oxidation with H1O1 gave the corresponding sulfonate and\ upon acidi_cation\ the free acid "Equation "02## ð78JA0662Ł[ A similar reaction occurred using "EtO#1P"O#CFBr1 and Na1S1O3 ð78CJC0684Ł[ The halogenated sulfones "65# were converted to "66# when their anion attacked PhHgCl "Equation "03## ð63JOM"60#224Ł[ Another organometallic mercury compound\ HOHgCI1SO2Na\ was obtained from the reaction of HgO and CHI1SO2Na ð24CB0402Ł[ O (EtO)2P F
O Br
+
Na2SO3
F
SO2Na
F
(13)
F
(75)
(74)
PhSO2CHX2
(EtO)2P
+
PhHgCl
ButOK, THF, –60 °C
(76)
PhSO2CX2HgPh
(14)
(77) X = Cl, Br
5[97[3 TWO HALOGENS AND TWO GROUP 04 ELEMENT FUNCTIONS 5[97[3[0 Two Halogens and Two Nitrogen Functions 5[97[3[0[0 Diamines and their derivatives The simplest compound of this class is per~uorodiaminomethane "68#\ which can be prepared by ~uorination either of cyanuric chloride "67# or of aminoiminomethane!sul_nic acid "79# "Scheme
Two Group 04 Elements
148
08# ð54ZOB0301\ 55JOC3121Ł[ The C!monochloro analogue of "68#\ that is FClC"NF1#1\ was formed from per~uoroguanidine and ClNO1 ð67IZV375Ł[ Tetramethylurea was converted into "Me1N#1CF1 when treated with COF1 in the presence of NaF ð51JA3164Ł[ Fluorine or chlorine ~uoride adds to the nitrile function in some per~uorocyanamides\ with the formation of perhalogenated methane! diamines\ as illustrated in Scheme 19 ð89JA617\ 81IC377Ł[ Chlorine ~uoride has also been added to the N1C bond of some halogenated imines\ in the presence of CsF^ for example\ "70# was converted into "71# "Equation "04## ð89JFC"37#284Ł[ A related addition of ClF occurred to the C1N bond of "73#\ which was obtained from "72# and LiORf "where Rf is a per~uoro group# "Equation "05## ð81JFC"46#182Ł[ When "73# "n 0\ Rf C"CF2#1CH2# was treated with C5F4SiMe2 and CsF\ ~uorine at the sp1 carbon was replaced by the C5F4 group ð82IC3791Ł[ Cl N
F2, 125 °C
N
Cl
N
Cl
F
NF2
F
NF2
(78)
NH
F2
H2N
(79)
SO2H (80)
Scheme 19
(CF3)2N
N
(CF3)2N
N
F3CN(F)
N
F2, CsF
(CF3)2NCF2NF2
ClF
(CF3)2NCF2NCl2
ClF
F3CN(F)CF2NCl2
Scheme 20
(CF3)2NC(F)
NCF3
ClF, CsF
(CF3)2NCF2NCl(CF3)
(81)
(15)
(82)
F (CF3)2NCF2N
F(2–n)
LiORf
(CF3)2NCF2N
(16) (ORf)n
F (83)
(84)
Insertion of alkenes and nitriles into the N0Cl bond of "71#\ as well as photolytic reactions of the latter with SF4Cl and CF2COCl\ occur readily ð89JFC"37#284Ł[ Several higher halogenated `em! diamines were produced in a similar way from "74# and halogenated alkenes which inserted into the N0Cl bond thermally^ for example "75# was obtained using CF11CClF "Equation "06## ð81IC377Ł[ When photolyzed alone "75# formed the imine "72# in high yield^ in the presence of halogenated alkenes\ insertion occurred and compounds such as "76# were formed "Scheme 10#[ Photolysis of the simpler N!chlorodiamine "71# led to the formation of the diazane derivative "77# "Equation "07##[ Compound "71# added to 0\0!di~uoroethylene and tri~uoroethylene on irradiation forming adducts such as "78# "Equation "08##[ F
F
F
Cl
∆
+
(CF3)2NCF2NCl2 (85)
(CF3)2NCF2N(Cl)CF2CCl2F
(17)
(86)
F
CH2CCl2F (CF3)2NCF2N CF2CCl2F (87)
F , hν
Cl (CF3)2NCF2N CF2CCl2F (86) Scheme 21
F
hν, –CCl3F
N (CF3)2NCF2 (83)
F
159
Two Halo`ens and Two Other Heteroatoms Cl
hν
(CF3)NCF2N
(CF3)NCF2N(CF3)N(CF3)CF2N(CF3)2
(18)
CF3 (82)
(88)
F
Cl
hν
+
(CF3)2NCF2N
(CF3)2NCF2N(CF3)CH2CClF2
(19)
F
CF3 (82)
(89)
Chlorine ~uoride has also been added to the C1N bond of a per~uorohydrazone^ the adduct\ upon irradiation with UV light\ was converted into a complex tetrazane having two CF1 groups ~anked by nitrogen functions ð78IC2234Ł[ A related per~uorohydrazone\ "89#\ added a methyl group and ~uorine to its double bond upon reaction with iodomethane and silver ~uoride^ compound "80# was formed "Equation "19## ð81IC3806Ł[ Some di~uoromethylene `em!diamines with alkyl or phenyl groups are also known[ A `em!diamine with two phenyl groups\ PhNHCF1NHPh\ was prepared from PhNHCF2 and aniline ð48ZOB1058Ł[ The bis"azo compound# O1NC5H3N1NCF1N1 NC5H3NO1 was the product from the reaction of di~uorodinitromethane with 3!nitroaniline ð81IC218Ł[ The preparation of the nitramine F1NCF1NO1 from CF1"OF#1 and F1NC"F#1NF has been described ð57USP2276922Ł[ A simple amine derivative\ di~uoro"bisisocyanato#methane "82#\ was produced upon thermolysis of "81# "Equation "10## ð73JOC3430Ł[ Some sulfur!containing amine derivatives have been reported\ derived from various simple compounds bearing a cyano group^ some examples are illustrated in Scheme 11 ð56MI 597!90\ 57ZN"B#632\ 75CB096Ł[ F
MeI, AgF
(CF3)2NN(Me)CF2N(CF3)N(CF3)2
(CF3)2NN N(CF3)N(CF3)2 (90) TMS-O TMS-O
(91) O-TMS
N
N
∆
O-TMS
SF4
N
F2S(O)N
N
F2S
F4SO
N
N
F
F N
F2S
F2SN
Br2, HgF2
N
F2S(O)N
N
N
SF4
N
NBr2
F2S O
F N
SF2 F O
F Cl2, HgF2
NCO (93)
SF2 F O
N
F2S
F2S
F
SF2
F F2S(O)N
NCO
N
F
O
F
(21)
F F (92)
H2N
(20)
N F
NCl2 F
Scheme 22
5[97[3[0[1 Dinitro compounds Di"halo#dinitromethanes of the general formula X1C"NO1#1 are known with all four halogens^ some mixed halogen compounds have also been reported[ Dichloro! and dibromodinitromethanes are formed in several degradative reactions of a variety of precursors "too many to mention in the space available here# by nitric acid[ The conversion of 1\3\5!trichloro! and 1\3\5!tribromoaniline into dichloro! and dibromodinitromethane\ respectively\ is an important preparative method
Two Group 04 Elements
150
ð33JOC308Ł[ A more conventional method for the preparation of dibromodinitromethane involved the reaction of sodium dinitromethanide with bromine after treatment with butyllithium\ or directly with bromine in THFÐHMPA "hexamethylphosphoramide# ð78ZOR1389Ł[ Phenyliodonium dinitro! methylide was converted in high yields into either dichloro! or dibromodinitromethane with the appropriate halogen\ NCS or NBS "Equation "11## ð67IZV1237Ł[ The very unstable diiodo! dinitromethane was reported to be formed upon acidi_cation of potassium iododinitromethanide ð13JCS331Ł[ Di~uorodinitromethane "84# was _rst prepared from di~uorodiazirine "83# and N1O3 "Equation "12## ð53JHC122Ł[ The same substrate "83#\ which on photolysis generates di~uorocarbene\ gave a 4) yield of "84# with NO^ the photochemical reaction of di~uorodiiodomethane in excess NO a}orded a 09) yield of "84# ð81IC218Ł[ The reactions of potassium trinitromethanide with ~uorineÐsodium ~uoride and also with potassium ~uoride again led to the formation of "84# ð57IZV318\ 57JOC2962Ł[ Di~uorodinitromethane was also formed in 27) yield from the reaction of di~uoronitroacetic acid with XeF1^ in a similar way\ ~uorochloronitroacetic acid produced ~uorochlorodinitromethane ð77IZV355\ 77IZV1528Ł[ The same compound was obtained when chlorotrinitromethane was treated with CsF in DMF ð69IZV1442Ł[ Chlorobromodinitro! methane was prepared from chlorine and ammonium bromodinitromethanide^ the latter was formed from dibromodinitromethane in liquid ammonia "Equation "13## ð33JOC308Ł[ O NO2
+
PhI
or
X2
X
NO2
X
NO2
NX
(22)
NO2 O X = Cl, Br F
N N
F
+
hν, –N2
N2O4
(94) Br
NO2
NO2
NH3
Br Br
NO2
–
NH4+ NO2
F
NO2
F
NO2 (95)
(23)
Cl2
Br
NO2
Cl
NO2
(24)
5[97[3[0[2 Cyclic compounds Several methods have been developed for the preparation of the important heterocycle di~uo! rodiazirine "83#[ Historically\ the _rst method involved cyclization of F1C"NF1#1 by ferrocene ð55JHC134Ł[ The same substrate was converted more e.ciently into "83# using tetrabutylammonium iodide "Scheme 12# ð56JOC0833\ 57JOC0736Ł[ Tetra~uoroformamidine "85# was also transformed e.ciently into "83#\ using either ferrocene or potassium iodide ð56JOC3934\ 57JOC0736Ł[ Tetra~uoro! formamidine was isomerized by potassium ~uoride at a low temperature to per~uorodiaziridine "86#\ an unstable compound which frequently exploded] with ferrocene this gave "83#^ when heated with caesium ~uoride it dimerized to form "87# "Scheme 13# ð57JOC2378Ł[ Curiously\ compound "87# was claimed in a patent to be a possible heat transfer ~uid ð81JAP93009272Ł[ A unique rearrangement leading to the formation of "83# occurred when di~uorocyanamide "F1NCN# was treated with caesium ~uoride at room temperature ð55IC0344Ł[ Chloro~uorodiazirine was obtained from di! chlorobis"di~uoramino#methane\ Cl1C"NF1#1\ after treatment with boric acid^ the precursor was prepared from per~uoroguanidine\ HCl and HNO2 ð56JOC0833\ 56USP2244381Ł[ Some further per! halogenated diaziridines are compounds "88#Ð"091#[ Their preparation involved the use of CsF or KF as catalysts at low temperatures[ Compound "88# was obtained from CF11NF or CF2N"F#C"F#1NF ð72JOC660Ł[ Compound "099# was formed from CF11NCl^ on treatment with mercury in tri~uoroacetic acid\ chlorine was replaced by hydrogen ð73JOC2489Ł[ Compound "090# was formed from CF11NF and CF11NBr\ which _rst gave CF2N"F#C"F#1NBr ð77JOC3332Ł[ Compound "091# was prepared from CF11NF and CF11NCF2 ð89JA617Ł[ Fluorine and chlorine*from either ClF or a mixture of chlorine and mercury di~uoride*readily add to cyanuric ~uoride "092# a}ording compound "093# "Equation "14## ð64MI 597!90\ 75CB096Ł[ Fluorine added to "092# in a complex way^ in addition to the per~uoro analogue of "093#\ per~uoro!
151
Two Halo`ens and Two Other Heteroatoms F
NF2
Bu4N+ I–
F
N
KF, MeCN/H2O
F
NF2
100%
F
N
100%
NF NF2
F
(94)
(96)
Scheme 23
F F
N
F 2N
N
F NF
KF, –160 °C
NF2
F
F
N
F
N
CsF, dimer
(96)
NF2
F
F
F (98)
(97) Scheme 24
F F
N
F
N
Cl F
N
F
N
CF3
Br F
N
F
N
CF3
(99)
CF3 F
N
F
N
CF3
(100)
CF3
(101)
(102)
0\2!diazolidine and noncyclic compounds such as CF2N"F#CF1N"F#CF2 were formed ð51JA1640Ł[ Per~uoro!1\4!diazahexa!1\3!diene "094#\ when heated with CsF\ was cyclized to a mixture of isomeric 0\2!diazolines "095# and "096#[ In acetonitrile in the presence of CsF\ both products gave the anion "097#\ which reacted with alkyl halides a}ording N!alkyl compounds\ for example "098# with iodomethane[ Compounds "097#\ "095# and "096# also underwent ~uoride ion induced reactions with per~uoroalkenes^ the main product\ when per~uorocyclopentene was used was "009# "Scheme 14# ð74JCS"P0#0080Ł[ The per~uoro analogue of "098# was converted to 1\1!dichloro! or 1\1!dibromo! dimethyl!0\2!diazolidine ð73JFC"13#346Ł[ Another heterocycle "001#\ was formed from "000# upon heating with CsF^ when irradiated in the presence of CsF\ "000# was transformed into a complex dimer "Equation "15## ð89HAC056\ 81ICA416Ł[ Compound "001# was also formed upon dimerization of "095# and "096# ð74JCS"P0#0080Ł[
N
F
F ClF or Cl2 + HgF2
N
Cl
F
Cl
N
Cl
N
F
Cl
F (103)
N
N
F
Cl
(104)
F F
F NCF3
F3CN
(25)
Cl
F F
F
CsF, 220 °C
F3C F
N
+
N
F3C
N
N
F F (107) 16%
F (106) 65%
(105)
F
F
MeCN, F– F
F
F F3C
N
N
F
F
F
F F
F F F
F
F
F F
F
F F
F3C F
(110)
F
F
F F F
F N
N–
F
F
(108) Scheme 25
MeI
F
F F3C
N
N
F
F
(109)
Me
Two Group 04 Elements
152
F F F
NCClF2 CsF, 110 °C
F 3C NCClF2
F
FF
F N
N
F
F (112)
(111)
F N CF3
N
(26)
F F
5[97[3[1 Two Halogens and Two Phosphorus Functions 5[97[3[1[0 Bis"phosphonates# The study of these compounds has been intensi_ed since two important discoveries were made] "i# the ability of Cl1C"PO2H1#1 "clodronic acid\ "004## to help in the process of bone formation^ and "ii# the various physiological properties of nucleotide analogues\ especially ATP\ in which an oxygen atom in the triphosphate unit is replaced by a di~uoromethylene group ð67JCE659\ 73JCS"P0#0008Ł[ Bis"halogenated# methylenebisphosphonic acids are usually prepared through halogenation of the appropriate tetraesters\ which are subsequently hydrolyzed[ The ester Cl1C"PO"OEt#1#1 was obtained in 61) yield by heating H1C"PO"OEt#1#1 with PCl4 at 039>C ð59ZOB0591Ł[ However\ the cheaper commercially available isopropyl tetraester "002# is the preferred starting material[ This was con! verted into its dichloro derivative "003# and then hydrolyzed to the acid "004# by heating in concentrated hydrochloric acid "Scheme 15# ð55BEP561194\ 57JOM"02#088\ 74JOM"180#034Ł[ The dibromo analogues and the relatively unstable diiodo analogues of "003# were prepared in a similar way by the hypohalite method ð60JOC0724Ł[ Several other tetraesters "symmetrical or mixed# of the general formula X1C"PO2R1#1 "where R was an alkyl group and X was chlorine or bromine# were prepared by the hypohalite method^ in which careful control of temperature\ pH\ and reaction time led to high yields ð81JCS"P1#724\ 81PS"69#072Ł[ The ester "003# was also converted to the acid "004# without hydrolysis by heating in sym!tetrachloroethane\ with evolution of propene ð56JOC3000Ł[ Since this acid is highly polar\ it was desirable to prepare some partial ester derivatives[ This was achieved via two methods] silyl derivatives and selective hydrolysis[ The _rst method was based on the obser! vations that the rate of silylation of methyl!containing mixed tetraesters follows the order methyl ×primary alkyl×secondary alkyl\ whereas the hydrolysis rate of silyl and alkyl esters follows the order SiMe2 ×tertiary alkyl×secondary alkyl×primary alkyl[ Taking into account these factors\ the preparation of several tri!\ di!\ and mono!esters was e}ected[ For example\ the ester "005# was converted _rst to "006# and then to the salt "007# in 76) yield "Scheme 16#[ The second approach was suitable for n!alkyl esters\ since branched chain alkyl groups in acidic conditions undergo hydrolysis faster than n!alkyl groups[ Thus\ "008# was transformed into "019# in 33) yield "Scheme 17# ð82TL3440Ł[ O P(OPri)2
O i, Na/toluene ii, Cl2 or NaOCl
P(OPri)2
Cl
P(OPri)2
Cl
P(OPri)2
O (113)
O HCl
Cl
P(OH)2
∆
Cl
P(OH)2
O
O
(114)
(115)
Scheme 26
Cl Cl O
O
O
P(OPri)2
P(OPri)2
P OPri OMe
(116)
TMS-Cl, NaI, MeCN
Cl
∆
Cl O
P OPri O-TMS
(117)
O MeOH, NaOH
P(OPri)2
Cl Cl O
P OPri ONa
(118)
Scheme 27
Di~uoro tetraesters\ as well as the free bisphosphonic acid "011# which is an isopolar analogue of pyrophosphoric acid\ were prepared by several routes[ Fluorination of "010# with perchloryl ~uoride
153
Two Halo`ens and Two Other Heteroatoms O
O i, MeSO3H, toluene, ∆ ii, NaOH
Cl
P(OPri)2
Cl
P(OHex)2
Cl
P(ONa)2
Cl
P(OHex)2
O
O
(119) Hex = n-C6H13
(120) Scheme 28
in a strongly basic environment gave "011# in good yields "R Et or Pri#^ this was converted with trimethylsilyl bromide into the silyl derivative "012#\ which then was hydrolyzed to the free acid "013#\ isolated as its trisdicyclohexylammonium salt "Scheme 18# ð70JOC3462\ 71JFC"19#506Ł[ Acetyl hypo~uorite was also an e.cient ~uorinating agent ð80BMC246Ł[ Coupling reactions have also been used^ for example\ the lithium salt obtained from HCF1P"O#"OEt#1 and lithium diisopropylamide "LDA# gave\ on reaction with "EtO#1P"O#Cl\ the tetraester "EtO#1P"O#CF1P"O#"EtO#1 in 63) yield ð71TL1212Ł[ The reaction between BrF1CPO"OPri#1 and "PriO#1PONa also gave "011# "R Pri# ð70CC829Ł[ The same compound was formed using CBr1F1 and "PriO#1PONa^ the mixed halogen tetraester FBrC"PO"OPri#1#1 was obtained from FCH"PO"OPri#1#1 and tetraisopropyl pyro! phosphate\ upon treatment with bromine in aqueous K1CO2 ð77JOM"239#82Ł[ The application of the MichaelisÐBecker variation to the preparation of di~uoromethylene esters has also been described ð79JFC"04#152\ 71JFC"19#010Ł\ as have other routes to compounds of this type ð83JOC1282Ł[ O
O
O
P(OR)2
F
P(OR)2
F
P(O-TMS)2
F
P(OR)2
F
P(O-TMS)2
FClO3, ButOK
P(OR)2
TMS-Br
O
O
H2O
F F
O
(122)
(121)
O P(OH)2 P(OH)2 O
(123)
(124)
Scheme 29
Coupling of X1C"PO2H1#1 with 4?!phosphoromorpholidate of adenosine resulted in the formation of "014# ð73JCS"P0#0008Ł[ In the same way\ the CF1 analogue of 2?!azido!2!deoxythymidine tri! phosphate was obtained ð80BMC246Ł[ Other nucleotide analogues with a CF1 group in the place of an oxygen next to the _rst phosphorus atom\ of the general formula "015#\ were prepared from the tris"tetrabutylammonium# salt of F1C"PO2H1#1 and the tosylate of the nucleoside^ these initially gave the CF1 pyrophosphate analogues\ which were converted with phosphate into "015# ð80TL5314Ł[ Isopentenyl and geranyl di~uoromethylenephosphonates and some nucleotide analogues were also prepared using this methodology ð75JOC3657\ 76JA4431\ 76JOC0683Ł[ X XO HO3P
P
O
OH
O P
O O
adenine
OH
HO3P
O
O P OH
F F
O P
O O
base
OH
HO OH (125) X = F, Cl
HO (126)
5[97[3[1[1 Cyclic compounds Reaction of the ylides "016# with triphenylphosphine led to the formation of diphosphiranes "017# "Equation "16## ð79IJC"B#509Ł[ Similar compounds "029# were obtained stereospeci_cally from trans! diphosphene "018# and dichloro! or dibromocarbenes "Equation "17## ð76T0682Ł[ Yields became quantitative when sonication was applied ð80TL4854Ł[ Bis"tri~uoromethyl#phosphine "020#\ upon treatment with ZnMe1 or triethylamine\ was converted via F2CP1CF1 to 0\2!diphosphetane "021# "Equation "18## ð61CC562\ 72IC1462\ 74PS"10#238Ł[ Thermolysis of Me2SnP"CF2#1\ however\ was more e.cient^ this initially gave F2CP1CF1\ which was found to be fairly stable[ Depending on the
Two Group 04 Elements
154
conditions\ the thermolysis products could be either F2CP1CF1 or "021# "a mixture of cis and trans isomers#\ along with some trimer\ that is\ 1\3\5!tris"tri~uoromethyl#!0\2\4!triphosphorin ð73AG"E#609Ł[ Similar thermolysis at 9[990 torr "9[02 Pa# of Me1NP"SnMe2#CF2 resulted in the formation of the monomer Me1NP1CF1\ which underwent polymerization^ when the polymer was heated at 499Ð599>C\ the dimeric compound "022# was formed ð81ZN"B#210Ł[ Treatment of Cl1PCHCl1 with triethylamine led to the formation of "023# via ClP1CCl1 ð70ZOB1529Ł[ Another heterocycle "024# was formed from the reaction of Cl1P"S#CF1P"S#Cl1 and butylamine ð76CZ065Ł[ X
+
–
Ph3P
+
PPh3
X
Ph3P
X
Ph3P
X
(127) X = Cl, Br
(27)
(128)
Ar
Ar P
P
+
+
CHX3
KOH
Ar
P
X
P
X
(28)
Ar (130)
(129) Ar = 2, 4, 6-But3C6H2 X = Cl, Br F
F3C 2 (CF3)2PH
P
Et3N, – 2HF
F P
F
P F
Cl
Cl F
P
(133)
But P N
F
P Cl
CF3
Cl Cl
Cl NMe2
(29)
P F (132)
(131) Me2N
F
F
Cl
P Cl
F (135)
(134)
5[97[3[1[2 Miscellaneous compounds When Me2GePMe1 was heated in benzene with Hg"CF2#1\ a mixture of products was formed\ including Me1PCF1PMe1 ð67BSF"1#250Ł[ Both isomeric 0\2!diphosphetanes "021# reacted with meth! anol "the cis isomer reacted faster#\ a}ording F2CP"OMe#CF1P"CF2#CHF1 and other products of further methanolysis ð74IC037Ł[ The chlorophosphine Cl1PCHCl1\ when heated with triethylamine and PCl2\ was transformed into Cl1PCCl1PCl1 ð70ZOB1529Ł[ The monomeric F1C1PCF2 reacted with several dialkylphosphines forming "025#\ which upon heating with elemental sulfur a}orded "026# "Scheme 29# ð89ZN"B#188Ł[ Compound "027# was converted into several derivatives\ as illus! trated in Scheme 20 ð76CZ065Ł[ Carbon vapour reacted with PCl2 forming Cl1PCCl1PCl1 ð69JCS"A#20Ł[ Some chlorinated and ~uorinated bis"phosphoranium# salts of the general formula R2P¦C−"X#P¦R2X− are formed in solution when phosphines are treated with CCl3\ CFCl2\ or CFBr2 ð66S588\ 77JOC255Ł[
F PCF3 F
+
R2PH
R2PHCF2PHCF3 (136) Scheme 30
'S'
R2P(S)CF2PHCF3 (137)
155
Two Halo`ens and Two Other Heteroatoms (PriO)2P(S)CF2P(S)(OPri)2
PriOH
F2PCF2PF2
SbF3
Cl2P(S)CF2P(S)Cl2
TMS-NMe2
PhPCl2
(138)
(NMe2)2PCF2P(NMe2)2
Cl2PCF2PCl2
Scheme 31
5[97[3[2 Two Halogens and Two Other Group 04 Element Functions The sole compounds in this category are "039# and "030#\ which were obtained upon thermolysis of "028# "Equation "29## ð73AG"E#609Ł[ F Me3SnAs(CF3)2
∆
F3 C
F
F3C
+
As CF3
As
F
As
As
CF3 F
F F
F F cis and trans (140)
(139)
F
As
(30)
F
CF3 (141)
5[97[4 TWO HALOGENS AND ONE GROUP 04 ELEMENT FUNCTION 5[97[4[0 Two Halogens\ a Phosphorus\ and a Metalloid or Metal Function When reacted with butyllithium in THF solution\ diethyl trichloromethylphosphonate "031# gives the salt "032# which can be converted into "033# upon treatment with trimethylsilyl chloride "Scheme 21# ð62JOM"48#126Ł[ The same salt "032# was formed from diethyl chloromethylphosphonate upon treatment with butyllithium and then CCl3 ð64S424Ł[ The di~uoro analogue of "032# was similarly obtained in situ from diethyl di~uoromethylphosphonate and LDA[ With TMS!Cl this a}orded TMS!CF1P"O#"OEt#1 in 76) yield\ while with Bu2SnCl the phosphonate Bu2SnCF1P"O#"OEt#1 was obtained in 66) yield ð71TL1212Ł[ The salt LiCF1P"O#Ph1 was formed in situ from HCF1P"O#Ph1 and LDA ð89TL4460Ł[ Several compounds with a P0Ge bond\ mainly germylphospholanes\ under! went CF1 insertion into this bond^ the mildest way to produce di~uorocarbene was the thermal decomposition of Hg"CF2#1 in benzene ð67BSF"1#250Ł[ Upon reaction with metallic cadmium the phosphonate "034# was converted into the stable salts "035# and "036# "Equation "20## ð70JFC"07#086Ł[ The same phosphonate "034# reacted similarly with metallic zinc to a}ord BrZnCF1P"O#"OEt#1^ after several days in contact with PhHgCl\ this gave another stable organometallic compound\ PhHgCF1P"O#"OEt#1 ð78JOC502\ 89JFC"38#64Ł[ The related compound PhHgCCl1P"O#"OMe#1 was formed from PhHgCCl1Br and P"OMe#2 ð55JOM"4#074Ł[ The stable copper compounds BrM! CuCF1P"O#"EtO#1 "M Cd\ Zn# were produced from the corresponding cadmium or zinc phos! phonates and CuBr ð81T078Ł[ A stable rhodium complex containing the group PCF1P has been described ð89JOM"288#078Ł[ O Cl3C
Cl Cl Li
BuLi, THF, –80 °C
P(OEt)2 (142)
O P(OEt)2
Cl Cl TMS
TMS-Cl, –80 °C
(143) Scheme 32
F F Br
O P(OEt)2
(145)
Cd
F F BrCd
O P(OEt)2 (144)
O P(OEt)2
(146)
+
F F Cd F F
O P(OEt)2 (31) P(OEt)2 O (147)
156
Two Metalloids 5[97[5 TWO HALOGENS AND TWO METALLOID FUNCTIONS 5[97[5[0 Two Halogens and Two Silicon Functions
The chemistry of these compounds is dominated by the work of G[ Fritz on carbosilanes^ most of his results have been summarized in a book and a review article ðB!75MI 597!90\ 76AG"E#0000Ł[
5[97[5[0[0 Linear carbosilanes A simple compound of this class is perchloro!0\2!disilapropane "037#\ which was obtained by photochlorination of the main product resulting from the reaction between chloroform and elemen! tal silicon in the presence of copper ð47CB11Ł[ It was also produced by photochlorination of Cl2SiCH1SiCl2 ð46IZV088\ 53CB0562Ł[ Perchloro!0\2!disilapropane "037# readily replaced one or more of its silicon!bound chlorine atoms^ for example\ upon treatment with SbF2 or ZnF1 it was converted to "038# ð53CB0562\ 60AG"E#409\ 61ZAAC"280#108Ł[ Further transformations were e}ected with LiAlH3] to "049# and to "040# "the latter with one equivalent of MeMgCl# "Scheme 22# ð60ZAAC"271#8\ 60ZN"B#379Ł[ Interestingly\ MeLi methylated exclusively the carbon atom of compound "037#[ In contrast\ the reaction of "049# with MeLi was very complex\ the major products being MeH1Si CCl1SiH2 and CCl1!containing 0\2\4!trisilapentanes[ The reaction of "049# with MeMgCl was similarly complex^ however\ in the presence of a great excess of MeMgCl\ the main product was TMS!CH1SiHMe1 ð67ZAAC"330#014Ł[ Photobromination of Cl2SiCH1SiCl2 by BrCl readily a}orded Cl2SiCBr1SiCl2 ð65ZAAC"308#102Ł[ A well!studied compound related to "037# is "042#^ it has been prepared by several methods[ One method was by reaction of "038# with MeLi ð60ZN"B#379Ł[ Another approach involved lithiation of dichloromethane "two equivalents of BuLi# and subsequent reaction with trimethylsilyl chloride ð56JCS"C#0369\ 61JOC1551Ł[ Alternatively\ the lithiated "041# a}orded "042#\ again with TMS!Cl "Scheme 23# ð69JOM"12#250Ł[ A better yield was achieved upon insertion of dichlorocarbene into the Si0Si bond of "043#[ The dibromo analogue at the central carbon of "042# was prepared from TMS!CBr1Li and TMS!Cl\ and also from the complex TMS!BrP"NEt1#2 and TMS!Br ð69JOM"13#536\ 69TL3582\ 89ZOB698Ł[ Cl3Si
SiCl3
Cl
Cl
(148)
ZnF2
MeMgCl
LiAlH4
F3Si
H3Si
SiF3
Cl
Cl
Cl
(149)
Cl3Si
SiH3 Cl
SiMeCl2
Cl
(150)
Cl
(151)
Scheme 33
TMS
Li
Cl
Cl
(152)
TMS-Cl
TMS Cl
TMS Cl
(153) Scheme 34
CHCl3/KOH, 18-crown-6
TMS
TMS
61%
(154)
Partially chlorinated 1\1!dichloro!0\2!disilapropanes such as "044# and "045# were also obtained from "041# and Me1SiCl1 or MeSiCl2 "Scheme 24# ð68ZAAC"337#44Ł[ Starting with PhMe1SiCCl1Li\ similar compounds were also formed[ A di}erent method is also accessible for such compounds^ for example\ Cl2SiCCl1SiMeCl1 was obtained through methylation of "Cl2Si#1CCl1 with MeMgCl ð60ZN"B#379Ł[ Full methylation of "038# at the silicon resulted in the formation of "042#[ Apart from halogenated silapropanes\ some related 0\2\4!trisilapentanes were also studied[ Photochemical chlorination of "046# produced "047#\ which reacted further with ZnF1 and with MeMgCl in the same manner as "037# "Equation "21## ð67ZAAC"328#050Ł[ Partial chlorination of "046# is also possible\ using sulfuryl chloride and benzoyl peroxide ð60ZAAC"271#106Ł[ The most interesting reaction of "047# was methylation with MeMgCl] when MeMgCl was in large excess "07 ] 0#\ the main products were TMS!C2C!TMS "36)# and CH11C"TMS#CH"TMS#1 "13)# ð63ZAAC"393#092Ł[ The same
157
Two Halo`ens and Two Other Heteroatoms
reaction was studied with some ~uorinated silicon compounds such as F2SiCCl1SiF1CH1SiF2 and F2SiCCl1SiF1CHClSiF2 ð67ZAAC"328#050Ł[ An octahedral silicon complex has been described\ result! ing from the reaction between 1\1?!bipyridyl and "Cl2Si#1CCl1 ð89CB834Ł[ TMS Cl
SiMeCl2
MeSiCl3
Cl (155)
TMS
Li
Cl
Cl
TMS
Me2SiCl2
Cl
Cl SiCl3
Si Cl
Cl (156)
(152) Scheme 35
Cl3Si
SiMe2Cl
Cl Cl
Cl
Cl2, hν
Cl3Si
Cl
SiCl3
Si Cl
(32)
Cl (158)
(157)
A fair number of di~uorocarbodisilanes are known[ Several disilanes of the general formula "048# and other related compounds reacted readily with di~uorocarbene\ produced by thermolysis of Me2SnCF2^ the products "059# resulted from CF1 insertion into the Si0Si bond "Equation "22##[ Some trisilanes also reacted in the same way[ For example\ FMe1Si"SiMe1#SiMe1F\ which was converted by single or double CF1 insertion to FMe1SiCF1SiMe1SiMe1F or "FMe1SiCF1#1SiMe1[ Compound "059# "X F# can react with Grignard and organolithium compounds "MeMgCl\ MeLi\ PhLi\ etc[#^ one or both silicon!bound ~uorine atoms are then replaced by an alkyl or phenyl group\ so that with MeLi either TMS!CF1SiMe1F or "TMS#1CF1 is obtained[ Other reactions at the Si0F bond in "FMe1Si#1CF1 involved LiAlH3\ which converted it to "HMe1Si#1CF1\ and Me1PLi\ which produced Me1PMe1SiCF1SiMe1F as well as "Me1PSiMe1#1CF1 ð72AG"E#629Ł[ XMe2Si
SiMe2X
[CF2]
XMe2Si F
(159)
SiMe2X
(33)
F
(160) X = F, Cl, Br, OMe
5[97[5[0[1 Cyclic carbosilanes Reaction of Cl2SiCH1CH1SiCl1CH1Cl with magnesium produced 0\2!disilacyclopentane "050#\ which upon photochlorination eventually gave the fully chlorinated compound "051# "Scheme 25#[ An interesting solvent e}ect was observed in the reaction of "051# with an excess of MeMgCl^ while in ether several products were formed\ the main product "55) yield# being Cl1C1CClSiMe1CCl1! TMS\ in pentane\ compound "052# was formed exclusively ð69ZAAC"261#10\ 68ZAAC"347#26Ł[ When MeSiCl2 or Me1SiCl1 are heated at 699>C\ they are converted to the cyclic carbosilane "053#\ which upon photochlorination a}ords the perchloro compound "054# "Scheme 26# ð59ZAAC"292#74Ł[ The partially brominated "055# was obtained from the photochemical reaction of "053# and bromine chloride\ whereas the bromo analogue of "053# gave the octabromo analogue of "055# "Scheme 26# ð64ZAAC"308#102Ł[ The hexa~uoro analogue of "053# underwent photochlorination to produce a mixture of 1\1!dichloro!\ 1\1\3\3!tetrachloro!\ and 1\1\3\3\5\5!hexachloro!hexa~uoro trisilacyclo! hexanes ð64ZN"B#854Ł[ The reactivity of these compounds is analogous to that already mentioned for their linear analogues\ for example "054# was converted by LiAlH3 into 1\1\3\3\5\5!hexa! chlorotrisilacyclohexane ð60ZAAC"271#8Ł[ Unusual reactivity was\ however\ noted in the case of MeMgCl^ with "054#\ four equivalents of MeMgCl gave the ring!contracted "056# in high yield[ Further reaction of "056# with more MeMgCl a}orded several products\ the major being "057# "Scheme 27# ð62ZAAC"284#048\ 62ZAAC"288#179Ł[ Several partially chlorinated 0\2\4!trisilacyclohexanes are known\ some resulting from the interaction of "054# with its fully hydrogenated analogue\ that is "H1SiCH1#2 ð60ZAAC"271#106Ł[ Their reactivity with MeMgCl is of interest\ since di}erent products are obtained in each case depending on the structure of the substrate "Scheme 28#[ The reactivities of partly brominated trisilacyclohexanes with Grignard and organolithium compounds exhibit some similarity to and a number of di}erences from their chloro analogues^ the most notable di}erence is the double substitution of carbon!bound bromine by butyl groups when butyllithium is used "Equation "23##[ Generally\ more results are available in the carbosilane _eld\ with ample discussion and mechanistic details ðB!75MI 597!90Ł[
158
One Metalloid Cl Cl2Si
Cl2, hν
SiCl2
Cl
Cl2Si
Cl
SiCl2
Cl
Cl
Cl
Cl
Si
Cl
Br
Br
Cl
Cl
Cl Si
Si Cl
Si
SiMe2
Cl Cl (163)
Cl
Si Cl
Si
Cl
Cl
Cl
Cl
(166)
Cl Cl
hν, Cl2, CCl4, ∆
BrCl, hν
Cl
Cl
Me2Si
pentane
Cl Cl (162) Scheme 36
(161)
Cl
MeMgCl
Cl
Cl
Cl Si
Si Cl
Si Cl
(164)
Cl Cl
Cl
Cl
(165)
Scheme 37 Cl (165)
4MeMgCl
Cl
Cl
Cl2Si
MeMgCl
SiCl2
Cl
Cl
TMS
TMS
Cl Si Cl
TMS (167)
(168)
Scheme 38
Cl Cl2Si Cl Cl
SiCl2 Cl
Cl
H2Si
Si Cl Cl Cl
Si H2
MeMgCl
SiH2 Cl Si H2 Cl
Cl
MeMgCl
Cl Me2Si
H2Si Cl
SiH2
Cl
Me2Si
SiMe2
MeMgCl
Me2Si Cl
SiMe2 Si H2
SiMe2
Cl
SiMe2 Cl Si
Cl H Me
Scheme 39 Br Me2Si
Br SiMe2 Br
Bu BuLi
Si Me2 Br
Me2Si
Bu SiMe2 Br
(34)
Si Me2 Br
5[97[5[1 Two Halogens and Two Boron or Other Metalloid Functions Two compounds of this type are known[ The _rst is Cl1BCCl1BCl1\ which was formed when carbon vapour reacted with either BCl2 or B1Cl3 ð58JCS"A#0771Ł[ The other is Cl2GeCCl1GeCl2^ this was obtained in a similar way from carbon vapour and GeCl3 ð69JCS"A#20Ł[ 5[97[6 TWO HALOGENS AND ONE METALLOID FUNCTION 5[97[6[0 Two Halogens\ a Silicon\ and a Metal Function Apart from Grignard and organolithium compounds which exist only in solution "Section 5[97[5[0#\ some stable compounds of this category are known with tin and mercury[ They are
169
Two Halo`ens and Two Other Heteroatoms
normally formed from the appropriate organometallic compound coupled with metal or silyl chlorides^ in one case\ an exchange reaction between organomercurials was noted[ Examples are given in Scheme 39 ð69JOM"12#250\ 69JOM"13#563\ 60JOM"16#08Ł[ Dichlorocarbene insertion into the Si0Hg and Si0Ge bond also occurs\ but the products are further transformed ð56JOM"6#P19Ł[
TMS Cl
TMS
Li
Cl
Cl
Li
+
Cl
Br Me3Sn Br
Cl
HgCl Cl
TMS
HgCl
+
HgCl2 Li
Cl TMS
Hg
Cl
Cl Cl
Cl TMS
+
Br
+
Br
TMS
Br TMS
+ HgPh2
Cl
HgPh Cl
1– 2
Cl
Br
Me3Sn
TMS-Cl
TMS
SnMe3
Me3SnCl
Br MgCl
SnMe3
Cl
Cl TMS
TMS
TMS
+ Me3SnCl
Br
TMS
Hg
Cl
Cl Cl
TMS Cl
+
1– HgPh 2 2
Scheme 40
5[97[7 TWO HALOGENS AND TWO METAL FUNCTIONS Stable isolable compounds of this category involve tin[ Most were prepared by insertion of dihalocarbenes\ from organomercurial precursors or chloroform "Equation "24## ð56JA1689\ 58JA0843\ 80SRI390Ł[ Coupling of Me2SnCBr1!TMS with Me2SnCBr1MgCl also produced "Me2Sn#1CBr1 ð69JOM"13#536Ł[ The theoretically interesting dilithiodi~uoromethane was shown by ab initio cal! culations to have a planar lithium bridged structure of CLi1F¦ F− ion pair character ð74CC4Ł[ R3Sn
SnR3
+
[CX2]
R3Sn X
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
SnR3
(35)
X
Comprehensive Organic Functional Group Transformations
6.09 Functions Containing One Halogen and Three Other Heteroatom Substituents ANGELA MARINETTI and PHILIPPE SAVIGNAC DCPH - Ecole Polytechnique, Palaiseau, France 5[98[0 ONE HALOGEN AND THREE CHALCOGENS 5[98[0[0 One Halo`en and Three Oxy`en Functions 5[98[0[1 One Halo`en\ Sulfur\ and Oxy`en Function 5[98[0[1[0 One halo`en and three sulfur functions 5[98[0[1[1 One halo`en\ two sulfur\ and one oxy`en function 5[98[0[2 One Halo`en\ Selenium\ and Sulfur Function 5[98[1 ONE HALOGEN AND TWO CHALCOGENS
161 161 162 162 165 165 166
5[98[1[0 One Halo`en\ Two Chalco`ens\ and a Nitro`en Function 5[98[1[1 One Halo`en\ Two Sulfur\ and a Phosphorus Function 5[98[1[2 One Halo`en\ Two Sulfur\ and a Metal Function 5[98[2 ONE HALOGEN AND ONE CHALCOGEN
166 167 167 168
5[98[2[0 One Halo`en\ One Chalco`en\ and Two Group 04 Elements 5[98[2[0[0 One halo`en\ one oxy`en\ and two nitro`en functions 5[98[2[0[1 One halo`en\ one sulfur\ and two nitro`en functions 5[98[2[0[2 One halo`en\ one chalco`en\ and two phosphorus functions 5[98[2[1 One Halo`en\ One Sulfur\ and Two Silicon Functions 5[98[3 ONE HALOGEN AND THREE GROUP 04 ELEMENTS 5[98[3[0 One Halo`en and Three Nitro`en Functions 5[98[3[0[0 Halotrinitromethanes 5[98[3[0[1 Miscellaneous halonitromethanes 5[98[3[0[2 Halotriaminomethanes 5[98[3[0[3 "Di~uoroamino#~uorodiazirine 5[98[3[0[4 Fluorine!containin` diaziridines 5[98[3[1 One Halo`en\ One Nitro`en\ and Two Phosphorus Functions 5[98[3[2 One Halo`en and Three Phosphorus Functions 5[98[4 ONE HALOGEN AND TWO GROUP 04 ELEMENTS
168 168 170 170 171 171 171 171 173 173 174 174 174 175 175 175 176
5[98[4[0 Metal Halodinitromethides 5[98[4[1 Metal Bis"phosphonyl#halomethides 5[98[5 ONE HALOGEN AND ONE GROUP 04 ELEMENT
177
5[98[6 ONE HALOGEN AND METALLOID FUNCTION "THREE\ TWO OR ONE\ TOGETHER WITH METALS#
178
5[98[6[0 One Halo`en and Three Metalloid Functions 5[98[6[0[0 Three silicon functions 5[98[6[0[1 Two silicon and a `ermanium function 5[98[6[0[2 Two silicon and a boron function 5[98[6[0[3 Three boron functions or two boron and a metal function
160
178 178 181 181 181
161
One Halo`en and Three Other Heteroatoms 182
5[98[6[1 One Halo`en\ Two Metalloid\ and One Metal Function 5[98[7 ACKNOWLEDGEMENTS
182
5[98[0 ONE HALOGEN AND THREE CHALCOGENS 5[98[0[0 One Halogen and Three Oxygen Functions Acyclic covalent halogenides having the general structure*one halogen and three oxygen func! tions*are known for chlorine and ~uorine[ In most cases\ the oxygen substituents are poly! ~uorinated or polynitrated groups[ Poly"nitro#alkyl chloro ortho!formates are reactive intermediates in the synthesis of explosive ortho!carbonates and are themselves explosive compounds ð72USP356604Ł[ They have been prepared by chlorination of the corresponding trichloromethyl disul_des "Scheme 0#^ their reaction with the HFÐpyridine complex yields ~uoro ortho!formates ð72JEM84Ł through a chlorineÐ~uorine exchange reaction[ Highly ~uorinated peroxide derivatives*exhibiting a better thermal stability than non! ~uorinated analogues*are prepared by CsF!catalyzed ~uorination of the corresponding carbonyl compounds "Equation "0## ð57JOC1984\ 65JFC"6#490Ł[ In both cases\ limitation of sample size and suitable safety equipment are required[ R
R O R
O
S S
Cl Cl Cl
+
O
Cl
Cl
Cl2
R
60 °C 95%
O
O
+ SCl2 + ClSCCl3
Cl O R
R R
R
O R
O
O Cl
+ HF/pyridine
25 °C 79%
O
R
O
F O
R
R R = C(NO2)2F Scheme 1
RO O
RO O FO RO O
CsF
+ F2
O
–78 °C
RO O
(1)
F
R = CF3, 100% SF5, 60%
Reaction of carbon tetrachloride with penta~uorophenol in the presence of aluminum chloride\ or with bromine ~uorosulfate\ gives the trisubstituted species in low yields and as a mixture with several by!products "Scheme 1# ð57IC323\ 77ZOR0402Ł[
CCl4 + F5C6OH
AlCl3 80 °C
CCl4 + FSO2OBr
22 °C
F5C6O F5C6O F5C6O 16% FSO2O FSO2O FSO2O
Cl
25% Scheme 2
Cl
+ (F5C6O)4C
+ ...
27% FSO2O
Cl
FSO2O
Cl
+
+ BrCl 50%
162
Three Chalco`ens 5[98[0[1 One Halogen\ Sulfur\ and Oxygen Function 5[98[0[1[0 One halogen and three sulfur functions "i# Acyclic covalent halo`enides
Compounds of this type have been reported with sul_de\ oligosul_de\ and sulfone substructures[ Polyhalogenated derivatives are by far the most numerous[ The principal methods of preparation are exempli_ed below[ "a# From thiocarbonyl compounds and halo`ens[ The oldest method of preparation was described by Hass and Klug ð55AG"E#734\ 57CB1598Ł[ This involves the rapid and quantitative addition of chlorine "or bromine# to bis"tri~uoromethyl# trithiocarbonate to give the sulfenyl chloride "Equation "1##[ Several examples of halogenations using chlorine and thionyl chloride have been described subsequently "Equation "2# and Table 0#[ Starting materials are either trithiocarbonates with strong electron withdrawing groups\ R0 and R1\ or sulfone derivatives[ Under similar conditions\ bromine and iodine failed to react with trithiocarbonate!S\S!dioxides "entries 1 and 2 in Table 0#[ F3CS S
+ Cl2 (or Br2)
–78 °C, 1h
F3CS
R1S
"X2"
S R2S
ClS F3CS F3CS 90% XS R1S R2S
Cl
(or
BrS F3CS F3CS 60%
Br )
(2)
(3)
X
Table 0 Halogenation of thiocarbonyl compounds[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R1 Rea`ents and conditions Yield ")# Ref[ Entry R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 0 CF2 CF2 FCl\ −79>C "mixture# 65CB0865 1 PhS PhSO1 Cl1\ CCl3 79 65CB0958 Cl1\ CCl3 77 65CB0958 2 PhS 3!Me[C5H3SO1 3 CN CN Cl1\ −09>C\ CH1Cl1 79 70CB0021 Cl2CS Cl1\ CCl3 80 73SUL74 4 Cl2CS 5 Cl2CCCl1S Cl2CCCl1S Cl1\ CCl3 099 74T4034 Cl2CS SO1Cl1\ CH1Cl1 87 74T4034 6 PhCH1 7 Me Me SO1Cl1\ −04>C\ pentane 42 73SUL130 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Chlorination with chlorine or thionyl chloride is a very e.cient approach to sulfenyl chlorides] most of the reactions reported in Table 0 are rapid\ clean\ and quantitative[ The sulfenyl chlorides thus obtained are useful starting materials for the synthesis of more elaborate\ trisubstituted trithio ortho!formates[ The most signi_cant examples of nucleophilic substitution reactions of the SCl function by amines\ thiols\ and amides "Equation "3## are given in Table 1[ The reactivity of the S0Cl bond is generally increased by electron withdrawing substituents R0 and R1[ Some of the poly~uoro derivatives are claimed to be fungicidal agents\ and the synthesis of the phthalimido derivative "entry 1 in Table 1# has been patented ð69GEP0897579Ł[ XS R1S R2S
Nu–
X X = Cl or F
NuS R1S R2S
X
(4)
"b# From thiocarbonyl compounds and sulfenyl halo`enides[ Thiocarbonates having the general structure ðR"S#nSŁ1C1S "n 0\ 1 and 2# are formed from thallium or barium thiocarbonates by reaction with sulfenyl chlorides "Equation "4# and Table 2#[ When an excess of sulfenyl chloride is used\ the transient thiocarbonate reacts further to give the chlorothio ortho!formate in fair to moderate yields "entries 0 and 1 in Table 2#[ The synthesis of various polyhalogenated ortho! formates bearing disul_de or trisul_de units has also been reported ð74T4034Ł[
163
One Halo`en and Three Other Heteroatoms Table 1 Nucleophilic substitution reactions of sulfenyl chlorides[
Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R1 Nu Conditions Yield ")# Ref[ R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * CF2 CF2 Et1NH petroleum 71 65CB0865 CF2 phthalimide C5H5\ Et2N 43 69GEP0897579\ 65CB0865 CF2 CF2 CF2 K!pyrrole pentane 55 72CB2214 Cl2CS Na phthalimide CH1Cl1\ H1O 49 74T4034 Cl2CS CF2 CF2 NH2 −79>C 56 63CZ098 morpholine CHCl2 89 65CB0958 PhS 3!Me[C5H3SO1 PhS Ph!SO1 morpholine CHCl2 76 65CB0958 PhS 3!Me[C5H3SO1 PhSH CHCl2 64 65CB0958 t Bu SH CHCl2 76 65CB0958 PhS 3!Me[C5H3SO1 3!Me[C5H3SO1Na C5H5 17 65CB0958 PhS 3!Me[C5H3SO1 PhS 3!Me[C5H3SO1 MeCOSH CCl3\ 49>C 84 75T628 CF2 AgCN 19>C 86 65CB0865 CF2 CF2 CF2 AgOCN 49>C 5 65CB0865 CF2 AgSCN 19>C 55 65CB0865 CF2 CF2 CF2 AgSeCN 19>C 68 65CB0865 SO1\ −19>C 81 70CB0021 CN CN H3NSCN CF2 CF2 F1C S hn 29 65CB0865 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
R 1S S
R2SX
R1S
R2SS R1S R1S
(5)
X
Table 2 Addition of sulfenyl chlorides to thiocarbonyl compounds[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0 R1 Rea`ents and conditions Yield ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * CF2S CF2 Tl1CS2 ¦F2CSCl 24 65CB2321 Cl2CS BaCS2 ¦Cl2C!S1Cl\ MeCN 09 74T4034 Cl2CS1 Cl2CS Cl2C Cl2CSCl\ MeCN\ 79>C 74T4034 Cl2CCl1C Cl2C!Cl1CSCl\ MeCN\ 79>C 45 74T4034 Cl2CCl1CS FCl1CCl1CS FCl1CCl1C FCl1C!Cl1C!SCl\ MeCN\ 79>C 74T4034 Cl SCl1\ 9>C 099 73SUL74 Cl2CS CF2 CF2 F2CSF\ −085 to −59>C 40 81ZN"B#258 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Sulfur dichloride reacts cleanly at low temperature with bis"trichloromethylthio# trithiocarbonate to give the corresponding chlorothio ortho!formate in quantitative yield "entry 5 in Table 2#[ The reaction of bis"tri~uoromethyl# thiocarbonate with tri~uoromethylsulfenyl ~uoride must be performed at very low temperature "−089>C#\ because of the much higher reactivity of F2CSF compared to F2CSCl[ The structures of tris"trichloromethyldithio#! and "trichloro! methyltrithio#chloro ortho!formate "entries 1 and 2 in Table 2# have been established by x!ray crystallography[ "c# By halo`enation of trisulfonylmethanes[ Trialkyl!\ triaryl!\ and tri~uoro!sulfonylmethanes are very strong acids^ in the presence of bases "Ag1CO2 or NaOH# the corresponding silver or sodium salts are formed[ They react smoothly with halogens "Cl1\ Br1\ and I1# "Equation "5# and Table 3#[ The iodo derivatives are generally less stable than their chloro or bromo analogs[ The ~uoro derivative could not to be isolated from the reaction of "F2CSO1#2C−Ag¦ with XeF1 ð77IC1024Ł\ but "FSO1#2CF is obtained from reaction of "FSO1#2CH with XeF1 ð79AG"E#831Ł[ A few examples of direct halogenation of trisulfonylmethanes in re~uxing CCl3 in the absence of any deprotonating agents have been reported "entries 7Ð05 in Table 3#[ Yields are satisfactory[ R1SO2
X2/Ag2CO3
SO2 R1SO
2
R2 or X2
R1SO2 R1SO
2
X
(6)
R2SO2
Only two examples of lithiated chlorobis"sulfonyl#methanes have been reported[ They react with
164
Three Chalco`ens Table 3 Halogenation of trisulfonylmethanes[
Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R1 Rea`ents and conditions Yield ")# Ref[ R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me Me Cl1\ NaOH\ H1O 77 35RTC42 84 35RTC42 Me Me Br1\ NaOH\ H1O F F Br1\ Ag1CO2 85 79AG"E#831\ 72ZOR68 85 79AG"E#831\ 72ZOR68 F F l1\ Ag1CO2 F F XeF1\ −09>C\ CF1Cl1 79AG"E#831 CF2 Cl1\ Ag1CO2\ 9>C\ CH1Cl1 89 77IC1024 CF2 CF2 CF2 Br1\ Ag1CO2\ 9>C\ CH1Cl1 83 77IC1024 Et Me Cl1\ 69>C\ CCl3ÐCHCl2 54 65ZOR447 81 65ZOR447 Et Me Br1\ 69>C\ CCl3ÐCHCl2 64 65ZOR447 Ph Me Cl1\ 69>C\ CCl3ÐCHCl2 Ph Me Br1\ 69>C\ CCl3ÐCHCl2 84 65ZOR447 Me Cl1\ 69>C\ CCl3ÐCHCl2 69 65ZOR447 3!Me[C5H3 3!Me[C5H3 Me Br1\ 69>C\ CCl3ÐCHCl2 79 65ZOR447 Me Cl1\ 69>C\ CCl3ÐCHCl2 59 65ZOR447 3!Cl[C5H3 3!Cl[C5H3 Me Br1\ 69>C\ CCl3ÐCHCl2 89 65ZOR447 Me Br1\ 69>C\ CCl3 52 65ZOR1472 3!Me!2!NO1[C5H2 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
phenylsulfenyl chloride at room temperature to a}ord chloro"phenylthio#bis"sulfonyl#methanes in low to moderate yield "Equation "6## ð61LA"647#021Ł[ i, BunLi ii, PhSCl
RSO2
PhS RSO2 RSO2
Cl RT
RSO2
Cl
(7)
R = Et, 17% Ph, 61%
"ii# Cyclic covalent halo`enides "a# From thiocarbonyl compounds and halo`ens or sulfenyl halides[ The previously described addition of halogens or sulfenyl halides to trithiocarbonates has been applied e.ciently to the synthesis of cyclic derivatives "Scheme 2# ð76SUL48\ 80CB1914Ł[ The four!membered cyclic thio! carbonyl compounds react considerably faster than their acyclic analogues[ This re~ects the dimin! ished ring strain upon sp1Ðsp2 rehybridization of the C!1 center in the dithietane[ F 3C
S
CH2Cl2
+ Cl2
S
Cl
S S
Cl
0 °C 100%
S
F3C
+
RSCl
25 °C
S
F3C
S
SCl
F3C
S
Cl
Cl
S
SSR
Cl
S
Cl
R = CCl3, 86% C2Cl5, 75% SCCl3, 58% SC2Cl5, 68% Scheme 3
"b# Fluorination of trithiosubstituted carbocations[ Exchange of the AsF5− counterion with a ~uoride anion in cationic 0\2!dithietane derivatives gives rise to a stable ~uorinated compound when R CF2\ or to an unstable one when R Me "Equation "7## ð89CB0524Ł[ Previously\ the same approach had been applied to the synthesis of symmetrical dithietanes from trithiomethyl car! bocations "Scheme 3# ð76CB318Ł[ The _rst step of the reaction is the dimerization of a ~uoro! dithioformate\ induced by the strong acidic medium[ Formation of the covalent C0F bond is then promoted by addition of ether\ as a solvent\ to the reaction mixture[
165
One Halo`en and Three Other Heteroatoms F
S +
F
S
F3CS
+
SR AsF6–
F3CS
SbF5, HF –30 °C
F
F
S
SR
25 °C
F
S
F
+ NaAsF6
(8)
R = CF3, 98% Me, unstable
S
S
2
SO2
NaF
F
S
+
F–
SCF3
F3CS
S
SCF3
F
S
F
ether 48%
SbF6–
Scheme 4
5[98[0[1[1 One halogen\ two sulfur\ and one oxygen function Only two examples of this class of compounds have been isolated and identi_ed] both are derived from carbohydrates and both are symmetrical disul_des resulting from chlorine addition to dithiocarbonates "Equation "8## ð58JOC0531Ł[ The _nal products precipitate from the solution as white solids[ They are used as intermediates in the synthesis of sugar chlorothioformates ð60CAR"05#034Ł[ S
S S
+ Cl2
S
RO
ClS RO Cl
ether
OR
S
S
SCl OR Cl
S
(9)
S S
=
S
RO
OR
bis (1,2:5,6-di-O-isopropylidine-3-O-thiocarbonyl-α-D-glucofuranose) disulfide, 100% bis (methyl 4,6-O-benzylidine-2-(and 3-) O-thio-carbonyl-α-D-glucopyranoside) disulfide, 35%
Work done in the early 0879s has shown that O\S!dimethyl dithiocarbonate reacts at 9>C with sulfuryl chloride to give the expected chlorinated adduct which undergoes a rapid intramolecular rearrangement to a}ord a methoxydichloro"methyldithio# derivative "Scheme 4# ð72TL4572Ł[ In the light of this result\ a reinterpretation of the earlier literature data on chlorination of thioesters seems to be necessary[ MeO S
ClS MeO MeS
+ SO2Cl2
MeS
Cl MeO MeSS
Cl
Cl
Scheme 5
5[98[0[2 One Halogen\ Selenium\ and Sulfur Function The methods available for the synthesis of haloselenothio ortho!formates are analogous to those used for the corresponding trithio ortho!formates\ but with fewer examples[ When sulfur and selenium substituents are perhalomethyl\ CFnCl"2−n#\ chloro ortho!formates have been isolated "Equation "09##^ the only bromo derivative cited ð75ZN"B#302Ł seems to be unstable[ "CF2Se#1C1S reacts with chlorine at low temperature by addition of halogen to the thiocarbonyl group "Equation "00## ð63CZ400Ł[ No experimental details have been given[ A report from the mid 0879s concerns the addition of sulfuryl "or selenyl# chlorides to thiocarbonyl derivatives under UV irradiation[ Physical and spectroscopical data of the new substances are provided[ "Table 4# ð75ZN"B#302Ł[ F3CSe S F3CSe
+
Cl2
–80 °C
ClS F3CSe F3CSe
Cl
(10)
166
Two Chalco`ens F3CSe
RS F3CSe F3CY
RCl
S F3CY
(11)
Cl
Table 4 Addition of sulfuryl and selenyl chlorides to thio! carbonyl derivatives[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Entry Y Rea`ents and conditions Yield ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 0 Se F2CSCl\ hn 77 74 1 Se F2CSeCl\ hn 2 Se F1ClCSCl\ hn 40 27 3 Se FCl1CSCl\ hn 4 S F2CSeCl\ hn 76 67 5 S F2CSCl\ hn ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
5[98[1 ONE HALOGEN AND TWO CHALCOGENS 5[98[1[0 One Halogen\ Two Chalcogens\ and a Nitrogen Function As far as covalent halides are concerned\ a few examples of this type have been described\ with either oxygen or sulfur as the chalcogens[ A unique compound containing two oxygen and a nitrogen functions was obtained by reaction of peroxydisulfuryl di~uoride with ClCN under thermal conditions "Equation "01## ð64IC481Ł[ The suggested mechanism involves formation of a nitrene and the reaction pathway shown in Scheme 5 is proposed to account for the addition of the FSO1O = radical to the unsaturated carbonÐnitrogen system[ This radical addition to ClCN occurs quan! titatively and is su.ciently facile to be synthetically useful[ (FSO2O)2N FSO2O FSO2O
80 °C, 12 h
CICN + (FSO2O)2
82%
FSO2O
FSO2O•
ClCN
FSO2O•
N• Cl
FSO2O FSO2O Cl
N:
+
FSO2O FSO2O Cl (FSO2O)2N FSO2O FSO2O
(FSO2O)2
(12)
Cl
N:
Cl
Scheme 6
Bis"2!nitroarylsulfonyl#bromonitromethanes are obtained from bis"arylsulfonyl#"methylsulfonyl# methanes "Scheme 6#[ After polynitration with HNO2ÐH1SO3 the methylsulfonyl group is easily removed in basic medium[ Two bromination methods\ direct bromination with potassium hypo! bromite and basic cleavage followed by bromine addition\ were outlined ð65ZOR1472Ł[ Arylazo derivatives of bis"arylsulfonyl#chloromethanes are yellow crystalline compounds which are readily soluble in most organic solvents[ They are prepared from bis"arylsulfonyl#chloro! methanes in basic medium by reaction with aryldiazonium chlorides "Equation "02## ð57ZOR213Ł[ 4-RC6H4SO2 Cl 4-RC6H4SO2
+
ArN2+Cl–
NaOH RT, 30min 80–94%
ArN N 4-RC6H4SO2 4-RC6H4SO2
R = H, Me, Cl, NO2 Ar = C6H5, 4-Me-C6H4, 4-Cl-C6H4, 4-O2N-C6H4, 4-MeO-C6H4, 4-HO2C-C6H4, 2-MeO, 5-Cl-C6H3, 2-Me, 5-Cl-C6H3
Cl
(13)
167
One Halo`en and Three Other Heteroatoms 4-RC6H4SO2 SO2Me
O2N ArSO2 ArSO2
HNO3/H2SO4 RT, 3h
4-RC6H4SO2
SO2Me
NaHCO3
R = H, 75% Me, 73% Cl, 80%
KOBr
ArSO2
Br2,CCl4
NO2
70 °C, 4h
ArSO2
O2N ArSO2 ArSO2
Br
R = H, 80% Me, 95% Cl, 85%
R = Me, 90% Cl, 85%
ArSO2 = 4-R, 3-O2N-C6H3 Scheme 7
5[98[1[1 One Halogen\ Two Sulfur\ and a Phosphorus Function Triethoxyphosphonium bis"phenylsulfonyl#methylide is one of the few known stable trialkoxyphosphonium ylides\ most of which are only reaction intermediates[ It reacts as a very weak nucleophile^ for example\ with bromine it gives the 0!bromomethylphosphonate in very good yield "Scheme 7# ð77S802Ł[ PhSO2 IPh
+
Cu(acac)3, CHCl3
(EtO)3P
80 °C, 7.5 h
PhSO2
PhSO2
Br2, CCl4
P(OEt)3 RT, 1h
PhSO2 87%
(EtO)2P(O) PhSO2 PhSO2 98%
Br
Scheme 8
Mixed sulfonicÐphosphonic acids have been synthesized for evaluation as potential electrolytes in fuel cells[ The starting material "EtO#1P"O#CFBr1 was converted into its disodium 0!~uoro! 0\0!disulfonylmethylphosphonate salt by repeated reaction with sodium dithionite and hydrogen peroxide "Scheme 8# ð78CJC0684Ł[ Yields were satisfactory[ (EtO)2P(O) Br Br
F
(EtO)2P(O) NaSO3 Br
F
(EtO)2P(O) NaSO2 Br
Na2S2O4, MeCN/H2O RT, 4 h 64%
(EtO)2P(O) NaSO3 NaSO2
NaS2O4 0 °C, 4 h 80%
H2O2
F 0 °C, 5 h 75%
F
H2O2 –15 °C, 1 h 32%
(EtO)2P(O) NaSO3 Br
F
(EtO)2P(O) NaSO3 NaSO3
F
Scheme 9
5[98[1[2 One Halogen\ Two Sulfur\ and a Metal Function All the known compounds bearing one halogen\ two sulfur\ and one metal function on the same carbon atom have the general structure "0#[ RSO2 –
X M+
RSO2
X = Cl,Br M = Li,Na,K,Ag R = Ph,CF3
(1)
It has been found that the action of strong bases "for R Ph# or even weak bases "for R CF2# leads to metallation at the C0H bond of bis"sulfonyl#halomethanes "Equation "03## ð61LA"647#021\ 62JOC2247\ 66ZOR164Ł[
168
One Chalco`en RSO2
RSO2
–
X + MY
+ YH
(14)
RSO2
RSO2 X = Cl, Br Cl, Br Cl, Br
X M+
MY = BunLi, MeONa / MeOH, KOH / H2O R = Ph K2CO3 / MeOH, Na2CO3 / MeOH, Ag2CO3 / MeOH CF3 MeONa / MeOH, BunLi Ph, Me, Et
pKa values for some monohalodisulfonylmethanes "R Ph\ Me\ Et# have been established by potentiometric titration in waterÐdioxane "0 ] 0# ð61LA"647#021Ł[ The metallohalomethanes are crys! talline substances\ soluble in water\ but insoluble in nonpolar or low polarity organic solvents[ They are very stable under ordinary conditions and have been found to be stable up to 149>C in some cases[
5[98[2 ONE HALOGEN AND ONE CHALCOGEN 5[98[2[0 One Halogen\ One Chalcogen\ and Two Group 04 Elements 5[98[2[0[0 One halogen\ one oxygen\ and two nitrogen functions "i# From per~uoroimines Addition of alcohols to N!~uoroimines gives adducts the stability which depends on the electron withdrawing character of the carbon substituents[ If these substituents are F and NF1 or F and CF2\ the adduct decomposes spontaneously with HF elimination to yield mainly a new ~uoroimine "Scheme 09#[ If both carbon substituents are NF1 groups\ stable adducts are obtained[ Interaction of these stable liquid compounds with NOF or NO1Cl causes replacement of the NHF group by F\ through an unstable intermediate bearing an N"F#NO substituent "Equation "04##[ The compounds described here are patented as good oxidants ð61USP2696444Ł and are shatteringly explosive under certain conditions[ Suitable protective equipment should be used during all phases of work ð62JOC0954Ł[ F
MeOH
NF F 2N
MeO F2N FHN
–HF
F
MeO NF
+ ...
F2N Scheme 10
MeO F2N FHN
MeO F2N F 2N
–HF
NF2
+
NOF (–HCl)
F
+
NNO (or NNO2)
(15)
(or NO2Cl)
Oxidation of per~uoroimines by aromatic peroxyacids or H1O1 a}ords oxaziridines "1# ð78USP3763764\ 81EUP385302Ł[ O F
N
R1R2N
R
(2)
"ii# From ~uorotrinitromethane In marked contrast to chloro! and bromotrinitromethane\ whose reactions with bases and reduc! ing reagents generally lead to nitroform anions\ ~uorotrinitromethane reacts with certain nucleo! philes with formal substitution of a nitro group "Equation "05## ð57JOC2962Ł[
179
One Halo`en and Three Other Heteroatoms O2N O2N O2N
F
+
RO O2N O 2N
RONa/ROH
F
+ NaNO2
(16)
R = Et, 74% CF3CH2, 55%
"iii# Diazirines from amidinium salts or ~uoroimines In 0854\ Graham reported the direct preparation of 2 aryloxy!2!halodiazirines by the action of aqueous NaOCl "or NaOBr# on various isoureas "Equation "06# and Table 5# ð54JA3285Ł[ Despite the importance of this interconversion\ the mechanism remains only partly elucidated[ The original suggestions are summarized in Scheme 00[ Not all of these intermediates have been isolated and characterized ð70JOC4937Ł[ R1O
NaOX
NH R2HN
N
OR1
N
X
(17)
Table 5 Preparation of 2!halo!\ 2!alkoxy!\ or aryloxy!diazirines[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R1 X Rea`ents and conditions Yield ")# Ref[ R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me H Cl NaOCl\ NaCl\ LiCl\ 14>C\ DMSO 59 54JA3285 Me H Cl NaOCl\ NaCl\ 14>C\ DMSO 53 68JCS"P1#0187 i H Cl NaOCl\ NaCl\ 14>C\ DMSO 47 68JCS"P1#0187 Bu Ph PhSO2 Cl NaOCl\ LiCl\ −4>C\ DMSOÐpentane 26 71JOC3066 H Cl NaOCl\ NaCl\ LiCl\ 14>C\ DMSO 75JA88 CD2 Me07O H Cl NaOCl\ NaCl\ LiCl\ 14>C\ DMSO 75JA88 H Cl NaOCl\ NaCl\ LiCl\ 14>C\ DMSO 46 76TL0858 PhCH1 PhCH1 H Br NaOBr\ 9>C\ DMSOÐpentane 24 89JPO583 PhCHD H Cl NaOCl\ 04>C\ DMSOÐpentane 89TL3604 H Cl NaOCl\ LiCl\ 4>C\ DMSOÐpentane 78TL1362 c!C2H4CH1 EtCHMe H Cl NaOCl\ LiCl\ 09>C\ DMSOÐpentane 81JA8275 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
RO NH
RO
NaOX
H 2N
OH–
RO
NaOX
NX
NX
H2N RO NX
–X–
XHN RO N: XN
XN
N
OR
N
X
–
Scheme 11
Diazirines have been widely investigated as sources of numerous halocarbenes[ Successive improvement of the synthetic approach\ by using N!substituted isoureas as starting materials\ greatly enlarged the scope and potential of diazirine chemistry[ As neat liquids\ the diazirines are unpredictably explosive at ambient temperatures\ but in solution they can be handled safely[ Chloro! or bromoalkoxydiazirines are converted into the corresponding ~uoroalkoxydiazirines simply upon stirring with anhydrous tetra!n!butylammonium ~uoride "tbaf# in acetonitrile "Equation "07## ð72JA5402\ 75JOC1057\ 75TL308\ 89JPO583Ł[ N
OR
Bun4NF, MeCN
N
OR
N
X
0–25 °C, 2–6 h
N
F
R = Ph X= Ph Me CH2Ph
Cl, 55% Cl, 39% Br, Cl, 40%
(18)
170
One Chalco`en
The reductive de~uorinationÐcyclization of methoxytri~uoroformamidine in the presence of ferrocene at room temperature represents an alternative approach to 2!~uoromethoxydiazirine "Equation "08## ð62JOC0954Ł[ MeO
Ferrocene
N
OMe
30%
N
F
NF F 2N
(19)
5[98[2[0[1 One halogen\ one sulfur\ and two nitrogen functions 0!Chloro!0\0!dinitromethyl sul_des or sulfones are the only reported representatives of this class of compounds[ They are usually obtained by treatment of the potassium salts of dinitromethyl sul_des or sulfones with chlorine "Equation "19## ð62IZV249\ 64IZV1649Ł[ The nucleophilicity of the potassium salts is so weak that they do not react even with iodomethane[ An alternative route to the analogous sul_de derivatives "Scheme 01# involves the addition of PhSCl to iodonium nitroylides\ which proceeds by cleavage of the intermediate iodonium salt ð67IZV1237Ł[ The iodonium nitroylide is a thermally unstable crystalline compound which decomposes rapidly in solvents like acetone\ ethanol\ and dichloromethane and explosively after isolation in air or under an inert gas[ Substituents such as NO1 on the benzene ring increase the stability of these dinitroylides[ O2N –
Cl2
R K+
ether or CH2Cl2
O2N
R O 2N O2N
(20)
Cl
R = MeSO2, 92% 2,4-(O2N)2-C6H3SO2, 30% MeS, 90% 2,4-(O2N)2-C6H3, 65% +
O2N
excess PhSCl
IPh O 2N
PhS O2N O2N
IPh
Cl–
PhS O2N Cl O2N 45%
+
(PhS)2C(NO2)2
Scheme 12
5[98[2[0[2 One halogen\ one chalcogen\ and two phosphorus functions The _rst approach to this kind of compound is a traditional MichaelisÐArbuzov reaction between triethyl phosphite and trichloromethyl phenyl ether "Scheme 02# ð69JPR364Ł[ Analogous tetraethyl halomethoxymethylene bisphosphonates are obtained by radical halogenation of the corresponding methoxymethylene bisphosphonates "Equation "10## ð73ZOB1493Ł[ (EtO)3P
+
PhOCCl3
120 °C
(EtO)2P(O)CCl2OPh
(EtO)3P 160 °C 64%
(EtO)2P(O) (EtO)2P(O) PhO
Cl
Scheme 13
(EtO)2P(O)
NBS, benzene
OMe (EtO)2P(O)
AIBN, 80 °C, 2-5 h, 52%
(EtO)2P(O) (EtO)2P(O) MeO
Br
(21)
Unexpectedly\ two products were obtained during the reaction of the methylene bisphosphonate salts\ ð""RO#1PO#1CHŁ−M¦ "M Li\ Na\ K#\ with CF2SCl[ The expected sulfenyl derivative is obtained in a mixture with chloro"tri~uoromethylthio#methylene bisphosphonate\ which results from a chlorination process "Equation "11##[ The use of aluminum trichloride reduces the proportion
171
One Halo`en and Three Other Heteroatoms
of chlorinated by!product "05)# with respect to the sulfonylated product "63)# ð74JCS"P0#0824Ł[ CClF1SCl and CCl1FSCl have also been used in analogous reactions[ i, BunLi ii, CF3SCl
(PriO)2P(O)
(PriO)2P(O) (PriO)2P(O) F3CS
ether
(PriO)2P(O)
(PriO)2P(O) Cl
+
(PriO)2P(O) SCF3
(PriO)2P(O)
43%
+
(22) (PriO)2P(O) 14%
43%
5[98[2[1 One Halogen\ One Sulfur\ and Two Silicon Functions Only one member of this family has been reported in the literature of the late 0879s onwards[ It was prepared by NBS bromination of bis"trimethylsilyl#methyl "trimethylsilyl#methyl sul_de "Scheme 03# ð76CPB0623Ł[ This compound is used as a precursor for the generation of a thiocarbonyl ylide\ whose 0\2 cycloaddition to several dipolarophiles leads to tetrahydrothiophene derivatives[ TMS
Na2S•5H2O
TMS
Bu4N+Br–, H2O, 100 °C, 5h 86%
TMS
Cl
TMS
TMS
i, BusLi, ii, TMS-Cl
S THF, TMEDA, 0 °C 72%
TMS NBS, CCl4
S TMS TMS
S RT. 100%
TMS
Br
Scheme 14
5[98[3 ONE HALOGEN AND THREE GROUP 04 ELEMENTS 5[98[3[0 One Halogen and Three Nitrogen Functions 5[98[3[0[0 Halotrinitromethanes Halotrinitromethanes have been extensively studied in view of their use as oxidants in mono! propellant fuels and in bipropellant systems with hypergolic fuels ð57USP2308514Ł[ The best methods for the preparation of halotrinitromethanes are electrophilic halogenations of trinitromethane salts "Equation "12##[ A wide range of halogenating agents has been tested in various reaction conditions^ the most successful syntheses are collected in Table 6[ In entry 0\ the reaction conditions have been optimized] aprotic solvents and room temperature "19>C# are essential factors[ Direct ~uorination of trinitromethane with ~uorine in water "89) yield# or methanol "69) yield# was also reported ð57IZV545\ 57IZV565Ł as a satisfactory synthetic method[ O2N –
O2N
NO2 M+
X-Y
O2N O2N O2N
X
+ M+Y–
Table 6 Electrophilic halogenation of nitroform salts[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ M XY Conditions X Yield ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * THF\ 14>C\ 00 h F 61 60IZV0376 K FClO2 K F1Xe MeCN\ 19>C F 67 76ZOR0546 H1O\ 9>C\ 0[4 h F 81 57JOC2979 Na F1:N1 NH3 F1:N1 H1O\ 9>C F 69 57IZV545 Cl 88 58IZV1506 Na NCS H1O\ 9>C\ 19 min K ClSO2F Cl1FC!CClF1\ −29Ð9>C Cl 71 65IZV378 Br 87 58IZV1506 Na NBS H1O\ 9>C\ 19 min K ICl CCl3\ 09>C\ 29 min l 60 66IZV1947 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
(23)
Three Group 04
172
When tetranitromethane reacts with anhydrous metal halides in aprotic dipolar solvents one of the nitro groups is replaced by a halogen "Equation "13## ð57USP2308514\ 58ZOR0206\ 69IZV1442\ 60IZV0962\ 61IZV0610\ 67USP3019893Ł[ O2N O2N O2N
NO2
O 2N O 2N O2N
DMF (or MeCN)
+
MX
+ MNO2
X
(24)
MX = KF, RbF, 58% CsF, 49% KF/OC(CF3)2, 90% LiCl, KCl, RbCl, CsCl, 40–60% LiBr, KBr, 23–30% Na(Cl)NSO2Ph, 49%
Halotrinitromethanes have also been obtained from arylthio!\ arylseleno!\ and arylantimono! trinitromethanes by cleavage of the carbonÐheteroatom bond\ through treatment with halogens\ or with sulfuryl chloride under mild conditions "Equation "14## ð63IZV0249\ 71IZV050\ 74IZV328Ł[ Treat! ment of arylthio! or arylseleno!trinitromethanes with gaseous hydrogen halides "HCl\ HF# in the presence of Lewis acids or mineral acids a}ords the corresponding halotrinitromethanes "Equation "15##[ The addition of a Lewis acid promotes the nucleophilic substitution of the chalcogenide group\ but yields remain unsatisfactory "0Ð29)# ð78IZV1095Ł[ O 2N O 2N O 2N X2 =
Y= S
Cl2 SO2Cl2 Br2 Cl2 Cl2 Br2
Sb Se
O 2N O2N O2N
O2N O2N O2N
X2
YR
R = Ph 2,4-(O2N)2-C6H3 2,4-(O2N)2-C6H3 Ph Ph Ph
Lewis acid
+ HX
YR
20 °C, 1h
X
(25)
+ RYX
DME, 0 °C, 2 h MeCN, 20 °C, 5 min MeCN, 20 °C, 5 min CH2Cl2, 20 °C, 3 h CH2Cl2, 20 °C, 1h CH2Cl2, 20 °C, 1h O2N O 2N O2N
86% 80% 78% 52% 79% 75%
+ RYH
X
(26)
Y = S, Se X = F, Cl Lewis acid = AlCl3, SbCl5 Solvent = CH2Cl2, MeCN, DMSO
Trinitromethyl sulfones were also tested as starting materials for the synthesis of halo! trinitromethanes "Equation "16##[ The C0SO1 bond was cleaved e.ciently by halogenated electro! philes "X1\ BrONO1\ HCl# ð66IZV264Ł[ O2N O2N O2N
MeCN
+
SO2Ph
X2 20 °C, 0.5–2.4 h
O2N O 2N O2N
X
+ RSO2X
(27)
X2 = Cl2, 80% Br2, 80%
Electrophiles "X1 Cl1\ Br1\ SO1Cl1\ NCS or NBS# very readily cleave the S0C bond of dimethyl! "trinitromethyl#sulfonium tetra~uoroborate to give the corresponding halotrinitromethanes in fair to good yields "59Ð79)# "Equation "17## ð66IZV1429Ł[ The starting material\ obtained by nitration of dimethylsulfonium dinitromethylide with nitronium tetra~uoroborate\ is stable for at least 13 h at 19>C[ It also reacts under mild conditions with nucleophiles "HCl\ HBr# to give the expected halotrinitromethanes[ In this case\ yields are low "05Ð22)# because of competing reactions between the product halotrinitromethanes and dimethyl sul_de[ O2N O2N O2N
MeCN
+
SMe2 BF4–
+
X2 –20 °C, 20 min
O2N O2N O2N
X
+ – + XSMe 2 BF4
(28)
173
One Halo`en and Three Other Heteroatoms
All the approaches described above employ the halogenation of preformed trinitromethyl moi! eties[ There is only one report of the nitration of a halodinitromethane[ Nitryl ~uoride was employed as the nitrating agent "Equation "18##[ The reaction did not require prior salt formation\ but the use of ammonium salts of halodinitromethane slightly increases the yield "to 44)# ð63IZV804Ł[ O 2N
+
X
O2N O2N O2N
MeCN
FNO2
–15 °C
O2N
(29)
X
X = F, 47% Br, 39%
5[98[3[0[1 Miscellaneous halonitromethanes Bromo! and chlorodinitromethanes react with a\a?!dicarbonylazo compounds to give N! "halodinitromethyl#hydrazine derivatives "Equation "29## ð64IZV1727Ł[ "Arylazoxy#dinitromethanes\ bearing an acidic proton\ undergo facile bromination in basic medium to give the "aryloxy#bromo! dinitromethanes "Equation "20## ð81MC41Ł[ Finally\ bis"di~uoroamino#~uoronitromethane ð"F1N#1"NO1#CFŁ has been identi_ed as a colorless gas ð57USP2276922Ł[ O 2N X
ROC
+
O2N
N
N
COR
O– +
+
N NAr
(30)
N COR
R = OMe, 81% NHMe, 67% OEt, 98% NH2, 87%
X = Cl Cl Br Br O 2N
H N COR
O 2N O 2N X
O2N O 2N Br
KOH
Br2
O 2N
O– +
(31)
N NAr
Ar = 2,4-(O2N)2•C6H3, 80%
5[98[3[0[2 Halotriaminomethanes Several poly"~uoroamino#halomethanes "Scheme 04# have been patented as precursors for bleach! ing agents\ explosives\ rocket fuels\ and pyrotechnic agents ð56JOC2748\ 56USP2243106\ 57IC0536\ 58USP2349651\ 61IC307\ 61USP2578459\ 62JOC0964\ 62USP2644393Ł[ This compilation is not exhaustive[ The various reported syntheses are performed on small scale and generally a}ord complex mixtures of ~uorinated products\ including those having the general structure "R1N#2CF[ The reaction between NCl2 and CCl3 in the presence of AlCl2 gives a mixture of four compounds\ one of them being "Cl1C1N#2CCl "16)# "Scheme 05# ð61RTC220Ł[ F2N F2N F2N
F2N F2N H2N
NCl3 + CCl4
AlCl3
F
F
Cl2C N Cl2C N Cl2C N 27%
F2N F2N F2N
F2N F 2N F O2N Scheme 15
Cl2C Cl
F2N F2N RFN
F
F 2N F2N (NF2)3C-N N
F
Br
N
Cl
Cl
+ (ClCN)3 +
+ Cl2C
Scheme 16
N Cl 35%
Cl3CN Cl
32%
0.7%
Three Group 04
174
5[98[3[0[3 "Di~uoroamino#~uorodiazirine "Di~uoroamino#~uorodiazirine was prepared from tris"di~uoroamino#~uoromethane by a reductive de~uorinationÐcyclization reaction with iodide ion in acetonitrile or with ferrocene "06)# "Equation "21## ð56JOC3934\ 57JOC0736\ 61USP2526552Ł[ Extreme caution should be used when manipulatin` "di~uoro! amino#~uorodiazirine because it can explode violently and it is sensitive to phase chan`es[ F2N F2N F2N
KI or ferrocene
F
N
NF2
N
F
(32)
5[98[3[0[4 Fluorine!containing diaziridines Penta~uoroguanidine undergoes rearrangement to a diaziridine in the presence of alkali metal ~uorides "MF# "Equation "22##[ CF3\ SiF3\ CO1\ and other impurites were observed in the reaction mixture[ Explosions occurred when the volatile diaziridine was condensed or volatilized[ The diaziridine is unstable at room temperature and must be stored at −67>C ð57JOC2378Ł[ A similar diaziridine was also obtained by a reductive de~uorinationÐcyclization reaction of bis"di~uoramino# ð"tri~uoromethyl#~uoraminoŁ~uoromethane "Equation "23## ð57JOC0736Ł[ F 2N NF F 2N
MF
FN
NF2
25%
FN
F
(33)
M = K, Rb F2N F 2N (F3C)FN
FN
ferrocene
F
N
33%
NF2 (34)
F
F3C
5[98[3[1 One Halogen\ One Nitrogen\ and Two Phosphorus Functions Compounds of this class bear\ essentially\ two phosphoryl groups and an isocyanate or ammonium function on the carbon atom[ The reaction of trichloromethyl isocyanate with various amounts of triethyl phosphite was studied under several conditions in order to determine the number of chlorine atoms of the trichloromethyl group which are active in the MichaelisÐArbuzov reaction[ With optimized stoichiometry of the reagents and reaction conditions\ a 22Ð31) yield of the diphosphonyl substituted derivative is obtained "Equation "24##[ In all cases side products are formed ð62ZOB433Ł[ The analogous reactions with a dialkyl halophosphite and trichloromethyl isocyanate a}orded only the corresponding bis"phosphoryl#halomethyl isocyanate in moderate to good yields "Equation "25##[ This reaction was extended to 1!chloro!0\2!dioxaphospholanes] as expected\ the MichaelisÐArbuzov rearrange! ment led to ring opening^ the yield is very low "5)# ð66ZOB1655Ł[ 2 (EtO)3P + Cl3CNCO
(EtO)2P(O) (EtO)2P(O) OCN
toluene 70-100 °C
2 (EtO)2P-X + Cl3C-NCO
∆
Cl
+ (EtO)3P(O) + [(EtO)2P(O)]2O (35)
X(EtO)P(O) X(EtO)P(O) OCN
Cl
(36)
X = Cl, 42% F, 79%
Dichloro~uoromethyl isocyanate has been used in a reaction with dialkyl chlorophosphites with a reagent ratio of 0 ] 1[ The main product was the "alkoxychlorophosphonyl#"alkoxy~uoro! phosphonyl#chloromethyl isocyanate^ it resulted from the reaction of the tautomeric form\ Cl1C1NC"O#F\ of the starting isocyanate with the chlorophosphite\ followed by a second
175
One Halo`en and Three Other Heteroatoms
MichaelisÐArbuzov reaction "Scheme 06# ð77ZOB0405Ł[ The same approach was extended to the synthesis of other substituted isocyanates by reaction of monophosphorylated dichloromethyl isocyanates with trialkyl! or dialkyl chlorophosphites "Equation "26## ð64ZOB0854Ł[ Tetraethyl "dimethylamino#methylbis"phosphonate# is methylated by dimethyl sulfate^ upon addition of gas! eous chlorine\ the resulting ylide undergoes a chlorinationÐelimination reaction to give the inner salt of triethyl chloro"trimethylammonium#methylbis"phosphonate# "Scheme 07# ð65JPR005Ł[ The inner salt was further hydrolyzed by aqueous HCl to the corresponding bisphosphonic acid "52)#[ Analogous aminophosphonic acids have been patented as herbicides ð79JAP7978109Ł[
RO
2 (RO)2PCl + Cl2FCNCO
F(RO)P(O) Cl OCN
RO
F P
–RCl
CCl2NCO
Cl F(RO)P(O) Cl(RO)P(O) OCN
(RO)2PCl
Cl –RCl
Cl
R = Me, 42% Et, 60% Scheme 17
(EtO)2P X
+
X(EtO)P(O) (Z1)(Z2)P(O) OCN
∆
(Z1)(Z2)P(O)CCl2(NCO)
(37)
Cl
X = EtO, Z1 = Z2 = Cl, 36% EtO, Z1 = Cl, Z2 = EtO, 6.5% Cl, Z1 = Z2 = Cl, 61% (EtO)2P(O)
Me2SO4
(EtO)2P(O) –
NMe2 (EtO)2P(O)
–HMeSO4
Cl2
+
NMe3
-EtCl 85%
(EtO)2P(O)
(EtO)2P(O) (O–)(EtO)P(O) Me3N +
Cl
Scheme 18
5[98[3[2 One Halogen and Three Phosphorus Functions Only one representative of this family is described^ it contains one bromine and three diethyl phosphoryl groups "Equation "27##[ Carbon tetrabromide reacts with triethyl phosphite under milder conditions than does carbon tetrachloride] in re~uxing benzene the reaction is complete after 0 h[ The yield of isolated product is 56) ð68ZOB0369Ł[ 3 (EtO)3P + CBr4
benzene ∆
(EtO)2P(O) (EtO)2P(O) (EtO)2P(O)
Br
(38)
5[98[4 ONE HALOGEN AND TWO GROUP 04 ELEMENTS Compounds of this class are essentially carbanions bearing `em!dinitro or diphosphorus functions and the halogen substituent^ they occur as reaction intermediates[
5[98[4[0 Metal Halodinitromethides The compounds described here are explosives and may detonate on grinding or impact[ Further! more\ ~uorodinitro compounds show varying degrees of toxicity and may cause painful burns when brought into contact with the skin[ Consequently\ they should be handled with care[
Two Group 04
176
The potassium bromo! and chlorodinitromethides were prepared from the corresponding 1!halo! 1\1!dinitroethanol in basic medium "Scheme 08#[ Unlike the chloro derivative which is unstable in the free state at room temperature\ the bromo derivative can be isolated\ recrystallized\ and air dried ð53JOC2476Ł[ O2N O2N HO
O2N
MeOH/H2O
+ KOH
X
–
RT X = Cl, Br, 50%
X K+
O2N
Scheme 19
The ~uorodinitromethide was obtained by reaction of ~uorotrinitromethane with hydroperoxide ions through displacement of one of the nitro groups "Scheme 19#[ The ~uorinated carbanion is unstable in solution and has been trapped by acid hydrolysis or reacted immediately ð57JOC2962Ł[ The silver salt of ~uorodinitromethane is equally unstable[ It is obtained by reaction of silver oxide with ~uorodinitromethane and reacts in situ with electrophiles to give C0C coupling reactions "Scheme 10# ð62S594Ł[ O2N O2N O2N
F
O2N
MeOH/H2O
+ H2O2 + KOH
–
–10 °C
H2SO4
F K+
O2N
O2N F O2N
X = Cl, Br, 50% Scheme 20
O2N F
O2N
acetone
+ Ag2O
–
2 0 °C, 18 h
O2N
F
O2N O2N R
R-X
Ag+ + H2O
O 2N
F
RX = MeI, 53% PhCH2Br, 20% CH2=CHCH2Cl, 68% Scheme 21
In contrast to the potassium and silver salts\ bis"~uorodinitromethyl#mercury is a white crystalline substance which is stable enough to be stored[ It reacts readily at room temperature with KI or KOH through a metal exchange reaction^ the potassium salt is formed according to Equation "28#[ It is slowly hydrolyzed in the presence of moisture[ The same mercury derivative is used as a starting material for the synthesis of symmetrical bis"chlorodinitromethyl#mercury by a transmercuration reaction "Equation "39##] the reaction with polynitro compounds bearing a labile hydrogen atom is performed in moist ether at room temperature ð56DOK"065#0975Ł[ O 2N
O 2N O 2N F
Hg + KI (or KOH)
–
2
F
K+
(39)
O2N 2
O2N O 2N F
O2N Hg
+
2
Cl O2N
2
79%
O2N O2N Cl
Hg
(40)
2
5[98[4[1 Metal Bis"phosphonyl#halomethides Halogenated methylenebis"phosphonic acids# have biological applications which are associated with their complexing properties for metal cations "Ca1¦\ Zn1¦\ etc[#[ Alkali metal salts of alkylidenebis"phosphonic acid# are known to improve the cleaning power of soaps and detergents ð55BEP561194Ł^ 0\0!bis"phosphonyl#!0!halo!0!metal derivatives are useful intermediates for the syn! thesis of substituted bis"phosphonic acids#[ The _rst preparation used a chlorineÐlithium exchange
177
One Halo`en and Three Other Heteroatoms
between dichloromethylenebis"phosphonate# and butyllithium "Equation "30## ð62JOM"48#126Ł[ Other metals "Na\ Tl# have been used as counterions ð74JOM"180#034\ 75JOM"298#C6Ł[ (RO)2P(O)
Cl
BunLi
(RO)2P(O)
(RO)2P(O)
Cl
THF, –80 °C
(RO)2P(O)
Cl Li+
–
+
BunCl
(41)
A second approach uses a!lithio!a!chloromethylphosphonates as starting materials[ Condensation with chlorophosphates in the presence of base "lithium diisopropylamide*LDA# a}ords the target compounds in quantitative yield "Equation "31## ð75JOM"293#172\ 76SC0448Ł[ (RO)2P(O)
(RO)2P(O)
2 LDA
Cl
+
–
(RO)2P(O)Cl THF, –78 °C
Cl Li+
(42)
(RO)2P(O)
Only one type of 0!halocarbanion bearing a phosphorus and a nitrogen function is known "Equation "32##[ It is used as an alkeneation reagent ð77JAP52116484Ł[ (RO)2P(O)
(RO)2P(O)
BunLi
–
X –78 °C
CN
X Li+
(43)
CN
X = Cl, Br
5[98[5 ONE HALOGEN AND ONE GROUP 04 ELEMENT Compounds of this class with a phosphorus and two silicon groups or with a phosphorus and one silicon group\ together with a lithium substituent\ have been described[ Most of them were prepared by reaction of dichlorobis"trimethylsilyl#methane with butyllithium and a trivalent chloro! phosphane "Scheme 11 and Table 7#[ The a!chlorophosphanes shown in entries 2\ 3\ and 4 are stable compounds\ while the analogous derivatives described in entries 0\ 1\ and 5 give spontaneously rearranged products at room temperature[ The product shown in entry 6 is stable at room tempera! ture\ but it rearranges to a 0!chlorophosphorane at 059>C[ TMS TMS
Cl Cl
BunLi
TMS –
TMS TMS R2R1P
R1R2P-Cl
Cl Li+
TMS R1 = R2 = Ph R1 = R2 = NMe2
Cl R1
TMS P
R2
TMS
Cl
R1 = R2 = (TMS)2CCl-Cl2C(TMS)2
TMS Cl TMS P
TMS TMS
Scheme 22
Table 7 Synthesis of chlorobis"trimethylsilyl#methylphosphanes[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R1 Chlorophosphane Yield ")# Ref[ Ent R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 0 Ph Ph Ph1PCl 72CB003 1 NMe1 NME1 "Me1N#1PCl 53a 72CB003 Cl Me1NPCl1 57 72CB003 2 NMe1 3 Ph Cl PhPCl1 72CB003 72CB003 4 Cl Cl PCl2 "0 eq# 5 ClC"TMS#1 ClC"TMS#1 PCl2 "9[22 eq# 43a 71TL1906\ 75IS006 "TMS#1CHPCl1 78CB342 6 Cl "TMS#1CH ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Reaction conditions] −009>C\ THF:ether:pentane[
a
Yields of _nal rearranged products[
178
Metalloid
In a second approach\ treatment of an a!lithio!a!~uoromethylphosphonate with bromo! or chlorotrimethylsilane gives a mixture of mono and bis"trimethylsilyl# derivatives because of a facile proton transfer "Equation "33##[ These products could not be usefully separated ð72CC775\ 75JCS"P0#0314Ł[ (PriO)2P(O)
LDA
F
+
TMS-Br (or TMS-Cl) THF, –78 °C
(PriO)2P(O) TMS TMS
(PriO)2P(O) F +
F
(44)
TMS
Only one example of a compound bearing a phosphorus\ a silicon\ a metal\ and a halogen function on the same carbon has been described[ It was prepared from diethyl trichloromethylphosphonate by chlorineÐlithium exchange in the presence of butyllithium and chlorotrimethylsilane at low temperature "Equation "34##[ The compound is obtained in quantitative yield and it can either be protonated by acids or alkylated ð77JOM"227#184Ł[ (EtO)2P(O) Cl Cl
(EtO)2P(O)
BunLi
+
Cl
–
TMS-Cl THF, –80 °C
Cl Li+
(45)
TMS
5[98[6 ONE HALOGEN AND METALLOID FUNCTION "THREE\ TWO OR ONE\ TOGETHER WITH METALS# 5[98[6[0 One Halogen and Three Metalloid Functions 5[98[6[0[0 Three silicon functions Organosilanes of this family have been widely investigated and several useful synthetic approaches have been described[ The _rst one is a carbonÐhalogen bond forming reaction] tris"trimethylsilyl#methane was halo! genated by means of NBS ð57CB1704\ 60JOM"18#278Ł or bromine under UV irradiation with or without solvents "Scheme 12# ð81OM1827Ł[ An alternative route consists of metallation of tris! "trialkylsilyl#methanes followed by halogenation of the resulting anions "Scheme 13# ð69JOM"13#418\ 75CB0344\ 78JOM"255#28Ł[ Halogenating agents are tetrabromomethane or dibromodi~uoromethane[ Crystal structure determinations of the silylated carbanionÐTHF adducts have been performed ð72CC716\ 72CC0289Ł[ TMS
Benzoylperoxide
+
TMS
NBS CCl4, 80 °C 52%
TMS TMS
hν
+
TMS
Br2 180–190 °C 75%
TMS
TMS TMS TMS
Br
TMS TMS TMS
Br
Scheme 23
TMS SiR3 TMS
MeLi
R3Si –
"Br"
TMS Li+ THF-ether
TMS R3Si = But2HSi But2FSi Me2PhSi
"Br" = CBr2F2 CBr2F2 CBr4
R3Si TMS TMS
Br
85% 90% 50%
Scheme 24
The most widely and routinely used approach is the silylation of lithiated carbanions derived from `em!dihalobis"trialkylsilyl#methanes[ While chlorobis"trialkylsilyl#methanes are not suitable reagents for preparation of the corresponding carbanions\ dichlorobis! or dibromo! bis"trialkylsilyl#methanes are readily metallated through halogenÐlithium exchange reactions[ The organolithium derivatives thus formed react with various chlorosilanes at low temperature to give the
189
One Halo`en and Three Other Heteroatoms
halotris"trialkylsilyl#methanes "Scheme 14# ð69JOM250\ 69JOM418\ 69JOM536\ 70CB1976\ 73ZAAC"409#058\ 75JOM"204#C4\ 76CB542\ 76CC0350\ 76JCS"P1#0936\ 78CC484Ł[ More often\ the halotris"trialkylsilyl# methanes were converted directly into new derivatives\ either by halogen substitution or by reactions at the silicon substituents[ X TMS TMS
TMS
BunLi
–
X THF, –100 °C
TMS
X Cl
R3SiY TMS-Cl
Br Cl Br Br Cl Cl
TMS-Cl Me2PhSiCl Me2PhSiCl (D3C)2PhSiCl (CH2=CH)Me2SiCl Y-C6H4SiMe2F Y = H, 4-MeO, 4-Cl, 3-CF3 Me2HSiCl Et2HSiCl Me2SiF2 MePhSiF2
Cl Cl Cl Cl
R3Si TMS TMS
R3SiY
Li+
X
X
Yield (%) 69 74 78 95 52 58 56 44
Scheme 25
Sodium metal may also be used to metallate dibromobis"trimethylsilyl#methane in a coupling reaction with chlorodiphenylsilane[ Bromine is then added in situ in order to perform bromination at both the carbon and silicon atoms "Scheme 15# ð78CB398Ł[ Other examples of carbonÐsilicon bond forming reactions from various starting materials have been described "Equation "35## ð66ZAAC"329#010\ 68JOM"067#00Ł[ When R02Si is a trichlorosilyl group and the electrophile is iodotrimethylsilane\ a signi_cant amount of bis"trichlorosilyl#trimethylsilylmethane "33)# is formed[ The same reaction was applied to the silylation of a cyclic six!membered carbosilane "Equation "36## ð68JOM"067#00Ł[ The _nal carbosilane could not be separated from the polymeric side products[ The yield was established after reduction of the SiCl and CCl groups with LiAlH3[ Br TMS TMS
Br
TMS
Na
+ Ph2HSiCl
– –
–2NaBr –NaCl
BrPh2Si TMS TMS
Br2
SiPh2H Na+
51%
TMS
Br
Scheme 26
Cl R13Si R13Si
i, BunLi ii, R23SiX
Cl
R13Si PhMe2Si Cl3Si Cl3Si Cl Cl Cl
Si
Cl Cl
Si
Cl Cl
Si Cl
R23Si R13Si R13Si Yield (%) 40 42 25
R23SiX PhMe2SiCl TMS-I TMS-Cl
Cl i, BunLi ii, TMS-I THF, –100 °C 42%
(46)
Cl
Cl Cl
Si
Cl TMS
Si
Cl Cl
Si Cl
+
polymers
(47)
After reaction between TMSCCl1SiMe1Cl and butyllithium at −099>C in ether\ and subsequent warming to 19>C\ dimeric carbosilanes are formed as the main products "Equation "37##[ Puri_cation by HPLC allowed elimination of the by!products and a}orded a mixture of the two isomers ð73JOM"160#096Ł[
180
Metalloid ClMe2Si TMS TMS
Me Me TMS Cl Si
BunLi
Me Me TMS TMS Si (48)
+
Cl ether, –100–20 °C
Cl TMS Si Me Me
Cl Cl Si Me Me
A great number of bromotris"trialkylsilyl#methane derivatives "Table 8# have been obtained in high yields through further displacement of a phenyl or a hydrogen "Y# by chlorine or bromine in "YR1Si#"TMS#1CBr\ as shown in Equation "38#[ Bromine substitution reactions at the silicon atom are also e}ected by various nucleophiles "AgF\ MeOH\ AgOP"O#Ph1\ etc[#\ as shown in Equation "49# and Table 09[ Table 8 Synthesis of "XR1Si#"TMS#1CBr "X Cl\ Br#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R Y X Rea`ents and conditions Yield ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me Ph Br Br1\ 59>C\ 1 h 85 70CB1976 Me Ph Cl Cll\ 69>C\ 19 h 63 70CB1976 Me Ph I I1\ 029>C\ 7 h 59 70CB1976 Ph Br Br1\ 59>C 71 76CB542 CD2 Ph H Br Br1 85 78CB398 77 78CB398 Ph H Cl Cl1 t Bu H Br Br1\ CCl3 099 75CB0344 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
YR2Si TMS TMS BrR2Si TMS TMS
+
Br
+
Br
XR2Si TMS TMS
X2
Br
XR2Si TMS TMS
X–
+
Br
(49)
YX
+
(50)
Br–
Table 09 Synthesis of "XR1Si#"TMS#1CBr[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Ent R X Rea`ents and conditions Yield ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 0 CD2 F AgF\ 59>C\ THF 56 76CB542 1 Me F AgF\ 55>C\ 49 h\ THF 37 70CB1976 78 78CB398 2 Ph F KHF1\ 53>C\ 1[4 h\ MeOH 82 78CB398 3 Ph OH H1O\ 14>C\ 61 h\ THF 4 Me OH H1O\ 14>C\ 0 h\ pentane 84 70CB1976 58 70CB1976 5 Me MeO MeOH : Et2N\ 54>C\ 09 h 6 Ph MeO MeOH\ 53>C\ 5 h 89 78CB398 7 Me PhO PhONa\ 000>C\ 099 h\ toluene 76 70CB1976 8 Me PhS PhSNa\ THF 40 70CB1976 09 Me 3!Me[C5H3SO1 AgX\ 14>C\ 3 h\ THF 77 70CB1976 00 Me 3!Me[C5H3SO1 AgX\ 045>C\ 0[4 h\Bu1O 64 70CB1976 AgX\ 14>C\ 3 h\ THF 79 70CB1976 01 Me MesSO2 02 Me Ph1P"O#O AgX\ 14>C\ 3 h\ THF 74 70CB1976 03 Me "PhO#PhP"O#O AgX\ 14>C\ 3 h\ THF 84 70CB1976 AgX\ 14>C\ 3 h\ THF 79 70CB1976 04 Me "PhO#1P"O#O ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Chlorotris"methoxydimethylsilyl#chloromethane can be prepared from chlorotris"trimethyl! silyl#methane by addition of a large excess of ICl in tetrachloromethane\ followed by a methanolÐ triethylamine mixture "Scheme 16# ð81JCS"D#0904Ł[ TMS TMS TMS
ICl
Cl CCl4, 20 °C, 4 h
ClMe2Si ClMe2Si ClMe2Si Scheme 27
Cl
MeOH/Et3N 20 °C, 72 h 65%
MeOMe2Si MeOMe2Si MeOMe2Si
Cl
181
One Halo`en and Three Other Heteroatoms
5[98[6[0[1 Two silicon and a germanium function Compounds containing two silicon functions and one germanium function have been prepared according to the general approaches reported above for the synthesis of halo! tris"trialkylsilyl#methanes "see Section 5[98[6[0[0#[ Thus\ chlorodimethylphenylgermane reacted with bromotris"trimethylsilyl#methyllithium at low temperature to give the corresponding germyldisilyl derivative "Equation "40## ð75CB1855Ł[ Cleavage of the phenyl substituent was then performed with bromine "Equation "41##[ The colorless\ solid product was obtained in good yield[ As reported above for silicon "Section 5[98[6[0[0#\ the bromo function on germanium can participate in further substitution reactions[ Br TMS TMS
i, BunLi ii, PhMe2Ge-Cl
Br
THF, Et2O, –110 °C 86%
PhMe2Ge TMS TMS
Br2
Br
60 °C, 2 h 88%
PhMe2Ge TMS TMS
Br
(51)
BrMe2Ge TMS TMS
Br
(52)
5[98[6[0[2 Two silicon and a boron function The only example of such compounds is bromoðbromobis"isopropyl#aminoborylŁbis"trimethyl! silyl#methane[ It is prepared by bromine addition to the corresponding methylidene! bis"isopropyl#aminoborane\ as shown in Equation "42# ð78CB484Ł[ The starting material is obtained by the thermolysis of ð~uorobis"isopropyl#aminoborylŁtris"trimethylsilyl#methane in the gas phase at 419>C "Equation "43##[ Br Pri2NB TMS Br TMS 79%
TMS Pri
+
2NB
Br2
TMS
Br
+
F Pri2NB TMS TMS
520 °C
TMS
Pri2NB
(53)
TMS TMS 21% TMS
(54)
Pri2NB
–TMS-F
TMS
5[98[6[0[3 Three boron functions or two boron and a metal function Conversion of tetrakis"tetramethylethylenedioxyboryl#methane to the corresponding tri! borylmethide anion is performed by adding two equivalents of methyllithium at low temperature ð63JOM"58#34Ł[ The lithiated carbanion is treated in situ with bromine in dichloromethane to a}ord the crystalline bromotriborylmethane "Scheme 17#[ This last compound reacts with one equivalent of methyllithium to give the bromodiborylmethide anion^ however the conversion is incomplete under these conditions[ The reaction of the carbanion with chlorotriphenyltin was performed but the _nal product was not completely characterized "Scheme 18#[ An analogous iodo derivative "C2H5O1B#1"Ph2Sn#CI was more fully characterized ð62JOM"46#120Ł[ The same approach has been applied to the synthesis of tris"trimethylenedioxyboryl#methane derivatives ð62JA4985\ 64JOM"82#10Ł[ The THF insoluble boryl substituted lithium salt was puri_ed by precipitation\ before reaction with bromine "Scheme 29#[
O B
C
O
2 MeLi
O B
C– Li+
CH2Cl2 82%
O 4
Br2
3
Scheme 28
O B
CBr
O 3
182
Metalloid O B
CBr
O
MeLi
B
–
Li+ Br
O
O 3
SnPh3
O
Ph3Sn-Cl
B O
Br 2
2
Scheme 29
O O
O
2 BunLi
B C
O
4
O
Br2
B C– Li+
B
CH2Cl2, –75–25 °C 42%
3
O
CBr 3
Scheme 30
5[98[6[1 One Halogen\ Two Metalloid\ and One Metal Function This class of compounds contains\ principally\ bis"trimethylsilyl#lithium derivatives which have been studied as potential precursors for metalloid substituted carbenes[ Dihalobis"trimethylsilyl#methanes are readily metallated with butyllithium at low temperature through a halogenÐlithium exchange reaction "Equation "44## ð69JOM"12#250\ 69JOM"13#536\ 69TL3582Ł[ The lithium salts are stable at −009>C[ In the absence of a trapping reagent\ the salts dimerize to give tetrasubstituted ethylene derivatives ð56AG"E#30\ 61AG"E#362Ł[ They were reacted with silicon\ tin\ germanium\ and phosphorus dihalogenides to a}ord 0\2!disila!\ distanna!\ or digerma!cyclobutanes ð63JA5126Ł and bis"methylene#phosphoranes\ respectively ð71AG"E#79Ł[ Preparation of the analogous organomercury reagent was carried out with "TMS#1C"Cl#Li and mercuric chloride in a 2 ] 0 ratio^ the yield of ð"TMS#1ClCŁ1Hg was 47)[ The major by!product has been isolated and characterized as a dimercury compound "Equation "45## ð69JOM"12#250Ł[ X TMS TMS
BunLi
TMS
THF, Et2O, pentane –110 °C
TMS
–
X
(55)
X Li+
X = Cl, Br
TMS ––
Cl
Li+
HgCl2
TMS
Cl TMS TMS
Hg 2
58%
+
Cl TMS TMS
TMS Hg
Hg TMS
Cl TMS TMS
(56)
3.4%
5[98[7 ACKNOWLEDGEMENTS In collecting the literature\ the authors have bene_ted greatly from collaboration with Mrs Francžoise Girard and Martine Rouyer\ who are gratefully acknowledged[
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.10 Functions Containing Four or Three Chalcogens (and No Halogens) ALEX H. GOULIAEV Aarhus University, A˚rhus, Denmark and ALEXANDER SENNING Technical University of Denmark, Lyngby, Denmark 5[09[0 TETRACHALCOGENOMETHANES 5[09[0[0 Four Similar Chalco`ens 5[09[0[0[0 Four oxy`en functions 5[09[0[0[1 Four sulfur functions 5[09[0[0[2 Four selenium or tellurium functions 5[09[0[1 Three Similar and One Different Chalco`en 5[09[0[1[0 Trioxy`en!substituted methyl chalco`ens 5[09[0[1[1 Trisulfur!substituted methyl chalco`ens 5[09[0[1[2 Triselenium! or tritellurium!substituted methyl chalco`ens 5[09[0[2 Two Similar and Two Different Chalco`ens 5[09[0[2[0 Dioxy`en!substituted methylene dichalco`ens 5[09[0[2[1 Disulfur!substituted methylene dichalco`ens 5[09[0[2[2 Diselenium! or ditellurium!substituted methylene dichalco`ens
184 185 185 290 296 297 297 298 200 200 201 201 202
5[09[1 TRICHALCOGENOMETHANES 5[09[1[0 Methanes Bearin` Three Oxy`ens and a Group 04 Element\ Metalloid or Metal Function 5[09[1[1 Methanes Bearin` Three Sulfurs and a Group 04 Element\ Metalloid or Metal Function 5[09[1[2 Methanes Bearin` Three Seleniums or Three Telluriums and a Group 04 Element\ Metalloid or Metal Function 5[09[1[3 Methanes Bearin` Three Dissimilar Chalco`ens and a Group 04 Element\ Metalloid or Metal Function
202 202 203
5[09[0 TETRACHALCOGENOMETHANES The compounds discussed here conform to the general formula "0#\ where X is a chalcogen[ X2R2 X3R3 X4R4
R1X1 (1)
184
206 206
185
Four or Three Chalco`ens
5[09[0[0 Four Similar Chalcogens Only the fully substituted derivatives of ortho!carbonic acid "1#\ tetrathioortho!carbonic acid "2#\ and tetraselenoortho!carbonic acid "3# are of preparative signi_cance in the synthesis of tetra! chalcogenomethanes with four similar chalcogens\ ðB!69MI 509!90\ B!69MI 509!91Ł[ With just one R group equaling hydrogen\ the lability of the compounds restricts them to being intermediates\ if present at all\ in solvolytic reaction sequences\ etc[ Tetratelluroortho!carbonates "4# are unknown[ Most known examples of "0# are symmetrically substituted^ acyclic as well as cyclic and spirocyclic versions of "0# have been prepared[ Examples of "0# where one or several chalcogen atoms "X S\ Se# are in a higher oxidation state than 1 are known\ but are rather rare ðB!69MI 509!91Ł[
R 1O
OR2 OR3 OR4 (2)
SR2 SR3 SR4
R1S (3)
SeR2 SeR3 SeR4
R1Se
TeR2 TeR3 TeR4
R1Te
(4)
(5)
5[09[0[0[0 Four oxygen functions Derivatives with four oxygen functions are derivatives of ortho!carbonic acid\ C"OH#3\ and have been reviewed extensively ðB!69MI 509!90\ 72HOU"E3#583Ł[ The vast majority are simple ortho!esters ""1# with R alkyl or aryl\ including cyclic and spirocyclic compounds#\ but mixed ester ortho!esters ""1# with R acyl# have also been described[ The available synthetic methods can be classi_ed as involving basic or acidic conditions[ In the latter case simple alkanols "which readily form carbenium ions under acidic conditions and are thus subject to C0O bond cleavage# can often not be used as starting materials[ An exception are 0!alkanols with strongly electron!withdrawing substituents "such as chlorine\ ~uorine\ or nitro substituents# in the 1!position\ where the formation of the corresponding carbenium ions is disfavored[ Those synthetic methods which also allow the elabo! ration of unsymmetrically substitutedortho!carbonic acid esters are particularly valuable "Tables 0Ð4#[ The preparation of symmetrical ortho!carbonates "1# is possible from appropriate C0 synthons "e[g[\ tetrachloromethane "5#\ trichloronitromethane "chloropicrin# "6#\ trichloromethanesulfenyl chloride "perchloromethyl thiol# "7#\ trichloroacetonitrile "8#\ trialkoxyacetonitriles "09#\ tri! chloromethyl isocyanide dichloride "00#\ aryl cyanates "01#\ and trialkoxycarbenium salts "02# and alkanols:metal alkoxides or phenols:phenoxides ð72HOU"E3#583Ł[ While the tetrasubstitution of tetrachloromethane "5# generally fails with simple alkoxides\ it does proceed satisfactorily with copper"I# phenoxides "Equation "0## ð63TL3398Ł[ The catalytic action of iron"III# chloride permits the corresponding synthesis of aliphatic ortho!carbonates "1# derived from 1!~uoro and:or 1!nitro substituted alkanols under acidic conditions "Equation "1## ð54JOC300Ł[ MeCN
CCl4 + 4ArOCu
C(OAr)4
(1)
40–60%
(6)
CCl4 +
(2)
R X
(6)
X
FeCl3
OH
–4HCl 20–92%
C(OCH2CX2R)4
(2)
(2)
Trichloronitromethane "6# and trichloromethanesulfenyl chloride "7# are more generally appli! cable as C0 synthons "Scheme 0# ð37JOC154Ł[ These reactions fail when applied to branched alkoxides[ Trialkoxyacetonitriles "09# have been particularly focused upon as precursors of ortho!carbonates "1# ð66S62\ 71LA496Ł[ Trichloroacetonitrile "8# reacts with alkoxides "including branched alkoxides# via the corresponding trialkoxyacetonitriles "09# to form ortho!carbonates "1# "Scheme 1#[ Both symmetrical "Alk0 Alk1# and unsymmetrical "Alk0 Alk1# tetraalkyl ortho!carbonates "1# are accessible in this way[ A broadly applicable synthesis of symmetrical tetraaryl ortho!carbonates "1# "including spirocyclic ortho!carbonates derived from dihydroxyarenes# employs trichloromethyl isocyanide dichloride
Tetrachalco`enomethanes Table 0 Selected symmetrical acyclic ortho!carbonates C"OR#3 "1#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R Boilin` point Meltin` point Ref[ ">C:torr# ">C# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me 003 −4[4 66S62 CF2 19[7 78JOC0889 Et 048 66S62 CCl2CH1 020 61S488 79:1[7 54JOC300 CClF1CH1 CF"NO1#1CH1 025 57USP2277036 052 56USP2295828 C"NO1#2CH1 CF2CF1 79 78JOC0889 Pr 113 37JOC154 Pri 69:09 66S62 CH11CHCH1 099:00 71LA496 54:9[0 54JOC300 CHF1CF1CH1 021 78JOC0889 CF2CF1CH1 Bu 162 37JOC154 Bui 134 26JCS716 CHF1"CF1#1CH1 024:9[94 54JOC300 i 70Ð71:9[9990 66S62 Pr "CH1#1 Me1CH"CH1#1 057:00 71LA496 67Ð68 66S62 ButCH1 CHF1"CF1#2CH1 024:9[94 54JOC300 Me"CH1#4 073Ð074:1 38DOK"57#404 090Ð092 66S62 c!C5H00 069:9[997 54JOC300 CHF1"CF1#4CH1 Me"CH1#6 131:1 −21 64FRP1124077 Me"CH1#7 126Ð139:0[4 38DOK"57#404 177Ð189:1 38DOK"57#404 Me"CH1#8 098Ð009:9[997 B!69MI 509!90 Ph"CH1#1 Ph 87 61S488 2!MeC5H3 73Ð74 63TL3398 3!MeC5H3 090 63TL3398 1!ButC5H3 148Ð159 61S488 044 61S488 1!ClC5H3 018Ð029 63TL3398 3!ClC5H3 3!"O1N#C5H3 116 61S488 001 61S488 3!"MeO1C#C5H3 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Table 1 Selected unsymmetrical acyclic ortho!carbonates C"OR0#2OR1 "1#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R1 Boilin` point Ref[ R0 ">C:torr# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me Bu 71LA496 Me Bus 71LA496 Me Et1N"CH1#1 71Ð72:04 71LA496 Et Me 051 66S62 Et Pr 53Ð55:09 71LA496 89Ð81:09 71LA496 Et Et1N"CH1#1 Et Ph 59Ð51:9[990 71LA496 Et 3!ClC5H3 89Ð81:9[990 71LA496 Bu Me 72HOU"E3#583 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Table 2 Selected unsymmetrical acyclic ortho!carbonates C"OR0#1"OR1#1 "1#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0 R1 Boilin` point Ref[ ">C:torr# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me Et 71LA496 Me Bu 72HOU"E3#583 Et c!C5H00 82Ð88:00 71LA496 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
186
187
Four or Three Chalco`ens Table 3 Selected unsymmetrical cyclic ortho!carbonates "1#[
Compound
Boiling point (°C/torr)
O
Ref.
OMe 71/15
84S837
O OMe O OMe 62/0.15 O
70USP3503993
OMe
O O
OMe
O
OMe
O
OEt
O
OEt
O
OPr
O
OPr
114.5/16
82LA507
123/15
64LA(675)142
147/12
64LA(675)142
Table 4 Selected spirocyclic ortho!carbonates "1#[ Compound
Boiling point (°C/torr) O
O
O O O O
Melting point (°C)
Ref.
145 121.0–121.5
77S73 92MM3829
86JAP(K)61289091 O
O
O
O
O
O
O
O
O
O
O
O
O
O
90–94/11
77S73
109–110 Ph 58 Ph
O
O
O
O
O
84S837
92MM3829
68/1.0
84S837
70/5
84S837
O
O O O O 138
82LA507
138.5
77S73
138.5
82LA507
O O O O O O O O O O
188
Tetrachalco`enomethanes Table 4 "continued#[
ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Compound Boilin` point Meltin` point Ref[ ">C:torr# ">C# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
O O 111
84S837
110
67JHC166
113
72S599
O O
But
O
O
O
O
O
O
O
O
But
O
O
O
O
O
O
O
O
156–157
86JOC370
>340
86JOC370
340
72S599
225
72S599
O O O O
Cl
Cl
O O O O
Cl
Cl
CCl3NO2 + 4AlkO– (7) AlkO–
CCl3SCl (8)
C(OAlk)4 (2)
CCl3SOAlk
3AlkO–
C(OAlk)4 (2)
Scheme 1
CCl3CN (9)
Alk1O–
Alk2O–
(Alk1O)3CCN (10)
60–80%
C(OAlk1)3OAlk2 (2)
Scheme 2
"N!trichloromethylcarbonimidic dichloride# "00# as its C0 synthon "Equation "2## ð61S488Ł[ This method is unsuitable for the preparation of aliphatic ortho!carbonates "1# "with the exception of tetrakis"1\1\1!trichloroethyl# ortho!carbonate#\ since these are cleaved by the hydrogen chloride evolved[ Cl
+ 4ArOH
N Cl3C (11)
Cl
1,2-C6H4Cl2 170 °C 66–92%
C(OAr)4 (2)
(3)
299
Four or Three Chalco`ens
Aryl cyanates "01# react with alkanols under acidic conditions to form tetraalkyl ortho!carbonates "1# in 19Ð39) yield "Equation "3## ð54CB2175Ł[ H+
ArOCN + 4AlkOH
(4)
C(OAlk)4 20–40%
(12)
(2)
Symmetrical tetraalkyl ortho!carbonates "1# are obtained from trialkoxycarbenium tetra~uoro! borates "02# and alkoxides "Equation "4## ð45CB1959Ł[ (AlkO)3C+ BF4–
AlkO–
(5)
C(OAlk)4
(13)
(2)
Treatment of thallium"I# alkoxides with carbon disul_de leads to O\O?!dialkyl thiocarbonates "03#\ which react further with the starting thallium compound to yield tetraalkyl ortho!carbonates "1#\ the driving force undoubtedly being the formation of the extremely insoluble thallium"I# sul_de "Scheme 2# ð61JOC3087Ł[ Dialkoxydibutylstannanes and carbon disul_de react similarly "Scheme 3# ð60JOC0065Ł[ Thiocarbonates "03# can also be similarly desulfurized by treatment with sodium carbonate to yield spirocyclic ortho!carbonates "1# ð56JHC055Ł[ RO
–Tl2S
2RO– Tl+ + CS2
2RO– Tl+
S
C(OR)4 –Tl2S
RO (14)
(2)
Scheme 3
RO
–Bu2SnS
Bu2Sn(OR)2 + CS2
S
Bu2Sn(OR)2
C(OR)4
–Bu2SnS
RO (14)
(2)
Scheme 4
Carbonic acid diesters "04# can be converted to the corresponding dichloro derivatives "05# with phosphorus pentachloride^ these in turn are treated with phenols or phenoxide ions to yield tetra! aryl ortho!carbonates "1#[ Unsymmetrical ortho!carbonates "1# can also be prepared in this way "Scheme 4# ð53LA"564#031Ł[ R1O
PCl5
R1O
Cl
2R2OH
R1O
OR2
R1O Cl (16)
–2HCl 78–93%
R1O
OR2
O R1O (15)
–POCl3
(2)
Scheme 5
Trans!esteri_cation of ortho!carbonates "1# with alkanols is another method for the preparation of ortho!carbonates\ even allowing the synthesis of unsymmetrically substituted esters[ Spirocyclic ortho!carbonates are obtained with a\v!alkanediols ð66S62\ 71LA496\ 81MM2718Ł[ With equimolar amounts of a\v!diol and tetramethyl ortho!carbonate\ a half!exchanged monocyclic intermediate can be isolated which\ with a second a\v!diol\ can form an unsymmetrical spirocyclic compound "Scheme 5# ð73S726Ł[ In principle all possible scrambling products of the trans!esteri_cation of ortho!carbonates C"OR0#3 with alcohols R1OH can be obtained "Scheme 6#[ Spirocyclic and oli! gospirocyclic ortho!carbonates "1#\ including unsymmetrical and substituted versions\ have been prepared in considerable variety as monomers for the production of polymers ð81JAP"K#93053974Ł[ Typical examples are 0\3\5\8!tetraoxaspiroð3[3Łnonane\ 0\3\5\09!tetraoxaspiroð3[4Łdecane\ 0\4\6\00! tetraoxaspiroð4[4Łundecane\ 0\4\6\01!tetraoxaspiroð4[5Łdodecane\ 0\5\7\02!tetraoxaspiroð5[5Łtri! decane\ and 7\09\08\19!tetraoxatrispiroð4[1[1[4[1[1Łheneicosane[ Trans!esteri_cation of spirocyclic ortho!carbonates with diols to yield new spirocyclic ortho!carbonates "1# has also been reported ð75JAP"K#50178980Ł[
290
Tetrachalco`enomethanes R1O
H+
C(OR1)4 + R2OH
OR2
R1O OR (2)
(2)
R2OH
C(OR2)4
2
(2)
Scheme 6 C(OAlk1)4
Alk2OH
C(OAlk1)3OAlk2
Alk2OH
C(OAlk1)2(OAlk2)2
(2)
(2)
Alk2OH
(2) Alk2OH
COAlk1(OAlk2)3
C(OAlk2)4 (2)
(2) Scheme 7
Simple ortho!carbonates such as tetramethyl\ tetraethyl\ and tetrapropyl ortho!carbonate can be ~uorinated with helium!diluted ~uorine in a cryogenic reactor to yield the corresponding per! ~uorinated ortho!esters[ The hydrogen ~uoride formed during the ~uorination is scavenged with solid sodium ~uoride to prevent cleavage of the carbonÐoxygen bonds "Equation "5## ð76JFC"26#216\ 78JOC0889Ł[ F2/NaF
C(OCnH2n+1)4
–120 °C 18–56%
(2) n = 1, 2, 3
C(OCnF2n+1)4
(6)
(2)
5[09[0[0[1 Four sulfur functions Compounds "2#\ including a considerable number of heterocyclic and spiroheterocyclic tetrathio! ortho!carbonic acid esters such as 1\1!dithio substituted 0\2!dithioles and 0\2!dithianes\ were brie~y reviewed in 0880 ð80SUL136Ł[ Tetrathioortho!carbonic acid and its tetrasodium salt are known\ but they are without preparative importance[ The simplest type of organic compounds _tting the above description are the symmetrical tetrathioortho!carbonates C"SR#3\ available from the corresponding alkali metal thiolate and a C0 synthon such as tetrachloromethane "5# "Scheme 7# ð72HOU"E3#694Ł[ With trichloromethanesulfenyl chloride "7# the corresponding reaction leads to tetrathiomethane units containing symmetrical disul_des "RS#2CSSC"SR#2 "06# "R Et\ Pr\ Bu\ But# in the case of aliphatic thiols "Equation "6## and trisul_des "RS#2CSSSC"SR#2 "R Ph\ 1!ClC5H3\ 3!ClC5H3\ 2!MeC5H3\ 3!MeC5H3\ 1\3\5!Me2C5H1\ 3!ButC5H3# in the case of aromatic thiols ð41RTC0960Ł[ Examples of "2# are shown in Tables 5Ð8[ –4NaCl
CCl4 + 4RSNa (6)
C(SR)4 (3) RSSR + HC(SR)3
Scheme 8
CCl3SCl (8)
+ RSNa
–RSSR
(RS)3CSSC(SR)3 (17)
(7)
Tris"methylthio#carbenium cations react with excess thiols\ RSH\ to give the corresponding tetrathioortho!carbonates C"SR#3 "Equation "7## ð57JOC2222Ł[ Unsymmetrical tetrathioortho! carbonates "R0S#1C"SMe#SR1 can be obtained from 1!"methylthio#!0\2!dithiolium cations and thi! olate anions R1S− "Equation "8## ð53ZC273Ł[ N\N?!Dinitroso!S!alkyl! or !arylisothioureas "08#\ obtained in situ from isothioureas "07# and nitrous acid\ have been reported to yield unsymmetrical or symmetrical tetrathioortho!carbonates "2# with thiols and symmetrical tetrathioortho!carbonates with base "Scheme 8 and Equations "09# and "00##[ The impossibility of obtaining tetra!t!butyl tetrathioortho!carbonate C"SBut#3 in this way has been stressed[ This is probably not due to problems with the method\ but rather to prohibitive steric congestion ð72HOU"E3#694Ł[
291
Four or Three Chalco`ens Table 5 Selected symmetrical acyclic tetrathioortho!carbonates C"SR#3 "2#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R Boilin` point Meltin` point Ref[ ">C:torr# ">C# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me 016:00 55 77S11 CF2 71:69 56JOC1952 Et 24[4 61RTC0006 Pr 012:9[05 57JOC2222 50[3 61RTC0006 Pri c!C5H00 058 70JAP"K#45014215 75MI 509!90 Me"CH1#4CHMe Me"CH1#09 75MI 509!90 75MI 509!90 Me"CH1#00 Me"CH1#06 62GEP0583109 Ph 048 61CB2179 3!BrC5H3 100 56BSF2122 101[5Ð102[5 61CB2179 3!ClC5H3 3!FC5H3 058 63CC523 015[2Ð016[7 61CB2894 1!MeC5H3 3!MeC5H3 036 63CC523 045 63CC523 3!MeOC5H3 1!naphthyl 025 57JOC2222 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Table 6 Selected unsymmetrical acyclic tetrathioortho!carbonates C"SR0#2SR1 "2#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0 R1 Boilin` point Meltin` point Ref[ ">C:torr# ">C# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me 74Ð75:9[1 61CB2179 Pri Ph Me 84[1Ð84[7 61CB376 Ph CF2 58ZOB0644 Ph 3!ClC5H3 080 02LA"285#0 3!CIC5H3 082 02LA"285#0 1!MeC5H3 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
–3MeSH
[(MeS)3C]+ [BF4]– + 4RSH
–H[BF4]
S +
SMe
(8)
C(SR)4 (3) S
SMe
S
SR
+ RS–
(9)
S
(3)
NH RS
N
HNO2
NH2
RS
(18)
NO 3RSH
N H (19)
NO
C(SR)4 –2N2, –2H2O
(3)
Scheme 9
N Alk
NO N H
S
NO
+ 3AlkSH
–2N2
C(SAlk)4 (3)
(19)
N RS
NO
N H (19)
NO
(10)
–2H2O
NH
+
RS
NH2 (18)
base
C(SR)4 –6N2, –4H2O
(3)
(11)
292
Tetrachalco`enomethanes Table 7 Selected cyclic tetrathioortho!carbonates "2#[ Compound
Melting point (°C)
F3CS
S
F3CS
S
F3CS
S
SCF3
F3CS
S
SCF3
O
S
SMe
S
SMe
Ref.
(boiling point 50 °C/10 torr)
77CB916
(boiling point 44 °C/5 torr)
77CB916
67AG(E)442
32.7 SMe
S
SMe
S
SPh
S
SMe
S
SC6H4Cl-4
S
SMe
S
SC6H4(NO2)-4
S
SMe
MeS MeS
S
S
S
SMe
S
SMe
64ZC384
63
64ZC384
88
64ZC384
93
64ZC384
21.5 (boiling point 88 °C/0.6 torr)
72CB3280
SMe
S
S
38
S
SMe 75RTC1
S (30)
72BCJ960
148.0–148.5 S
S
SO2C6H4Me-4 4-MeC6H4SO2 (35)
Dithio! ð51RTC0998Ł and trithiomethanide ð61CB2179Ł ions can be sulfenylated with dialkyl or diaryl disul_des to yield the corresponding symmetrical or mixed tetrathioortho!carbonates "2# "Equations "01#Ð"04##[ Na+ –[CH(SEt)2] + EtSSEt
Li+ –[C(SMe)3] +
S S – Li+
MeSSMe
+ MeSSMe S
NaNH2/NH3
–MeSLi
C(SEt)4 (3)
C(SMe)4 (3)
(12)
(13)
S
–MeSLi
(14) S MeS
S (3)
293
Four or Three Chalco`ens Table 8 Selected spirocyclic tetrathioortho!carbonates "2#[
Compound
Melting point (°C) S
S
CF3
S
S
CF3
Ref.
85.5–86.5
70JOC3470
142–143
67JOC2567
209
91CB2025
S
S
S S CF3 S S S
S
CF3
(32) S
S
S
S
88EUP293749 S
S
SMe
S
S
SAc
83MI 610-01 F3C
S
S
F3C
S
S
CF3 44
91CB2025
130
67JOC2567
120
67JOC2567
165
70JHC201
CF3
(33) S
S
S S S S S
S
S S S S S
S
S
S
117.5–120.0
75JCS(P1)270
S S 82BCJ1106 S S S
S 163
76JPR(318)127
S S (27) S
S
S
S
O
S
S
O
O
S
S
O
O O
120–121
61E566
237–238
65LA(689)179
O O
SS S
S S
S Ph
160.5–161.0 (dec.)
67CB767
294
Tetrachalco`enomethanes Table 8 "continued#[
Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Compound Boilin` point Ref[ ">C# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
S
S
S
S
187–188
86JOC370
–CH2(SR1)2
2Li+ –[CH(SR1)2] + 2R2SSR2
C(SR1)2(SR2)2 –2R2SLi
(15)
(3)
The cyclic trithiocarbonate 0\2!dithiane!1!thione "19# has been treated with a secondary amine to form the corresponding spirocyclic tetrathioortho!carbonate "2# "Equation "05## ð51JOC3957Ł[ 0\2! Dithiolane!1!thione "12# reacts with 1!phenyloxirane "44^ R Ph# to yield the corresponding mono! substituted 0\3\5\8!tetrathiaspiroð3[3Łnonane as a by!product "cf[ Scheme 08# ð80HCA0499Ł[ S 2
S
–S=C[N(CH2CH2OH)2]2
+ HN(CH2CH2OH)2
S
(16)
–H2S
S (20)
S
S S (3)
Similarly\ cyclic trithiocarbonates such as "19# and cyclic "N!cyanoimino#dithiocarbonates "10# react with a\v!alkanedithiols to form the corresponding symmetrical or unsymmetrical spirocyclic compounds "2# "Scheme 09 and Equation "06## ð56JOC1456\ 61USP2541145Ł[ S
S S
+ HS
SH
SH
S (3) Scheme 10
S (20)
SH
S
HS
CN
S n( )
N S
SH ( )m
(21)
S
–H2S
n(
S
S
S
S
S S (3)
( )m
)
S
(17)
(3)
Carbon disul_de has been subjected to double insertion of an a!thioxo carbene leading to a symmetrical spirocyclic compound "Equation "07## ð50E455Ł[ N 2
+ CS2
N S
∆
S
S
–2N2
S
S
(18) (3)
The ð1¦1Ł addition of a thioketene such as bis"tri~uoromethyl#thioketene "11# to a cyclic tri! thiocarbonate such as 0\2!dithiolane!1!thione "12# has been shown to yield the corresponding unsymmetrical spirocyclic compound "Equation "08## ð69JOC2369Ł[ F3C
S •
F3C (22)
S
+
S
S
CF3
S
S (3)
CF3
(19)
S S (23)
The 1!azido!0\2!dithiole "13# decomposes in boiling dioxan with formation of the corresponding
295
Four or Three Chalco`ens
spirocyclic tetrathioortho!carbonate "16#[ The corresponding carbene "14# "formed by loss of hydra! zoic acid# and 0\1!cyclohexanedithione "15# "formed by loss of nitrogen and hydrogen cyanide# have been invoked as putative intermediates "Scheme 00#[ A more rational synthesis of "16# from sodium 0\1!cyclohexenedithiolate "18# and a trithiocarbenium salt "17# "Equation "19## has been developed by the same author ð65JPR016Ł[ S –N2
S
–HCN
S
(26)
S (24)
S
19%
N3 –HN3
S
S S (27) m.p. 162–164 °C
S : S (25) Scheme 11
S +
SMe I–
S–Na+
EtOH
S–Na+
reflux, 30 min 61%
S
S
+
(20)
S (28)
(29)
S S (27)
The obscure reaction of methyl chlorodithioformate with methylmagnesium iodide furnishes the tetrathiepane derivative "29# "Table 7# ð64RTC0Ł[ Finally\ trans!esteri_cation of symmetrical tetrathioortho!carbonates "2# with thiols\ including a\v!alkanedithiols\ is possible "Equation "10## ð69JHC190Ł[ A number of benzo annellated 0\3\5\8! tetrathiaspiroð3[3Łnonanes with polymerizable alkenyl side chains have been prepared in this way ð78JAP"K#90071200Ł[ Interestingly\ there is no record of the corresponding trans!esteri_cation of ortho! carbonates "1# with thiols[ HS
C(SMe)4
( )n
SH n(
TsOH/C6H6
S
S
S
S
)
( )n
(3)
(21)
(3)
Treatment of 1\1!dichloro!2\3!bis"tri~uoromethyl#!0\2!dithiole "20# with 0\1!ethanedithiol leads to the corresponding unsymmetrical tetrathiaspiro compound "21#[ The latter reacts with 0\0\0\2\2\2! hexa~uoro!1!butyne to yield 1\2\6\7!tetrakis"tri~uoromethyl#!0\3\5\8!tetrathiaspiroð3[3Łnona!1\6! diene "22#\ which is also formed by oxidation of the corresponding monocyclic sul_ne "23# with m! chloroperbenzoic acid "Scheme 01# ð80CB1914\ 83CB422Ł[ F3C
S
Cl
HSCH2CH2SH
S
F3C
S
Cl
57%
S
S CF3 (32) m.p. 209 °C
(31)
S
S
CF3
S
S
CF3
F3C
CF3
F3C
S
S
CF3
F3C
S
S
CF3
mcpba
F3C
S
F3C
S
S
–CH2=CH2
(32) m.p. 209 °C
CF3
S
(33) m.p. 44 °C
42%
O
(34)
Scheme 12
Of the many theoretically possible partially or fully oxidized derivatives of tetrathioortho!carbon! ates\ only a few have been prepared[ Partially ð22RTC812\ 22RTC0928Ł and fully ð00LA"273#211Ł S! brominated derivatives of symmetrical compounds are known "Scheme 02#[ The corresponding S! iodination of tetramethyl tetrathioortho!carbonate stops after the introduction of three S!iodo
296
Tetrachalco`enomethanes
functions[ Additional iodine does not attack the fourth sulfur atom\ instead it attacks the iodide ions to form triiodide ions "Scheme 03#[ C(SR)4 + 4Br2 (3)
CHCl3
–2Br2
+
[ C ( SR )4 ] 4Br–
+
[ (RS)2C ( SR )2 ] 2Br–
Br
EtOH
(RS)2C ( SR )2
Br
O
Scheme 13
C(SMe)4 + 2I2 (3)
CS2
+
[ (MeS)2C ( SMe )2 ] 2I–
I2
+
[ MeSC ( SMe )3 ] 3I–
I
I2
+
[ MeSC ( SMe ) ] 3I3–
I
I
Scheme 14
The disulfoxide tetraphenyl tetrathioortho!carbonate S\S?!dioxide has been prepared by solvolysis of the corresponding S\S\S?\S?!tetrabromo derivative "Scheme 02# ð22RTC0928Ł[ Disulfones "R0S#1C"SO1R1#1 ð37RTC783\ 41RTC398\ 61LA"647#021\ 71CC0072Ł and trisulfones "R0S#C"SO1R1#1SO1R2 ðB!69MI 509!90Ł are also accessible "Scheme 04#[ The disulfone "24# "Table 7# has been prepared in 77) yield by copper"II#!catalyzed copyrolysis of the corresponding cyclic disul_de and di"p!tolylsulfonyl#diazomethane ð61BCJ859Ł[ MeSCH(SO2Me)2 + MeSO2SMe CHCl(SO2Me)2 + PhSCl
EtO–/EtOH H–/THF
(MeS)2C(SO2Me)2 (PhS)2C(SO2Me)2
O Et3N/CH2Cl2
H2C(SO2Et)2 + 2 MeS N
(MeS)2C(SO2Et)2
O Scheme 15
The failure in a number of attempts to obtain octaoxides C"SO1R#3 of tetrathioortho!carbonates "2# has been attributed to the fact that they must be regarded as mixed anhydrides of two extremely strong acids\ the trisulfone CH"SO1R#2 and the sulfonic acid RSO2H\ and thus subject to facile hydrolysis[ The synthesis of the sulfenic acid derivatives trisð"tri~uoromethyl#thioŁmethanesulfenyl chloride "CF2S#2CSCl and N\N!diethyl!trisð"tri~uoromethyl#thioŁmethanesulfenamide "CF2S#2CSNEt1 is par! ticularly intriguing "Scheme 05# ð65CB0865Ł[ [(CF3)S]2CCl–S–NR2 + Hg[S(CF3)]2
[(CF3)S]3C–S–NR2
HCl
[(CF3)S]3CSCl
Scheme 16
5[09[0[0[2 Four selenium or tellurium functions The chemistry of tetraselenoortho!carbonic esters "3# is not well developed^ only two compounds\ tetrakis"tri~uoromethyl# tetraselenoortho!carbonate CðSe"CF2#Ł3 and tetraphenyl tetraselenoortho! carbonate C"SePh#3\ have been synthesized so far[ The former is prepared by reaction of mercury"II# tri~uoromethaneselenolate "25# with tetrabromomethane^ a contamination with 4) unreacted tetrabromomethane could not be removed "Equation "11## ð73T3852Ł[ The latter is obtained by selenenylation of tris"phenylseleno#methanide ion with diphenyl diselenide "Scheme 06# ð61CB400Ł[ While this is the only reported application of this synthetic concept\ it should also be useful for the preparation of unsymmetrical tetraselenoortho!carbonates "3#[ [(CF3)Se]2Hg + CBr4 (36)
65 °C
C[Se(CF3)]4 (4)
(22)
297
Four or Three Chalco`ens (PhSe)3CH
LiN[CH2CHMe2]2
PhSeSePh
[(PhSe)3C]– Li+
C(SePh)4 (4)
THF/–40 °C 89%
Scheme 17
No tetratelluroortho!carbonates "4# have been reported so far ðB!75MI 509!91\ B!76MI 509!90\ The reason that their synthesis does not even seem to have been attempted must be their expected instability\ with the possible exception of per~uoroalkyl tetratelluroortho!carbonates[ 89HOU"E01:b#0Ł[
5[09[0[1 Three Similar and One Different Chalcogen This category theoretically consists of thioortho!carbonates "26#\ selenoortho!carbonates "27#\ telluroortho!carbonates "28#\ trithioortho!carbonates "39#\ selenotrithioortho!carbonates "30#\ tel! lurotrithioortho!carbonates "31#\ triselenoortho!carbonates "32#\ triselenothioortho!carbonates "33#\ triselenotelluroortho!carbonates "34#\ tritelluroortho!carbonates "35#\ tritellurothioortho!carbonates "36#\ and selenotritelluroortho!carbonates "37#[ None of the above selenium! and:or tellurium! containing compounds have yet been reported ðB!75MI 509!91\ B!75MI 509!92\ B!76MI 509!90\ 89HOU"E01:b#0Ł[
R1O
R1S
R1Se
OR2 OR3 SR4 (37)
R1O
SR2 SR3 SeR4 (41)
R1 S
SeR2 SeR3 TeR4 (45)
R1Te
OR2 OR3 SeR4 (38)
SR2 SR3 TeR4 (42) TeR2 TeR3 OR4 (46)
R1O
R1Se
OR2 OR3 TeR4 (39)
R1 S
SeR2 SeR3 OR4 (43)
R1Te
R1Se
TeR2 TeR3 SR4 (47)
SR2 SR3 OR4 (40) SeR2 SeR3 SR4 (44)
R1Te
TeR2 TeR3 SeR4 (48)
5[09[0[1[0 Trioxygen!substituted methyl chalcogens The vast majority of known thioortho!carbonates "26# are cyclic ortho!esters^ the simple compound "MeO#2CSMe has\ however\ been prepared ð72HOU"E3#692\ 89MI 509!90Ł[ Thioortho!carbonic acid tetraalkyl esters "26# have been postulated as intermediates in the preparation of tetraalkyl ortho! carbonates "1# from trichloromethanesulfenyl chloride "7# and sodium alkoxides "cf[ Scheme 0# ð37JOC154Ł[ Disul_des of the type "RO#2CSSCCl2 "38# and "RO#2CSSC"OR#2 "49# are formed con! comitantly upon treatment of 1!~uoro! and:or 1!nitroalkanols with trichloromethanesulfenyl chlor! ide "7# and base under phase!transfer conditions "Scheme 07 with\ for example\ R "O1N#1CFCH1# ð72JOC2243Ł[
RO
HO–/PTC
ROH
+ CCl3SCl
S CH2Cl2/H2O
RO (14)
(8) RO S RO (14)
HO–/PTC
+ ROH + CCl3SCl
(RO)3C
CH2Cl2/H2O
S
S
(49) 65–80%
(8) Scheme 18
CCl3
+
(RO)3C
S
S
(50) 6–11%
C(OR)3
298
Tetrachalco`enomethanes
O\O!Disubstituted thiocarbonates "03# react with nitrile oxides such as "40# to give the cor! responding cyclic ortho!ester such as "41# "Equation "12## ð50AG545\ 61CB1704Ł[ Ph PhO
N S
+
Ph
PhO (14)
CNO
S
(51)
(23)
O
PhO
OPh (52) m.p. 79 °C
The oxidation of 0\2!benzodioxole!1!thione "42# with lead"IV# acetate to yield the disul_de "43# is hardly a general reaction "Equation "13## ð56JCS"C#796Ł[ O
O
lead tetraacetate
S
S
O
S
(24) O
O (53)
O OAc AcO (54) m.p. 156 °C
5[09[0[1[1 Trisulfur!substituted methyl chalcogens The chemistry of trithioortho!carbonates "39# is strongly dominated by cyclic compounds ð72HOU"E3#693Ł[ See Table 09 for examples[ Spirocyclic trithioortho!carbonates "39# are accessible from 0\2!dithiole!1!thione "45# and 0\2! dithiolane!1!thione "12#\ and 1!substituted oxiranes "44#\ both possible isomers being formed in total yields of 39Ð59) "Scheme 08# ð80HCA0499Ł[ Acyclic ð50AG545\ 61CB1704\ 80TL3218Ł as well as cyclic ð56BSF1128Ł trithiocarbonates "46# and C! sulfonyldithioformates "59# add nitrile oxides "47# to give the corresponding 0\3\1!oxathiazoles "48# and "50#\ respectively "Scheme 19# ð65CB0958Ł[ Nitrosoalkenes such as 0!nitroso!0!phenylethene "51# react with trithiocarbonates such as diphenyl trithiocarbonate to form the corresponding 3H!0\4\1! oxathiazines such as "52# "Equation "14## ð74TL1020Ł[ Ph
PhS
+ NO
S PhS
S
CH2Cl2 20–30 h 93%
(62)
N
SPh
(25)
O
SPh (63) m.p. 124–125 °C
Pyrolysis of O\O?!alkanediyl S\S?!dimethyl bis"dithiocarbonates# "53# yields the corresponding O\S!alkanediyl S\S!dimethyl trithioortho!carbonates "54# "Scheme 10# ð67S175Ł[ Carbohydrate derivatives containing cyclic trithioortho!carbonate groups have been prepared in the same way ð65S338\ 68CAR"63#016Ł^ cf[ ð65JCS"P0#1001Ł[ 0!Oxa!3\5\8!trithiaspiroð3[3Łnon!1!ene derivatives "56# are accessible by S!alkylation of 0\2!dithio! lane!1!thione "12# and subsequent deprotonation to the corresponding thiocarbonyl ylide "55#\ which _nally rearranges "Scheme 11# ð61BCJ0686Ł[ The trithiocarbenium salt "57# can be treated with simple primary or secondary alkanols to yield the corresponding trithioortho!carbonates "58# "Equation "15## ð53ZC273Ł[ S +
SMe
S I– (68) R = Me, Pr, Pri
+ ROH
–HI
S
SMe
S
OR
(26)
(69)
209
Four or Three Chalco`ens Table 09 Selected cyclic trithioortho!carbonates "39#[
Compound
Ref.
Boiling point (°C/torr)
O
SMe
S
SMe O
SMe
S
SMe
O
SMe
S
SMe
O
SMe
S
SMe
110–112/4
78S286
(melting point 29 °C)
78S286
140–142/8
78S286
78S286 O
SMe
S
SMe
S
OR
190–193/2
78S286
64ZC384 S (69)
SMe R
S
O
S
S
S
O
S
S
R
S
O
R
S
S
S
O
S
S
S
O
S
S
91HCA1500
91HCA1500
91HCA1500 R 91HCA1500
91HCA1500 R
S
O S
+ R
S (23)
(55)
S
O S
S (56)
+ R (55)
O
TiCl4
S
DCE –20 °C
S
S (40)
TiCl4
S
O
DCE –20 °C
S
R
Scheme 19
O
S
S (40)
S
O
S
S (40)
+ S (40)
R
R = Me, CH2Cl, Et, Bu, CH2COBut, Ph DCE = ClCH2CH2Cl
S
R
+
R
200
Tetrachalco`enomethanes R2
R 1S
N R2
+
S R1S (57)
CNO
S
O
R1S
(58)
SR1
(59) R3
R1SO2
N R3
+
S R2S (60)
CNO
S
O
R1SO2 SR2 (61)
(58) Scheme 20
(CH2)n MeS
O
( )n
O
SMe
S
∆
O
S
MeS
(64) MeS
O
( )n
O
S
S SMe (65)
∆
SMe
O
S
90%
S
MeS
SMe (65) n=2 b.p. 110–112 °C (at 4 torr)
(64) n=2
Scheme 21
O S
Ar S
S
+
+
O
S
O NaH
S
MeCN
Br
S
Ar
Br–
–
S +
S
MeCN
Ar
90%
S
(23)
(66) S
S
S
O
Ar
(67) Scheme 22
Bis"tri~uoromethyl#thioketene "11# adds to O\S!dialkyl dithiocarbonates "69# to form the cor! responding 0\2!dithietanes "60# in high yields "Equation "16## ð69JOC2369Ł[ R1O
F 3C • F3C (22)
S
+
F3C
S
OR1
F3C
S
SR2
S R2S (70)
(27) (71)
5[09[0[1[2 Triselenium! or tritellurium!substituted methyl chalcogens No compounds answering this description appear to be on record\ cf[ ðB!75MI 509!91\ B!75MI 509!92\ B!76MI 509!90\ 89HOU"E01:b#0Ł[
5[09[0[2 Two Similar and Two Different Chalcogens This category theoretically includes selenothioortho!carbonates "61#\ tellurothioortho!carbonates "62#\ selenotelluroortho!carbonates "63#\ selenodithioortho!carbonates "64#\ tellurodithioortho!
201
Four or Three Chalco`ens
carbonates "65#\ selenotellurodithioortho!carbonates "66#\ diselenotelluroortho!carbonates "67#\ diselenotellurothioortho!carbonates "68#\ ditellurothioortho!carbonates "79#\ selenoditelluro! ortho!carbonates "70#\ and selenoditellurothioortho!carbonates "71#\ none of which are known ðB!75MI 509!91\ B!75MI 509!92\ B!76MI 509!90\ 89HOU"E01:b#0Ł[ R1O
R1S
OR2 SR3 SeR4 (72)
R1 O
SR2 OR3 TeR4 (76)
R1S
OR2 SR3 TeR4 (73)
SR2 SeR3 TeR4 (77)
TeR2 OR3 SR4
R1Te
R1O
R1Se
R1S
SeR2 OR3 TeR4 (78)
TeR2 OR3 SeR4
R1Te
(80)
OR2 SeR3 TeR4 (74)
SR2 OR3 SeR4 (75)
R1Se
TeR2 SR3 SeR4
R1Te
(81)
SeR2 SR3 TeR4 (79)
(82)
5[09[0[2[0 Dioxygen!substituted methylene dichalcogens No examples of selenothioortho!carbonates "72#\ tellurothioortho!carbonates "73#\ or seleno! telluroortho!carbonates "74# are known ðB!75MI 509!91\ B!75MI 509!92\ B!76MI 509!90\ 89HOU"E01:b#0Ł[ OR2 SR3 SeR4
R1 O
OR2 SR3 TeR4
R1O
(83)
(84)
R1O
OR2 SeR3 TeR4 (85)
5[09[0[2[1 Disulfur!substituted methylene dichalcogens 1\1!Dichloro!0\2!benzodioxole "75# reacts with benzenethiolate to give the dithioortho!carbonate 1\1!bis"phenylthio#!0\2!benzodioxole "76# "Equation "17## ð53LA"564#031Ł[ Bis"tri~uoromethyl# thioketene "11# undergoes cycloaddition with O\O!disubstituted thiocarbonates "03# to yield the corresponding 0\2!dithietanes "77# "Equation "18## ð69JOC2369Ł[ O
Cl
O (86)
Cl
PhSH/Et3N THF
O
SPh (28)
RO
F3C S
RO (14)
70 °C, 30 min 61%
+
• F3C (22)
O SPh (87) m.p. 98.5–99.5 °C F3C
S
OR
F 3C
S
OR
S
(29) (88)
The mercury"II# salt of N\N!bis"tri~uoromethyl#hydroxylamine\ ð"CF2#1NOŁ1Hg\ reacts with thio! phosgene with the formation of the transient corresponding O\O!disubstituted thiocarbonate\ which in turn dimerizes to 1\1\3\3!tetrakisðbis"tri~uoromethyl#aminoxyŁ!0\2!dithietane ð73JFC"13#374Ł[ Cyclic trithiocarbonates "89# react with 2\3\4\5!tetrachloro!o!benzoquinone "o!chloranil# "78# to form spirocyclic dithioortho!carbonates "80# "Equation "29## ð62ZC354Ł[
202
Trichalco`enomethanes Cl
Cl O
Cl
S
+ Cl
S
Cl (89)
O
S
Cl
O
S
(30)
–[S] 20–70%
S
O
Cl
Cl (91)
(90)
Aryl N\N!dimethyldithiocarbamates with electron!withdrawing substituents in the aryl group such as "81# react with methanolic sodium nitrite to form cyclic bis"dithioortho!carbonates# linked via a peroxide group such as "82# "Equation "20## ð68JOC156Ł[ S S
NMe2 NO2
O2N
NO2
NO2 NaNO2 MeOH
S
O O
S (31)
48 h 15%
S OMe MeO S
F3C
CF3
CF3
(93) m.p. 177.0–178.5 °C
(92)
Tellurodithioortho!carbonates "83# and selenotellurodithioortho!carbonates "84# are unknown ðB!75MI 509!91\ B!75MI 509!92\ B!76MI 509!90\ 89HOU"E01:b#0Ł[
R1S
SR2 OR3 TeR4 (94)
R1 S
SR2 SeR3 TeR4 (95)
5[09[0[2[2 Diselenium! or ditellurium!substituted methylene dichalcogens No selenium and:or tellurium compounds _tting this description appear to be on record ðB!75MI 509!91\ B!75MI 509!92\ B!76MI 509!90\ 89HOU"E01:b#0Ł[
5[09[1 TRICHALCOGENOMETHANES 5[09[1[0 Methanes Bearing Three Oxygens and a Group 04 Element\ Metalloid or Metal Function Ethyl N\N!dimethylcarbamate upon sequential treatment with triethyloxonium tetra~uoroborate and sodium ethoxide yields 25) of the corresponding acetal Me1NC"OEt#2 ð50LA"530#0Ł[ N\N\N?\N?! Tetrasubstituted ureas upon treatment with phosgene yield the corresponding formamidinium chlorides which form the corresponding urea acetals with ethoxide[ The latter react with ethanol to give R1NC"OEt#2 ð53CB0121Ł[ Corresponding methyl compounds R1NC"OMe#2 have also been prepared[ These compounds are remarkably stable to hydrolysis[ Transesteri_cation is possible ð72HOU"E3#609Ł\ for example of Me1NC"OMe#2 with isopropanol to yield Me1NC"OPri#2 ð66S62Ł[ N!Methyl!N\O!bis"tributylstannyl#!1!aminoethanol "85# reacts with 0\2!dioxolane!1!thione "86# to form the corresponding spirocyclic compound "87# "Equation "21## ð63JOM"61#092Ł[ O
Me Bu3Sn
+
N
OSnBu3 (96)
O
O (32)
S O (97)
O
N Me (98)
Trialkoxycarbenium ions "typically obtained by alkylation of carbonates# react with sodium dialkylphosphites to form the corresponding phosphonates in 48Ð57) yield\ for example "88# "Equation "22## ð77ZOB1056\ 77ZOB1057Ł[ The same products are accessible in 51Ð79) yield by
203
Four or Three Chalco`ens
reaction of symmetrical ortho!carbonates C"OR0#3 with dialkylphosphorous acid anhydrides "R1O#1P0O0P"OR1#1 ð56ZOB1026\ 77ZOB0816Ł[ The reaction of trialkoxycarbenium ions with lithium dialkylphosphides gives "trialkoxymethyl#phosphines such as "099# "Equation "23## ð77ZOB0336Ł[ Dioxymethanephosphonates such as "090# upon electrochemical methoxylation yield the cor! responding ortho!esters such as "091# in 27Ð61) yield "Equation "24## ð76S33Ł[ [(EtO)3
+
C]+
O
EtO EtO EtO
(BuO)2PONa
(33)
P(OBu)2 (99)
(BuO)3C+
Cl
+
O
O
MeOH/0.1 M MeONa
(34)
Cl
O
OMe
Cl
O
P(OPh)2
(35)
P(OPh)2
2e–
O
Cl
BuO PBu2 BuO BuO (100)
Bu2PLi
O (101)
(102)
5[09[1[1 Methanes Bearing Three Sulfurs and a Group 04 Element\ Metalloid or Metal Function Methyl N\N!dimethyldithiocarbamate after S!methylation with dimethyl sulfate and subsequent treatment with sodium ethanethiolate forms Me1N0C"SMe#1SEt ð69BCJ2417Ł[ Aminotrithio! ortho!formates such as "093^ Z S# have been prepared from trithiocarbenium salts and imidazoles ð50LA"530#0Ł[ 1!Alkylthio!0\2!dithiolylium cations "e[g[\ 092^ Z S# react correspondingly "Equation "25## ð69TL370Ł[ Heterocyclic aminotrithioortho!formates such as "095# are accessible by double addition of 1!alkylthiiranes "094# to methyl isothiocyanate "Equation "26## ð78NKK52Ł[ A similar reaction of 1!iodoalkyl isothiocyanates with sulfur nucleophiles has been reported ð70JCS"P0#41Ł[ Methyl isothiocyanate reacts with undiluted bis"tri~uoromethyl#thioketene "11# in a 0 ] 2 ratio to form the spirocyclic aminotrithioortho!formate "096# "Equation "27## ð67JOC1499Ł[ In an obscure reaction between 4!chloro!1!nitroaniline and 0\2!thiazolidine!1!thione "097#\ the corresponding bicyclic aminotrithioortho!formate "098# is formed "Equation "28## ð66USP3920117Ł[ 2\4!Dimethyl! thiazoloð1\2!bŁthiazolium bromide "009#\ upon heating with aqueous base\ forms the amino! trithioortho!formate "000# "Equation "39## ð56JOC1963Ł[ 1\2\4\5!Tetrahydrothiazoloð1\2!bŁ thiazolium bromide "001# reacts with sodium benzenethiolate in ethanol to form the bicyclic aminotrithioortho!formate "002# "Equation "30##^ analogous compounds have been prepared in a similar manner ð60JCS"C#092Ł[ The betaine "004# formed by reaction of benzo!0\2!dithiole!1!thione "003# and triethyl phosphite has been reported to interact with 0!"0!propenyl#piperidine to form the aminotrithioortho!formate "005# "Scheme 12# ð63CB2044Ł[ The corresponding reaction with piperidine yields the derivative "006# "Scheme 13# ð63CB2044Ł[ Thiobenzoyliminodithiocarbonates such as "007# have been shown to react with diphenyldiazomethane with 0\3!cycloaddition to form two stereoisomers of the spiro heterocycle "008# "Equation "31##\ the reaction probably taking place by way of a thiirane intermediate ð67BCJ290Ł[ Ph S
Ph +
N
+
Z
MeCN
N H
SEt (103) Z = S, Se
Ph
(105) R = Me, Et
S
N
(36) Ph
(104)
+ R
SEt
N
S 2
Z Et3N
Me
N
•
S
Me N
S
S
(37)
S R
(106)
R
204
Trichalco`enomethanes CF3 F3C F 3C Me
N
•
+
S
undiluted
3
•
S
Me N S
CF3
S
CF3
(38)
S 0 °C
F3C
S F3C
(22)
CF3 (107) m.p. 121.5–122.5 °C
NH2
S S
NO2
Ar
S
+
S (39)
S N
N H (108)
Cl
(109)
S N S
S +
O
HO–/H2O
S
N
S 30 min 67%
Br–
(40)
S N
(110)
(111) m.p. 194–194.5 °C (dec.)
S
S
PhSNa EtOH
(113) m.p. 80–81 °C
+
–
+ P(OEt)3
SP(OEt)3
SEt
S
N
30%
S
(114)
S N
S
S
N
24 h 20%
Br– (112)
S
SPh S (41)
N+
S
S
(115)
(116) b.p. 190 °C (at 0.6 torr)
Scheme 23
S
SH
S
N
S
S S
+
NH
S
55%
S
S
S
N
S 42%
m.p. 158 °C Scheme 24
(114)
S N S
Ph S
(118)
+ Ph2CN2
Et2O, RT –N2 51%
(117)
S
N
S
S
Ph (119) two stereoisomers
Ph Ph
(42)
205
Four or Three Chalco`ens
Azidotrithioortho!formates such as "010# can be obtained from trithiocarbenium salts such as "019# and azide ions "Equation "32## ð54ZC275\ 65JPR"207#016\ 70JCS"P0#507Ł[ Although azidotrithioortho! formates "011# can be isolated at low temperatures they are mostly used in situ for the elaboration of nitrogen! and sulfur!containing heterocycles[ With triphenylphosphine\ azidotrithioortho!formates "011# form the corresponding adducts "012# "Equation "33## ð65JPR016Ł[ Trichloronitromethane "6# reacts with potassium O\O!diethyldithiophosphate with substitution of the three chlorine atoms to yield the nitrotrithioortho!formate "013# "Equation "34## ð59JAP5907088Ł[ A similar reaction of trichloromethyl isocyanide dichloride "00# with ammonium O\O!diethylthiophosphate leads to the ð"dichloromethylene#aminoŁtrithioortho!formate "014# "Equation "35## ð52BEP516375Ł[ Analogous reactions of trichloromethyl isocyanide dichloride "00# with sodium N\N!dimethyl! and N\N!diethyl! dithiocarbamate have been reported ð57BRP0986126Ł[ S SMe S ClO4– (120)
N3
SR1 SR2 SR3 (122)
Cl3CNO2 +
S
NaN3
+
(43)
MeCN
SMe
S (121)
+ PPh3
Ph3P
SR1 SR2 SR3
N N N
(44)
(123) 3(EtO)2PS2K
(45)
(O2N)C[SP(S)(OEt)2]3 (124)
(7)
Cl
Cl
+ 3(EtO)2POSNH4
N
(46)
N C[SP(O)(OEt)2]3
Cl
Cl3C
N3
Cl (125)
(11)
Bis"phenylthio#sul_ne "015# reacts with 1!diazopropane with 0\2!dipolar addition across the C1S bond to form the corresponding thiadiazole derivative "016# "Equation "36## ð62TL2478Ł[ PhS
C6H6
+ Me2CN2
S PhS
O
N N
PhS
–10 °C 58%
(47)
S
PhS
O (127) m.p. 55 °C (dec.)
(126)
Trisulfonylmethanes CH"SO1R#2 when treated with nitric acid:sulfuric acid yield the corres! ponding C!nitro compounds "O1N#C"SO1R#2[ In cases where R is an electron!rich aryl group\ aromatic nitration takes place simultaneously ð65ZOR1472Ł[ Trithiosubstituted methanephosphonic acid diesters "020# have been prepared in 53Ð62) yield by addition of alkanethiols to phosphonodithioformates "017#\ followed by subsequent S!alkylation and deprotonation of the asymmetrical disul_des "018# formed to the corresponding ylides "029#\ which then rearrange to "020# "Scheme 14\ where LDA is lithium diisopropylamide# ð81JOC3496Ł[ Methyl diethylphosphonodithioformate "021# yields the symmetrical sul_de "022# in poor yield when subsequently treated with ethylmagnesium bromide and diethyl disul_de "Scheme 15# ð78TL2304Ł[ 2\3!Dicyano!0\2!dithiole!1!thione "023# reacts with trimethyl phosphite in boiling toluene to give the corresponding 1!methylthio substituted 1!phosphonic acid dimethyl ester "024# "Equation "37## ð67JOC484Ł[
O
S
(R1O)2P
O R3SH
(R1O)2P
SR2 (128)
SR2
SR3
O LDA, R4X
(R1O)2P
SSR3
–
S+
R4
O 64–73%
(R1O)2P
SR2
(129)
(130) Scheme 25
(131)
SR2 SR3 SR4
206
Trichalco`enomethanes O
O S
THF
+ EtMgBr
(EtO)2P
–78 °C
SMe (132)
(EtO)2P EtS MeS
O S
P(OEt)2 MgBr SMe
O EtSSEt
(EtO)2P
O S
P(OEt)2
EtS SEt MeS SMe (133)
–78 °C 9%
Scheme 26
NC
NC
CN PhMe
S
S S
(134)
+ P(OMe)3 reflux, 6 h 15%
S MeS
CN S
(48)
P(OMe)2
O (135) m.p. 140–141 °C
The anions of trithioortho!formates "including oligothiaadamantanes# can be silylated with tri! methylchlorosilane to yield "trimethylsilyl#trithioortho!formates "Me2Si#C"SR#2 ð56AG"E#331\ 61CB376\ 66CB1779Ł[ The anion of tri!t!butyl trithioortho!formate CH"ButS#2\ however\ resists trimethyl! silylation ð66CB1779Ł[ Methanetrisulfonyl tri~uoride and trimethylchlorosilane form "trimethyl! silyl#methanetrisulfonyl tri~uoride "Me2Si#C"SO1F#2 ð72ZOR68Ł[ The lithium salts of trithioortho!formates\ "RS#2CLi\ are important intermediates in a number of synthetic procedures[ Lithiated trithioortho!formates "including mixed compounds#*obtained by metalation of a trithioortho!formate CH"SR#2 ð64CC105Ł\ by cleavage of a tetrathioortho!carbonate C"SR#3 with butyllithium ð61CB376Ł\ or by addition of an organolithium compound to a trithio! carbonate ð73TL880Ł*play an important role as in situ synthetic intermediates\ that is as acyl anion equivalents ð61CB2179\ 61CB2781\ 80S236\ 80TL5218\ 81BMC0596Ł and in the synthesis of tetrathioortho! carbonates "2# "see Section 5[09[0[0[1#[ In a {{one!pot|| reaction\ trithiocarbenium salts ðC"SR1#1SR01ŁX can be reduced with sodium borohydride and subsequently metalated with methyl! lithium to yield mixed lithiotrithioortho!formates "R0S#1"R1S#CLi ð82T2924Ł[ Isotopically labeled lithiotrithioortho!formates "RS#2CLi have also been prepared ð73HCA0972Ł[ In solution\ lithio! trithioortho!formates are in equilibrium with the corresponding dithiocarbene and lithium thiolate ð56AG"E#332\ 61CB376\ 61CB2179\ 67CB2533Ł[ Silylation of lithiotrithioortho!formates leads to the cor! responding trialkylsilyl derivatives\ for example triphenyl "trimethylsilyl#trithioortho!formate\ "Me2Si#C"SPh#2[ The lithium salt of tris"tri~uoromethylsulfonyl#methane\ ð"CF2#SO1Ł2CLi\ is a key electrolyte in nonaqueous batteries ð82JAP"K#94951589Ł[ Sodiotrithioformates\ "RS#2CNa\ are analogously prepared from trithioortho!formates and sodium amide in liquid ammonia ð74HOU"E4#2Ł[ Like their lithium counterparts they are used in situ for synthetic purposes[
5[09[1[2 Methanes Bearing Three Seleniums or Three Telluriums and a Group 04 Element\ Metalloid or Metal Function Triselenoortho!formates such as trimethyl triselenoortho!formate\ CH"SeMe#2 ð68JOM"066#0\ and triphenyl triselenoortho!formate\ CH"SePh#2 ð61CB400Ł\ have been lithiated with lithium diisopropylamide and other metalation reagents[ The lithio derivatives are useful as synthetic acyl anion equivalents[ No tellurium compounds of the above description are on record ðB!75MI 509!91\ B!76MI 509!90\ 89HOU"E01:b#0Ł[ 70TL3998Ł\
5[09[1[3 Methanes Bearing Three Dissimilar Chalcogens and a Group 04 Element\ Metalloid or Metal Function 1!Alkylthio!0\2!thiaselenolylium cations "e[g[\ "092^ Z Se## probably react with imidazoles to form "093^ Z Se# "Equation "25## ð69TL370Ł[ Subsequent treatment of 2!methyl!0\2!benzothiazol! 1!one "025# with triethyloxonium tetra~uoroborate and sodium ethoxide leads to 1\1!diethoxy!2!
207
Four or Three Chalco`ens
methyl!1\2!dihydro!0\2!benzothiazole "026# "Scheme 16# ð50LA"530#0Ł^ the corresponding reaction between 1!chloro!2!methyl!0\2!benzothiazolium tetra~uoroborate "027# and resorcinol "028# leads to the spirocyclic compound "039# "Equation "38## ð57CB0026Ł[ S
S
Et3O+ BF4–
+
O CH2Cl2 50 °C, 3 h 98%
N Me
S
EtO– Na+
OEt
OEt N OEt Me
EtOH 75%
N Me BF4–
(136)
(137) b.p. 126 °C (at 1 torr), m.p. 28 °C Scheme 27
OH
S +
Cl
+
N Me BF4–
(138)
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
OH (139)
S
NEt3
O (49)
MeCN 1–2 h 95%
N O Me (140) m.p. 117–119 °C
Comprehensive Organic Functional Group Transformations
6.11 Functions Containing Two or One Chalcogens (and No Halogens) WOLFGANG PETZ Gmelin-Institut der Max-Planck-Gesellschaft, Frankfurt, Germany and FRANK WELLER Fachbereich Chemie der Universita¨t Marburg, Germany 5[00[0 INTRODUCTION
219
5[00[1 DICHALCOGENOMETHANES
219
5[00[1[0 Methanes Bearin` Two Similar Chalco`ens 5[00[1[0[0 Two oxy`ens and a `roup 04 element and:or a metalloid and:or a metal function 5[00[1[0[1 Two sulfurs and a `roup 04 element and:or a metalloid and:or a metal function 5[00[1[0[2 Two seleniums or two telluriums and a `roup 04 element and:or a metalloid and:or a metal function 5[00[1[1 Methanes Bearin` Two Dissimilar Chalco`ens 5[00[1[1[0 Oxy`en\ sulfur and two functions derived from a `roup 04 element\ metalloid and:or a metal 5[00[1[1[1 Oxy`en and selenium\ or oxy`en and tellurium and two functions derived from a `roup 04 element\ metalloid and:or a metal 5[00[1[1[2 Sulfur and selenium\ or sulfur and tellurium and two functions derived from a `roup 04 element\ metalloid and:or a metal 5[00[2 MONOCHALCOGENOMETHANES
219 219 211 223 224 224 225 225 225
5[00[2[0 Methanes Bearin` One Oxy`en Function and Three Functions Derived From the Group 04 Element\ Metalloid and:or a Metal 5[00[2[0[0 Compounds with the OCN2 core 5[00[2[0[1 Compounds with the OCNSiTa core 5[00[2[0[2 Compounds with the OCPSiTa core 5[00[2[0[3 Compounds with the OCFe2 core 5[00[2[0[4 Compounds with the OCCo2 core 5[00[2[0[5 Compounds with the OCW2 core 5[00[2[0[6 Compounds with the OCRu2 core 5[00[2[0[7 Compounds with the OCOs2 core 5[00[2[0[8 Compounds with the OCFe1Ni core 5[00[2[0[09 Compounds with the OCFe1Co core 5[00[2[0[00 Compounds with the OCFe1Rh core 5[00[2[0[01 Compounds with the OCFe1Mn core 5[00[2[0[02 Compounds with the OCRu1W core 5[00[2[0[03 Compounds with the OCW1Ru core 5[00[2[1 Methanes Bearin` One Sulfur Function and Three Functions Derived from the Group 04 Element\ Metalloid and:or a Metal
208
226 226 226 227 227 239 231 232 233 235 235 236 236 237 237 237
219
Two Or One Chalco`ens
5[00[2[1[0 Compounds with the SCN2 core 5[00[2[1[1 Compounds with the SCSi2 core 5[00[2[1[2 Compounds with the SCSi1P core 5[00[2[1[3 Compounds with the SCPSiLi core 5[00[2[1[4 Compounds with the SCSi1Li core 5[00[2[1[5 Compounds with the SCN1Fe core 5[00[2[1[6 Compounds with the SCNSnPt core 5[00[2[1[7 Compounds with the SCSiSnLi core 5[00[2[1[8 Compounds with the SCFe2 core 5[00[2[1[09 Compounds with the SCCo2 core 5[00[2[1[00 Compounds with the SCFe1Co core 5[00[2[1[01 Compounds with the SCCo1W core 5[00[2[2 Methanes Bearin` One Selenium or One Tellurium Function and Three Functions Derived from the Group 04 Element\ Metalloid and:or a Metal 5[00[2[2[0 Compounds with the SeCN2 core 5[00[2[2[1 Compounds with the SeCSi2 core 5[00[2[2[2 Compounds with the TeCSi2 core
237 238 249 240 240 240 240 240 241 241 241 242 243 244 244 245
5[00[0 INTRODUCTION The compounds in Chapter 5[00 are discussed as follows] _rst those compounds with a group 04 element at the carbon atom^ second those compounds with metalloids "other main group elements#^ and _nally transition metal functions[ Compounds with dissimilar atoms at the carbon atom are discussed after compounds with similar atoms[
5[00[1 DICHALCOGENOMETHANES 5[00[1[0 Methanes Bearing Two Similar Chalcogens Dichalcogenomethanes with similar chalcogens and further atoms other than chalcogens or halogens have only been described with the O1C\ S1C\ and Se1C units^ compounds with the Te1C unit could not be found[
5[00[1[0[0 Two oxygens and a group 04 element and:or a metalloid and:or a metal function Up to 0884\ compounds with the "RO#1C unit bonded to group 04 elements other than N have not yet been described[ Compounds in which this unit is connected to metalloids or metal functions could also not be found[
"i# Compounds with the O1CN1 core Compounds with the O1CN1 core are urea acetals and the chemistry of these compounds and other O! and N!functional orthocarbonic acid derivatives has been reviewed by Kantlehner et al[ ð66S62Ł[ No common method exists to prepare all these types of compounds\ but there are some general procedures[ As illustrated in Scheme 0\ Meerwein has reported that various dialkyl! aminoethoxycarbenium tetra~uoroborates can be reversibly converted into the acetals "0# by treatment with anhydrous NaOEt in acetonitrile ""0a#\ 45)^ "0c#\ 54)^ "0d#\ high#^ with BF2^ reconversion into the water!soluble salts occurs quantitatively[ The preparation of the acetals "0#
210
Dichalco`enomethanes
cannot be performed in alcohol because in this solvent one NMe1 group is readily replaced to give R1NC"OEt#2 compounds ð50LA"530#0Ł[ Me2N
NaOR
OR
+
Me2N
Me2N
OR
Me2N
OR
(1) a; R = Et b; R = Me Me
Me N
NaOEt
OEt
+
N Me
N
OEt
N
OEt
Me (1c) Me
Me N
NaOEt
OEt
+
N
N
OEt
N
OEt
Me
Me
(1d) Scheme 1
Compound "0a# and the corresponding methoxy derivative "Me1N#1C"OMe#1 "0b# are obtained by reacting NaOR in a similar procedure with ð"Me1N#1CClŁCl ð53CB0121Ł\ "Me1N#1CF1 ð66S62Ł\ or "Me1N#1C"OR#CN ð71LA496\ 89LA854Ł^ the compounds are also formed as a side product during the preparation of the triamine "Me1N#2COR in a one!pot reaction from the formamidinium chloride ð"Me1N#1CClŁCl and HNMe1 "to give ðC"NMe1#2ŁCl and ðH1NMe1ŁCl# followed by treating the mixture with NaOR in THF^ the alcohol formed reacts further with the triamine to give "Me1N#1 C"OMe#1 or "Me1N#1C"OEt#1\ respectively ð68LA1978Ł[ The reactions are shown in Scheme 1[ Me2N
OR
Me2N
Me2N
CN
Me2N
+
OEt
CN–
NaOR
Me2N
F
Me2N
F
NaOR
Me2N
OR
Me2N
OR
Me2N +
Cl
Cl–
Me2N
(1) HOR
Me2N
OR
Me2N
NMe2
Me2N +
NMe2
–OR
Me2N Scheme 2
The _rst report about acetals with the O1CN1 core appeared in 0848 in a short note by Stachel[ As depicted in Scheme 2\ alcoholysis of the cyclic N\N?!diacylurea dichloride derivative\ which has been obtained from oxalyl chloride and diisopropylcarbodiimide\ produces the corresponding acetals "0# ""0e#\ R Me\ m[p[ 014>C^ "0f#\ R Et\ m[p[ 036>C#[ With ethylene glycol the stable spiroacetal "0g# "m[p[ 134>C\ dec[# is formed ð48AG135Ł[ Whereas the methods in Schemes 0 to 2 comprise alcoholysis of diaminodihalogenomethanes\ acetals can also be produced by aminolysis of dioxodihalogenomethanes[ Thus\ 1\1!dichloro!0\2! benzodioxole in ether reacts with piperidine ð53LA"564#031Ł or morpholine ð61G447Ł with cooling to
211
Two Or One Chalco`ens Pri O
O
Pri
N
OR
N
OR
O HOR
O
Pri
N
Cl
N
Cl
Pri
HO
O
N
O
O
N
O
OH
Pri
Pri (1g)
(1e, f) Scheme 3
give the corresponding acetals "1a# and "1b# in 73) and 61) yield\ respectively ""1a#\ m[p[ 73Ð 74>C^ "1b#\ m[p[ 019Ð011>C# "Scheme 3#[ O
O
N
O
N
N H
O
Cl
O
Cl
O
N H
O
N
O
N O
(2a)
(2b) Scheme 4
A more complicated procedure for the preparation of acetals is based on the extrusion of "Bu2Sn#1S during the reaction of N\N?!bis"tributylstannyl#!N\N?!dimethylethylenediamine with ethylene thionocarbonate in chloroform to form the spiroacetal "2# in 76) yield "b[p[ 68Ð78>C:3 mm Hg#[ Analogously\ the symmetrical acetal "3# "b[p[ 30>C:0 mm Hg# was obtained in 89) yield by react! ing the bifunctional organotin compounds O\N!bis"tributylstannyl#!N!methylethanolamine with 2!methyl!1!oxazolidinethione[ The compounds have been puri_ed by distillation ð69MI 500!90Ł "Scheme 4#[ Me N
Me SnBu3 SnBu3
N
O
+
N
O
N
O
S O
Me
Me
(3) Me N
Me
SnBu3 + O
Me
N
N
O
O
N
S O
Me (4) Scheme 5
The structure of the anhydronucleoside "4# has been con_rmed by x!ray structure analysis[ The compound was obtained in 54) yield by treatment of the epoxide "a mixture of isomers# with BF2 etherate in THF at room temperature[ Compound "5# was crystallized by slow evaporation of acetoneÐacetonitrile solution ð70CC679Ł[
5[00[1[0[1 Two sulfurs and a group 04 element and:or a metalloid and:or a metal function Most of the compounds in this section are based on the coordination chemistry of the fragment S1CPR2 in which the two sulfur atoms and the carbon atom interact with a mononuclear or dinuclear transition metal fragment in an allyl!like manner[ Compounds with the S1CPMo\ S1CPW\ and S1CPMn core have been described[ The coordination mode of the S1CPR2 ligand has been studied ð82OM3156Ł[
212
Dichalco`enomethanes NHAc NHAc
N O O
O
N
O
N
N O
O
O
O
O
(5)
O
(6)
"i# Compounds with the S1CN1 core There are only few compounds described in the literature with the S1CN1 core and because of the di}erent natures of the compounds a common method of preparation for these compounds cannot be formulated[ The starting materials for the preparation of "PhS#1C"NO1#1 "6# are various highly reactive ylides^ these are treated with benzensulfenyl chloride as shown by pathways "a#Ð"d# in Scheme 5[ Thus\ the ylide Me1S¦0C−"NO1#1 in acetonitrile or dichloromethane "pathway "a## with 1 moles of PhSCl at room temperature produces "6# "colorless crystals\ m[p[ 50Ð51>C# in 59) or 39) yield\ respectively[ It was assumed that the salt "7# is formed in the _rst step\ which is further converted into "6# with the liberation of Me1SCl1[ With the ylide Ph1S¦0C−"NO1#1 under similar conditions "pathway "b##\ "6# was obtained in 81) yield ð64IZV1510\ 66IZV028Ł[ Similarly\ the selenium dinitro ylide Ph1Se¦0C−"NO1#1 was reacted "pathway "c## to give "6# in 74) yield with removal of the selenium as Ph1SeCl1[ Puri_cation was achieved by extraction of the dried reaction mixture with hot heptane followed by cooling with dry ice ð67IZV0980Ł[ The iodonium ylide PhI¦0C−"NO1#1 in ether produces "6# in only 19) yield "pathway "d## along with PhSC"NO1#1Cl "34)#^ the compounds were separated by preparative TLC ð65IZV1539\ 67IZV1237Ł[ NO2
+
Me2S
–
PhSCl
NO2
PhS
NO2
Me2S
NO2
Cl (8) (a) PhSCl
+
Ph2Se
NO2
PhSCl
NO2
PhS
PhSCl
NO2
(c)
+
Ph2S
–
PhS
NO2
(b)
NO2 –
NO2
(7) (d)
+
PhI
PhSCl
NO2 –
NO2 Scheme 6
Thiourea derivatives such as S1C"NHAc#1 containing electron!acceptor substituents on nitrogen undergo a radical S!arylation by phenyl radicals "generated from N!nitrosoacetanilide# to generate the radical ðPhSC"NHAc#1Ł = [ Decomposition produces further radicals from which "8# "m[p[ 099Ð 094>C# could be isolated as a product of recombination in 05) yield "Equation "0##[ The reaction was carried out in acetone followed by addition of alcohol ð71IZV359Ł[
213
Two Or One Chalco`ens NHAc
PhS
NHAc
NHAc
PhS
NHAc
PhS + PhS
(1) (9)
Yellow crystals of "09# "m[p[ 034Ð035>C# have been obtained in 10) yield by reacting 1!methyl! cyclopentanone with CS1 in aqueous ammonia at 9>C[ The product was puri_ed by recrystallization from acetic acidÐwater ð62JCS"P0#0998Ł "Equation "1##[ NH2
CS2, NH4OH
O
N
(2)
SH SH
(10)
Compound "00# was shown by NMR spectroscopic studies to be formed when the trimerization product of 1 moles of MeN1C1S and 0 mole of MeN1C1O was allowed to react with ethylene oxide as depicted in Equation "2# ð52BAU0273Ł[ The preparation of "01# has also been described ð57MI 500!90Ł[ Me
Me
N
S
O
S
N
O
S (3)
S Me
N
N
Me
Me
O
N
N
Me
O (11) PhO O O PhO
S
O N N
S
N N O
Cl
Cl
(12)
The cyclic cationic cobalt carbene complex "02# reacts with CS1 in acetone "1 h at 59>C# to the dark brown dimetallaspirocarbene complex "03# as depicted in Equation "3#^ the structure of the compound was con_rmed by x!ray analysis[ The dication was obtained in 47) yield as the PF5 salt and crystallizes with 9[4 mole of acetone ð74CB2040Ł[ PMe3 Cp Co 2
O
N
Me
+
CS2
Me
(13)
N
PMe3 S
Co Cp
2+
(4)
Cp Co S N Me3P Me (14)
"ii# Compounds with the S1CP1 core There are only three quite di}erent compounds known with the S1CP1 core[ The 0\2!dimethyl! 1\1\3\3!tetrakis"trimethylsilylsulfano#!0\2!diphosphetane "04# "m[p[ 009>C# has been prepared in 68) yield from the reaction of methylbis"trimethylsilyl#phosphine with CS1 in 0\1!dimethoxyethane at −29>C[ In the _rst step CS1 inserts into the starting material and the insertion product dimerizes to "04#[ The compound crystallizes from cyclopentane at −67>C as shown in Equation "4# ð73ZAAC"406#64Ł[
214
Dichalco`enomethanes Me TMS Me
CS2
P
TMS
S
P
S
TMS
TMS
S
P
S
TMS
(5)
TMS
Me (15)
The dithioacetal "05# is formed in 84) yield by sulfenation of the corresponding methylene compound with MeSSO1Me[ The starting materials were adsorbed on Al1O2ÐKF and left at room temperature for 0 h according to Equation "5#[ The compound was extracted with dichloromethane and puri_ed by chromatography ð81SC0248Ł[ O
O
(EtO)2P
Al2O3–KF
(EtO)2P
SMe
(EtO)2P
MeSSO2Me
(EtO)2P
SMe
O
(6)
O (16)
Green crystals of the cationic complex "06# form in 39) yield from a hot mixture of MeC! "CH1PEt1#2 "triphos# and Fe"BF3#1 = 5 H1O in dichloromethaneÐethanol when CS1 is passed through the solution ð79AG0944\ 70JOM"107#70Ł[ Et
Et Et
P Et Et P
S
P
2+
P [BF4]2–
Fe S
Et
Et
Et
P Et
Et (17)
"iii# Compounds with the S1CSi1 core The compounds of the type "R0S#1C"SiMe1R1#1 "07# have been prepared by three related methods[ The methods described in Table 0 start from various lithium salts[ Method 0 is the reaction of "TMS#1CLi1 with 3 moles of MeSSO1Me in at −67>C in THF ð77TL4126Ł[ Method 1 is the reaction of the corresponding "RS#1CH1 with BuLi followed by addition of RMe1SiCl to give _rst "RS#1CH! "SiMe1R#\ which is again treated with BuLi:RMe1SiCl ð89CL0300Ł[ A similar procedure generates the heterocycles "07e# and "07f# ð56JA320\ 56JA323Ł[ Method 2 is the reaction of "TMS#1C"SPh#Li with PhSSPh in THF ð73JOC057Ł[ The compound "07a# forms also as an equimolar mixture with "TMS#1C1O during the reaction of "TMS#2CSMe with mcpba at −67>C in dichloromethane ð75TL4874Ł[ Table 0 Preparation of "R0S#1C"SiR12#1\ compounds "07a#Ð"07f#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ M[p[ Method Yield Ref[ "07# R SiR02 ">C# ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a Me TMS 0 74 77TL4126 b Me SiMe1Ph 1 59 89CL0300 c Et TMS 1 89CL0300 d Ph TMS 1\ 2 61\ 50 73JOC057 e 0"CH1#20 TMS 18[5Ð29 1 85 56JA323 SiPh2 106 1 56JA320 f 0"CH1#20 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
The compound "TMS#1C"SH#SOEt was proposed to be an intermediate during the thermal decomposition of "TMS#1CHSSOEt to give _nally TMS!C"S#SEt via a sila!Pummerer type rearrangement ð74TL1148Ł[
215
Two Or One Chalco`ens
"iv# Compounds with the S1CGe1 core The germanium derivative "08#\ analogous to the heterocycles "07e#\ has been prepared in a similar two!step procedure as described in method 1 in Table 0 ð56JA320Ł[
S Et3Ge
S GeEt3
(19)
"v# Compounds with the S1CSn1 core One compound of this type is described in the literature[ Colorless crystals of "MeS#1C"SnMe2#1 "19# "m[p[ 80Ð81>C# have been obtained in 89) yield by addition of ClSnMe2 to a solution of "MeS#1"Me2Sn#CLi in THF at −67>C[ The compound was puri_ed by vacuum distilation ð66CB730Ł[
"vi# Compounds with the S1CNa1 core Only one compound with this core\ "PhOSO1#1CNa1\ has been mentioned in the literature ð57MI nothing is reported about the nature of the C0Na bond[
500!90Ł^
"vii# Compounds with the S1CNSi core The compound "MeS#1C"N1CHPh#TMS "10# has been obtained by the reaction of PhCH1N1C"SMe#1 with lithium diisopropylamide "LDA# in THF at −67>C followed by addition of TMS!Cl together with the silylated product PhCH1N1C"SMe#"SCH1TMS#[ The compound ratio varies between 29:69 and 64:14 as monitored by NMR spectroscopy and depends on the time when TMS!Cl was added to the reaction mixture^ chromatography over silica gel with petroleum ether:benzene produces "10# in 7) yield ð64AG338\ 79LA0640Ł[
"viii# Compounds with the S1CPSi core Mikolajczyk and co!workers describe the formation of "MeS#1C"P"1O#"OEt#1#"TMS# "11#\ when the salt ð"MeS#1C"P"1O#"OEt#1#ŁLi is treated with TMS!Cl in THF at −67>C[ The compound was characterized by a 20P NMR signal at d 26[3 ppm ð78S090Ł[
"ix# Compounds with the S1CSiGe core The only compound with this core has been reported by Brook et al[ In a procedure described for the heterocycles "07e#\ "07f#\ and "08#\ the 1\1!disubstituted 0\2!dithiane "12# has been obtained in two steps by lithiation of the 1!germyl!0\2!dithiane followed by addition of TMS!Cl "method 1 for "07## ð56JA320Ł[
S Et3Ge
S TMS
(23)
"x# Compounds with the S1CSiLi core The structure of compounds with this core is not reported[ Ionic "ð"RS#1C"SiR2#ŁLi# or covalent formulation is possible[ Reich reported a low!temperature multi!NMR study involving
Dichalco`enomethanes
216
"PhS#1C"SiMe1 Ph#Li "and similar compounds#[ In THFÐether the compounds are present as contact ion pairs\ whereas in hexamethylphosphoric triamide "HMPTA# weakening of the C0Li bond occurs with formation of separated ion pairs ð82AG0378Ł[ The compounds have generally been obtained by treating the corresponding "RS#1C"SiR2#H with BuLi or a lithium amide in a polar solvent such as THF or diethyl ether[ Thus\ a solution of "MeS#1C"TMS#Li is obtained by addition of "MeS#1C"TMS#H to a solution of LDA in a mixture of THF\ hexane\ and HMPTA at −67>C ð66CB730Ł[ Similarly\ addition of BuLi to a THF solution at −69 to −49>C of the appropriate "RS#1C"SiR2#H species can also be achieved ð62CB1166Ł[ In most cases the compounds have been generated in situ and used as nucleophiles to produce an elementÐcarbon bond in the reaction with elementÐhalogen compounds[ The following species have been used in this manner] "MeS#1C"TMS#Li ð62CB1166\ 64AG26\ 72JA6608\ 74TL2920\ 78TL6922\ 89CL0300Ł\ "PhS#1C"TMS#Li ð73JOC057Ł\ "MeS#1C"SiMe1Ph#Li\ "EtS#1C"TMS#Li\ "EtS#1C"SiMe1 Ph#Lið89CL0300Ł\ "MeS#1C"SiMe1But#Li ð74TL0892Ł\ "SCH1CH1CH1S#C"TMS#Li\ and "SCH1SCH1 S#C"TMS#Li ð62CB1166Ł[
"xi# Compounds with the S1CSnLi core The compounds "MeS#1C"SnPh2#Li\ "MeS#1C"SnBu2#Li\ and "MeS#1C"SnMe2#Li have been obtained by reacting "MeS#1CHLi with the corresponding R2SnCl compounds followed by treating of the resulting "MeS#1CHSnR2 with LDA in THFÐHMPTA at −67>C ð64AG26Ł[ The compound "MeS#1C"SnMe2#Li has similarly been prepared in a THFÐhexaneÐHMPTA mixture ð66CB730Ł[ In all cases the compounds were used in solution for further reactions[
"xii# Compounds with the S1CPCr core The compound "PhS#1C"PPh2#Cr"CO#4 "13# was presented at a symposium without further details of its preparation ð64JOM"83#118Ł[ The compound can be considered to result from the coordination of the ylide "PhS#1 C1PPh2 to the 05!electron fragment Cr"CO#4 via the carbon atom[
(CO)5Cr
SPh PPh3 SPh
(24)
"xiii# Compounds with the S1CPMo core The coordination chemistry of the adduct S1CPR2 "R Me\ Et\ cyclohexyl "Cy## towards various molybdenum compounds has been explored by the group of Miguel\ Carmona and others[ This ligand coordinates in a h2!pseudoallylic manner to one or two transition metals or to one transition metal and a main group element with formation of a S1CPMo core[ The _rst compound in this series\ the dimeric species "Mo"CO#1"S1CPEt2#"PEt2##1 "14#\ has been detected by Bianchini and prepared either from Mo"CO#2"C6H7# and S1CPEt2 or from irradiating the h0!bonded complex "CO#4MoS1CPEt2 in 59) and 39) yield\ respectively ð71OM667Ł[ The addition of SnBuCl2 to "14# leads to "15# "58) yield# in which the two sulfur atoms form bridges to the tin atom ð81AG70Ł^ the reactions are summarized in Scheme 6[ Red crystals of "16# have been obtained by two routes[ Starting from MoHCl"CO#1"PMe2#2 the complex is formed in low yield with CS1 by elimination of HCl[ The compound is also formed in an unusual reaction on heating a solution of Mo"C1S3#"C1H3#"PMe2#2 at 49>C under 1 atm CO[ Alkylation leads to the cationic species "17# as depicted in Scheme 7 ð81JCS"D#1296\ 82IC4458Ł[ The related mononuclear compound "18# is produced in 64) yield by insertion of CS1 into the Mo0P bond of MoCl"NO#"PMe2#3[ Replacement of Cl and one PMe2 by the chelating ligand ðS1CNMe1Ł− results in the formation of the yellow complex "29# in about 49) yield as shown in Scheme 8 ð78IC1019Ł[
217
Two Or One Chalco`ens
Mo(CO)3C7H8
OC PR3 S PR3 OC Mo S S Mo CO R3 P CO S PR3
S2 CPEt3
UV, THF
(CO)5MoS2CPEt3
(25) R = cyclohexyl R = Et R = Bu SnBuCl3
S PR3 S Cl Cl Sn Mo CO Bu CO Cl PR3
S2CPR3
NCMe Cl CO Mo Sn Cl OC CO Bu NCMe Cl
(26) Scheme 7
S MoH(Cl)(CO)2(PMe3)3
CS2
PMe3
S
CO
Me3P Mo CO Me3P CO
Mo(C2S4)C2H4)(PMe3)3
(27) RI
R S
+
PMe3
S
Me3P Mo CO Me3P CO (28) R = Me, Et Scheme 8
S
S MoCl(NO)(PMe3)4
CS2
PMe3
S
Cl Mo PMe3 Me3P NO
S
Na[S2CNMe2]
PMe3
S Mo PMe3 S NO Me2N (30)
(29) Scheme 9
Dinuclear compounds\ in which the S1CPR2 group is bridging to another transition metal via the sulfur atoms\ have been realized with Mn!\ Re!\ and Ru!containing fragments[ Thus\ reaction of "CO#2"Br#Mn"S1CPR2# with Mo"CO#2"NCMe#2 in THF produces the purpleÐred complex "20# in quantitative yields as shown in Scheme 09 "M Mn#[ One CO group at the Mo atom can be replaced by monodentate phosphines to give "21# ð80JOM"319#C01\ 82OM0283Ł^ whereas the action of chelating ligands R1PEPR1 "E O\ R Et^ E CH1\ R Me\ Ph# produce red "22# in 69Ð79) yield ð82OM0283Ł[ Reduction of "20# with Na0Hg in THF produces the anion "23#\ probably with
218
Dichalco`enomethanes
formation of a Mo0Mn bond ð82OM1777Ł[ The analogous Re!containing compounds "20Ð23^ M Re# have been obtained ð83JOM"356#120Ł[ S
Br
S S
CO M CO
PR3
Mo(CO)3(NCMe)3
S CO
S S
S S
PR2
Mo CO CO CO (34)
PR3
CO M Mo CO CO CO CO Br CO
E R2P
CO M CO CO
Na/Hg
PR3
L
(31)
S
PR3
S
PR3
CO M Mo CO CO CO CO Br L
CO M Mo CO CO CO CO Br PR2 R2P E (33) a; E = O; R = Et b; E = CH2; R = Me c; E = CH2; R = Ph
(32)
Scheme 10
If the starting complex Mo"CO#2"NCMe#2 is treated with the cationic species ð"h!Me5C5# ClRuC"S1CPCy2#Ł¦ in THF\ "24# is formed instantaneously as depicted in Scheme 00[ This complex undergoes substitution of one CO group to a}ord the cationic dicarbonyls "25#^ all compounds have been prepared as the PF5− salts ð81POL1602Ł[ +
Mo(CO)3(NCMe)3
S PCy3
Ru Cl S
S Ru
S
+
Mo CO CO Cl CO
S
S
PCy3 L
Ru
+
PCy3 Mo CO CO Cl L
(36) a; L = PEt3 b; L = P(OMe)3
(35) Cy = cyclohexyl Scheme 11
A further series of compounds with the S1CPMo core is depicted in Equation "6#[ The reaction of "h2!allyl#"CO#1BrM"h1!S1CPR2# "M Mo\ W^ R cyclohexyl\ Pri# with Mo"CO#2"NCMe#2 in dichloromethane produces a series of four compounds of the type "26# with M? Mo\ M Mo or W in yields up to 89) ð83OM0225Ł[ CO
S M
PR3
Mo(CO)3(NCMe)3
S
CO
S PR3
S
Br
M1 CO
CO M1
= Mo, W M2 = Mo, W R = Cy, Pri
CO CO CO
M2 Br
(37)
(7)
229
Two Or One Chalco`ens
"xiv# Compounds with the S1CPW core There are only few compounds with this core which resemble those of the corresponding Mo compounds[ Thus\ the series of four compounds "26# in Equation "6# have also been obtained with M? W ð83OM0225Ł[ The reaction sequence shown in Scheme 00 under similar conditions with W"CO#2"NCMe#2 leads to the corresponding cation "27# and the substitution product "28# ð81POL1602Ł[ S
S
+
W
Ru Cl
S
S
PCy3 CO CO CO
W
Ru Cl
(38)
+
PEt3 CO CO PEt3
(39)
Cy = cyclohexyl
Starting with WHCl"CO#1PMe2\ the red complex "39# is formed in 79) yield by reacting with CS1^ HCl is eliminated[ This compound can be transferred into the cationic species "30# in 49) yield upon alkylation with MeI^ the corresponding reaction of the analogous Mo compounds is depicted in Scheme 7 ð82IC4458Ł[ Me PMe3
S
+
S
S
PMe3
S
Me3P W CO Me3P CO
Me3P W CO Me3P CO
(41)
(40)
The tungsten ylide compound "PhS#1C"PPh2#W"CO#4 "31# was presented at a symposium without further details of preparation ð64JOM"83#118Ł^ it is the tungsten analogue of the chromium complex "13#[ SPh PPh3 SPh
(CO)5W (42)
"xv# Compounds with the S1CPMn core Compounds with this core are only known with the S1CPR2 ligand bonded in a h2!manner and bridging two transition metals[ Starting with the ionic compound "23# "M Mn# in which the ligand is h2!bonded to the Mo atom\ the reaction with ClSnPh2 in THF induces a change in the coordination mode and leads to the red compounds "32# "R cyclohexyl\ Pri# in 69Ð79) yield ð82OM1777Ł[ S S Ph3Sn CO Mo CO CO
PR3 Mn CO CO CO (43)
The heterobimetallic compound ReMn"CO#5S1CPCy2 "33#\ in which the Mo"CO#2SnPh2 fragment of "32# is replaced by the isoelectronic Re"CO#2 fragment\ is obtained in 43) yield either by the reaction of "CO#2BrMn"h1!S1CPCy2# or the cation ð"CO#3Mn"h1!S1CPCy2#Ł¦ with NaðRe"CO#4Ł in
220
Dichalco`enomethanes
THF or by the reaction of "CO#2BrRe"h1!S1CPCy2# with NaðMn"CO#4Ł as shown in Scheme 01 ð80OM273Ł[
S
CO
Na[Re(CO)5]
PCy3
Mn CO
S
S
Br
CO CO Re CO
S CO
PR3
Br Na[Mn(CO)5]
Mn CO CO CO (44)
CO
S PCy3
Re CO
S CO
Na[Re(CO)5]
CO + S Mn S CO CO
CO
PCy3
Cy = cyclohexyl Scheme 12
The preparation of a series of homobinuclear compounds starting from "34# is summarized in Scheme 02[ The basic compound "34# can be prepared by several routes[ Thus\ similar to its Re analogue "33#\ it forms by the action of NaðMn"CO#4Ł on "CO#2BrMn"h1!S1CPCy2# or the cationic species ð"CO#3Mn"h1!S1CPCy2#Ł¦ ð80OM273Ł[ Yields of about 79Ð89) are obtained when Mn1"CO#09 is re~uxed with S1CPCy2 or S1CP"Pri#2 in toluene or dichloromethane ð76CC361\ 80OM0572Ł[ A stepwise CO substitution of "34# by monodentate ligands or by the chelating ligand Ph1PCH1PPh1 generates the derivatives "35#Ð"37# ð76CC361\ 80OM0572Ł[ Reduction of "34# with LiðBHEt2Ł leads to the intermediate lithium salt "38# which\ on alkylation\ can be transformed into the orange hydrido compounds "49# ð80OM2994Ł[
S
S (CO)3Mn
–
PR13
R2X
R2 S
S
PR13
Mn(CO)3 (CO)3Mn
H (49) Mn(CO)5Br Li[HBEt3]
S2CPR13
Mn(CO)3 H
(50) R2 = Me, CH2Cl
S PR13
(CO)3BrMn
NaMn(CO)5 +
(CO)3Mn
S
PR13
Mn(CO)3
(45) R = Cy, Pri
PR13
(CO)4Mn
S
S
S
S S2CPR13
L
Mn2(CO)10 P
P
S
S S
S (CO)2Mn
PR13
Mn(CO)2
P
L(CO)2Mn
Mn(CO)3 (46)
S L(CO)2Mn
Cy = cyclohexyl Scheme 13
S
PR13
Mn(CO)2L (47)
L = P(OMe)3, P(OPh)3, P(OEt)3, PEt3, CNBut
P (48)
PR13
221
Two Or One Chalco`ens
"xvi# Compounds with the S1CPNi core Two types of compounds with the S1CPNi core have been described[ Bianchini reported the structure of the cationic brown complex "40#\ which has been obtained in 75) yield by reacting the nickel"9# complex NiN"CH1CH1PPh1#2 with MeSO2F in CS1 solution and crystallization with NaBH3 from acetoneÐether ð72JOM"135#C02\ 73JOM"169#140Ł[ S
N
S
Ph2P Ni PPh2 Ph2P S MeS (51)
S R3P
Ni PR3 S (52)
The second type was prepared by Ibers and co!workers[ Thus\ addition of 1 equivalents of S1CPR2 to a solution of Ni"cod#1 in THF produced the compounds "41# "R Me\ Et# containing two S1CPR2 units under head!to!tail dimerization of two CS1 molecules and movement of one PR2 molecule to the nickel atom ð72IC300Ł[ The compound "41# with R Me has also been obtained according to Equation "7# by reacting the nickel acyclic compound with CS1 in ether ð77OM1466Ł[
(52)
+ CS2 Ni Me3P
(8)
PMe3
"xvii# Compounds with the S1CPPt core One type of compound with the S1CPPt core has been reported[ Thus\ S!alkyl "triphenyl! stannyl#dithioformates Ph2SnC"S#SR "R Me\ CH1Ph\ allyl# react in benzene solution with one equivalent of the Pt"9# complex "PPh2#1Pt"h!CH11CH1# to give the corresponding pale yellow "42# in quantitative yields as shown in Equation "8#[ The molecular structure of the methyl derivative is reported ð72IC2699Ł[ Ph3P
RS
S Pt
+ Ph3Sn
Ph3P
SR
SnPh3
Ph3P Pt
–C2H4
Ph3P
(9)
S (53)
"xviii# Compounds with the S1CFe1 core Various di}erent types of compounds have been described[ Seyferth reported the preparation of "43# in a two!step reaction starting from a dithioformate esterÐFe1"CO#5 complex which contains an acidic hydrogen atom[ Deprotonation with LDA followed by treatment with iodomethane produce orange "43^ R0 R1 Me# in 66) yield ð72OM0585Ł[ The starting lithiated species "having a S1CLiFe core# rearranges to a salt!like product which on alkylation with R?X compounds can be transformed into "43#\ in which di}erent organic groups are located on sulfur as depicted in Scheme 03[ The compounds can be viewed as complexes of Fe1"CO#5 with the six!electron sulfonium ylide donor R1S1C1S ð76OM172Ł[ A related complex has been prepared by Busetto and co!workers[ The complex "44# with four iron atoms\ in which the CS1 group functions as an eight!electron donor\ was prepared by reacting FpC"S#SFp "Fp CpFe"CO#1# with excess Fe1"CO#8 in toluene[ Among others\ the dark green compound "44# could be separated by column chromatography in 8) yield ð75G090Ł[ A series of compounds in which a carbene ligand C"SR#1 functions as a four!electron donor forming a S1CFe1 core has been described by Angelici and co!workers[ The cationic carbene complex ðCp"CO#"MeCN#Fe1C"SR#1Ł¦ reacts in THF with ð"CO#2FeNOŁ− to give the violet compounds "46# in 39Ð64) yield[ The route outlined in Scheme 04 can also be extended to produce compounds
222
Dichalco`enomethanes R2 S
S
(CO)3Fe
R1
R1
LDA
S S
(CO)3Fe
Fe(CO)3
Fe(CO)3
(54) LDA R2 X
Li S
R1S S
(CO)3Fe
R1
–
S (CO)3Fe
Fe(CO)3 R1 R2
Fe(CO)3
= Me, Et = Me, Et, allyl Scheme 14
O S Cp(CO)Fe
S
FeCp(CO) S
(CO)3Fe
S (CO)3Fe
Fe(CO)3 Fe(CO)3
S
Fe(CO)3
(55)
(56)
with the S1CFeCo and S1CRuCo core[ With PEt2\ the complex "46# containing the C"SMe#1 ligand is transformed into the black complex "47# "m[p[ 091Ð093>C# in 82) yield ð75IC1766Ł[ One 49! electron trinuclear complex with the S1CFe1 core is also described[ As depicted in the structure of "45#\ the carbene ligand of "46# can also serve as a m2!3!electron donor[ Compound "45# was one of the compounds obtained from irradiating a mixture of Fe"CO#4 with the trithiocarbonate complex "CO#4Cr0S1CS"CH1#1S in THF^ column chromatography yields black crystals "m[p[ 019>C# in about 03) yield ð73JOM"151#58Ł[ R SR OC Fe MeCN
R
S
+
R
S
S
[(Ph3P)2N][(CO)3FeNO]
Fe Fe(CO)(NO)
SR
OC
Fe Fe(NO)(PEt3) OC
O
O
(57) SR
PEt3
R S
SMe
S
SMe ,
S
(58) S
= SR
,
S
Scheme 15
"xix# Compounds with the S1CFeCo core The single type of compound with this core resembles compounds "46# and "47# in which the 02! electron fragment Fe"CO#NO is replaced by the isoelectronic fragment Co"CO#1 as depicted in Scheme 05[ A solution of the appropriate cationic carbene complex ðCp"CO#"MeCN#Fe1C"SR#1Ł¦ in THF was combined with an equimolar solution of NaðCo"CO#3Ł[ Red to black solids "48# were obtained in 59Ð69) yield by column chromatography on silica gel[ The compounds "48# can be converted into the phosphine!substituted derivatives "59# in similar yields as reported for the iron
223
Two Or One Chalco`ens
analogues by reacting with PEt2 in dichloromethane ð75IC1766Ł[ The chemistry of "48# has been described ð73OM0927\ 74OM0115Ł[ R SR OC Fe MeCN
R
S
+
R
S
S
[(Ph3P)2N][Co(CO)4]
PEt3
Fe Co(CO)2
SR
OC
Fe Co(CO)(PEt3) OC
O
O
(59) SR
R S
SMe
S
SMe ,
S
(60) S
= SR
,
S
Scheme 16
"xx# Compounds with the S1CCoRu core The compound Cp"CO#1Ru"m!C"SMe#1#Co"CO#1 "50# has been prepared analogously to "48# in Scheme 05 but starting with the cationic carbene complex ðCp"CO#1"MeCN#Ru1C"SMe#1Ł¦^ red crystals of "50# "m[p[ 009Ð001>C# are produced in 51) yield ð75IC1766Ł[ Me S
Me S Ru Co(CO)2
OC O (61)
5[00[1[0[2 Two seleniums or two telluriums and a group 04 element and:or a metalloid and:or a metal function "i# Compounds with the Se1CSi1 core Only one compound with this core has been described[ DuMont and co!workers reported the formation of the yellow triselenacyclopentane derivative "51# "m[p[ 048>C# in less than 4) yield by reacting a solution of "TMS#2CSeSeSeC"TMS#2 in dioxane with copper powder for 2 days at 79Ð89>C^ the main product is "TMS#2CSeSeC"TMS#2 ð89CB1214Ł[ TMS TMS
Se Se Se
TMS TMS
(62)
"ii# Compounds with the Se1CSiLi core The compound "PhSe#1C"TMS#Li has been mentioned as being formed in situ by the consecutive reaction of "PhSe#1CH1 with LDA followed by treatment with TMS!Cl[ Further reactions with ketones are described ð66CB741Ł[ "iii# Compounds with the Se1CPPd core The redÐviolet to blueÐviolet compounds "52a#Ð"52c#\ containing two Se1CPPd centers\ form in about 79) yield upon the reaction of "Ph2P#1Pd"h1!CSe1# with various methyl substituted
224
Dichalco`enomethanes
phosphine "PR2 PMe2\ PMe1Ph\ PMePh1# ligands as depicted in Equation "09#[ The compounds show decomposition points "DTA# of 040\ 048\ and 005>C\ respectively ð74ZN"B#0240Ł[ The structure of one derivative "PR2 PMe2# has been con_rmed by an x!ray di}raction study ð75JOM"200#52Ł[ R3P
Se R3P Pd R 3P
Se
PR3
R3P
Se
Pd Pd
Se
Se PR3
(10)
Se PR3
(63) a; PR3 = PMe3 b; PR3 = PMe2Ph c; PR3 = PMePh2
5[00[1[1 Methanes Bearing Two Dissimilar Chalcogens 5[00[1[1[0 Oxygen\ sulfur and two functions derived from a group 04 element\ metalloid and:or a metal "i# Compounds with the OSCN1 core Compounds with this core are restricted to the species "53#Ð"55# and there is no common method of preparation[ The spirocyclic compound "53# was obtained when the N!TMS ester of tri! thioisocyanuric acid was reacted with ethylene oxide in the presence of tetramethylethylammonium bromide[ The compounds have been characterized by 0H NMR spectroscopy^ no further details of preparation are available ð52BAU0273Ł[ The compound "54# has been described ð64YGK025Ł[ The compound "55# "m[p[ 055Ð057>C# has been obtained in 80) yield by reacting 3!"2!methyl! thioureido#phenyl N!methoxycarbonyl!N!methylcarbamate with dimethyl sulfate in acetone ð64MI 500!90Ł[ The radical "56# was reported to be formed upon x!ray irradiation of hydrous carnidazole at 66 K^ addition of a radiogenic NO1 radical to the C1S bond was postulated ð81C029Ł[
Me
H
Me
S N
O
N
S
N S
MeS
N CN
HO
N CN
O
Me
SMe
(64)
(65) N O
H MeS
N Me
O
N
O
OMe
NO2
N
N MeOS(O)2O
Me H
H (66)
N
S OMe NO2
(67)
"ii# Compounds with the OSCSi1 core The preparation of the O!Si hemithioacetals "57# and "58# have been reported by Ricci et al[ Thus\ treatment of "TMS#1CHSMe with n!buthyllithium in ether at −59>C followed by addition of bis"trimethylsilyl# peroxide "BTMSPO# for oxysilylation produced a 0 ] 0 mixture of unreacted starting material and "57#[ Minor amounts of "58# were detected by GCÐMS analysis upon reacting "TMS#1CHSMe with mcpba in dry dichloromethane at −67>C ð75TL4874Ł[
225
Two Or One Chalco`ens TMS
TMS
TMS
Li
MeS
OR
PhS
OMe (70)
(68) R = TMS (69) R = OCOC6H4Cl-3
"iii# Compounds with the OSCSiLi core Lithiation of the O\S!acetal MeO"PhS#CHTMS with s!butyllithium in the presence of TMEDA at −67>C generates "69# ð75JOC768Ł[ A similar preparation with n!butyllithium in THF was described ð72SC874Ł[ The lithiated acetal has not been isolated and was used for the conversion of ketones into ketene!O\S!acetals[ 5[00[1[1[1 Oxygen and selenium\ or oxygen and tellurium and two functions derived from a group 04 element\ metalloid and:or a metal Compounds with OSeC or OTeC fragments with adjacent group 04 elements\ metalloids or transition metals have not yet been described[ 5[00[1[1[2 Sulfur and selenium\ or sulfur and tellurium and two functions derived from a group 04 element\ metalloid and:or a metal "i# Compounds with the SSeCSiLi core According to low!temperature 0H NMR studies\ the compound PhS"PhSe#CLiSiMe1Ph is present in THF and also in THFÐHMPTA solution as a separated ion pair with diastereomeric TMS groups up to −19>C[ At about 6>C in THFÐether\ the signals coalesce^ a rotation barrier around the C0S bond was suggested ð82AG0378Ł[ "ii# Compounds with the SSeCPPd core The only three compounds in this series are reported by Werner et al[ As with their S1 analogues and in a manner related to Equation "09#\ various Pd"PR2#3 compounds "PR2 PMe2\ PMe1Ph\ PMePh1# add CSSe in ether to give the dimeric red compounds "60a#Ð"60c# in about 74) yield as shown in Equation "00#[ From spectroscopic data the authors could not decide between the two possible isomers involving a Se or a S bridge of the Pd0C bond ð74ZN"B#0240Ł[ R3P Pd(PR3)4
S
CSSe
R3P
Pd Se
R3P
Se Pd
PR3 S PR3
Se
+
R3P
S Pd Pd
PR3 Se
(11)
S
PR3 (71) a; PR3 = PMe3 b; PR3 = PMe2Ph c; PR3 = PMePh2
5[00[2 MONOCHALCOGENOMETHANES The majority of compounds in this section contain a m2!CER carbyne ligand "E chalcogen# bridging a triangular face of a transition metal cluster compound[ R can also be a 05! or 06!electron transition metal fragment\ for example C4H4Fe"CO#1\ Mn"CO#4\ etc[ In this case the CE unit can be considered as m3!bridging[ Not included are cluster compounds in which only the 05!electron ligand CE coordinates at an appropriate trinuclear cluster in a m2!manner[ Many compounds in this series also arise from the coordination of a E1CXY compound at a transition metal in an h1!manner[ The bonding of a CER fragment to main group elements is restricted to few examples bearing the OCN2 core[ Thus\ no compounds with the ECSi2\ ECP2\ or related units have been described[
226
Monochalco`enomethanes
The compounds are arranged in a manner such that the CER fragment "E chalcogen# is bonded to three identical main group elements\ mixed main group elements\ mixed main and group transition metal elements\ three equal transition metal elements\ and di}erent transition metal elements[ 5[00[2[0 Methanes Bearing One Oxygen Function and Three Functions Derived From the Group 04 Element\ Metalloid and:or a Metal 5[00[2[0[0 Compounds with the OCN2 core Two types of compounds with the OCN2 core have been described[ Kantlehner et al[ reported the preparation of the carbonic orthoamide derivatives "61a#Ð"61c# "R Me\ Et\ Pri# which form upon addition of the corresponding alcohol!free NaOR to ðC"NMe1#2ŁCl in THF solution[ Fractional distillation produced "61a# "m[p[ 39Ð31>C#\ "61b# "b[p[ 59Ð64>C at 09 torr#\ and "61c# "b[p[ 28Ð39>C at 9[0 torr# in 43)\ 28) and 53) yields\ respectively ð68LA1978Ł[ Compounds "61a# and "61b# have also been obtained by treating C"NMe1#3 with an equimolar amount of the corresponding HOR as depicted in Scheme 06 ð65JOM"094#C08Ł[ Me2N NMe2 Cl–
+
Me2N
NaOR
Me2N Me2N Me2N
HOR
OR
Me2N Me2N Me2N
NMe2
(72) a; R = Me b; R = Et c; R = Pri Scheme 17
Spirocyclic compounds in this series form as 2 ] 0 adducts of various alkyl isocyanides with aminoaziridines in acetonitrile "Scheme 07#[ The compounds "62a# "m[p[ 064Ð071>C# and "62b# "m[p[ 050Ð051>C# are formed in 82) and 53) yield\ respectively[ Protonation of "62a# with aqueous HCl results in the formation of the cationic compound "63# in 32) yield ð70LA153Ł[ +
Ph 3
N R1
•
O
Ph
R2
N
R1 O N
O N
+ R2
NMe2
N
Me2N
N R1
Ph HCl
Et Me2N
O
(73) a; R1 = Me; R2 = Me b; R1 = Et; R2 = H
Me O N
O N
N N H Me
Cl–
O
(74)
Scheme 18
The spirocyclic compound "64# is probably formed as an intermediate similar to Scheme 4\ when Me2SnNMeCH1CH1NMeSnMe2 is allowed to react with the appropriate ethylene thionocarbonate^ the compound could not be isolated ð69MI 500!90Ł[ Me N
O
N
N
Me Me (75)
5[00[2[0[1 Compounds with the OCNSiTa core Compounds with this core can formally be considered as adducts of pyridine derivatives at h1! bonded tantalum silaacyl compounds via the acyl carbon atom[ The starting unstable silaacyl
227
Two Or One Chalco`ens
complex C4"Me#4Cl2Ta"h1!C"O#TMS# has been obtained by CO insertion into the Ta0Si bond of C4"Me#4Cl2TaTMS[ The orange compounds "65# precipitate from pentane solution in about 89) yield upon addition of the appropriate pyridine derivative NR1 ""65a#\ NR1 pyridine\ m[p[ 84Ð87>C^ "65b#\ NR1 NC4H3Me!3^ "65c# NR1 NC4H2Me1!1\5# as follows from Scheme 08[ Donor exchange occurs in "65a# with the stronger base 3!methylpyridine to give "65b# and excess pyridine! d4 liberates 0 equiv[ of pyridine from "65a# with incorporation of the deuteriated donor ð78JA038Ł[ (C5Me5)Cl3Ta-TMS CO
(C5Me5)Cl3Ta
CO/PR3
O CO/NR2
TMS PR3
(C5Me5)Cl3Ta
NR2
PR3
O
(C5Me5)Cl3Ta
O
TMS
TMS
Pr3P
R2N (76) a; NR2 = NC5H5 b; NR2 = NC5H4Me-p c; NR2 = NC5H3Me2-o,o
(77) a; R = Me b; R = Et c; R = OMe Scheme 19
5[00[2[0[2 Compounds with the OCPSiTa core Closely related to the compounds with the OCNSiTa core are those with the OCPSiTa core which were prepared in a manner analogous to the pyridine derivatives "65# as depicted in Scheme 08[ Starting again with C4"Me#4Cl2TaTMS\ addition of PR2 under CO pressure "9[44 MPa^ 79 psi# produced the compounds "66# in about 74Ð89) yield as pale yellow powders[ However\ solutions of "66# in benzene or diethyl ether are intensely colored ""66a#\ blue^ "66b#\ deep purple^ "66c#\ dark red# and decomposition occurs within a few hours[ PMe2 converts "65a# into "66a# in 89) yield ð78JA038Ł[ The structure of "66b# was established by an x!ray study ð78JA038\ 89AX1263Ł[ 5[00[2[0[3 Compounds with the OCFe2 core This section includes compounds in which the m2!bonded COR group bridges the face of a triangular cluster or one face of a tetrahedral cluster\ contributing three electrons to the number of 37 or 59 CVE[ Not included are butter~y clusters with 51 CVE\ in which the carbon atom is bonded to four Fe atoms ð74JA7025\ 74JA7036Ł[ The neutral orangeÐred biscarbyne complexes "67# "a\ R Me# can be prepared either by alky! lation of the anion ðFe2"CO#8"m2!MeCO#Ł− with excess MeSO2F in dichloromethane at elevated temperature in about 09) yield ð72CC0446Ł or in not speci_ed yield "b\ R Et# by alkylation of the anion ðFe2"CO#8"m2!CMe#"m2!CO#Ł− with ðEt2OŁBF3 ð74OM0325Ł[ Replacement of CO in "67b# by PPh2 leads to "68# in about 84) yield[ Both compounds can also be generated from the cor! responding m2!h1 alkyne complexes as depicted in Scheme 19 ð74OM0325Ł[ The dark red ferrocenyl derivative "79# forms in 2) yield along with bisalkylidyne complexes "70a# and "70b#\ and "67a# by reacting ferrocenyllithium with Fe1"CO#8 in THF at room temperature^ the compounds could be separated by column chromatography over silica gel ð89ZN"B#336Ł[ The bisalkylidyne complex "70a# in which two m2!COMe groups are symmetrically bonded to a trinuclear cluster was earlier prepared in about 04) yield by reduction of Fe2"CO#01 with n! butyllithium and subsequent treatment of the reaction mixture with ðMe2OŁBF3 or in a similar procedure from HFe2"m1!COMe#"CO#09 in 11) yield using t!butyllithium ð77OM701Ł[ Anionic species with one m2!COR and one m2!CO function have also been isolated[ One route starts with the trinuclear dianion ðFe2"CO#00#Ł1−\ which reacts with the electrophiles MeSO2F\ EtSO2F and MeCOCl to produce the red compounds "71a#Ð"71c# "R Me\ Et\ MeCO# obtained as the ð"Ph2P#1NŁ salts in 62)\ 32) and 75) yield\ respectively ð68IC0125Ł[ A similar reaction using
228
Monochalco`enomethanes O
–
O
–
Fe(CO)3
Fe(CO)3
(CO)3Fe
(CO)3Fe
Fe (CO)3 Me+
Fe(CO)3
Et+
OR Fe(CO)3 (CO)3Fe
Fe(CO)3
CO
PPh3 –CO
(78) a; R = Me b; R = Et
OEt
OEt Fe(CO)3
Fe(CO)3 (CO)3Fe
(CO)3Fe
Fe(CO)2PPh3
Fe(CO)4 PPh3
T
OEt
(79)
Fe(CO)3 (CO)3Fe
Fe(CO)3PPh3
Scheme 20
OMe Fe(CO)3 (CO)3Fe
Fe(CO)3 Fc (80)
Fe(CO)3
Fe(CO)3 (CO)3Fe
–
O
OMe
Fe(CO)3
OR (81) a; R = Me b; R = O(CH2)4OMe
(CO)3Fe
Fe(CO)3 OR
(82) a; R = Me b; R = Et c; R = COMe d; R = COCH=CHMe e; R = COCH=CHPh f; R = CH2OMe
unsaturated acyl halides as electrophiles gave "71d# and "71e# in low yields ð78JOM"257#088Ł[ The other route comprises the reaction of ðFe1"CO#7Ł1− with ClCH1OMe in THF to produce the red salt "71f# "R CH1OMe#\ which was isolated in 11) yield as the NEt3 salt ð70CC078\ 70CC1385Ł[ The brown complex "72# with one Cp ring coordinated at one Fe atom of the trinuclear core has only been obtained as a by!product during the formation of heterodinuclear and trinuclear compounds[ The structure was con_rmed by an x!ray determination ð76OM708Ł[ The complex forms in 2[3) yield upon reacting HFe2"m!COMe#"CO#09 with "Ni"m!CO#"Cp1#1 ð75OM0092Ł or in about 4) yield from "cyclooctene#1Fe"CO#2 and Cp"CO#Fe"m!CO#"m!COMe#Mn"CO#"h4!CH2C4H3#\ with the main product being a complex with a OCFe1Mn core ð76JA1732Ł[ OMe O Fe(CO)3 CpFe
Fe(CO)3
O (83)
239
Two Or One Chalco`ens
The unstable hydrido complex "73# was mentioned as being formed from hydrogenation of the cluster HFe2"m!COMe#"CO#09^ however\ its stable dark purple SbPh2 derivative "74# can be isolated in 11) yield if the reaction is carried out in the presence of excess of the ligand ð72OM108Ł[ The related complex "75# in which the three hydrogen atoms\ serving as one!electron donors\ are replaced by the three!electron donor Bi atom is obtained in 54) yield by alkylation of the anion ðBiFe2"CO#09Ł− with MeSO2CF2 in CH1Cl1 solution ð75IC1361Ł[ OMe H (CO)3Fe H
Fe(CO)3 H Fe(CO)3
OMe H
Fe(CO)2 H Fe(CO)2
(CO)3Fe H
Ph3P
OMe
SbPh3
Fe(CO)3 (CO)3Fe Fe(CO)3
H
CO Pt Fe(CO)3
(CO)3Fe
Fe(CO)3
Bi SbPh3
(84)
(85)
(86)
OMe (87)
The trinuclear hydrido cluster HFe2"m!COMe#"CO#09 gave black crystals of the heteronuclear tetrahedral cluster Fe2Pt"m2!H#"m2!COMe#"CO#09"PPh2# "76# in about 49) yield when it was allowed to react with Pt"C1H3#1PPh2 at room temperature in ether ð71CC40Ł[ The anionic tetranuclear black purple cluster ðFe3"m!CO#"m2!COMe#"CO#00Ł− "77# was obtained by alkylation of the dianion ðFe3"CO#02Ł1− with either ðMe2OŁ¦ðBF3Ł− ð79CC679\ 79CC670Ł or MeSO2F ð79CC667\ 71JA4510Ł\ both in dichloromethane\ in about 44) yield^ the compound was isolated as the ð"Ph2P#1NŁ salt[ O
Fe(CO)3 Fe(CO)3
–
(CO)2Fe Fe(CO)3 OMe (88)
5[00[2[0[4 Compounds with the OCCo2 core This section contains two types of compounds with this core[ A few derivatives of the trinuclear cluster Cp2Co2"m2!COR#1 are known\ whereas the majority of compounds are based on the trinuclear cluster Co2"CO#8"m2!COR#\ in which R represents various organic substituents including main group or transition metal elements[ Starting material for the second series is mainly Co1"CO#7 or the covalent trinuclear cluster Co2"CO#8"m2!COLi#[ Thus\ the reaction of Co1"CO#7 with the trialkylborane adducts R2NBH2 produces the black compounds "78a# and "78b# in moderate yields ð57IC1154Ł[ A similar treatment of Co1"CO#7 in THF with the adducts Et2NBX2 "X Cl\ Br# gives "78c# and "78d# ð61JOM"35#038\ 64JOM"091#098\ 65ZN"B#231Ł[ Co1"CO#7 is also the starting material for the preparation of the red siloxy compound "89c#\ which can be obtained in 43) yield by reacting with 0!hydrosilatrane in THF ð82IC4772Ł\ whereas redÐ black "89a# "m[p[ 097>C dec[# and "89b# "m[p[ 80Ð82>C# have been obtained by the reaction of "CO#8Co2"m2!COLi# with the corresponding ClSiR2 in diethyl ether in 33) and 19) yield\ respec! tively ð69JOM"13#C50Ł[ Various compounds with Ti\ Zr or Hf ""80#Ð"82## in the apical position have also been prepared[ Thus\ one equivalent of "CO#8Co2"m2!COLi# reacts with Cp1MCl1 "M Ti\ Zr\ Hf# in toluene to produce the deep red to black colored cluster compounds "80# "a\ m[p[ 023>C\ 46) yield^ b\ m[p[ 027Ð030>C\ 61) yield^ c\ m[p[ 028Ð031>C\ 77) yield#[ Two equivalents of "CO#8Co2"m2!COLi# in a similar procedure leads to the disubstituted compounds "81# "a\ m[p[ 047Ð059>C\ 28) yield^ b\ m[p[ 034>C\ 24) yield^ c\ m[p[ 034>C\ 54) yield#[ Treatment of "80# with solid NaOH in toluene results in the formation of the oxo!bridged derivatives "82# "a\ m[p[ 054>C\ 25) yield^ b\ m[p[ 059Ð 053>C\ 04) yield^ c\ m[p[ 045Ð059>C\ 08) yield# ð67CB0592Ł[ Compound "80a# can also be obtained from Co1"CO#7 and Cp1TiCl1 ð65JOM"002#56Ł[ Black crystals of "83# are formed in 12) yield from NaðCo"CO#3Ł and CpTiCl2 in toluene ð67CB0128Ł[ The chromium!substituted complex "84#\ which
230
Monochalco`enomethanes
is extremely sensitive to atmospheric oxygen and moisture\ forms in about 59) yield by treatment of Co1"CO#7 with Cp1Cr1"m!OCMe2#1 ð89JOM"273#168Ł\ while the red complex "85# is the product of the reaction of Co1"CO#7 with one equivalent of pyridine in similar yield ð76AG570Ł[ All the main group and transition metal!substituted compounds are summarized in Scheme 10[ But Cp O
[Co]3
Co(CO)4 Ti
CpCr
O
py
CrCp
O
O
py
But
[Co]3 [Co]3
py O
Co py
[Co]3
[Co]3 (94)
(95) CpTiCl3
[Co]3
OLi
LiCo(CO)4
(96)
Cp2Cr2(OBut)2
py
O
R3NBX3
Co2(CO)8
BX2NR3
[Co]3 Cp2MCl2
(89) a; R = Me, X = H b; R = Et, X = H c; R = Et, X = Cl d; R = Et, X = Br
HSi(C2H4)3N R3SiCl
MCpCl O
O
[Co]3 (90) a; SiR3 = SiMe3 b; SiR3 = SiPh3 c; SiR3 = Si(C2H4)3N
[Co]3 (91) [Co]3
SiR3
OLi
NaOH
O
Cp2 M
O
Cp2 M
O
O
Cp2 M
O O
[Co]3
[Co]3
[Co]3 [Co]3
(93)
[Co]3
O = (CO)3Co
(92) (91)–(93) a; M = Ti b; M = Zr c; M = Hf
Co(CO)3 Co(CO)3
Scheme 21
The starting material for many compounds in Scheme 10\ black crystals of "CO#8Co2"m2!COLi#\ have been obtained from LiCo"CO#3 and Co3"CO#01 or Co1"CO#7 in ether as Et1O ð68CC285Ł or Pri1O adducts ð79AG300Ł[ The compound can be freed from ether upon reacting with Ph1O ð70AG83Ł[ Addition of dry HCl in hexane gives red crystals of the corresponding acid "CO#8Co2"m2!COH# "86#\ which rapidly decomposes at room temperature ð68CC286Ł^ the acid can be stored under CO or Ar at liquid!nitrogen temperature ð70AG83Ł[ With NEt2 the dark violet adduct "CO#8Co2"m2! COH = NEt2# is obtained ð70AG104Ł[ Acetylation of "CO#8Co2"m2!COLi# with MeCOBr in benzene at room temperature gives "CO#8Co2"m2!COCOMe ""87#\ m[p[ 012>C# in 56) yield ð65CB2228Ł[ The alkyl derivatives "88# have been obtained by di}erent routes[ The red!black methyl derivative "88a# can be obtained from Co1"CO#7 either by reacting with MeOCHCl1 in THF in 16) yield ð62JOM"49#154Ł or by reacting with Fe2"H#"m!COMe#"CO#09 in 37) yield ð76OM708Ł[ The consecutive addition of LiPh:ether at −59>C and Et2OBF3 in CH1Cl1 at −09>C to a solution of Co1"CO#7 does not form a Fischer!type carbene complex but leads to the formation of "88b# "the ethyl derivative# in about 3) yield ð72M740Ł[ The organic species are shown in Scheme 11[ The second type of compound with the Co2CO core comprises two species and has been reported by the group of Floriani[ The compounds originate from trimerization of a CpCo fragment which
231
Two Or One Chalco`ens Et
OH
O
[Co]3 (97)
i, LiPh ii, Et3OBF4
HCl
[Co]3
LiCo(CO)4
OLi
[Co]3 (99b)
Co2(CO)8 MeOCHCl2
MeCOBr
O OMe
O O [Co]3 (98)
[Co]3
O =
[Co]3 (99a)
Co(CO)3
(CO)3Co
Co(CO)3
Scheme 22
forms from CpCo"CH11CH1#1 upon losing the labile bonded ethylene molecules[ Thus\ black crystals of "099# crystallized in 37) yield from a toluene solution when the ethylene complex was allowed to react with Cp1Ti"CO#1^ in contrast to the other m2!COTi species discussed above with Ti"IV#\ the titanium atom has the oxidation number 2[ Reaction of "099# with excess TMS!Cl in THF replaces both Cp1Ti fragments by TMS groups with formation of red!violet "090# in about 45) yield ð75AG172\ 77NJC510Ł[ The formation of the compounds is depicted in Scheme 12[ OTiCp2
O-TMS
CoCp Cp2Ti(CO)2 + CpCo(CH2=CH2)2
– CH2=CH2
CoCp TMS-Cl
CpCo CoCp OTiCp2 (100)
CpCo CoCp O-TMS (101)
Scheme 23
5[00[2[0[5 Compounds with the OCW2 core The only compound with this core\ W3"OCH1Pri#01"CO#2 "091#\ has a structure equivalent to a {{spiked triangle[|| The dark green compound forms in ½49) yield when CO is added to a hexane solution of the butter~y cluster W3"OCH1Pri#01 for 13 h^ _ve bridging OR groups "R CH1Pri# stabilize the W0W bonds and the two CO groups are cis at one basal W atom ð78JA6172\ 89JOM"283#154Ł[
O RO RO
W(OR)3
OR OR OR W(CO)2 W
(RO)2W O R
OR
(102)
232
Monochalco`enomethanes 5[00[2[0[6 Compounds with the OCRu2 core
Compounds with this core comprise homometallic and heterometallic species\ both with the same m2!COMe ligand[ The homometallic compounds are collected in Scheme 13[ The Ru analog H2Ru2"m2!COMe#"CO#8 "092# of the Fe cluster "73# has been obtained as bright orange crystals in 82) yield upon heating the trinuclear precursor HRu2"m!COMe#"CO#09 in hexane in the presence of H1 ð74JOM"176#246Ł[ Replacement of three CO groups in the basal plane by the tripod ligand MeC"CH1PPh1#2 gives the yellow "093# in about 49) yield with a face!capped structure[ The introduction of the smaller tridentate ligand HC"PPh1#2 under the same conditions gives orange "094#\ in which the ligand behaves as a bidentate bridge spanning two equatorial sites on two Ru atoms ð80OM1273Ł[ PPh2 replaces one or two CO groups to give "095# and "096# in 29) and 03) yield\ respectively ð78OM0169Ł[ 0\2!Cyclohexadiene behaves as a 3!electron donor to one Ru atom and replaces one CO and H1 and reacts in the presence of diethyl fumarate to give "097# in low yield ð72OM0068Ł[ Deprotonation of "092# with K!Selectride:THF gives the anion "098#\ which can be isolated as the ð"Ph2P#1NŁ salt ð78OM0169Ł[ OMe H
OMe H
Ru(CO)3 H Ru(CO)2PPh3
(CO)3Ru H
+
(CO)3Ru H
(106)
Ru(CO)2PPh3 H Ru(CO)2PPh3
(107) PPh3
OMe
(CO)3Ru H
Ru(CO)3 H Ru(CO)3
OMe
–
K
H (CO)3Ru H
(109)
OMe
Ru(CO)3 H Ru(CO)3
H2
Ru(CO)4 (CO)3Ru H
Ru(CO)3
(103) (Ph2P)3CH (Ph2PCH2)3CMe
OMe H (CO)3Ru
OMe H
Ru(CO)3 Ru (CO)2 (108)
Ru(CO)2
(CO)3Ru H Ph2P
OMe
Ru (CO)2
PPh2
H PPh2
H (CO)3Ru H
(CO)2 Ru PPh2 H Ru PPh2 (CO)2
PPh2
(105)
(104) Scheme 24
A series of heterometallic compounds are summarized in Scheme 14[ Some compounds are derived from a homometallic trinuclear species by replacement of one or more bridging H atoms by the isolable AuPR2 group or a similar one!electron donating group[ Thus\ treatment of the basic compound "092# with AuMePPh2 under mild conditions produces three orange compounds in which one "000#\ two "001#\ or all "002# bridging H atoms of "092# are replaced by the AuPPh2 unit ð71CC662\ 72JCS"D#1488\ 72JOM"138#162\ 78OM0169Ł[ A similar reaction starting from the anion "098# and the corresponding ClMPPh2 produces "000# "M Au#\ "003# "M Ag# and "004# "M Cu# in about 54Ð64) yield^ these compounds can be converted into "005#Ð"007# by treating with PPh2 in re~uxing CH1Cl1 in yields greater than 89) ð78OM0169Ł[ The anion "098# reacts with ðRh"CO#2"PPh2#1Ł− in methanol at −19>C to form the red air!stable tetranuclear complex "008# in 79) yield ð78CC0918Ł[
233
Two Or One Chalco`ens OMe
(CO)3Ru H ClMPPh3
OMe
–
H
[Rh(CO)3(PPh3)2]–
Ru(CO)3 H Ru(CO)3
Ru(CO)3 Rh(CO)2PPh3 Ru(CO)3
(CO)3Ru H
(109)
(119)
OMe
OMe H (CO)3Ru H
AuMePPh3
Ru(CO)3 MPPh3 Ru(CO)3
(103)
AuMePPh3
Ru(CO)3 H Ru(CO)3
(111) + (CO)3Ru Ph3PAu
(111), (114), (115)
(112)
PPh3
(CO)3Ru H
+
(111), (116) ; M = Au (114), (117) ; M = Ag (115), (118) ; M = Cu
OMe H
AuPPh3
OMe Ru
Ru(CO)3 MPPh3 Ru(CO)2PPh3
Ru Au
Ru
Au
Au
(113) Ru = Ru(CO)3 Au = AuPPh3
(116), (117), (118) Scheme 25
The red compound "019# with three transition metals is obtained in about 4) yield by reducing the tetrahedral cluster Ru2RhH1"CO#09"PPh2#"m!COMe# in THF with KðBHBu2Ł followed by addition of solid Au"PPh2#Cl in dichloromethane at −89>C ð80JCS"D#0906Ł^ the reaction is depicted in Equation "01#[ (CO)2 Rh Ru(CO)3
H
O K[BHBu3]
MeO
(CO)2 Rh
Au(PPh3)Cl
(CO)3Ru H
Ru(CO)2 PPh3
PPh3 Ru(CO)2
(CO)3Ru Au PPh3
(12)
Ru(CO)3
(120)
The only compound with a m2!CORu ligand spanning a Ru2 plane is described by Geo}roy and co!workers[ The complex "010# forms either in about 4) yield by reacting the cluster Ru2"CO#8 "m2!CO#"m2!NPh# with diphenylacetylene or in 38) by reacting the starting cluster with one of the other reaction products\ a metallapyrrolidone complex as depicted in Scheme 15 ð75OM1450Ł[
5[00[2[0[7 Compounds with the OCOs2 core Closely related to the iron cluster "73# and its ruthenium derivative "092# is the corresponding osmium compound "011#[ It is similarly obtained in about 82) yield by heating HOs2"m!COMe# "CO#09 with H1 in hexane for 1 h ð72OM108Ł^ as depicted in Equation "02#\ the reaction is reversible and carbonylation regenerates the starting complex ð74JOM"176#246Ł[
234
Monochalco`enomethanes Ph Ph
N
Ph
PhC2Ph
Ru(CO)3
(CO)3Ru
(CO)3Ru
Ru(CO)3
O
N
Ph
Ru(CO)3
O
Ph N
PhC2Ph
Ru(CO)3 Ru
Ph (CO)3Ru Ph
O
N
Ru(CO)3
O
Ru (CO)2 (121) Scheme 26
OMe
OMe Os(CO)4 (CO)3Os H
Os(CO)3
H
CO H2
(CO)3Os H
Os(CO)3 H Os(CO)3
(13)
(122)
The related compound "012# with a boroxine center could be isolated as a pale yellow precipitate upon hydroboration of "m!H#1Os2"CO#09 by THF = BH2 in dichloromethane solution\ and the struc! ture was con_rmed by an x!ray structure determination ð73CC281Ł[ Os3CO
B O
O B
B
O
OCOs3
O
OCOs3
OCOs3 =
H (CO)3Os H
Os(CO)3 H Os(CO)3
(123)
A series of compounds with two bridging carbyne ligands have been described by Shapley and co!workers as shown in Scheme 16[ Thus\ sequential addition of phenyllithium and MeSO2CF2 in a Fischer!type manner to an ethereal solution of HOs2"m!COMe#"CO#09 at 9>C produces orangeÐ red air!stable crystals of "013# "m[p[ 026Ð028>C# in 30) yield[ Protonation with HSO2CF2 retains the framework and gives the anionic complex "014#^ the proton bridges one Os0Os bond[ CO substitution with excess of PPh2 gives a mixture of the orangeÐred compounds "015# "19) yield# and "016# "43) yield#\ which could be separated by TLC techniques ð75OM0646Ł[ Treatment of "013# sequentially with phenyllithium and MeSO2CF2 provided red crystals of the Fischer!type carbene complex "017# in 55) yield^ the structure was con_rmed by an x!ray analysis ð78JOM"260#146Ł[ Small amounts "09)# of the cluster "018# "Os5"CO#06"py#1# were formed\ when Os5"CO#07 was treated with excess pyridine "py# in dichloromethane^ the major product was the dianion ðOs4"CO#04Ł1−^ the yield can be enhanced to 19) by addition of Me2NO to the reaction mixture[ An x!ray analysis con_rmed the structure with one osmium atom in a {{spike|| arrangement ð73CC0978Ł[
235
Two Or One Chalco`ens OMe Os(CO)4 (CO)3Os Os(CO)3 H OMe
OMe
i, PhLi ii, MeSO3CF3
Os(CO)3 (CO)3Os PPh3
H+
Os(CO)3
Ph (126)
Os(CO)3 H Os(CO)3
(CO)3Os
OMe Os(CO)2PPh3
(CO)3Os
OH–
+
Ph (125)
Os(CO)3 Ph–/Me+
2 PPh3
Ph (124) OMe
OMe Os(CO)3
Os(CO)3
Ph3P(CO)2Os
(CO)3Os Os(CO)2PPh3
Os(CO)2 Ph
Ph
OMe
Ph (128)
(127) Scheme 27 O
Os(CO)2(py)2 Os(CO)2
(CO)3Os Os(CO)3 (CO)3Os
Os(CO)3 (129)
py = pyridine
5[00[2[0[8 Compounds with the OCFe1Ni core Only one compound with this core has been described[ BlueÐgreen crystals of Fe1Ni"m2!COMe# "m2CO#"Cp# "029# were obtained in 34) yield when HFe2"m!COMe#"CO#09 was allowed to react with "Ni"CO#Cp#1 in toluene on heating in a Carius tube[ The compound was separated by chromatography and the structure was con_rmed by an x!ray analysis ð75OM0092Ł[ OMe
OMe Ni
(CO)3Fe
M (CO)3Fe
Fe(CO)3 O (130)
Fe(CO)3
H O
(131) a; M = Co b; M = Rh
5[00[2[0[09 Compounds with the OCFe1Co core The related complex "020a^ M Co# is derived from "029# by replacement of the Ni atom by the isoelectronic CoH unit[ The greenÐbrown complex in which the hydrogen atom bridges the Fe0Fe
236
Monochalco`enomethanes
bond has similarly been obtained in 46) yield by reacting HFe2"m!COMe#"CO#09 with Co"CO#1Cp[ Reaction of "020a# with MeAuPPh2 leads to the replacement of hydrogen by AuPPh2 with result of black crystals of "021# in about 52) yield ð75OM0092Ł[ As shown by the same group\ HgPh1 in toluene at 89>C similarly produces "022a^ M Co# as the sole product ð76CC036Ł[ OMe OMe
M OMe
Co
(CO)3Fe Fe(CO)3 Hg
(CO)3Fe Fe(CO)3
Ph3PAu
(CO)3Fe
O Fe(CO)3
M
O
O (132)
(133) a; M = Co b; M = Rh
5[00[2[0[00 Compounds with the OCFe1Rh core The preparation of "020b^ M Rh# is carried out in a manner similar to its cobalt derivative by reacting HFe2"m!COMe#"CO#09 with Rh"CO#1Cp^ black crystals are obtained in 54) yield ð75JOM"209#56Ł[ The analogous reaction with HgPh1 leads to "022b^ M Rh#^ however\ the solid! state structure shows bridging of the mercury atom the Fe0Rh bonds[ In solution a polytopal rearrangement takes place with the mercury atom migrating around the Fe1Rh triangle ð76CC036Ł[
5[00[2[0[01 Compounds with the OCFe1Mn core The heterotrinuclear cluster "023# has been prepared in 79) yield from "cyclooctene#1Fe"CO#2 and Cp"CO#Fe"m!CO#"m!COMe#Mn"CO#"h4!MeC4H3#^ a minor product is a similar complex with a OCFe2 core ð76JA1732Ł[ As depicted in Scheme 17\ addition of excess diazomethane ð76JA1732Ł or diazoethane ð77OM683Ł to "023# stereospeci_cally yields the m2!methoxycarbyne\ m1!alkylidene cluster "024# in 04) "a\ R H# or 51) "b\ R Me# yield\ respectively[ The ethylidene cluster "024b^ R Me# decomposes at room temperature within 7Ð09 days to give small amounts of the isomer "024c# by ethylidene {{rotation[|| Further decomposition products comprise other dinuclear and trinuclear species ð77OM683Ł[ OMe
OMe Cp(CO)Fe
O
Mn(CO)CpMe
(C8H14)2Fe(CO)3
CHRN2
MnCpMe O Fe(CO)3
CpFe O
O (134) OMe
OMe
O
O MnCpMe O Fe(CO)3
CpFe
8d
MnCpMe O
CpFe Fe(CO)3
R (135) a; R = H b; R = Me
(135c) Scheme 28
237
Two Or One Chalco`ens
5[00[2[0[02 Compounds with the OCRu1W core The tetranuclear species "025# "a\ R H^ b\ R Me#\ in which the m!COMe group bridges one heteronuclear face of the tetrahedral cluster have been prepared by heating a mixture of Ru2"CO#09"m! COMe#H and the corresponding hydrido complex Cp?W"CO#2H "Cp? C4H4\ C4Me4# in toluene for 0 h ð89JCS"D#2922Ł[ The same group reported a similar reaction with CpW"CO#2C2CPh\ which leads to "026# ð80OM1374Ł[ OMe
OMe Ru(CO)3
Ru(CO)2
(CO)3Ru
(CO)3Ru W(CO)2C5R5
W(CO)Cp
Ru(CO)3
Ru (CO)2
O
Ph
(136)
(137)
5[00[2[0[03 Compounds with the OCW1Ru core With one equivalent of CpW"CO#2H the tetranuclear complex "026# is converted into the penta! nuclear complex "027# in which the COMe group bridges a W1Ru face in a m2!manner[ The reaction has been performed in re~uxing toluene to give red crystals in 13) yield ð80OM1374Ł[ OMe CO W Ph
Ru W Ru
O
Ru CO (138) Ru = Ru(CO)2 W = WCp
5[00[2[1 Methanes Bearing One Sulfur Function and Three Functions Derived from the Group 04 Element\ Metalloid and:or a Metal The compounds in which two or three di}erent elements are attached to the SC carbon atom are represented by only a few examples[ Main group compounds consist with few exceptions of species with the SC"TMS#2 fragment[ The majority of samples in this section\ however\ are based on Co2 cluster compounds with a m2!C1S ligand or similar clusters in which one or two Co atoms are replaced by other transition metals^ addition of an electrophile at the C1S sulfur atom gives a m2! methylidine ligand which contributes three electrons to the cluster[
5[00[2[1[0 Compounds with the SCN2 core A series of compounds of the general type RSC"NO1#2\ in which the NO1 groups are bound to the carbon atom via the nitrogen atoms\ have been described by a Russian group[ The compounds have been obtained by the reaction of KC"NO1#2 with the appropriate RSCl in dimethoxyethane or ether at about 9>C[ Recrystallization from chloroformÐhexane produced 1\3!"NO1#1C5H2SC"NO1#2 "m[p[ 57Ð58>C# in 49) yield and PhSC"NO#2 "m[p[ 01Ð02>C# in 82) yield\ respectively ð62IZV249Ł[ MeSC"NO1#2 was similarly obtained in 82) yield but puri_ed by distillation "b[p[ 39>C at 0 mm Hg# ð62IZV249\ 64IZV0558Ł[ The compounds 3!"NO1#C5H3SC"NO1#2 "m[p[ 014Ð016>C# and 3! MeOC5H3SC"NO1#2 "m[p[ 25Ð28>C# have been prepared in the same manner in dichloromethane
238
Monochalco`enomethanes
solution in 76) and 69) yield\ respectively ð63IZV0249Ł[ PhSC"NO1#2 is also produced in 19) yield by the reaction of K"C"NO1#2 with ðPhSŁðBF3Ł ð64IZV0558Ł[ Reactions with hydrogen halides have been described ð78IZV1095Ł[
5[00[2[1[1 Compounds with the SCSi2 core The key compound for this series is HC"TMS#2\ which can be converted into HSC"TMS#2 "028# in 35) yield by treatment with MeLi and then with elemental sulfur after extractive puri_cation with methanolÐKOH followed by sublimation ð74TL0980\ 74TL1148Ł[ A similar procedure with HC"Si! Me1Ph#2 generates pale yellow crystals of HSC"SiMe1Ph#2 "039# in 09) yield\ melting at 190Ð192>C ð76IC0377Ł[ DuMont and others obtained several sulfur!rich species using HC"TMS#2 or HSC"TMS#2 as starting materials as shown in Scheme 18[ Thus\ treatment of "028# with SCl1 gives yellow "030# in 34) yield[ This compound is also produced along with "031# by oxidation of "028# with air ð74TL0980\ 82CB0244Ł[ Desulfurization of the tetrasulfane "031# to "030# can be performed with elemental mercury[ The corresponding disulfane "032# forms as a mixture with the methyl derivative "033# ð82CB0244Ł[ The latter can also be obtained from "TMS#2CLi and Me1S ð89JOM"287#54Ł[ Starting with a lithiated 1!ðð"trimethylsilyl#methylŁthioŁtetrahydropyran and TMS!Cl the compound "034# was prepared in 72) yield ð74JA5618Ł "Equation "03##[ TMS TMS TMS
S
TMS TMS
TMS TMS S
TMS TMS
TMS
MeLi/S8/H+
TMS TMS TMS
+ TMS TMS TMS
SCl2
Me/LiBr2
(143)
SMe
S
S
S
TMS TMS
TMS TMS TMS
(141)
SH Hg
(139)
O2
(144)
TMS
S
TMS TMS
S
S
TMS TMS S
TMS
(142)
Scheme 29
TMS TMS
i, BuLi
O
S
TMS
ii, TMS-Cl
O
S
(14)
TMS
(145)
Several S!metalated derivatives have been prepared by the groups of Power and Lappert and the compounds are summarized in Scheme 29^ starting materials are the hydrogen compounds "028# and "039# or the corresponding lithium salts[ The pale yellow trimeric and tetrameric silver com! pounds "035# "55) yield# and "036# "81) yield\ m[p[ 124>C# are the result of the reaction with NEt2 and AgNO2 in re~uxing benzene or acetonitrile\ respectively^ the compounds contain six! and eight! membered AgS rings ð76IC0377Ł[ A similar tetrameric gold compound "037# has been prepared in 58) yield from the lithium compound and AuCl\ whereas Ph2PAuCl produces the monomeric compound "038# "m[p[ 193Ð196>C# as colorless crystals in 58) yield ð82IC4015Ł[ The reaction of "028# with MðN"TMS#1Ł1 compounds "M Sn\ Pb# produces various dimeric or polymeric species "049#Ð"041# containing the SCSi2 core^ the polymeric lithium salt was obtained with butyllithium in hexane ð74CC0665Ł[ The lithium salt LiSC"TMS#2 = 2[4THF was reported to be a dimer with a square Li1S1 core and was prepared in the presence of small amounts of THF ð74CC0563Ł[
249
Two Or One Chalco`ens TMS TMS TMS
TMS TMS TMS
AuClPPh3
SAuPPh3
TMS TMS TMS
AuCl
SLi
SAu 4
(148)
(149) Li
RMe2Si RMe2Si SH RMe2Si (139) R = Me (140) R = Ph
TMS
TMS TMS
S
S
TMS TMS
Pb
Pb
S
S TMS
4
M[N(TMS)2]2 M = Sn, Pb
Pb(NMe2)2
TMS
RMe2Si RMe2Si SAg RMe2Si (146) R = Me (147) R = Ph
AgNO3
TMS TMS
R2N
TMS TMS
TMS TMS S
Pb
Pb
NR2
S
TMS TMS
TMS
(150)
TMS TMS
S
TMS TMS
(151)
TMS TMS
Sn S
TMS TMS (152)
n
Scheme 30
5[00[2[1[2 Compounds with the SCSi1P core Two di}erent compounds with this core have been described[ The reaction of MesP1C"TMS#1 "Mes mesityl# with 03 S7 leads to an inseparable mixture of MesP"S#1C"TMS#1 and the thiaphos! phirane MesP"1S#"m!S#C"TMS#1 "042#[ The mixture is completely converted into "042# by addition of a second equivalent of sulfur "Scheme 20# ð73CC587Ł[ An additional compound with the SCSi1P core\ "043#\ has been described as very water sensitive and has been prepared by reacting "EtO#1 P"O#CSMe"TMS#Li with TMS!Cl in THF at −67>C ð78S090Ł[ S TMS mes
1/
P
mes
8 S8
P TMS
TMS
TMS 1/
4
S8
S8
TMS mes
P
TMS
S (153) Scheme 31 O P EtO EtO
TMS TMS TMS
(154)
240
Monochalco`enomethanes 5[00[2[1[3 Compounds with the SCPSiLi core
"EtO#1P"O#CSMe"TMS#Li results from lithiation of "EtO#1P"O#CHSMe"TMS# with BunLi in THF at −67>C and was not isolated[ The species reacts with ketones and aldehydes and can be used to transfer the "EtO#1P"O#CSMe"TMS# fragment to various substrates ð78S090Ł[ 5[00[2[1[4 Compounds with the SCSi1Li core PhSCLi"TMS#1 "044^ R Ph# is obtained in situ by dropwise addition of butyllithium in hexane to PhSCH"TMS#1 in THF at −67>C[ This and similar lithium compounds have been formulated as ionic species and have been used to replace the oxygen atom of various epoxides by the carbene PhS"TMS#C to give cyclopropanes ð78TL6922Ł[ The methyl derivative has been obtained similarly in 099) yield ð66CB741Ł[ RS
Li
TMS
TMS
(155)
5[00[2[1[5 Compounds with the SCN1Fe core The reaction of Fe1"CO#8 with tetramethylthiourea in ether for 13 h followed by chromatography in Fluorosil leads to Fe1"CO#5"SC"NMe1#1# "045# in 1[5) yield along with Fe2"CO#8S1 "9[0)# and "Me1N#1C1S0Fe"CO#3 "5[1)# "Equation "04## ð63IC114Ł[ Me NMe2 Fe2(CO)9 + (Me2N)2CS
Fe3(CO)9S2 +
Me
+
(CO)4FeS NMe2
NMe2
N S
(CO)3Fe
(15)
Fe(CO)3
(156)
5[00[2[1[6 Compounds with the SCNSnPt core Compounds of the general type "PPh2#1Pt"SCSnPh2NR1# "046^ NR1 NMeH\ N"CH1#3# are prepared by the reaction of the corresponding Ph2SnC"S#NR1 with "PPh2#1PtC1H3 in benzene for 13 h[ The pale yellow products were precipitated with hexane and recrystallized from benzeneÐ hexane[ The yields were approximately 49)^ by!products are the corresponding Sn!bonded species "PPh2#1PhPtSn"Ph#1C"S#NR1 "Equation "05## ð72IC2699Ł[ The compounds can also be considered in terms of an h1!coordination of S1C"SnPh2#NR1 at the Pt fragment[ S
Ph3P Pt Ph3P
Ph3P
+ Ph3Sn
–C2H4
NR2
Pt
S
Ph3P Ph3Sn
(16) NR2
(157) NR2 = NMeH,
N
5[00[2[1[7 Compounds with the SCSiSnLi core The compounds RSCLi"TMS#"SnMe2# "047^ R Me\ Ph# have been obtained in 099) yield by lithiation of the corresponding RSCH"TMS#"SnMe2# with LDA in THFÐHMPTA ð66CB741Ł[ RS Me3Sn (158)
TMS Li
241
Two Or One Chalco`ens
5[00[2[1[8 Compounds with the SCFe2 core Only one compound of this type has been described[ The tetranuclear compound Fe3"CO#00"CS#S "048# was obtained as one of the products from the reaction of Fe2"CO#01 with CS1 in hexane solution at 79>C under 09 atm COÐAr pressure[ Both the compounds in Equation "06# have been formed in about 3) yield ð79CC701Ł[ S
Fe(CO)3 Fe(CO)2
Fe3(CO)12 + CS2
(CO)3Fe
+ Fe3(CO)9S2
(17)
Fe(CO)3 S (159)
5[00[2[1[09 Compounds with the SCCo2 core The compounds with this core are derived from Co2Cp2"m2!CS#"m2!S# and the hypothetical cluster anion ðCo2"CO#8"m2!CS#Ł−^ both are electron precise cluster compounds[ Of the two sulfur atoms of the _rst species\ only that at the m2!C1S ligand is nucleophilic enough to react with a variety of electrophilic reagents Y to produce compounds of the general type Co2Cp2"m2!CSY#"m2!S#^ the corresponding Co2"CO#8"m2!CSY# compounds are formed in a complex reaction from Co1"CO#7[ The electrophile Y can be a cationic group R¦ or a 05!electron transition metal Lewis acid as shown in Scheme 21[ Starting from Co2Cp2"m2!CS#"m2!S#\ the alkylating agents RI "R Me\ Et\ Pri# produce the black salts ðCo2Cp2"m2!CSR#"m2!S#ŁI "059aÐc# from a THF solution in about quantative yields[ The reaction with PriI has only been conducted in an NMR tube[ A decreasing reactivity order MeI×EtI×PriI was found\ indicated by an increasing reaction time in the order 0 h\ 4 h\ 4 days\ respectively[ Black crystals of Co2Cp2"m2!CSCr"CO#4#"m2!S# "050# have been obtained in 24) yield by treating a freshly prepared THF solution of "CO#4CrTHF with Co2Cp2"m2!CS#"m2!S#^ the complex could be puri_ed by recrystallization from THFÐhexane ð68AG552\ 79CB0543Ł[ S
Cr(CO)5
CoCp CpCo
S
(CO)5CrTHF
S CoCp
CoCp
CoCp
S (161)
S
Scheme 32
+
CoCp RI
CpCo
R
CpCo CoCp S (160) a; R = Me b; R = Et c; R = Pri
The reaction of CS1 with Co1"CO#7 results in the formation of more than eight di}erent sulfur! containing products\ similar to that with Fe2"CO#01[ Separation by column chromatography or by thin!layer chromatography gave compounds which could be isolated in low yields and identi_ed by x!ray di}raction analysis[ Reaction time\ solvents\ and the workup procedure all a}ect the product distribution found[ Thus\ a 3 ] 0 mixture of the components in light petroleum gave "051# after a reaction time of 7 h and puri_cation by thin!layer chromatography ð72CC0502Ł^ additionally\ isomers have also been isolated ð71IC2670Ł[ Wei described the preparation of "052# and unidenti_ed products using the same or a slightly modi_ed procedure ð73IC1862Ł^ some of the products are summarized in Scheme 22[ Earlier results concerning these compounds have been reported from the group of Marko and co!workers ð57JOM"00#196Ł[
5[00[2[1[00 Compounds with the SCFe1Co core The 49!electron cluster compounds Fe1CoCp1"CO#4CSR "053# "a^ R Me^ b^ R CH1Ph# can be prepared by the reaction of the corresponding bridging thiocarbyne complexes ðCp"CO#Fe"m!CO#
242
Monochalco`enomethanes O S
(CO)3Co CS2
(CO)3 Co Co(CO)3 (CO)2 S (CO)2 S S S Co Co Co (CO)3 Co(CO) Co(CO)3 3 + (CO) Co C + (CO)9Co3CC 8 3 Co(CO)3 Co Co S (CO)2 S (CO)2 Co(CO)3
(162) 8h
Co2(CO)8
(CO)2 S Co
CS2 24 h
S
S Co(CO)3
Co (CO)2 Co(CO)3
(CO)3Co
Co(CO)3 (163) Scheme 33
"m!SR#ŁPF5 with excess NaðCo"CO#3Ł "prepared in situ by combining Co1"CO#7 with _nely ground NaOH# in THF under UV photolysis at room temperature[ Extraction of the neutral cluster compounds with benzene and recrystallization from dichloromethaneÐhexane produces brownish! purple crystals[ Whereas "053a# is isolated in a yield of about 79)\ the similar route to "053b# gives the compound in 17) yield but requires photolysis at 01>C[ Phosphines replace one CO group at the Co atom when the reaction is carried out in dichloromethane to give "054# and "055# in good yields "Table 1\ entries 0 to 5# as illustrated in Scheme 23 ð77JOM"283#072Ł[ Me S CO
O Ph2P
Co
PPh2
Ph2 P
CpFe Fe Cp
SR SR Cp(CO)Fe
FeCp(CO)
O
O
+
P Ph2
(165) Co(CO)2
Na[Co(CO)4]
CpFe FeCp(CO)
Me S
O O (164) a; R = Me b; R = CH2Ph
O Co(CO)PR3 PR3
CpFe FeCp(CO)
Cy = Cyclohexyl
O (166) a; PR3 = PMe3 b; PR3 = PEt3 c; PR3 = PCy3 d; PR3 = PHPh2 e; PR3 = PMePh2
Scheme 34
5[00[2[1[01 Compounds with the SCCo1W core Only one set of compounds of this type has been described[ The 37!electron cluster compounds "056a#Ð"056e# "Table 2# have been obtained by addition of Co1"CO#7 to an equilibrium mixture of
243
Two Or One Chalco`ens Table 1 Preparation of "054# and "055# from "053^ R Me# by CO:phosphine exchange[
Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Entry Product Phosphine Decomp[ temp[ Time Yield ">C# "h# ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 097 8 82 0 "055a# PPh2 1 "055b# PEt2 84 0[4 57 84 01 43 2 "055c# PCy2 3 "055d# PHPh1 89 4 52 4 4 "055e# PMePh1 5 "054# Ph1PCH1PPh1 89 34 46 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Table 2 Properties of the compounds "056a#Ð"056e#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0 R1 Yield M[p[ "056# R2 ")# ">C# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a Ph CO1Me CO1Me 70 47 CO1Me 55 b Me CO1Me c Ph CF2 CF2 28 d Me CF2 CF2 34 H 79 013 e Me CO1Me ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
the two isomers of the carbene complex "diphos#"CO#2W1CS1C1R0R1 in dichlormethane solution[ After 01 h reaction time the compounds could be precipitated with hexane[ From "056e# two isomers were formed according to the orientation of the R0CCR1 unit[ The yields of the compounds are given in Scheme 24 ð77JOM"283#072Ł[ R1
R2
CO R32 P W P R32
S R32 P
CO S R1
CO
S
W
S R2
P R32
Co2(CO)8
CO CO
CO R1 S
O
(CO)2 Co S
R32 P W P CO R32
R2
Co(CO)2
O (167)
Scheme 35
5[00[2[2 Methanes Bearing One Selenium or One Tellurium Function and Three Functions Derived from the Group 04 Element\ Metalloid and:or a Metal The compounds bearing the SeC or TeC unit\ with few exceptions\ are restricted to samples with the TMS group and thus contain the tris"trimethylsily#methyl function\ "TMS#2C[ This section refers mainly to work of the research groups of Sladky\ duMont\ and Arnold[
244
Monochalco`enomethanes 5[00[2[2[0 Compounds with the SeCN2 core
Only one compound in this series has been described\ by a Russian group in connection with compounds containing the related SC"NO1#2 fragment[ The compound PhSeC"NO1#2 has been prepared by addition of KðC"NO1#2Ł to a solution of PhSeCl in CH1Cl1 solution[ KCl was removed and the resulting dried oil was triturated with hexane^ the reaction could also be carried out with PhSeBr and the yield of the compound was about 099) in each case ð71IZV050Ł[ Reactions of the compound with various M0Hal compounds have been described ð78IZV1095Ł[
5[00[2[2[1 Compounds with the SeCSi2 core This section contains compounds of the general type "TMS#2CSeX in which the selenium atom is further bonded to either hydrogen\ alkyl\ aryl\ halogen\ chalcogen\ or gold[ The "TMS#2C group is abbreviated below as Tsi[ A list of compounds prepared by the groups of Sladky\ duMont and Arnold along with conditions and yields are collected in Table 3 and a survey of reactions is shown in Schemes 25Ð27[ Table 3 Preparation and properties of compounds with the Si2CSe core[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Entry Structure Color Preparation Yield Ref[ "m[p[^ >C# ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 74CC0799 0 "060# Red "193# TSiLi ¦ Se^ H1O\ O1 84 82ZAAC"508#0582 1 "064# ¦ Se:I1 2 "064# Red "192# "060# ¦ Cu^ 89 >C\ THF 35 89CB1214 84Ð87 82ZAAC"508#0582 3 "065# RedÐbrown "081# "060# ¦ Br1 4 "067# YellowÐbrown "190# "060# ¦ SO1Cl1 85 82ZAAC"508#0582 68 77CB1098 5 "066# BlackÐviolet "060# ¦ I1^ toluene 6 "068# Yellow "012# "067# ¦ Me2SiCN\ CH2CN 78 82ZAAC"508#0582 53 82ZAAC"508#0582 7 "079# Orange "039# "067# ¦ KSCN in CH1Cl1 8 "070# Yellow "83# "066# ¦ S^ toluene 4 82ZAAC"508#0582 09 "064# ¦ S:I1 in toluene 37 00 "071# "066# ¦ Se^ toulene 4 82ZAAC"508#0582 01 "072# "066# ¦ S^ toluene 09 82ZAAC"508#0582 02 "073# Colorless "064# ¦ MeLi^ THF 42 78CB1168 03 "074# Colorless "064# ¦ PhLi 32 78CB1168 04 "063# Colorless "74# "064# ¦ TSiLi:THF 62 78CB1168 05 "069# Colorless "69# "064# ¦ TSiLi:THF 7 78CB1168 06 Pale yellow "058#"THF¦#HSO2CF2 82 82JA5666 07 "058# Light orange TSiLi ¦ Se^ DMF 62 82JA5666 08 "061# Colorless "dec[# "058# ¦ AuCl^ THF 54 82IC4015 64 82IC4015 19 "062# Colorless "073Ð078# "058# ¦ Ph2PAuCl^ ether 10 "069# ¦ Ph2PAuN"SiMe2#1 65 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
TsiLi has been reported to undergo insertion of two equivalents of selenium to give TsiSeSeLi "057# in THF solution ð74CC0799Ł and insertion of one equivalent of selenium to give "058# in the presence of dimethoxyethane\ which on protonolysis leads to the hydride "069# ð82JA5666Ł^ addition of H1O and oxidation with O1 give bisðtris"trimethylsilyl#methylŁtriselenide\ TsiSeSeSeTsi "060# ð74CC0799Ł "Scheme 25#[ The middle selenium atom of "060# can be removed to give TsiSeSeTsi "064#\ which has been used as starting material for a variety of other TsiSeR compounds ð78CB1168\ 89CB1214\ 82ZAAC0582Ł[ TsiSeH (170)
H+/ether
TsiSeLi•DME (169)
Se/DME
TsiLi
Se
TsiSeSeLi (168)
H2O2/O2
TsiSeSeSeTsi (171)
Cu
TsiSeSeTsi (175)
Scheme 36
The gold compounds "061# and "062# have been obtained by treatment of TsiLi = DME with AuCl or AuClPPh2\ respectively\ as depicted in Scheme 26 ð82IC4015Ł[
245
Two Or One Chalco`ens
The production of TsiSeH "069# and TsiSeC3H6O "063# from TsiSeSeTsi "064# in THF was reported to be a result of a single electron!transfer reaction "SET# via the TsiSe = radical ð78CB1168Ł[ TMS TMS TsiSeAuPPh3
Ph3PAuCl
AuCl
TMS
TsiSeLi•DME
(173)
TMS TMS
Se Au Se Au
(169)
Au
Se Au Se
TMS
TMS
TMS
TMS TMS TMS TMS (172)
TSi = (TMS)3C Scheme 37
As shown in Scheme 27 the Se0Se bond in the diselenide "064# can be cleaved by various oxidizing agents[ While Br1 ð89CB1214Ł and I1 ð77CB1098Ł lead to the corresponding halides "065# and "066#\ respectively\ the chloride "067# is obtained by reacting with SO1Cl1^ the introductions of pseudo! halogen CN− or SCN− can by achieved by treating the chloride with the appropriate TMS!X ð82ZAAC"508#0582Ł[ A reversible reaction with elemental sulfur or selenium generates a mixture of further chalcogen!rich derivatives "070Ð072# which can also be obtained starting from "064# ð82ZAAC0582Ł[ The action of LiR "R Me\ Ph# on the diselenide "064# generates the species TsiSeMe "073# and TsiSePh "074#\ respectively ð82ZAAC"508#0582Ł[ (170) +
SeTsi
O
(174) TsiLi Hg
TSiSeSeSeTsi (171) TsiSeSeSeSeTsi (182)
Se
TSiSeSSeTsi (181) TsiSeSSSeTsi (183)
S
TsiSeSeTsi (175)
RLi
Br2 SO2Cl2
I2
TsiSeR (184) ; R = Me (185) ; R = Ph
Hg
TsiSeBr TsiSeCl
TsiSeI
(178)
(177)
(176)
TMS-X
Tsi = (TMS)3C
TsiSeX (179) ; X = CN (180) ; X = SCN Scheme 38
5[00[2[2[2 Compounds with the TeCSi2 core Most of the compounds which have been described with the SeCSi2 core are also known with the TeCSi2 core and\ similarly to the selenium derivatives\ only compounds with the TMS group are known[ Thus\ compounds of the general type "TMS#2CTeX in which the tellurium atom is further bonded to hydrogen\ alkyl\ aryl\ halogen\ chalcogen\ or some transition metals have been prepared by the same working groups as reported for the corresponding selenium compounds[ A list of compounds along with conditions and yields are collected in Table 4 and a survey of reactions is shown in the Schemes 28Ð39[ As with selenium\ insertion of two equivalents of tellurium into the C0Li bond of TsiLi produces TsiTeTeLi "075#\ which can also be obtained by addition of tellurium to the monotelluride "076#[ Oxidation of the lithium salt "075# with H1O:O1 generates the tritelluride TsiTeTeTeTsi "077# from
246
Monochalco`enomethanes Table 4 Preparation and properties of compounds with the Si2CTe core[
Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Entry Structure Color Preparation Yield Ref[ "m[p[\ >C# ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 0 "075# "076# ¦ Te 74CC0799 1 "076# Orange "030Ð034# THF!adduct^ TsiLi ¦ Te\ THF 45 82JA5666 2 "078# ¦ Li 74CC0799 3 "077# RedÐblack From decomp[ of "089# 74JOM"184#C0 59 74CC0799 4 "075# ¦ H1O:O1 5 "078# "076# ¦ Se 74CC0799 6 "089# "075# ¦ ClP"But#1^ not isol[ 74JOM"184#C0 74CC0799 7 "080# "076# ¦ SeCl1 8 "081# Red "080# ¦ Hg in pentane 74CC0799 09 "078# ¦ Se\ ultrasound 29 h 84 80OM1090 74JOM"184#C0 00 "082# "076# ¦ ClP"But#1 01 "083# From decomp[ of "082# 74JOM"184#C0 02 "084# Yellow "042Ð043# "076# ¦ H¦ in ether 70 82JA5666 03 "085# Colorless "076# ¦ AuCl 31 82IC4015 04 "086# Yellow "076# ¦ ClAuPPh2 54 82IC4015 05 "087# "076# ¦ Cp1TiCl1^ unstable 82JA434 06 "088# Red "076# ¦ Cp1ZrCl1 46 82JA434 07 "199# Orange "078# ¦ S\ ultrasound 29 h 84 80OM1090 08 "190# BlueÐblack "009# "078# ¦ SO1Cl1 84 78CB0144 84 78CB0144 19 "191# BlueÐblack "009# "078# ¦ Br1 10 "192# BlueÐblack "009# "078# ¦ I1 84 78CB0144 50 78CB1168 11 "193# Bright yellow "79# Tsi1Te1 ¦ RLi in THF 12 "192# ¦ MeLi in THF 74 78CB0144 46 78CB1168 13 "194# Bright yellow "36# Tsi1Te1 ¦ RLi in THF 14 "192# ¦ PhLi in THF 79 78CB0144 "192# ¦ AgCNb 61 80CB0020 15 "195# Yellow "039#a 16 "196# Dark red "014#a "192# ¦ AgSCNb 76 80CB0020 "192# ¦ AgSeCNb 71 80CB0020 17 "197# Red "029#a a b "192# ¦ AgNCO 62 80CB0020 18 "198# Red "½019# 29 "109# Deep red "024#a "192# ¦ AgN2b 80CB0020 73 20 "192# ¦ TlOEt:TMS!N2b 21 "100# Dark red "034#a "192# ¦ Ag1NCNb 76 80CB0020 "192# ¦ K1NSNb 81 80CB0020 22 "101# Orange "039#a 23 "102# Colorless "58# "078# ¦ TSiLi in THF 65 78CB1168 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a
With decomposition[
b
In benzene[
which the middle tellurium atom can be removed with mercury to give "078#^ the latter compound is also formed by oxidation of the lithium salt "076# with elemental Se ð74CC0799Ł[ Reaction of "075# with ClP"But#1 produces the ditellurophosphine "089# ð74JOM"184#C0Ł[ The reactions are summarized in Scheme 28[ TsiLi Te Te ClPBut2
TsiTeTeLi
TsiTeLi
(186)
(187)
TsiTeTePBut
2
(190)
H2O/O2
Li
Se
Hg
TsiTeTeTeLi
TsiTeTeLi
(188)
(189)
Scheme 39
TsiTeLi "076# is starting material for a variety of derivatives as depicted in Scheme 39[ This compound has also been described as the THF solvate TsiTeLi"THF#1 ð82JA5666Ł[ Action of SeCl1 leads to "080# ð74CC0799Ł\ which can be deselenated to "081#\ while reaction with ClP"But#1 gives the tellurophosphine "082#[ At room temperature this tellurophosphine is not stable and converts into
247
Two Or One Chalco`ens
"083# and TeðP"But#1Ł1 ð74JOM"184#C0Ł[ With tri~ic acid and the THF solvate "076# the corresponding acid "084# is obtained ð82JA5666Ł[ The THF solvate "076# is also the starting material for some transition metal derivatives[ With AuCl and Ph2PAuCl the tetranuclear species "085# and the mononuclear compound "086#\ respec! tively\ have been prepared^ the structure of the tetranuclear compound is identical to the structure of the corresponding selenium compound "061# ð82IC4015Ł[ LiCl elimination proceeds also with Cp1MCl1 "M Ti\ Zr#\ to give the Cp1M"TeTsi#1 compounds "087# and "088#\ respectively ð82JA434Ł[ TsiTeH (195) Au4(TeTsi)4 (196) TsiTeAuPPh3
AuCl H+ SeCl2
ClAuPPh3
TsiTeLi
Cp2MCl2
(197)
TsiTeSeSeTeTsi
(187)
(191)
ClPBut2
Cp2M(TeTsi)2 (198); M = Ti (199); M = Zr
Hg
TsiTePBut2
TsiTeSeTeTsi
(193)
(192)
TsiTeTsi (194) Scheme 40
The chemistry of TsiTeTeTsi "078# is summarized in Scheme 30[ Ultrasonic activation in the presence of elemental sulfur or selenium leads to the insertion of one chalcogen molecule to give "TsiTe#1E "199^ E S#\ "081^ E Se# ð80OM1090Ł[ The tellurohalogenides "190#Ð"192# have been prepared by the reaction of "078# with SO1Cl1\ Br1\ or I1\ respectively[ The chloride "190# can be alkylated with MeLi to give "193# or arylated with PhLi or PhMgBr to produce "194# ð78CB0144Ł^ both compounds can also be prepared from Tsi1Te1 and the corresponding RLi ð78CB1168Ł[ Halogen exchange in the iodide "192# with various AgX compounds leads to the compounds "195#Ð"109#[ A similar reaction with two equivalents of the iodide and Ag1NCN or Ag1NSN generates the carbodiimide "100# and the sulfur diimide "101#\ respectively[ The compound TsiTeOEt was mentioned in a dissertation ð80CB0020Ł[ Finally\ the addition of TsiLi to a solution of "078# leads to the incorporation of a THF molecule to produce air!stable "102# "m[p[ 58>C# in about 65) yield ð78CB1168Ł[ E
TsiTeETeTsi (200); E = S (192); E = Se
TsiTeX (201); X = Cl (202); X = Br (203); X = I
TsiTeTeTsi (189)
TsiLi/THF AgY
LiR Ag2NEN
O
TeTsi (213)
TsiTeY (206); Y = CN (207); Y = SCN (208); Y = SeCN (209); Y = NCO (210); Y = N3
TsiTeNENTeTsi (211); E = C (212); E = S
TsiTeR (204); R = Me (205); R = Ph
Scheme 41
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.12 Functions Containing at Least One Group 15 Element (and No Halogen or Chalcogen) DUNCAN CARMICHAEL, ANGELA MARINETTI and PHILIPPE SAVIGNAC DCPH–Ecole Polytechnique, Palaiseau, France 5[01[0 METHANES BEARING FOUR GROUP 04 ELEMENTS 5[01[0[0 Four Similar Group 04 Element Functions 5[01[0[0[0 Four nitro`en functions 5[01[0[0[1 Four phosphorus functions 5[01[0[1 Three Similar and One Different Group 04 Element Functions 5[01[0[1[0 Three nitro`en functions 5[01[0[1[1 Three phosphorus functions 5[01[0[2 Two Similar and Two Different Group 04 Element Functions 5[01[0[2[0 Two nitro`en functions 5[01[0[2[1 Two phosphorus functions
259 259 259 254 255 255 255 256 256 256
5[01[1 METHANES BEARING THREE GROUP 04 ELEMENTS AND A METALLOID OR A METAL 5[01[1[0 Three Similar Group 04 Elements 5[01[1[0[0 Three nitro`en functions 5[01[1[0[1 Three phosphorus functions
257 257 257 258
5[01[2 METHANES BEARING TWO GROUP 04 ELEMENTS AND METALLOID AND:OR METAL FUNCTIONS
269 269 269 269
5[01[2[0 Two Similar Group 04 Elements 5[01[2[0[0 Two nitro`en functions 5[01[2[0[1 Two phosphorus functions 5[01[3 METHANES BEARING ONE GROUP 04 ELEMENT AND METALLOID AND:OR METAL FUNCTIONS 5[01[3[0 Nitro`en Functions 5[01[3[1 Phosphorus Functions 5[01[3[1[0 One phosphorus and three silicon functions 5[01[3[1[1 One phosphorus\ one metal and two silicon functions 5[01[3[2 Arsenic or Antimony Functions
248
261 261 261 261 262 263
259
At Least One Group 04 Element
5[01[0 METHANES BEARING FOUR GROUP 04 ELEMENTS 5[01[0[0 Four Similar Group 04 Element Functions 5[01[0[0[0 Four nitrogen functions Cyclic\ acyclic and spirocyclic compounds bearing four nitrogen functions are known[ In all cases\ at least two of the nitrogen functions are identical\ and totally symmetrical compounds also exist[ Examples of this class of compound\ where the tetracoordinated carbon is bound to the nitrogen atom of amino\ dialkyl or diarylamino\ ~uoroamino\ amido\ hydrazino\ nitro\ and isocyano functions\ have been prepared[ No single method has been shown to be compatible with every one of these functions\ but a number of syntheses are reasonably general[ These are detailed below[
"i# By nucleophilic exchan`e of chlorine atoms "a# From 1\1!dichloro!3\4!imidazolidinediones and analo`ues[ The 1\1!dichloro!3\4!imidazolidi! nediones react with primary or secondary amines to give the corresponding tetraaminomethanes\ by successive replacement of both chlorine atoms[ Dehydrohalogenation may be e}ected by an excess of the amine itself\ or by the addition of bases such as triethylamine or K1CO2 "Equation "0# and Table 0#[ R1 O
N
R1 Cl
O
N
NR32
O
N
NR32
+ 2R32NH O
N
(1)
Cl
R2
R2
Table 0 Nucleophilic exchange of chlorine atoms with amines on 1\1!dichloro!3\4!imidazolidinediones[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Rea`ents Conditions ")# Ref[ R0\ R1 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me1CH morpholine Dioxane\ Et2N\ 14>C\ 1 h 17 69CB655 N!Me!piperazine Dioxane\ Et2N\ 14>C\ 1 h 52 69CB655 Me1CH Me1CH pyrrolidine Dioxane\ 3 equiv[ amine\ 14>C 35 62CB1204 piperidine Dioxane\ 3 equiv[ amine\ 14>C 70 62CB1204 Me1CH 3!NO1C5H3 morpholine Dioxane\ 3 equiv[ amine\ 14>C 64 62CB1204 1!MeC5H3 morpholine Dioxane\ 3 equiv[ amine\ 14>C 76 62CB1204 morpholine Dioxane\ 3 equiv[ amine\ 14>C 52 62CB1204 C5H00 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
The benzylthiolate leaving group may also be used in place of chloride ð67JPR224Ł[ Diamines lead to spirocyclic derivatives "Equation "1# and Table 1#[ 1\1?!Spiroimidazolidine!3?\4?!dione derivatives have been patented as stabilizers for color photographic materials ð65GEP1359229Ł[ R1 O
N
R1 Cl
HR3N
Et3N
HR3N
dioxane, 25 or 60 °C
+ O
N R2
Cl
O
N
NR3
O
N
NR3
(2) R2
A related reaction of 1\1!dichloro!1\5!dihydro!3\5!pyrimidinediones with simple or chelating amines proceeds through a substitution of both chlorine atoms to give open or spirocyclic tetraa! mines\ respectively "Equation "2##[ Yields are moderate to good "Table 2# ð77CZ271Ł[
Four Group 04 Elements
250
Table 1 Nucleophilic exchange of chlorine atoms with diamines on 1\1! dichloro!3\4!imidazolidinediones[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Rea`ents ")# Ref[ R0\ R1 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me1CH "MeNHCH1#1 34 69CB655 C5H00 "MeNHCH1#1 41 69CB655 "MeNHCH1#1 00 69CB655 Me\ C5H00 Me1CH 0\1!"NH1#1C5H3 65 69CB655 c!C5H00 0\1!"NH1#1C5H3 81 69CB655 0\1!"NH1#1C5H3 54 69CB655 3!MeC5H3 H\ Ph 0\1!"NH1#1C5H3 56 67JPR224 0\1!"NH1#1C5H3 44 67JPR224 H\ 1!ClC5H3 67 67JPR224 H\ PhCO 0\1!"NH1#1C5H3 H\ PhCH1 0\1!"NH1#1C5H3 46 67JPR224 triphenylguanidine 27 69ZC29 Me1CH c!C5H00 triphenylguanidine 04 69ZC29 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
R1
O N
R2
Cl
+ R3
N
NR42
R3
N
NR42
amine
(3)
Cl
N R1
O
R1
O R2
O
R1
Table 2 Nucleophilic exchange of chlorine atoms with amines on 1\1!dichloro!1\5! dihydro!3\5!pyrimidinediones[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R0\ R1\ R2 Rea`ents Conditions ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * c!C5H00^ Cl^ Cl pyrazole THF\ 14>C 68 phenoxazine THF\ 14>C 25 c!C5H00^ Cl^ Cl c!C5H00^ Cl^ Cl "PhNHCH1#1 THF\ 14>C 33 3!Ph!0\1!"NH1#1C5H2 THF\ 14>C 25 c!C5H00^ Cl^ Cl Ph^ Ph^ Cl phenoxazine THF\ 14>C 67 Ph^ Ph^ Cl 0\1!"NH1#1C5H3 THF\ 14>C 12 Me1CH^ Cl^ Cl tetramethyl!1\1?!diimidazole THF\ Et2N\ 14>C 23 "PhNHCH1#1 THF\ 14>C 33 c!C5H00\ Me\ Me c!C5H00\ Me\ Me homopiperazine THF\ K1CO2\ 14>C 07 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
"b# From 1!chloro\1!aminoiminium salts[ Tetrakis"dimethylamino#methane\ the _rst tetra! aminomethane described in the literature\ was synthesized in 69) yield by allowing tetra! methylchloroformamidinium chloride to react with lithium dimethylamide in benzene at room temperature "Equation "3## ð55JA1774Ł[ Homologous tetraaminomethanes\ prepared analogously\ have been patented as aminating agents\ herbicides\ insecticides\ bactericides\ and catalysts for urethane polymerization ð69USP2440307Ł[ +
Me2N
Cl–
Cl
2Me2NLi
Me2N
C6H6, 25 °C 70%
Me2N
NMe2 NMe2 NMe2
(4)
The preparation of a dibenzoanellated tetraaminomethane from 1!chloro!0\2!dimethyl!benzo! imidazolium tetra~uoroborate and N\N!dimethyl!ortho!phenylenediamine has been reported "Equa! tion "4## ð57CB0026Ł[ +
Me
Me Me NHMe
N Cl N Me
BF4–
+ NHMe
Et3N MeCN, 25 °C 32%
N
N
N
N
(5) Me Me
251
At Least One Group 04 Element
This synthetic methodology has been extended to the synthesis of the tetraazamethanes indicated in Scheme 0[ The properties of these compounds were subsequently investigated by photoelectron spectroscopy ð75JOC269Ł[ Me Me
Me Me N
N
N
N
Me Me
Me Me
N
N
N N
N
N
N N
Me Me
Me Me
Scheme 1
"c# Tetrakis"0!pyrazolyl#methane from CCl3 [ Tetrakis"0!pyrazolyl#methanes have been widely investigated as polydentate ligands in transition metal organometallic complexes[ The parent com! pound was _rst synthesized in low yield "01)# from carbon tetrachloride and an alkali!metal pyrazolide ð69JA4007Ł[ The conversion was improved slightly "19)# under solidÐliquid phase transfer catalysis conditions "Equation "5## ð73OPP188Ł[ Nonetheless\ these syntheses remain less e.cient than a two!step procedure starting from phosgene and sodium pyrazolide salts "see Section 5[01[0[0[0["v##[ N 4
NH
N
KOH, K2CO3
+ CCl4
N Bun4NHSO4, CCl4
(6)
C 4
"d# Tetrakis"di~uorosulfoximidoyl#methane from CCl3 [ The title compound may be prepared directly from CBr3 and the corresponding organomercury reagent\ but the reaction gives a number of products and yields are poor] the desired compound was only detected by mass spectroscopy[ A more practical synthesis involves the interaction of carbon tetrachloride with bis"di~uoro! sulfoximidoyl#mercury and treatment of the resulting intermediate with tris"di~uorosulf! oximidoyl#borane[ Nonetheless\ the yield remains low "5)# "Scheme 1# ð68CB0078Ł[ Hg(NSOF2)2
CCl4
F2C(NSOF2)2
145 °C, 20 h 82%
B(NSOF2)3
C(NSOF2)4
–78 °C, 3 h 6%
Scheme 2
"ii# By addition to carbonÐnitro`en double bonds A wide variety of NH functionalities add to activated carbonÐnitrogen double bonds[ Thus\ ammonia\ 3!cyanoaniline\ 3!tri~uoromethylaniline\ hydrazine\ tri~uoroacetylhydrazine and suc! cinimide react with penta~uoroguanidine at low temperatures to give the corresponding tetraa! zamethanes "Scheme 2# ð62JOC0964Ł[ In the case of relatively basic amines\ such as NH2\ BunNH1 and Me1NH\ spontaneous elimination of HNF1 occurs below room temperature\ to give a poly! ~uoroguanidine having a di}erent substitution pattern[ These reactions are dan`erous\ and should be performed in polar solvents in order to reduce the risks of explosion] suitable protective equipment should be used durin` all phases of work[ F2N
R1R2NH
F2N
NR1R2
dimethylether –63 °C
F2N
NHF
NF F2N
R1R2N 20 °C
NF
+ F2NH
F2N
Scheme 3
The _rst!formed tetraaminomethanes "Scheme 2# are useful synthetic intermediates[ Bis"di! ~uoroamino#"~uoroamino#aminomethane may be treated with elemental ~uorine at low tem! perature to give\ amongst other products\ the highly explosive tetrakis"di~uoroamino#methane ð61USP2578459\ 61USP2552510\ 62JOC0964Ł\ C"F1N#3 which has been patented as a rocket!propellant oxidizer "Equation "6## ð61USP2588983\ 62USP2644393Ł[
Four Group 04 Elements F2N
NH2
F2/N2
F2N
NHF
–30 °C, 5 h
252 (7)
C(NF2)4
Similarly\ ammonia adds to ðbis"di~uoroamino#~uoromethylazoŁtri~uoroformamidine giving an unstable adduct\ which undergoes low temperature ~uorination[ Fluoropentakis"di~uoroamino# azomethane is formed in low yield by this method "Scheme 3# ð61IC307Ł[ F2 N
F2N
NH2
N N
NHF
NH3
NF N N
F2/N2
CCl2F2, –96 °C, 2.5 h
(F2N)2FC
CCl2F2, –110 °C, 6 h 10%
(F2N)2FC (F2N)3C
N N CF(NF2)2 Scheme 4
Penta~uoroguanidine may be subjected to an analogous addition of isocyanic acid\ which gives bis"di~uoroamino#~uoroaminomethyl isocyanate[ This isocyanate and the other derivatives described in this section are reported to be very powerful explosives which are extremely sensitive to impact\ friction\ and perhaps temperature chan`es[ Quantities as small as 099 m` should be re`arded as dan`erous[ The _rst formed isocyanate product may react with a further equivalent of isocyanic acid to give the cyclic derivative shown in Equation "7# ð62JOC0979Ł[ F
O F 2N
F2N
HNCO
NCO
+
NF urea (cat.), –30 °C, 3 h
F 2N
F2N
N
NF2
N
NF2
(8)
HN
NHF O
F
Other tetraazamethanes may be obtained from bis"di~uoroamino#~uoroaminomethyl isocyanate[ Treatment with elemental ~uorine alone permits substitution of hydrogen by ~uorine without a competing reaction at the isocyanate moiety[ However\ ~uorination in the presence of sodium ~uoride gives tetrakis"di~uoroamino#methane "81)# "Scheme 4# ð62JOC0977\ 62USP2622259Ł[ F2N F2N
NCO NHF
F2/He 0 °C
F 2N F 2N F 2N
NCO
F2/NaF
F 2N F2N F2N
NF2
Scheme 5
Addition of ethanol to bis"di~uoroamino#~uoroaminomethyl isocyanate results in the trans! formation of the NCO function into the corresponding ethylcarbamate ð62JOC0979Ł[ Tris "di~uoroamino#methyl isocyanate also undergoes addition of alcohols\ water and amines at the isocyanate function "Table 3# ð62JOC0972Ł[ Table 3 Addition of water\ alcohols and amines at the isocyanate function[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Isocyanate Rea`ents and conditions Products ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * "F1N#1"HNF#C"NCO# EtOH\ −085:14>C "F1N#1"NHF#C"NHCO1Et# "F1N#2C"NCO# HOCH1CH1OH\ 14>C ""F1N#2CNHCO1CH1#1 69 H1C1CHCH1OH\ 14>C "F1N#2CNHCO1CH1CH1CH1 80 "F1N#2C"NCO# "F1N#2C"NCO# ether\ NH2\ −085:14>C "F1N#2CNHCONH1 62 ether\ 9[2NH2\ −085:14>C ""F1N#2CNHCO#1NH 49 "F1N#2C"NCO# "F1N#2C"NCO# "H1N#1\ MeCN\ −085:14>C ""F1N#2CNHCONH#1 40 H1O "F1N#2CNH1 "F1N#2C"NCO# "F1N#2C"NCO# "F1N#2CNH1:Ph2PO ""F1N#2CNH#1CO ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Although most of the compounds described in this section are high explosives\ some related methodologies have been applied to more classical synthetic procedures[ Thus\ 0\2!bis"methoxycarbonyl#!S!methyl isothiourea "BMMTU#\ a widely used reagent for the preparation of benzimidazole!1!carbamates from ortho!phenylenediamines\ reacts in slightly acid
253
At Least One Group 04 Element
media with 1!aminobenzamides\ to give 1\1!biscarbamates in yields ranging from 45) to 64) "Scheme 5#[ This reaction permits the synthesis of potential medicinal products\ fungicides and antiparasitic agents ð89S040Ł[ O X
O i
NH2
X
O X
ii
NH2
NH NHCO2Me
Y
Y
NO2
Y
NH2 Z
Z
Z
i, Raney - Ni, N2H4, MeOH, 25 °C, 3 h ii, MeO2CN=C(SMe)NHCO2Me, MeOH, MeCO2H, reflux, 2 h
N H
NHCO2Me
Z Yield (%) X Y H H H 61 OMe OMe H 75 OMe OMe OMe 56
Scheme 6
The reaction of two equivalents of isocyanate with pentasubstituted guanidines gives a cyclo! adduct having an s!triazine structure[ This reaction does not appear to be completely general[ Thus\ pentamethylguanidine reacts with both phenyl and methyl isocyanate\ but N!phenyl! tetramethylguanidine undergoes reaction with methyl isocyanate but not with phenyl isocyanate[ With N!phenyltetramethylguanidine and an equimolar mixture of the two isocyanates\ an unsym! metrically substituted s!triazine is produced "Equation "8## ð57TL4926Ł[ R2
O R12N
2R1NCO
NR2
R1
NR12
N
NR12
(9)
N
ether, RT
R12N
N
R1
O R1,
R2
= Me, C6H5
"iii# By addition to nitro`enÐnitro`en double bonds Azodicarboxylate esters react either with trinitromethane in dioxane ð64IZV1727Ł\ or with its mercury salts in water ð66IZV0452Ł\ to give "trinitromethyl#hydrazine derivatives[ Nitroform reacts analogously with azocarboxamides "Scheme 6#[ dioxane, 20 °C, 4 d
EtO2CN
NCONHMe
+ (O2N)3CH
(O2N)3C 90%
EtO2CN
NCO2Et
+ Hg(C(NO2)3)2
i, H2O, 20 °C
N NHCO2Et CONHMe
(O2N)3C
ii, HCl conc. 88%
N NHCO2Et CO2Et
Scheme 7
"iv# From carbanions bearin` two nitro`en substituents Ammonium trinitromethanide reacts readily with nitryl ~uoride to form tetranitromethane in excellent yield[ Trinitromethane itself is ionized su.ciently in acetonitrile to interact directly with nitryl ~uoride but the yield is slightly poorer in this case "Equation "09## ð60IZV0483\ 63IZV804Ł[ (O2N)3C– NH4+
NO2F
C(NO2)4
(10)
MeCN 90%
Reaction of bis"benzotriazolyl#methane with n!butyllithium and tosyl azide gave the `em!diazido compound in moderate yield] the expected monoazido compound appears to be more reactive than
Four Group 04 Elements
254
the starting material[ A further Staudinger phosphorylation reaction with triphenylphosphine gave a product\ presumed to be the corresponding bis"triphenylphosphoranylidene# compound\ which was too unstable to be isolated "Scheme 7# ð89JCR"S#229Ł[ N
N
N
N
N N
BunLi, TsN3
N
N3
PPh3
N N
N PPh3
N
THF, –78 °C 22%
N
N3
THF, 25 °C, 5 h
N N
N PPh3
N
N
N N
N
Scheme 8
"v# Miscellaneous syntheses This section comprises a number of unrelated synthesis of which two are particularly important[ The _rst constitutes the most e}ective preparation of tetranitromethane\ which is obtained in approximately 59) yield by the reaction of anhydrous nitric acid with acetic anhydride below 09>C "Equation "00## ð44OSC"2#792Ł[ The product is a high explosive\ and should be puri_ed only by steam distillation[ The synthesis has been adapted to the preparation of the labelled compound C"NO104#3 in 39) overall yield from sodium nitrate ð89MI 501!90Ł[ 4(MeCO)2O + 4HNO3
C(NO2)4
10 °C
+ 7MeCO2H + CO2
(11)
The second important synthesis produces tetrakis"0!pyrazolyl#methanes\ which have been pre! pared through a two!step process from the appropriate pyrazolide salt and phosgene[ Thermolysis of the intermediate 0\0?carbonyldipyrazole at 089>C in the presence of cobalt"II# chloride induces an autocondensation reaction which gives the tetrakis"0!pyrazolyl#methanes in a total yield of 49) "Scheme 8# ð62CJC1337Ł[ N N– Na+
N
COCl2
CoCl2
N ether, reflux 80%
N
CO
N 190 °C, 16 h 50%
2
C 4
Scheme 9
Interaction of 0\3\6\09!tetraazacyclododecane and ethyl orthocarbonate in acidic ethanol gives solutions which contain a tricyclic guanidinium ion!amino compound] the reaction proceeds in nearly quantitative yield[ The corresponding covalent tetracyclic tetraazatridecane may be obtained by neutralization\ extraction into benzene\ and subsequent drying by azeotropic distillation "Scheme 09#[ The conformation of the two macrocycles\ and the equilibrium which relates them\ was studied by NMR spectroscopy ð63T0658Ł[ NH HN NH HN
C(OEt)4, HCl EtOH
NH
N
NaOH
+
N
N
Cl–
C6H6, H2O
N
N
N
N
Scheme 10
5[01[0[0[1 Four phosphorus functions Very few papers dealing with the synthesis of this class of compounds have appeared[ Nonetheless\ a number of patents describing the use of methanetetraphosphonic acid and its derivatives in
255
At Least One Group 04 Element
detergents ð64USP2781565Ł or as chelating agents for heavy metal ions ð73USP3339535Ł have been disclosed[ Chlorodimethylphosphine displaces all four chlorine atoms of carbon tetrachloride\ to give tetrakis"dichlorodimethylphosphoranyl#methane in 71) yield[ The pentacoordinated phosphorus derivative was converted into the corresponding oxide upon basic hydrolysis "79) yield# "Scheme 00#[ The reaction is not general and fails for reagents such as PCl2 and MePCl1\ presumably because of their lower electron density at the phosphorus atom ð56ZOB1402Ł[ CCl4
Me2PCl
NaOH, H2O
C[Me2PCl2]4
160 °C, 3 h 82%
C[P(O)Me2]4
81%
Scheme 11
The only spiroð1[1Łtetraphosphapentane which is known to date was prepared by the reaction of carbon tetrachloride with 0\1!dipotassium di!tert!butyldiphosphide\ in 1) yield after chro! matography on alumina[ Of the two anti!isomers which are observed\ the sterically more hindered one converts slowly into the favored isomer at room temperature "Scheme 01# ð72AG"E#521Ł[ But
But P (ButP—PBut)2– 2K+
P
CCl4
But P
pentane, –78 °C
But
P
But
+
P
P
But
P But
P But
Scheme 12
5[01[0[1 Three Similar and One Different Group 04 Element Functions 5[01[0[1[0 Three nitrogen functions Only two compounds bearing three nitrogen functions are known] both are cyclic compounds containing three nitrogens and a phosphorus atom[ Both syntheses involve the participation of a phosphorus substituted C0N double bond\ and in each case two of the nitrogen atoms are included in the ring[ In the _rst case\ the interaction of diethyl phosphite with diphenylcarbodiimide gave an inter! mediate amidinophosphinic acid which underwent a ð1¦1Ł cycloaddition reaction with phenyl isocyanate[ The _nal product is obtained in 54) yield "Scheme 02# ð70ZOB0924Ł[
PhN
•
NPh
(EtO)2P(O)H
NHPh PhN P(O)(OEt)2
Ph PhNCO 80 °C, 5 h 65%
O N
PhHN (EtO)2(O)P
N Ph
Scheme 13
In the second case\ two equivalents of C!phosphorylated C!chlorohydrazones are reacted with the potassium salt of alanine[ Both the amino and the carboxylate groups act as nucleophiles resulting in substitution of the chlorine atom of the phosphorylated substrate[ The linear product is converted\ through the steric pressure\ into the cyclic tautomer by addition of the N0H function to the C1N double bond "Scheme 03# ð89ZOB0879Ł[ 5[01[0[1[1 Three phosphorus functions The only representatives of this class of compound bear one nitrogen and three phosphorus functions[ All the synthetic methods involve at least one MichaelisÐArbuzov type reaction as an intermediate step[ Reactions between triethyl phosphite and trichloromethylamines or trichloromethyl isocyanate a}ord tris"diethoxyphosphinyl#methylamines or isocyanates\ respectively "Equation "01# and Table 4#[
Four Group 04 Elements P(O)(OMe)2
CO2– K+
H2N
256
+
(4-O2NC6H4)NHN Cl (MeO)2(O)P
HN-CHMe-C(O) N NH(CO)-P(O)(OMe)2 (4-O2NC6H4)NHN
NHNHC6H4(4-NO2) C(O)P(O)(OMe)2 N
HN
C6H4(4-NO2)
N
P(O)(OMe)2
C6H4(4-NO2)
O Scheme 14 3(EtO)3P
+ ZCX3
(12)
ZC[P(O)(OEt)2]3
Table 4 Reactions of triethyl phosphite with trichloromethylamines or iso! cyanate[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Conditions ")# Ref[ ZCX2 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * "Me1N#CCl2 CH1Cl1\ −39>C\ 0 h 60 61ZOB0058 "0!morpholino#CCl2 CH1Cl1\ −39>C\ 0 h 66 61ZOB0058 toluene\ 89>C\ 0[4 h 45 62ZOB433 "OCN#CCl2 "OCN#CBr2 toluene\ 89>C\ 0[4 h 12 78ZOB460 CH1Cl1\ −79:14>C 63GEP1126768 "Me1N#CCl2 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Unsymmetrically substituted tris"phosphoryl#methylanilines were obtained transiently through a two!step synthesis starting from N!phenylcarbonimidic dichloride[ An initial MichaelisÐArbuzov reaction between a trialkyl phosphite and the dichloroimine led to the corresponding bis"phos! phoryl#imine which was then reacted with various R1P"O#H compounds] addition of the P0H function to the C1N double bond a}orded the tris"phosphoryl#methylanilines[ These compounds\ which were originally thought to be stable ð61JPR76Ł\ rearrange spontaneously by migration of one of the phosphoryl groups from the carbon to the nitrogen atom "Scheme 04# ð61JPR858\ 75JPR120Ł[ 2R2POR + Cl2C
[R2P(O)]2C
NPh
NPh
R2P(O)H
PhHN
[R2P(O)]2C
NPh P(O)R2
P(O)R2 P(O)R2 P(O)R2
PhN P(O)R2
R2(O)P
Scheme 15
5[01[0[2 Two Similar and Two Different Group 04 Element Functions 5[01[0[2[0 Two nitrogen functions Only one report of compounds bearing two nitrogen functions exists[ Treatment of a benzene solution of amidines with chlorobis"diethoxyphosphonyl#methyl iso! cyanate in the presence of triethylamine readily yields cyclic s!triazin!1"0H#!ones "Equation "02## ð64ZOB1982Ł[
H2N NH R
+
(EtO)2P(O) (EtO)2P(O) Cl
H N
O NCO
P(O)(OEt)2
Et3N
N
NH
C6H6, 20 °C, 2 h
R R = CCl3, 79%; Ph, 75%
5[01[0[2[1 Two phosphorus functions See Section 5[01[0[2[0[
P(O)(OEt)2 (13)
257
At Least One Group 04 Element
5[01[1 METHANES BEARING THREE GROUP 04 ELEMENTS AND A METALLOID OR A METAL 5[01[1[0 Three Similar Group 04 Elements 5[01[1[0[0 Three nitrogen functions Compounds bearing three nitrogen functions essentially comprise derivatives of trinitromethane[ In cases where they are not explicitly described as stable\ they are probably best treated as explosive and should be handled with care[ The most widely studied reagent of this class is bis"trinitromethyl#mercury which may be easily prepared\ in 79) yield\ by reaction of HgO with trinitromethane in ether at room temperature "Equation "03## ð59IZV494Ł[ HC(NO2)3 +
ether
Hg[C(NO2)3]2
HgO
(14)
15 min
The interaction of this reagent with a wide range of ethers\ aliphatic and aromatic nitro compounds\ nitramines and halocarbons has been investigated[ The molecular complexes which are formed have been studied by IR and NMR spectroscopy[ A number of lead references may be consulted ð57IZV1728\ 58IZV1293\ 61MI 501!90Ł[ Bis"trinitromethyl#mercury undergoes metathesis reactions with R1Hg species to a}ord the mixed derivatives RHgC"NO1#2 "Equation "04##[ In the case where R Bun\ the direct reaction of tri! nitromethane with dibutylmercury in ethanol leads to the same product ð56JOM"8#4Ł[ HgR2 +
EtOH
RHgC(NO2)3
Hg[C(NO2)3]2
(15)
reflux, 6 h
R = Ph, 86%; Bun, 50%
The related aryl"trinitromethyl#mercury may also be prepared from diphenylmercury and tetra! nitromethane in a wide range of solvents such as MeCN\ sulfolane and chloroform\ probably by a radical mechanism "Equation "05## ð63ZOR0682Ł[ HgPh2 +
sulfolane
PhHgC(NO2)3
C(NO2)4
(16)
80 °C, 10 h 46%
Bis"trinitromethyl#mercury reacts with either piperidine or chlorodialkylamines to give "tri! nitromethyl#mercuric amides in very high yields "Equation "06## ð56IZV1697Ł[ Hg[C(NO2)3]2 +
ether
R2NHgC(NO2)3
R2NX
(17)
0 °C, 3 h
R2NX = N-chloropiperidine, 92%; N-chlorodimethylamine, 91%; piperidine (2 equiv.), 30%
The adduct of 1\1?!azobis"isobutyronitrile# with Hg"C"NO1#2#1 reacts as a mercurating agent towards 1\3!dioxypentane to a}ord 2!"1\3!dioxopentyl#trinitromethylmercury "Equation "07## ð66IZV0452Ł[ Hg[C(NO2)3]2 +
MeCOCH2COMe
AIBN
(MeCO)2CHHgC(NO2)3
(18)
Insertion of alkenes into the C0Hg bond of bis"trinitromethyl#mercury has been studied[ Cyclohexene undergoes trans!addition whilst norbornene gives an exo!cis product\ as found in the case of more classical mercuration reactions "Equation "08## ð57IZV0527Ł[
Hg[C(NO2)3]2 +
MeNO2 20 °C, 10 d 42%
HgC(NO2)3 C(NO2)3
(19)
Three Group 04 Elements and a Metalloid
258
A similar addition to 2\4!dinitrocyclopentene has been reported ð69IZV1097Ł but the stereo! chemistry of the addition was not de_ned[ The reaction with allyltrimethylsilane is relatively complex] after the _rst mercuration\ the elim! ination of trimethylsilane generates a new site of unsaturation which undergoes a second addition of the organomercury reagent "Equation "19## ð62RZC0132Ł[ 2Hg[C(NO2)3]2 +
TMS 62%
(O2N)3C (O2N)3CHg
C(NO2)3 HgC(NO2)3
(20)
Several metal salts of trinitromethane\ M¦−C"NO1#2\ have been prepared] their stability depends quite strongly upon the counterion[ Alkaline metals and ammonium salts are reported to decompose exothermically\ without explosion\ upon heating ð66IZV0854Ł[ The speci_c impulse properties of compounds such as Me1AlC"NO1#2 and LiC"NO1#2 have been measured ð60USP2451298Ł\ and Me2SiC "NO1#2 decomposes violently ð82TL0748Ł[ The alkali metal salts "K\ Rb\ Cs# and ammonium compounds of the trinitromethanide anion may be prepared by reaction of trinitromethane with the corresponding hydroxide ð66IZV0854Ł\ whilst the Al\ Mg\ B\ Be and Li salts were prepared from the metal alkyls and a stoichiometric amount of HC"NO1#2 or BrC"NO1#2 in pentane ð60USP2451298Ł[ The silver salt may be prepared in situ from HC"NO1#2 and silver oxide in MeCN ð52T"S#066Ł[ It reacts with chlorodiphenylstibine to a}ord diphenyl"trinitromethyl#stibine "64Ð79) yield#\ which is also accessible less e.ciently in 29Ð49) yield from the potassium salt "Equation "10## ð74IZV328Ł[ MC(NO2)3 +
Ph2SbCl
CH2Cl2
Ph2SbC(NO2)3
(21)
20 °C, 4 h
M = K, Ag
Finally\ two potassium salts of a "dinitromethyl#hydrazine\ K¦−C"NO1#1N"COR#NHCOR\ have been very brie~y described\ but no synthetic details were given ð64IZV1727Ł[ 5[01[1[0[1 Three phosphorus functions A wide variety of methanes having a lithium or sodium atom and three phosphorus substituents have been prepared as anionic tripod ligands for coordination chemistry[ Variants having tri! and pentavalent phosphorus atoms are known\ and syntheses have been devised which permit the targeting of ligands containing any desired combination of oxygen and sulfur!bound phosphorus atoms[ The synthesis of the alkali!metal derivatives has been accomplished by proton abstraction from the parent methane\ HtrisXYZ\ with various reagents[ Selected examples are given in Table 5 "Equation "11##[ The lithium salts containing phosphorus"V# atoms are fairly air stable and can be stored for several months without change[ An x!ray crystal structure determination of LiC"PMe1#2 shows that the lithium atom is bound to both of the phosphorus lone pairs and to the carbon atom ð73CC458Ł[ This implies that the charge is delocalized over the phosphorus and the carbon atoms and indicates that reactivity towards electrophiles is complex[ P(Y)R2 R2(X)P P(Z)R2
R 1M
M
P(X)R2 P(Y)R2 P(Z)R2
Table 5 Metalation reactions of HtrisXYZ[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield HTrisXYZ Rea`ents and conditions ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * HCðP"O#Ph1Ł2 LiOMe\ CH1Cl1\ 14>C\ 4 h 67 75IC1588 NaH\ THF 89JA6873 HCðP"O#Ph1Ł2 HCðP"O#Ph1Ł1ðP"S#Ph1Ł LiOMe\ CH1Cl1\ 14>C\ 4 h 71 75IC1588 LiOMe\ CH1Cl1\ 14>C\ 4 h 62 75IC1588 HCðP"O#Ph1ŁðP"S#Ph1Ł1 HCðP"S#Ph1Ł2 LiOMe\ CH1Cl1\ 14>C\ 4 h 61 75IC1588\ 71CC829 HCðP"S#Me1Ł2 ButLi\ THF\ −19:14>C\ 4 h 65 71CB707 ButLi\ pentane\ 14>C\ 09 h 62 68ZN"B#0067 HC"PMe1#2 HCðPPh1Ł2 LiOMe\ MeOH ×55 75IC1588 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
(22)
269
At Least One Group 04 Element
The analogous Hg {{trisS2|| derivatives are prepared directly by reaction of the parent methane {{HtrisS2|| with the corresponding metal halides in ethanol solution] the cadmium analogues may be prepared similarly in the presence of a mild base such as triethylamine "Equation "12## ð74IC1778Ł[ In the solid state\ the complexes are bound through the sulfur atoms\ but there is some circumstantial evidence for coordination to carbon in solution[ P(Y)R2
MX2
R2(Y)P
P(Y)R2 P(Y)R2 P(Y)R2
XM
P(Y)R2 M Hg Hg Cd Cd
3P(Y)R2 3P(S)Ph2 P(S)Ph2[P(S)Me2]2 3P(S)Ph2 P(S)Ph2[P(S)Me2]2
X Cl Cl Cl Cl
(23)
Yield (%) 92 85 94 56
5[01[2 METHANES BEARING TWO GROUP 04 ELEMENTS AND METALLOID AND:OR METAL FUNCTIONS 5[01[2[0 Two Similar Group 04 Elements 5[01[2[0[0 Two nitrogen functions There appears to be only one compound of this general class which has featured in the literature[ Lithiation of N!"benzotriazol!0!ylmethyl# pyrrole with n!butyllithium and subsequent addition of chlorotrimethylsilane gave a mixture of products which included the bis"trimethylsilyl# derivative "Equation "13## ð78JHC718Ł[ The reported yield was relatively low "25)#\ but it appears that the method could be synthetically useful if two equivalents of n!butyllithium and chlorotrimethylsilane were used[
N
N N
N
i, BunLi ii, TMS-Cl
N
N
TMS N TMS
N
(24)
5[01[2[0[1 Two phosphorus functions A few compounds in which a carbon atom bears two phosphorus and two silicon functions have been described[ All have trimethylsilyl substituents\ but the phosphorus moieties may be either phosphines "PR1#\ phosphonium salts "PR2¦#\ phosphorus ylides "1PR1# or phosphaalkenes "R1C1P#[ The earliest report of such a compound concerned a bisphosphonium salt\ prepared by addition of two equivalents of chlorotrimethylsilane to a symmetrical dimethyltetraphenylcarbo!diphosphorane "Equation "14##[ This phosphonium salt is relatively unstable and decomposes within a few minutes ð65ZN"B#610Ł[ TMS-Cl
Ph2MeP
•
PMePh2
C6H6
+
Ph2MeP TMS
+
PMePh2 TMS
(25) 2Cl–
A second example involves the addition of a chlorophosphaalkene to a phenyl! or alkylnyllithium reagent\ which gives a phosphinomethyl substituted phosphaalkene[ It is proposed that the reaction
Two Group 04 Elements and Metalloid
260
proceeds through the intermediacy of a lithium bis"trimethylsilyl# phosphinomethanide which reacts with a second equivalent of the chlorophosphaalkene "Scheme 05# ð75CB1598Ł[ TMS
TMS
Li
2RLi ether, –78 °C, 2 h
TMS
R2P
TMS
TMS
ether, –78 °C, 2 h
R2P
P
TMS
ClP TMS
TMS
ClP
TMS TMS
R = TMSC≡C, 70%; PhC≡C, 60%; Ph, 54% Scheme 16
In the case where R TMS!C2C\ a subsequent pyrolysis gave a bis"trimethylsilyl#!substituted diphosphirane in 31) yield] this reaction proceeds through an intramolecular ð1¦1Ł cycloaddition involving the P0C double bond and one of the C0C triple bonds\ and a subsequent rearrangement "Equation "15## ð75CB1598Ł[ TMS
TMS P TMS (TMSC≡C)2P
∆
TMS
toluene, 100 °C, 20 min
TMS
TMS •
TMS
P
TMS
P
(26)
TMS TMS
The last compound is a phosphino!phosphorane derivative\ which is prepared in poor yield by means of a zirconium!mediated synthesis "Scheme 06# ð82OM1646Ł[ TMS
TMS LiC(PMe)2(TMS)2
(C5H5)2ZrCl2
(C5H5)2ClZr
TMS P
ether, –78/25 °C
Me
LiC(PMe)2(TMS)2 ether, –78/25 °C, 18 h
Me
TMS
P
TMS
PMe2
TMS
Scheme 17
Compounds containing two phosphorus\ a silicon and a lithium function as substituents at the central carbon are also known[ Bis"phosphino#methanides and a bis"thiophosphinyl#methanide have been prepared by metalation with n!butyllithium of the corresponding trisubstituted methanes "Equation "16## ð77ZN"B#0305\ 81CB0222Ł[ P(X)Me2 Me2(X)P
BunLi
Li
TMS
P(X)Me2 P(X)Me2 TMS
(27)
X = lone pair, hexane, 30 °C, several days, 99% X = S, toluene, –78/25 °C, 12 h, 95%
The mercuration of methylenediphosphonate compounds which contain an acidic hydrogen is known[ Reaction of mercuric acetate with a methylenediphosphonate in re~uxing tetrahydrofuran provokes bis"mercuration# at the carbon atom with the loss of acetic acid[ The product undergoes redistribution reactions with other organomercurials "Scheme 07# ð62JOM"48#120Ł (EtO)2(O)P
P(O)(OEt)2
Hg(OAc)2
AcOHg
P(O)(OEt)2
THF, 70 °C
AcOHg
P(O)(OEt)2
HgX2
XHg
P(O)(OEt)2
XHg
P(O)(OEt)2
X = Br, THF, 17 h, 73%; Cl, THF, ∆, 26 h, 72%; Ph, EtOH, ∆, 60% Scheme 18
Methylenediphosphines react in a similar fashion with a mixture of mercuric acetate and the DMSO adduct of mercuric tri~ate\ Hg"DMSO#5"OSO1CF2#1[ The _rst\ monomercurated\ product reacts further with mercuric acetate to give an unstable dimercurated compound which could not
261
At Least One Group 04 Element
be isolated "Equation "17## ð73OM0805Ł[ It should be noted that such a mercuration reaction failed for a related tris"phosphino#methane ð75JOM"290#158Ł[
Ph2P
Hg(OAc)2, Hg(DMSO)6(OTf)2
PPh2
AcOHgPh2P
MeOH, 25 °C
HgOAc HgOAc PPh2HgOAc
2+
2TfO–
(28)
5[01[3 METHANES BEARING ONE GROUP 04 ELEMENT AND METALLOID AND:OR METAL FUNCTIONS 5[01[3[0 Nitrogen Functions A computer search of the Chemical Abstract Data Base has not revealed any compound belonging to this subgroup[
5[01[3[1 Phosphorus Functions 5[01[3[1[0 One phosphorus and three silicon functions The most important compounds bearing one phosphorus and three silicon functions are methanes which carry one phosphorus and three trimethylsilyl functions[ Many of these compounds may be prepared directly from PCl2\ or the corresponding chlorophosphine\ and tris"trimethyl! silyl#methyllithium "Equation "18## according to the conditions outlined in Table 6[ The experimental procedure employed for this transformation appear to be quite critical to the success of the reaction[ A similar series of reactions which involve the related reagent "PhMe1Si#2CLi has been described] the reaction with PCl2 proceeds in 50) yield ð78JOM"255#28Ł[ TMS TMS TMS
Li
R2PCl
TMS TMS TMS
PR2
(29)
Table 6 Reactions of tris"trimethylsilyl#methyllithium with chlorophosphanes[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R1PX Conditions ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * PCl2 THF\ 9>C\ 1 h 54 79ZC042 THF!ether\ 19>C\ 1 h 54 78JOM"255#28 THF\ 9:14>C\ 1 h 56 89IS124 MePCl1\ ButPCl1\ Et2CPCl1\ PhPCl1\ THF\ 55>C\ 7 h ×69 79ZC308\ 70ZAAC"362#74 TMSCH1PCl1\ 1\3\5!Me2!C5H1PCl1 Ph1PCl ether\ 39>C\ 1 h 37 72JCS"D#894 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Treatment of tris"trimethylsilyl#methyllithium with "trimethylsilyl#aminodi~uorophosphines causes the replacement of one of the ~uorine atoms by tris"trimethylsilyl#methyl group[ Small quantities of tris"trimethylsilyl#methyldi~uorophosphine are also formed[ Upon heating\ these com! pounds are easily transformed in phosphaalkenes through elimination of ~uorotrimethylsilane\ presumably because of sterical pressure "Scheme 08# ð73ZN"B#0499Ł[
TMS TMS TMS
TMS ∆ TMS N R F2P N TMS P R TMS F R = adamantyl, 46%; But, 79%; mesityl, 60%; TMS, 48% Scheme 19 TMS
Li
+
TMS
TMS P N
TMS
R
One Group 04 Element and Metalloid
262
The reactivity of tris"trimethylsilyl#methyllithium towards electrophiles is complicated by ex! change reactions[ Thus\ this lithium reagent reacts with phosphorus tribromide to give principally bromotris"trimethylsilyl#methane\ and only traces of dibromo"tris"trimethylsilyl#methyl#phosphine[ If required\ dibromo"tris"trimethylsilyl#methyl#phosphine may be prepared e.ciently by reaction of BBr2 with the corresponding dichloro derivative[ The compound "TMS#2CPCl1 has also been used for the synthesis of "TMS#2CPH1\ "TMS#2CPH1 = BH2 and "TMS#2CP"O#Cl1 by reaction with LiAlH3\ NaBH3 and AgNO2 respectively ð78JOM"255#28Ł[ Reduction of "TMS#2CPCl1 with ButLi\ sodium naphthalenide or "TMS#2CLi gives the bis"tri! s"trimethylsilyl#methyl#diphosphene "Equation "29## ð71TL3830\ 71JA4719Ł[ TMS TMS TMS
TMS TMS TMS
PCl2
TMS TMS TMS
P
P
(30)
A similar interaction of "TMS#2CPCl1 with lithium trimethylsilylphosphides leads to silyl!sub! stituted diphosphines[ The triphenylsilyl derivative is stable but its trimethylsilyl analogue evolves to give a compound having a tetraphosphabicyclobutane structure "Scheme 19# ð78OM1389Ł[ TMS TMS TMS
LiP(TMS)SiR3
PCl2 ether, –70/25 °C
TMS TMS TMS
TMS R = Me TMS P PSiR3 TMS R = Me, unstable; Ph, 61%
P P
P P
TMS TMS TMS
Scheme 20
The diphosphene "TMS#2CP1PC"TMS#2 undergoes further transformations at the phosphorusÐ phosphorus double bond[ These include ozonolysis ð73CC0511Ł\ ð1¦0Ł cycloadditions with carbenes ð78CC482Ł or isonitriles ð81ZAAC"506#42Ł and reactions with HCl ð75JCS"D#0790Ł] each of these transformations leaves the tetrasubstituted carbon atom unchanged[ A reaction producing a carbon atom bearing one phosphorus and three silicon functions through addition of a phosphorusÐoxygen bond to a transient silaethene is known[ The addition of "PhO#1P"O#OSiMe2 to the silicon carbon double bond is favored over a competing insertion of the C1Si function into the O0Si linkage "Scheme 10# ð70CB2494Ł[ Me (PhO)2(O)P Si Me
TMS Br TMS
TMS
BunLi
TMS-OP(O)(OPh)2
Me2Si ether, –78 °C
TMS
ether, –78/25 °C 82%
TMS (PhO)2(O)P TMS
SiMe2(O-TMS)
Scheme 21
Finally\ the reaction of iodotrimethylsilane with bis"trimethylsilyl#methylene trimethylphos! phorane leads to an iodophosphonium compound in 74) yield "Equation "20## ð69CB2337Ł[ TMS
+ TMS-I
Me3P TMS
+
25 °C, 4 d 85%
Me3P
TMS TMS I– TMS
(31)
5[01[3[1[1 One phosphorus\ one metal and two silicon functions Most of the compounds which fall within this section are organolithium reagents\ but a number of organoaluminum compounds are also known[ Bis"trimethylsilyl#phosphinomethanes\ R1PCH"TMS#1\ may be metalated by BunLi to give the corresponding organolithium reagents "Equation "21## "R Ph ð73CB1952Ł^ R Me ð77ZN"B#0305Ł#[ A crystal structure determination of bis"trimethylsilyl#dimethylphosphinylmethyllithium shows a dimeric structure for its TMEDA adduct[ In accordance with the ambidentate reactivity which these compounds show towards electrophiles\ each lithium atom is bound to carbon and to phosphorus ð73CB1952Ł[
263
At Least One Group 04 Element TMS Li TMS TMS R = Me, TMEDA, hexane, 25 °C, 7 d, 76% R = Ph, DME, hexane, 25 °C, 12 h, 95% TMS
R 2P
BunLi
(32)
R2P
Bis"trimethylsilyl#methylphosphonates and !phosphine oxides are also metalated by LDA and methyllithium\ respectively[ Yields are good to excellent "Equation "22## ð73JOC4976\ 76JOM"212#024Ł[ The metalation of dialkylmethyl phosphonates by three equivalents of LDA and subsequent treat! ment with two equivalents of chlorotrimethylsilane also provides a simple and e.cient route to the same carbanions "X MeO\ 57)^ EtO\ 74)^ PriO\ 14)# ð76JOM"212#024Ł[ TMS
RLi
X2(O)P
TMS Li TMS
X2(O)P
TMS X EtO MeO Ph
(33)
RLi Conditions Yield (%) LDA THF, –50 °C >91 LDA THF, –50 °C >92 MeLi 0 °C
Lithium to aluminum exchange reactions of bis"trimethylsilyl#dimethylphosphinomethyllithium have been reported[ The reactions are generally complex and give cyclic structures[ A number of examples are given in Scheme 11 ð89"CC#0510\ 80"CC#355\ 80OM1773Ł[ Me Me2P
TMS Li(TMEDA) TMS
Me2P
+ AlCl3
pentane, –78/25 °C 80%
TMS
Cl Al Si
Me
Me2P
TMS Li(TMEDA) TMS
pentane/toluene
+ Me2AlCl
Me2Al TMS
–78/25 °C 84%
TMS
TMS
TMS PMe2 Me
Cl Li(TMEDA) P Me2
Scheme 22
5[01[3[2 Arsenic or Antimony Functions Tris"trimethylsilyl#methyldichloroarsane\ which forms the starting point for the preparation of each arsenic containing compound of this general type\ may be prepared from AsCl2 and "TMS#2CLi "Equation "23## ð72TL1658Ł[ The conditions employed were similar to those used for the preparation of its phosphorus analogue ð79ZC042Ł[ TMS TMS TMS
Li
TMS TMS TMS
+ AsCl3
AsCl2
(34)
The chlorine atoms of "TMS#2CAsCl1 may be substituted either by a methoxyl group or by an allenyl function[ Subsequent transformations give a dimer which results from the head!to!tail dimerization of the As0C double bonds of two 0!arsabutatriene units "Scheme 12# ð89TL5220Ł[
TMS TMS TMS TMS
Cl As
Ph
NaOH
Ph
MeOH 82%
• TMS
TMS TMS TMS
OMe As •
Ph
ButLi
Ph
–78 °C 47%
Ph
Ph
As •
• As
Ph TMS
Scheme 23
TMS TMS
TMS TMS
Ph
One Group 04 Element and Metalloid
264
Reduction of "TMS#2CAsCl1 by t!butyllithium ð72TL1658Ł or organometallic complexes ð75ZN"B#080Ł leads to a tris"trimethylsilyl#methyl!substituted diarsene\ whose crystal structure ð74JCS"D#272Ł\ electrochemical properties ð76JCS"D#138Ł\ oligomerization reactions ð73JCR"S#163Ł\ and sulfuration ð72TL1658Ł have been described "Equation "24##[ TMS TMS TMS
AsCl2
TMS TMS TMS
As
As
TMS TMS TMS
(35)
Reduction of a mixture of "TMS#2CAsCl1 and "TMS#2CPCl1 by t!butyllithium gave the phos! phaarsene "TMS#2CAs1PC"TMS#2\ and the symmetrical diarsene and diphosphene in unspeci_ed yield ð72TL2514Ł[ Finally\ the synthesis of the highly photosensitive "TMS#2CSbCl1 from "TMS#2CLi and SbCl2 has been described brie~y\ but no experimental details were given ð74JA7100Ł[
5[01[4 ACKNOWLEDGEMENTS In collecting the literature\ the authors have bene_ted greatly from collaboration with Ms Francžoise Girard\ who is gratefully acknowledged[
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.13 Functions Containing at Least One Metalloid (Si, Ge or B) and No Halogen, Chalcogen or Group 15 Element; Also Functions Containing Four Metals PAUL D. LICKISS Imperial College of Science, Technology and Medicine, London, UK 5[02[0 METHANES CONTAINING AT LEAST ONE METALLOID "AND NO HALOGEN\ CHALCOGEN OR GROUP 04 ELEMENT# 5[02[0[0 Methanes Bearin` Four Metalloid Functions 5[02[0[0[0 Four similar metalloid functions 5[02[0[0[1 Three similar and one different metalloid function 5[02[0[0[2 Two similar and two different metalloid functions 5[02[0[1 Methanes Bearin` Three Metalloid Functions and a Metal Function 5[02[0[1[0 Three similar metalloid functions 5[02[0[1[1 Other mixed metalloid functions 5[02[0[2 Methanes Bearin` Two Metalloid and Two Metal Functions 5[02[0[2[0 Two Si and two metal functions 5[02[0[2[1 Two Ge and two metal functions 5[02[0[2[2 Two B and two metal functions 5[02[0[2[3 Other combinations of two metalloids and two metal functions 5[02[0[3 Methanes Bearin` One Metalloid and Three Metal Functions 5[02[0[3[0 One Si and three metal functions 5[02[0[3[1 One Ge and three metal functions 5[02[0[3[2 One B and three metal functions 5[02[1 METHANES BEARING FOUR METAL FUNCTIONS 5[02[1[0 5[02[1[1 5[02[1[2 5[02[1[3
Methanes Bearin` Four Similar Metals Methanes Bearin` Three Similar and One Different Metal Function Methanes Bearin` Two Similar and Two Different Metal Functions Methanes Bearin` Four Different Metal Functions
5[02[2 METHANES BEARING MORE THAN FOUR METALLOID OR METAL FUNCTIONS
266
267 267 267 276 277 289 289 286 287 287 399 399 390 390 390 393 393 393 393 394 394 394 395
267
At Least One Metalloid or Metal
5[02[0 METHANES CONTAINING AT LEAST ONE METALLOID "AND NO HALOGEN\ CHALCOGEN OR GROUP 04 ELEMENT# There are a huge number of potential substitution patterns at tetravalent carbon covered by the title of this section[ Besides the elements speci_cally excluded in the title of the section and the lanthanides\ the actinides and Fr\ Ra and Tc*there are 36 elements which could be considered as substituents to be covered in the section[ There are 129299 possible combinations ""3¦n−0#;:3;"n−0#; for n 36# of these 36 elements at four coordinate carbons "not including a further 067254 optical isomers generated by having four di}erent elements as substituents#[ About 59 i[e[\ 9[915) are discussed below[ Thus it is clear that there is still enormous scope for the synthetic chemist in the preparation of such organometallic compounds[ It has been impossible to carry out a comprehensive search of the literature for all the possible functions covered under this heading\ but it is hoped that the majority of important functions have been found[ In some cases\ carbon substituted by four metals may better be regarded as an interstitial carbide and more the province of the inorganic chemist^ such species have been omitted[
5[02[0[0 Methanes Bearing Four Metalloid Functions There are a large number of compounds known containing a carbon substituted by four silicon functions^ such compounds may be prepared in a wide variety of ways[ In view of the number of tetrasilylmethanes known\ surprisingly\ there seems to be no analogous germanium substituted species\ although this is presumably due to a lack of synthetic e}ort rather than any inherent instability[ A relatively small number of methanes substituted by four boron functions have been prepared\ and there is also a range of compounds containing either a variety of metalloid functions or mixed metalloid and metal functions[
5[02[0[0[0 Four similar metalloid functions "i# Four Si functions "a# Tetrasilylmethanes from in situ couplin` reactions[ A range of compounds containing the Si3C function has been prepared by in situ coupling reactions in which most\ if not all of the four Si0C bonds are formed in the same reaction[ Simple compounds of the type "R01R1Si#3C can be made by coupling reactions using di}erent metals and di}erent halomethanes according to the general reaction "Equation "0##[ The range of precursors used for this type of synthesis and the products obtained are given in Table 0[ R12R2SiCl
+ metal + tetrahalomethane
(R12R2Si)4C
+ metal halide
(1)
Table 0 Reagents used in and products formed from in situ coupling reactions[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield ")# Ref[ Chlorosilane Metal Halomethane Si3C Product ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * TMSCl Mg CBr3 "TMS#3C 17 53JOC842 TMSCl Mg CBrCl2 "TMS#3C 19 53JOC842 "TMS#3C 29 53JOC842 TMSCl Mg CBr1Cl1 TMSCl Li CBr3 "TMS#3C 17 54JOM"3#87 "TMS#3C 22Ð55[4 53MI 502!90\ 54JOM"3#87 TMSCl Li CCl3 Me1SiHCl Mg CBr3 "Me1HSi#3C 44Ð59 53JOC842\ 74JOM"183#294 Mg CCl3 "PhMe1Si#3C 00 69JOM"13#78 PhMe1SiCl PhH1SiCl Mg CBr3 "PhH1Si#3C ca[ 34 89AG"E#190 Mg CBr3 "MeCl1Si#3C 75ZN"B#0416 MeSiCl2 SiCl3 Mg CBr3 "Cl2Si#3C 75ZN"B#0416 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
The in situ tetrasilylation reactions may be written as simple sequential metallationÐsilylation steps\ but actually the mechanism is likely to be rather more complicated as rapid ligand exchange between TMS\ Br and Li has been shown to occur even at low temperatures in the TMSCl:CBr3:Li system ð69TL3582Ł[ Sequential lithiationÐsilylation reactions can also be carried out using CH1Cl1
268
At Least One Metalloid
and BunLi in a 0 ] 3[4 ratio\ quenching with TMSCl to give "TMS#3C in 25) yield ð61JOC1551Ł[ The coupling of CLi3\ either as a solid or in solution\ with TMSCl gives a 4) yield of "TMS#3C ð61CC0967\ 73AG"E#884Ł[ The tetrasilylation of CCl3 can also be achieved electrochemically\ silylation using TMSCl and an aluminium anode giving "TMS#3C in 59) yield along with di! and trisilylated products ð77JOM"247#20Ł[ The coupling reaction between "0# and CCl3 in the presence of lithium "Equation "1## a}ords the heptasilað3[3[3Łpropellane "1#^ again all four Si0C bonds are formed in a single reaction[ This reaction presumably proceeds in a stepwise manner with sequential formation of chloromethyl lithium reagents which react in turn with the four Si0Br groups in the organosilicon precursor[ However\ there may be rapid exchanges between Li\ Cl\ Br and silyl groups also taking place as mentioned above for the TMSCl:CBr3:Li system[ Perhaps not surprisingly for such a complicated reaction\ the yield is low "4)# ð65ZAAC"308#1Ł[
Me2Si Me2Si
Si
SiMe2
Me2Si Br
SiMe2 Br (1)
Me2Si Me2Si
SiMe2
Si
(2)
+ CCl4 + 8Li
Br SiMe2 Br
Si Si Me2 Me
2
Si Me2
+ 8LiCl
(2)
The phenylsilylmethane "PhH1Si#3C "see Table 0 for its synthesis# is of interest as it is the precursor to "BrH1Si#3C\ via Si0Ph bond cleavage by HBr\ which may then be reduced under phase transfer conditions using LiAlH3 to give "H2Si#3C\ the Si:C inverse of the well!known Me3Si ð89AG"E#190Ł[ This silane cannot be prepared from "Cl2Si#3C as both trisilylmethyl and Cl2Si− anions are good leaving groups and attempted reductions lead to Si0C bond cleavage[ Interest in "H2Si#3C and other H2Si substituted methanes stems from their potential as chemical vapour deposition precursors to thin _lms of amorphous hydrogenated silicon carbide ð81JOM"318#0Ł[ "b# Formation by reaction between a trisilyllithiomethane and a halo! or pseudohalosilane[ The reactions between tris"trimethylsilylmethyl#lithium "for its synthesis see 5[02[0[1[0 "i# "a## and halo! or pseudohalosilanes have been used to prepare a large number of tetrasilylmethanes via the simple coupling reaction outlined in Equation "2#[ (TMS)3CLi
+ R1R2R3SiX
(TMS)3CSiR1R2R3
+ LiX
(3)
The range and yields of compounds prepared by the method given in Equation "2# are given in Table 1[ The formation of such compounds is greatly a}ected by steric factors^ for example\ addition of more than one equiv[ of the lithium reagent "TMS#2CLi "{TsiLi|# to a di!\ tri! or tetrahalosilane does not lead to the substitution of more than one Tsi group for a halide^ i[e[\ it does not seem to be possible to attach more than one Tsi group to any one Si atom[ It should also be noted that\ for the synthesis of the most sterically hindered compounds\ improved yields are obtained if silyl ~uorides are used rather than silyl chlorides "presumably again for steric reasons#^ for example\ TsiLi reacts with Ph1SiCl1 and with Ph1SiF1 to give TsiSiPh1X products in 7 and 65) yield\ respectively^ see Table 1[ A variety of other trisilylmethyllithium reagents that are less symmetrical than TsiLi have also been prepared "see 5[02[0[1[0["i#"a##\ and they react in a similar way with halosilanes to give tetrasilylmethanes "Table 2#[ The variety of functional groups that may be present in the tri! silylmethyllithium reagents is greater than might be expected considering the reactivity of normal alkyllithium reagents with functional organosilanes[ This unusual compatibility of a functional group on silicon and an alkyllithium function is presumably due to the fact that the reagents are often prepared at very low temperatures and also because steric constraints are likely to hinder the attack of one bulky molecule on another[ Tetrasilylmethane products may also be formed in the reactions of disilylmethane derivatives with lithium or organolithium reagents[ The reaction of "TMS#1CCl1 with four equivalents of lithium in the presence of PriSiF2 at room temperature gives "TMS#1C"SiPriF1#1 in 37) yield ð74JOM"180#166Ł[ Alternatively\ "TMS#1CLi1 can be prepared "see 5[02[0[2[0# at room temperature and it reacts with TMSCl to give "TMS#3C in 20) yield ð77TL4126Ł[ The reactions of "TMS#1CClLi with halosilanes often gives mixtures containing tetrasilylmethane products as well as the expected trisilylmethanes "Equation "3## ð73ZAAC"409#058Ł[
279
At Least One Metalloid or Metal
Table 1 Products obtained from the reaction between "TMS#2CLi "TsiLi# and halo! or pseudohalosilanes R0R1R2SiX[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Product ")# Ref[ RR0R1SiX ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * TMSCl TsiTMS 46Ð74 69JOM"13#418\ 66JOM"031#28\ 81OM1827 TMSCN TsiTMS 67 75JOC2434 Me1Si"N2#1 TsiSiMe1N2 71AG"E#332 SiH1Cl1 TsiSiH1Cl 82TH50290 MeSiHCl1 TsiSiMeHCl 08Ð44 69JOM"13#418\ 68JCR"S#01 TsiSiMeF1 58 74ZN"B#0912 MeSiF2 SiF3 TsiSiF2 57Ð63 73ZAAC"409#064\ 75JOM"298#136 TsiSi"But#F1 41Ð60 73ZAAC"409#064\ 75JOM"298#136 ButSiF2 TsiSi"Pri#F1 56 76JOM"212#0 PriSiF2 Me1SiF1 TsiSiMe1F 54 76JOM"212#0 TsiSiEt1F 39 69JOM"13#418 Et1SiF1 Pri1SiF1 TsiSi"Pri#1F 51 76JOM"212#0 TsiSiPhF1 56 73ZAAC"409#064 PhSiF2 Me1SiHCl TsiSiMe1H 76 69JOM"13#418 SiCl3 TsiSiCl2 67 69JOM"13#418 TsiSiMe1OMe 59 69JOM"13#418 Me1SiCl"OMe# Si"OPri#Cl2 TsiSiCl1"OPri# 39 69JOM"13#418 TsiSiMe1Cl 71 69JOM"13#418 Me1SiCl1 TsiSiEt1Cl 37 69JOM"13#418 Et1SiCl1 EtMeSiHCl TsiSiEtMeH 59 69JOM"13#418 PhSiCl2 TsiSiPhCl1 64 69JOM"13#418 TsiSiPhHCl 06 69JOM"13#418 PhSiHCl1 TsiSiPh1Cl 7 69JOM"13#418 Ph1SiCl1 Ph1SiF1 TsiSiPh1F 65 69JOM"13#418 PhMeSiHCl TsiSiPhMeH 79 69JOM"13#418 PhMeSiF1 TsiSiPhMeF 63 69JOM"13#418 TsiSiPh1OMe 8 69JOM"13#418 Ph1SiF"OMe# PhMe1SiF TsiSiMe1Ph 02 70JOM"110#02 TsiSiMe1"CH1CH1# 44 74JOM"180#14 Me1"CH11CH#SiCl Me1"CH11CHCH1#SiCl TsiSiMe1"CH1CH1CH1# 27 74JOM"180#14 Me1"PhC2C#SiF TsiSiMe1"C2CPh# 05 74JOM"180#14 TsiSiMe1"CH1Ph# 19 74JOM"180#14 Me1"PhCH1#SiF TsiSi"CH1CH1#1Cl 40 75JCS"P1#0178 "CH11CH#1SiCl1 "Cl2Si#1O "TsiSiCl1#1O 04[4 89JOM"287#48 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Tsi "Me2Si#2C[
TMS TMS
Li
+ R1R2SiF2
trisilyl products
Cl
TMS
SiR1R2F
TMS
SiR1R2F
+
(4)
R1 = R2 = F, 41% R1 = F, R2 = Me, 36% R1 = Me, R2 = Ph, 36% R1 = F, R2 = Ph, 29% R1 = F, R2 = But, 71%
"c# Formation via addition reactions of silenes[ Cyclic compounds containing an Si3C function in the ring are formed in similar reactions to those shown in Equation "3#^ for example\ in Scheme 0 the initial metallation gives rise to a lithium reagent that can readily eliminate a salt to give a highly reactive silene "Si1C containing species# which rapidly dimerises in a head!to!tail manner to give "2# in 31) yield ð73ZAAC"409#058Ł[ Similarly\ the reaction between "TMS#1CBrLi and Me1SiCl1 gives a 29) yield of "3#\ presumably via initial formation of "TMS#1CBr"SiMe1Cl#\ which undergoes Li:Br exchange with the original lithium reagent to give "TMS#1CLi"SiMe1Cl#\ which then eliminates LiCl[ Finally\ the silene "TMS#1C1SiMe1 which is formed\ dimerises ð65JOM"005#146Ł[ A range of trisilylmethyllithium species "TMS#1CLi"SiMe1X# "X F\ Cl\ Br\ I\ PhS\ Ts\ TsO\ MsO\ Ph1PO1\ Ph1PO2\ Ph1PO3# have been prepared "see 5[02[0[1[0["i#"a# for details# which\ in the absence of any trapping reagent\ "cf[ reactions in Table 2# eliminate LiX at various temperatures ranging from about −099>C to above room temperature to give the silene "TMS#1C1SiMe1 which rapidly dimerises to give the disilacyclobutane "3# ð70CB1976\ 70CB2494\ 70CB2407Ł[ "For reactions
270
At Least One Metalloid
Table 2 Tetrasilylmethanes from the reaction of miscellaneous trisilyllithiomethanes with halosilanes[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield Lithiomethane Halosilane Product ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * "PhMe1Si#2CLi SiCl3 "PhMe1Si#2CSiCl2 81JOM"316#8 SiH1Cl1 "PhMe1Si#2CSiH1Cl 48 82TH50290 "PhMe1Si#2CLi MeSiHCl1 "PhMe1Si#2CSiMeHCl 72 74JCS"P1#618 "PhMe1Si#2CLi "PhMe1Si#2CLi Me1SiHCl "PhMe1Si#2CSiMe1H 64 74JCS"P1#618 Me1SiHCl "p!MeC5H3SiMe1#2CSiMe1H 83JOM"355#24 "p!MeC5H3SiMe1#2CLi "MeOMe1Si#2CLi Me1SiHCl "MeOMe1Si#2CSiMe1H 78 75CC0932\ 81JCS"D#0904 "MeOMe1Si#2CLi Me1SiCl1 "MeOMe1Si#2CSiMe1Cl 33 81JCS"D#0904 Ph1SiClH "MeOMe1Si#2CSiPh1H 54 81JCS"D#0904 "MeOMe1Si#2CLi R1C"SiMe1Ph#Lia Me1SiHCl R1C"SiMe1Ph#"SiMe1H# 51 82JCS"P1#48\ 83JOM"355#24 R1C"SiMe1Ph#Li Et1SiHCl R1C"SiMe1Ph#"SiEt1H# 43 82JCS"P1#48 Et1SiF1 R1C"SiMe1Ph#"SiEt1F# 29 82JCS"P1#48 R1C"SiMe1Ph#Li R1C"SiMe1Ph#Li Et1SiCl1 R1C"SiMe1Ph#"SiEt1Cl# 8[4 82JCS"P1#48 Me1SiHCl R1C"SiMe1C5H3Y#"SiMe1H# 83JOM"355#24 R1C"SiMe1C5H3Y#Lib R1C"SiMe1OMe#Li TMSCl R2C"SiMe1OMe# 70CB1976 Me1SiHCl R1C"SiMe1OMe#"SiMe1H# 51 75JCS"P1#0252 R1C"SiMe1OMe#Li R1C"SiMe1OMe#Li Me1SiCl1 R1C"SiMe1OMe#"SiMe1Cl# 34 74JCS"P1#0576 Ph1SiHCl R1C"SiMe1OMe#"SiPh1H# 30 76JCS"P1#780 R1C"SiMe1OMe#Li RC"SiMe1OMe#1Li Me1SiCl1 RC"SiMe1OMe#1"SiMe1Cl# 81JCS"D#0904 R1C"SiMe1H#Li Et1SiCl1 R1C"SiMe1H#"SiEt1Cl# 71 82JCS"P1#280 Me1SiCl1 R1C"SiMe1H#"SiMe1Cl# 64 82JOM"340#34 R1C"SiMe1H#Li Me1SiCl1 R1C"SiMe1Cl#1 20 65JOM"005#146 R1C"SiMe1Cl#Li R1C"SiMe1Bun#Li TMSCl R2CSiMe1Bun 70CB1976 R1C"SiMe1N2#Li Me1SiHCl R1C"SiMe1N2#"SiMe1H# 39 82JOM"340#34 Me1SiCl1 R1C"SiEt1H#"SiMe1Cl# 54 82JCS"P1#280 R1C"SiEt1H#Li Me1Si"CH1CH1#Cl R1C"SiMe1CH1CH1#1 59 76JCS"P1#0936 R1C"SiMe1CH1CH1#Li R1C"SiMe1CH1CH1#Li Me1SiHCl R1C"SiMe1CH1CH1#"SiMe1H# 56 76JCS"P1#0936 Me1SiCl1 R1C"SiMe1CH1CH1#"SiMe1Cl# 55 76JCS"P1#0936 R1C"SiMe1CH1CH1#Li R1C"SiMe1CH1CH1#Li TMSCl R2CSiMe1"CH1CH1# 77 76JCS"P1#0936 R1C"SiMe1CH1CH1#Li Et1SiCl1 R1C"SiMe1CH1CH1#"SiEt1Cl# 43 76JCS"P1#0936 Et1SiHCl R1C"SiMe1CH1CH1#"SiEt1H# 54 76JCS"P1#0936 R1C"SiMe1CH1CH1#Li Ph1SiHCl R1C"SiMe1CH1CH1"SiPh1H# 47 76JCS"P1#0936 R1C"SiMe1CH1CH1#Li R1C"SiMe1CH1CH1#Li PhMeSiHCl R1C"SiMe1CH1CH1#"SiPhMeH# 58 76JCS"P1#0936 TMSCl R2CSiMe1CH1TMS 89 80OM440 R1C"SiMe1CH1SiMe2#Li "21# TMSCl "22# 72ZAAC"386#008 "24# ClSi"CH1TMS#2 "25# 72ZAAC"386#008 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a
R TMS[
b
Y p!OMe\ p!Me\ p!Cl or m!CF2[
TMS
SiPhMeF
TMS
SiPhMeF
TMS
Li
+ BunLi TMS
Cl
TMS TMS
Ph Si
TMS
PhMeSi
x2
TMS
Me
TMS SiMePh
TMS (3) cis and trans TMS Me2Si
TMS
TMS
SiMe2
TMS (4) Scheme 1
–LiF
271
At Least One Metalloid or Metal
involving the thermally generated silene "Cl2Si#1C1SiCl1 see 5[02[0[0[0"i#"d#[# Addition of various organosilanes to a reactive Si1C bond can also lead to formation of the Si3C function[ Thus\ addition of "PhO#1P"O#TMS to the silene "TMS#1C1SiMe1 "4# gives "TMS#2CSiMe1OP"O#"OPh#1 ð70CB2494Ł while addition of TMSX gives "TMS#2CSiMe1X "X Cl\ OMe\ NMe1 or OPh# ð70CB2494Ł and addition of Ph1C1NSiMe2 a}ords "5#\ which when heated at 058>C rearranges to give "TMS#2CSiMe1N1CPh1 "Scheme 1# ð70CB2407\ 76ZN"B#0944\ 76ZN"B#0951Ł[ The silene "4# also reacts with SiF3 "but not with SiCl3# to give "TMS#1C"SiF2#"SiMe1F# ð73JOM"162#030Ł[ Addition of PhCN to two equivs[ of the silene "4# gives "6# which rearranges to give "7# which reacts with methanol at 059>C to give "8# "Scheme 1# ð70CB2407\ 76ZN"B#0951\ 76ZN"B#0944Ł[ TMS TMS TMS
SiMe2X
X = Cl, OMe, NMe2 or OPh
TMS-X
Me2 N Si TMS Ph
Ph Ph
N
Si TMS Me2
TMS TMS
TMS
N-TMS
TMS
Ph
Me2Si
SiMe2
TMS
N
TMS
Ph
TMS
(5)
Ph (6)
(7)
169 °C
TMS
Me2 N Si TMS TMS
Ph MeOH
TMS
SiMe2OMe
160 °C
TMS
SiMe2OMe
Ph Si Me2
TMS
(TMS)3CSiMe2N Ph
(8)
(9) Scheme 2
Intramolecular elimination of LiBr may also lead to cyclic products "09# from simple Si0C bond formation "Scheme 2# ð70ZAAC"370#59Ł[ Alternatively\ elimination of LiBr from "00^ n 9# presumably forms silene "01#\ which dimerises to give "02# "Scheme 2# ð70ZAAC"370#59Ł[ The organo! metallic syntheses of carbosilanes are reviewed in ð63TCC32Ł[ (CH2—SiMe2)nBr Me2Si Me2Si
Br SiMe2
H2 C
(CH2—SiMe2)nBr Me2Si BunLi
Li
Me2Si
Si Me2
SiMe2
–LiBr
n = 1 or 2
Me2Si
SiMe2
Me2Si
SiMe2
n
Si Me2 (11)
Si Me2 (10)
n=0 Me2 Si SiMe2 Me2Si
SiMe2
x2
Si Me2 (12)
Me2Si
SiMe2
Me2Si
SiMe2
Me2Si
SiMe2 Si Me2 (13)
Scheme 3
The very slow di}usion of oxygen from the air into an Et1O solution of the NMe2 adduct of silene Me1Si1C"SiMe2#"SiMeBut1# a}ords "03#[ Although it is unclear how "03# is formed it may again be
272
At Least One Metalloid
via an initial head!to!tail dimerisation of the silene and then further reaction with the oxygen ð78ZN"B#685Ł[ Me2 Si
But
2MeSi
O SiMe2
Me2Si
SiMe2
But2MeSi (14)
"d# Thermolytic or photolytic methods[ The perchlorotetrasilylmethane "Cl2Si#3C is a high melting product from a {direct synthesis| type of reaction in which CCl3 is passed over an Si:Cu mixture "in a manner reminiscent of the preparation of methylchlorosilanes from MeCl and Si:Cu# at tem! peratures above 299>C[ This again is likely to be a stepwise reaction "as in the in situ couplings above# in which C0Cl groups are replaced sequentially by SiCl2 groups ð48CB0907Ł[ Similar reactions involving "Cl2Si#2CCl in SiCl3 or Si1Cl5 over Si:Cu at high temperatures also yield "Cl2Si#3C in up to 33) yield[ A surprising coproduct in this type of reaction is "04# which could be formed from the dimerisation of the silene "Cl2Si#1C1SiCl1 ð50EGP11058\ 52CB1783\ 73ZAAC"401#020Ł[ Compound "04# is also formed in 15) yield when "Cl2Si#2CCl is passed over a 09 ] 0 Fe:Cu mixture at 249>C ð53CB0000Ł[ The disilylmethane "Cl2Si#1CCl1 reacts with Si:Cu at 299Ð249>C to give "Cl2Si#3C "04# and the spirocyclic compounds "05^ n 0 to 2# ð76AG"E#0000Ł[ Thermolysis of "06# similarly a}ords the spirocyclic compound "07# "Equation 4# ð76AG"E#0000\ 82ZAAC"508#0383Ł[
Cl3Si Cl3Si
Cl
Cl2 Si
Cl3Si
SiCl3
Cl3Si
Si SiCl3 Cl2 (15)
Cl2 Si Si Cl2 (17)
Cl2 Si
Si Cl2
Si Cl2
SiCl3 SiCl3 n
(16) n = 1, 2 or 3
Cl2 Cl2 Cl2 Si Si Si
Si
SiCl2 Cl
Cl2 Si
Cl2Si 330 °C
SiCl2
(5)
Si Si Si Cl2 Cl2 Cl2 (18)
The thermolysis of 0\1!disilacyclobutanes "08# with exocyclic double bonds causes rearrangement to a 0\2!disilacyclobutane system "19# or "10# containing an Si3 substituted carbon ð68JA0237\ 71JOM"125#6\ 77CL0330Ł[ The two types of product "19# and "10# may arise from di}erent mechanistic pathways^ product "19# from a concerted 0\1!silyl shift and product "10# by breakdown of "08# into two silenes\ one of which can undergo rapid ligand exchange "which is thought to occur in a number of other related silenes# to give "11# which then reacts with the silatriene in a head!to!tail fashion to give "10#[ Alternatively\ the two silenes may recombine\ without rearrangement\ in a head!to!tail fashion "Scheme 3# ð68JA0237\ 71JOM"125#6\ 77CL0330Ł[ The gas phase pyrolysis of Me3Si at 699>C a}ords a large number of compounds\ many of which are carbosilanes containing the 0\2\4\6!tetrasilaadamantane framework[ However\ some that are formed in low yield contain Si2C2 rings having a boat conformation such as "12# and "13# ð62AG"E#543\ 63ZAAC"393#0Ł[ The pyrolytic preparation of the carbosilanes is not very convenient as it leads to the formation of a large number of products which have to be separated by distillation\ fractional crystallisation\ or high!performance liquid chromatography "HPLC# ð73ZAAC"401#82Ł[ The synthesis of carbosilanes by pyrolysis or organometallic synthetic routes has been reviewed ð76AG"E#0000Ł\ and discussed in detail ð54MI 502!90Ł[ Photolysis "or thermolysis for R Me# of the bis"silyldiazomethyl# compounds "14#\ in the absence of trapping agents\ gives rise to low yields of "15# "a much higher yield is obtained by thermolysis# presumably via dicarbene "16# which undergoes the well!known silylcarbene to silene rearrangement to give "17# which cyclises in a predominantly head!to!tail fashion to give "15# "Scheme 4# ð80JA6689Ł[
273
At Least One Metalloid or Metal R2 Si
TMS TMS
•
SiR2
TMS (19)
TMS
R2 Si
TMS
silyl migration
TMS
• Si R2
TMS
TMS
(20)
silene formation
TMS
R group scrambling
TMS •
•
SiR2
+
SiR2
TMS
RMe2Si SiMe2
TMS
RMe2Si (22)
head-to-tail cycloaddition
head-to-tail cycloaddition with TMS • • SiR2 TMS
(20) R = Me, Ph, m-tolyl or p-tolyl
R2 Si
TMS
SiMe2R
• Si SiMe2R Me2
TMS (21) Scheme 4
Me Si Me Si Si MeSi
N2
Me
Si Si
Si Si
MeSi
SiMe
Me Si Me Si SiMe
Si
Si
(23)
(24)
hν
RMe2Si R = Me or Ph
(25)
SiMe2R SiMe2 Me2Si
SiMe2
Me2 Si Si Si Me2 Me2
:
Me2 N2 Si Si SiMe2R Si Me2 Me2
:
RMe2Si
Me
SiMe2R
(27)
RMe2Si SiMe2 Me2Si SiMe2
SiMe2R (26)
RMe2Si (28)
Scheme 5
"e# Transition metal catalysed reactions[ The palladium catalysed reactions between isocyanides and oligosilanes in the presence of 0\0\2\2!tetramethylbutyl isocyanide gives products "18# from tetrasilanes ""29# from the hexasilane TMS"SiMe1#3TMS# in which both the C to N triple bond and three Si0Si bonds have been broken[ The mechanism of this surprising reaction is unclear "the reaction works\ but less well\ in the absence of the butyl isocyanide# but the _rst step is thought to involve insertion of the RNC into a terminal Si0Si bond of the oligosilane "Equation "5## ð78"CC#0383\ 80JA7788Ł[
274
At Least One Metalloid R3
Me
Me R1
Me2 R1 Si Si 2 Si R Si Me2 R2
R1R2MeSi
10 mol% Pd(OAc)2
+
NC
R1R2MeSi
But
NC
R3
Me2 Si N Si Me2
R3 (6) R3
(29)
R1 = R2 = R3 = Me, 40% R1 = R2 = Me, R3 = Pri, 45% R1 = R2 = Ph, R3 = Me, 31% R1 = R2 = Ph, R3 = Pri, 62%
Me2 Si TMS N TMS Si Si Me2 Me2
Pri
Pri
(30)
"f# Rearran`ements of carbosilanes caused by AlBr2[ A range of cyclic compounds containing Si3C functions has been prepared by treatment of a carbosilane containing an Si2C or Si3C centre\ to which is attached a carbosilane chain\ with AlBr2[ The reactions proceed at between room temperature and 79>C and usually lead to Si0C bond cleavage and formation of Me3Si as a by! product as the ring is formed[ Thus\ "TMS#2C"SiMe1CH1#1TMS "prepared from "TMS#2CSiMe1Cl\ see Table 1# initially a}ords cyclic compound "20#\ which reacts further with AlBr2 to give additional Si3C substituted products "Scheme 5# ð72ZAAC"386#10\ 72ZAAC"386#008\ 72ZAAC"386#023Ł[ Me2 Si Si Me2
AlBr3
(TMS)3C(SiMe2CH2)2TMS
SiMe2 TMS
+ Me4Si
TMS (31) AlBr3
Me2 Si Me2 Si (TMS)4C + (TMS)3CSiMe2Br
+
+ CH4 + Me4Si +
TMS
Me Si Si Me2
Me
Me2 Si Me2 Si Br
Si Me2 Si TMS
Si
+
Si Me2
Br
TMS
Me Si Si Me2
Scheme 6
Cyclic trisilylmethyllithium reagents may also be used as precursors to complicated carbosilanes^ thus "21# reacts with TMSCl to give "22# "see Table 2#\ which reacts with AlBr2 to give "23#\ and lithium reagent "24# can be used to prepare the cyclic compound "25# which contains an Si3C group "see Table 2# "Scheme 6# ð72ZAAC"386#008Ł[ Lithium compounds "51# which are formed by a rearrangement "see Section 5[02[0[1[0"i#"a## also react with TMSCl to give tetrasilyl substituted products "26# ð66ZAAC"329#026Ł[
275
At Least One Metalloid or Metal Me2 Me Si Si SiMe2 Si Si Me2 Me2 Li
TMS-Cl
(32)
AlBr3
MeSi
(33) Me2 Si Me2 Si
Me Si Si Me (34)
SiMe
Me Si Me2 Si
ClSi(CH2TMS)3
Li
Me Si
Me2 Si
Me2 Si
Me2 Me Si Si SiMe2 Si Si Me2 Me2 TMS
Si(CH2TMS)3
Me Si Si Me2 (36)
Si Me2 (35) Scheme 7
"ii# Four Ge functions The abundance of compounds containing the Si3C group discussed in the previous section might suggest that at least some similar Ge3C containing compounds should be known[ However\ there do not seem to have been any compounds containing this grouping prepared[ There would not appear to be any inherent reason why such compounds should not be stable^ ab initio calculations on "H2Ge#3C suggest a greater stability than "H2Si#3Si\ a known stable "albeit highly reactive# compound ð70TCA174Ł[ The reasons for the rarity of tetragermylmethanes are probably the higher costs involved for germanium compounds\ the relative lack of interest in organogermanium chem! istry generally when compared with organosilicon chemistry\ and some of the preparative routes used for the silicon compounds not being readily applicable to corresponding germanium species[ It should\ however\ be possible to prepare compounds containing the Ge3C group by\ for example\ a route involving sequential metallations of a halomethane followed by reaction with an organo! germanium halide[
"iii# Four B functions Although the synthesis of such compounds does not seem to have been achieved*calculations on the structures of C"BH1#3 and the spirocycle "27# have been carried out[ Both compounds\ despite the presence of electropositive substituents and:or small rings\ were found to prefer the usual tetrahedral geometry at carbon rather than a planar geometry ð65JA4308Ł[ Compounds containing the CB3 function can be prepared by an in situ coupling in a manner similar to that for CSi3 functions as described above[ Thus the reaction "Equation "6## gives the methanetetraboronic ester in 49Ð59) yield and can be carried out easily on a scale giving 019Ð049 g product ð57JA1083\ 58JOM"19#08Ł[ The preparation of ð02CŁC"B"OMe#1#3 starting from ð02CŁCCl3 has been reported to occur in a similar manner ð80AG"E#0377Ł[ Disproportionation of HC"B"OMe#1#2 in the presence of Et2B also occurs to give low yields of C"B"OMe#1#3 ð64LA0228Ł[ Reactions of C"B"OMe#1#3 with the a\ v!alkanediols HO"CH1#nOH "n 1 or 2# gives products "28# which have been found to be more synthetically useful than the methyl ester ð62JOM"46#120Ł[ The pinacol ester C"BO1C1Me3# is similarly prepared from the methyl ester and pinacol ð63JOM"58#34Ł[
Me2Si R
SiMe2 TMS Si Me2 TMS
(37) R = H or TMS
O HB
BH
HB
BH (38)
( )n
C B O
(39)
n = 2 or 3 4
X
TMS TMS TMS
B N
R
R (40) R = Me; X = Cl R = H; X = F
276
At Least One Metalloid 4ClB(OMe)2 + CCl4 + 8Li
THF
C[B(OMe)2]4 + 8LiCl
(7)
Carbon vapour produced from arcing electrodes reacts with B1Cl3 to give C"BCl1#3 as a white crystalline solid\ presumably formed by insertion of C atoms into the B0B bond of B1Cl3[ The reaction of C atoms with B1F3 gives low yields of C"BF1#3 in a similar manner ð58JCS"A#0771Ł[
5[02[0[0[1 Three similar and one different metalloid function "i# Three Si functions and one Ge function The reactions of trisilyllithiomethanes with germanium halides proceed in a manner similar to those described above for silicon halides and the expected products from lithium halide elimination are formed[ Thus "TMS#1"MeOMe1Si#CLi and Me2GeBr give "TMS#1"MeOMe1Si#CGeMe2 in 78) yield ð76JCS"P1#664Ł[ The disilylgermyllithiomethane "TMS#1"Me2Ge#CLi reacts similarly with Me1SiHCl to a}ord "TMS#1"Me2Ge#CSiMe1H in 35) yield ð76JCS"P1#668Ł[ The reaction of TsiLi with Me2GeBr\ Me1GeCl1\ Et1GeBr1\ GeCl3\ EtGeCl2\ Et1GeCl1 or Ph1GeCl1 gives TsiGeMe2 "69Ð 79)#\ TsiGeMe1Cl "59)#\ TsiGeEt1Br "47)#\ TsiGeCl2\ TsiGeEtCl1\ TsiGeEt1Cl and TsiGePh1Cl\ respectively ð69JOM"13#418\ 68JCR"S#01\ 68BAU1111\ 79JOM"191#046Ł[ In a manner reminiscent of the silicon analogues described above\ a germanium halide may also add across the reactive double bond of a silene\ i[e[\ "TMS#1C1SiMe1 reacts with Me2GeCl to give "TMS#1C"GeMe2#"SiMe1Cl# in 74) yield ð76ZN"B#0951Ł[ In an Si2Ge substituted methane the germanium may also be divalent rather than the more usual tetravalent[ For example\ the reaction between TsiLi and Me4C4GeCl gives TsiGeMe4C4 in 51) yield ð80OM2727Ł and in a transmetallation reaction TsiLi reacts with the bulky germylene C4Me4GeCH"TMS#1 to give TsiGeCH"TMS#1 in 54) yield ð80OM0536Ł[
"ii# Three Si functions and one B function The reaction of TsiLi with B"OMe#2 does not proceed in the simple manner expected\ but use of three equivs[ of B"OMe#2 a}ords\ after an aqueous workup\ a mixture of TsiB"OMe#1\ TsiB "OMe#OH and TsiB"OH#1 ð75JOM"297#150Ł\ while a nonaqueous workup allows TsiB"OMe#1 to be isolated as product in good yield ð78JCS"D#336\ 78CB0946Ł[ Surprisingly\ the reaction between TsiLi and BF2 in Et1O:THF does not a}ord TsiBF1 but rather TsiB"F#O"CH1#3Tsi in 44) yield in which a ring!opened THF molecule has been incorporated into the product[ The mechanism by which this compound is formed is not known in detail^ the product is unusual as reactions between TsiLi and other metal or metalloid halides generally give products derived from the simple elimination of a lithium halide ð71JOM"124#154Ł\ and the reaction between TsiLi and Ph1BBr does a}ord TsiBPh1 ð73JOM"161#0Ł[ In contrast to the TsiLi analogue\ the reaction between "PhMe1Si#2CLi and BF2 = Et1O in THF does give the expected product\ "PhMe1Si#2CBF1\ in 74) yield ð78JCS"D#336Ł[ The lower reactivity of "PhMe1Si#2CLi compared with TsiLi towards the BF2:THF system and towards other metalloid halides is probably associated with their di}erence in structure\ the compound containing phenyl being a molecular species and TsiLi ionic "see 5[02[0[1[0"i#"a# for further details of these organolithium compounds#[ Addition of BF2 across the reactive double bond of the silene "MeBut1Si#"TMS#C1SiMe1 gives "MeBut1Si#"TMS#C"BF1#"SiMe1F# in about 69) yield ð72AG"E#0994\ 75CB0356Ł[ Surprisingly\ this product is also formed in 54) yield from the reaction between "TMS#1CLi"SiBut1F# and BF2\ presumably via rearrangement to "TMS#"FMe1Si#CLi"SiBut1Me# and subsequent formation of the silene to which the BF2 adds ð75CB0356Ł[ Although the reaction between TsiLi and BF2 is compli! cated\ the reaction between TsiLi and "TMS#1NBF1 a}ords TsiB"F#N"TMS#1 ð74AG"E#213Ł[ The reaction between PhCH1B"OMe#1 and TsiLi in a 0 ] 0 ratio gives TsiB"OMe#CH1Ph in 35) yield ð89CB636Ł and the reaction between TsiLi and ButBF1 a}ords TsiB"F#But in 67) yield ð78CB0946Ł[ TsiLi also reacts with "TMS#RNBF1 "R Me\ Pri\ TMS\ But2# to give TsiB"F#NR"TMS# in yields
277
At Least One Metalloid or Metal
of 48) "R Me# and 72) "R Pri# and with dichloro"1\1\5\5!tetramethylpiperidino#borane to give chloro"1\1\5\5!tetramethylpiperidino#!tris"trimethylsilyl#methylborane "39^ R Me\ X Cl# in 21) yield ð75CB0006Ł[ Such compounds readily eliminate TMSF to give TsiB2NR species "R But or TMS#[ Similarly TsiLi reacts with Pri1N1BF1 to give TsiB"F#NPri1 in 67) yield ð76CB0958Ł[ The reaction between TsiLi and "1\5!dimethylpiperidino#di~uoroborane gives the ~uoroborane "39# "R H\ X F# as an oil in 60) yield ð78CB484Ł[
"iii# Three Ge functions and one Si or B function[ Also three B functions and one Si or Ge function No compounds containing these functions seem to have been prepared[ This is not surprising for the case of the CGe2 compounds when it is taken into account that there are neither CGe3 functions as described in 5[02[0[0[0["ii# nor CGe2M species[ Again this lack of compounds is not likely to be due to a problem of inherent instability of such species but rather a lack of interest in their synthesis[ The lack of CB2Si or CB2Ge functions is more surprising as both the CB3 function and various CB2M functions are known "see 5[02[0[1[0"ii# below#[ The synthesis of these mixed metalloid compounds could probably be easily achieved in a manner similar to those\ for example\ of CB2Sn functions^ i[e[\ by reaction between a CB2Li function and a silicon or germanium halide such as TMSCl or Ph2GeCl[
5[02[0[0[2 Two similar and two different metalloid functions "i# Two Si and two Ge functions When it is considered that there are a large number of compounds containing the CSi3 function\ and no compounds containing the CGe3 function known\ it can be expected that there will only be a handful of compounds known which contain the CSi1Ge1 function[ Such compounds have been prepared using methods that have been widely used for the synthesis of CSi3 functions\ and many more species could no doubt be prepared in similar ways[ The reaction between the highly reactive dilithiomethane "TMS#1CLi1 and Me2GeCl gives the expected "TMS#1C"GeMe2#1 in 79) yield ð77TL4126Ł[ This compound is also produced as a by!product "in up to 29) yield# from the low temperature reaction between "TMS#1CCl1\BunLi and Me2GeBr ""TMS#1C"GeMe2#Cl being the desired product# ð76JCS"P1#668Ł[ The reaction between Me1GeBr1 and two equivs[ of "TMS#1CBrLi at low temperature gives compounds "30# and "31# in 06 and 3[3) yields respectively[ These products presumably arise from lithium:halogen exchange after the initial C0Ge bond formation as shown in Scheme 7 ð65JOM"005#146Ł[ Wiberg has shown independently that a variety of lithium compounds "TMS#1C"GeMe1X#Li "X F\ Br\ OMe\ etc[^ see 5[02[0[1[1"i## eliminate LiX to give germene "32# which does then dimerise ð75CB1855\ 75CB1879Ł[ R
Li
R
GeMe2Br
R
Br
+ Me2GeBr2 R
Br R = TMS R
Ge R Me2
Li
R
Br
R
GeMe2Br
R
Li
+ R2CBr2
Me2GeBr2
–LiBr
Me2 Ge R x2
R
R
R
R
GeMe2Br
R
GeMe2Br
GeMe2 R
(41)
(43)
(42)
Scheme 8
"ii# Two Si\ one Ge and one B function Compounds containing the CSi1GeB function do not appear to be known[ However\ they are likely to be readily available from the reaction of one of the several known CSi1GeLi containing compounds with a boron halide or B"OMe2#[
278
At Least One Metalloid "iii# Two Si and two B functions
As for the case of the CSi1Ge1 function there are very few compounds known containing the CSi1B1 group[ The reaction of the unsaturated boron compound "33# with RBBr1 species gives products "34# "32) yield# and "35# "42) yield# that are the result of a formal addition across the C1B bond "Scheme 8# ð78CB484Ł[ TMS TMS Br2B
TMS B NPri2
+ BBr3
TMS
NPri2
NPri2
BrMe2Si TMS MeBrB
B Br
(44)
B Br
(46)
MeBBr2
NPri2 TMS B TMS MeBrB Br (45) Scheme 9
The reactions of the dilithium reagent "36# give a variety of cyclic compounds containing the CSi1B1 function "see also Equation "05## which appear to arise via an intramolecular cyclisation and a double substitution at the triply bonded carbon "Scheme 09# ð78AG"E#670\ 78AG"E#673Ł[
TMS
Ar B
2 MeI
TMS
B Ar Ar = 2, 4, 6-Me3C6H2, 89% Ar = 2, 3, 5, 6-Me4C6H, 100%
Ar Li B TMS
Li B Ar
F2BAr
TMS
Ar B
BAr B Ar Ar = mesityl, 92% Ar = 2, 3, 5, 6-Me4C6H, 81% TMS
TMS (47) Scheme 10
The unsaturated borane "72# "see 5[02[0[1[1"ii## reacts with Ar1BBF1 to give the cyclic species "37# which rearranges slowly to give "38# "Equation "7##[ This has been structurally characterised by x!ray crystallography ð80AG"E#483Ł[ Ar1 B TMS Ar2B
Ar1B
BAr1
B B TMS Ar1
(48) Ar = 2, 4, 6-Me3C6H2 Ar1 = 2, 3, 5, 6-Me4C6H or 2, 4, 6-Me3C6H2
Ar2B
B
TMS
(8)
TMS (49)
Treatment of the dianion "49# with Ph2PAuCl or CH1Br1 gives compounds "40#\ "41# and "42# in 11\ 29\ and 42) yields respectively\ all of which seem to have been formed via a silyl migration and a geminal substitution "Scheme 00# ð75AG"E#0001\ 78CB0770Ł[
"iv# Two Ge and two B functions[ Also two Ge\ one Si and one B function[ Also two B\ one Si and one Ge function As might be expected from the paucity of CSi1Ge1 and CSi1B1 containing species\ there appear to be have been no compounds prepared containing the CGe1B1\ CGe1SiB\ or CB1SiGe functions[ Again there is not likely to be any good reason why such compounds should not be made[ Reactions between appropriately substituted lithiomethanes and halometalloids should readily a}ord the required functions[
289
At Least One Metalloid or Metal 2–
NPri2 B TMS
TMS
TMS
0 °C
+ Ph3PAuCl
TMS
B NPri2 (50) CH2Br2
TMS
NPri2 B AuPPh3 AuPPh3 B NPri2 (51)
Ph3PAuCl –50 °C
NPri2 B
TMS
NPri2 B AuPPh3
TMS
B NPri2
TMS
B NPri2 (52)
(53) Scheme 11
5[02[0[1 Methanes Bearing Three Metalloid Functions and a Metal Function 5[02[0[1[0 Three similar metalloid functions "i# Three Si functions "a# Three Si and one `roup 0 metal function[ The "TMS#2C "Tsi# group has been attached to a wide variety of metals and metalloids usually using the lithium reagent TsiLi[ The bulk of the Tsi group means that molecules containing it often have novel structures or contain elements in unusual oxidation states[ The size of the Tsi group has been discussed in terms of a {cone angle| "a term more commonly used in phosphine chemistry# and when attached to Si\ Ge\ or Sn it has a cone angle of 197>\ 085>\ and 089> respectively ð80MI 502!90Ł[ The metallation of TsiH by MeLi in THF:Et1O occurs readily to give a dark\ redÐbrown solution of TsiLi in about 5 h at the re~ux temperature or 19 h at room temperature ð69JOM"13#418\ 66CB741Ł[ Improvements to this preparation have been reported[ These involve removal of the Et1O from the reaction solution by distillation\ thus allowing a higher re~ux temperature and complete metallation in 1 h^ removal of any residual MeLi from the reaction mixture by addition of TMSOMe or TMSOEt which reacts with MeLi but not TsiLi^ determination of the extent of reaction by treatment of an aliquot of the reaction solution with TMSCl and determining the "TMS#3CÐ"TMS#2CH ratio by 0H NMR spectroscopy ð73JOM"158#106Ł[ The TsiLi produced in this way is remarkably stable for an alkyllithium reagent\ a 9[04 M solution in THF having a half!life in re~uxing THF of 69 h ð69JOM"13#418Ł[ The ease of preparation\ relative stability "and hence relative ease of handling# and the steric requirements of the bulky Tsi group have made TsiLi a useful and widely applicable reagent in the preparation of unusual organometallic compounds many of which are described elsewhere in this chapter[ Metallation of TsiH does not occur with BunLi:Et1O:THF\ BunLi:C4H01:TMEDA\ ButLi:C4H01\ or ButLi:THF[ As these are more powerful metallating agents than MeLi\ steric e}ects would seem to play an important role in these reactions ð62JOM"44#198Ł[ The addition of the base hexa! methylphosphoric triamide "HMPT# to reaction solutions does\ however\ promote metallation and TsiLi is formed in good yield from TsiH using ButLi:THF:HMPT as the metallating agent at −67>C ð74CB1382Ł[ "See below for the reaction between TsiH and ButLi:C4H01:TMEDA at room temperature[# When prepared in THF from TsiH and MeLi\ the TsiLi may be isolated as a crystalline solid in 54) yield[ Characterisation by x!ray crystallography shows that\ in the solid state\ the lithium compound is not simply TsiLi\ but that it actually has an unusual ate composition "Tsi1Li# "Li"THF#3# ð72CC716Ł[ In THF or toluene solution the unusual ionic form is also predominant\ but at low temperatures and low concentration a second form thought to be TsiLi"THF#n "n 0 or 1# can be detected by NMR spectroscopy[ A di}erent form\ thought to be an aggregate of some kind\ is also observed in toluene[ At higher temperatures the two forms interconvert rapidly on the NMR timescale and the 0H NMR signal for the TMS groups is commonly seen as a broad singlet at 89 MHz or two singlets at 299 MHz at room temperature ð82JCS"D#2148Ł[
280
At Least One Metalloid
Preparation of TsiLi may also be achieved by reaction of TsiBr with BunLi "at −64>C#\ PhLi or with lithium metal ð66JOM"031#28\ 81OM1827Ł[ These methods give good yields which may be deter! mined by derivatisation with TMSCl\ but the method involving the metallation of TsiH by MeLi is to be preferred in most cases as TsiH is much more readily available than TsiBr[ TsiLi may also be prepared by treatment of TsiSPh with Linaphth:THF at −67>C^ however\ this is again not a very convenient route as the phenylthio starting material is much more di.cult to prepare than TsiH[ However\ this route may be of use on occasions when a complete absence of halogen in the system is required as the methods involving transmetallation using\ for example\ MeLi or BuLi usually have some residual halogen present from the lithium reagents preparation ð73JOC057Ł[ TsiLi as a TMEDA adduct "Tsi1Li#"LiTMEDA1# is formed in 53) yield by metallation of TsiH in hexane in the presence of TMEDA over 79 h at room temperature ð76CB0958Ł[ The reaction between TsiH and MeLi "evidently containing some LiCl from the MeLi preparation# in the presence of Me1N"CH1#1NMe"CH1#1NMe1 "PMDETA# again gives a TsiLi!like species[ Again crystallography shows that an ate species is present in the solid state\ this time containing a novel\ linear\ chlorine centred cation as shown in "43# ð75CC858Ł[ The reaction between TsiHgBun and BunLi at 54Ð69>C in the absence of solvent gives the highly reactive\ solvent!free TsiLi which has been characterised by x!ray crystallography and found to be a bridged dimer "TsiLi#1 in the solid state[ Although this synthesis of TsiLi requires several more steps than the others described\ the absence of solvent\ particularly THF*which can cause side reactions when the lithium reagent is used*may mean that this is the method of choice if a coordinated solvent is likely to be troublesome ð80AG"E#213Ł[
TMS TMS TMS
TMS TMS TMS
Li
+
–
NMe2 Me2N MeN Li
Li NMe
Cl
NMe2 Me2N (54)
The metallation of "PhMe1Si#2CH with MeLi proceeds in a similar manner to TsiH to give "PhMe1Si#2CLi which can be isolated as a solid in 56) yield[ This reagent is generally less reactive than TsiLi "it does not react with TMSCl or Me1SiCl1# and has been found to have a monomeric structure "44# in the solid state ð72CC0289\ 74JCS"P1#618Ł[ PhMe2Si PhMe2Si
THF Li
Me2Si
(55)
The metallation of several other Si2CH functional trisilylmethanes by MeLi or BunLi has also been reported to occur easily and to give preparatively useful reagents[ For example\ compounds "21# and "24# are formed from the corresponding C0H compounds by treatment with MeLi:THF and with BunLi:TMEDA respectively ð72ZAAC"386#008Ł[ The lithium reagent "TMS#1"PhMe1Si#CLi is formed from the metallation of "TMS#1"PhMe1Si#CH with MeLi in re~uxing THF ð76CC0350Ł\ and trisilylmethane "45# is also metallated by MeLi to give "46# "Equation "8## ð72ZAAC"386#10Ł[ The trisilylmethane derivative "47# may also be metallated by MeLi in THF:Et1O "Equation 09# to give lithium reagent "48# but little chemistry has been carried out with the reagent ð77JOM"230#098Ł[ SiMe2Ph Me2Si
SiMe2 Si Me2 (56)
Li MeLi
Me2Si
SiMe2Ph SiMe2
Si Me2 (57)
(9)
281
At Least One Metalloid or Metal Me2 Si Me Si
Me Si
Me2 Si Me Si
SiMe2 Me Si
MeLi
Me2 Si
Me Si
SiMe2 Me Si (10)
Me2 Si Li
(58)
(59)
The stabilising e}ect of three a!silyl groups can be seen in the reactions of species "59# with BunLi:TMEDA[ The initial reaction products are the HSi1C carbanions "50# but these rearrange to give the more stable Si2C carbanions "51# "Equation "00## ð66ZAAC"329#026Ł[ Li Me2Si R
SiMe2 Si Me2
BunLi/TMEDA
TMS
Me2Si R
SiMe2 Si Me2
TMS
(61)
(60) R = H or TMS
Me2Si
SiMe2
R
TMS Si Me2 Li
(11)
(62)
More reactive metallating agents such as ButLi:TMEDA and BunLi:ButOK react readily with "TMS#1CHSiMe1CH1TMS to give "TMS#1CLiSiMe1CH1TMS in ×89) yield ð80OM440Ł[ This is\ perhaps\ surprising as although the carbanion is stabilised by three a!silyl groups "rather than two if the CH1 group had been metallated# reaction of the closely related "TMS#2CH with ButLi: C4H01:TMEDA gives "TMS#1CHSiMe1CH1Li in which metallation of a methyl group rather than the central methine CH has occured ð62JOM"44#198Ł[ The highly sterically hindered ~uorosilane But1FSiCH"TMS#1 reacts with MeLi in THF at room temperature over a period of a week to give the alkyllithium reagent But1FSiCLi"TMS#1 which rearranges over a period of weeks to give Me1FSiCLi"TMS#"SiBut1Me# which has been characterised by x!ray crystallography ð76OM24Ł[ The metallation of the central carbon by MeLi rather than substitution of F for Me on the silicon is surprising and is presumably due to the severe steric hindrance at the silicon bearing the ~uorine together with the fact that the carbanion formed is stabilised by three a!silyl groups ð72AG"E#0994\ 73JOM"160#270\ 75CB0344Ł[ The formation of Si2LiC functions may also be achieved from Si2XC substituted methanes "X halogen# using either other lithium reagents or lithium metal[ A range of substituted aryl silanes "TMS#1"YC5H3Me1Si#CCl "Y H\ p!OMe\ p!Me\ p!Cl\ m!CF2# reacts with BunLi at −009>C to give the corresponding lithium reagents "TMS#1"YC5H3Me1Si#CLi which react readily with chlorosilanes to give Si3C containing compounds ð83JOM"355#24Ł[ A range of "TMS#1"XMe1Si#CLi species may be prepared according to the general Equation "01#[ Such compounds are useful precursors to "TMS#1C1SiMe1 via LiX elimination "which takes place readily except when X MeO\ PhO\ Bun or Ph which are stable# and the lithium reagents are not\ therefore\ usually isolated as pure compounds ð66AG"E#217\ 70CB1976\ 70CB2494\ 70CB2407\ 75JOM"204#8Ł[ The reaction between "TMS#1"MeOMe1Si#CCl and BunLi in THF:hexane at −79>C gives "TMS#1 "MeOMe1Si#CLi which reacts with silyl halides to give CSi3 functions ð76JCS"P1#780Ł[ The reagent can similarly be prepared at −009>C in THF:Et1O:pentane ð81JOM"326#30Ł[ The phenyl containing compound "TMS#1"PhMe1Si#CLi can be prepared from the corresponding chloride using BunLi at −009>C ð81JOM"326#30Ł[ The vinylsilane "TMS#1"CH11CHMe1Si#CCl and BunLi at −099>C in THF:Et1O:pentane gives the organolithium compound "TMS#1"CH11CHMe1Si#CLi which reacts with various organosilicon halides to give tetrasilylmethanes ð76JCS"P1#270\ 76JCS"P1#0936Ł[ The silyl hydride "TMS#1"HMe1Si#CCl reacts with BunLi at −009>C in THF:Et1O:pentane to give "TMS#1 "HMe1Si#CLi ð81JOM"326#30Ł[ TMS
SiMe2X
+ BunLi TMS
Br
< –78 °C
TMS
SiMe2X
+ BuBr
(12)
TMS
Li X = F, Cl, Br, I, OMe, OPh, Ph, Bun, Ph2, PO2, etc.
The reaction of "TMS#1CBr"SiPh1X# "X F or Br# with PhLi gives the corresponding lithium reagents "TMS#1CLi"SiPh1X# "again substitution of Ph for X does not occur#[ The Si0H compounds
282
At Least One Metalloid
"TMS#1CM"SiPh1H# "M Li or Na# are also formed in good yield from the reaction between "TMS#1CBr1\ Ph1SiHCl and M in THF at −67>C[ Treatment of "TMS#1CBr"SiPh1Br# with two equivs[ of RLi or treatment of "TMS#1CLi"SiPh1Br# with a second equiv[ of RLi a}ords further trisilyllithium reagents "TMS#1CLi"SiPh1R# "R Me\ Bun\ Ph or OPh# ð78CB398Ł[ The metallation of a trisilylmethylhalide may also be accomplished by reaction with lithium metal[ Thus\ "PhMe1Si#2CCl reacts with two equivs[ of lithium to give "PhMe1Si#2CLi and LiCl ð66ZAAC"329#010Ł[ Lithium reagent "ClMe1Si#1CLi"SiMe1CCl1H# is probably formed as an intermediate "which rapidly eliminates LiCl# on treatment of "ClMe1Si#1CCl"SiMe1CCl1H# with BunLi ð66ZAAC"329#010Ł[ The methoxysilane "MeOMe1Si#2CCl reacts with BunLi at −67>C to give the lithium compound "MeOMe1Si#2CLi which\ in the solid state\ is actually a dimer\ ð"LiC"SiMe1OMe#2#1Ł having the unusual structure "52# where the lithium atoms are solvated intramolecularly by the methoxy groups rather than by solvent molecules ð75CC0932Ł[ O O
Li
Si
O Si Si
Si
Li
Si O Si
O
Coordination around the central carbon in [{LiC(SiMe2OMe)3}2]. Methyl groups have been omitted for clarity.
O
(63)
The reaction between TsiH and methylsodium in Et1O in the presence of TMEDA gives a dialkylsodiate "Na"TMEDA#"Et1O#"NaTsi1# containing a linear "Tsi0Na0Tsi#− anion in a manner similar to the metallation of TsiH by MeLi described above ð83AG"E#0157Ł[ A sodium reagent formulated as TsiNa\ which can be derivatised with MeI to give TsiMe\ appears to be formed in low yield in the reaction between "TMS#3C and NaOMe:hexamethylphosphoramide"HMPA# ð62TL3082Ł[ The alkylpotassium compounds TsiK and "PhMe1Si#2CK may both be made in two ways^ either by treating the analogous lithium reagents with ButOK\ or by treating the parent hydrocarbons with MeK\ the latter being preferred ð83OM642Ł[ "b# Three Si and one `roup 1 metal function[ The highly reactive source of magnesium "Mg"an! thracene#"THF## reacts with TsiCl in THF at 9>C to give the Grignard reagent TsiMgCl in 89) yield ð77JOC2023Ł[ The analogous bromide can also be prepared in 64) yield "determined by double titration# from the reaction between TsiBr and Mg in Et1O ð81OM1827Ł[ The reaction between magnesium etherate and TsiLi in a 0 ] 0 ratio gives complex "53# "characterised by x!ray crys! tallography# ð77JCS"D#270Ł[ When "53# is heated it decomposes to give the lithium!free derivative Tsi1Mg which x!ray crystallography reveals has the linear structure "54# ð77JCS"D#270\ 78CC162Ł[ Although this compound would appear to have potential as a mild alternative to TsiLi for the introduction of the Tsi group into compounds it is rather unreactive[ For example\ it does not react readily with CO1\ MeI\ Me2COCl or TMSCl[ This is presumably because of the steric protection of the C0Mg bonds by the bulky alkyl groups ð78CC162\ 83JOM"379#088Ł[ The reaction between TsiBr and Mg in THF gives complex "55#[ Reactions of this type are complicated by the presence of MgBr1 which arises from the reaction of Mg with BrCH1CH1Br used to activate the Mg ð83JOM"358#018Ł[ (THF)2 TMS
Br Mg
Br TMS TMS (64)
Li(THF)2
TMS TMS TMS
Mg (65)
TMS TMS TMS
TMS TMS TMS
Br Mg
Br
Mg(THF)3
Br (66)
"c# Three Si and one `roup 01 metal function[ The reaction of about 0[4 equivs[ of TsiLi with ZnCl1\ CdCl1\ or HgCl1 a}ords the Tsi1M species in 31\ 11 and 24) yields respectively ð79JOM"089#090Ł[ A better yield is obtained in the reaction between two equivs[ of TsiLi "evidently containing some residual MeLi from the metallation of TsiH# and anhydrous ZnCl1 which a}ords a mixture of Tsi1Zn "50)# and TsiZnMe "01)# as crystalline solids ð80JOM"310#064Ł[ These compounds are remarkably thermally and chemically stable because of the high degree of steric hindrance provided by the two bulky Tsi groups to the reactive M0C bonds ð79JOM"089#090Ł[ The reaction of TsiLi with ZnX1 in a 0 ] 0 stoichiometry a}ords ð"TMS#2C#nXn¦0 ŁLi[1THF = Et1O species "X Cl\ n 1^ X Br\ n 0#^ the chloride reacts with a variety of lithium reagents to give TsiZnR compounds "R Me\ Bun\ "TMS#1CH\ Tsi\ "TMS#1N\ etc[# ð83JOM"358#024Ł[
283
At Least One Metalloid or Metal
The reaction between "PhMe1Si#2CLi and anhydrous ZnCl1 in THF gives a product formulated as Li"THF#1""PhMe1Si#2CZnCl1#\ probably having structure "56#[ When heated\ "56# a}ords a sublimate "PhMe1Si#2CZnCl which is dimeric in the solid state "as are the analogous Cd and Hg complexes formed in a similar way# and which can be hydrolysed to give the corresponding hydroxide "PhMe1Si#2CZnOH ð75CC897\ 82JOM"351#34Ł[ In the solid state this unusual alkylzinc hydroxide has the OH bridged dimeric structure "57# ð75CC897Ł[ Reaction of the lithium reagent "TMS#1 "HMe1Si#CLi with MBr1 a}ords ""TMS#1"HMe1Si#C#1M "M Zn\ Cd or Hg# species in 07 and 19) yields for the M Cd and Hg compounds respectively[ The Zn compound reacts with various electrophiles such as Br1 and CF2CO1H to give compounds that are the products from reactions with the Si0H groups rather than the C0Zn bonds ð76JOM"219#026\ 89CC0360Ł[ The reaction of ZnBr1 with two equivs[ of the lithium reagents "TMS#1"XMe1Si#CLi a}ord ""TMS#1"XMe1Si#C#1Zn in yields of 67 and 49) for X H and X OMe respectively ð81JOM"326#30Ł[ Similarly the reactions of CdCl1 with "TMS#1"XMe1Si#CLi reagents a}ord ""TMS#1"XMe1Si#C#1Cd in yields of 39\ 55\ and 29) respectively for X H\ OMe and Ph ð81JOM"326#30Ł[ The reaction of two equivs[ of "TMS#1"MeOMe1Si#CLi with HgBr1 at −009>C gives ""TMS#1"MeOMe1Si#C#1Hg in 29) yield ð80JOM"394#038Ł[ PhMe2Si PhMe2Si PhMe2Si
PhMe2Si PhMe2Si PhMe2Si
Cl Li(THF)2
Zn Cl (67)
H O Zn
Zn O H
SiMe2Ph SiMe2Ph SiMe2Ph
(68)
The reaction of one equiv[ of TsiLi and one of CdBr1 in Et1O:THF a}ords\ after crystallising from cyclohexane\ a 10) yield of the trimeric bridged complex "Li"THF#3#""CdTsi#2"m!Br#2"m2!Br##\ the anion of which has the structure "58#\ which is based on a cube with one corner missing[ A second product "69# may be obtained from the reaction in 02) yield by extraction of the reaction residue with heptane[ The mechanism by which "69# is formed is not known in detail but it is likely to involve some accidental hydrolysis and formation of LiOTMS ð77JCS"D#270Ł[ The reaction of slightly less than one equiv[ of TsiLi and CdCl1 gives some Tsi1Cd and a 49) yield of TsiCdCl1 Li"THF#[ On sublimation\ the complex breaks down to give TsiCdCl ð77JCS"D#270Ł[ X!ray crys! tallography shows that the lithium salt and the alkylcadmium chloride have\ in fact\ the dimeric and tetrameric structures "60# and "61# ð77CC0278Ł[ A similar complex\ Li"THF#1CdBr1"C"SiMe1Ph#2#\ is formed in the reaction between "PhMe1Si#2CLi and CdBr1^ this also breaks down on heating to give "PhMe1Si#2CdBr ð77JCS"D#270Ł[ This complex\ which readily forms a hydrate when crystallised from wet THF\ has also been shown to have a dimeric structure "62# ð77CC0278Ł[ R Br
Cd Br
Cd
Br
Br
R = (TMS)3C Cd
TMS
THF Li
Br
O Li
R
Cd
R
THF LiTHF
Br
(TMS)3C
Br
(TMS)3C
(69)
(70)
(THF)2 Li Cl Cl Cl Cd Cd Cl (71)
C(TMS)3
R Cl
Cd
R Cd Cl R Cl Cd Cl Cd R (72)
R = C(TMS)3
Br (PhMe2Si)3C Cd
Cd C(SiMe2Ph)3
Br (73)
The reaction between one equiv[ of TsiLi and HgCl1 in re~uxing THF:Et1O a}ords Tsi1Hg in a 09) yield "19) yield is obtained if HgBr1 is used instead of the chloride# as a colourless solid\ while reaction of TsiLi with HgBrMe gives TsiHgMe in 31) yield ð66JCR"S#005Ł[ The reaction between one equiv[ of TsiLi and HgBr1 at 9>C a}ords TsiHgBr in a yield of 62) ð80AG"E#213Ł[ This bulky alkylmercury bromide reacts with Grignard reagents to give TsiHgR species "R Me\ Pri\ But or Ph# and the chloride "PhMe1Si#2CHgCl with lithium reagents or PhCH1MgCl to give "PhMe1Si#2CHgR compounds "R Me\ Bu\ Ph\ Tsi or PhCH1# ð84UP 502!90Ł[ The bromide TsiHgBr is also formed in the reaction between "Fe"CO#3"HgTsi#1# "obtained from the reaction between TsiHgCl and
284
At Least One Metalloid
"Fe"CO#3#1−# and either HgBr1 or "Fe"CO#3"HgBr#1# ð68JCS"D#656Ł[ The reaction of HgBr1 with one equiv[ of the lithium reagent TMS1"H1C1CHMe1Si#CLi a}ords TMS1"H1C1CHMe1Si#CHgBr in 14) yield ð76JOM"219#026Ł[ The reaction of HgCl1 and slightly less than two equivs[ of TsiLi in re~uxing Et1O has also been reported to give a 69) yield of Tsi1Hg and between HgCl1 and slightly less than two equivs[ of TsiMgBr a 71) yield of the same dialkylmercury species[ This is one of the few examples known of the use of a reagent other than TsiLi for the introduction of the Tsi group ð81OM1827Ł[ "d# Three Si and one `roup 02 metal function[ A low yield of TsiAlCl1 is obtained from the reaction between TsiLi and AlCl2 in THF:Et1O[ The low yield is probably due to the THF reacting and forming compounds of the type TsiAl"Cl#O"CH1#3Tsi as seen in the case of the reaction with BF2 "See 5[02[0[0[1"ii## ð72JOM"138#12Ł[ "See below for the formation of a further TsiAl derivative formed by reduction of a TsiTl species[# The reaction of Ga1Br3 = 1 dioxane with TsiLi coordinated to ether solvents "THF or Et1O# leads only to the isolation of TsiH but if solvent!free TsiLi is used "see 5[02[0[1[0"i#"a## then the unusual tetragallium tetrahedrane "63^ M Ga# is formed as an air!stable solid in 45) yield[ The indium analogue of "63^ M In# is similarly formed from TsiLi and In1Br3 = 1 TMEDA ð81AG"E#0253Ł[ The bulky lithium reagents "PhMe1Si#2CLi and TsiLi react with GaCl2 to give products of formula Li"THF#1GaCl2R "R "PhMe1Si#2C or Tsi# in 81 and 43) yields respectively[ For the case when R "PhMe1Si#2C x!ray crystallography has shown that the structure of the alkylgallium complex has the chlorine bridged structure "64# ð76JCS"D#636Ł[ The reaction between an excess of TsiLi "evidently containing some residual MeLi# and GaCl2 gives a solid thought to be TsiGa"OH#Me which is presumably formed by hydrolysis of TsiGaClMe in the work up ð72JOM"138#12Ł[ C(TMS)3 M (TMS)3C
M
M M
C(TMS)3
M = Ga or In
Cl
Cl
Li(THF)2
Ga
C(TMS)3
(PhMe2Si)3C
(74)
Cl (75)
The reaction between InCl2 and TsiLi gives a complicated alkylindium halide "65# containing coordinated LiCl[ The indium complex has been reduced using LiAlH3 to give a complex metal hydride "66# which when hydrolysed gives a cage compound "O"TsiIn#3"OH#5# having the structure "67# ð75CC897\ 76JCS"D#636Ł[ R In HO
Cl Li(THF)3 (TMS)3C In Cl Cl (76)
(THF)2 Li H H (TMS)3C
In
H
O
In C(TMS)3 H
H (77)
OH OH
R
In
In O H O H
In
R OH
R
(78)
The reaction between TlCl2 and TsiLi gives a compound formulated as Li"THF#TlCl2C"TMS#2 in 34) yield but it is not clear whether this compound has a structure containing two bridging Cls as in the gallium complex "64# above\ only one bridging Cl as in the indium compound "65#\ or some other structure[ It is likely\ however\ that at least two Cls bridge to the Li in order to satisfy the coordination sphere of the Li present[ Reduction of the thallium compound with LiAlH3 leads to transfer of the Tsi group and the formation of Li"THF#2AlH2Tsi ð76JCS"D#636Ł[ "e# Three Si and one `roup 03 metal function[ The reactions between TsiLi and Me2SnCl\ Ph2SnCl\ "PhCH1#1SnCl1\ SnCl3\ EtSnCl2\ Me1SnCl1\ Ph1SnCl1\ or SnBr3 a}ord TsiSnMe2 "79)#\ TsiSnPh2 "23)#\ TsiSn"CH1Ph#1Cl "30)#\ TsiSnCl2\ TsiSnEtCl1\ TsiSnMe1Cl\ TsiSnPh1Cl and TsiSnBr2 "containing some impurities# respectively ð68BAU1111\ 89JCS"D#1532Ł[ Treatment of "Me2Sn#3C with one equiv[ of MeLi followed by one equiv[ of TMSCl gives a low yield of TsiSnMe2 together with a variety of other tetrametallomethanes ð74JOM"180#068Ł[ The reactive silene "TMS#1C1SiMe1 undergoes addition with Me2SnCl to give "TMS#1C"SiMe1Cl#"SnMe2#
285
At Least One Metalloid or Metal
ð76ZN"B#0951Ł[ The reaction of "PhMe1Si#2CLi with Me1SnCl1 in THF:Et1O gives "PhMe1Si#2 CSnMe1Cl in 79) yield ð76JOM"214#006\ 77JOM"244#22Ł[ This is in contrast to the lack of reaction between "PhMe1Si#2CLi and Me1SiCl1\ the longer C0Sn bond length presumably lowering the degree of steric hindrance at the central carbon[ The reaction of TsiLi with Me1SnCl1 and Ph1SnCl1 gives TsiSnMe1Cl and TsiSnPh1Cl in 64 and 39) yields respectively ð77JOM"244#22Ł[ The reaction of the related lithium reagent "TMS#1"Me2Sn#CLi with Me1SiCl1\ TMSCl or Me1SiHCl gives "TMS#1"Me2Sn#CSiMe1X species "X Cl\ Me\ or H# in 64\ 73\ and 59) yields respectively ð77JOM"244#22Ł[ The reactions of TsiLi with lead halides proceed in a manner similar to those for the tin compounds[ Thus reactions with Me2PbCl\ Et2PbCl and Ph2PbCl a}ord TsiPbMe2 "68)#\ TsiPbEt2 "48)# and TsiPbPh2 "49)# respectively ð71ICA"47#038Ł[ The reaction between two equivs[ of TsiLi and Ph1PbCl1 does not lead to formation of Tsi1PbPh1 "presumably because of the severe steric repulsion between two Tsi groups at a tetrahedral centre# but rather to the unexpected dilead compound TsiPbPh1PbPh2 in 18) yield ð82JCS"D#1780Ł[ "f# Three Si and one transition metal function[ The reaction between 0 equiv[ of TsiLi and MnCl1 gives a product "Li"THF#3#"Tsi2Mn2Cl3THF# "68# in 59) yield which may be regarded as an {alkylmanganese chloride|[ Reaction of TsiLi with CoCl1 is thought to give a similar cobalt con! taining species ð74CC423\ 77JCS"D#270Ł[ The monomeric two!coordinate manganese complex Tsi1Mn is formed in ca[ 54) yield as a pale yellow solid from the reaction between 1 equiv[ TsiLi and MnCl1 in THF ð74CC0279Ł[ The preparation of Tsi1Ni has been reported but few details of the compound are available ð60SAP6993811Ł[ C(TMS)3
–
Cl Mn (TMS)3C
Cl
Mn Cl
[Li(THF)4]+
Cl Mn THF
C(TMS)3 (79)
The Gilman reagent "Li"THF#3#"CuTsi1# may be isolated as a solid in 15) yield from the reaction between TsiLi and CuI[ As in the case of other Tsi1M species there is a linear Tsi0M0Tsi arrangement in the solid state ð73JOM"152#C12Ł[ The reaction between TsiLi and AgI in THF gives the ate complex "Li"THF#3#"Tsi1Ag# as a colourless solid in 69) yield which has been structurally characterised ð73CC769Ł[ The reaction of TsiLi with LAuCl"L Et2P\ Ph2P or Ph2As# gives TsiAuL complexes as stable white crystalline solids ð67JCR"S#069Ł[
"ii# Three Ge functions As has been seen in sections above there is a general lack of compounds containing several germanium atoms attached to the same carbon and there do not appear to be any compounds containing the Ge2MC grouping known[ Such compounds should be readily available via the routes used to prepare the many analogous Si2MC containing functions as described above[
"iii# Three B functions The CB3 substituted compound C"B"OMe#1#3 reacts with bases MeLi\ LiOMe or BunLi to give a compound that may be formulated as C"B"OMe#1#2Li which reacts with Ph2SnCl or Ph2SnBr to give C"B"OMe#1#2SnPh2 in 41 and 54) yield respectively ð58JA5430\ 62JOM"46#114\ 63JOM"58#42Ł[ The lith! ium compound also reacts with Me2SnCl to give C"B"OMe#1#2SnMe2\ but rapid disproportionation in the case of similar lead species means that C"B"OMe#1#2PbPh2 cannot be isolated from the reaction between the lithium reagent and Ph2PbCl ð58JA5430\ 62JOM"46#114Ł[ The pinacol ester C"BO1C1Me3#3 also reacts with MeLi to give C"B1C1Me3#2Li in a similar manner ð63JOM"58#42Ł[ These lithium reagents would no doubt react with a wide range of other metal and metalloid halides allowing a large number of currently unknown CB2M functions to be prepared[
286
At Least One Metalloid 5[02[0[1[1 Other mixed metalloid functions "i# Two Si\ one Ge and one metal function
Compounds of the general type "TMS#1C"XMe1Ge#CBr "X F\ Br\ OMe\ OPh\ SPh\ "PhO#1PO1\ etc[# react with BunLi or PhLi at low temperature "−67 to −019>C# to give lithium compounds "TMS#1"XMe1Ge#CLi\ many of which are thermally unstable\ eliminating LiX to give the germene "TMS#1C1GeMe1 in a manner analogous to that of the trisilyl substituted compounds "see 5[02[0[1[0"i## ð75CB1855\ 75CB1879Ł[ The metallation of "TMS#1"Me2Ge#CCl can similarly be achieved by BunLi at −009>C to give "TMS#1"Me2Ge#CLi which is relatively thermally stable ð76JCS"P1#668Ł[ This lithium compound would almost certainly react with many metal and metalloid halides to give a wide range of CSi1GeM species if required[ The reaction of "TMS#1"FMe1Ge#CBr with But2SiNa gives a quantitative yield of the cyclic species "30# "see 5[02[0[0[2"i##[ This presumably arises by dimerisation of the germene "TMS#1C1GeMe1 formed by the elimination of NaF from the highly reactive "TMS#1"FMe1Ge#CNa intermediate ð75CB1855\ 75CB1879Ł[
"ii# Two Si\ one B and one metal function The reduction of "79# with four equivs[ of lithium "Scheme 01# a}ords the unsaturated boron compound "70# which may also be written as its tautomer "71#[ Mono protonation a}ords a compound analogous to "70# containing the "TMS#1CH group which suggests that one of the lithium atoms was associated with the Si1B substituted carbon ð77AG"E#850Ł[ The structure of the 1\2\4\5! Me3C5H analogue of "70# and "71# in the solid state shows that the structure is actually better represented by "72# ð89AG"E#0921Ł[ Mes Cl
B
TMS
+ 4Li Cl
B
2LiCl +
Mes
B
TMS Mes (80)
Li Mes C B Li TMS TMS
(81) Scheme 12
Mes
Mes
Li B
B TMS TMS (82)
Et2O Ar
Li Ar
B
C
B TMS
Li Et2O
TMS
(83) Ar = 2, 3, 5, 6-Me4C6H
The addition of lithium to "TMS#1C1BAr "Ar mesityl or 1\2\4\5!tetramethylphenyl# gives a radical anion which dimerises to give "73#[ X!ray crystallography shows that the compound "73# "with Ar mesityl# has short C0Li and short B0Li distances[ The reaction of "74^ Ar 1\2\4\5! tetramethylphenyl# "see 5[02[0[0[2"iii## with ButLi gives "75# "Equation "02## in which there is again an L!aryl interaction ð89AG"E#0929Ł[ TMS TMS Li
B
Li
B
TMS TMS (84)
287
At Least One Metalloid or Metal
But TMS
B B
TMS
Li
B
ButLi, ∆
B B
B
(85)
TMS (13) TMS
(86)
"iii# One Si\ one Ge\ one B and one metal function[ Also two Ge\ one Si and one metal function[ Also two Ge\ one B and one metal function[ Also Two B\ one Si and one metal function[ Also two B\ one Ge and one metal function Very few examples of compounds containing these functions seem to have been prepared[ Com! pounds containing such functions should\ however\ be available from synthetic routes described above in this section[ In particular\ such functions should be available from the reactions between suitably substituted lithium reagents and appropriate metal halides[ The reaction of "76^ R Pri1N# with two equivs[ of potassium gives "77^ M K\ R Pri1N# in which the ring carbons can be considered to have B1KSiC substitution ð75AG"E#0001Ł[ The related lithium complex "77^ M Li\ R But# can be prepared in a similar way "Equation "03##\ although its actual structure is a {sandwich| with four lithium atoms between two puckered rings and a complicated coordination pattern between the 3 Li\ 1 B and 1 ring carbon atoms ð75AG"E#0000Ł[ TMS
TMS BR
+ 2M
TMS (87)
RB
: :
RB
2–
BR
2M+
(14)
TMS (88)
R = NPri2, M = K R = But, M = Li
5[02[0[2 Methanes Bearing Two Metalloid and Two Metal Functions 5[02[0[2[0 Two Si and two metal functions The reaction between lithium vapour and "TMS#1CCl1 gives "TMS#1CLi1 in 15) yield as deter! mined by reaction with D1O ð73CC0553Ł[ The dilithium reagent is also produced\ together with "TMS#1CH1\ on the thermolysis of "TMS#CHLi at 059>C ð77PO1912Ł[ A more practical synthesis of "TMS#1CLi1 is from the reaction between "TMS#1CCl1 and four equivs[ of LiDBB "DBB 3\3?!di! t!butylbiphenyl#[ Relatively little synthetic work seems to have been done with this interesting dilithium reagent but it has been shown to react with Me2SnCl to give "TMS#1C"SnMe2#1 ð77TL4126Ł and it is likely that it would react with other metal halides to give further novel Si1M1C substituted compounds[ The reaction of "36# "Scheme 09# with Me2SnCl not only gives compounds containing the CSi1B1 function but also the CSi1Sn1 function "see 5[02[0[0[2"iii## ð78AG"E#670\ 78AG"E#673Ł[ For a further example of a compound containing the CSi1Li1 function\ see the CSi1BLi containing structure "72# ð89AG"E#0921Ł[ The di!Grignard reagent "TMS#1C"MgBr#1 may be prepared in several ways "Scheme 02#\ the best probably being the route using just Mg metal and the halomethane[ This route gives a yield of about
288
At Least One Metalloid
59) but the di!Grignard reagent is rather unreactive towards electrophiles and gives relatively low yields of ditin compounds "presumably via halogen exchange# "TMS#1C"SnMe2#"SnMe1X# "X Cl or Br# when treated with Me2SnCl ð78TL5084Ł[ The low reactivity of the di!Grignard reagent is thought to be due to the shielding of the carbanionic centre by the four relatively bulky groups "1×TMS and 1×MgBr"THF#1# attached to it when crystallised from THF:hexane ð81JA6291Ł[ (TMS)2CBr2 + Mg
Mg/Hg + (TMS)2CBr2
(TMS)2C(MgBr)2
(TMS)2CCl2 + MgBr2 + LiDBB
DBB = But
But
Scheme 13
The Al1Si1C species "78# and "89# are both predicted to have planar geometries at carbon and to be stable in the gas phase or in an inert matrix[ It is not clear\ however\ how such unusual species could be prepared ð80CC0425Ł[ Si
Si
Al
Al
Si
Al
Al
(89)
Si
(90)
The reaction between "TMS#1CBrLi and Me1SnCl1\ Me1SiCl1\ or Me1GeBr1 in a 1 ] 0 ratio gives the cyclobutane species "80# in 19\ 25 and 06) yields respectively[ Although the mechanism of formation of these rings was thought to be via a series of transmetallation steps\ more recent work suggests that the doubly bonded species "TMS#1C1MMe1 which dimerise readily in a head!to!tail fashion may well be the source of the rings[ Acyclic species "81# and "82# are formed in the tin case by treatment with Br1 and MeLi "Scheme 03# ð63JA5126\ 65JOM"005#146Ł[ TMS Br
TMS BrMe2Sn TMS
Sn Me2
Br2
TMS
TMS
Me2M
MMe2
TMS
TMS
(91)
TMS
(92)
M = Sn
i, MeLi ii, H2O M = Sn
TMS
TMS Me3Sn TMS
Sn Me2
TMS
(93) Scheme 14
The reaction between "TMS#1CCl1 and Me2SnLi in THF gives "TMS#1C"SnMe2#1 in 65) yield[ Further reaction of this ditin compound with MeLi in THF gives the potentially useful lithium reagent "TMS#1"Me2Sn#CLi which reacts with silylchlorides to give Si2SnC functions and could\ no doubt\ be used to attach the "TMS#1"Me2Sn#C group to a variety of metals thus increasing the number of Si1SnMC functions known ð76CC0072\ 77JOM"244#22Ł[ The ditin compound is also formed in 12) yield as one component of a complicated mixture formed from the reaction of "Me2Sn#3C with one equiv[ of MeLi followed by one equiv[ of TMSCl ð74JOM"180#068Ł[ Treatment of "TMS#1"BrMe1Sn#CBr with PhLi at −009>C in Et1O a}ords "TMS#1"BrMe1Sn#CLi which readily eliminates LiBr to give the highly reactive unsaturated "TMS#1C1SnMe1^ this di! merises to give the distannacyclobutane in good yield ð80AG"E#82Ł[ The major product from the reaction between "TMS#1CClLi and HgCl1 is not the expected ""TMS#1CCl#1Hg\ but the Hg1Si1C functional species "83# "27) yield# which is presumably formed from the desired product via transmetallation reactions ð69JOM"12#250Ł[ A transition metal complex "84# containing a carbon substituted by two silicon and two tungsten
399
At Least One Metalloid or Metal
atoms is formed in low yield in the reaction between WCl3 and Na:Hg in DME followed by treatment with three equivs[ of "TMS#1NLi[ The mechanism by which "84# is formed is unknown ð77POL1938Ł[ TMS
TMS
Hg
TMS TMS
Hg
TMS
Cl
Cl
TMS
(94)
Me2 Me2 Si Si
TMS-N
W
W TMS-N
N-TMS
W
W
N-TMS Si N Me TMS 2
Si Me2 N TMS
Si Me2
Si Me2 (95)
5[02[0[2[1 Two Ge and two metal functions There do not appear to be any compounds containing this function known but they could\ no doubt\ be prepared in similar ways to the analogous Si1M1C containing species described above in 5[02[0[2[0[
5[02[0[2[2 Two B and two metal functions The CB2Sn substituted compound C"B"OMe#1#2SnPh2 rapidly undergoes base!catalysed dis! proportionation to give a high yield of C"B"OMe#1#1"SnPh2#1 together with C"B"OMe#1#3[ This type of disproportionation occurs even more readily for the lead analogue and only C"B"OMe#1#1"PbPh2#1 is isolated in attempts to prepare C"B"OMe#1#2PbPh2 ð58JA5430\ 62JOM"46#120Ł[ The propane! diolboronic esters "85# react with BuLi to give lithium compounds "86# which react with metal halides Ph2MCl to give compounds "87# containing M1B1C functions in good yields "Scheme 04#[ The lithium reagents "86# could presumably be used to prepare a wider range of M1B1C functions by treatment with various metal halides ð62JOM"46#120Ł[ O Ph3MC
BuLi
B O (96)
3
O
Li
Ph3M'Cl
B Ph3M
O
2
(97) M = M' = Sn, 84%; M = M' = Pb, 39%; M = Sn, M' = Pb, 79%
O
Ph3M B Ph3M'
O
2
(98)
Scheme 15
Addition of ButLi to the unsaturated boron species "88# leads to formation of a dilithium salt in 49) yield which x!ray crystallography shows to have a diboraallene structure "099# in the solid state "Equation "04## ð77AG"E#0269Ł[ The dilithium reagent has been used to prepare several other compounds containing multiply bonded boron atoms ð89AG"E#288Ł[
390
At Least One Metalloid –
Mes Mes
B
• TMS
Et2OLi Mes B
ButLi
Li+
LiOEt2 Mes B
But
TMS (99)
(15)
But
(100)
The reaction between a dilithium reagent and two equivs[ of Me2SnCl "Equation "05## a}ords a B1Sn1C substituted species "Ar mesityl\ 82) Ar 1\2\4\5!Me3C5H\ 87)#[ Presumably treatment of the dianion with other metal halides would lead to further B1M1C containing compounds ð78AG"E#673Ł[ Li Ar
B
Li Ar
TMS
Ar
B
TMS
B
SnMe3
TMS
B
SnMe3
+ 2Me3SnCl
+ 2LiCl
TMS
(16)
Ar Ar = 2, 4, 6-Me3C6H2, 93% Ar = 2, 3, 5, 6-Me4C6H, 98%
(47)
Treatment of the dianion "49# with Ph2PAuCl gives compounds "40# in 11) yield\ containing both B1Si1C and Au1B1C groupings "see 5[02[0[0[2"iv## which seem to have been formed via a silyl migration and a geminal substitution ð75AG"E#0001\ 78CB0770Ł[ Calculations on the B1Li1C functional compound "090# have shown that a planar coordination at C is energetically preferable to a tetrahedral con_guration but the compound does not seem to have been made ð65JA4308\ 76T0908Ł[ Li
Li
HB BH (101)
5[02[0[2[3 Other combinations of two metalloids and two metal functions There are very few\ if any\ compounds known containing mixed metalloids and two metal functions[ However\ they should be available by the routes described above for related compounds containing two of the same metalloid[
5[02[0[3 Methanes Bearing One Metalloid and Three Metal Functions 5[02[0[3[0 One Si and three metal functions The main component of the mixture formed on treating "Me2Sn#3C with MeLi followed by one equiv[ of TMSCl is "Me2Sn#2CTMS\ but this does not seem to have been isolated as a pure compound ð74JOM"180#068Ł[ A similar lead compound\ "Me2Pb#2CTMS\ is formed in the reaction between "Me2Pb#2CLi "see 5[02[1[1# and TMSCl ð80SA"A#738Ł[ Reactions between the lead substituted lithium reagent and other halosilanes would no doubt allow a range of "Me2Pb#2CSiR2 compounds to be prepared[ The reaction between trihalomethanes and Co1"CO#7 gives trinuclear complexes containing m2! carbyne ligands\ e[g[\ "091# in Equation "06#[ This reaction can be extended to include silyl substituted trihalomethanes^ thus\ Me1SiHCCl2\ TMSCX2 "X Cl or Br#\ or PhMe1SiCCl2 react with Co1"CO#7 to give complexes "091# "R0R1R2 Me1OH "after some hydrolysis in the workup#\ Me2 and PhMe1# ð62JOM"49#154\ 68JOM"067#116Ł[ Unfortunately\ silyltrihalomethanes are di.cult to make and an alter! native route to the carbyne species is to treat methylidyne or bromomethylidyne tricobalt! nonacarbonyl complexes with silanes R0R1R2SiH as shown by the general Equation "06# ð66JA4198\
391
At Least One Metalloid or Metal
68JOM"067#116\ 70JOM"110#146Ł[ The route using the m2!CH species is probably the better one as it does
not generate HBr which can cause unwanted side reactions such as Si0Ph bond cleavage at the silicon[ Once formed\ the complexes "091# can undergo a variety of reactions at silicon without disrupting the cluster framework thus enabling a wider range of compounds to be easily prepared ð66JA4198Ł[ X
(CO)3Co
SiR1R2R3
+ R1R2R3SiH
Co(CO)3
(CO)3Co
Co (CO)3
X = H or Br
Co(CO)3
+ HX
(17)
Co (CO)3 (102)
The reaction of silicon hydrides that are themselves within a transition metal complex with HCCo2"CO#8 has also given compounds containing an SiCo2C grouping "see Scheme 05# ð81JOM"326#212Ł[
SiR2H Fe
SiR2CCo3(CO)9 R = Me or Ph
Fe
HCCo3(CO)9 SiR2CCo3(CO)9
SiR2H Fe
Fe
SiR2H
R = Me, Et or Ph SiR2CCo3(CO)9
Scheme 16
Cobalt bridged carbyne complexes of the type shown above in Equation "06# undergo metal substitution reactions giving mixed metal clusters as shown in Scheme 06[ Alternatively\ mixed metal clusters may be prepared from mixed metal carbyne clusters "Scheme 06# ð89JOM"270#150Ł[ SiEt3
(CO)3Co
Co(CO)3
Co (CO)3
SiEt3
+ NaMCp(CO)3
(CO)3Co
M = Mo or W
MCp(CO)2 Co (CO)3
Et3SiH
(CO)3Co
MCp(CO)2 Co (CO)3
Scheme 17
The cobalt mediated cleavage of alkynes and concomitant build!up of clusters seems to be a general reaction and a wide range of compounds have been prepared using this type of methodology[ Thus various alkynes and dialkynes react with either "h4!C4H4#Co"CO#1 or "h1!C1H3#1Co"h4!C4H4# to give tricobalt cluster species containing m2!CSiMe2 ligands as outlined in Equation "07# ð70JOM"106#094\ 71JOC2081\ 75OM283Ł[ Such reactions are clearly complicated and often give low yields of the compounds shown in Equation "06# together with numerous other products although\ in some cases\ the intermediates may be isolated and fully characterised[
392
At Least One Metalloid n-decane
TMS
+ CpCo(CO)2
TMS
reflux
TMS TMS
TMS CpCo TMS
CpCo
CoCp Co
TMS
Cp
+ CpCo
CoCp
+ CpCo
Co
CoCp Co
Cp
CpCo
CoCp Co
Cp
TMS
(18)
Cp
TMS
TMS
The reaction between CpCo"CO#1 and TMSC2CC2CTMS gives structure "092# ð68JA1657Ł[ The hexametallic complexes "093# rearrange on ~ash vacuum pyrolysis at 449>C to give the isomers "094# containing two m2!CTMS ligands "Equation "08## ð72JA0273Ł[ TMS
CpCo
CoCp Co Cp
TMS (103)
SiR23
SiR23 R1Co
CoR1 Co
R1Co
R1
CoR1 Co R1
R1Co
CoR1 Co
R1Co
R2 = Me
R1 = η5-C5H5
R2 = Me
R1 = η5-MeC5H4
R2
R1 = η5-C5H5
= Et
(19)
CoR1 Co
R1 SiR23 (104)
∆
R1 SiR23 (105)
Cluster formation also occurs when nickelocene is treated with alkyllithium reagents[ Thus TMSCH1Li gives the carbyne bridged cluster "095# and "096# "if excess lithium reagent is used# as a blackÐviolet solid in 04) yield which may also be obtained from the reaction between nickelocene and the nickel alkyl complex "097# "Scheme 07# ð68JOM"067#260Ł[ The bimetallic asymmetrically bridging alkylidyne complex "098# reacts with low valent transition metal fragments to form a range of trimetallic species\ "009#\ "000# and "001# in good yield containing a m2!CSiPh2 ligand which bridges three di}erent transition metals "Scheme 08# ð77JOM"244#120Ł[
393
At Least One Metalloid or Metal TMS TMS
Cp2Ni +
BunLi, RT
Li CpNi
NiCp
Ph3P
Ni Cp
excess TMS
Cp2Ni +
(106)
Li
Ni
TMS
(108)
TMS
TMS
NiCp
Ni (107)
Ni Cp Scheme 18
SiPh3 CuCl
CpCOW OC
CuCl
SiPh3
SiPh3 Pt(PPri3)
CpCOW C O
Pt (PPri3) (110)
Fe2(CO)9 Et2O/CO
(109)
Cp(CO)2W
Pt(CO)(PPri3) Fe (CO)3 (111)
Fe2(CO)9 Et2O
SiPh3 Pt(PPri3) Fe (CO)3
CpCOW OC
(112) Scheme 19
5[02[0[3[1 One Ge and three metal functions Germanes\ R2GeH\ react in a similar way to the silanes discussed above in 5[02[0[3[0 with the methylidyne cluster HCCo2"CO#8 to give germyl substituted methylidynes[ For example\ germanes Ph2GeH\ MePh"0!naphth#GeH\ Et2GeH\ Bun2GeH\ Et1ClGeH and "PhCH1#1ClGeH all give the appropriate R2GeCCo2"CO#8 species with structure similar to the silicon analogues "091# above "Equation "06## ð66JA4198\ 68JOM"067#116\ 79JOM"077#218\ 70JOM"110#146Ł[
5[02[0[3[2 One B and three metal functions There seem to be few compounds known containing this type of function although they may be available by treatment of a methylidyne cluster with R1BH species in the same way that the silyl and germyl substituted carbyne complexes described above are made[
5[02[1 METHANES BEARING FOUR METAL FUNCTIONS 5[02[1[0 Methanes Bearing Four Similar Metals Calculations on the structures of CLi3 and C"BeH#3 have been carried out in order to ascertain whether the small electropositive substituents might promote planar rather than tetrahedral geometry at carbon[ In both cases tetrahedral geometry is still preferred ð65JA4308Ł[ The synthesis of CLi3 may be achieved in several ways[ The original synthesis involved the reaction of CCl3 with lithium vapour at 649>C giving a 39[4) yield as determined by deuterolysis to give CD3 ð72JOM"138#0Ł[ More convenient and apparently higher yielding syntheses involve the reaction
Four Metal Functions
394
between C"HgEt#3 and ButLi or those between C"HgCl#3 and either ButLi or lithium metal ð73AG"E#884Ł[ Tetralithiomethane reacts in a variety of complicated ways with simple derivatising agents and its synthetic use is therefore probably limited[ The tetrastannylmethane "Me2Sn#3C is formed as a readily sublimable solid from the reaction between Me2SnLi and either CHCl2 or CCl3 in THF ð64OMS"09#07\ 73JOM"155#26Ł[ The compound has also been prepared enriched in 02C at the central carbon by use of ð02CŁCCl3 in a similar reaction ð68JOM"061#182Ł[ The reaction between CCl3 and four equivs[ of Me2SnNa a}ords only 07) "Me2Sn#3C at room temperature but 30) if carried out at −12>C ð65JOM"011#060Ł[ The reaction between "Me2Sn#3C and one equiv[ of MeLi followed by one equiv[ of Me2PbCl a}ords a mixture of tetrametallomethanes including a very low yield of "Me2Pb#3C ð74JOM"180#068Ł[ The tetra! stannylmethane also reacts with various electrophilic reagents to give other substituted Sn3C com! pounds as a result of cleavage of the Sn0Me bonds only ð73JOM"155#26Ł[ The reaction between four equivs[ of Ph2PbLi and CCl3 a}ords the stable crystalline solid "Ph2Pb#3C[ The compound is sparingly soluble in organic solvents and only decomposes at 181Ð183>C ð54RTC32Ł[ The reaction of ethanol in alkaline solution with mercuric oxide gives a species C1Hg5"OH#5 known as {ethane hexamercarbide|[ This material dissolves in aqueous solutions of carboxylic acids to give crystalline compounds C"HgOCOR#3 "R Me or CF2# which have been characterised by x!ray crystallography and which react with MeSH in H1O to give C"HgSMe#3 ð63CC535\ 66ZN"B#0911Ł[ Tetramercuriomethanes may also be prepared from C"B"OMe#1#3 by treatment with various mercury compounds[ Thus\ reactions with Hg"OAc#1 and with EtHgOAc a}ord C"HgOAc#3 and C"HgEt#3 respectively ð69JA120\ 73AG"E#884Ł[ Reactions between the acetate C"HgOAc#3 and HF\ halide or cyanide ions gives the compounds C"HgX#3"X F\ Cl\ Br\ I\ or CN# ð67JOM"042#0\ 68ZN"B#289\ 73AG"E#884Ł[
5[02[1[1 Methanes Bearing Three Similar and One Different Metal Function The reaction between "Me2Sn#3C and one equiv[ of MeLi followed by one equiv[ of Me2PbCl a}ords a mixture of tetrametallomethanes including "Me2Sn#2CPbMe2 and "Me2Pb#2CSnMe2 in yields of 33 and 7) yields respectively[ Unfortunately\ although the yield of the PbSn2C compound is reasonable\ it is likely to be di.cult to separate such a mixture and the reaction is\ therefore\ of little synthetic use ð74JOM"180#068Ł[ The lithium reagent "Me2Sn#2CLi may be observed by NMR spectroscopy from the reaction between "Me2Sn#3C and MeLi in Et1O ð70JMR"33#43Ł[ A similar lead! substituted methyllithium "Me2Pb#2CLi may be prepared by treating "Me2Pb#2CH with MeLi in THF ð80SA"A#738Ł in the same way as "TMS#2CLi is prepared from "TMS#2CH "5[02[0[1[0"i#"a##[ The lead substituted compound could presumably be used in the same way as the silicon substituted lithium reagent to prepare a wide variety of compounds containing the "Me2Pb#2C group by reaction with suitable metal or metalloid halides[
5[02[1[2 Methanes Bearing Two Similar and Two Different Metal Functions The reaction between "Me2Sn#3C and one equiv[ of MeLi followed by one equiv[ of Me2PbCl a}ords a mixture of tetrametallomethanes including a 15) yield of "Me2Pb#1C"SnMe2#1 ð74JOM"180#068Ł[
5[02[1[3 Methanes Bearing Four Different Metal Functions Although there are a potential 024640 di}erent combinations "and their optical isomers# of 32 di}erent metals at a tetrahedral carbon centre very few seem to have been prepared[ A comprehensive search of the literature for such a large number of functional groups is clearly very di.cult to carry out\ and it is quite possible that many such groupings have been missed in compiling this chapter[ It is hoped that omission of such groupings will not be serious for the organic chemist[
395
At Least One Metalloid or Metal
5[02[2 METHANES BEARING MORE THAN FOUR METALLOID OR METAL FUNCTIONS The structures of magnesium ð80AOC"21#036Ł\ lithium ð74AOC"13#243Ł and Na\ K\ Rb\ or Cs ð76AOC"16#058Ł compounds are usually complicated in the solid state often having carbon with a coordination number greater than four[ Such species will not be further described here and are fully discussed in the reviews referred to[ There are a variety of carboranes known in which the cage carbons have a metal or metalloid substituent[ Such compounds usually contain carbon with a formal coordination number greater than four and are\ therefore\ strictly outside the coverage of this section\ however a few representative compounds are given below[ The reaction between C1B09H01 with BuLi a}ords "002# which reacts with various mercury salts to give compounds of type "003# "Equation "19## ð56JOM"6#274\ 57BAU303\ 62JGU737Ł[ Such compounds will not be discussed further here but they have been the subject of several reviews "see for example\ ð89AOC"29#88\ 81CRV114\ 81CRV140Ł and references therein#[ Li
HgR
BH
HB BH BH
BH 2RHgCl
BH BH BH
BH
HB BH BH
Li
BH BH BH
(20) HgR
BH
B H (113)
B H (114)
Carbon may have six!coordinate octahedral geometry in complexes containing dicationic ions such as in "004# formed according to Equation "10#[ Such compounds may be characterised by x! ray crystallography and the central carbon observed by ð02CŁCNMR spectroscopy ð77AG"E#0433\ 80AG"E#0377Ł[ AuL C[B(OMe)2]4 + 6LAuCl + 6CsF
6CsCl + 2B(OMe)3 +
LAu
2+
AuL C
LAu
[MeOBF3]–2
(21)
AuL AuL
L = Ph3 or Ph2(p-Me2NC6H4)P
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
(115)
Comprehensive Organic Functional Group Transformations
6.14 Functions Containing a Carbonyl Group and at Least One Halogen GEOFFREY E. GYMER and SUBRAMANIYAN NARAYANASWAMI Pfizer Central Research, Sandwich, UK 5[03[0 CARBONYL HALIDES WITH TWO SIMILAR HALOGENS
397
5[03[0[0 Carbonic Di~uoride\ COF1 5[03[0[0[0 From carbonic dichloride "phos`ene# 5[03[0[0[1 From carbon monoxide 5[03[0[0[2 Oxidative methods 5[03[0[0[3 Other methods 5[03[0[1 Carbonic Dichloride "Phos`ene#\ COCl1 5[03[0[1[0 Phos`ene toxicity 5[03[0[1[1 Handlin` phos`ene 5[03[0[1[2 Preparation of phos`ene*an overview 5[03[0[1[3 Laboratory methods suitable for preparin` phos`ene 5[03[0[1[4 Other laboratory preparations of phos`ene 5[03[0[1[5 Puri_cation of phos`ene 5[03[0[1[6 Preparation of isotopically labelled phos`ene 5[03[0[1[7 Phos`ene alternatives 5[03[0[2 Carbonic Dibromide\ COBr1 5[03[0[3 Carbonic Diiodide\ COI1
397 398 398 309 309 300 300 300 301 301 302 303 303 304 306 307
5[03[1 CARBONYL HALIDES WITH TWO DISSIMILAR HALOGENS 5[03[1[0 One Fluorine and Chlorine\ Bromine or Iodine Function 5[03[1[0[0 Carbonic chloride ~uoride\ COClF 5[03[1[0[1 Carbonic bromide ~uoride\ COBrF 5[03[1[0[2 Carbonic ~uoride iodide\ COFI 5[03[1[1 One Chlorine and Bromine or Iodine Function 5[03[1[1[0 Carbonic bromide chloride\ COBrCl 5[03[1[1[1 Carbonic chloride iodide\ COClI 5[03[1[2 One Bromine and One Iodine Function 5[03[1[2[0 Carbonic bromide iodide\ COBrI 5[03[2 CARBONYL HALIDES WITH ONE HALOGEN AND ONE OTHER HETEROATOM FUNCTION 5[03[2[0 One Halo`en and One Oxy`en Function 5[03[2[0[0 Fluoroformate esters\ ROCOF 5[03[2[0[1 Preparation of chloroformate esters\ ROCOCl 5[03[2[0[2 Preparation of bromoformate esters\ ROCOBr 5[03[2[0[3 Preparation of iodoformates\ ROCOI 5[03[2[1 One Halo`en and One Sulfur Function 5[03[2[1[0 Fluorothiolformate esters\ RSCOF 5[03[2[1[1 Chlorothiolformate esters\ RSCOCl 5[03[2[1[2 Bromothiolformate esters\ RSCOBr 5[03[2[1[3 Iodothiolformate esters\ RSCOI
396
307 307 307 319 319 319 319 310 310 310 310 310 311 313 320 320 320 321 323 325 326
397
Carbonyl Group and at Least One Halo`en
5[03[2[2 One Halo`en and One Nitro`en Function 5[03[2[2[0 Carbamoyl ~uorides\ R0R1NCOF\ and other N!~uorocarbonyl compounds 5[03[2[2[1 Carbamoyl chlorides\ R0R1NCOCl\ and other N!chlorocarbonyl compounds 5[03[2[2[2 Carbamoyl bromides\ R0R1NCOBr\ and other N!bromocarbonyl compounds 5[03[2[2[3 Carbamoyl iodides\ R0R1NCOI 5[03[2[3 One Halo`en and One Phosphorus Function 5[03[2[3[0 Chlorocarbonyl derivatives of phosphorus"III# 5[03[2[3[1 Chlorocarbonyl derivatives of phosphorus"V# 5[03[2[4 One Halo`en and One As\ Sb or Bi Function 5[03[2[5 One Halo`en and One Metalloid "B\ Si or Ge# Function 5[03[2[6 One Halo`en and One Metal Function 5[03[2[6[0 Halocarbonyl complexes of _rst transition series metal "iron and chromium# 5[03[2[6[1 Halocarbonyl complexes of second transition series metals "ruthenium and rhodium# 5[03[2[6[2 Halocarbonyl complexes of third transition series metals "rhenium and iridium#
326 326 331 341 343 343 343 343 344 344 344 344 345 346
5[03[0 CARBONYL HALIDES WITH TWO SIMILAR HALOGENS Compounds of formula X1C1O\ where X F\ Cl\ Br or I\ are currently named in Chemical Abstracts as carbonic dihalides[ Other names commonly applied to these compounds are carbonyl dihalides\ carbonyl halides and halophosgenes[ The latter derives from the historical name phosgene\ which is still the term most commonly used to describe carbonic dichloride[ Methods of synthesis have been previously reviewed^ the review by Hagemann ð72HOU"E3#0Ł is particularly important because it also covers the remit of Section 5[03[1 and includes some pre! parative details[ This area is covered comprehensively in Beilstein up to the end of 0879[ By far the most important member of this class is carbonic dichloride\ which will henceforth be referred to by its more common name\ phosgene[ Phosgene is an important industrial chemical used mainly in the manufacture of polyurethanes and polycarbonates[ Although the organization of this section retains the logical sequence by commencing with discussion of the synthesis of carbonic di~uoride in Section 5[03[0[0\ it may be prudent of the reader also to take note of some aspects discussed in Section 5[03[0[1\ concerning the preparation and safe handling of phosgene\ and possible ways of avoiding its use[ 5[03[0[0 Carbonic Di~uoride\ COF1 Carbonic di~uoride\ also called carbonyl di~uoride and ~uorophosgene\ is a stable\ colourless gas\ b[p[ −72>C[ It is commercially available from several suppliers^ the industrial preparation probably involves the reaction of carbon monoxide with elemental ~uorine[ In common with all carbonyl dihalides\ it is extremely toxic[ In addition\ hydrolysis and other nucleophilic attack leads to the formation of hydrogen ~uoride\ with all its attendant hazards[ The suitability of glass apparatus for the preparation or reaction of carbonic di~uoride should be carefully considered[ If signi_cant quantities of hydrogen ~uoride could be generated during the reaction or work!up procedure\ then failure of glass apparatus may occur with potentially disastrous results[ Gaseous products can be freed of hydrogen ~uoride by passage through a copper tube packed with sodium ~uoride pellets ð59IS044Ł[ Glass is inert to pure carbonic di~uoride[ Three prinicipal routes to carbonic di~uoride have been described\ together with several mis! cellaneous preparations "Scheme 0#[ 〈62JA4275〉 COCl2 〈80JFC(15)423〉 〈71GEP2105907〉 CO 〈60IS(6)155〉
NaF or Et3N•3HF AgF2 or NH4F
Cl3COCOCl NH4F
〈84JAP8439705〉
COF2 RuO4 (cat.)
F
F
F3C F 〈79JFC(13)175〉
SO3
NaOCl
BrXCF2 (X = Cl, Br) Scheme 1
〈75GEP2261108〉
Two Similar Halo`ens
398
5[03[0[0[0 From carbonic dichloride "phosgene# Transhalogenation of phosgene with various ~uorine donors is a well!described method of preparing carbonic di~uoride[ The early work of Steinkopf and Herold led to the preparation of impure carbonic di~uoride in low yield[ They achieved this by warming a mixture of arsenic tri~uoride and phosgene ð19JPR68Ł[ Emeleus and Wood devised a substantially improved procedure using antimony tri~uoride^ they obtained carbonic di~uoride of 89Ð84) purity\ free from hydrogen chloride\ from which it cannot be separated by distillation ð37JCS1072Ł[ This method was further re_ned by Haszeldine and Iserson\ who added chlorine to the mixture to form pentavalent antimony salts\ allowing them to obtain carbonic di~uoride of 84) purity in 79Ð74) yield ð46JA4790Ł[ These reactions were performed at quite high pressures and temperatures\ and these methods were superseded by the work of Tullock and co!workers\ who were able to prepare carbonic di~uoride of 84) purity in 69Ð79) yield through the reaction of phosgene and sodium ~uoride in acetonitrile at 29Ð24>C and atmospheric pressure ð51JA3164\ B!64MI 503!90Ł[ This is an excellent preparative method\ only equalled by the alternative of Franz\ who has used the triethylamine trishydrogen ~uoride complex and phosgene in acetonitrile at room temperature to give carbonic di~uoride in quantitative yield\ containing carbon dioxide as the only impurity ð79JFC"04#312Ł[ A similar method employing ammonium hydrogen ~uoride as the ~uorine source is also reported to give carbonic di~uoride in 89) yield\ together with 7) carbonic chloride ~uoride ð60GEP1094896Ł[ Another potentially useful route in! volves substitution of trichloromethyl chloroformate for phosgene using similar reaction con! ditions\ thus avoiding to some extent the dangers associated with the handling of phosgene ð73JAP7328694Ł[ Because of the extreme toxicity of phosgene\ alternatives are described in Section 5[03[0[1[7[ Two gas phase reactions leading to carbonic di~uoride are worthy of mention\ since they can be run as continuous ~ow procedures\ suitable for industrial production[ In the _rst\ thionyl ~uoride "from thionyl chloride and sodium ~uoride# and phosgene are passed as a 3 ] 0 mixture over iron"III# chloride at 399>C to give carbonic di~uoride in 85) yield ð79EGP028825Ł[ Many other catalysts have been examined\ and the SOFCl and SOCl1 formed during the reaction can be recycled by treatment with NaF to regenerate thionyl ~uoride[ The second method involves the preparation of carbonic chloride ~uoride by passing phosgene over calcium ~uoride at 199Ð449>C\ and then passing it over activated carbon\ when metathesis to carbonic di~uoride and phosgene takes place ð77EUP142416Ł[ In these last two preparations it should be borne in mind that at the elevated temperatures employed\ phosgene is at least partly dissociated to carbon monoxide and chlorine\ and thus ~uorination of carbon monoxide may be the predominant reaction pathway[ Finally\ Glemser and Biermann have prepared carbonic di~uoride in quantitative yield by passing a 0 ] 0 mixture of phosgene and nitrogen tri~uoride through a nickel tube heated to 399>C ð56CB1373Ł[ These workers were fully aware that ~uorination of carbon monoxide produced by thermal de! composition of phosgene could explain the reaction course observed[ The same workers have shown that ~uorination of CO with NF2 does in fact yield COF1 in nearly quantitative yield ð56CB0073Ł[
5[03[0[0[1 From carbon monoxide The ~uorination of carbon monoxide with elemental ~uorine is probably the preferred method of production of carbonic di~uoride on an industrial scale\ since it is amenable to continuous ~ow technology ðB!78MI 503!90Ł[ As with many reactions employing elemental ~uorine\ this does not appear to be a straightforward process ð23ZAAC"110#043Ł^ however\ it had already been found to be satisfactory as a preparative procedure by the 0839s ð33MI 503!90\ B!52MI 503!90Ł[ In the latter preparation\ carbon monoxide is actually burnt in an atmosphere of electrolytically generated ~uorine\ and Kwasnik refers to the risk of violent explosion if the procedure is incorrectly conducted[ This method has now been improved by introducing carbon monoxide into the liquid HF electrolyte used for the ~uorine preparation ð69JAP6915500Ł[ The purity of the COF1 produced is apparently improved when potassium ~uoride is added to the electrolyte ð58USP2350949Ł when COF1 is the sole product[ A well!described laboratory procedure by Tullock and co!workers exists for the ~uorination of carbon monoxide by a more amenable method[ Carbon monoxide and helium are mixed together and passed through a copper tube containing silver"II# ~uoride[ An exothermic reaction ensues\ to give COF1 contaminated with HF\ which is removed by passing the e/uent gases through sodium ~uoride pellets[ Upon condensation\ the COF1 is obtained in 69Ð74) yield and greater than 88)
309
Carbonyl Group and at Least One Halo`en
purity[ This method avoids the low!temperature fractional distillation usually necessary to obtain pure product ð59IS044Ł[ Fluorination of carbon monoxide with sulfur hexa~uoride under the in~uence of IR radiation has also been claimed as a simultaneous preparation of carbonic di~uoride and sulfur tetra~uoride ð70CZP197140Ł[ A less attractive but high!yielding method involves passing an equimolar mixture of carbon monoxide and NF2 through a nickel tube heated to 349Ð419>C\ to give COF1 in 89Ð84) yield based on NF2 ð56CB0073Ł[ NF2 is prepared by electrolysis of molten ammonium ~uoride hydro~uoride\ so this is not normally an accessible laboratory method ð55CB260Ł[ Olah and Kuhn prepared carbonic di~uoride as a pure side!product in 50) yield when in pursuit of carbonic bromide ~uoride by the exothermic reaction of bromine tri~uoride with carbon monoxide ð45JOC0208Ł[ This method is well described\ but is probably unacceptably hazardous ðB!52MI 503!90Ł[
5[03[0[0[2 Oxidative methods Oxidation of terminal 0\0!di~uoroalkenes*in practice usually per~uoroalkenes*leads to car! bonic di~uoride[ One method stands out as being particularly suitable for laboratory use\ namely catalytic ruthenium tetroxide oxidative cleavage[ Commercially available per~uoropropene can be oxidized by a catalytic quantity of ruthenium tetroxide in Freon 002 with gradual addition of peracetic acid\ periodic acid or sodium hypochlorite to regenerate the catalyst[ The products are TFA and COF1\ both in high yield ð68JFC"02#064Ł[ It is reasonable to speculate that if tetra! ~uoroethylene was used in the reaction\ the sole product would be COF1\ possibly constituting a very simple and controllable small!scale laboratory preparation[ Oxidation of tetra~uoroethylene with oxygen at 199Ð349>C has been used as a very high!yielding industrial preparation ð54NEP5498407Ł\ which can be made more controllable by dilution with Freons ð63URP313798Ł[ Carbonic di~uoride is also produced in quantitative yield from per~uoropropene and oxygen under IR radiation\ in the presence of SF5 as a radiation absorber ð89CZP153247Ł[ Terminal 0\0!di~uoroalkenes can also be ozonised to give carbonic di~uoride with high implied yields^ however\ this has not yet been developed as a synthetic route to COF1 ð79JA6461\ 78BAU0469Ł[ Finally\ carbonic di~uoride can be prepared by oxidation of chloro! or bromodi~uoromethane with oxygen at 199Ð499>C\ a method suitable for an industrial ~ow process ð78EUP209144Ł[
5[03[0[0[3 Other methods The reaction of ~uorohalomethanes with sulfur trioxide provides a versatile route to all carbonic ~uoride halides[ Carbonic di~uoride is thus available by reaction of either dibro! modi~uoromethane or bromochlorodi~uoromethane with SO2[ The presence of catalysts such as sulfuric acid or mercury"I# or mercury"II# salts is bene_cial\ and is in fact necessary for e.cient reaction of the second substrate[ In this manner\ dropwise addition of dibromodi~uoromethane to SO2 at 24Ð33>C gave 52) carbonic di~uoride based on starting material consumed ð63GEP1150097Ł[ The scope of this reaction in fact extends beyond that encompassed above\ as will be demonstrated in subsequent sections of this chapter\ making it probably the most general laboratory method available[ Fluorination of carbonyl sul_de also provides a route to carbonic di~uoride[ When carbonyl sul_de is passed through a copper tube packed with cobalt tri~uoride maintained at 199>C\ the e/uent gases comprise only COF1 and SF5\ which are readily separated by low!temperature frac! tionation ð41JA4681Ł[ In a second example\ carbonyl sul_de diluted with helium is introduced into an electrolyte consisting of sodium ~uoride in anhydrous hydrogen ~uoride[ Electrolysis produces carbonic di~uoride\ 70)\ and sulfur hexa~uoride\ 88) ð65JAP6529923Ł[ Lastly\ in a patent to the Dow Chemical Company\ heating a mixture of calcium ~uoride\ titanium dioxide and carbon at 1799Ð2499>C under argon gives rise to carbonic di~uoride as the only volatile product[ This industrial process uses very cheap starting materials which may compensate for the large of amount of energy consumed^ it can be operated continuously\ and various other ~uoride sources and oxides are also satisfactory ð56USP2211712Ł[
Two Similar Halo`ens
300
5[03[0[1 Carbonic Dichloride "Phosgene#\ COCl1 Named in Chemical Abstracts as carbonic dichloride\ COCl1 is more commonly known as phos! gene[ Other commonly encountered names are carbonic acid dichloride\ carbonyl dichloride and carbonyl chloride[ It is an important building block for the chemical industry[ It is a colourless gas\ b[p[ 7>C\ of legendary toxicity ðB!82MI 503!90Ł[ In 0877 the consumption of phosgene in the USA alone was 0[5×098 pounds "6[2×097 kg#\ of which approximately 89) was absorbed by the manufacturers of polyurethane plastics ðB!78MI 503!90Ł[ It is thus widely available\ and is supplied either as a liqui_ed gas in a pressurized cylinder\ or in solution\ most commonly as a 19) by weight solution in toluene[ A comprehensive review of the methods of preparation of phosgene would not in the authors| opinion be of great value since the vast majority of methods are of no synthetic importance^ phosgene is so widely available and so toxic that its preparation in the laboratory should be severely questioned[ Exceptions to this are the production of minute quantities of isotopically labelled material\ which are covered in detail later in this section[ Instead the authors intend to devote part of this section to informing readers on the safe use of phosgene and its replacement by less hazardous alternatives[ Phosgene preparation has been reviewed up to the end of 0814 ð19JCS0309\ 16CRV098Ł[ Subsequent reviews relating to phosgene appear to pay little attention to its synthesis ð71KO"06#305\ 72HOU"E3#0Ł[ This is not surprising since the current method of phosgene manufacture has been known since 0767 ð0767G122Ł[
5[03[0[1[0 Phosgene toxicity In order to handle phosgene in a safe manner\ an appreciation of its toxicity is necessary[ Phosgene is an insidious poison[ The initial e}ects of irritation to the eyes and mucous membranes often disappear upon removal from exposure^ however\ within 13 h\ pulmonary oedema\ due to lung tissue acylation\ commonly develops[ This is often fatal[ At high exposures "×199 ppm#\ phosgene can pass into the blood\ and death from congestive heart failure follows[ From animal and\ more sadly\ human experiments the following generalization emerges] LC49 "lethal concentration to 49) of recipients# 469 ppm min[ This implies that 09 ppm exposure for 0 h or 099 ppm for 5 min would exceed the LC49[ In the event of phosgene exposure\ the casualty should be at once removed from exposure\ kept warm and rested[ Arti_cial respiration and external cardiac massage should be employed where necessary[ Mouth to mouth resuscitation can be employed without undue risk to the operator[ Removal of contaminated clothing and copious irrigation of the skin and eyes with water are also necessary[ In all cases the casualty should be removed to hospital and kept under observation[ Medical treatment may involve corticosteroids\ administration of oxygen and other symptomatic measures ðB!82MI 503!91Ł[
5[03[0[1[1 Handling phosgene Phosgene should always be used in a fume hood with powerful extraction[ Two persons should be present during the entire period that exposure could occur[ A method of monitoring phosgene concentration is advisable[ A simple method is to tape phosgene indicator papers to the fume hood sill[ These are prepared by soaking _lter papers in a 09) alcoholic solution of equal parts of p!dimethylaminobenzaldehyde and diphenylamine\ and allowing to dry[ These yellow papers turn deep orange in the presence of dangerously high concentrations of phosgene ðB!78MI 503!91Ł[ A Draeger pump speci_c for phosgene is a more sophisticated safeguard[ Reactions quite often require an excess of phosgene\ or fail to proceed\ in both cases leaving residual phosgene at the end of the experiment[ This must be purged from the reaction mixture by a vigorous stream of nitrogen\ the e/uent gas being scrubbed with sodium hydroxide solution[ Phosgene may still be present after this operation\ so reaction solvent subsequently evaporated o} should also be freed from phosgene before being discarded[ This could be achieved by addition of a reactive amine or alcohol\ which would convert any remaining phosgene to a urea or carbonate[ Several excellent alternatives to phosgene have been developed^ these will be reviewed in Section 5[03[0[1[7[ However\ sometimes phosgene provides the simplest\ cleanest way of accomplishing a desired reaction[
301
Carbonyl Group and at Least One Halo`en
5[03[0[1[2 Preparation of phosgene*an overview Phosgene was _rst prepared by the interaction of chlorine and carbon monoxide in the presence of sunlight\ by John Davy "the brother of Sir Humphrey Davy# in 0701 ð19JCS0309Ł[ The name is derived from two Greek words meaning {light| and {I produce|[ By 0767\ Paterno replaced photoinduction by passing the gases over active carbon in the form of animal charcoal ð0767G122Ł[ This method is still employed today for the manufacture of billions of kilograms of phosgene each year[ Currently the process is run at 49>C and 4Ð09 atm in the presence of activated carbon to produce phosgene at a cost of less than 49 cents per pound\ or 14 cents per kilogram ðB!78MI 503! 90Ł[ In 0758 the only other preparation to have withstood the test of time was discovered by Schutzenberger ð0758BSF087Ł[ This involves reaction of carbon tetrachloride with sulfur trioxide[ The reaction is conveniently done in oleum\ a solution of sulfur trioxide in sulfuric acid ð08CR"058#06Ł[ Armstrong reported that hexachloroethane also produced phosgene under the same conditions ð0769CB629Ł[ It was also discovered that the use of sulfuric acid without the addition of sulfur trioxide still led to the production of phosgene ð16CRV098Ł[ The oleum process was used to produce phosgene in Italy during the First World War\ but could not compete with the continuous catalytic process discovered by Paterno[ Many other methods have been developed\ often alternative ways of combining chlorine and carbon monoxide\ with chlorine present as a metallic chloride ð17G332\ 29CB0110Ł or nonmetallic chloride such as SCl1 ð57FRP0415847Ł[ Many catalysts have also been considered as alternatives to activated carbon in the Paterno process ð71MI 503!90Ł[ Several methods involving the oxidation of chloroform or carbon tetrachloride were also developed\ using oxygen ð13MI 503!90Ł or chromium reagents ð0782CB0889Ł[ Pyrolysis of various compounds containing chlorine\ carbon and oxygen has also often led to the production of phosgene\ notably oxalyl chloride\ which when heated in a sealed vessel at 239>C for 69 h gave phosgene in quantitative yield together with carbon monoxide ð02CB0315Ł[ A more recent example involves the decomposition of trichloroacetic acid at 299Ð399>C ð61URP234983Ł[ Other substrates were also pyrolysed to give phosgene in this patent[
5[03[0[1[3 Laboratory methods suitable for preparing phosgene Should the laboratory preparation of phosgene be undertaken\ great care must be taken that safe handling practices are adopted[ It is well to remember that the most hazardous part of any process is often the dismantling of apparatus and disposal of residues[ The reader is urged to consult Section 5[03[0[1[1[ Some examples are shown in Scheme 1[ 〈79JOC3573〉
CO
Cl3COCOCl
Active carbon or pyridine
Cl2, Bun3PO
〈85JOC715〉 〈82JAP8292513〉
COCl2 SO3 or H2SO4
O2, hν
Cl
Cl
Cl
Cl
〈88JAP88319205〉
〈52HOU(8)84〉 〈B-56MI 614-01〉 CCl4
Scheme 2
"i# Preparation of phos`ene from carbon tetrachloride and sulfuric acid In this method\ carbon tetrachloride is dropped into 099) sulfuric acid containing 1) by weight ignited kieselguhr maintained at 019Ð029>C[ The evolved phosgene is absorbed into toluene\ in which it is extremely soluble\ whilst the hydrogen chloride produced passes through ðB!45MI 503!90Ł[
Two Similar Halo`ens
302
"ii# From carbon tetrachloride and oleum This method is essentially that of Grignard and Urbain ð08CR"058#06Ł^ however\ it is more accessible through Houben!Weyl ð41HOU"7#73Ł[ When 34) oleum is heated to 67>C and treated dropwise with carbon tetrachloride\ phosgene is evolved\ which is passed through sulfuric acid and collected "81)#[
"iii# From trichloromethyl chloroformate\ Cl2COCOCl The use of trichloromethyl chloroformate as a phosgene alternative will be dealt with in detail in Section 5[03[0[1[7[ However\ dropwise addition of trichloromethyl chloroformate to carbon tetrachloride containing a trace of pyridine gives\ after 29 min\ 89) conversion to phosgene\ with no chloroformate remaining ð71JAP7181402Ł[ The authors suggest that the less carcinogenic solvent dichloromethane should be substituted for carbon tetrachloride in this preparation[ A solution of trichloromethyl chloroformate in THF is also rapidly decomposed to phosgene by the addition of activated charcoal ð74JOC604Ł[
5[03[0[1[4 Other laboratory preparations of phosgene Four methods follow which are possibly suitable for the small!scale preparation of phosgene[ Three of these are less attractive because of special conditions employed "irradiation\ pressure# or lack of detail[ The fourth is a demonstration experiment designed for educational purposes and may not be of synthetic utility[
"i# Phosphine oxide!catalysed reaction of chlorine and carbon monoxide Workers at the Ube Chemical Industries Company have published a series of patents in which phosgene is produced in high yield "×89)# by the phosphine oxide! or sul_de!catalysed reaction of chlorine with carbon monoxide under pressure in carbon tetrachloride\ tetrachloroethane\ chlo! robenzene or dichlorobenzene ð67GEP1700209\ 79JAP79025004\ 79JAP79051304Ł[ An example of this work has appeared in a more accessible source ð68JOC2462Ł[ This reaction was carried out under a pressure of 4 kg cm−1 of carbon monoxide with tri!n!butylphosphine oxide as a catalyst[
"ii# From paraformaldehyde\ carbon tetrachloride and aluminum trichloride Carbon tetrachloride\ paraformaldehyde and aluminum chloride in the mole ratio 0 ] 9[4 ] 9[4 were warmed together at 24Ð39>C for 1Ð1[4 h\ then heated under re~ux for 9[4Ð0 h to give phosgene in quantitative yield after careful decomposition with ammonium hydroxide ð57ZPK0279Ł[ The quantity of ammonium hydroxide used is obviously crucial\ since phosgene reacts rapidly with ammonia[
"iii# Photochemical oxidation of tetrachloroethylene Air or oxygen is bubbled through tetrachloroethylene whilst irradiation is carried out using light with a wavelength of 199Ð189 nm[ This method is claimed to be very controllable and capable of producing phosgene in high yield ð77JAP77208194Ł[
"iv# Oxidation of chloroform or carbon tetrachloride usin` a platinum metal catalyst In experiments designed to demonstrate the preparation\ quanti_cation and reactions of phosgene\ chloroform or carbon tetrachloride is oxidised with oxygen in the presence of platinum metal[ The resulting phosgene is assayed by reaction with sodium iodide and titration\ and converted to crystal violet dye with dimethylaniline and aluminum chloride ð67MI 503!90Ł[
303
Carbonyl Group and at Least One Halo`en
5[03[0[1[5 Puri_cation of phosgene Phosgene from cylinders is approximately 88) pure\ the remainder comprising of carbon mon! oxide\ carbon dioxide\ air\ hydrogen chloride and water[ Laboratory phosgene prepared by some routes may also contain chlorine[ Glemser suggests that evaporation of 19) of the volume of phosgene at room temperature and pressure\ and low!temperature vacuum distillation\ with frac! tionation of the remainder leads to a very pure product ðB!52MI 503!91Ł[ Chlorine in phosgene can be detected by bubbling the gas through mercury[ Discolouration indicates the presence of chlorine\ which can be removed by passage through two washbottles containing cottonseed oil ð52OSC"3#413Ł[ A suitable method for removing bromine from carbonic bromide ~uoride involves passing the gas through irradiated trichloroethylene ð62AG"E#807Ł[ This method may also be suitable for removing chlorine from phosgene[
5[03[0[1[6 Preparation of isotopically labelled phosgene Only phosgene labelled at the carbon atom with 00C\ 02C or 03C will be covered in this section\ although other phosgenes labelled at oxygen and chlorine are known[ The authors feel that labelling at carbon is the most relevant\ particularly for the preparation of labelled drug molecules\ which is the major use of labelled phosgenes[
"i# Carbon!00!labelled phos`ene Two European groups have prepared 00C!labelled phosgene by several routes\ resulting in di}erent speci_c activities[ This isotope is a positron emitter with a half!life of only 11 min and is valuable for the study of interactions of drug molecules with receptors by positron emission tomography\ and for nuclear medicine imaging[ It is obviously necessary to prepare and use the ð00CŁCOCl1 rapidly\ and all methods use ~ow techniques to sequentially execute the various steps involved[ Early work employed bombardment of nitrogen by a cyclotron proton beam in the presence of oxygen to produce either ð00CŁCO ð67MI 503!91Ł or ð00CŁCO1 ð66MI 503!90\ 67MI 503!92Ł by the nuclear reaction 03N"pa#00C[ The latter was then reduced by zinc at 399>C to ð00CŁCO[ The ð00CŁCO was then either photochemically united with chlorine ð67MI 503!91\ 70MI 503!90Ł\ or chlorinated over platininum"IV# chloride ð66MI 503!90\ 72MI 503!90Ł at 189Ð329>C to produce ð00CŁCOCl1[ By the photolytic method\ the speci_c activity was below 099 mC mmol−0 19 min after the reaction commenced ð67MI 503!91Ł[ This was improved to 399Ð499 mC mmol−0 by employing the pla! tininum"IV# chloride route ð72MI 503!90Ł[ However\ more recently a new route involving the pro! duction of ð00CŁCH3 by bombardment of nitrogen in the presence of hydrogen has been developed[ The ð00CŁCH3 is then chlorinated by copper"II# chloride at 279>C\ and oxidized to ð00CŁCOCl1 over iron _lings ð76MI 503!90Ł[ The speci_c activity 29 min after the commencement of the process was 0399Ð0599 mC mmol−0[ Many medically useful molecules have been prepared from ð00CŁCOCl1\ including urea\ pimozide\ diphenylhydantoin\ dimethyloxazolidinedione and ketanserin ð72MI 503!90Ł[
"ii# Carbon!02!labelled phos`ene Great insight can be obtained into small moleculeÐenzyme interactions through 02C NMR studies[ For this reason\ many 02C!labelled drug molecules have been synthesized\ and several of these have employed ð02CŁCOCl1 in their preparation[ Two methods of preparation have been used\ both scaled! down versions of standard phosgene preparations[ "a# From irradiation of 02CO and chlorine[ Stoichiometric amounts of chlorine and ð02CŁCO were condensed into an evacuated ~ask and externally cooled with liquid nitrogen[ The ~ask was then allowed to warm up and was irradiated for 2 h[ A quantitative yield of ð02CŁCOCl1 was claimed^ however\ subsequent reaction gave phosgene!derived products in only 69) yield ð89MI 503!90Ł[ "b# From carbon tetrachloride and sulfuric acid[ Oleum was added dropwise to 87) sulfuric acid until a yellow colour persisted\ to give 099) sulfuric acid[ A small quantity of freshly ignited Celite was added\ followed by ð02CŁCCl3[ The mixture was heated to 039>C\ and the ð02CŁCOCl1 evolved was collected in dry toluene cooled in an iceÐsalt bath\ whilst the hydrogen chloride produced was
304
Two Similar Halo`ens
allowed to escape through a calcium chloride drying tube[ Although the gain in weight of toluene suggested almost quantitative conversion to ð02CŁCOCl1\ subsequent reaction with methanol gave phosgene!derived products in only 59) yield ð76MI 503!91Ł[
"iii# Carbon!03!labelled phos`ene In all recent applications ð03CŁCOCl1 has been purchased from one of the established sources[ However\ the methods used above for the preparation of ð00CŁCOCl1 and ð02CŁCOCl1 should also be suitable for ð03CŁCOCl1\ starting from ð03CŁCO1\ ð03CŁCO\ ð03CŁCH3 or ð03CŁCCl3[ An early preparation of ð03CŁCOCl1 from ð03CŁCO and chlorine by UV irradiation has been reported ð37JA0857Ł[
5[03[0[1[7 Phosgene alternatives There has been rising pressure to avoid the use of isocyanates\ and their precursor phosgene\ in recent years[ Since over 89) of world consumption of phosgene is in the preparation of isocyanates for polyurethane manufacture\ and a further 6) is destined for polycarbonate production\ if these plastics could be formed by alternative routes the use of phosgene worldwide would virtually cease[ As will be discussed later in this section\ the majority of phosgene alternatives suitable for the preparation of _ne chemicals are not only expensive\ but are generally derived from phosgene[ For productions purposes\ the alternatives must be cheap and must be prepared in a manner which avoids the use of hazardous reagents[ The candidate which ful_ls these criteria is dimethyl carbonate\ prepared from methanol\ oxygen and carbon monoxide in the presence of a copper catalyst at less than ,0 per pound ",1 per kilogram#[ A discussion on the replacement of phosgene by dimethyl carbonate\ and on other nonphosgene routes to isocyanates\ carbonates and urethanes was published in 0878 ðB!78MI 503!90Ł[ Several laboratory alternatives to phosgene will now be discussed[
"i# Trichloromethyl chloroformate "diphos`ene#\ Cl2COCOCl All compounds bearing the 0OCCl2 leaving group are potential phosgene sources\ and this should be borne in mind during their use and subsequent disposal[ Under many reaction conditions\ trichloromethyl chloroformate reacts with nucleophiles in such a way that the phosgene formed during the _rst acylation step is destroyed by a second molecule of the nucleophilic species at a more rapid rate than the original attack on trichloromethyl chloroformate^ thus\ 9[4 mol of the reagent is equivalent to 0[9 mol of phosgene\ the latter being present only in minute concentration during the reaction[ This leads to its common name\ {diphosgene| "Scheme 2#[ However\ there are several circumstances which lead to rapid and total conversion of trichloromethyl chloroformate into phosgene[ These include high temperature ð0776JPR88Ł or contact with iron"III# oxide ð08JPC387Ł\ activated charcoal ð74JOC604Ł or pyridine ð71JAP7181402Ł[ It must be assumed that many other commonly encountered substances will also catalyse this transformation[ Thus\ trichloromethyl chloroformate\ b[p[ 017>C\ is a stable and easy to handle alternative to phosgene^ it is widely and commercially available\ or readily prepared by chlorination of methyl chloroformate ð68OS"48#084Ł[ In many transformations\ yields are comparable to those achieved with phosgene^ however\ in some instances signi_cantly lower yields are reported ð79JOC3948Ł[ In a paper on the preparation of chiral oxazolidinones\ Pridgen et al[ list many applications for which trichloromethyl chloroformate has proved satisfactory ð78JOC2120Ł[ The authors suggest that whilst the use of this reagent will normally be much less hazardous than the use of phosgene\ the same high standard of safety precautions must be taken since there is a risk that considerable and unexpected concentrations of phosgene may be present during and after reaction[
Cl Cl
Cl O O
O Cl Nu
+
Nu
O Cl
+
Cl
O
O Cl
+ Cl–
Nu
2
+
Nu
Cl
2 ROH Scheme 3
+ 2Cl–
RO
Cl
2 Nu•HCl
305
Carbonyl Group and at Least One Halo`en
"ii# Bis"trichloromethyl# carbonate "triphos`ene#\ Cl2COCO1CCl2 The use of bis"trichloromethyl# carbonate as a phosgene alternative is a logical extension of the work described above[ This compound is a stable crystalline solid\ m[p[ 70Ð72>C\ commercially available\ or readily prepared by chlorination of dimethyl carbonate ð76AG"E#783Ł[ It has the advantage as a solid of being easy to weigh\ thus simplifying quantitative additions[ As might be predicted\ 0 mol of reagent is equivalent to 2 mol of phosgene\ although in practice this stoichiometry does not always lead to maximum yields "Scheme 3#[ Whilst no speci_c references to the extensive decomposition of bis"trichloromethyl# carbonate to phosgene have been discovered\ its similarity to trichloromethyl chloroformate strongly suggests that the same safety precautions should be employed[ O Cl3CO
Cl O
Cl
Cl
Nu
Cl
Cl
Cl
O
Cl
+
O
Nu
+
Cl–
O Cl
Nu Cl Cl– +
Cl
O
+
O
+ +Nu
Cl
Cl
Nu
O Cl
Nu
2 Nu
O
+ 3 Cl–
3 +Nu
Cl 3 ROH
O
+ 3 Nu•HCl
3 RO
Cl
Scheme 4
Eckert and Forster have described a range of applications for bis"trichloromethyl# carbonate\ encompassing most of the reactions commonly achieved by phosgene[ The yields achieved with strictly stoichiometric quantities of triphosgene range from 57) to 83) ð76AG"E#783Ł[ Subsequently\ its use in the preparation of N!carboxyanhydrides of a!amino acids ð77TL4748Ł\ a!chloro! chloroformates ð78TL1922Ł and quinazolinediones ð80SC174Ł\ all in good yields\ has been reported[
"iii# N\N?!Carbonyldiimidazole N\N?!Carbonyldiimidazole "0# appears an excellent substitute for phosgene when its role is to insert a carbonyl function between two nucleophilic groups to complete a _ve! or six!membered ring[ The nucleophilic groups can be amines\ enamines\ alcohols\ enols\ thiols or enethiols\ and the heterocycles formed may be either aromatic or nonaromatic^ the examples are numerous\ and the yields normally high[ This application is exempli_ed by formation of the cyclic carbonate from cis! cyclohexane!0\1!diol in 83) yield ð64SC36Ł\ and by benzimidazolones from o!phenylenediamines at room temperature ð45AG643\ 54JHC30Ł in yields of 79Ð89)[ The use of phosgene to perform this ring closure often requires high temperatures[ Examples of most other transformations more commonly employing phosgene are also reported for carbonyldiimidazole^ a brief selection follows[ O N
N
N
N
(1)
Symmetrical and unsymmetrical ureas can be prepared by reaction with a single amine ð45AG643Ł\ or sequentially with two di}erent amines ð80JOC780Ł[ Carbamates can result from sequential reaction
306
Two Similar Halo`ens
with an alcohol and an amine ð80JOC780Ł[ Aldoximes are converted into nitriles in quantitative yield ð71SC14Ł[ Isocyanates may be prepared from amines in good yield ð50AG55Ł[ By preparing the bismesylate salt of carbonyldiimidazole\ formamides can be dehydrated to isonitriles ð71JCR"S#68Ł[
"iv# Carbonates as phos`ene alternatives The role of dimethyl carbonate as an industrial substitute for phosgene has already been alluded to[ Such relatively unactivated molecules are used in laboratory synthesis\ but the reaction conditions are often quite harsh^ for example\ 2!aminoalkanols and diethyl carbonate give high yields of the cyclic carbamates in the presence of sodium methoxide at 019>C ð79LA011Ł[ Many more activated carbonates have been developed[ Commercially available N\N?!disuccinimidyl carbonate "1# is a very useful reagent^ a recent example of sequential reaction with complex alcohols and a complex amine to give good yields of carbamates by workers from Merck\ Sharp + Dohme is worthy of mention ð81TL1670Ł[ Bis"1!pyridyl# carbonate "2# also performs similar reactions\ and has been exploited by the same workers to form carbamates[ In this case\ even tertiary alcohols give excellent yields providing the alkoxide salt is used ð80TL3140Ł[ Examples of high!yielding ring formation by carbonyl insertion have also been reported for this reagent ð75H"13#0514Ł[ Ueda et al[ report that N\N?!"carbonyldioxy#bisbenzotriazole "3# may have similar utility ð72S897Ł[ O
O O
N O
O
O (2)
O
O
N
N O
N
O
O (3)
N
N
N
O
O
N
N N
(4)
"v# Chloroformates as phos`ene alternatives The role of tricholoromethyl chloroformate as a phosgene substitute has already been discussed[ Several other chloroformates also ful_l this role[ Amongst these\ commercially available 3!nitro! phenyl chloroformate is very useful[ The mixed carbonates formed by its reaction with alcohols are often stable to ~ash chromatography\ yet are su.ciently reactive to form carbamates with amines at room temperature ð81EUP375837Ł[ Further applications of 3!nitrophenyl chloroformate and sev! eral other bifunctional chloroformates have been reported ð82S092Ł[
5[03[0[2 Carbonic Dibromide\ COBr1 Carbonic dibromide\ also commonly called bromophosgene\ carbonyl bromide and carbonyl dibromide\ is a colourless liquid\ b[p[ 54Ð56>C ð62T2298Ł[ It is stable in the absence of light at −09>C^ however\ at higher temperature or in the presence of light\ dissociation into bromine and carbon monoxide takes place[ For this reason\ relatively little has been published on its preparation and reactions[ The _rst synthesis of pure carbonic dibromide was carried out by von Bartal in 0894 ð95LA"234#223Ł[ It is to his credit that the yield and purity of COBr1 produced by his method have not been signi_cantly improved[ The most accessible description of this preparation is that reported by Fodor and co!workers ð62T2298Ł[ Carbon tetrabromide was melted and heated to 014>C\ and concentrated sulfuric acid was added dropwise\ with vigorous stirring[ The crude distillate was freed from bromine by the passage of ethylene[ Redistillation gave pure carbonic dibromide in 57) yield[ Storage of this material\ even at low temperature\ is not advisable\ since any decomposition can lead to a buildup of pressure because of the formation of carbon monoxide[ As with all the carbonic halides\ the extreme toxicity of carbonic dibromide dictates that all procedures should be carried out in a fume hood with good extraction[ Several other preparations of carbonic dibromide have been attempted[ The thermal decompo! sition of oxalyl bromide at 049Ð044>C with subsequent cooling of the autoclave to −79>C before opening has been reported to give carbonic dibromide in a distilled yield of 19) ð02CB0315Ł[ Attempts to prepare carbonic dibromide by passing carbon monoxide over heated bromides of
307
Carbonyl Group and at Least One Halo`en
platinum and gold led only to evolution of bromine\ presumably by dissociation of carbonic dibromide at the elevated temperatures used ð29CB0110Ł[ Finally\ carbon tetrabromide has been oxidised photochemically to carbonic dibromide by molecular oxygen in the presence of bromine as a sensitizer ð26CB0979Ł[ This experiment was not designed to be of synthetic utility\ but might warrant further investigation[
5[03[0[3 Carbonic Diiodide\ COI1 The preparation of carbonic diiodide has never been successfully demonstrated[ Theoretical calculations of its thermodynamic properties ð71MI 503!91Ł and of its electronic structure ð89MI 503! 91Ł have been reported[ The dissociation temperature of carbonic dibromide is approximately −09>C ð62T2298Ł\ and for carbonic ~uoride iodide\ below −19>C ðB!52MI 503!90Ł^ thus\ carbonic diiodide would be expected to dissociate at temperatures well below this[ Attempted preparation from carbon monoxide and platinum tetraiodide led to liberation of iodine at 024>C\ well below the thermal decomposition temperature of platinum tetraiodide[ This probably indicates the for! mation and instantaneous dissociation of carbonic diiodide ð29CB0110Ł[ In a less brutal series of experiments\ Staudinger and Anthes concluded that the dissociation temperature of carbonic di! iodide was below −79>C ð02CB0315Ł[ This result was based on the formation of iodine by the reaction of oxalyl chloride and sodium iodide at low temperature[
5[03[1 CARBONYL HALIDES WITH TWO DISSIMILAR HALOGENS 5[03[1[0 One Fluorine and Chlorine\ Bromine or Iodine Function 5[03[1[0[0 Carbonic chloride ~uoride\ COClF Carbonic chloride ~uoride is a stable\ colourless gas\ b[p[ −36>C[ In company with all other carbonic dihalides\ it is extremely toxic[ The production of hydrogen ~uoride on hydrolysis is an added risk[ Some suggestions concerning the safe handling of this class of compounds can be found in Section 5[03[0[1[1[ Other names which have been used for this compound are carbonyl chloride ~uoride\ carbonyl chloro~uoride\ chlorocarbonyl ~uoride and chloro~uorophosgene[ It is not commercially available^ however\ it is of some importance in the synthesis of ~uoroformates\ which are a valuable class of intermediates[ Several methods are available for its preparation "Scheme 4#[
〈46JA1672〉 COCl2
〈73CB1752〉 COCl2 COF2
COCl2 〈48JCS2183〉 〈63JOC1639〉 〈88EUP253527〉
SbF3 or AsF3 or CaF2
HF
SOF2
∆ SiF4 or NF3
COClF
CO, –18 °C
ClF 〈B-63MI 614-01〉
〈80EGP139936〉 COCl2
∆ SO3
O2, e–
Cl2CFH 〈51MI 614-01〉 Scheme 5
COCl2 〈64JOC3007〉 〈67CB2484〉
Cl3CF 〈73AG(E)918〉 〈74GEP22611088〉 〈B-75MI 614-01〉
Two Dissimilar Halo`ens
308
"i# From carbonic dichloride "phos`ene# The _rst successful preparation of carbonic chloride ~uoride was by Emeleus and Wood\ who heated phosgene with antimony tri~uoride in a 3 ] 0 molar ratio\ with the addition of some antimony pentachloride\ at 024>C for 0 h[ The condensed product was puri_ed by low!temperature distillation\ and was isolated in 69) yield ð37JCS1072Ł[ Upon repeating this work\ Haszeldine and Iserson reported a purity of 84)\ with carbon dioxide as the major contaminant ð46JA4790Ł[ In an extension of this work\ Christie and Pavlath substituted arsenic tri~uoride for antimony tri~uoride\ achieving a yield of over 89) ð54JOC0528\ 72HOU"E3#0Ł[ An industrial gas phase process has also been patented by ICI in which phosgene is passed over calcium ~uoride at 199Ð449>C to give carbonic chloride ~uoride as the major product ð77EUP142416Ł[ Several nonmetallic ~uorinating agents have also been successfully employed[ Christie and Pavlath passed a 0 ] 0 molar ratio of phosgene and silicon tetra~uoride through a quartz tube heated at 319>C to give carbonic chloride ~uoride in quantitative yield\ with more than 39) conversion at a single pass ð53JOC2996Ł[ Glemser and Biermann obtained carbonic chloride ~uoride in 54) yield by passing nitrogen tri~uoride and phosgene in a 0 ] 1 molar ratio through a metal tube heated at 209>C[ The only other product formed was carbonic di~uoride\ with 71) conversion of phosgene[ Higher temperatures led exclusively to carbonic di~uoride ð56CB1373Ł[ Finally\ by an industrial gas phase process it is claimed that the reaction of thionyl ~uoride with phosgene over a Lewis acid catalyst at 299Ð399>C can be made to yield either carbonic di~uoride or carbonic chloride ~uoride by varying molar ratios and conditions[ The thionyl ~uoride could be regenerated by reaction of the sulfur!containing by!products with sodium ~uoride ð79EGP028825Ł[ Carbonic chloride ~uoride has also been prepared in 49) yield by reaction of phosgene with anhydrous hydrogen ~uoride at 79>C ð35JA0561Ł[
"ii# From sulfur trioxide and ~uorotrichloromethane Preparations of carbonic chloride ~uoride from phosgene inevitably involve either gas streams\ usually at high temperature\ or the use of pressure vessels[ For this reason\ its production from ~uorotrichloromethane and oleum or sulfur trioxide is much more suitable for laboratory use[ Four minor variations of this method are reported by Siegemund\ giving yields from 59) to 72)[ The reaction appears quantitative\ but total conversion of the perhalogenomethane is not achieved[ The highest yield resulted from slow treatment of sulfur trioxide with ~uorotrichloromethane ð62AG"E#807Ł^ however\ methods involving oleum may be more simple to carry out ð62AG"E#807\ 63GEP1150097\ B!64MI 503!90Ł[
"iii# From carbon monoxide and chlorine mono~uoride Carbonic chloride ~uoride is formed in 74Ð89) yield by the combination of excess carbon monoxide and chlorine mono~uoride at −07>C ðB!52MI 503!90Ł[ Small quantities of carbonic di~uoride and phosgene are also formed in this reaction\ but can readily be removed by low! temperature distillation[
"iv# Metathesis from carbonic di~uoride and phos`ene During experiments designed to prepare various perhalomethanes\ Haszeldine and Iserson fre! quently found carbonic chloride ~uoride amongst the products isolated from the co!pyrolysis of carbonic di~uoride and phosgene over carbon powder at temperatures of 399Ð349>C ð46JA4790Ł[ Subsequently\ Jackh and Sundermeyer have proposed this as a convenient synthetic method\ claiming a 29) yield of carbonic chloride ~uoride from heating a 0 ] 0 molar ratio of phosgene and carbonic di~uoride ð62CB0641Ł[ Unfortunately\ no details are given^ however\ in laboratories used to the safe handling and distillation of gases\ this preparation\ which uses two commercially available starting materials\ may be worth pursuing[
319
Carbonyl Group and at Least One Halo`en
"v# By photochemical oxidation of dichloro~uoromethane A mechanistic investigation of the chlorine sensitised photochemical oxidation of dichloro! ~uoromethane by molecular oxygen has been reported by Schumacher ð40MI50390Ł[ Whilst not suitable as a preparative method in this form\ the high yield "84)# could prove attractive to laboratories equipped to carry out photochemistry on a synthetic scale[
5[03[1[0[1 Carbonic bromide ~uoride\ COBrF Carbonic bromide ~uoride is a stable\ colourless gas\ b[p[ −10>C[ It is also commonly called bromo~uorophosgene\ carbonyl bromo~uoride and carbonyl bromide ~uoride[ It must be assumed to have the high toxicity associated with all phosgene analogues[ Carbonic bromide ~uoride has been prepared by two methods[
"i# From bromine tri~uoride and carbon monoxide Bromine tri~uoride is maintained at a temperature between 7>C and 29>C whilst a stream of carbon monoxide is passed through it[ This process must be carefully controlled\ since bromine tri~uoride solidi_es at 7>C\ and the exothermic reaction can become explosive above 29>C[ Frac! tional condensation separates the carbonic bromide ~uoride from carbonic di~uoride\ which is formed in an equimolar amount[ Redistillation gives pure carbonic bromide ~uoride in 74) yield ð45JOC0208\ B!64MI 503!90Ł[ A minor variation of this preparation is reported to give COBrF in greater than 89) yield ðB!52MI 503!90Ł[
"ii# From tribromo~uoromethane and sulfur trioxide Slow addition of tribromo~uoromethane to sulfur trioxide at 39>C yields carbonic bromide ~uoride "53)#\ contaminated with a considerable amount of sulfur dioxide[ This method also produces an equimolar amount of bromine\ which can be removed by passing the evolved gases through irradiated trichloroethylene before condensation ð62AG"E#807\ 63GEP1150097Ł[
5[03[1[0[2 Carbonic ~uoride iodide\ COFI Carbonic ~uoride iodide is a colourless gas\ b[p[ −19[5>C ðB!52MI 503!90Ł or ¦12[3>C ðB!64MI The great discrepancy between the two reported boiling points may be due to the instability of this rarely reported compound[ Above −19>C\ decomposition occurs with the liberation of iodine[ The only published synthesis involves the agitation of iodine penta~uoride under 019 atm pressure of carbon monoxide for 6 d[ The major products are carbonic di~uoride and iodine^ however\ carbonic ~uoride iodide can be isolated in 01) yield by low!temperature distillation at reduced pressure ðB!52MI 503!90\ B!64MI 503!90Ł[ 503!90Ł[
5[03[1[1 One Chlorine and Bromine or Iodine Function 5[03[1[1[0 Carbonic bromide chloride\ COBrCl Carbonic bromide chloride is a colourless gas\ b[p[ 24Ð26>C\ _rst prepared by Besson in 0784 by the reaction of phosgene with boron tribromide at 049>C ð0784BSF333Ł[ Von Bartal repeated this work ð95LA"234#223Ł\ and also reported a preparation from phosgene and aluminum tribromide ð96MI 503!90Ł[ The only other published account of the synthesis of this compound is by Garino\ who claimed that carbonic bromide chloride is formed by aerial oxidation of chlorobromoiodomethane ð15G736Ł[
310
One Halo`en 5[03[1[1[1 Carbonic chloride iodide\ COClI
Carbonic chloride iodide has never been reported\ and\ by extrapolation from the stabilities of other carbonic dihalides\ its decomposition temperature would be considerably below −19>C[
5[03[1[2 One Bromine and One Iodine Function 5[03[1[2[0 Carbonic bromide iodide\ COBrI Carbonic bromide iodide has also never been reported\ and would be expected to be unstable at temperatures considerably below −19>C[
5[03[2 CARBONYL HALIDES WITH ONE HALOGEN AND ONE OTHER HETEROATOM FUNCTION 5[03[2[0 One Halogen and One Oxygen Function Carbonyl halides with one halogen and one oxygen function are named in Chemical Abstracts as esters of the respective carbonohalidic acid^ however\ they are almost universally referred to as halogenoformates in the chemical literature\ and this nomenclature will be adopted in this section[ Other names sometimes encountered\ and exempli_ed by ethyl chloroformate\ are ethyl car! bonochloridate\ ethyl chloroformic ester\ ethoxycarbonyl chloride and ethyl chlorocarbonate[ The free parent halogenoformic acids are unknown\ but their esters are generally stable[ Chloroformates are important in the preparation of many _ne chemicals\ particularly carbamates\ which are com! monly used as amine!protecting groups in peptide chemistry[ Fluoroformates are also used to prepare such carbamates\ especially when the oxygen substituent is a tertiary alkyl group\ where the improved thermal stability relative to the corresponding chloroformate is an advantage[ One potentially valuable attribute of ~uoroformates is their stability in dipolar aprotic solvents such as DMF and DMSO^ under these conditions\ chloroformates react exothermically to form complex products[ Thus\ where insolubility is a problem\ alkoxycarbonylation with ~uoroformates in a polar medium provides an alternative[ This has been demonstrated by the protection of carbohydrates as their carbonate derivatives ð89JOC0740Ł[ Another important use of ~uoroformates is in the con! version of alcohols to their respective ~uorides by catalysed or thermally induced loss of carbon dioxide from the alcohol ~uoroformate ð44JA4922\ 54JOC3093Ł[ The carbonyl function of ~uoro! formates can also be ~uorinated with sulfur tetra~uoride to give the stable 0OCF2 moiety "Scheme 5# ð81GEP3912096Ł[ –CO2
O RO
F
SF4
RF
〈55JA5033〉 〈65JOC4104〉
ROCF3 〈92GEP4023107〉
Scheme 6
The preparation of chloroformates has been comprehensively reviewed up to 0871 ð53CRV534\ ~uoroformates have been similarly treated ðB!61MI 503!90\ 72HOU"E3#8Ł[ Bromoformates have been rarely reported\ and most aliphatic iodoformates are unstable^ some examples of aromatic iodoformates and aliphatic iodoformates with stabilising features will be discussed[ The sulfur analogues of haloformates and halothiolformates are also well known and are covered in Section 5[03[2[1[ However\ the analogous sellenium and tellurium compounds have not been described[ 72HOU"E3#8Ł^
311
Carbonyl Group and at Least One Halo`en
5[03[2[0[0 Fluoroformate esters\ ROCOF Two general methods are available for the preparation of ~uoroformates^ preparations of a!~uoroalkyl ~uoroformates and a!chloroalkyl ~uoroformates are covered separately[ The synthesis of several miscellaneous unusual ~uoroformates is also included[
"i# Preparation from alcohols or phenols and carbonic halide ~uorides This method is not very attractive as a general laboratory method since the carbonic halide ~uorides are highly toxic gases[ In addition\ only carbonic di~uoride is commercially available[ Although not usually reported\ carbonates would be formed as by!products unless a large excess of the phosgene analogue is used[ This would not hinder isolation\ however\ which is normally carried out by distillation[ Emeleus and Wood originally developed this method\ exploring the use of both carbonic di~uoride and carbonic chloride ~uoride in the presence of pyridine to prepare ethyl ~uoroformate and phenyl ~uoroformate ð37JCS1072Ł[ It is notable in this report that whilst ethyl ~uoroformate could be prepared by merely bubbling carbonic di~uoride through a solution of ethanol and pyridine in toluene\ a similar experiment with phenol led to diphenyl carbonate in quantitative yield[ However\ phenyl ~uoroformate was isolated in 49) yield when phenol and excess carbonic di~uoride were heated in benzene solution to 099>C in an autoclave[ This suggests that in the presence of pyridine\ phenyl ~uoroformate reacts much more rapidly with phenol than ethyl ~uoroformate reacts with ethanol[ In reactions involving carbonic chloride ~uoride\ only ~uoroformates were formed*no chloroformates were detected[ Emeleus and Wood also state that the ~uoroformates they prepared were more thermally stable and less rapidly hydrolysed than their chloroformate counterparts[ A patent from Merck describes the preparation of ~uoroformates from primary and secondary alcohols and carbonic di~uoride under pressure at 069>C ð81GEP3912096Ł[ A well!described method for the preparation of t!butyl ~uoroformate by Ugi and Wackerle involves the generation of carbonic chloride ~uoride from ~uorotrichloromethane and oleum\ and immediate reaction with t!butanol and triethylamine in ether ð64S487Ł[ The reported yield exceeds 89)^ t!butyl ~uoroformate is su.ciently stable to be stored\ in contrast to the corresponding chloroformate\ which is stable only at low temperature\ rapidly decomposing to t!butyl chloride and carbon dioxide[ This compound is thus a useful reagent for amine protection[ Voelter and co!workers have also exploited the same method for the preparation of ~uoroformates for use as amine protecting group precursors[ Thus\ Adpoc ~uoride "4# was prepared from 1!"0!adamantyl#propan!1!ol as a crystalline solid in 84) yield ð79CC0154Ł\ and t!Bumeoc ~uoride "5# as an unstable oil in 60) yield ð72LA137Ł[ Finally\ Olah and Kuhn have prepared alkyl ~uoroformates in good yield from primary and secondary alcohols by reaction with carbonic bromide ~uoride ð45JOC0208Ł[ This method is technically very demanding\ and in the authors| view should not be attempted[ A compilation of ~uoroformates prepared from carbonic dihalides up to 0868 has been published ð72HOU"E3#8Ł[ OCOF OCOF
But But
(5)
(6)
"ii# Preparation from chloroformates\ carbonates or carbamates and a ~uoride source "a# From chloroformates[ In cases where the chloroformate is readily available\ several excellent methods exist for transhalogenation to the corresponding ~uoroformate[ The early work of Gos! wami and Sarker ð22JIC426Ł\ extended by Nakanishi et al[ ð44JA2988Ł using thallium"I# ~uoride\ has been superseded\ and it is recommended that this method should not be attempted[ By using potassium ~uoride and a catalytic 07!crown!5 phase transfer agent\ Olofson and Cuomo were able to prepare aryl and primary and secondary alkyl ~uoroformates at room temperature in yields of 79Ð84)[ Yields were diminished by conducting the exchange at elevated temperatures\ due to
312
One Halo`en
catalysed decomposition of the products to ~uorides with the liberation of carbon dioxide ð68JOC0905Ł[ A similar method has used tetrabutylammonium ~uoride or triethylbenzylammonium chloride and potassium ~uoride to prepare primary and secondary alkyl ~uoroformates in yields ranging from 31) to 81) ð71SC402Ł[ In 0875\ Japanese workers reported that a carefully dried mixture of calcium and potassium ~uorides e}ected 84) conversion of ethyl chloroformate to ~uoroformate at room temperature in acetonitrile ð75CC682Ł[ These methods appear attractive because of their simplicity and high yields[ Other methods involving chloroformates and a ~uoride source have also been reported ð72HOU"E3#8Ł[ "b# From 0!chloroethyl carbonates[ Olofson and co!workers have developed a very general and high yielding preparation of ~uoroformates by the reaction of potassium ~uoride with 0!chloroethyl carbonates of most alcohols or phenols\ catalysed by 07!crown!5 ð89JOC0736Ł[ The reaction proceeds by ~uoride attack on the carbonate to give the ~uoroformate and the 0!chloroethoxide anion\ which eliminates chloride\ yielding acetaldehyde "Scheme 6#[ Removal of this volatile product ensures the reverse reaction does not occur[ The use of 0\1\1\1!tetrachloroethyl carbonates in this reaction also leads to high yields of ~uoroformates ð75EUP065031Ł[ The extra labour involved in preparing the 0!chloroalkyl carbonates will in many cases be amply rewarded by the versatility of this reaction^ the scope includes carbonates derived from tertiary and benzylic alcohols[ O
Cl
O Cl
ROH
Cl O
RO
O
KF, 18-crown-6
O
+ MeCHO F
RO
F– R = n-octyl, But, Ph, PhCH2 Scheme 7
"c# From alkyl carbamates[ Olah and Welch have devised a simple method for preparing primary\ secondary and tertiary alkyl ~uoroformates in yields usually between 49) and 79) by the diazo! tisation of alkyl carbamates in commercially available pyridinium poly"hydrogen ~uoride# "Scheme 7#[ Isolation is simply achieved by extraction with ether and removal of the solvent\ followed by distillation ð63S543Ł[ O RO
O
NaNO2, HF, pyridine
N2+
RO
0 °C
NH2
O
+ N2 + HF
F– RO
F
HF R = Me, Pri, But Scheme 8
"iii# Preparation of haloalkyl ~uoroformates The reaction of carbonic di~uoride with ketones proceeds by addition of its elements across the carbonyl group to yield a!~uoroalkyl ~uoroformates[ These can be stable compounds^ in the case of cyclohexanone the adduct can be isolated in 67) yield as a distillable liquid[ Not surprisingly\ thermal or boron tri~uoride!catalysed decomposition of these adducts yields `eminal di~uoro derivatives and carbon dioxide "Scheme 8# ð51JA3164Ł[ In a more complex manner\ reaction of carbonic di~uoride with DMSO yields ~uoromethyl ~uoroformate in 27) yield[ This reaction probably proceeds by an initial Pummerer rearrangement\ but the mechanism of the subsequent steps is not clear ð74JFC"17#108Ł[ The formation of v!chloroalkyl ~uoroformates by the reaction of carbonic chloride ~uoride with
O
F COF2
F OCOF
∆ or BF3 –CO2
Scheme 9
F
313
Carbonyl Group and at Least One Halo`en
cyclic ethers has also been reported[ Excellent yields are obtained with oxirane\ oxetane and tetrahydrofuran in the presence of tri!n!butylamine[ Tetrahydropyran also gives the corresponding product\ but in much lower yield "Equation "0## ð54JOC0528Ł[ Carbonic di~uoride does not follow the same reaction course with oxirane\ instead giving 1!"tri~uoromethoxy#ethyl ~uoroformate\ CF2O"CH1#1OCOF[ Larger ring sizes do not appear to have been studied ð53JOC00Ł[ O Cl
(CH2)n
O
O
F, n-Bu3N n = 2–5
Cl
( )
(1)
n
O
F
"iv# Miscellaneous ~uoroformates Tri~uoromethyl ~uoroformate\ CF2OCOF\ was formed in poor yield "04)# from the reaction of carbonic di~uoride with cyanogen ~uoride at low temperature[ A possible mechanism has been proposed ð70JFC"07#148Ł[ This compound has also been prepared in high yield by the insertion of carbon monoxide into tri~uoromethyl hypo~uorite under photochemical conditions ð54CC130Ł[ The _nal three preparations in this section are included to exemplify unusual ~uoroformates which have been reported[ The authors suggest that these preparations are too hazardous to be undertaken except in laboratories where the handling of unpredictably explosive compounds is routine[ Bis"~uoroformyl# peroxide has been studied by several groups as a radical source[ It is prepared by mixing streams of oxygen\ carbon monoxide and ~uorine in precise proportions[ Powerful explosions result if the conditions deviate from those reported ð61IC1420Ł[ Reaction of bis"~uoro! formyl# peroxide with a caesium ~uoride for a prolonged period at −39>C gave tri~uoromethyl ~uoroformyl peroxide in 38) yield\ b[p[ −05>C[ A mechanism has been suggested ð61IC1420Ł[ A low yield of the primitive ~uoroformate ~uorocarbonyl hypo~uorite can be prepared from bis"~uoroformyl# peroxide and ~uorine under UV irradiation and puri_ed by fractional distillation\ m[p[ −030>C\ b[p[ −44>C ð56JA4050Ł[ Reaction of ~uorocarbonyl hypo~uorite with sulfur tetra~uoride under irradiation leads to a low yield of the unusual penta~uorosulfur ~uoroformate ð56JA4050Ł[ These reactions are summarised in Scheme 09[ O CsF
O O2 + CO + F2
F
O O
F3C
O
O
F
–40 °C
O
F O
F2, hν
O SF4, hν
FO
F
F5SO
F
Scheme 10
5[03[2[0[1 Preparation of chloroformate esters\ ROCOCl "i# From alcohols and phos`ene Chloroformates are most commonly prepared from an alcohol or phenol and phosgene\ under a variety of conditions[ This method of synthesis has been thoroughly reviewed up to 0871 ð41HOU"7#090\ 53CRV534\ 72HOU"E3#8Ł[ The authors will\ therefore\ restrict discussion to some general comments and recent modi_cations or extensions[ The articles cited above contain references to numerous examples of aliphatic ð53CRV534Ł and aromatic ð53CRV534\ 72HOU"E3#8Ł chloroformates made by this method[ Although the use of phosgene can often be avoided by the use of various mixed carbonates or phosgene equivalents "see Section 5[03[0[1[7#\ it is sometimes the best or most convenient method for the preparation of chloroformates on a laboratory scale[ Strict adherence to safe working procedures must be practised at all times\ especially during workup procedures\ since an excess of phosgene is often used "see Section 5[03[0[1[1#[
314
One Halo`en
Primary and secondary alcohols can react with phosgene to form chloroformates in the absence of a base[ An excess of phosgene is often employed\ which\ together with low temperatures "usually room temperature or below#\ reduces the formation of carbonates formed by reaction of a further molecule of alcohol with the initially formed chloroformate[ On a laboratory scale\ commercially available 19) phosgene in toluene is a safe and convenient source of this reagent[ Many solvents have been used\ the only requirement being that they do not react rapidly with phosgene\ or with the chloroformate produced[ DMF and DMSO cannot be used for this reason "see Section 5[03[2[0#^ however\ high yields have been recorded in the presence of considerable concentrations of water ð63MIP50300Ł[ The use of a molar equivalent of a tertiary base\ most often triethylamine\ pyridine or dimethylaniline\ is often advantageous\ enabling the quantity of phosgene used to be reduced\ and allowing reaction in the presence of acid!sensitive groups which would be otherwise destroyed by the hydrogen chloride produced as formation of the chloroformate proceeds[ The addition of a tertiary base\ or preformation of the alcoholate anion\ is generally essential for the successful preparation of tertiary chloroformates^ they are also often thermally unstable\ undergoing quite clean decomposition to the tertiary alkyl halide and carbon dioxide at or below room temperature ð70JOC0619Ł[ This occurs to a greater or lesser degree with retention of con_guration in the case of optically active alcohol substrates ð71JOC2410\ 75JOC0079Ł[ This complication can be avoided by substituting the corresponding tertiary ~uoroformate\ which is much more thermally stable "see Section 5[03[2[0#[ Phenols do not generally react with phosgene at room temperature in the absence of an acid acceptor[ Good yields can\ however\ be achieved in chlorobenzene at 015>C with the addition of a catalytic quantity of stearyltrimethylammonium chloride[ The reaction will proceed slowly even at room temperature ð54CI"L#680Ł[ In the presence of a base such as dimethylaniline\ reaction is often rapid and complete at 9>C ð56JOC299Ł[ Examples of the use of a two!phase system using concentrated aqueous sodium hydroxide as the base are well described in Houben!Weyl ð72HOU"E3#8Ł[ A few examples will now be discussed that illustrate a particular point\ or which may prove to be useful extensions of the reaction of alcohols with phosgene[ Tertiary chloroformates bearing an electron!withdrawing group on the a carbon atom are ther! mally stable and apparently more resistant to hydrolysis than their unsubstituted analogues ð60JOU0832\ 67AG"E#250Ł[ Notwithstanding\ a satisfactory preparation of t!butyl chloroformate has been reported[ By working at low temperature it proved possible to prepare t!butyl chloroformate from potassium t!butoxide and phosgene in a distilled yield of 50)[ This material showed no evidence of decomposition after 1 months of storage at −14>C ð70JOC0619Ł[ At the other extreme\ primary and secondary alkyl chloroformates have been prepared from the corresponding alcohols and phosgene in good yield in the vapour phase under continuous ~ow conditions\ using a reaction time of 2Ð3 s at 099Ð149>C ð40JA2685Ł[ This method might form the basis of an industrial process[ The problem of completely removing the tertiary base and its hydrochloride from chloroformates which cannot be distilled because of scale or instability may have been resolved by Dreiding and Egli\ who employed poly"3!vinylpyridine# as an acid acceptor to prepare chloroformate "6# in excellent yield "Equation "1## ð75HCA0331Ł[ In this case\ the use of triethylamine caused partial decomposition of the product[ During the preparation of a specialised amine!protecting group in the "a!~uorenyl#methoxycarbonyl "Fmoc# family\ Ramage and Raphy found that the modi_ed ~uorenylmethyl chloroformate could not be prepared by reaction of phosgene with the hydroxy! methyl~uorene in the presence of base because of spontaneous fragmentation to the corres! ponding alkene[ This was overcome by converting the alcohol into the O!trimethylsilyl ether\ which with phosgene gave the chloroformate under neutral conditions "Scheme 00# ð81TL274Ł[ Finally\ chloroformate preparation using phosgene generated in situ has been reported[ In a method which may be of industrial signi_cance\ Japanese workers treated butanol with chlorine and carbon monoxide in the presence of phosphine oxides at room temperature at 59 kg cm−1 pressure to give a 82) yield of butyl chloroformate ð68JAP6850010Ł[ On a laboratory scale\ should the preparation of a chloroformate using diphosgene "see Section 5[03[0[1[7# prove unsatisfactory\ addition of activated charcoal to the reaction will decompose the diphosgene completely to phosgene in solution[ This method has been used to advantage in the preparation of carbamoyl chlorides\ and should also be applicable to chloroformates ð74JOC604\ 89JMC1090Ł[ OH
OCOCl COCl2, poly(4-vinylpyridine), 0 °C
O
O
(2) O
H
O
H (7)
315
Carbonyl Group and at Least One Halo`en NEt3 H Tbf
COCl2
O
O Tbf
Cl
OH O
Tbf O-TMS
TMS-Cl
Tbf
Tbf
COCl2 –TMS-Cl
O Tbf
Cl
=
Scheme 11
A series of chiral chloroformates has been prepared for the separation of optically active amines by derivatization and reverse!phase liquid chromatography[ Formation from the respective alcohols with phosgene in the presence of triethylamine proceeded in all cases without detectable racemization ð89JC482Ł[ Some representative structures\ "7#\ "8# and "09#\ are shown[ Finally\ the chloroformate of cyclic peroxide 2!hydroxymethyldioxetane "00# has been prepared with phosgene and pyridine in the standard way[ In common with many less exotic chloroformates\ it is stable to ~ash chro! matography on silica ð75S229Ł[ OCOCl O O
OCOCl CO2But (8)
OCOCl
O
OCOCl O
ONO2 (9)
(10)
(11)
"ii# From alcohols and diphos`ene or triphos`ene The roles of diphosgene and triphosgene as alternatives to phosgene have already been explored "see Section 5[03[0[1[7#[ Konakahora et al[ have described the preparation of several sensitive chloroformates using these reagents\ and they discuss the e}ect of tertiary base nucleophilicity on the yield obtained ð82S092Ł[ A potentially useful modi_cation of this method has been developed by Japanese workers\ who were able to prepare the chloroformate "01# in high yield using an in situ two!step procedure[ Initial treatment of the alcohol with diphosgene and a tertiary base gave a large amount of the corresponding carbonate[ This was avoided by _rst treating the alcohol with two equivalents of diphosgene in the absence of base to give a 0 ] 0 mixture of chloroformate and carbonate[ Addition of a catalytic amount of pyridine to this mixture converted the carbonate to chloroformate\ leading to its formation in an overall 67) yield "Scheme 01# ð80TL3260Ł[ The use of diphosgene and triphosgene in chloroformylation has been reviewed ð78MI 503!93\ 89MI 503!92Ł[
"iii# By chlorination of ROC"1X#Y compounds "X\ Y S or O# The chlorination of a variety of carbonates\ xanthates and thionoesters leads to chloroformates ð53CRV534Ł[ These methods are generally not of great synthetic importance because the starting materials are usually less available than the corresponding alcohol\ which is more commonly used for chloroformate synthesis[ In instances where attempts to form a chloroformate led only to the symmetrical carbonate\ treatment of the latter with thionyl chloride or phosphorus pentachloride may o}er a useful method of recovering the situation "Equation "2##[ Certain alcohols cannot readily
316
One Halo`en O OH
O
Cl3COCOCl
O
Nu– O
Cl
O
+ 3 Cl–
+
3 Nu = pyridine
1 : 1 Nu
O
Cl
O O
O–
Nu+
O
O O
Cl Cl
O
Cl
Cl–
+ COCl2 + Cl–
O
Cl
Cl
(12) Scheme 12
be converted to chloroformates with phosgene in the presence of base because of chemical instability[ These include alcohols with a b electron!withdrawing group[ A high!yielding method of preparing chloroformates from alcohols of this type has been devised by Gilligan and Sta}ord\ who _rst converted the alcohol to O!alkyl S!ethyl thiocarbonate with commercially available S!ethyl car! bonochloridothioate in the presence of iron"III# chloride[ This product is then treated with sulfuryl chloride to provide the chloroformate in high yield "Scheme 02# ð68S599Ł[ Some of the alcohols described in this report contained b!nitro or b\b!dinitro functions^ compounds of this type present a serious explosion hazard and should only be handled in laboratories equipped to deal with such eventualities[ However\ this method is probably quite general^ it could also prove valuable in avoiding the symmetrical carbonate by!products which often reduce yields in chloroformate synthesis[ O
O
(3)
Cl
RO
EWG
EtSCOCl
OH
+ RCl + SO2
OR
RO
EWG
O
SOCl2
SEt
SO2Cl2
O
EWG
O EWG = electron-withdrawing group
Cl O
Scheme 13
Another use of this method is described by Folkmann and Lund in the preparation of acyl! oxymethyl chloroformates as precursors of pharmaceutical pro!drugs[ In this case\ chlorination of the intermediate thiocarbonate "02# is best achieved by sulfuryl chloride at room temperature in the presence of BF2 = Et1O^ chlorine will also perform this cleavage "Equation "3## ð89S0048Ł[ O
O R1
O
O
SR2
O
O
SO2Cl2, BF3•OEt2, 0 °C
(4) R1
O
O
Cl
(13)
"iv# By electrophilic substitution of chloroformates containin` aromatic rin`s A variety of aromatic electrophilic substitutions have been carried out on compounds in which the chloroformate group is already present[ In the search for new amine!protecting groups in the
317
Carbonyl Group and at Least One Halo`en
Fmoc family\ Carpino brominated "8!~uorenyl#methyl chloroformate in the presence of iron"III# chloride to give the 1\6!dibromo analogue in 26) yield ð79JOC3149Ł[ Nitration of 3!methylphenyl chloroformate is reported to give 3!methyl!2!nitrophenyl chloroformate "76)# ð79GEP1819275Ł[ Phenyl chloroformate has been converted into its 3!sulfonic acid analogue by sulfur trioxide in a similarly high yield ð80EUP304362Ł[ "v# Other methods Hypochlorites bearing electron!withdrawing groups undergo carbon monoxide insertion into the O0Cl bond at low temperatures to give chloroformates in excellent yield[ Thus\ a series of per~uoroalkyl hypochlorites gave per~uoroalkyl chloroformates in quantitative yield ð58TL612Ł[ Chlorine tri~uoromethanesulfonate "03# also undergoes a similar reaction to give the mixed anhy! dride "04# in 71) yield "Equation "4## ð71JFC"08#116Ł[ CO, –110–0 °C
ClOSO2CF3
(5)
ClCO2SO2CF3
(14)
(15)
Electrophilic carbonylation of several substrates has been performed by treating an equimolar mixture of bromine and antimony pentachloride with carbon monoxide in liquid sulfur dioxide to yield the chloro!oxocarbonium ion "05#\ which can be captured by ethanol to give ethyl chloro! formate "Scheme 03# ð62TL1176Ł[ Br2 + SbCl5 + CO
liquid SO2
[BrCO]+ [SbCl5Br]–
[ClCO]+ [SbCl4Br2]– (16)
ROH
ROCOCl + H+ [SbCl4Br2]– Scheme 14
Two methods of preparing methyl chloroformate from palladium bis"methoxycarbonyl# com! plexes have been reported ð82JOM"340#132Ł[ Since in these complexes the methoxycarbonyl ligand is obtained by treatment of a simple palladium complex with carbon monoxide in methanol\ and the chlorine atom for the decomposition step is supplied by copper"II# chloride or chlorine\ it is possible that this could form the basis of a catalytic preparation[ "vi# Preparation of halo`enated chloroformates "a# a!Haloalkyl chloroformates[ Two important compounds in this class are commercially avail! able] trichloromethyl chloroformate\ which has been already discussed as a phosgene alternative "see Section 5[03[0[1[7#\ and a!chloroethyl chloroformate\ which has found use in the N!dealkylation of tertiary amines ð73JOC1970Ł[ The preparation of mono!a!chloroalkyl chloroformates can be carried out most conveniently by the reaction of phosgene ð73JOC1970Ł\ or a phosgene equivalent ð78TL1922Ł\ with an aldehyde at or below room temperature "Scheme 04#[ Formaldehyde ð72GEP2130457Ł and benzaldehyde ð72HOU"E3#8Ł also undergo this reaction\ but it has not been reported for ketones[ Alternatively\ chloroformates bearing a hydrogen atoms can be readily chlori! nated photochemically[ Whilst this is an excellent method of preparing trichloromethyl chloro! formate ð68OS"48#084Ł\ and presumably other fully a!chloro!substituted chloroformates\ attempts to prepare partially a!chlorinated compounds result in the formation of mixtures[ Thus\ partial chlorination of methyl chloroformate yields both chloromethyl chloroformate and dichloromethyl chloroformate\ which can be isolated in moderate yield by fractional distillation[ These compounds can be freed from associated trichloromethyl chloroformate by treatment with charcoal\ when only the latter decomposes to phosgene ð89S0048Ł[ An alternative radical chlorination employing sulfuryl chloride can also be used to prepare a!chloroethyl chloroformate in 40) yield ð80JAN0972Ł[ RCHO + COCl2 R RCH2OCOCl
O
Cl SO2Cl2
R = H, alkyl, Ph Scheme 15
O
Cl
318
One Halo`en
"b# b!Chloroalkyl chloroformates[ The preparation of b!chloroalkyl chloroformates is well described ð72HOU"E3#8Ł[ The most general method involves pyridine!catalysed addition of phosgene to an oxirane\ _rst described by Malinovsky and Modyantseva ð42JGU118Ł[ The reaction usually proceeds regiospeci_cally with unsymmetrical oxiranes to give the product with the chlorine on the less substituted carbon atom "Equation "5## ð42JGU118\ 46JCS1624Ł[ Several b!chloroalkyl chloro! formates have also been prepared by addition of chlorine to chloroformates bearing allyl or propargyl groups ð48JAP483153Ł[ Treatment of ethylene carbonate with phosphorus"V# chloride also gives b!chloroethyl chloroformate in high yield ð50CB433Ł[ O
R1
COCl2, pyridine
R3
R2 O
R1 Cl
R2
O
(6)
Cl
R3
"vii# Preparation of enol chloroformates\ R0R1C1CR2OCOCl The simplest member of this class\ vinyl chloroformate\ was the _rst to be prepared\ by pyrolysis of ethylene glycol bis"chloroformate#[ This has been well described by Lee\ who was able to achieve a moderate yield using a ~ow process ð54JA2832Ł[ An earlier report describing 1!propenyl chloroformate ð23JA1996Ł has been reinvestigated by Olofson et al[\ who could not reproduce the work ð67JOC641Ł[ This group has subsequently carried out the majority of work in this area[ The _rst general synthesis emerged after failure to trap enolates prepared by many methods with phosgene[ The reaction of ethyl 1!propenyl ether with mercury"II# oxide gave di"ace! tonyl#mercury"II# in quantitative yield[ Reaction with phosgene at 9Ð14>C led to 1!propenyl chloro! formate in 75) distilled yield "Scheme 05# ð67JOC641Ł[ Another method of some generality has since been developed[ Initially\ Olofson and co!workers developed a simple and convenient synthesis of 1\1!dichlorovinyl chloroformate by zinc dehalogenation of the adduct between phosgene and trichloroacetaldehyde "Scheme 06# ð89JOC1139Ł[ Subsequently they have increased the scope of this method to the preparation of other enol chloroformates ð89JOC4871Ł[ OEt
O HgO, Hg(OAc)2
(MeCOCH2)2Hg
COCl2
O Cl
Scheme 16
Cl3CCHO
Cl3C
O
O
Cl
COCl2
O
Cl
Zn
O Cl
Cl Cl
Scheme 17
The corresponding imidate chloroformates "06#\ derived from secondary amides and phosgene\ have also been reported "Equation "6## ð72HOU"E3#8Ł[ O ButNHCOMe
COCl2
O ButN
(7) Cl •HCl
(17)
"viii# Preparation of oxime chloroformates\ R0R1C1NOCOCl Chloroformates derived from oximes and their tautomeric C!nitroso compounds have been used as intermediates in the preparation of oxime carbonates\ which have been suggested as t!butoxycarbonylating agents ð66BCJ607Ł and as precursors to photolabile amine!protecting groups ð78TL0890Ł[ The oxime chloroformates were prepared in the standard way from the oxime and
329
Carbonyl Group and at Least One Halo`en
phosgene or trichloromethyl chloroformate with pyridine or N\N!dimethylaniline\ in inert solvents "Equation "7##[ R1
R1
COCl2
NOH
NOCOCl
R2
(8)
R2
Conversion of the nitroso compound "07# to a mixture of "E#! and "Z#!oxime chloroformates "19# was accomplished by _rst treating "07# with TMS!Cl and zinc to give the silyl protected oxime "08#\ followed by subsequent reaction with phosgene "Scheme 07# ð78IZV1738Ł[ Cl N O
Zn, TMS-Cl
COCl2
NO-TMS
Cl
NOCOCl
Cl (18)
Cl (19)
(20)
Scheme 18
"ix# Formation of chloroformic acid anhydrides Anhydrides of chloroformic acid with both carboxylic and sulfonic acids have been reported[ They are prepared at low temperatures\ and are very reactive[ Amino acids protected as their N!benzyloxycarbonyl derivatives form anhydrides on reaction with phosgene and triethylamine at −69>C ð46HCA593Ł[ These anhydrides react with alcohols at −69>C to form esters[ Reaction of unprotected amino acids with phosgene or bis"trichloromethyl# carbonate "triphosgene# without base at room temperature yields the cyclic amino acid carboxyanhydrides[ Since the amino group of the amino acid is protonated to a great extent under these conditions\ it is possible that a similar anhydride formed by reaction of the carboxylate with phosgene is initially formed\ followed by ring closure onto the amine function "Scheme 08# ð77TL4748Ł[ R1
R1
R1
COCl2, Et3N
CbzNH
CO2H
Cl
O
CbzNH
–70 °C
O
R2OH
CbzNH
CO2R2
O O
NH3+ BnO2C
HN
Cl3COCOCl –
CO2
50 °C
O BnO2C O
Scheme 19
The anhydride of chloroformic acid and tri~uoromethanesulfonic acid is formed by insertion of carbon monoxide into the O0Cl bond of chlorine tri~uoromethanesulfonate at low temperature "see Equation "4## ð71JFC"08#116Ł[
"x# Miscellaneous unusual chloroformates The 06O NMR spectrum of the peroxy chloroformate "10# has been reported[ This compound was prepared from t!butyl hydroperoxide\ presumably by reaction with phosgene\ and is stable at room temperature ð76TL5332Ł[ ButOOCOCl (21)
Also reported is the reaction of phosgene with Hg"OSeF4#1 to give stable chlorocarbonyl penta! ~uoroselenate\ ClCOOSeF4 ð70ZAAC"361#15Ł[ The corresponding ~uorocarbonyl derivative has been known for some time ð62IC658Ł\ but was prepared by the reaction of FOSeF4 with carbon monoxide[
320
One Halo`en 5[03[2[0[2 Preparation of bromoformate esters\ ROCOBr
Bromoformates are poorly represented in the chemical literature[ Rosenmund and Doring pre! pared several alkyl bromoformates and benzyl bromoformate by the reaction of the appropriate alcohols with carbonic dibromide\ and reported that they tended to decompose within a few days ð17AP"155#166Ł[ A much more convenient method involves halogen exchange between the corresponding chloroformate and anhydrous hydrogen bromide in methylene chloride\ catalysed by tetrabutylammonium bromide[ In this manner\ very high distilled yields of phenyl bromoformate and 1\1\1!trichloroethyl bromoformate were achieved ð77S396Ł[
5[03[2[0[3 Preparation of iodoformates\ ROCOI Stable iodoformates have only been prepared in the last 19 years[ In general\ they require some steric or electronic feature to render them su.ciently stable to allow their isolation[ Thus\ attempts to form the iodoformate from cholesteryl chloroformate and sodium iodide led to 2!iodocholesterol in 49) yield\ presumably by decomposition of the unstable intermediate iodoformate ð56JOC1522Ł[ Ho}mann and Iranshahi report that attempts to isolate iodoformates by halogen exchange were unsuccessful with unhindered primary\ secondary or benzyl chloroformates ð73JOC0063Ł[ The _rst stable iodoformate was prepared by irradiation of 8!triptycyl hydrogen oxalate "11# in the presence of iodine and mercury"II# oxide[ The 8!triptycyl iodoformate "12# proved to be very stable to loss of carbon dioxide\ only decomposing to give 8!iodotriptycene "13# at 159>C "Scheme 19#[ This would be expected for an ionic reaction occurring at the bridgehead carbon ð60JCS"C#2655Ł[ Subsequently\ a range of carefully chosen iodoformates was prepared in high yield from the corresponding chloroformates by halogen exchange with sodium iodide in acetonitrile "Table 0#[ They could be stored at −19>C over copper powder[ Phenyl iodoformate was su.ciently stable to be distilled at 57>C and 0 torr\ and underwent reaction with copper"I# cyanide to give the corresponding cyano! formate in good yield ð73JOC0063Ł[ O = Trip
Trip
O
I2, HgO, hν
OH
55%
Trip
O (22)
O
I
260 °C
Trip
I
–CO2
O (23)
(24)
Scheme 20
Table 0 Formation of iodoformates from chloroformates[ ROCOCl R
NaI, MeCN
ROCOI
Temperature (°C)
Yield (%)
CH2=CH
25
80
Ph
70
85
ButCH2
70
75
25
64
5[03[2[1 One Halogen and One Sulfur Function Care should be exercised when searching or naming compounds of this class\ RSCOHal\ because confusion can sometimes arise over the nature of the connectivity[ It is not always clear whether the acid component is connected to the alcohol or thiol by a C0S or C0O bond[ This ambiguity is circumvented by the Chemical Abstracts nomenclature^ the title compounds are named as car!
321
Carbonyl Group and at Least One Halo`en
bonohalidothioic acid S!esters[ Alternative names are formic acid halothio!S!esters or halo! thiolformate esters[ For convenience\ the last name will be used throughout this work[ However\ many examples also exist where the sulfur atom is connected to atoms other than an alkyl or aryl carbon^ these can no longer be regarded as halothiolformates\ and are named appropriately as they occur\ for example chlorocarbonylsulfenyl chloride\ ClCOSCl[
5[03[2[1[0 Fluorothiolformate esters\ RSCOF Several general methods of synthesis of ~uorothiolformate esters are described by Heywang ð72HOU"E3#8Ł^ latterly\ publication in this area has been dominated by Haas and Della Vedova ð80ZAAC"599#034Ł\ however their work has emphasized inorganic and spectroscopic aspects\ so it will not be covered in depth here[
"i# Preparation from carbonic dihalides and thiols or thiophenols Thiols and thiophenols react with carbonic chloride ~uoride and carbonic bromide ~uoride in the presence of base to give ~uorothiolformate esters in good yields ð54JOC0206Ł[ It is also reported that tri~uoromethyl disul_de\ CF2SSH\ reacts with carbonic di~uoride in the presence of potassium ~uoride at −14>C to give CF2SSCOF in 44) yield ð65JA5434Ł[ If the scope of this reaction can be extended to include thiols and thiophenols this could be a more convenient route\ since carbonic di~uoride is commercially available[
"ii# Preparation from chlorothiolformates The treatment of chlorothiolformate esters with hydrogen ~uoride at room temperature gives excellent yields of ~uorothiolformate esters by halogen exchange ð54JOC0206Ł[
"iii# Preparation from ~uorocarbonylsulfenyl chloride and bromide\ FCOSHal Fluorocarbonylsulfenyl halides react with a wide range of nucleophiles by displacement of the halogen from the sulfenyl halide function ð56AG"E#694\ 58CB1607\ 69AG"E#355\ 62JFC"2#272\ 80SA"A#0508\ 80ZAAC"599#034Ł[ Some of these reactions are summarized in Scheme 10[ Fluorocarbonylsulfenyl chloride is itself prepared by treating chlorocarbonylsulfenyl chloride with antimony tri~uoride in sulfolane at 89>C ð58CB1607Ł\ whilst ~uorocarbonylsulfenyl bromide is prepared from ~uoro! carbonylsulfenyl chloride by reaction with trimethylsilyl bromide ð80ZAAC"599#034Ł[ A comparison of the reactivities of chlorocarbonylsulfenyl chloride and ~uorocarbonylsulfenyl chloride with amines shows that chlorocarbonylsulfenyl chloride initially reacts at the carbonyl group\ whilst ~uoro! carbonylsulfenyl chloride reacts at the sulfur atom ð62JFC"2#272Ł[
"iv# Rearran`ement of aryl ~uorothionoformates As the key step in the preparation of thiophenols from phenols\ aryl ~uorothionoformates are thermally rearranged to ~uorothiolformates at temperatures of 199Ð499>C "Equation "8## ð77USP3643961Ł[ O
F
∆, 200–500 °C
S
S
F (9) O
"v# Reaction of FCOSCl with electron!rich aromatic systems Fluorocarbonylsulfenyl chloride reacts with pyrrole in the presence of pyridine at −19>C to give 1!pyrrolyl ~uorothiolformate in 68) yield ð66CB56Ł^ however\ whilst chlorocarbonylsulfenyl
322
One Halo`en
〈69CB2718〉 〈67AG(E)705〉
O NCS F 〈69CB2718〉 〈67AG(E)705〉 O F
S
F
S
S
F
S
〈70AG(E)466〉 〈73JFC(3)383〉
F O
RSH
SCN
H 2S
S
F
AgCN
H2O
O
O
AgCO2CF3
CF3 S O 〈70AG(E)466〉 〈73JFC(3)383〉 O F
Cl
F, hν
F
F3C
R1
O F
H N
S
R2
F
TMS-NSO
O R2
〈73JFC(3)383〉 F
N S H
F
S O
F
S
S N
R1
O
S
S
AgOCN
–CO2
Cl
Cl
F, hν
F3CS Cl
O S N H
〈70AG(E)466〉
SCl(or Br)
F
SNCO
CF3
(CF3)2Hg S
O
〈69CB2718〉 〈67AG(E)705〉
F
O
O SSR
F
SCN
–CO2
O F
O
SCF3 hν
〈91ZAAC145〉
O
AgSCN
O F
〈91SA(A)1619〉 〈91ZAAC145〉 〈73JFC(3)383〉
S
F
S O
S
Cl
SNSO
F
F
F
F
F
S
〈70AG(E)466〉
O 〈70AG(E)466〉
〈91ZAAC145〉 Scheme 21
chloride undergoes the analogous reaction with thiophene in the presence of tin"IV# chloride\ the ~uorocarbonyl analogue is prepared by reaction of ~uorocarbonylsulfenyl chloride with thi! enylmagnesium bromide only in poor yield "Equation "09## ð65CB1364Ł[ O ClSCOF
X
R
X
S
X = S; R = MgBr X = NH; R = H
F
(10)
"vi# Preparation of b!~uoroalkyl ~uorothiolformates Compounds of the structure "14# have been reported to undergo chlorineÐ~uorine exchange with spontaneous rearrangement in the presence of hydrogen ~uoride at −09>C to give b!~uoroalkyl ~uorothiolformates "Equation "00## ð77JFC"39#254Ł[ The reaction appears quite general\ but yields vary in the range 29Ð59)[ O R
F S
Hal F
Hal
HF, –10 °C
R
F S
F
Hal = Cl, F
(11)
O
(25)
"vii# Other methods Penta~uorosulfur carbonyl ~uoride F4SCOF has been prepared in low yield "09Ð04)#\ by the irradiation of oxalyl ~uoride in the presence of disulfur deca~uoride\ F4SSF4\ or penta~uorosulfur hypo~uorite F4SOF[ It appears to be a water!sensitive\ stable gas "b[p[ −09>C\ approximately#^ the structure is supported by extensive spectroscopic and analytical evidence ð57JA2843Ł[
323
Carbonyl Group and at Least One Halo`en
5[03[2[1[1 Chlorothiolformate esters\ RSCOCl The preparation of chlorothiolformates has been thoroughly reviewed by Heywang up to 0871 ð72HOU"E3#8Ł[ This section will thus brie~y cover the principal methods\ supplemented by any relevant material[
"i# Preparation from thiols or thiophenols and phos`ene The overwhelming majority of alkyl or aryl chlorothiolformates are prepared from the cor! responding thiol or thiophenol or its sodium salt\ and phosgene ð72HOU"E3#8Ł[ If the sodium salt is not used\ active carbon\ or an organic base such as triethylamine ð77EJM"12#450Ł\ pyridine ð66JOC2575Ł or dimethylaniline ð60BCJ1404Ł is often added\ but the reaction will usually proceed in the absence of base ð73ZAAC"497#025Ł[ Many literature examples employ a considerable excess of phosgene\ often many times the theoretical amount necessary[ There is no evidence to suggest that this practice leads to increased yields providing a base is present\ and it should be vigorously discouraged on the grounds of safety[ The replacement of phosgene by trichloromethyl chloro! formate has also been successfully achieved ð74JHC0532Ł[ In this report\ sodium hydride was used to prepare heterocyclic thiol sodium salts in situ[ This is usually more convenient than forming the salt using aqueous sodium hydroxide followed by precipitation and drying ð62BCJ0158Ł[ It appears that chlorothiolformates may be more thermally stable than their chloroformate counterparts^ t!butyl chlorothiolformate can be distilled at 32>C and stored for several weeks at 3>C without signs of decomposition ð66JOC2575Ł[
"ii# Preparation from sulfenyl chlorides and carbon monoxide Alkyl and aryl sulfenyl chlorides are converted to chlorothiolformate esters in high yield when treated with carbon monoxide at pressures of 69Ð399 bars[ Electronegatively substituted sulfenyl chlorides such as 1\3!dinitrobenzenesulfenyl chloride and trichloromethanesulfenyl chloride failed to react under these conditions ð57CC416Ł[
"iii# Preparation from thiiranes and phos`ene Ring opening of thiiranes with phosgene under pyridine catalysis gives b!chloroalkyl chloro! thiolformate esters in a manner analogous to the corresponding reactions with oxiranes "Equation "01## ð72HOU"E3#8Ł^ however\ the regioselectivity may not be the same[ S COCl2 +
Cl pyridine
R R
S
Cl
(12)
O
"iv# Preparation by controlled hydrolysis of trichloromethanethiol derivatives Trichloromethanesulfenyl chloride can be hydrolysed in good yield to chlorocarbonylsulfenyl chloride\ ClCOSCl\ by treatment with sulfuric acid containing the calculated quantity of water ð53GEP0113619Ł[ This method has also been employed in the preparation of bis"chlorocarbonyl# disul_de from bis"trichloromethyl# disul_de ð62CL0204Ł^ however\ other workers have had di.culty reproducing this result ð72JOC3649Ł[ A milder hydrolysis using dilute hydrochloric acid in re~uxing
324
One Halo`en
acetone enabled the preparation of "16# from "15# in 69) yield ð75SUL82Ł[ Previous attempts to prepare this compound by addition of chlorocarbonylsulfenyl chloride to cyclohexene resulted in the formation of "18# through the intermediacy of the thiirane "17# "Scheme 11# ð69AG"E#43Ł[ SCCl3
S
H2O, acetone, HCl
Cl
Cl (27)
(26) S
Cl
+ ClSCOCl Cl
Cl O
–COCl2
ClSCOCl
S
O (28)
(27) O S
S
Cl
Cl (29) Scheme 22
"v# Preparation from alkoxydichloromethanesulfenyl derivatives The thermal ð70LA0133Ł or Lewis acid!catalysed ð53FRP0261860Ł elimination of alkyl chlorides from a range of alkoxydichloromethanesulfenyl compounds "29# provides a general route to certain classes of chlorocarbonylsulfenyl derivatives[ This area has been extensively covered in a series of publications by Barany and co!workers[ This work is summarized in Scheme 12 ð72JOC3649\ 72TL4572\ 73JCS"P0#1504\ 73JOC0932\ 75JOC0755Ł[ This reaction has been used for the e.cient preparation of ð07OŁchlorocarbonylsulfenyl chloride ð73MI 503!91Ł[ O
S
+ Cl
SCl
Cl
RO
(X = SCOCl)
O
S RO
SMe
SO2Cl2
Cl
Cl2
RO
Cl SX (X = SCl)
(30)
(X = Cl)
SX
Cl
∆ –RCl
(X = SMe)
ROCSCl
Cl SCl2 (X = SCl)
S RO
Cl
RO
S
S
Cl
Cl
S
OR
∆, –2RCl
Cl O Cl
O S
S
S
Cl
Scheme 23
"vi# Miscellaneous reactions leadin` to chlorocarbonylsulfenyl derivatives Chlorocarbonylsulfenyl chloride reacts with silver"I# cyanide to give chlorocarbonyl thiocyanate\ in 54) yield ð58CB1607Ł^ several other nucleophiles also react preferentially at sulfur to give the products shown in Scheme 13 ð69AG"E#43Ł[ In the case of tri~uoroacetamide\ further reaction to the
325
Carbonyl Group and at Least One Halo`en
1!oxo!0\2\3!oxathiazole occurs ð76JFC"25#318Ł[ In the reaction of bis"bistri~uoromethyl! aminoxy#mercury"II# "20# with thiophosgene\ migration of the bis"tri~uoromethyl#amino groups from oxygen to sulfur occurs\ leading to "21# in 50) yield "Scheme 14# ð73JFC"13#374Ł[ Reaction of thiophosgene with bis"tri~uoromethyl# sul_ne "22# also proceeds through a rearrangement to give "24#\ possibly through the intermediacy of "23# "Scheme 15# ð74CB3442Ł[ In the reaction of the allenic alcohol "25# with thiophosgene\ the initially formed carbonochloridothionic acid O!ester undergoes a ð2\2Ł sigmatropic rearrangement to the vinylic chlorothiolformate "26# ð81AG"E#755Ł[ This is an example of the rearrangement of an allylic ester "Scheme 16#\ and thus may be very general^ however\ no examples appear in Houben!Weyl ð72HOU"E3#8Ł[ N S R
O
〈87JFC(36)429〉
O
〈69CB2718〉
O SCl
F
O
O
SSCN
SCN
SNR2
Cl
〈69CB2718〉
O
〈70AG(E)54〉
SbF3
AgSCN
SNHCOR
Cl
O
O RCONH2
SCl
R2N
AgCN
AgOCN
O Li
F3C
SCl RO 〈70AG(E)54〉
N RSH
RfOLi
O
CF3
O O
SORf
Cl
SNCO Cl 〈69CB2718〉
F3C
O SOR
Cl
SCl
Cl
ROH
O
〈69CB2718〉
O
R2NH
SCN
Cl
〈87JFC(36)429〉
Cl
S N
CF3
〈87JFC(36)429〉
SSR Cl 〈70AG(E)54〉 Scheme 24
S ((CF3)2NO)2Hg
CSCl2, –78 °C
(CF3)2N
O (CF3)2N
Cl
O
S (32)
(31)
Cl
Scheme 25
Cl– F3C S O F3C
CSCl2
F3C
S O
F3C
S
F3C
SCl Cl
F3C
Cl
O
(34)
SCl
–COS
F3C
Cl
–COCl2
F 3C
S
F3C
S
∆
S
Cl (33)
F3C
(35) Scheme 26
5[03[2[1[2 Bromothiolformate esters\ RSCOBr Bromothiolformate esters have rarely been reported[ Haas and Lieb have prepared tri~uoromethyl bromothiolformate by halogen exchange from tri~uoromethyl ~uorothiolformate and boron tri! bromide ð67CB1780Ł^ Haas et al[ also used the same method to prepare bis"bromocarbonyl# disul_de
326
One Halo`en OH
•
O
NaH, CSCl2
•
S
O
∆
Cl
S
Cl
(37)
(36) O S
O
∆
Cl
S
Cl
Scheme 27
from bis"~uorocarbonyl# disul_de ð62JFC"2#272Ł[ A poorly characterized example of carbon mon! oxide insertion into methanesulfenyl bromide to give methyl bromothiolformate is also reported ð72HOU"E3#8Ł[ This method is analogous to the reaction of sulfenyl chlorides with carbon monoxide and should proceed under milder conditions in view of the lower S0Br bond strength[
5[03[2[1[3 Iodothiolformate esters\ RSCOI This class of compound does not appear to have been reported[
5[03[2[2 One Halogen and One Nitrogen Function Compounds of the structure HalCONR0R1 are referred to in Chemical Abstracts as substituted carbamic halides[ Alternative names are halogenoformic amides\ carbamyl halides and carbamoyl halides[ The last name will be adopted in this work\ in line with common usage[ Other classes of compound incorporating the HalCON functionality also exist\ notably those where the nitrogen atom is part of a pseudohalide "e[g[\ isocyanate# or is part of an imide group[ These compounds are variously named\ often as halogenocarbonyl derivatives[ The entire scope of this section is comprehensively reviewed in Houben!Weyl up to 0871] carbamoyl halides by Heywang ð72HOU"E3#25Ł^ bis"halogenocarbonyl# amines\ HalCONRCOHal\ by Hagemann ð72HOU"E3#0908Ł^ halogenocarbonylcarbamic acid esters and amides\ HalCONRCOX "X O\ N\ S# by Kraatz ð72HOU"E3#0912Ł and Baasner ð72HOU"E3#0967Ł^ halogenocarbonylisocyanide dihalides and deriva! tives\ HalCON1CHal1\ by Hagemann ð72HOU"E3#0069Ł^ HalCON1CHalX "X O\ N\ S# by Salz! burg ð72HOU"E3#0066Ł^ HalCONRCHal2 and derivatives by Marhold ð72HOU"E3#0192Ł^ halogenocarbonyl isocyanates\ HalCONCO\ by Hagemann ð72HOU"E3#0123Ł^ and halogenocarbonyl ureas\ HalCONRCONRX "X O\ N\ S#\ by Lieb ð72HOU"E3#0164Ł and Botta ð72HOU"E3#0202Ł[ The present authors do not hope or wish to incorporate this vast\ well!researched body of knowledge into this review[ Their aim is to introduce readers to the main synthetic methods employed in this area\ incorporating some more recent references\ where they exist[
5[03[2[2[0 Carbamoyl ~uorides\ R0R1NCOF\ and other N!~uorocarbonyl compounds The most important members of this class are carbamoyl ~uorides bearing one further substituent on the nitrogen atom\ RNHCOF[ Because of their thermal and chemical stability relative to the corresponding carbamoyl chlorides\ they are used as intermediates in the synthesis of important fungicides and insecticides where nitrogen substitution can be carried out\ even in the presence of tertiary bases\ without elimination to the isocyanate[ These N\N!disubstituted carbamoyl ~uorides can then be further reacted with amines or alcohols to give\ respectively\ ureas and carbamates[
"i# Preparation from carbonic ~uoride halides Although preparation from carbonic ~uoride halides is analogous to the very versatile reaction of phosgene with amines under base!catalysed conditions to form carbamoyl chlorides\ it is not a reliable or accessible general method for the preparation of carbamoyl ~uorides[ Carbonic chloride ~uoride reacts predictably with diphenylamine to produce diphenylcarbamoyl
327
Carbonyl Group and at Least One Halo`en
~uoride in good yield ð79EUP41731Ł^ however\ carbonic chloride ~uoride is not commercially avail! able\ so this method is not very attractive[ On the other hand\ carbonic di~uoride is commercially available^ however\ its reaction with amines does not usually result in the formation of carbamoyl ~uorides^ reaction with piperidine or dimethylamine at room temperature leads to oxidative ~uo! rination to form the N!~uoro derivative in reasonable yield\ with the formation of carbon monoxide ð73CC305Ł[ The same authors did isolate the carbamoyl ~uoride "28# in 69) yield from the reaction of "27# with carbonic di~uoride "Equation "02##[ However\ some classes of nitrogen compound are ~uorocarbonylated by carbonic di~uoride[ Secondary amides give moderate yields of N!~uoro! carbonyl derivatives^ however\ it is di.cult to prevent concomitant conversion of the amide carbonyl function to a `em!di~uoride ð51JA3164Ł[ The N!methoxycarbonyl!N!trimethylsilylhydrazine "39# is converted to the N!~uorocarbonyl derivative "30# at −19>C in quantitative yield "Equation "03## ð71ZN"B#70Ł[ This may indicate that compounds with less basic nitrogen atoms are more likely to lead to N!~uorocarbonyl products[ Benzophenone imine is also reported to react with carbonic di~uoride to give N!~uorocarbonylation in 39) yield ð57ZOR619Ł\ whilst at elevated temperatures N!aryldi~uoroazomethines "31# add the elements of carbonic di~uoride under ~uoride catalysis to give N!~uorocarbonyl!N!tri~uoromethylanilines "32# in good yield "Scheme 17# ð54JOC3227Ł[ In a similar reaction\ carbonic di~uoride adds to the imino~uoride from HF and HCN to give CF1HNHCOF in 69) yield ð51JA3164Ł[ Phenyl isocyanate also adds carbonic di~uoride under caesium ~uoride catalysis to give N\N!bis"~uorocarbonyl#aniline in 84) yield ð51JA3164Ł[ Finally\ in a complex reaction\ carbonic di~uoride reacts with cyanogen ~uoride to give bis"tri! ~uoromethyl#carbamoyl chloride\ "CF2#1NCOF\ in low yield ð70JFC"07#148Ł[ This compound can also be prepared in high yield by the ~uorination of dimethylcarbamoyl chloride[ COF COF2, 25 °C
N
N
O P O (38) CO2Me Me2N
N
CO2Me
COF2, –20 °C
Me2N
TMS (40)
PhNCS
HgF2
(13)
O P O F (39)
N
(14)
COF (41)
F PhN F (42)
O COF2
Ph
N
F
CF3 (43)
Scheme 28
"ii# Preparation from carbamoyl halides by halo`enÐ~uorine exchan`e N!Carbonyl chlorides of many types of are readily prepared^ thus\ they make ideal starting materials for the preparation of the corresponding N!carbonyl ~uorides[ Several methods have been reported[ The use of potassium ~uoride in sulfolane requires high temperatures\ and is thus limited in its application^ any aliphatic chlorine atoms present are also likely to be exchanged ð67GEP1695572Ł[ The use of the phase transfer catalyst 07!crown!5 enables the exchange to take place in high yield at room temperature\ either in the presence or the absence of solvent ð68JOC0905Ł[ A more recent report from Japanese workers suggests that a carefully dried mixture of potassium and calcium ~uorides can e}ect quantitative exchange at 49>C in acetonitrile ð75CC682Ł[ Although reported examples are restricted to the preparation of N\N!disubstituted carbamoyl ~uorides\ the last two methods may be applicable to N!monosubstituted derivatives\ unless the basic nature of potassium ~uoride precludes this[ Predictably\ carbamoyl bromides are also reported to undergo exchange ð67GEP1695572Ł^ however\ this is of little synthetic use\ due to their relative inaccessibility[
328
One Halo`en "iii# Preparation from alkyl or aryl isocyanates and hydro`en ~uoride or other ~uoride sources
The method of choice for the preparation of carbamoyl ~uorides bearing one further substituent on nitrogen involves addition of hydrogen ~uoride to an isocyanate[ Alkyl and aryl isocyanates react with hydrogen ~uoride in ether at room temperature to give quantitative yields of the cor! responding N!monosubstituted carbamoyl ~uorides ð34JCS753Ł[ By conducting the reaction at −79>C\ hydrogen ~uoride will also add to cyanic acid\ HOCN\ to give the unsubstituted carbamoyl ~uoride\ H1NCOF\ which is a stable solid\ m[p[ 36>C ð39CB066Ł[ A more convenient\ but lower yielding\ method uses the commercially available\ stable pyridinium poly"hydrogen ~uoride# as both a solvent and hydrogen ~uoride source\ providing both alkyl and aryl carbamoyl ~uorides in 39Ð59) yield ð68JOC2761Ł[
"iv# Preparation from other carbamoyl ~uorides The thermal and base stability of monosubstituted carbamoyl ~uorides\ RNHCOF\ relative to their carbamoyl chloride counterparts renders them excellent intermediates for the preparation of further carbamoyl ~uorides by reaction at the nitrogen atom with a range of electrophilic reagents[ The reaction with a wide variety of sulfenyl chlorides in the presence of a tertiary base has been thoroughly investigated because the products can be transformed into a range of fungicidal and insecticidal carbamates by reaction with hydroxyl compounds or amines "Scheme 18#[ O Me Bun2NSCl pyridine R = Me
O R
N H
F
N
SNBun2 〈78JOC3953〉 O
SCl2, pyridine
F
Me R = Me
N
O
R12NH
Me
F
O Ar
Me
N
OR2
SNR12 〈84USP4473580〉
O PhNH2
N
F
N SNR12
SCl 〈82USP4333883〉 ClSCX3, Et3N R = Ar
O R2OH
F
Ar
N
N H
Ph
X = halogen
SCX3 〈82EUP46557〉
SCX3 〈82JFC(19)553〉 Scheme 29
Other transformations which have been successfully carried out on particular carbamoyl ~uorides are aromatic nitration and catalytic hydrogenation of aromatic nitro groups\ both in good yield ð79EUP41731Ł\ acylation with phosgene ð63GEP1200551Ł\ sulfoxide formation using m!chloro! perbenzoic acid ð70USP3144242Ł\ and stannylation with allyltin"II# halides ð66USP3947438Ł[
"v# Carbamoyl ~uorides arisin` from ~uorination Carbamoyl ~uorides are often formed when appropriate substrates\ notably isocyanates\ are ~uorinated[ However\ in common with many other ~uorinations of organic compounds\ the struc! ture of the products can rarely be predicted[ Fluorination of n!propyl isocyanate with ~uorine in Freon 00 can give n!propyl!N!~uorocarbamoyl ~uoride in up to 39) yield[ Further studies show that the product does not arise from addition of ~uorine to the C1N of the isocyanate "Scheme 29# ð56JOC0522Ł[ In two related reactions\ the ~uorination of tri~uoromethyl isocyanate ð68CB1047Ł and tri~uoroacetyl isocyanate ð75JFC"23#140Ł with xenon di~uoride led to good yields of the ~uoro! carbonylhydrazines "34# and "35#\ respectively[ Their formation can be explained as arising from
339
Carbonyl Group and at Least One Halo`en
elimination of xenon from intermediates of structure "33# "Scheme 20#[ Tri~uoromethyl isocyanate reacts with several other ~uoride sources to give a range of products "Scheme 21#[ O
O Prn
N
•
HF
O
F2
Prn
Prn
F N H Scheme 30
F
N F
CF3
F3C F3C
NCO
N N XeF2
Xe CONCO
FCO
COF (45)
– Xe
F N
XeF2
F3C
R = CF3
O
R = CF3
– Xe
R
– CF4 R = COF
2
COF
FCO
R = COF
N N
(44) FCO
COF (46)
Scheme 31
O F3C HF
F3C
N
•
O
〈57ZOB2243〉
Cl
ClF
Br
F
N H
F3C
CO, hν
N
COCl F3 C
COF 〈73IC2890〉
CsF
CF3 N
〈74JA1770〉
N COF
〈76IZV209〉
COF Scheme 32
Electrochemical ~uorination of dimethylcarbamoyl chloride\ Me1NCOCl\ gives almost exclusively the per~uorinated product\ "CF2#1NCOF ð47JOC0465Ł[ When _ve! or six!membered cyclic ureas "36# are ~uorinated in water\ v!di~uoroaminoalkylcarbamoyl ~uorides "37# are formed in poor yield "Equation "04## ð69JA1985Ł[ Finally\ a range of "~uorocarbonyl#imidosulfur compounds R0R1S1NCOF have been prepared^ ~uorination of CF2SNCO at low temperature leads to the formal 0\2!addition of ~uorine\ to give CF2FS1NCOF in good yield ð72CB0146Ł[ Compounds of the same class are formed in almost quantitative yield by the reaction of sulfur tetra~uoride ð75IS09Ł or substituted analogues ð80CB1300Ł with silyl isocyanates "Scheme 22#[ H N O
F2, H2O
( )n N H (47)
n = 2, 3
F2N
( )n
H N
F
(15)
O (48)
"vi# Carbamoyl ~uorides from tri~uoromethylamines\ R0R1NCF2 N\N!Disubstituted formamides can be ~uorinated by silicon tetra~uoride in the presence of potassium ~uoride to give tri~uoromethylamines\ R0R1NCF2[ Where R0 and R1 are alkyl groups\ addition of these compounds to crushed ice results in the carbamoyl ~uorides R0R1NCOF in over 69) yield ð72JFC"12#196Ł[ Per~uoroalkyl tertiary amines bearing at least one CF2 group\ Rf0Rf1NCF2\ are converted to the carbamoyl ~uorides Rf0Rf1NCOF in 27Ð51) yield by 29) oleum\ preferably with catalysis by MoCl4[ Where more than one NCF2 group is present\ only one is converted to give the mono~uorocarbonyl derivative ð78JFC"34#182Ł[
330
One Halo`en R
F S
R
F
Me2N
TMS-NCO
S NCOF
R = F, CF3
Me2N F
SF4
Si(NCO)4
S NCOF F
Scheme 33
"vii# Miscellaneous reactions yieldin` carbamoyl ~uorides A variety of N!unsubstituted aziridines have been shown to react with tri~uoromethyl hypo! ~uorite\ CF2OF\ at −39>C to give 49Ð099) yields of aziridine!N!carbonyl ~uorides "38#[ These can rearrange on storing at room temperature to give high yields of b!~uoroalkyl isocyanates "49# in high yields "Scheme 23# ð79JFC"04#26Ł[ R2
R2
R1 NH
O
R1
CF3OF
F– R3
R3 R4
R1
RT, several days
R3 N R4
F
N (at least two R groups = H)
F
R4 (49)
R2
•
O
(50)
R1, R2, R3, R4 = H, Me, Ph Scheme 34
The per~uorinated oxaziridine "40# reacts with a wide range of nucleophiles\ in the presence of sodium ~uoride\ generally giving ~uorocarbonyl derivatives "41# in varying yields by attack at the nitrogen atom[ Reactions with diethylamine and potassium thiocyanate did not follow this course\ and sodium azide and sodium cyanate failed to react "Scheme 24# ð68JFC"03#178Ł[ N!Monosubstituted carbamoyl ~uorides have been prepared by the reaction of an alcohol or an alkene with cyanogen chloride and HF "Equation "05## ð62GEP1231759Ł[ Finally\ a report claiming the formation of F1NCOF in high yield by isomerisation of tri~uoronitrosomethane\ CF2NO ð25CB573Ł\ has been reinvestigated and found to be incorrect^ the product appears to be a mixture of tri! ~uoronitromethane and hexa~uoroazoxymethane "42# ð43JCS808Ł[
F3C
O
O
O F 3C
F
N F
N +
F
F3C
+ F–
N
F
+ HF
Nu
NuH
NuH (51)
(52)
NuH = MeOH (80%), PriOH (88%), ButOH (93%), MeCO2H (32%), EtSH (30%); and KCN (40%) Scheme 35
OH (CH2)n
or
H N
ClCN, HF
(CH2)n
(CH2)n
F 3C
F n = 3, 4
(16)
O
+
N NCF3 –O
(53)
"viii# Preparation of ~uorocarbonyl isocyanate Whilst the chemistry of chlorocarbonyl isocyanate has been extensively explored\ and has been the subject of several reviews "see Section 5[03[2[2[1#\ the reactions of ~uorocarbonyl isocyanate do
331
Carbonyl Group and at Least One Halo`en
not appear to have been similarly examined^ this is probably because no convenient synthesis yet exists[ Until the early 0889s\ all the methods available involved the use of COF1\ often at high temperatures[ However it has been shown that commercially available chlorocarbonyl isocyanate will undergo halogen exchange in moderate yield with chlorine ~uoride or xenon di~uoride[ The methods available are summarized in Scheme 25[ Several preparations of ~uorocarbonyl iso! thiocyanate\ FCONCS\ have also been described "Scheme 26#[ These are mainly analogous to those described for ~uorocarbonyl isocyanate^ formation by halogen exchange has not yet been investigated[ 〈73CB1752〉 NCO O NCO KOCN
COF2 180 °C 100%
COF2 400 °C
〈67AG(E)871〉
KOCN
〈73CB1752〉
75%
KF 8%
22%
O
O
ClF
F NCO b.p. 26 °C
COF2 280 °C
Cl
51%
〈92ZAAC150〉
XeF2
70%
Si(NCO)4
COF2 280 °C
〈67CB1082〉
NCO
36%
TMS-NCO 〈67CB1082〉 Scheme 36
NCS O NCS 〈73CB1752〉
TMS-NCS COF2 50 °C 17%
COF2 140 °C
COF2 50 °C
O F NCS b.p. 63.5 °C
AgCN 20%
20%
KSCN 〈67AG(E)871〉
〈67AG(E)871〉
100%
Scheme 37
O F SCl 〈67AG(E)705〉
5[03[2[2[1 Carbamoyl chlorides\ R0R1NCOCl\ and other N!chlorocarbonyl compounds Carbamoyl chlorides are quite often rather unreactive towards nucleophiles\ and can often be puri_ed by chromatography and recrystallised from alcohols without decomposition[ Perhaps because of their relative lack of reactivity\ or\ in 0882\ the discovery of their carcinogenic potential ðB!82MI 503!90Ł\ their use in synthesis has been quite limited[ Carbamoyl chlorides bearing one further substituent on the nitrogen atom are important intermediates in the preparation of isocyanates\ but are not usually isolated[ Carbamoyl chloride itself\ H1NCOCl\ is well described but of limited stability^ it has found use in the amidation of aromatic systems under FriedelÐCrafts conditions ðB! 53MI 503!90Ł[ Some classes of N!chlorocarbonyl compounds are very reactive^ when the nitrogen is part of an aromatic ring system\ reaction with alcohols is often instantaneous[ This section encompasses a diversity of compound types[ The authors have ordered the contents by reagent and:or reaction type\ rather than by the structure of the product formed[ The exception to this is the _nal subsection\ which is devoted to the synthesis of chlorocarbonyl pseudohalogenides[ This area\ up to 0871\ is covered in great depth in Houben!Weyl\ volume E3^ this work includes many tables of speci_c compounds and synthetic details[
332
One Halo`en "i# Methods involvin` the use of phos`ene
Most compounds with a nitrogen atom bearing a hydrogen or TMS function\ or which can tautomerize to yield a nitrogen atom bearing a hydrogen\ will react with phosgene to give various N!chlorocarbonyl compounds[ This is by far the most commonly encountered method of preparing such compounds[ The use of phosgene can often be avoided by substituting one of the phosgene alternatives\ diphosgene or triphosgene^ these are treated separately in the next subsection[ What follows is an attempt to make some general comments for various classes of nitrogen compounds\ which are summarized in Scheme 27Ð31[ Compounds which react abnormally with phosgene are discussed at the end of this subsection[ "a# Reaction of phos`ene with secondary amines\ R0R1NH\ to `ive R0R1NCOCl[ Since reactions of nucleophiles with phosgene proceed with the elimination of hydrogen chloride\ it might be expected that the reaction of phosgene with basic secondary amines should proceed to the stage where 49) of the amine is converted to product\ whilst the remainder is converted to the non! nucleophilic amine hydrochloride[ This is in fact the case at temperatures near to ambient and below ð74CB1183Ł^ however\ at re~ux in toluene with an excess of phosgene\ total conversion to the carbamoyl chloride can occur in excellent yield ð77MI 503!90Ł[ The addition of a tertiary base as an HCl acceptor not only allows full utilisation of the secondary amine\ but also enables the quantity of phosgene to be reduced[ Stoichiometric amounts of phosgene can sometimes lead to yields approaching 84) ð78JCS"P0#0616Ł^ however\ the use of 0[4Ð1[9 equivalents is more usual[ As the quantity of phosgene is reduced\ the possibility of symmetrical urea formation increases[ This is rarely speci_cally mentioned as a problem in the literature^ however\ isolated yields of carbamoyl chlorides are often only moderate[ An internal tertiary basic centre obviates the need for the addition of a further HCl acceptor in some cases ð76IJC"B#637Ł^ the success of this reaction depends on the tertiary centre hydrochloride of the starting material being to some extent soluble in the reaction medium\ so the use of a more polar solvent may be bene_cial in this case[ In the reaction of secondary amines with phosgene\ anion formation using sodium hydride can also lead to high yields of carbamoyl chlorides ð78MI 503!92Ł^ this method is potentially useful when separation of the product from the tertiary base hydrochloride could be problematical[ Alternatively\ the use of an N!trimethylsilylamine as the amine component should allow smooth reaction with phosgene\ volatile trimethylsilyl chloride being the only by!product ð58ZOB1487Ł[ N\N!Disubstituted carbamoyl chlorides can be very stable^ examples exist of reactions in tri~uoroacetic acid and water leaving the carbamoyl chloride unchanged ð89S0954Ł[ "b# Reaction of phos`ene with primary amines\ RNH1\ and ammonia\ to `ive RNHCOCl and H1NCOCl[ Phosgene reacts with primary amines to give N!monosubstituted carbamoyl chlorides\ RNHCOCl[ On treatment with tertiary bases\ or thermally\ under re~ux in benzene or toluene\ these carbamoyl chlorides eliminate hydrogen chloride to give isocyanates in high yield[ Because of the uncertainty involved in isolating the carbamoyl chlorides due to their instability\ the preferred substrate for further reactions is usually the isocyanate^ the reaction of nucleophiles with isocyanates gives rise to the same product as the corresponding N!monosubstituted carbamoyl chloride\ and often with the advantage that no acid acceptor is necessary "Scheme 27#[ Mono! or bisilyl!substituted primary amines react with phosgene at 9>C to give isocyanates directly\ with no isolable carbamoyl chloride intermediates ð58ZOB1487Ł[ R1NH2
COCl2
∆ or Et3N
R1NHCOCl R2OH
HCl
R1NCO
–HCl R2OH
R1NHCO2R2 Scheme 38
Primary amines react cleanly with phosgene in the gas phase at 164>C to give 69Ð89) yields of N!monosubstituted carbamoyl chlorides^ ammonia undergoes the same reaction at 399Ð499>C to give carbamoyl chloride ð38AG072\ 49JA0777Ł[ Although secondary amines also undergo this reaction\ it is most unlikely to be the best method of preparation of any particular N\N!disubstituted carbamoyl chloride[ "c# Reaction of phos`ene with tertiary amines[ The initial reaction of phosgene with tertiary amines gives rise to acylammonium salts ð81JOC4025Ł[ These will often eliminate an alkyl chloride on standing for 13Ð61 h at room temperature to give N\N!disubstituted carbamoyl chlorides[ On hydrolysis\ the unstable N!carboxylic acids lose carbon dioxide to give secondary amines "Scheme
333
Carbonyl Group and at Least One Halo`en
28# ð64LA1116\ 72JHC0366\ 74AF106\ 78AF428Ł[ This dealkylation can proceed in good yield\ and is a useful alternative to the Von Braun reaction\ which utilises cyanogen bromide to accomplish the same transformation ð19CB590Ł[ Pyridine was thought to form a stable bispyridinium salt "43# with phosgene ð45CB1451Ł[ Reinvestigation has led to reassignment of the structure as "44# ð77JOC5034Ł[ R1 N Me
R1 + N
COCl2
R2
R2
Cl–
Me
R1 N COCl
–MeCl
COCl
H2O
R2
R1 NH
+ CO2 + HCl
R2
Scheme 39
O
H
+
+
N
N
+
N
2Cl–
N
COCl (55)
(54)
Cl–
"d# Reaction of phos`ene at heteroaromatic nitro`en atoms[ Aromatic heterocycles which carry a hydrogen atom on a cyclic nitrogen\ or which can tautomerize to do so\ react with phosgene to give N!chlorocarbonyl derivatives^ amongst these are imidazole ð68LA0645Ł\ benzimidazole ð66S693Ł and 4!aryl!0\2\3!oxadiazol!1"2H#!ones ð78JHC120Ł[ Indole reacts with phosgene to give the unexpected product "45# ð73IJC"B#875Ł[ N!Trimethylsilyl heterocycles also react with phosgene to give similar products^ examples include imidazoles and pyrazoles ð79ZOB764Ł\ and 0\1\3!triazoloð3\2!aŁpyridin! 2"1H#!one ð72BCJ1858Ł[ In the latter example\ the N!trimethylsilyl derivative "46# and the parent heterocycle "47# react with phosgene to form di}erent N!chlorocarbonyl compounds "Scheme 39#[
NH
N COCl (56)
COCl N N
N-TMS
COCl2
N
N+ N
N
RCO2H –CO2
N
O–
O (57)
NCOR O COR
N N
NH O
N
COCl2
N
RCO2H
NCOCl –CO2
O
N
N+ N O–
(58) Scheme 40
These heterocyclic N!chlorocarbonyl compounds are usually very reactive towards nucleophiles[ "e# Reaction of other N0H compounds with phos`ene[ Many other classes of N0H!containing compounds also react with phosgene with the elimination of HCl to give N!chlorocarbonyl deriva! tives[ These include oximes\ hydrazines\ ureas\ guanidines\ carbazates and sulfamoyl chlorides[ Imines\ amides and N!silyl amides also react\ but the initial products can sometimes rearrange[ Compounds which have tautomeric forms containing N0H bonds can also react to give the N!chlorocarbonyl derivatives of that tautomer^ N!substituted iminoethers "48# follow this path\
334
One Halo`en
unless the oxygen substituent is a silyl group "59#\ when they give the product expected from their amide tautomer[ These reactions are summarized in Scheme 30[ NCO 〈80S85〉 R
Ar R2 = H 〈8OT3543〉 R2 = COMe 〈78JCS(P1)1066〉
Cl R = alkyl
OMe 〈72S81〉 N COCl
COCl N
R1
OR2
O HN
N N
COCl
R 〈80S85〉 〈68ZOR720〉 〈69CB2972〉
Ar
〈82MI 614-03〉 HN
H N
R1
O
OR2
NH
OMe N (59) R1 N NHR3 R2
NH
COCl R
N
R1 N NR3COCl R2 〈91AP917〉
COCl
SO2Cl
R
H N
R
Ar
N Ph
SO2Cl
〈78GEP2828969〉
NMeCOCl
N
〈86TL113〉
Ph
COCl2
NHMe
ArNHNHCO2R R 1N
COCl Ar
N
R 1N
NHR3 O
NHCO2R
〈85SC697〉
RHN
NR3COCl
R2N
R2N 〈89JMC228〉
NHR R3 R4
O
Cl R1
RHN
NHR2
NRCOCl
RCO
Me N
R2
R3
R2
R4
NR1COCl
NR1 TMS
TMS-O
N
O
N R
〈72S39〉
〈64JOC2401〉 O R1
(60)
NHR2
〈61GEP115721O〉 〈86JOC3494〉
COCl N
O
RCONMeCOCl
N
O
〈69ZOB220〉 〈77ZOB1063〉
R
〈89MI 614-04〉
Scheme 41
"f# Reactions of compounds containin` C0N multiple bonds with phos`ene[ Many compounds which contain carbon multiply bonded to nitrogen initially add phosgene across the carbonÐnitrogen bond to give a!chloroalkyl N!chlorocarbonyl derivatives[ If these adducts possess the capacity to eliminate HCl\ this is likely to occur[ This behaviour is found in suitably substituted imines[ Where elimination of HCl cannot occur\ the initial adducts are stable\ and can be useful bifunctional intermediates in heterocyclic synthesis[ Certain imines\ carbodiimides\ nitriles and cyanamides fall into this category[ These reactions are summarized in Scheme 31[ "`# Abnormal reactions of N0H compounds with phos`ene[ N\N!Diphenylformamidine "50# reacts with two molecules of phosgene\ exemplifying at the same time the two modes of reaction discussed in the two previous subsections[ Although the initial product "51# cannot eliminate HCl readily\ it is extremely sensitive to hydrolysis\ and it is the initial hydrolysis product "52# which eliminates HCl to form N!chlorocarbonyl!N!phenylformamide "53# "Scheme 32# ð75JOC3372Ł[ The rearrangement of v!alkoxyalkyl! and v!phenoxyalkylcarbamoyl chlorides "54# to the v!chloroalkyl carbamates "55# proceeds even at room temperature when n 1 or 2[ More vigorous heating leads to the cyclic carbamates "56# ð64JCS"P0#0725Ł "Scheme 33#[ When 2!hydroxymethylpiperidine reacts with phosgene as its PTSA salt the expected chloro! formate "57# is formed[ If the chloroformate free base is liberated at −59>C with triethylamine\
335
Carbonyl Group and at Least One Halo`en 〈63JOC1427〉 〈78JOC4530〉 NRCOCl 〈81JOC5226〉
Cl RN
Ph
Cl ArN
NCOCl Cl 〈71BCJ2182〉
COCl
R N CH2
N • N Ph
Ar
R
N
〈87JHC945〉 R N
Cl
Cl
NCOCl
N
Ar
Ar
COCl2
NRCOCl Cl 〈73CJC333〉
Cl 〈69BRP1169158〉
Me2N
N
R1 R2 R3
Me2N NCOCl Cl 〈77GEP2708024〉
R4 NR5
R1
R2
Cl R4 3 NR5COCl R 〈72S39〉
–HCl R1 = H
R2
R4
R3
NR5COCl
Scheme 42 O
COCl H PhN
2 COCl2
PhN
COCl (63)
(62)
+ PhNCO
N COCl
PhN
COCl (61)
Ph
OH
PhN
PhN
CHO
PhN
H2O
Cl
H
Cl
(64)
Scheme 43
R1 N CO2R2 (CH2)n R1 N (CH2)n
R1 N Cl
(CH2)n
O O R2
RT
Cl–
Cl (66)
O
O+ R2
180 °C
Cl–
(65)
R1 N (CH2)n
O
+ R2Cl
O (67) Scheme 44
migration of the chlorocarbonyl group from oxygen to nitrogen occurs\ to give the stable carbamoyl chloride "58# in high yield[ The same reaction course was observed for 2!hydroxypiperidine[ Com! pounds "57# and "58# readily cyclise in the presence of triethylamine to give the bicyclic carbamate "69# "Scheme 34# ð79JOC4214Ł[ The N!chlorocarbonyl derivatives of the O!benzylhydroxylamine "60# and proline "62# cyclise readily to give the corresponding anhydrides "61# ð81TL1518Ł and "63# ð80JOC640Ł "Scheme 35#[ "ii# Methods involvin` diphos`ene or triphos`ene The role of trichloromethyl chloroformate "diphosgene# and bis"trichloromethyl# carbonate "tri! phosgene# as alternatives to the use of phosgene has already been discussed "see Section 5[03[0[1[7#[ In the preparation of carbamoyl chlorides both reagents react to give the same product as would have been anticipated if phosgene had been employed to carry out the transformation "Scheme 36#[
336
One Halo`en OH
OCOCl COCl2, 0 °C
+
+
NH2
NH2
H+
OH
OCOCl
(68)
COCl2, RT Et3N, –60 °C
NH
NCOCl
Et3N, RT
COCl2
OH
–65 °C
O
O
Et3N, RT
NCOCl
N (70)
(69) Scheme 45
O NHOCH2Ph
PhCH2O
COCl2, 45 °C
O
N
Cl
70 °C
PhCH2O
N
O
OH
CO2H
O
O (71)
(72)
O
COCl2, Et3N
N H
O
N
N
CO2H
OH
O
Cl
O
O
(73)
(74) Scheme 46
COCl N O
R
O N
Ar
〈92S1216〉
Me Ph
COCl 〈86MI 614-01〉
O-TMS Ar
Ph
NMe
COCl N
〈92TL3483〉
O
Cl3COCOCl (diphosgene) Et3N
R
NHMe
N
NHBn
(Cl3CO)2CO (triphosgene) pyridine
COCl
N
R
H N
R Me NBn
〈92JMC3641〉
NH
Cl
COCl
NHR
2
〈91TL259〉
〈87AG(E)894〉
Cl
N
NR
COCl
2
COCl Scheme 47
〈89TL3229〉
337
Carbonyl Group and at Least One Halo`en
"iii# The reaction of isocyanates with X0Cl to `ive RNXCOCl Isocyanates add hydrogen chloride\ acyl chlorides\ sulfur dichloride\ other sulfenyl chlorides and phosgene across the C1N bond to give N!carbonyl chlorides[ Vinyl isocyanates add two molecules of hydrogen chloride to give reactive bifunctional electrophiles "64# ð79AG"E#190Ł\ and carbonyl isocyanates R0CONCO react with phosphorus"V# chloride to give "65# ð54TL1312\ 55CB128Ł\ the unsaturated analogues of "64#[ Reaction with boron trichloride leads to dimerisation and formation of N!chlorocarbonyl ureas "66# ð69AG"E#261Ł[ These reactions are summarized in Scheme 37[ Many of these products are useful intermediates for the synthesis of heterocycles^ several examples are illustrated[ 〈1899CB1116〉 〈71GEP2128672〉 SCl R N COCl
O
Cl
H2N
(COCl)2 R=
HCl
〈86JOC3781〉
R •
NHCOX X (75)
〈80AG(E)201〉
O R = R1CO PCl5
BCl3
O
NCOCl
N R = alkyl COCl2 active carbon
COCl (77)
R1
R1COCl
N
COCl
R N
R1
R N
COCl
(76) 〈65TL2423〉 〈66CB239〉 O
Cl
COR1
〈71GEP1932830〉
N R
Cl
Cl
S NRCOCl
COCl pyridine
R1
SCl
R N
R N
R2
2HX (X = Cl, Br, I)
N
O
R1
CH=CR1R2
H R N 〈70AG(E)372〉
O 〈84JOC3675〉
COCl
R=H i.e. HOCN HCl
∆ or tertiary base
O
COCl R N
SCl2
COCl
Cl
R N
H R N
Cl
O
R1
〈85EUP136147〉 〈70GEP2008115〉
O
S N
N R O
〈66AG(E)672〉
Scheme 48
"iv# Methods involvin` reaction with carbon monoxide The N!chloro derivatives of primary and secondary alkylamines can be carbonylated by carbon monoxide at 59 atm in the presence of palladium metal or palladium"II# salts[ The products are N!monosubstituted carbamoyl chlorides "29Ð39)# and N\N!disubstituted carbamoyl chlorides "51Ð 88)#\ respectively "Scheme 38# ð60JOC747\ 81MI 503!90Ł[ The iron tricarbonyl complex "67# adds the isobutyronitrile anion[ Oxidation of the reaction mixture with copper"II# chloride produced the carbamoyl chloride "68# in 61) yield "Equation "06## ð77MI 503!91Ł[
R1
H N
Cl
HOCl
R2
R1 R1
N
COCl
CO, Pd
R2
R2
= = alkyl, 62–69% R1 = H, R2 = alkyl, 33–38% Scheme 49
R1
N
R2
338
One Halo`en N
–
Ph
N, CuCl2, –78 °C
N Ph
Ph
72%
(17)
NCOCl Ph
Fe(CO)3 (78)
(79)
"v# Preparation from formamides\ R0R1NCHO Several methods of converting formamides into carbamoyl chlorides have been reported\ employ! ing various chlorinating mixtures\ and usually proceeding in 59Ð69) distilled yields[ These methods are summarized in Table 1[ Table 1 Methods for the conversion of formamides into carbamoyl chlorides[ R1R2NCHO R1
R2
R1R2NCOCl Conditions
Yield (%)
Me
Me
SO2Cl2, 180 °C
Me
Me
SO2Cl2, pyridine, CH2Cl2, RT
Me
62AG861 62
Me
77
SCl2, pyridine, CH2Cl2
–(CH2)5–
68CB113
59
–(CH2)2O(CH2)2– Me
68CB113
69
–(CH2)4–
Me
Ref.
66
n-C8H18
70 PCl3, SOCl2
Ph
71CB969
62
"vi# Chlorination of carbamic acid esters\ thiolesters and related compounds Carbamic acid esters can be cleaved by various chlorinating agents to yield N!chlorocarbonyl compounds[ This provides a method of converting primary or secondary amines to carbamoyl chlorides in good yield without the use of phosgene or a phosgene equivalent "Table 2#[ In a variant of this reaction\ chlorine cleaves 2\4!dioxo!0\1\3!dithiazolidines to yield bis"chlorocarbonyl#amines "Equation "07## ð69S431Ł^ in a similar reaction\ the compound "79# produces chlorocarbonyl iso! cyanide dichloride "70# "Equation "08## ð60CB1621Ł[ Table 2 Cleavage of carbamic acid esters[ R1R2NH R1
R1R2NCOX
reagent
R1R2NCOCl
R2
X
Reagent
Yield (%)
Ref.
1° or 2° alkyl
OEt
POCl3
42–79
87SC1887
Me
Me
O-TMS
PCl5
83
81MI 614-02
Ph
Me
O-TMS
PCl5
80
91OM366
1° or 2° alkyl
(NO2)2CFCH2
(NO2)2CFCH2
SEt
SO2Cl2
85
82JCED97
(NO2)3CCH2
H
SEt
PhSCl (or Cl2)
84
85JOC5879
349
Carbonyl Group and at Least One Halo`en O R N
S
Cl2
S
25–83%
COCl (18)
R N
O
COCl
R = alkyl, Bn, Ar
Cl N
S
Cl2
S
53%
Cl
COCl (19)
N Cl
O (80)
(81)
"vii# Other methods of preparin` N!chlorocarbonyl compounds Photochemical chlorination of N!methylocta~uoropyrrolidine leads to the trichloromethyl deriva! tive "71# in 84) yield\ which can be converted to the N!chlorocarbonyl compound "72# by treatment with oleum at room temperature in 73) yield ð72JFC"11#410Ł[ N!Trichloromethyl!2\5!dihydro!0\1! oxazines "73# can also be hydrolysed to the corresponding N!chlorocarbonyl compounds "74# in good yield^ however\ only brief treatment with water was necessary to accomplish this transformation ð78CJC1042Ł[ F F F F
F F
X
N
R
O
N F X (82) X = CCl3 (83) X = COCl F
(84) X = CCl3 (85) X = COCl
Certain strained heterocycles are cleaved by hydrogen chloride to give N!chlorocarbonyl products^ thus 0\2!diazetidine!1\3!dione "75# provides the urea derivative "76# in 80) yield "Equation "19## ð55CB2092Ł\ whilst diaziridinones "77# lead to hydrazine derivatives "78# in good yield "Equation "10## ð58JOC1143Ł[ O HN
HCl
NH
O (86)
H2NCONHCOCl
(20)
(87)
O HCl
R
N N (88)
RNHNRCOCl
(21)
R (89)
Chlorocarbonyl isocyanate can undergo cycloadditions to multiple bonds to produce N!chloro! carbonyl derivatives^ in this way\ the enamine "89# gave the N!chlorocarbonylazetidine "80# in 75) yield "Equation "11## ð66ZOR189Ł\ and nitrile oxides "81# gave 0\1\3!oxadiazol!4!ones "82#\ also in high yields "Equation "12## ð77S883Ł[ Pyrrole forms a stable N!carboxylic acid\ which reacts normally with oxalyl chloride or the Ghosez reagent to form unstable N!chlorocarbonylpyrrole ð73CC529\ 76JOC1208Ł[
340
One Halo`en O O ClCON
•
N
–20 °C
N
+
O
n = 3, 85% n = 4, 86%
(CH2)n
O
(CH2)n
(22)
N COCl
(90)
ClCON
•
+
O
(91)
+
Ar
N O
–
N O
Ar
(23)
O
N COCl (93)
(92)
"viii# Preparation of chlorocarbonyl isocyanate and isothiocyanate Chlorocarbonyl isocyanate is a thermally stable\ very reactive bifunctional molecule\ and is of considerable importance\ particularly in the preparation of heterocyclic compounds[ It is a commercially available colourless liquid\ b[p[ 53>C\ which can be stored inde_nitely in the absence of moisture[ It was _rst prepared in 0858 by Gottardi and Henn in poor yield by the photolysis of chlorine isocyanate ð58M0759Ł[ Several other methods have been reported\ involving high!temperature reac! tions of phosgene with isocyanates or cyanates ð62CB0641Ł^ however\ only one method\ due to Hagemann\ has emerged as both high yielding and economical[ In this synthesis\ inexpensive methyl isocyanate or cyanogen chloride is converted in high yield to N!chlorocarbonyl isocyanide dichloride\ which is partially hydrolysed with methanesulfonic acid under carefully controlled conditions to give N!chlorocarbonyl isocyanate in over 89) yield "Scheme 49# ð62AG"E#888Ł[ The chemistry of chlorocarbonyl isocyanate has been extensively reviewed ð66AG"E#632\ 89H"20#0266\ 82T2116Ł[ O C (N
•
Si(N
O)2
〈73CB1752〉
COCl2
•
〈73CB1752〉
COCl2
180 °C 56%
O)4
250 °C 54%
O
Cl
Cl2, hν
N
•
O
COCl2, 400 °C
Cl N
15%
〈69M1860〉
•
O
〈73CB1752〉
90%
N
O
KOCN
2%
Cl
Cl
O
O2S Me
MeSO3H
O
COCl2 active carbon 150 °C 89%
Cl
Cl N Cl 〈73AG(E)999〉 Cl2, hν 90%
Me ClCN
N Scheme 50
•
O
341
Carbonyl Group and at Least One Halo`en
The sulfur analogue\ N!chlorocarbonyl isothiocyanate\ may have been prepared as early as 0859 by the reaction of phosgene with lead"II# thiocyanate ð59AP"182#049Ł^ however\ full characterisation was not carried out[ Jackh and Sundermeyer failed to prepare this compound from phosgene and potassium thiocyanate\ probably due to its instability at the high temperatures employed ð62CB0641Ł[ A further preparation from chlorocarbonyl isocyanide dichloride and phosphorus"V# sul_de ð58AG"E#19Ł has been disputed by Bunnenberg and Jochims\ who failed to repeat this work^ however\ these workers _nally successfully prepared N!chlorocarbonyl isothiocyanate in high yield by thermal elimination of carbon monoxide from oxalyl chloride isothiocyanate at 74>C in the presence of active carbon "Scheme 40# ð70CB0635Ł[ (COCl)2
ClCOCO
NH4SCN, liquid SO2
ClCO
85 °C
N
•
S
N
•
S
–CO 87%
93%
Scheme 51
5[03[2[2[2 Carbamoyl bromides\ R0R1NCOBr\ and other N!bromocarbonyl compounds Although carbamoyl bromides have been known for well over 099 years\ their appearance in the literature is quite rare\ and they do not seem to have any uses unique to themselves[
"i# Preparation of N!monosubstituted carbamoyl bromides from isocyanates and hydro`en bromide This is the only important general synthetic method for N!monosubstituted carbamoyl bromides\ RNHCOBr^ it can also be used to prepare the parent unsubstituted carbamoyl bromide\ H1NCOBr\ which can be isolated as a pure solid\ m[p[ 16>C\ but is of very limited thermal stability[ Examples of compounds prepared by this route are shown in Table 3[ Both N!aryl! and N!alkylcarbamoyl bromides can be prepared by this method^ a\b!unsaturated isocyanates add a further molecule of hydrogen bromide to form a!bromoalkylcarbamoyl bromides "Equation "13## ð79AG"E#190Ł[ R1
2 HX
R1
X
X = Cl, Br, I
R2
NHCOX
(24) R2
N
•
O
Table 3 Reaction of isocyanates with hydrogen bromide[ R N
•
O
+
HBr
R
RNHCOBr Ref.
H
40CB177
Me
64CB3162
Et
1866BSF435
Ph
1895MI 614-01
"ii# Preparation of N\N!disubstituted carbamoyl bromides "a# Preparation from carbamoyl chlorides and hydro`en bromide[ Dimethylcarbamoyl chloride undergoes halogen exchange with hydrogen bromide at room temperature without solvent to give dimethylcarbamoyl bromide in 89) distilled yield ð48CCC659Ł[ Presumably this method could be extended to the preparation of a wide range of N\N!disubstituted carbamoyl bromides[ "b# Preparation from N\N!disubstituted formamides[ N!Formylpiperidine is converted into piperidine!N!carbonyl bromide in 11) yield by the reaction of phosphorus"III# chloride and thionyl bromide ð60CB858Ł[ In common with the preceding method\ this is likely to be of some generality for preparing N\N!disubstituted carbamoyl bromides[ "c# Preparation from secondary amines and carbonic dibromide[ Although this method has an
342
One Halo`en
obvious analogy with the preparation of N\N!disubstituted carbamoyl chlorides from secondary amines and phosgene\ it has not been used to prepare the bromine analogues[ This is principally because carbonic dibromide is not readily accessible[
"iii# Other methods of preparin` N!bromocarbonyl compounds In common with many other isocyanates\ ~uorocarbonyl isocyanate\ FCONCO adds hydrogen bromide to give iminodicarboxylic acid bromide ~uoride\ FCONHCOBr\ as a hygroscopic solid that is unstable in air ð62CB0641Ł[ Radical bromination of methyl isocyanate initially gives tri! bromomethyl isocyanate\ Br2CNCO\ which rapidly equilibrates with its isomer\ bromocarbonyl isocyanide dibromide\ Br1C1N!COBr[ Radical bromination of neopentyl isocyanate follows the same course\ resulting in a tautomeric mixture of ButCBr1NCO and ButCBr1NCOBr ð71CB759Ł[ A similar tautomerism is observed when benzophenone imine\ Ph1C1NH reacts with oxalyl bromide\ with loss of carbon monoxide\ to give a mixture of Ph1C1NCOBr and Ph1BrCNCO ð60ZOR1118Ł[ Bromine will cleave thiol ester functions in the same manner as observed for chlorine^ thus\ the cyclic disul_de "83# and thiolcarbamate "84# both yield bis"bromocarbonyl#methylamine on treat! ment with bromine "Scheme 41# ð57FRP0406268\ 64GEP1240445Ł[ Formation of N!bromocarbonyl compounds from the corresponding N!~uorocarbonyl compounds by halogen exchange has also been reported^ thus\ "85# on treatment with aluminum"III# bromide gave the bromocarbonyl deriva! tive "86# "Equation "14## ð62GEP1020678Ł[ Treatment of 3!bromo!2!arylsydnones bearing an ortho! carbonyl function in the aryl group "87# with bromine or hydrogen bromide leads to 0!bromo! carbonylindazoles "88#[ The reaction tolerates a wide variety of carbonyl functions\ and usually proceeds in high yield "Equation "15## ð82TL128Ł[ O Me
Br2
S
N
S
COBr Me
N
Me
N
Br2
COBr
SMe
O
O (94)
COBr
(95) Scheme 52
Cl2FCSNRCOF (96)
AlBr3
Cl2FCSNRCOBr (97)
(25)
R COR N+
Br
N
Br2, hν or HBr
N 39–89%
(26)
N
O
COBr O– (98)
(99)
R = H, Me, CH2Br, CBr3, Ph, OMe, OEt, NHMe
"iv# N!Bromocarbonyl isocyanate and isothiocyanate N!Bromocarbonyl isocyanate\ BrCONCO\ has been prepared by the reaction of commercially available chlorocarbonyl isocyanate with boron tribromide ð80ZAAC"599#034\ 81SA"A#0068Ł[ The sulfur analogue\ bromocarbonyl isothiocyanate\ was prepared 09 years previously by the same route as chlorocarbonyl isothiocyanate\ by thermal decarbonylation of oxalyl bromide thiocyanate\ BrCO! CONCS\ at 74>C in the presence of active carbon in 35) yield[ The compound is a distillable oil\ stable at −07>C for more than 0 week ð70CB0635Ł[
343
Carbonyl Group and at Least One Halo`en
5[03[2[2[3 Carbamoyl iodides\ R0R1NCOI Only one instance of relatively stable carbamoyl iodides has been reported[ When a\b!unsaturated isocyanates are treated with two equivalents of hydrogen iodide\ a!iodoalkylcarbamoyl iodides are formed "Equation "16## ð68EUP6387\ 79AG"E#190Ł[ Thus\ it appears that the stability of carbamoyl iodides is such that more examples could perhaps be prepared[ By analogy with iodoformates\ ROCOI "see Section 5[03[2[0[3#\ similar stabilising features could be incorporated to enable isolation[ R
2 HI
R
I (27)
N
•
–50 °C
O
NHCOI
R = H, Me (m.p. 10 °C, 77%), Et
5[03[2[3 One Halogen and One Phosphorus Function 5[03[2[3[0 Chlorocarbonyl derivatives of phosphorus"III# The reaction of trimethylsilylphosphines with one equivalent of phosgene gives rise to intermediate chlorocarbonyl phosphorus"III# compounds[ In the case of t!butyltrimethylsilylphosphine\ ButPHTMS\ this intermediate\ ButPHCOCl "099#\ is stable at low temperatures\ but loses carbon monoxide on warming[ Treatment with base leads to the phosphaketene ButP1C1O\ which is stable below −59>C\ and adds hydrogen chloride to regenerate the chlorocarbonyl derivative "099# ð72TL1528Ł[ The analogous reaction with t!butylbis"trimethylsilyl#phosphine gives the similar intermediate "090#^ however\ this loses TMS!Cl at −89>C to give the same phosphaketene[ When ButP"TMS#1 is treated with two equivalents of phosgene\ the reaction follows a di}erent course\ through the chlorocarbonyl compound "091#\ which was characterised at −39>C by 20P NMR spectroscopy\ to t!butyldichlorophosphine\ ButPCl1 ð72CB098Ł[ These transformations are sum! marized in Scheme 42[ Mesitylbis"trimethylsilyl#phosphine "092# reacts with phosgene via the uniso! lated chlorocarbonyl intermediate "093#\ which eliminates TMS!Cl to a}ord the stable phosphaketene "094# "Scheme 43# ð72AG"E#674Ł[ Cl –CO
TMS ButP
COCl2
ButP H
COCl ButP
H
H (100)
–HCl +HCl
ButP
•
O
–90 °C
TMS ButP
COCl2
COCl ButP
TMS
–TMS-Cl
TMS (101)
2 COCl2
O-TMS ButP PBut ClOC
Cl ButP Cl
(102) Scheme 53
5[03[2[3[1 Chlorocarbonyl derivatives of phosphorus"V# Only one compound of this type has been reported in the literature^ "dimethoxyphosphinyl#formyl chloride "MeO#1P"O#COCl "095# was characterized as a stable\ distillable liquid\ prepared by the
344
One Halo`en But
But
But TMS
But
But
P(TMS)2
But
P
P
•
O
COCl But
But
But
(103)
(104)
(105)
Scheme 54
Arbuzov reaction of trimethyl phosphite with phosgene "Equation "17#\ R Cl# ð46IZV37Ł[ In view of the fact that a simple\ functionalised derivative such as "095# would be expected to have been the subject of further investigations\ this report must be treated with some caution^ however\ the Arbuzov reaction of trimethyl phosphite with aliphatic acid chlorides to yield stable a!keto! phosphonic acid dimethyl esters has also been described "Equation "17#\ R Me# ð34BAU253Ł\ so the analogous reaction with phosgene to yield "095^ R Cl# would not be surprising[ O (MeO)3P + RCOCl
(MeO)2PCOR (106)
R = Cl, Me
(28)
5[03[2[4 One Halogen and One As\ Sb or Bi Function Preparations of these classes of compound have not been reported[ 5[03[2[5 One Halogen and One Metalloid "B\ Si or Ge# Function Preparations of these classes of compound have not been reported[ 5[03[2[6 One Halogen and One Metal Function Metal complexes containing a metalÐhalocarbonyl bond have been reported in all three transition metal series\ but not for the lanthanides or actinides[ The stability of these complexes varies considerably\ the most stable being isolable solids\ una}ected by air^ most are intermediates of very limited stability\ or unexpected products of little importance[ 5[03[2[6[0 Halocarbonyl complexes of _rst transition series metal "iron and chromium# "i# Iron complexes Pentacarbonyl iron has been reported to form an iodocarbonyl iron intermediate on reaction with iodine ð57JOM"02#300Ł[ Subsequently\ tricarbonyl"cyclohexadienyl#iron cation has been shown to give a similar iodocarbonyl complex "096# on treatment with tetraethylammonium iodide in acetone or methyl nitrite with the exclusion of light[ It can be isolated in admixture with a second product\ where the cyclohexadiene ring has been iodinated[ It is stable in the absence of light and has an iodocarbonyl C1O stretching frequency in the IR spectrum at 0624 cm−0 "Equation "18## ð75JOM"201#C10Ł[
Et4NI
(29)
Fe+
Fe CO
OC CO
COI
OC CO (107)
345
Carbonyl Group and at Least One Halo`en
"ii# Chromium complexes When a mixture of tricarbonyl"benzene#chromium and a sterically hindered nitroso compound are subjected to photolysis in carbon tetrachloride\ the chlorocarbonyl chromium complex "097# is formed "Equation "29## ð73MI 503!90Ł[
RN O, hν
(30)
CCl4
Cr
Cr
CO
OC
COCl
OC
CO
N
O R (108)
But R = But,
But But
5[03[2[6[1 Halocarbonyl complexes of second transition series metals "ruthenium and rhodium# "i# Ruthenium complexes When Ru2"CO#01 and bis"triphenylphosphine#nitrogen chloride are stored in THF for 0 h at room temperature\ the dark redÐbrown solution formed contains the chlorocarbonyl ruthenium complex "098#\ which is not isolated\ but can be characterized by IR spectroscopy\ the chlorocarbonyl C1O stretching frequency occurring at 0665 cm−0 ð76JA5904Ł[ (OC)4Ru
Ru(CO)4 Ru
OC
OC CO (109)
COCl
"ii# Rhodium complexes A stable chlorocarbonyl rhodium complex is formed when "009# is treated with oxalyl chloride in toluene at room temperature "Equation "20##[ The yellow precipitate of "000# is stable in air ð58JOM"08#050Ł[ The chlorocarbonyl C1O stretching frequency is at 0579 cm−0[ A second stable complex "001# is formed from the reaction of bis"cyclooctene#chlororhodium with acrolein and 0\1! bis"diphenylphosphino#ethane ð63NKK621Ł[ Ph3P Ph Ph
ClOC
PPh3
RhI P
(COCl)2, RT
Cl OC
Ph P
Rh
Ph3P (111)
(110)
Ph3P PPh3 Rh COCl CHO (112)
Ph (31)
346
One Halo`en
Another chlorocarbonylrhodium complex appears in Chemical Abstracts^ however\ this is a case of ambiguous naming\ as the chlorine and carbonyl functions are individually bonded to rhodium ð57IS88\ 61CL372Ł[
5[03[2[6[2 Halocarbonyl complexes of third transition series metals "rhenium and iridium# "i# Rhenium complexes Bromination of tricarbonyl"cyclopentadienyl#rhenium"I# leads to an intermediate bromocarbonyl rhenium complex "002# which can decarbonylate to the _nal product "003# "Scheme 44# ð76IZV0560Ł[
Br2
–CO
ReI
OC
Br
Re
Re
COBr
CO
OC
OC
CO
CO
CO
(113)
(114)
Br Br
Scheme 55
"ii# Iridium complexes A series of ~uorocarbonyl iridium"III# complexes have been prepared by the reaction of xenon di~uoride with a range of pentacoordinate iridium"I# cations[ Most of these complexes are stable at room temperature[ Extensive structural studies have been carried out\ including an x!ray charac! terisation[ The ~uorocarbonyl C1O stretching frequency for "004# is at 0645 cm−0[ This work is summarised in Scheme 45 ð77CC418\ 82JCS"D#0920Ł[ L Ir
L
+
OC CO
+
OC
XeF2, 0 °C
F Ir
OC
COF
OC L
L
L = PMe3 (115), PEt3, PMe2Ph, PEt2Ph, PEtPh2 L
L
Cl Ir
XeF2, –20 °C
CO
OC
Cl
L CO
Ir L
Cl
+
Ir
COF
F L
OC
COF
F L
1:3
L = PMe3 +
L L Ir
+
L XeF2, –60 °C
L
CO
F Ir COF
L
L
L
L L = PMe3 Scheme 56
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.15 Functions Containing a Carbonyl Group and at Least One Chalcogen (but No Halogen) HEINER ECKERT and ALFONS NESTL Technischen Universita¨t Mu¨nchen, Garching, Germany 5[04[0 CARBONYL CHALCOGENIDES WITH TWO SIMILAR CHALCOGEN FUNCTIONS 5[04[0[0 Two Oxy`en Functions 5[04[0[0[0 Dialkyl carbonates from phos`ene and substitutes 5[04[0[0[1 Dialkyl carbonates from inor`anic carbonates 5[04[0[0[2 Dialkyl carbonates from urea derivatives 5[04[0[0[3 Dialkyl carbonates from carbon oxides and alcohols 5[04[0[0[4 Dialkyl carbonates from formates and ketones 5[04[0[0[5 Cyclic carbonates and transesteri_cation 5[04[0[0[6 Dialkyl carbonates by iodolactonization 5[04[0[0[7 Acyl carbonates 5[04[0[0[8 Carbonates by electrochemistry 5[04[0[0[09 Carbonates via ozonolysis 5[04[0[0[00 Carbonates by miscellaneous methods 5[04[0[0[01 Monoalkyl carbonate complexes 5[04[0[0[02 Polycarbonates 5[04[0[1 Two Sulfur Functions 5[04[0[1[0 Dialkyl dithiocarbonates from phos`ene and COS 5[04[0[1[1 Dialkyl dithiocarbonates by thioneÐthiol rearran`ement 5[04[0[1[2 Dialkyl dithiocarbonates by ð2\2Ł!si`matropic rearran`ement 5[04[0[1[3 Other methods 5[04[0[2 Two Selenium Functions 5[04[1 CARBONYL CHALCOGENIDES WITH TWO DISSIMILAR CHALCOGENIDE ATOM FUNCTIONS 5[04[1[0 Oxy`en and Sulfur Functions 5[04[1[0[0 Dialkyl thiocarbonates from activated carbonates 5[04[1[0[1 Dialkyl thiocarbonates from alkoxycarbonyl sulfenyl chlorides 5[04[1[0[2 Dialkyl thiocarbonates from orthoformates 5[04[1[0[3 Dialkyl thiocarbonates from ethyl xanthate potassium salt 5[04[1[0[4 Miscellaneous thiocarbonates from carbonothioic acid salts 5[04[1[0[5 Other methods 5[04[1[0[6 Alkoxycarbonyl protectin` `roups for sulfur!containin` amino acids 5[04[1[1 Oxy`en and Selenium or Tellurium Functions 5[04[1[2 Other Dissimilar Chalco`enide Functions 5[04[1[2[0 Oxy`en and selenium functions 5[04[1[2[1 Oxy`en and tellurium functions 5[04[1[2[2 Sulfur and selenium functions 5[04[2 CARBONYL CHALCOGENIDES WITH A CHALCOGEN FUNCTION AND ONE OTHER HETEROATOM FUNCTION
359 359 359 351 352 352 355 356 357 358 358 358 358 369 369 360 360 360 361 362 363 363 363 363 367 367 367 368 379 379 370 371 371 371 371 372 372 372
5[04[2[0 Oxy`en and Nitro`en Functions 5[04[2[0[0 Urethanes from chloroformates
348
359
Carbonyl Group and at Least One Chalco`en 373 373 373 374 374 375 375 377 377 378 378 378 389 380 380 381 381 382 383 383 383 384 385 385 385 386 386 386 387
5[04[2[0[1 Urethanes from dialkyl carbonates 5[04[2[0[2 Urethanes from urea 5[04[2[0[3 Urethanes from isocyanates 5[04[2[0[4 Urethanes from isocyanides 5[04[2[0[5 Oxazolidones "cyclic urethanes# 5[04[2[0[6 N!Carboxy a!amino acid anhydrides 5[04[2[0[7 Urethanes as protection for amino functions 5[04[2[0[8 Polyurethanes 5[04[2[0[09 Carbazates 5[04[2[0[00 Azidoformates 5[04[2[1 Oxy`en and Phosphorus Functions 5[04[2[1[0 Phosphinecarboxylates from alkali metal phosphides and carbon dioxide 5[04[2[1[1 Phosphinecarboxylates by the Arbuzov reaction and related methods 5[04[2[2 Oxy`en and Other Heteroatom Functions 5[04[2[2[0 Oxy`en and boron functions 5[04[2[3 Sulfur and Nitro`en Functions 5[04[2[3[0 Thiocarbamates from chlorothioformates and amines 5[04[2[3[1 Thiocarbamates from carbamoyl chlorides and thiols 5[04[2[3[2 Thiocarbamates from isocyanates and thiols 5[04[2[3[3 Thiocarbamates from 0!chlorothioformimidates 5[04[2[3[4 Thiocarbamates from alkylamide salts\ carbon monoxide\ and sulfur 5[04[2[3[5 Thiocarbamates by ð2\2Ł!si`matropic rearran`ement 5[04[2[3[6 Thiocarbamates from 1!dialkyliminium!0\2!oxothiolane iodides 5[04[2[3[7 Thiocarbamates as amine protective `roups 5[04[2[3[8 Thiocarbamates by other methods 5[04[2[4 Sulfur and Phosphorus Functions 5[04[2[5 Other Mixed Systems 5[04[2[5[0 Selenium and nitro`en functions 5[04[2[5[1 Tellurium and nitro`en functions
5[04[0 CARBONYL CHALCOGENIDES WITH TWO SIMILAR CHALCOGEN FUNCTIONS 5[04[0[0 Two Oxygen Functions 5[04[0[0[0 Dialkyl carbonates from phosgene and substitutes Carbonic acid is principally a difunctional carboxylic acid\ therefore there are many preparative methods which provide access to a great variety of its organic derivatives and which di}er widely in rate and selectivity of reactions and reagents[ Phosgene ð53CRV534\ 62CRV64\ B!80MI 504!90Ł\ as the formal carboxylic acid dichloride of carbonic acid\ is a highly reactive reagent which a}ords high turnovers and good yields[ Thus\ both sym! metrical and unsymmetrical dicarbonates\ the latter via chloroformates\ can easily be produced[ Generally phosgene is blown into the reacting alcohol at temperatures of about 49Ð79>C[ The reaction runs at lower temperatures in the presence of acid acceptors such as amines or inorganic hydroxides[ It can also be accelerated catalytically with N\N!dialkylamides or quaternary ammonium salts\ particularly the adduct of two moles of pyridine and one mole of phosgene\ which can also be isolated[ Instead of alcohols and phenols\ the corresponding alcoholates and phenolates can be reacted with phosgene[ The manufacture of diethyl carbonate from phosgene and ethanol with a purity of 88[8) is described in a patent ð75JAP50007238Ł[ The phosgenation of alcohols can be carried out in a one!step as well as in a two!step process "Scheme 0#[ O R1
O R2
+ HCl R 1O
Cl
Scheme 1
Cl O
50–80 °C
OH + R1 O
+ HCl R 1O
Cl
Cl
O
50–80 °C
OH +
OR2
350
Two Similar Chalco`ens
The advantages of the two!step process for producing diethyl carbonate in technical plants have been described ð83JAP95930908Ł[ The greatest advantage of this process is formation of the intermediate chloroformate\ which allows the preparation of a great number of mixed esters of carbonic acid in a well!de_ned way[ In a similar manner to that described for reactions of phosgene\ chloroformate esters react either with alcohols under re~ux or in the presence of amines such as dimethylaniline or pyridine[ Here also crystalline adducts of one mole of chloroformate ester and two moles of pyridine can be isolated[ Alkali alcoholates also react with success[ A useful building block for palladium!catalyzed carbonÐcarbon bond formation by conversion of the carbonic acid ester into a carbon acid ester is methyl propargyl carbonate\ which can be prepared from methyl chloroformate and propargyl alcohol in high yield "Equation "0## ð82S0098Ł[ Even the lithium acetylide derived from this building block is stable under the reaction conditions required for further C0C connections\ as shown in a stereoselective synthesis of the side chain of glaucosterol ð76T4204Ł[ O OH
O
pyridine
(1)
Et2O, RT, 3 h 82%
Cl
MeO
OMe
O
+
Similar substituted 1!alkyl carbonates are used in a synthesis of 0\1!dien!3!ynes ð80JOM"306#294Ł[ A structurally related carbonate with a terminal ethynyl group is prepared according to Equation "1#[ It is a key intermediate in the preparation of "¦:−#!pentalenolactone "E#!methyl ester ð80HCA354Ł[ Reduction of geranylacetone to the corresponding alcohol and conversion into the methyl carbonate a}ords a juvenile hormone analogue "III# ð77ZN"B#0927Ł[ MgBr i, ii, ClCO2Me
(2)
95%
CHO
OCO2Me
The conditions required to form the carbonate from an alcohol and methyl chloroformate are so mild that allenes are stable and not subject to rearrangement as shown in Equation "2# ð89TL4518Ł[ Optically active alcohols react with retention of con_guration "Equation "3## ð77JOC3308Ł[ Nine di}erent alkyl allyl carbonates were prepared from allyl chloroformate and the corresponding racemic alcohols with _nal racemic resolution ð82T09614Ł[ R2
R2
•
•
ClCO2Me
R1
(3)
R1
HO
MeO2CO Ph
Ph
O
pyridine
+ OH
MeO
O
(4)
OMe
Cl O
In 0889 Olofson and co!workers reported the _rst synthesis of O!butadienyl carbonates derived from a\b!unsaturated aldehydes[ Treatment of crotonaldehyde with KOBut in THF at −67>C a}ords the enolate\ which is converted to the carbonate by treatment with the chloroformate "Scheme 1#[ If the aldehyde bears a substituent in the a!position the "E#!butadienyl carbonates are formed exclusively ð89TL0394Ł[ O
O
KOBut
O– K+
Cl
OR
58–83%
R = Et, neopentyl, allyl, CH2CCl3 Scheme 2
O
OR O
351
Carbonyl Group and at Least One Chalco`en
Trialkylsilyl enol ethers react well with ~uoroformates in the presence of a catalytic amount of PhCH1NMe2¦F− "btaf#[ The enolcarbonate from 1!methylcyclohexanone is formed in this way in good yield as illustrated in Equation "4# ð79TL708Ł[ O-TMS
O O
CO2Et
btaf (cat.)
+
+ TMS-F F
EtO
(5)
90%
btaf = benzyltrimethylammonium fluoride
This method cannot be used for enolate or silyl enol ethers derived from aldehydes because of aldol or Michael condensation with another molecule of aldehyde[ To solve this problem\ aldehydes are treated with HF in the presence of an 07!crown!5 catalyst[ The enolates are generated and can be trapped e.ciently as formed with ~uoroformates to give vinylic carbonates[ Fluoroformates can be prepared by halide exchange from the chloroformates and two equivalents of KF "Scheme 2# ð89JOC0Ł[ R1
R1
O
O–
+ F – + KF R2
+ KHF2
R2
R1
O– R2
O
O
R1
+ F
OR3
O
OR3
+ F–
R2 Scheme 3
In all the reactions so far described\ phosgene is the basic chemical used for the preparation of carbonates in a direct way as well as being used in the synthesis of the chloroformates[ To avoid the di.culties associated with the toxicity of phosgene\ substitutes for phosgene have been developed ðB!80MI 504!90Ł[ The liquid trichloromethyl chloroformate "diphosgene# was introduced by Kurita and co!workers and by Ugi and co!workers ð65JOC1969\ 66AG"E#148Ł[ Much safer in storage\ trans! portation and handling is the crystalline bis"trichloromethyl# carbonate "triphosgene#\ which was introduced by Eckert in 0876 ð76AG"E#783\ 89MI 504!91Ł[ Since then\ triphosgene has become well! established for industrial use[ Bis"trichloromethyl# carbonate itself is a dialkyl carbonate and is prepared by radical chlorination of dimethyl carbonate in excellent yield up to 88)[ Carbonate esters 03C!labeled at the carbonyl group can be synthesized by a method utilizing the readily available "03C#phosgene\ which is _rst converted to an isolable alkyl or aryl chloroformate and subsequently reacted with the appropriate alcohol to give the corresponding ester ð75MI 504!90Ł[
5[04[0[0[1 Dialkyl carbonates from inorganic carbonates Carbonic acid esters can be prepared in phase!transfer catalyzed reactions from primary alkyl halides and a mixture of dry potassium hydrogen carbonate and dry potassium carbonate in nonpolar solvents[ The conversion is ine}ective in the absence of hydrogen carbonate and catalyst[ This method uses methyltrioctylammonium chloride as catalyst and toluene or petroleum ether as solvent\ forming symmetric dialkyl carbonates in a one!step process with alkyl groups C5ÐC05 in yields of 56Ð75)[ The unsymmetrical benzyl hexyl carbonate is obtained by reacting dry potassium hydrogen carbonate with benzyl bromide followed by reaction with dry potassium carbonate and hexyl bromide\ yielding 23) of product ð70CB0109Ł[ In a related publication the e}ect of variation of the phase!transfer catalyst is described ð73JOC0011Ł[ Dialkyl carbonates are also easily prepared by the heterogeneous reaction of solid potassium carbonate with alkyl bromides in DMF or DMSO in the presence of organostannyl compounds such as hexabutyldistannoxane or chlorotributylstannane[ A mixed catalytic system consisting of a tributylstannyl compound and 07!crown!5 was e}ective even in less polar solvents[ Well!known phase!transfer catalysts such as 07!crown!5 or benzyltriethylammonium chloride were slightly e}ective but not su.ciently so for this heterogeneous reaction[ It was found by the
352
Two Similar Chalco`ens
authors that the reaction was distinctly accelerated by the addition of triorganostannyl compounds\ especially tributylstannyl compounds\ while the tetrabutyl and dibutyl compounds were not active[ DMF and DMSO were good solvents for this reaction[ Alkyl bromides were more e}ective reagents than the corresponding chlorides or iodides "Equation "5## ð70CL638Ł[ O
cat.
K2CO3 + 2RBr
(6)
+ 2KBr RO
OR
5[04[0[0[2 Dialkyl carbonates from urea derivatives A laboratory method for dialkyl carbonates makes use of 0\0?!carbonylbis"3!benzylidene!0\3! dihydropyridine# as a reagent "Equation "6## ð79S374Ł[ The required activation energy for this reaction is delivered by the aromatization energy from the 0\3!dihydropyridine system to the 3! substituted pyridine[ O N
N
O
+ 2 ButO
THF, 25 °C
+ 2ButOH
N
(7)
OBut
5[04[0[0[3 Dialkyl carbonates from carbon oxides and alcohols Strong bases readily absorb carbon dioxide[ This fact is exploited in the synthesis of carbonates with at least one tertiary alkyl group[ In a two!step process the sodium alcoholate of t!butanol reacts with carbon dioxide to form the stable sodium t!butyl carbonate which reacts with methyl or ethyl iodide to the corresponding mixed carbonates "Scheme 3# ð60ZOR162Ł[ ButOH + Na + CO2
O
6 h, reflux
ButO
O
RI, DMF
O– Na+
ButO
+ NaI OR
R = Me, Et Scheme 4
The reaction with carbon dioxide is also carried out with acetylenic alcohols catalyzed by cobalt! ocene "CoCp1#[ a!Ethynyl tertiary alcohols such as 1!methyl!2!butyn!1!ol undergo cycloaddition with CO1\ yielding a!methylene cyclic carbonates in good yield in the presence of CoCp1 and triethylamine[ In general the reaction is carried out in a temperature range of 79>C to 099>C\ giving yields from 71) to 76) depending on the alcohol "Equation "7##[ Propargyl alcohol\ an a!ethynyl primary alcohol\ a}ords dipropargyl carbonate in only 5) yield and a!"0!alkynyl# tertiary alcohols do not react with carbon dioxide[ It can be presumed that cobaltocene is oxidized to the cobalt! ocenium ion ðCoCp1Ł¦ in the presence of water or alcohol if air is present[ R1 R1 OH + CO2 R2 R1 = Me, Et R2 = Me, Et, Bui R1 ≠ R2
R2
CoCp2 NEt3
O
O
(8)
O
Another method for obtaining symmetrical carbonates from CO1 and alcohols uses triphenyl! phosphane and diethyl azodicarboxylate "dead#[ The authors obtained dipentyl carbonate in 77)
353
Carbonyl Group and at Least One Chalco`en
yield by this route\ di!s!butyl carbonate in 79) yield\ bis"1!ethylhexyl# carbonate in 63) yield\ and diallyl carbonate in 64) yield "Equation "8## ð71JOC4198Ł[ H
O 2ROH + CO2 + Ph3P + dead OR
RO
+ Ph3P O + EtO2C N N CO2Et
(9)
H
dead = diethyl azodicarboxylate
The _rst step of the reaction is the formation of monoalkyl carbonate ion from the alcohol and CO1[ The presence of triethylamine increases the amount of the ion[ The monoalkyl carbonate then undergoes cyclization in the presence of cobaltocene as shown in Scheme 4 ð76BCJ0193Ł[ –
O OH + CO2 + NEt3
[NHEt3H]+
CoCp2
O
O CoII protonolysis
O
O
O
O
O O
Scheme 5
Carbon monoxide alkoxylation reactions have been described[ CO is a low!cost product obtained in many industrial processes and is a good ligand for transition metals^ transition metal catalyzed reactions are therefore obviously possible[ In the late 0859s\ Saegusa and co!workers described a method for producing dimethyl carbonate[ This preparation is carried out by reaction between cupric methoxide and carbon monoxide in pyridine as solvent[ It may be assumed that MeOCOCuOMe is _rst formed by the insertion of carbon monoxide into the copperÐoxygen linkage^ this then decom! poses to produce dimethyl carbonate "Scheme 5# ð57TL720Ł[ This reaction depends strongly on the temperature and reaches its optimum at 69>C[ O
O
CO
Cu(OMe)2
MeO–Cu
OMe
MeO
OMe
Scheme 6
In a similar process\ carbonylation of 0!propanol and 0!butanol in the presence of equivalent amounts of CuCl1 under a pressure of 19Ð099 atm of CO at 59>C yielded in the corresponding carbonates dipropyl carbonate "71)# and dibutyl carbonate "53)#[ At temperatures above 099>C the proportion of the corresponding alkyl formates increases distinctly ð62IZV796Ł[ Nefedov and Sergeeva in a series of three publications describe access to symmetrical and unsymmetrical car! bonates in one! or two!step processes using mercury"II# acetate[ The reactions are carried out in an autoclave with a CO pressure of 099 atm and temperatures of 199Ð119>C[ The formation of the carbonates is described from the following alcohols\ the yield of the carbonate being given in parentheses] methanol "23)#\ ethanol "26)#\ 0!propanol "33)#\ 1!propanol "20)#\ 0!butanol "40)#\ 1!methyl!0!propanol "37)#\ 2!methyl!0!butanol "27)#\ 0!hexanol "33)#\ and 0!heptanol "31)# "Scheme 6# ð61IZV0524\ 61IZV1622\ 62IZV451Ł[ O
O
O
O
+ CO + ROH Hg
MeO
OMe O
O
Hg
RO O
+ Hg + MeCO2H
+ ROH RO
Hg
+ MeCO2H OMe
OMe
RO Scheme 7
OR
354
Two Similar Chalco`ens
All the methods described above use transition metal"II# salts as oxidizing agents[ Another reagent for the oxidation is selenium[ Using a temperature of 19>C and 0 atm of CO\ carbonates from methanol\ ethanol\ 0!propanol\ and 0!butanol were prepared in yields ranging from 83) to 88)[ Benzyl alcohol a}ords the corresponding carbonate under these conditions in 65) yield[ With secondary alcohols such as 1!propanol and cyclohexanol\ and with t!butanol\ yields are 5) to 05) under these conditions[ THF is e}ectively used as solvent "Scheme 7# ð60TL3774Ł[ This approach is achieved more conveniently in a catalytic cycle using oxygen as the oxidizing agent[ For the preparation of dialkyl carbonates derived from primary alcohols under conditions as described above\ reactions according to Scheme 8 are achieved in excellent yields[ The intervention of carbonyl selenide as an intermediate in the catalytic cycle o}ers a reasonable interpretation "path a#\ although there could be another path\ in which the intermediacy of carbonyl selenide is not required "path b# ð64BCJ097Ł[ RO–
Se + CO
SeCO –
O SeCO + RONa
Na+ Se
RO –
O
O
+ –OR
Na+
+ NaSe–
Se
RO
RO
OR
Scheme 8
NaOH
CO
Se
O2
NaOR
(path b) SeCO
NaSeH (RO)2CO
NaOR –
O ROH
(path a)
Na+ RO
Se
Scheme 9
The commercially available and cheap di!t!butyl peroxide is used in another catalytic cycle[ Di! t!butyl peroxide is an e.cient and convenient oxidant in the copper"I# chloride!catalyzed oxidative carbonylation of alcohols to dialkyl carbonates[ The carbonate ester synthesis can be carried out e.ciently with a stoichiometric amount of methanol and "ButO#1 by using pyridine or a substituted pyridine as a catalyst promoter at 89Ð099>C and with CuCl as catalyst[ With 1\5!dimethylpyridine "81>C\ 49 atm#\ yields of dimethyl carbonate and t!butanol are higher than 89) "Scheme 09# ð76CC309Ł[ For the preparation of dimethyl carbonate the best combination is carbon monoxide\ methanol\ and air^ a good yield of 78) is obtainable[ The catalytic system for this purpose is MnCl1ÐCuCl1Ð LiCl "9[4 ] 1[4 ] 1[4# "Equation "09## ð66IZV252Ł[ Patents for producing dimethyl carbonate\ used commercially in the synthesis of triphosgene\ and diethyl carbonate appeared during 0881 and 0882[ The catalysts are mostly copper"I# salts\ some! times promoted by amines such as trialkylamines\ 1!hydroxypyridine\ dipyridyl\ imidazole and phenanthroline^ good results can also be achieved using Co"acac#1 as catalyst[ One patent o}ers the possibility of producing carbonates from C0 to C09 alkanols and from C2 to C5 cycloalkanols ð81JAP93943045\ 81JAP93097654\ 81JAP93245335\ 82EUP417387\ 82EUP423434\ 82JAP94144190\ 82JAP94209533Ł[ Carbonates are also produced as described in a large group of patents using similar metal catalysts to those given above and additionally the nitrous acid ester from the alcohol which is introduced into the carbonate ð82EUP447885\ 82EUP448990\ 82EUP448101\ 82GEP3023577\ 82JAP94144086\ 83EUP470139Ł[
355
Carbonyl Group and at Least One Chalco`en O 2 ROH + CO +
1/ 2
+ H2O
O2 OR
RO O 2 ROH + 2 CO +
1/ 2
O2
OR + H O 2
RO O O
C2H4 + 2 ROH + 2 CO +
1/
2
O2
OR
RO
+ H2O
O Scheme 10
O
cat.
CO + O2 + MeOH
(10) MeO
OMe
5[04[0[0[4 Dialkyl carbonates from formates and ketones It is reported by Kondo et al[ that selenium acts as an unusual oxidizing agent of formates in the presence of alkoxides to a}ord dialkyl carbonates in excellent yields at room temperature under nitrogen "Scheme 00\ reaction 0#\ and the facile oxidation of the NaSeH thus formed to Se with molecular oxygen "reaction 1# initiates a catalytic reaction "reaction 2#[ Formation of the dialkyl carbonates is not observed when formates are allowed to react with sodium alkoxide under the same conditions in the absence of Se "Scheme 00# ð63TL792Ł[ O
O
+ NaOR1 + Se
+ NaSeH
R2O
R2 O
O2
NaOR1 + H2Se
NaSeH + R1OH O R2O
Se + H2O
reaction 2
O
Se
+ NaOR1 + 1/2 O2
reaction 1
OR1
+ NaOH R2O
reaction 3
OR1
Scheme 11
In contrast to the classical BaeyerÐVilliger oxidation of ketones to esters\ no simple methodology exists for the double oxidation of ketones to carbonates[ It is reported that the formal equivalent of a double BaeyerÐVilliger reaction is easily accomplished under mild conditions by oxidation of diethyl ketals with peroxycarboxylic acid[ This facile double oxidation of ketals to orthocarbonates provides an e.cient method for the removal of a carbonyl function from a ketone[ In this reaction the diethyl carbonate is formed in a yield of 49) with 07) of the orthocarbonate "Equations "00# and "01## ð71JA0658Ł[ O Et EtO
OEt
Et
Et
EtOH, H+
Et
EtO
OEt
Et
Et
O
2 mcpba
+ EtO
OEt
(11)
EtO
OEt
EtO
OEt
(12)
356
Two Similar Chalco`ens 5[04[0[0[5 Cyclic carbonates and transesteri_cation
Cyclic carbonates are obtained most simply by reacting phosgene with ethane!0\1!diol at room temperature "Equation "02## ð13JCS"014#1148Ł[ Another method makes use of sodium hydro! gencarbonate as carbonyl source and 1!chloroethanol "Equation "03## ð17GEP405170Ł[ A further gas! phase process uses ethylene oxide and carbon dioxide to produce the cyclic carbonate over charcoal at a temperature of 109>C "Equation "04## ð28GEP639255Ł[ O OH
HO
+ COCl2
O
(13)
O
O OH
Cl
+ NaHCO3
O
O
+ NaCl + H2O
(14)
O
(15)
O O
+ CO2
O
A viable alternative to the traditional method of producing dimethyl carbonate is its generation through transesteri_cation of ethylene carbonate with methanol "Equation "05##[ Dimethyl car! bonate is useful as a gasoline octane enhancer\ methylating agent and urethane precursor[ This reaction is a classical ester exchange\ subject to the general rules of acid and base catalysis[ Bases are generally more e}ective\ the equilibrium being reached more rapidly with bases which have comparable pKb values[ E}ective soluble bases include alkali metal alkoxides\ carbonates\ bicar! bonates and phenoxides^ particularly e}ective are sodium and potassium bicarbonate ð80JMOC278Ł[ Transesteri_cation is also used industrially to produce dimethyl carbonate and diethyl carbonate as shown in recent patents[ Tertiary amines\ nitrogen heterocycles such as dbu\ and quaternary ammonium groups _xed on basic anion exchangers are used as catalysts ð77JAP52127932\ 82EUP432123\ 83EUP472678Ł[ O O O
O
+
+ 2 MeOH MeO
OMe
OH
HO
(16)
Laufer and co!workers have investigated the di}erence between the use of phosgene and triphos! gene to generate a cyclic carbonate derived from a catechol derivative[ Treatment of equimolar amounts of 3!nitrocatechol and dmap in THF with excess phosgene "19) in toluene# consistently produces o!"3!nitrophenylene# carbonate as pale yellow needles in 39Ð34) yield[ Doubling the amount of dmap did not signi_cantly alter the yield of o!"3!nitrophenylene# carbonate\ but replacing phosgene by 1:2 mole of triphosgene per mole of 3!nitrocatechol and raising the temperature to 49Ð59>C improved the yield to 70) "Equation "06## ð78OPP660Ł[ OH
O
O2N
OH
Cl3CO
O
THF, dmap
+ 2/3 OCCl3
50–60 °C
O
(17)
O
O 2N
dmap = dimethylaminopyridine
The proper choice of protecting groups is critical in the synthesis and derivatization of prosta! glandins[ During the course of the authors| research it was necessary to produce 0\2!hydroxy! prostanoid intermediates with a base!labile protecting group[ The reaction with triphosgene gave the 0\2!cyclic carbonate of the prostaglandins "0# "Equation "07## ð82TL284Ł[ O
O
HO
OH
Cl3CO
OCCl3
pyridine, CH2Cl2
O
O
(18)
357
Carbonyl Group and at Least One Chalco`en CO2Bn
O O O O-TBDMS (1)
Kang et al[ have described the regioselective protection of 0\1\2!\ 0\1\3!\ and 0\1\4!triols as 4! membered cyclic carbonates with triphosgene[ The substituted 0\1\2!triol "1S\2S#!3!benzyloxy!0\1\2! butanetriol\ "S#!0\1\3!butanetriol and "1R\2S#!4!tetradecene!0\1\2!triol all react with triphosgene to a}ord the 0\1!cyclic carbonates "Equations "08#Ð"10##[ "3S\4S#!5!Benzyloxy!0\3\4!hexanetriol also reacts in a regioselective manner to form the 3\4!cyclic carbonate "Equation "11## ð83SC294Ł[ OH
OH triphosgene
BnO
BnO
OH
(19)
OH
O
O O
OH
HO
triphosgene
OH O
OH
(20)
O
O
O C8H17
OH
triphosgene
HO
C8H17
O
O
(21)
OH
OH
O OH triphosgene
BnO
O
O
(22)
OH OH
BnO OH
5[04[0[0[6 Dialkyl carbonates by iodolactonization Iodocyclization of a series of homoallylic t!butyl carbonates is an e.cient and moderately erythro stereoselective method for the functionalization of homoallylic alcohols with 0\2!relative asymmetric induction\ as shown in the example in Equation "12# ð71JOC3902Ł[
O OBut
–20 °C, 5–10 h 77%
I
I
I2 (3 equiv.), MeCN
O
O
O
+
O
(23)
O
O erythro 10
O
:
threo 1
In a variation of the method\ the iodolactonization is performed on lithium alkenyl carbonates\ prepared in quantitative yield by bubbling CO1 through a THF solution of lithium alkoxides at
358
Two Similar Chalco`ens
room temperature for 0 h[ The iodolactonization reaction is carried out in homogenous THF solution at room temperature by adding 1[1 equivalents of I1 dissolved in THF to the carbonate ð71JOC3515Ł[ An important intermediate in the total synthesis of nonactin is obtained by iodolactonization of 0\6!octadien!"S#!3!ol!3!t!butylcarbonate to yield 0!iodo!6!octene!1\3!diol 1\3!cyclic carbonate in a cis:trans ratio of 5[4 ] 0[ Further reduction of the iodo group leads to 6!octene!1\3!diol 1\3!cyclic carbonate in 44) yield ð73JA4293Ł[ The same reaction has also been used to solve problems in very complex syntheses of natural products ð82JOC2692Ł[
5[04[0[0[7 Acyl carbonates A well!established coupling reagent in peptide chemistry is the tetraethylammonium salt of an acid\ usually an N!terminal protected amino acid or a peptide\ and a chloroformate "Equation "13##[ The advantage of this acyl carbonate as a coupling reagent in peptide chemistry is that it can form a peptide bond in high yield and without racemization[ The by!products are gaseous carbon dioxide and the corresponding low!boiling alcohol\ which can easily be separated from the product[ In contrast\ the by!products generated in some other methods are often di.cult to remove[ This coupling technique using acyl carbonates proved its superiority in the synthesis of encephalin analogues ð68HCA287Ł[ O
O R
O– NHEt3+
+ Cl
O
THF
O
R
–20 °C
O O
O
(24)
5[04[0[0[8 Carbonates by electrochemistry Carbonic acid esters can be produced by electrolysis of carbon monoxide and the corresponding alcohol in the presence of a halide electrolyte[ The latter plays a catalytic role in carbonate formation[ The e.ciency of the process depends\ among other variables\ on the starting alcohol ð67MI 504!90Ł[ Electrolytic carbonylation of methanol in the gas phase under atmospheric pressure at 232 K is described by Otsuka et al[ The anode in this process is doped with PdCl1 and CuCl1[ The desired product\ dimethyl carbonate\ is produced at 9[79 V ð83CL384Ł[ Several carbonates are also formed in low yield by the anodic oxidation of aqueous potassium butyrate ð78JCR"S#04Ł[
5[04[0[0[09 Carbonates via ozonolysis Ozonolysis of tetramethoxyethylene leads via the ozonide to dimethyl carbonate "19Ð39)# "Scheme 01#[ Higher temperatures and a lower initial concentration of tetramethoxyethylene result in increased yields of dimethyl carbonate ð77CJC1123Ł[ Diethyl carbonate has also been reported as a product of ozonolysis of a ketene diacetal ð81CB1382Ł[ MeO
OMe
MeO
OMe
O O3
O
O
O
+ other by-products MeO MeO
OMe OMe
MeO
OMe
Scheme 12
5[04[0[0[00 Carbonates by miscellaneous methods Diethyl carbonate is obtained in 01) yield by the reaction of di~uorodinitromethane with sodium ethoxide and _nal hydrolysis with H1SO3 "Equation "14## ð71JGU020Ł[ Treatment of carbon disul_de with diethoxytin yields diethyl carbonate over several steps "xanthate\ orthothiocarbonate# "Scheme 02# ð67BCJ2438Ł[
369
Carbonyl Group and at Least One Chalco`en O2N
2 NaOEt +
NO2
F
Sn(OEt)2
F
S
CS2
EtOSn
(25)
12%
EtO
S
Sn(OEt)2
S
O
H2O, H2SO4
OEt
OEt
Sn(OEt)2
+ (EtOSn)2S
EtO
OEt
O
EtOSnS
OEt
EtO
OEt
+ EtOSnSEt EtO
OEt
Scheme 13
5[04[0[0[01 Monoalkyl carbonate complexes The tertiary phosphine!coordinated palladium"9# complexes Pd"styrene#L1 "L PMe2\ PMe1Ph\ PMePh1# react readily with allylic carbonates "methyl 1!methylallyl carbonate and allyl ethyl car! bonate# in THF to a}ord cationic "p!allyl#palladium complexes having an alkyl carbonate anion ðp!allylPdL1Ł¦ðOCOORŁ− "R Me\ Et#[ These complexes are extremely moisture!sensitive and react readily with water to give the corresponding hydrogencarbonate[ Preparation of the corresponding "p!allyl#platinum carbonates leads to analogous products "Scheme 03\ Equation "15## ð81OM060Ł[ + Pt(cod)2
L
OCO2Me
L
+H2O
[OCO2Me]–
Pt
+ 2PMe3
+ 1/
O H O
Pt
2
–MeOH
L
+
L
O 2
2
L = PMe3 Scheme 14
OCO2R
OCO2R
+ PdL
(26)
Pd L
5[04[0[0[02 Polycarbonates Interfacial polycondensation is currently used for the industrial production of polycarbonates[ Bisphenol A is reacted with phosgene at 19Ð39>C in a two!phase mixture consisting of an aqueous alkaline phase and an immiscible organic phase[ The reaction is described in Equation "16#[ O
+
x Na+ O–
Cl
O– Na+
O O
20–40 °C
x
+
Cl
2x NaCl
R3N
(27)
O x
Another method is melt transesteri_cation[ Diphenyl carbonate is transesteri_ed in the melt with
360
Two Similar Chalco`ens
bisphenol A to form polycarbonates[ During this process phenol is removed by distillation "Equation "17## ðB!81MI 504!90Ł[ O
+
n
PhO
OH
HO
OPh
O O
O
190–320 °C
n
+
(28)
2n PhOH
n
As previously described diphenyl carbonate can be obtained from dialkyl carbonates[ The poly! carbonate is prepared using high!purity starting materials "diphenyl carbonate\ bisphenol A#\ improved catalyst systems\ high!viscosity reactors\ and an alternative process route ð80AG"E#0487Ł[ Such a process has been described in a patent ð82EUP450252Ł[ Triphosgene has recently received attention as a substitute for phosgene owing to the development of ecologically more favorable\ phosgene!free production processes[ The same polycarbonate can be obtained by reaction of bisphenol A with triphosgene in the presence of triethylamine as described by Eckert ð76AG"E#783Ł[
5[04[0[1 Two Sulfur Functions 5[04[0[1[0 Dialkyl dithiocarbonates from phosgene and COS Symmetrical S\S?!dialkyl dithiocarbonates are usually synthesized by reacting phosgene with thiols or their sodium salts "Equation "18## ð0761JPR"1#366\ B!51MI 504!90Ł[ O
O
+ 2 NaSR Cl
R
Cl
S
S
(29)
R
Carbon oxysul_de is a good alternative to phosgene for making symmetrical S\S?!dialkyl dithio! carbonates[ Carbon oxysul_de is prepared by triethylamine catalysis from carbon monoxide and elemental sulfur[ With triethylamine and water the reactive species triethylammonium dithio! carbonate is formed[ The latter is alkylated by alkyl halides in 52Ð099) yield "Scheme 04# ð89CL700Ł[ This preparative method is straightforward and convenient^ it avoids the use of toxic phosgene and of thiols[ Et3N
CO + S
COS O
2 COS + H2O + Et3N HS
S– Et3NH+
O
O
+ 2 RX HS
+ CO2
S– Et3NH+
63–100%
RS
SR
X = Cl, Br, I R = Bn, Et, Bun, Hexn, Octn, CH2=CHCH2, 4-MeC6H4CH2, 3,4-Me2C6H3CH2 Scheme 15
5[04[0[1[1 Dialkyl dithiocarbonates by thioneÐthiol rearrangement Previously described synthetic routes restrict the variety of possible products to the symmetrical ones[ For mixed dialkylated dithiocarbonates R0SCOSR1 "R0 R1#\ a common method is the
361
Carbonyl Group and at Least One Chalco`en
thioneÐthiol rearrangement "Schoenberg rearrangement#\ which makes use of an O\S!dialkyl xan! thate R0OCSSR1 "Equation "29##[ The alcohols which are used for this xanthate synthesis vary from simple saturated ð70JOC2030Ł and unsaturated ð61CPB1237\ 81JOC1412Ł alkanols up to complex precursors of natural products\ for example "¦#!milbemycin!b2 ð71JA3697\ 74CC0215Ł\ angelasidine A ð77TL3846Ł\ and kaurenoide ð70JCS"P0#0182Ł[ Xanthates can also be prepared by methylation of potassium O!alkyl xanthates by dimethyl sulfate "alkyl C0ÐC7 functions# in the presence of sodium hydrogencarbonate in water ð70S038Ł[ R1
R2
OH + CS2 +
S
NaH, Na or ButOK
I
(30) R1O
SR2
The thioneÐthiol rearrangement "Equation "20## is a formal interchange of the thione sulfur and the oxygen from the ester component and is principally thermally activated[ It occurs in conjunction with the thermal elimination and is catalyzed by acids such as TFA ð70JOC2030Ł\ by amino com! pounds "for example tricaprylmethylammonium chloride# ð70S038Ł\ 3!piperidinopyridine ð81OPP199Ł\ pyridine N!oxide ð76H"15#1472\ 78CPB465Ł\ 3!dimethylaminopyridine N!oxide ð77H"16#1216Ł\ and by other species including BF2 = Et1O ð67CPB2796Ł\ AlCl2 ð62CPB593Ł\ 1\3\5!trinitroalkoxybenzenes ð63TL3368Ł\ palladium\ platinum\ rhodium\ iridium ð75IJ149Ł\ and phase!transfer catalysts ð79S264Ł[ Yields of 47Ð099)\ mostly in the range 69Ð79)\ are obtained[ Two!phase reactions use quarternary ammonium salts as phase!transfer catalysts[ However\ these conditions proved inadequate in the case in which the O!alkyl group was not methyl and when both alkyl groups were methyl\ because side reactions "hydrolysis and subsequent reactions in the main# were in competition with the rearrangement to S\S?!dialkyl dithiocarbonates[ In this cases the tricaprylmethylammonium salts are used with advantage ð79S264\ 70S038Ł[ cat. or ∆
S R1O
SR2
O (31) R1S
SR2
5[04[0[1[2 Dialkyl dithiocarbonates by ð2\2Ł!sigmatropic rearrangement These rearrangements represent important organic transformations\ especially because of the high stereochemical control that accompanies them[ They are induced thermally[ The following examples of ð2\2Ł sigmatropic rearrangements a}ord S\S!dialkyl dithiocarbonates by intramolecular alkyl migration "Equation "21## ð61CPB1237Ł[ This is a convenient method for the syntheses of dithiocarbonates "1#\ "2# and "3# from myrtenol\ trans!pinocarveol and perillyl alcohol\ respectively ð74JOC007Ł[ Intermediate dithiocarbonates are useful in the preparation of methyl ent!06\06\06! tri~uorokaur!04!en!08!oate and ent!05\05!di~uoro!06!norkauran!08!oic acid ð70JCS"P0#0182Ł[ The _rst synthesis of angelasidine A was accomplished in eight steps starting from farnesol[ The quar! ternary carbon atom of the agelasidine A was constructed by the successful application of the hetero!Claisen allyl xanthate rearrangement[ This methodology provides the basis for a general and e.cient route to the agelasidinine skeleton ð77TL3846Ł[ R
R
∆
S
(32)
O
S
SMe
O
SMe
SMe
S
S
(2)
O
SMe
O S
O
(3)
SMe
(4)
362
Two Similar Chalco`ens
An important step in the total synthesis of milbemicin!b2 is also a hetero!Claisen rearrangement "Equation "22## ð71JA3697\ 74CC0215Ł[ This natural product has enormous potential as a broad! spectrum antiparasitic agent[ O
MeS OH
S
O
O
O
O
SPh
(33)
SPh OP
OP
The next two examples deal with transfer of chirality\ since ð2\2Ł!sigmatropic rearrangement is an important tool for regioselective transformation of allylic alcohols to allylically rearranged products[ This is demonstrated in the asymmetric synthesis of thiotetronic acids\ which is based upon an allyl xanthate to dithiocarbonate rearrangement "Equation "23## ð76CC0117Ł[ For this purpose b! cyclodextrin is used as a catalyst to give the product in good yield and enantiomeric excess of 35) "Equation "24## ð80TL6446Ł[ b!Cyclodextrin provides a chiral environment of an inclusion complex with the xanthates to induce chirality[ The application of ð2\2Ł!sigmatropic rearrangements in the late stages of synthetic sequences has\ however\ been limited by the generally elevated temperatures that are required to induce reaction[ For this and other reasons a number of attempts have been made to _nd catalysts for these sigmatropic rearrangements[ Notable among the attempts is the work of Overman ð73AG"E#468Ł\ who observed that Hg"II# and Pd"II# complexes caused accelerations of the order of 0909 over the thermal uncatalyzed Cope rearrangements[ The overall stereochemistry of the reaction was similar to that of the corresponding uncatalyzed rearrangement ð71JA6114Ł[ An example of this method is shown in Equation "25# ð75IJ149Ł[ EtO2C
EtO2C
SC(O)SMe
(34)
OCS2Me
R O
H
RS
O
S S
[3,3]
O S
H (35)
*
2–5 °C
R = Me, Et, Bn
S O
O SMe
S
O
+ SMe
S
(36) SMe
5[04[0[1[3 Other methods Besides these classical methods\ some less common synthetic approaches have been published[ Sigmatropic rearrangements normally introduce the sulfur into position three of an alkene\ but there is an example in which sulfur is transferred from position 5 to position 0 of a terminal alkene\ accompanied by the formation of a carbonÐcarbon bond "ring closure#[ The authors propose a free radical mechanism for this isomerization of an S!methyl hex!4!enyl xanthate to an S!cyclo! pentylmethyl S?!methyl dithiocarbonate "Equation "26## ð82JOC1783Ł[
363
Carbonyl Group and at Least One Chalco`en O O H
13
O
MeOCO H
H
12
MeOCO
9 11
H
O
(37)
2
15
3
7
S
6
H
S
10
O
1
4 5
SMe
O
O
14
8
SMe
O
A variation of thioneÐthiol rearrangement starting with O!alkyl S!methyl xanthates a}ords bis"methylthio carbonyl# poly!sulfanes "4# via sulfenyl chloride intermediates ROC"SCl#"Cl#SMe ð73JCS"P0#1504\ 72JOC3649Ł[ O
O Sn
MeS
SMe
(5) n = 1 to 6
A method which makes no use of rearrangement and works under very mild thermal conditions is the oxygenation of the lithio derivatives of a!phosphoryl dithiocarbonates "Equation "27## ð73TL1378Ł[ O
Li
O
O2
SR
(EtO)2P
SMe
–78 °C
+ (EtO)2PO2Li RS
(38)
SMe
R = Me, Et
b!Amino!substituted dithiocarbonates are prepared in a simple HBr!catalyzed hydrolysis of substituted thiazolines "Equation "28## ð53JOC1331Ł[ S 6 mol l–1 HBr
S N NH2•2HBr
O HBr•H2N
4 h, reflux 61%
NH2•HBr
S
S
(39)
5[04[0[2 Two Selenium Functions Se\Se?!Dibenzyl diselenocarbonate is prepared in 48) yield by decomposition of dibenzyl tri! selenocarbonate in the presence of an oxygen base such as potassium hydrogencarbonate\ and of mercury dichloride "Equation "39## ð79T0340Ł[ Mechanistic studies on this reaction showed that oxygen bases react in a classic additionÐelimination reaction\ yielding an intermediate benzyl diselenocarbonate anion[ Se
O
80% acetone/water, reflux
(40) BnSe
SeBn
KHCO3, HgCl2
BnSe
SeBn
5[04[1 CARBONYL CHALCOGENIDES WITH TWO DISSIMILAR CHALCOGENIDE ATOM FUNCTIONS 5[04[1[0 Oxygen and Sulfur Functions 5[04[1[0[0 Dialkyl thiocarbonates from activated carbonates The dominant method for producing dialkyl thiocarbonates and bis"dialkoxycarbonyl# sul_des uses alkyl chloroformates and sul_des[ Bis"methoxycarbonyl# sul_de can be prepared by reacting methyl chloroformate and lithium
364
Two Dissimilar Chalco`enides
sul_de in THF to a}ord the product in 40) yield[ Commercial anhydrous Li1S does not dissolve in THF and has to be prepared freshly "Equation "30## ð68T1218\ 67CC727Ł[ O
O
THF
2
O
+ Li2S MeO
(41)
+ 2 LiCl 51%
Cl
MeO
S
OMe
These compounds may also be obtained in very high yields by the reaction of alkyl chloroformates with sodium sul_de nonahydrate in a solidÐliquid system consisting of dichloromethane\ the above! mentioned salt\ and hexadecyltributylphosphonium bromide as phase!transfer catalyst[ A typical procedure consists of the slow addition of 09 mol) excess of powdered sodium sul_de to a well! stirred solution of the alkyl chloroformate and hexadecyltributylphosphonium bromide "4 mol) with respect to the sul_de# in dichloromethane at 9>C[ Bis"alkoxycarbonyl# sul_des are not formed or formed only in low yields without the catalyst[ With the catalyst\ the high yields obtained under mild conditions\ the use of cheap and common laboratory reagents\ the absence of side reactions\ and the simple workup\ make this procedure useful for preparation of bis"alkoxycarbonyl# sul_des "Equation "31## ð71SC786Ł[ O
+ Na2S MeO
O
cat., CH2Cl2
2
O
+ 2 NaCl 93%
Cl
MeO
S
(42)
OMe
cat. = C16H33(C4H9)3P+ Br–
The above methods deal with the reaction of alkyl chloroformates with inorganic sul_des a}ording S!acyl thiocarbonates[ By using thiols instead of inorganic sul_des\ mixed alkyl thiocarbonates can be formed[ An obvious route to unsymmetric alkyl derivatives of thiocarbonic acid uses alkyl chloroformates\ which are obtained from the corresponding alcohol and phosgene[ Because of the toxicity of phosgene\ chloroformates can also be prepared with advantage using triphosgene[ The previously described alkyl chloroformates react with alkanethiols to give alkyl thiocarbonates[ The reaction can be used to obtain branched and unsymmetric dialkyl thiocarbonates "Equation "32## ð65BSF490Ł[ Taylor and co!workers have synthesized S!ethyl O!methyl thiocarbonate\ S! isopropyl O!methyl thiocarbonate\ and S!butyl O!methyl thiocarbonate for use in mechanistic studies of thermal eliminations[ They all are prepared by reacting methyl chloroformate and the corresponding thiol in the presence of pyridine to trap the HCl evolved "Equation "33## ð72JCS"P1#180Ł[ Cl
S
O
O
+
O
(43)
O SH
O MeO
O
pyridine
RSH +
+ Py•HCl
Cl
MeO
(44)
SR
R = Et, Pri, Bu
1!Thiomethyl!1!phenyl!0\2!indanedione is also transformed to the corresponding thiocarbonates as described by Marshalkin et al[ by using methyl and phenyl chloroformates in the presence of the base triethylamine\ as outlined in Equation "34# ð74ZOR0569Ł[ O
O Ph
O SH
O R = Me, Ph
RO
Ph
Et3N
+
(45)
S
Cl O
OR O
365
Carbonyl Group and at Least One Chalco`en
Polyethyleneoxydiisothiocyanates can be obtained by thermolysis of the thioacyl O!ethyl thio! carbonate\ which can easily be prepared by reacting ethylene dithiocarbamate\ ethyl chloroformate\ and triethylamine "Scheme 05# ð74ZOB1099Ł[ H
O
N
S– NEt3+
S H O EtO
O
N
n
S
S
N
n
N
S
H
H
O
+ EtO
S– NEt3+
S
Cl
∆
O
S
OEt
O
SCN
– COS
n
+ EtOH
NCS
n = 1, 2, 3, 4 Scheme 16
The above examples all describe a simple way to obtain the alkyl thiocarbonates[ This class of compounds is also used\ for example\ in the synthesis of juvenile hormone analogues ð77ZN"B#0927Ł\ and as intermediates in prodrug synthesis ð89S0048Ł[ S!Ethoxycarbonyl O!ethyl dithiocarbonate can be obtained by the Holmberg method\ which consists of the reaction of sodium O!ethyl dithio! carbonate with ethyl chloroformate using acetone or ethanol as solvent "Equation "35## ð74PS"14#80Ł[ S
O
S
O
+ EtO
SNa
(46)
+ NaCl EtO
EtO
Cl
S
OEt
1!Propoxycarbonyl thiocyanate can be prepared by the reaction of isopropyl chloroformate with a rhodanide anion ð77PS"28#146Ł[ Ethyl"methoxycarbonylthio#phenylarsine sul_de "5# can be prepared as a by!product in a yield of 16) by reacting ethylmethylphenylarsine sul_de with methyl chloroformate in boiling benzene ð65JGU1330Ł[ S
O
Et As S Ph
OMe
(6)
Esters of O\O!dialkyl dithiophosphoric acids are of marked interest because of their exceptional insecticidal properties and low mammalian toxicity[ These esters can be prepared by reaction of O\O!diethyl dithiophosphoric acid salts with methyl chloroformate\ isopropyl chloroformate\ or benzyl chloroformate to a}ord the corresponding diethyl S!alkoxy!carbonyl dithiophosphate in yields from 51) to 79) depending on the reaction conditions[ The best results are obtained in benzene at 79>C\ but yields are also acceptable when the reaction is carried out in acetonitrile at 19>C "Equation "36## ð75CI"L#039Ł[ S EtO P EtO
benzene or MeCN
O S– Et3NH+
+ Cl
S EtO P
OR
EtO
R = Me, Et,
Pri,
O (47) S
OR
Bn
S!Vinyl O!t!butyl thiocarbonate is obtained "59)# from S!"b!chloroethyl# chlorothioformate by reaction with potassium t!butoxide at −29>C[ The chloroformate can be prepared by reacting phosgene with thiirane at −09>C "Scheme 06# ð66MI 504!91Ł[ O
O S
+
–10 °C
Cl
Cl
Cl
S Scheme 17
O
KOBut, –30 °C
Cl
S
OBut
366
Two Dissimilar Chalco`enides
Thiocarbonates are also important as nonisoprenoid juvenile hormone analogues[ For example\ 1!"2!phenoxyphenoxy#ethanol is condensed with ethyl chloroformate\ giving S!ethyl O!1!"2! phenoxyphenoxy#ethyl thiocarbonate "Equation "37## ð78ZN"B#872Ł[ O O
OH +
O
EtS
Cl
O
O
O
SEt
(48)
O
Ethyl chloroformate also reacts with nitro alcohols in the presence of anhydrous iron"III# chloride to form the respective O!alkyl S!ethyl thiocarbonates[ The reaction proceeds vigorously at ambient temperature\ is complete in a few minutes\ and is essentially quantitative "Equation "38## ð68S599Ł[ It is remarkable that iron"III# chloride exhibits no catalytic e}ect with other alkoxycarbonyl chlorides[ O Cl
O
FeCl3/CH2Cl2
R OH +
(49)
–HCl
SEt
RO
SEt
R = (O2N)3CCH2, FC(NO2)CH2, MeC(NO2)2CH2, O2NCH2CH2
A substitute for an S!alkyl thiochloroformate is an S!alkyl thiocarbonylimidazolium chloride[ Such nitrogen!containing compounds\ for example tertiary amines or imines\ are very good acylating co!reagents ð67T2094Ł[ Another activation of the alkyl thioformate group is provided by the cor! responding bromothioformate\ an example of which is easily derived from tri~uoromethyl thio~uoroformate by halogen interchange[ This species reacts well with sodium cyanide to a}ord the tri~uoromethyl thiocyanoformate "Equation "49## ð67CB1780Ł[ O F 3C
O
+ NaCN S
F3C
Br
(50)
+ NaBr S
CN
In the case of tertiary alkyl groups the corresponding chloroformate is unstable[ In these cases activation is provided by the carbonic acid anhydride[ Both thiophenol and butanethiol react rapidly with di!t!butyl dicarbonate under phase!transfer conditions using the anhydrous potassium carbonate 07!crown!5 system\ and a}ord good yields of the corresponding t!butoxycarbonyl deriva! tives "Equation "40##[ In contrast\ the reaction with aqueous sodium hydroxide and tetra! butylammonium hydrogensulfate does not lead to product\ because the thiocarbonates are immediately hydrolyzed back to the starting thiols ð74CJC042Ł[ O
O
ButO
O
O
K2CO3, 18-crown-6
+ RSH
(51)
OBut
OBut
RS R = Ph, 96%; Bun, 90%
Cyclic thiocarbonates are of especial interest in the chemistry of sugars[ Methyl 1\5!di!O!methyl! 2\3!O!thiocarbonyl b!D!galactoside is added to a solution of methyl iodide and propylene oxide sealed in a glass ampoule and heated to 79>C for 03 h to a}ord the iodothiocarbonates in 88) yield "Equation "41## ð76AJC684Ł[ The importance of thiocarbonates formed by reaction with chloro! formates is also documented in several patents ð70USP113665\ 72MIP7292592\ 80MIP8009528\ 82GEP3039335Ł[ O O S
OMe O
O OMe
MeI,
OMe
O
MeS
OMe
O
O
14 h, 80 °C
I
OMe
OMe OMe
+
I MeS
O O OMe
O
OMe
(52)
367
Carbonyl Group and at Least One Chalco`en
5[04[1[0[1 Dialkyl thiocarbonates from alkoxycarbonyl sulfenyl chlorides Alkoxycarbonyl sulfenyl chlorides are highly reactive electrophilic thiocarboxylating reagents[ Methoxycarbonyl sulfenyl chloride is an established reagent[ This reagent can be used to form S! aryl thiocarbonates from aromatic compounds in the presence of Lewis acids such as AlCl2 or BF2 in methylene chloride or carbon disul_de "Equation "42##[ These thiocarbonates hydrolyze in methanolic potassium hydroxide to the aryl mercaptans in yields of 89) ð66ZC300Ł[
O ClS
S
AlCl3
+ OMe
OMe O
70%
S O
:
3
OMe (53)
+ 1
a!Sulfenylated ketones are also available in a regioselective a!methoxycarbonyl sulfenylation of various ketones or aldehydes employing methoxycarbonyl sulfenyl chloride[ Addition of the corresponding ketones or aldehydes to one equivalent of the reagent in chloroform at room tem! perature for 13 h provides a!methoxycarbonyl sulfenylated carbonyl compounds in good yields[ As an example\ the reaction of nonan!3!one is shown in Equation "43# ð81JOC0942Ł[ O O
O
CHCl3
+ ClS
OMe
S
74%
OMe
(54)
O
Alkanesulfenyl methyl thiocarbonates can also be obtained[ Reaction of benzyl thiol with methoxycarbonyl sulfenyl chloride in methanol yields the disul_de "Equation "44## ð79JOC160Ł[ O Ph
SH
O
+ ClS
Ph
OMe
S
(55) S
OMe
The reagent methoxycarbonyl sulfenyl chloride is easily prepared by reacting methanol with chlorocarbonyl sulfenyl chloride ð77JHC082Ł[
5[04[1[0[2 Dialkyl thiocarbonates from orthoformates O\S!Diethyl thiocarbonate is prepared by reaction of 1!ethoxy!0\2!oxathiolane with t!butyl per! oxide as radical initiator "Equation "45##[ The key step is hydrogen atom abstraction by the initiator[ Under same reaction conditions\ butyl diethoxymethyl sul_de is converted into S!butyl O!ethyl thiocarbonate "Equation "46## ð70ZOR0428\ 74ZOR1195\ 75JOU169Ł[ Lauryl peroxide has also been used as initiator instead of t!butyl peroxide ð76JGU254Ł[ S OEt
120–140 °C 50%
O
OEt S
OEt
O
But2O2
(56) EtS
OEt
O
But2O2 50%
(57) S
OEt
5[04[1[0[3 Dialkyl thiocarbonates from ethyl xanthate potassium salt In research on model systems for disul_de prodrug formation\ dithiocarbonates are often inter! mediates[ They are obtained by the reaction of an alkyl iodide and ethyl xanthate potassium salt[ The thiocarbonate from an alkyl isoalloxazine is obtained in good yield "Equation "47## ð80JMC1938Ł[
368
Two Dissimilar Chalco`enides N
N
O N
N
0 °C to RT CH2Cl2
O
( )n
+
I
N
O (58)
S– K+
EtO
N N
N
O
( )n
OEt
S O
O n = 3–8
5[04[1[0[4 Miscellaneous thiocarbonates from carbonothioic acid salts In reactions analogous to the oxidation of xanthates to dixanthogens and the oxidation of dixanthates to tetraxanthogens\ monothiocarbonates and bis"monothiocarbonates# can be oxidized to the corresponding disul_des[ The oxidation of potassium monothiocarbonates is performed rapidly and quantitatively using iodine "Equation "48## ð62AJC644Ł[ O
O
I2
RO
S– K+
RO
S
(59) S
OR
O
Potassium monothiocarbonates such as potassium O!ethyl thiocarbonate can act as sulfur nucleo! philes and undergo addition to electrophiles such as epoxides or alkyl halides "Equations "59# and "50## ð72JOC4922Ł[ OH
O
O
S
+ S– K+
EtO
(60)
OEt
16% + by-products
O
O Br
O
Br Br
S
+ EtO
S– K+
OEt
+
S
OEt S
OEt
(61)
O O 28%
17%
It is known that the polarizability of chalocogens depends on their position in the periodic table[ In the case of charged species the counterion also plays an important role[ If the counterion is changed to a tertiary amine\ particularly dbu\ thiocarbonates are obtained in optimum yields by S! alkylation of the ammonium salts "Equations "51# and "52# and Table 0#[ The reagent itself is easily prepared by reacting carbon monoxide\ elemental sulfur\ and an alcohol in an autoclave in the presence of dbu "Equation "51## ð77TL3656Ł[ O R1OH + CO + S
dbu
R1O
S– (dbuH)+
(62)
dbu = 1,5-diazabicyclo[5.4.0]undec-5-ene
O
O R2X
R1O
S– (dbuH)+
R1O
SR2
(63)
The nature of the alkylating agent is also important in this type of reaction[ If iodomethane is used\ excellent yields of products are usually obtained ð89ZOB0715Ł[ The potassium O!alkyl thiocarbonate\ used as above\ can also be prepared by a selenium!catalyzed reaction of alcohol\ carbon monoxide\ and sulfur to react in a second step with alkyl halides to a}ord the desired product ð89TL3662Ł[ Using a potassium O!alkyl thiocarbonate\ unsymmetrical dialkoxycarbonyl sul_des are obtained in a reaction with O!alkyl chloroformates "Equation "53## ð89S714Ł[
379
Carbonyl Group and at Least One Chalco`en Table 0 Formation of unsymmetrical thiocarbonates from alcohols and alkyl halides "Equations "51# and "52##[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Alcohol Alkyl halide Product Yield a ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * BunOH PhCH1Br BunOC"O#SCH1Ph 75 BunOC"O#SCH1CH1CH1 099 CH11CHCH1Br n n Bu I BuOC"O#SBu 64 MeOC"O#SCH1Ph 63 MeOH PhCH1Br EtOH PhCH1Br EtOC"O#SCH1Ph 82 PrnOH PhCH1Br PrnOC"O#SCH1Ph 75 i i PhCH1Br Pr OC"O#SCH1Ph 71 Pr OH PhCH1Br n!C09H10OC"O#SCH1Ph 70 n!C09H10OH PhCH1OH PhCH1Br PhCH1OC"O#SCH1Ph 72 PhCH1Br CH11CHCH1OC"O#SCH1Ph 60 CH11CHCH1OH CH2OCH1CH1OH PhCH1Br CH2OCH1CH1OC"O#SCH1Ph 76 t t PhCH1Br Bu OC"O#SCH1Ph 41 Bu OH ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a
Isolated yields based on alcohol used[
acetone/H2O 0 °C to RT
O
O
+ S – K+
R1O
OR2
Cl
O
O
(64) R 1O
93–98%
S
OR2
5[04[1[0[5 Other methods Ozonolysis of 0!methoxyvinyl aryl sulfones leads to S!aryl O!methyl thiocarbonate S\S!dioxides in good yield[ The ozonolysis is carried out in ethyl acetate in the presence of tetracyanoethylene "TCNE# "Equation "54## ð65S397Ł[ O O3, MeCO2Et, TCNE
SO2Ar
MeO
(65)
SO2Ar
MeO
Carbamoyldisul_des are obtained by reacting O!alkyl chlorothioformates with chlorocarbonyl sulfenyl chloride in the presence of phenylmethylamine followed by hydrolysis "Equation "55## ð75JOC0755Ł[ S
O
O
i, PhNHMe
RO
+ RO
Cl
ClS
S
ii, H2O
Cl
S
NMePh
(66)
O
5[04[1[0[6 Alkoxycarbonyl protecting groups for sulfur!containing amino acids The sulfur terminus of cysteine is protected reversibly by easily removable protecting groups of the thiocarbonate type[ Cysteine can also be protected simultaneously at the thiol group and at the amino function "Equation "56##[ To prevent oxidation to the disul_de\ the sodium salt of the thiol group is dissolved in degassed oxygen!free water ð89MI 504!90Ł[ The allyloxycarbonyl residue can also be introduced as a side chain protection for the SH group via the chloroformate "Equation "57## ð82MI 504!90Ł[ Other protecting groups such as isobutyloxycarbonyl are similarly introduced with success to form the thiocarbonate from sulfur!containing amino acids ð81JC130Ł[ O HS
O OH
H
N
i, ii
Ph
H
S
OH H
O
i, Na, NH3(l), –40 °C; ii, Ph
O
O
O
O
N
(67) Ph
O Cl, –15 °C to –5 °C, 90 min, H2O, pH 9–10
370
Two Dissimilar Chalco`enides O O
O
O
O
H2O, pH 7.5
Cl + HS
OH H
N
O
S
t-BOC
OH H
N
(68)
t-BOC
t-BOC = t-butoxycarbonyl
5[04[1[1 Oxygen and Selenium or Tellurium Functions Selenocarbonates are prepared in a convenient one!pot synthesis as described by Segi et al[ The reaction of bis"trimethylsilyl# selenide with BunLi followed by alkylation with an alkyl halide gives alkyl silyl selenides[ The repetition of a similar one!pot reaction with another mole of BunLi\ and the appropriate chloroformate yields unsymmetrical selenocarbonates[ By this route Se!hexyl O! ethyl selenocarbonate\ Se!benzyl O!ethyl selenocarbonate and Se!hexyl O!phenyl selenocarbonate have been prepared in yields from 22) to 64) "Equations "58#Ð"61## ð78CL0998Ł[ BunLi
TMS-SeMe3
(69)
LiSe-TMS 0 °C, 30 min, THF
30 °C, 2 h
LiSe-TMS + R1X
(70)
R1Se-TMS BunLi
R1Se-TMS
O R2O
O
30 °C, 2 h
R1SeLi +
(71)
R1SeLi
0 °C, 30 min
(72) R1Se
Cl
OR2
R1 = C6H13, PhCH2 R2 = Et, Ph
Alternatively\ the reaction of BunLi and selenium gives lithium n!butyl selenide[ The latter reacts in a further step with ethyl chloroformate to produce the selenocarbonate in 04) yield "Scheme 07# ð64BCJ097Ł[ Instead of the lithium salt\ a sodium alkyl selenide can be used[ It is prepared from an alkyl selenol and elemental sodium[ The subsequent step is the reaction with alkyl chloroformates as described above "Scheme 08# ð73ZAAC"402#072Ł[
Se + BunLi
THF, 0 °C
BunSeLi
O
ClCO2Et, 0 °C
BunSe
15%
OEt
Scheme 18
R1SeH + Na
–H2
R1Se– Na+
O
ClCO2R2
R1Se
OR2
Scheme 19
Selenocarbonates with long!chain alkyl groups are prepared by reacting didecyl diselenide\ sodium borohydride\ and methyl chloroformate[ The tellurocarbonates can be obtained in the same way ð80JCS"P1#490Ł[ Tellurodicarbonic acid diesters are obtained as reasonably stable oily compounds by reacting alkyl chloroformates with sodium telluride\ prepared in situ from sodium hydride and tellurium in
371
Carbonyl Group and at Least One Chalco`en
dry DMF\ under phase!transfer conditions[ The yields of diesters range from 28) to 58) "Equation "62## ð78BCJ1006Ł[ O
O
O
2
+ Na2Te
(73)
Cl
RO
RO
OR
Te
R = Me, Et, Pri, Bn
5[04[1[2 Other Dissimilar Chalcogenide Functions 5[04[1[2[0 Oxygen and selenium functions Se!Decyl O!methyl carbonate is prepared by reacting elemental selenium\ hydrazine hydrate\ and 0!bromodecane to yield didecyl selenide\ which reacts in a further step with methyl chloroformate to a}ord the product in 58) yield "Scheme 19# ð80JCS"P1#490Ł[ O
Se +
( )
Br
H2N
9
NH2
( )
Se
9
NaOH MeOH
Se
MeO
( )
O Cl
( )
MeOH
9
9
Se
OMe
Scheme 20
5[04[1[2[1 Oxygen and tellurium functions Te!Decyl O!methyl carbonate can be prepared "29)# from elemental tellurium by its reduction with sodium borohydride and alkylation with 0!bromodecane\ followed by further reaction with methyl chloroformate "Equation "63## ð80JCS"P1#490Ł[ Tellurodicarbonic acid diesters can be syn! thesized by reacting alkyl chloroformates with sodium telluride in the presence of tetrabutyl! ammonium bromide[ The products tellurodicarbonic acid dimethyl!\ diethyl!\ diisopropyl!\ and dibenzyl esters are obtained in reasonable yields of 28Ð58) ð78BCJ1006Ł "Equation "64##[ i, NaBH4, Me(CH2)9Br, DMF
Te
O
O ( ) 9
ii, MeO
+ Na2Te RO
OMe
(74)
Cl
O 2
Te
Cl
O
O
benzene, RT
(75) RO
Te
OR
R = Me, Et, Pri, Bn
5[04[1[2[2 Sulfur and selenium functions S\Se!Dialkyl thioselenocarbonates are prepared in an experimental route starting with the alkylselenol\ as described by Sturm and Gattow[ Sodium ethyl selenide undergoes reaction with S!ethyl thiocarbonate to a}ord S\Se!diethyl thioselenocarbonate in 35) yield "Equation "65## ð73ZAAC"403#019Ł[ O
O
EtSeNa + Cl
SEt
46%
(76) EtSe
SEt
S\Se!Dialkyl thioselenocarbonates are also prepared using mercury reagents[ A typical procedure uses tri~uoromethyl bromothioformate and bis"tri~uoromethylseleno#mercury[ The mixture is
372
One Chalco`en
allowed to react to 029>C over 05 h[ S\Se!Bis"tri~uoromethyl# thioselenocarbonate is obtained in 80) yield "Equation "66## ð67CB1780Ł[ O
O
+ Hg(SeCF3)2 F3CS
+ CF3SeHgBr
91%
Br
F3CS
(77)
SeCF3
5[04[2 CARBONYL CHALCOGENIDES WITH A CHALCOGEN FUNCTION AND ONE OTHER HETEROATOM FUNCTION 5[04[2[0 Oxygen and Nitrogen Functions Urethanes are carbonic acid derivatives containing a carbonyl function directly connected to an alkoxy function and an amino function[ They are important for producing pharmaceuticals and polymers\ and therefore many preparative methods exist[ The formal constitution allows a great deal of variety in the alkoxy component as well as the basic amino function[ In general two synthetic approaches to urethanes can be distinguished^ the _rst method involves a carbonic acid derivative of an alcohol or of a phenol reacting with ammonia or an amine^ the second method involves a carbonic acid derivative of ammonia or an amine reacting with an alcohol or a phenol[
5[04[2[0[0 Urethanes from chloroformates Chloroformates are easily prepared using the readily available triphosgene bis"trichloro! methyl#carbonate ð76AG"E#783Ł[ Chloroformates react easily with ammonia or amines[ n!Butyl chloroformate reacts in concentrated aqueous ammonia to a}ord the corresponding urethane\ the excess ammonia absorbing the hydrochloric acid "Equation "67## ð19JCS697Ł[ This reaction can also be carried out in organic solvents such as ether or toluene[ Of course\ half of the ammonia\ and therefore half of the amine\ is lost as its hydrochloride^ to prevent this\ a tertiary amine\ sodium carbonate or sodium hydroxide is used to absorb the HCl[ For example\ ethyl N!aziridinylurethane is prepared by reacting ethyleneimine and ethyl chloroformate in the presence of triethylamine "Equation "68## ð49LA"455#118Ł[ O
Cl
O
NH2
+ 2 NH3
+ NH4Cl
(78)
O
O O N H + EtO
O
Et3N, benzene
N
60%
Cl
(79)
OEt
A cancer research group in Omaha has developed a convenient method for synthesizing N! ð2HŁmethyl N!nitroso carbamate transfer reagents[ The corresponding intermediates succinimidyl N!methyl carbamate "6#\ penta~uorophenyl N!methyl carbamate "7# and 0\1\1\1!tetrachloroethyl N! methyl carbamate "8# are obtained by reacting triphosgene ð76AG"E#783Ł or 0\1\1\1!tetrachloroethyl chloroformate with N!hydroxysuccinimide\ penta~uorophenol\ or tetrachloroethanol with methyl! amine[ Yields vary from 24) to 85) ð80MI 504!91Ł[
O
H F
O
H O
F
N N O
F
Me
O
F
N O
O
Cl Me Cl3C
O
H
F (7)
(8)
N
(9)
Me
373
Carbonyl Group and at Least One Chalco`en
5[04[2[0[1 Urethanes from dialkyl carbonates Urethanes are also available from dialkyl carbonates by partial aminolysis[ This procedure is advantageous if mild reaction conditions are necessary[ The components\ for example\ diethyl carbonate and ethylenediamine\ are mixed and heated gently to a}ord ethyl N!1!amino! ethylcarbamate "Equation "79## ð23GEP565938Ł[ H
O
+ EtO
OEt
NH2
H2N
N
H2N
OEt
(80)
O
Urethanes are also available from cyclic carbonates[ Einhorn obtained catechol carbonic acid diethylamide from catechol carbonate and diethylamine "Equation "70## ð0787LA"299#034Ł[ O
O
NEt2 (81)
O + Et2NH
O OH
O
Aminolysis of ethyl isopropenyl carbonate with 1!phenylethylamine a}ords O!ethyl N!1!phenyl! ethylurethane in excellent yield[ The advantages of this method are the mild reaction conditions\ the high yield\ the absence of an additional base\ and the formation of acetone as the only by! product "Equation "71## ð67TL2626Ł[ H
O O
OEt
NH2
+ Ph
OEt +
N
Ph
90%
O (82)
O
5[04[2[0[2 Urethanes from urea Urea is suitable as a cheap starting material for N!unsubstituted urethanes[ If urea and alcohols are heated at high temperature\ the corresponding urethanes are obtained in good yields[ In this way carbamic acid benzyl ester can be obtained in yields of 76) by heating benzyl alcohol and urea in the presence of Zn"OAc#1 for 7 h at 049>C "Equation "72## ð35ZN"B#407Ł[ Urea salts\ especially urea nitrates\ can also be used to obtain the urethanes ð0788GEP003285Ł[ O
+ Ph H2N
O
Zn(OAc)2
OH
NH2
(83)
87%
H2N
O
Ph
5[04[2[0[3 Urethanes from isocyanates Isocyanates react easily and mostly quantitatively with alcohols\ particularly primary alcohols\ to produce urethanes "Equation "73##[ However phenolic hydroxy functions react slowly and only in fair yields[ For this reason\ urethanes containing phenolic groups are prepared more advan! tageously by the chloroformate route ðB!20MI 504!90Ł[ O R1NCO + HOR2
R1
N
OR2
(84)
H
Urethanes can also be formed if Hofmann degradation\ Curtius degradation\ or Lossen rearrange! ment is performed in the presence of alcohols or phenols[
374
One Chalco`en
The cephalosporin derivative "09# was prepared in a study of the e}ect of varying the substituent at C!2[ The urethane is prepared by reaction of the 2!desacetyl cephalosporin derivative with benzyl isocyanate "77) yield# ð81JMC2620Ł[ O
MeO
O S
H
N
N
O
Ph
O O
N
Me
O OH
O (10)
5[04[2[0[4 Urethanes from isocyanides If isobutyraldehyde and cyclohexyl isocyanide are added to a solution of n!butylamine in methanol which is saturated with carbon dioxide\ and the solution is then allowed to stand for 19 h at about 19>C\ the urethane can be isolated in almost quantitative yield "Scheme 10# ðB!60MI 504!90Ł[ An analogous four!component condensation "3CC# is observed with benzylamine\ n!butyraldehyde\ and cyclohexyl isocyanide[ BunNH2 + MeOH + CO2
BunNH3+ MeOCO2–
Pri BunNH MeO
PriCHO, c-C6H11NC
Pri NH-c-C6H11
BunN
N-c-C6H11 O
O OMe
O
O Scheme 21
5[04[2[0[5 Oxazolidones "cyclic urethanes# Easy access to oxazolidones is given by reacting ethanolamine with potassium cyanate in an aqueous solution to a}ord 1!hydroxyethylurea\ which cyclizes on distillation to the desired product "Scheme 11# ð92CB0179Ł[ The hydroxyethylurea can also be prepared using methods described above[ O H HO
NH2
H2O
+ KNCO
N
HO
distil.
NH2
O
NH
O Scheme 22
1!Bromoethoxycarbonyl!protected amino acids\ glycine or L!valine\ can generate 1!oxazolidone N!acetic acid "00# or 1!oxazolidone N!isovaleric acid "01# under very strongly alkaline conditions\ like 0 mol l−0 sodium hydroxide\ as described by Eckert and Ugi ð68LA167Ł[ O O
O N
OH
O
N
O (11)
OH O
(12)
375
Carbonyl Group and at Least One Chalco`en
Oxazolidin!1!ones can be prepared in a simple one!step procedure using triphosgene ð76AG"E#783Ł[ L!Serine reacts with 0:2 equivalent of triphosgene at room temperature in dioxan and sodium hydroxide to yield 56) of 3!carboxyoxazolidin!1!one "Equation "74## ð82SC1728Ł[ 1!Amino!4! methoxyphenol can similarly be converted into 5!methoxybenzoxazolinone "Equation "75## ð78S764Ł[ CO2H 1/
+
NH2
3
Cl3CO
CO2H
1 mol l–1 NaOH dioxan
O
OH
MeO
(85)
NH
O
OCCl3
O OH
O
+
1/ 3
NH2
THF, RT, 30 min
MeO
O O
Cl3CO
OCCl3
75%
(86)
N H
5[04[2[0[6 N!Carboxy a!amino acid anhydrides N!Carboxy a!amino acid anhydrides "NCAs#\ or Leuchs anhydrides ð95CB746\ 63HOU"04:1#076Ł\ constitute a special category of mixed anhydrides which achieve both amino group protection and carboxylate activation of a!amino acids simultaneously[ The apparent advantage of the concurrent amine protection and carboxylate activation in NCAs is\ however\ counterbalanced by their high reactivity[ These reagents are sensitive to moisture and are prone to polymerization[ NCAs can be prepared by a facile one!pot reaction at room temperature[ In a typical reaction a N!t!BOC!amino acid and triphosgene are stirred in ethyl acetate at room temperature[ Triethylamine addition to the solution is accompanied by an instantaneous precipitation of triethylammonium chloride to a}ord an intermediate\ which reacts with the loss of carbon dioxide within 1Ð19 h depending on the amino acid to give the desired product[ By this method the NCA of glycine is obtained in a yield of 72) "Scheme 12# ð81JOC1644Ł[ O
ButO
Cl
O
O N H
OH
Cl3CO
O OCCl3
O
Et3N
O
O
O HN
O
ButO
+ CO2 + ButCl O
N H
Scheme 23
Daly and co!workers describe a preparative route which also uses triphosgene[ Treatment of a suspension of L!phenylalanine in anhydrous tetrahydrofuran with 0:2 equivalent of triphosgene at 39Ð49>C leads to a completely homogeneous solution a}ording L!phenylalanine NCA within 2 h in a yield of 72) "Equation "76## ð77TL4748Ł[ O
O OH
NH2
O
+ 1/3
Cl3CO
50 °C, THF
OCCl3
O HN
(87)
O
5[04[2[0[7 Urethanes as protection for amino functions To establish chemoselectivity it is often necessary to block amino functions\ particularly in peptide and nucleotide chemistry\ by reversibly protecting them\ mainly by protective groups of the urethane type[ These can easily be introduced as well as cleaved by standard methods ð63HOU"04:0#35\ B!71MI
376
One Chalco`en 504!91Ł[
Usually benzyloxycarbonyl! "Z!# ð21CB0081Ł\ t!butoxycarbonyl! "t!BOC!# ð46JA5079Ł\ and ~uorenylmethoxycarbonyl! "FMOC!# ð69JA4637Ł residues are applied[ In some cases\ increased selectivity combined with particularly mild reaction conditions is achieved by special methods[ Examples include reagents with b!haloalkyl groups ð65AG"E#570\ 68LA167Ł particularly the 1\1\1! trichloro!t!butoxycarbonyl! "TCBOC!# residue ð67AG"E#250Ł[ A comprehensive survey of carbamate protection of amino functions is available ðB!80MI 504!92Ł[ The following examples illustrate recent uses of carbamate protection in synthesis[ In a synthetic approach to the alkaloid lycorine the amino function of an intermediate is protected by an ethoxycarbonyl residue\ which is introduced by ethyl chloroformate in the presence of triethylamine ð89H"29#728Ł[ Water!soluble analogues of the important antitumor alkaloid camptothecin have been developed by SmithKline Beecham Pharmaceuticals[ The amino group in a polyfunctional intermediate is protected by the Z!residue\ introduced with benzyl chloroformate\ as shown in Equation "77# ð80JMC87Ł[ NO2
H N
NO2
Z–Cl
*HCl
Z N
CH2Cl2, Et3N, 0 °C
Me
O
(88) Me
O
The problem of guanidino function protection has been taken up by Dodd and Kozikowski in the conversion of alcohols to guanidines[ The latter are blocked by Z! or t!BOC!groups[ Thus N\N?! bis"benzyloxycarbonyl#guanidine or N\N?!bis"t!butoxycarbonyl#guanidine react as nucleophiles in the Mitsunobu protocol with several di}erent alcohols according to Equation "78#\ a}ording the corresponding alkylguanidine in excellent yields\ in most cases more than 84) ð83TL866Ł[ H R1
N
N
R1
+
HO
H
R2
R3
R1
dead
H PPh3
NH2
N
N R1
(89)
R3 NH2
R2
R1 = t-BOC or Z
As part of a total synthesis of thymosin b3\ an optimized conventional synthesis of the C!terminal tridecapeptide fragment "20Ð32# is described by Link and Voelter ð82ZN"B#0999Ł[ The N!terminal a! amino group is protected by Z! and the o!amino functions of lysines by t!BOC!residues\ as shown in the following sequence "20Ð32# of thyrosin b3] Z!Lys"t!BOC#!Glu"O!But#!Thr"But#!Ile!Glu"O! But#!Gln!Glu"O!But#!Lys"t!BOC#!Gln!Ala!Gly!Glu"O!But#!Ser"But#!OBut[ t!BOC!Group protection is also useful in an e.cient procedure for the synthesis of phos! phoropeptides by the t!BOC mode solid phase method[ A phosphothreonine!containing peptide related to the EGF receptor protein was synthesized by this methodology ð82CL0390Ł[ For alkylating both ends of tetraamines\ reversible masking of all amino groups is necessary and can be performed by reaction with t!BOC!O!t!BOC ð80JMC458Ł[ Previously described protecting groups\ Z\ BOC\ and FMOC residues are also used in the pharmaceutical and other industries as amino function blocking groups\ as shown in some patents from the 0889s ð82EUP459629\ 82EUP436588\ 82MIP8294915Ł[ An e.cient Leu!enkephalin synthesis using highly lipophilic ferrocenylmethyl "Fem#\ t!BOC\ and TCBOC residues has been performed by Eckert et al[ ð80ZN"B#228Ł[ Introduction of the TCBOC! residue into the building block H!Fem!Gly!OMe is carried out with 1\1\1!trichloro!t!butyl chloro! formate\ yielding 62) product\ as shown in Equation "89#[ The chloroformate TCBOC!Cl is easily obtained by reaction of 1\1\1!trichloro!t!butanol with triphosgene\ as described by the same author ð76AG"E#783Ł[ H N
O
TCBOC N
OMe
+ TCBOC-Cl
pyridine
Fe
OMe (90)
Fe
TCBOC = Cl3CCMe2OCO
O
377
Carbonyl Group and at Least One Chalco`en
The extremely selective and mild cleavage of b!haloalkoxycarbonyl groups makes them excep! tionally useful in semisyntheses of highly sensitive penicillin and cephalosporin derivatives\ as recently demonstrated by Eckert ð89ZN"B#0604Ł[ Introduction of the 1\1!dibromopropoxycarbonyl group by means of its chloroformate at D!phenylglycine produces 89) of the urethane[ The TCBOC!residue is also suitable for amino function protection in nucleotide chemistry[ Ugi and co!workers prepared all possible N!protected nucleosides with TCBOC!residue\ as exempli_ed by the nucleic acid bases N!TCBOC!adenine "02# and N!TCBOC!uracil "03# ð72T1196\ 74ACS"B#650Ł[ A di!TCBOC!adenine derivative is also described by Ugi in the direct synthesis of cyclic AMP derivatives ð82ACS014Ł[ O
CCl3
HN N N
O
O
O N
CCl3 O
N
N
N
O (14)
(13)
An example of another special protective group for amino function protection is the 1!trimethyl! silylethoxycarbonyl residue TMS!CH1CH1OCO "TEOC#[ It proved useful in the key step of a highly stereoselective three component coupling in the _rst total synthesis of the antitumor antibiotic "¦#! hitachimycin[ The urethane intermediate is obtained by reaction with the corresponding chloro! formate in excellent yield\ according to Equation "80# ð81JA7997Ł[ PMB H HN
PMB H
TEOCN Ph
Ph TEOCCl
S
(91)
S
K2CO3, THF 99%
S
S
O-PMB
O-PMB TEOC = 2-trimethylsilylethoxycarbonyl PMB = p-methoxybenzyl
5[04[2[0[8 Polyurethanes Polyurethanes are an important class of polymers ðB!78MI 504!90Ł[ They are produced by poly! addition of diisocyanates with diols[ Typical representative monomers are hexamethylene!0\ 5!diisocyanate\ phenylene!0\3!diisocyanate\ diphenylmethane!3\3?!diisocyanate\ and naphthalene!0\4! diisocyanate as the isocyanate component and 0\3!butanediol\ 0\3!bis"2!hydroxypropyl#benzene\ 0\3!bis"1!hydroxyethoxy#benzene\ 1\1!bisð3!"1!hydroxyethoxy#phenylŁpropane as the diol com! ponent[ Patent literature in this _eld provides information on advances ð81GEP3104537\ 81GEP3108307\ 81JAP94228115\ 81JAP94228431\ 81JAP95922997Ł[
5[04[2[0[09 Carbazates Generally carbazates can be divided into two groups] monoacylated and bisacylated derivatives[ They are obtained simply by reacting alkyl or aryl chloroformates with hydrazine hydrate\ or with alkyl! or arylhydrazine derivatives[ Monocarbazates are formed exclusively by carrying out the above reactions in organic solvents such as chloroform or acetone under ice cooling ð72HOU"E3#162\ 80TL09942\ 82JA7787Ł "Equation "81##[ O O
Ph Cl
+ H2N–NH2•H2O
CHCl3
O O
Ph N NH2 H
(92)
378
One Chalco`en
Instead of chloroformates\ unsymmetrically substituted O!alkyl O?!phenyl carbonates can be used^ the phenoxy group activates the carbonate ester ð57HCA511\ 73CJC463Ł Equation "82##[ H2NNH2
Dpoc–O
Dpoc
N H
NH2
(93)
O Dpoc =
O
Another method for preparing monoacylated carbazates makes use of dialkyl dicarbonates^ thus\ 0!ethoxycarbonyl!0!methylhydrazine is formed by reacting methylhydrazine and diethyl carbonate ð72HOU"E3#163Ł "Equation "83##[ OEt
OEt
O O O
+
Me
N H
NH2
O – CO2 –EtOH
OEt
(94)
N NH2 Me
Bisacylated hydrazines\ particularly the symmetrical ones\ are obtained very easily by reacting chloroformates and hydrazine hydrate in aqueous solution ð55CB1928\ 72HOU"E3#168Ł[ In aqueous solution dialkyl dicarbonates also react with hydrazine hydrate to give N\N?!bis! "alkoxycarbonyl#hydrazines[ Also\ mixed anhydrides prepared from potassium alcoholate\ carbon dioxide\ and dialkyl chlorophosphate react with hydrazine to give bisacylated hydrazines ð72HOU"E3#168Ł[ An acylated carbazate derivative is generated in the reaction of a diaziridinone with the sodium salt of malonitrile in addition to a pyrazoline and a tetraazaspirononane derivative ð81JOC6248Ł[ 5[04[2[0[00 Azidoformates Azidoformate esters\ N2CO1R\ can be prepared by either of the following general routes] "0# the diazotization of the corresponding carbazates NH1NHCO1R^ "1# the reaction of chloroformates ClCO1R with sodium azide or a similar reagent ð72HOU"E3#173Ł[ The chloroformate can be generated in situ from an alcohol and phosgene^ this is illustrated by the conversion of a 06!hydroxysteroid into the corresponding chloroformate "Equation "84## ð80JCS"P0#26Ł[ Alkylcarbonic diethylphosphoric anhydrides\ RCOCO1P"O#"OEt#1\ have been used as alternatives to chloroformates^ for example\ a convenient preparation of t!butyl azidoformate\ BOC!N2\ is the reaction of t!butylcarbonic diethylphosphoric anhydride with potassium azide ð77OSC"5#196Ł[ OH O COCl2 NaN3
O
N3
(95)
MeO
5[04[2[1 Oxygen and Phosphorus Functions The main interest in phosphoryl O!alkyl carbonates is based on the potential biological activity of these phosphorus compounds ð77JMC0720\ 89BBR"060#347\ 82MI 504!92Ł[ In particular\ AZT phos! phonates have been investigated as possible prodrugs in HIV!research ð89BBR"061#177\ 80MI 504!91\ 82MI 504!91Ł[ 5[04[2[1[0 Phosphinecarboxylates from alkali metal phosphides and carbon dioxide Kuchen and co!workers have prepared the lithium and sodium salts of diphenylphos! phinecarboxylic acid from the easily available lithium and sodium diphenylphosphides and carbon dioxide ð80PS"59#176\ 82PS"72#54Ł "Equation "85##[
389
Carbonyl Group and at Least One Chalco`en O Ph2PM + CO2
(96) O– M+
Ph2P M = Na, Li
These compounds rapidly decompose in protic media\ undergoing decarboxylation and formation of diphenylphosphine[ Treatment of the phosphinecarboxylates with TMS!Cl leads to the trimethyl! silyl ester\ and with dimethyl sulfate to the methyl ester\ whereas reaction with alkyl iodides gave only the dialkyldiphenylphosphine with liberation of carbon dioxide "Scheme 13#[ Ph2PH H2O
O
O
TMS-Cl
Ph2P
O-TMS
O
(MeO)2SO2
O– M+
Ph2P
Ph2P
OMe
–CO2 RI Ph2PR Scheme 24
Bubner and Balszuweit synthesized methyl di!n!butoxyphosphinecarboxylate oxide\ "BUO#1 P"O#CO1Me\ in a similar way starting from sodium di!n!butyl phosphite ð76ZAAC"435#031Ł[ 5[04[2[1[1 Phosphinecarboxylates by the Arbuzov reaction and related methods Reaction of alkyl chloroformates with monoalkylphosphines a}ords monoalkylphos! phinecarboxylates^ for example\ phenyl phenylphosphinecarboxylate is obtained in 77) yield ð70ZN"B#809Ł "Equation "86##[ H Ph
P
H
O
K2CO3
+ H
PhO
Cl
P
Ph
88%
OPh
+ HCl
(97)
O
Alkyl dialkoxyphosphinecarboxylate oxides are prepared by reacting alkyl chloroformates and trialkyl phosphites in a typical Arbuzov reaction ð89BBR"060#177Ł "Equation "87##[ If alkoxy"methyl# phosphinecarboxylate oxides are desired\ they can easily be prepared from dialkoxyphos! phinecarboxylates by addition of methyl iodide ð77PS"24#218Ł "Scheme 14#[ O
O
+ (RO)3P RO
Cl
O
O MeI
P
(98)
O
O RO
OR P OR
RO
RO
OMe
RO
OR
+
P
OMe
I–
– RI
RO Me
Me
OMe
P O
Scheme 25
Similarly\ Prishchenko and co!workers have used methyl chloroformate instead of methyl iodide to obtain the phosphinedicarboxylate ð76JGU0373\ 76JGU0159\ 77PS"24#218Ł "Equation "88##[ O
O
O
MeO
+ (EtO)2P
OMe
Cl
OMe
P OEt
OMe O
O
(99)
380
One Chalco`en
Iyer et al[ produced bis"trimethylsilyloxy#phosphinecarboxylates by treatment of tris"trimethyl! silyl# phosphite with alkyl chloroformates ð78TL6030Ł "Scheme 15#[ In the same way\ alkyl"trimethyl! silyl#phosphinecarboxylates are prepared by the use of alkylbis"trimethylsiloxy#phosphines ð75ZAAC"431#26Ł[ A great variety of silylated phosphinecarboxylates have been prepared by Issleib et al[ ð74ZAAC"429#05Ł[ These silylated compounds are suitable for further derivatization[ O H
P
O
TMS-O
TMS-Cl
P O-TMS
OH
ClCO2R
P TMS-O TMS-O
TMS-O
OH
OR O
R = Me, Et, Ph, 2,4-Cl2C6H3 Scheme 26
Acylation of the silylated phosphinosaccharide shown in Equation "099# by benzyl chloroformate is the best method for introducing the carboxylate function at phosphorus ð78CAR"083#198Ł[
O
O
O
O
ClCO2Bn
O
O O
O
O
(100)
O O
P
P
O-TMS
OBn
O
5[04[2[2 Oxygen and Other Heteroatom Functions 5[04[2[2[0 Oxygen and boron functions Trimethylamine!carboxyborane is obtained by activating the cyano group in trimethylamine! cyanoborane by ethylation with triethyloxonium tetra~uoroborate\ followed by hydrolysis of the resulting nitrilium salt with water "Scheme 16#[ Me3NBH2CN + Et3O+ BF4–
CH2Cl2 ∆
Me3NBH2CNEt+ BF4– + Et2O
2 H2O
Me3NBH2CO2H + EtNH3+ BF4–
Scheme 27
Similar amine!carboxyboranes are obtained by the same route ð68JINC0112\
73IC2952\ 73IC3211\
77JOM"233#18\ 78IS"14#68\ 89IC443Ł[
Esteri_cation of the alkylamine!carboxyboranes can be performed in di}erent ways[ Reacting trimethylamine!carboxyborane with methanol using dcc as coupling reagent yields 71) of the corresponding methyl ester ð75S722\ 78IS68Ł "Equation "090##[ O Me3N
B H2
OH
+ MeOH
dcc, CH2Cl2 RT, 1 week
O Me3N
B H2
OMe
(101)
dcc = dicyclohexylcarbodiimide
To obtain the esters in good yields\ alkylamine!carboxyboranes can be treated with the cor! responding chloroformate of the alcohol[ For example\ trimethylamine!carboxy borane methyl ester is obtained "73)# by reacting trimethylamine!carboxyborane and methyl chloroformate with triethylamine ð78IS"14#68Ł "Equation "091##[ O Me3NBH2CO2H +
Cl
OMe
+ Et3N
CH2Cl2
Me3NBH2CO2Me + Et3N•HCl + CO2
(102)
cat., 0 °C
The ester can also be prepared by reacting trimethylamine!carboxyborane with trimethyl ortho! formate in the presence of boron tri~uoride etherate ð81S279Ł "Equation "092##[ Another route
381
Carbonyl Group and at Least One Chalco`en
also starting with trimethylamine!carboxyborane uses N\N?!carbonyldiimidazole as the activating reagent to obtain trimethylamine!imidazole!carbonylborane\ which then reacts with sodium ethox! ide to give the corresponding ethyl ester in a yield of 31) ð74ZN"C#233Ł[ O Me3N
B H2
OH
O
Et2O•BF3
+ HC(OMe)3
Me3N
98%
B H2
(103)
OMe
A method that di}ers from the previously described routes has been developed by Miller\ who has successfully synthesized the 1!carboxylic acid derivative of 0\0\3\3!tetramethyl!0\3!diazonia!1\4! diboratacyclohexane ð80IC1117Ł "Scheme 17#[ H Me2N H2B
H
B
I
Me2N
+ Me3N•BH2N
NMe2 H Me2N H2B
C
NBH2NMe3+ I–
B
H2B
0.5 mol l–1 NaOH
NMe2 H
O
B
0.15 mol l–1 H+
+ 2H2 + Me3N + B(OH)4–
Me2N
NMe2 NH2
H2B
B CO2H NMe2
Scheme 28
Alkylphosphine!carboxyboranes can be obtained in a similar manner[ Triphenylphosphine!car! boxyborane and tricyclohexylphosphine!carboxyborane both are obtained by reacting the cor! responding cyanoborate with triethyloxonium tetra~uoroborate followed by hydrolysis with water to yield the products in 29) and 64) yields\ respectively ð70JINC346\ 81AP"214#156Ł "Equation "093##[ R3P
B H2
O
i, EtO3+ BF4–
CN
R3P
ii, H2O
B H2
(104)
OH
R = Ph, cyclohexyl
Triethyl phosphite!carboxyborane is obtained by a di}erent hydrolysis procedure starting from triethyl phosphite!cyanoborane as outlined in Scheme 18 ð80T5804Ł[ (EtO)3P
B H2
CN
i, EtO3+ BF4–
O (EtO)3P
ii, NaOH (aq.)
B H2
O N H
Et
3 mol l–1 HCl
(EtO)3P
B H2
OH
Scheme 29
5[04[2[3 Sulfur and Nitrogen Functions 5[04[2[3[0 Thiocarbamates from chlorothioformates and amines The synthesis and use of disubstituted thiocarbamates has been well!documented in the literature ðB!69MI 504!90\ B!66MI 504!90\ B!71MI 504!90Ł[ Simple thiocarbamates\ such as N\S!diethyl thiocarbamate and S!ethyl N!phenyl thiocarbamate\ are readily obtained from the reaction of the appropriate amine with ethyl chlorothioformate "Equation "094## ð74JOC4768Ł[ O
O R–NH2 +
R Cl
SEt
N H
SEt
(105)
382
One Chalco`en 5[04[2[3[1 Thiocarbamates from carbamoyl chlorides and thiols
Another method is based on the treatment of thiols with carbamoyl chlorides in the presence of bases or alkali metal thiolates[ In an example reported in 0878\ Threadgill and Gledhill converted N!t!BOC!cysteine methyl ester into the S!"N\N!dimethylcarbamoyl#cysteine derivative in excellent yield by reaction with dimethylcarbamoyl chloride and pyridine "Equation "095## ð78JOC1839Ł[ Me2N SH
O
pyridine
S
+ t-BOC-NH
Cl
CO2Me
NMe2
O (106)
96%
t-BOC-NH
CO2Me
A special synthesis starting from dialkylcarbamoyl chlorides and episul_des in equimolar amounts at 099Ð019>C in the presence of triethylamine or pyridine as catalyst leads to S!1!chloroalkyl N\N! dialkyl thiocarbamates "in analogy to similar epoxide reactions# in yields of 49Ð79) ð57ZOR0550Ł "Equation "096##[ O
O S
R2
+ R1
N
R2
Cl
N R2
R2
R1
S
(107)
Cl
D|Amico and Schafer reported an alternative synthesis of disubstituted thiocarbamates by using potassium alkyl or benzyl dithiocarbonates ð79PS"7#290Ł[ Treatment of these dithiocarbonates with disubstituted carbamoyl chlorides a}ords disubstituted thiocarbamates "Scheme 29#[ R2 –COS
O R2
N
Cl
+ R1O
N
R3
S– K+
OR1
S O
N
SR1
O (A)
R2
S
R3
R3
R2
O R3
N
OR1
S (B)
R1 = Me, Et, Bu Scheme 30
In all probability a mixed anhydride is formed but immediately decomposes to give carbonyl sul_de and the disubstituted thiocarbamate "A#[ The proposed nucleophilic displacement mechanism is depicted in Scheme 20[ Nu O Me
N
S O
S
O
–COS
R1
Me
Me
+ R1Nu S–
N Me S
O S
Nu = R1O
Me S–
O
S
N
R1
Me O Me
N
O S–
+
Me
Me
N Me
Scheme 31
SR1
–COS
383
Carbonyl Group and at Least One Chalco`en
5[04[2[3[2 Thiocarbamates from isocyanates and thiols A widely used route to thiocarbamates is the reaction of isocyanates with thiols "Equation "097##[ In comparison with alcohols\ thiols are less reactive[ Thus the use of higher temperatures or of catalysts such as triethylamine ð46JA255Ł\ dabco\ diacetoxydibutyl stannate ð68GEP1810029Ł\ or triton B "benzyltrimethylammonium hydroxide# ð79AP"202#884\ 70AP"203#204Ł is necessary[ O R2 N C O
R2
+ HS–R1
(108)
SR1
N H
Threadgill and Gledhill synthesized S!"N!alkylcarbamoyl# derivatives of cysteine\ cysteinylglycine and glutathione by this route ð78JOC1839Ł[ Thus N!t!BOC!cysteine methyl ester was carbamoylated smoothly using the appropriate isocyanate in dichloromethane "Equation "098##[ SH
t-BOC-NH
NHR
S
+
R
CO2Me
(109)
O CO2Me
N C O t-BOC-NH
Cysteinylglycine and glutathione derivatives were prepared in the same way[ Many of the depro! tected S!carbamoylamino acids and peptides are metabolites of the corresponding N!alkyl!for! mamides in rodents and in humans[
5[04[2[3[3 Thiocarbamates from 0!chlorothioformimidates Hydrolysis of chlorothioformimidates is another way of preparing thiocarbamates ð55AG109Ł "Equation "009##[ The methods of preparation of the precursors are described in Section 5[19[0[2[1[ In an anhydrous medium these alkylimino chloromethyl sul_des give\ after addition of carboxylic acid and base\ N!acylated thiocarbamates "Scheme 21# ð71JCS"P0#1702Ł[ These are formed by acyl migration from oxygen to nitrogen[ Cl Ph
N
O S
R
NaOH (aq.)
Ph
Cl
R = –(CH2)– ,
N H
S
R
(110)
Cl
, Pr
Cl R1N SR2
R1
R3CO2H base
R2S
R1 N
O O
R3 R3
SR2
N O
O
Scheme 32
5[04[2[3[4 Thiocarbamates from alkylamide salts\ carbon monoxide\ and sulfur An e.cient synthesis of S!alkyl thiocarbamates was developed by Mizuno et al[ ð80TL5756Ł[ The key step of this synthetic method is conversion of a carbamoyllithium species\ generated from a lithium dialkylamide and carbon monoxide\ into the lithium thiocarbamate by addition of elemental sulfur[ In the subsequent step\ S!alkylation with alkyl halides a}ords various S!alkyl thiocarbamates in yields of 44Ð88)[ The reaction provides a useful method for the synthesis of S!alkyl thio!
384
One Chalco`en
carbamates because of the mild reaction conditions\ good yields and easy availability of the reagents "Scheme 22#[ CO (1atm)
THF
R1R2NH + BuLi
R1R2NLi –78 °C, 1 h
–78 °C to –20 °C
O R1
N
O –
S8
Li+
O R 3X
R1
S– Li+
N
–78 °C to 0 °C
R2
R1
R2
N
SR3
R2
Scheme 33
In an earlier work\ Mizuno prepared ammonium thiocarbamates in the presence of selenium as catalyst to obtain S!alkyl thio!carbamates ð78AG"E#341Ł[ The use of selenium as a catalyst for the synthesis of S!alkyl thiocarbamates was described by Koch ð64TL1976Ł\ who treated primary amines with disul_des and carbon monoxide in the presence of selenium "Equation "000##[ The conditions required are mild and aromatic amines can be used provided that triethylamine is added as a cocatalyst[ In the catalyzed system a selenocarbamate intermediate may be involved similarly to the method described by Mizuno and co!workers "Equa! tion "001## ð78AG"E#341Ł[ R2 S
R1–NH2 +
O Se
+ CO
S
R1
O R1
N
Se–
2 SR2 + HSR
(111)
2 – SR2 + R S + Se
(112)
N
R2
H O
R2 + S
R1
S R2
H
N H
5[04[2[3[5 Thiocarbamates by ð2\2Ł!sigmatropic rearrangement Various thiocarbamates were prepared by Koch[ An elegant path to S!aryl thiocarbamates is the thermal rearrangement "NewmanÐKwast rearrangement# of O!aryl thiocarbamates "Equation "002##[ S R
N
O O
Ar
∆
R
R
N
S
Ar
(113)
R
This reaction is formulated as an intramolecular four!membered ring process ð60BCJ0282Ł\ whereas thermal treatment of O!allyl thiocarbamates to S!allylthiocarbamates is described as a ð2\2Ł!sig! matropic rearrangement "Equation "003## ð68CL0250Ł[ R3
R3
S
R2 R1
O
N Me
Me
S
∆
R2
R1 O
Me
(114)
N Me
The thiocarbamates are derived from allylic alcohols after treatment with sodium hydride and N\N!dimethylthiocarbamoyl chloride[ The distillation of this mixture provides the requisite allylic thiocarbamate[ The thiocarbamates have been used by Mimura and co!workers as key intermediates for the stereoselective synthesis of trisubstituted alkenes and of various types of a\b!unsaturated carbonyl compounds ð68CL0250Ł[ For the synthesis of N\N!disubstituted thiocarbamates it is also possible to use COS addition to secondary amines and alkyl halides in aqueous sodium hydroxide "Equation "004## ð79PS"7#290Ł[ This
385
Carbonyl Group and at Least One Chalco`en
method requires the reaction to be carried out at low temperatures "9Ð09>C#[ An excess "29Ð39)# of the secondary amine must be employed in order to minimize the hydrolysis of carbonyl sul_de to carbon dioxide and hydrogen sul_de[ O
R1 N H + COS + NaOH + R2X
R2S
R1
R1 + NaX + H2O
N
(115)
R1
5[04[2[3[6 Thiocarbamates from 1!dialkyliminium!0\2!oxothiolane iodides When working with 1!alkylimino!0\2!oxathiolanes\ Hoppe and Follmann discovered a new method for the preparation of S!vinyl thiocarbamates ð66AG"E#351Ł[ By elimination of HI from 1! dialkyliminium!0\2!oxathiolane iodides\ S!vinyl thiocarbamates are formed "Scheme 23#[ N S
Me
Me MeI
O
+
N
S
Me
R1
S
I–
O
R2
O
–HI
R2 R1
R3
NMe2 R2
R2 R3
R3 Scheme 34
5[04[2[3[7 Thiocarbamates as amine protective groups The thiol!labile dithiasuccinoyl "Dts# Na!amino protecting group and N!thiocarboxy anhydrides of a!amino acids are reported to have certain advantages for peptide synthesis ð57JA2143Ł[ These amino function protecting groups are available from the appropriate ethoxythiocarbonyl derivatives of amino acids "Scheme 24#[ A convenient procedure for the synthesis of ethoxythiocarbonyl derivatives was developed by Barany ð67JOC1829Ł[ O
O
S
N
S
EtO
R1
O
N
Y1
N
R1
S O
H
O
H
R1
S
Y1
O
Y1 = –OH, –OR2, –NHCH(R3)COY2 Scheme 35
5[04[2[3[8 Thiocarbamates by other methods Akiba and Inamoto developed a synthesis of S!alkyl thiocarbamates in which the conversion of an imino group into a carbonyl group is achieved via a nitrosimine ð62CC02Ł[ A mixture of the S! alkylisothiourea or its hydrobromide and isopentyl nitrite in benzene was heated at 49Ð59>C to obtain the S!alkyl thiocarbamate in good yield "Scheme 25#[ +
NH2Br– R1S
NR2R3
Pri
NNO
ONO
R1S
NR2R3
R1 = Bn, Et; R2 = Me, Et, Ph; R3 = Ph Scheme 36
O
–N2
R1S
NR2R3
386
One Chalco`en
The synthesis of rather exotic thiocarbamates is described by Schroll and Barany ð75JOC0755Ł[ The reaction of alkoxydichloromethyl chlorocarbonyl disul_des with an excess of N!methylaniline leads to the postulated key intermediate "A# in Scheme 26\ which o}ers three pathways to di}erent thiocarbamates[ O Cl
S
Cl
S
Cl
OR excess PhNHMe
Ph Me
N
O
O Me
S
Cl
N
Cl
Ph
S
S
Me
N
OR
O
Ph Me
N
S O
Ph
Me S
N Ph
(A)
O RO
S O
S
N
Me Ph Scheme 37
5[04[2[4 Sulfur and Phosphorus Functions It is known that O!alkylthiocarbonyl compounds undergo alkyl migration from oxygen to sulfur[ The ethyl ester of dibutylphosphonous acid reacts with alkyl chlorothioformates to yield phosphinyl alkylthioformates "Equation "005##[ The reaction of the components is accompanied by a thioneÐ thiol rearrangement which occurs at 09Ð24>C^ thus\ the expected phosphinyl thionoformates are not obtained[ Two mechanisms of the rearrangement are possible at the stage of formation of the intermediate product of the Arbuzov reaction[ In the _rst case\ a four!centered cyclic transition state is formed\ similar to that in the thioneÐthiol rearrangement[ In a second variant the authors propose that the phosphorus atom becomes pentavalent\ forming a P0S bond in a three!membered ring[ Stabilization is due to the transfer of the alkyl cation to the sulfur atom ð77ZOB15Ł[ O
S Bun2POEt + MeO
Cl
Bun2P
SMe
+ EtCl
(116)
O
Analogous compounds from the patent literature are important as plant growth regulators\ and are obtained from trialkyl phosphites and chlorothioformates ð63USP2738091\ 64GEP1324396Ł[
5[04[2[5 Other Mixed Systems 5[04[2[5[0 Selenium and nitrogen functions Selenocarbamates can be obtained as described by Kondo and co!workers by reaction of an amine\ carbon monoxide\ and elemental selenium\ followed by treatment with an alkyl halide\ in good to excellent yields ð78AG"E#341Ł[ Se!n!Butyl N\N!diethyl selenocarbamate is prepared quan! titatively by this procedure using n!butyl iodide "Equation "006##[
387
Carbonyl Group and at Least One Chalco`en O
i, CO (1 atm) ii, BunI, THF
Et2NH + Se
(117)
SeBun
Et2N
A di}erent route to the same selenocarbamate uses N\N!diethylcarbamoyl chloride and lithium n!butylselenide ð68S486Ł "Equation "007##[ O
O
BunSeLi + Et2N
+ LiCl
65%
Cl
(118)
SeBun
Et2N
3!Methyl!1!phenyl!0\1\3!selenadiazolidine!2\4!dione is obtained by pyrolyzing 1!methyl!3!phenyl allophanoyl selenocyanate with elimination of HCN ð71TL1722Ł "Equation "008##[ O Ph
N
N
H
Me
O Se
CN
–HCN
N
O
∆
Me
O
(119)
N Se Ph
5[04[2[5[1 Tellurium and nitrogen functions A tellurocarbamate\ Te!butyl N\N!diethyl tellurocarbamate is synthesized by reacting metallic tellurium with n!butyllithium at 9>C and further reaction with diethylcarbamoylchloride "Scheme 27# ð89SC692Ł[ O 0 °C, THF
Te + BunLi
BunTeLi
Et2N
O
Cl, 25 °C
Et2N
TeBun
Scheme 38
Another convenient method to obtain unsymmetrical tellurocarbamates uses bis"N\N!dimethyl! carbamoyl# ditelluride\ which is prepared in 47) yield by treating DMF with sodium metal and elemental tellurium under argon ð74CL0560Ł[ Reduction of this reagent by sodium borohydride and further reaction of the resulting monotelluride with n!hexyl iodide a}ords Te!n!hexyl N\N!dimethyl tellurocarbamate in an excellent yield of 81) "Equation "019## ð81CL0278Ł[ O
O Me2N
Te
NMe2
Te
i, ii
Me2N
Te
C6H13
(120)
O i, NaBH4 (2.2 equiv.), Et2O, –50 °C; ii, n-C6H13I, EtOH, reflux
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.16 Functions Containing a Carbonyl Group and Two Heteroatoms Other Than a Halogen or Chalcogen ANTHONY F. HEGARTY and LEO J. DRENNAN University College Dublin, Republic of Ireland 5[05[0 FUNCTIONS CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGENS OR CHALCOGENS# 5[05[0[0 Carbonyl Derivatives with Two Nitro`en Functions 5[05[0[0[0 Acyclic ureas 5[05[0[0[1 Cyclic ureas 5[05[0[0[2 Carbamoyl azides 5[05[0[1 Carbonyl Derivatives with One Nitro`en and One P\ As\ Sb or Bi Function 5[05[0[1[0 Carbonyl derivatives with one nitro`en and one phosphorus"III# function 5[05[0[1[1 Carbonyl derivatives with one nitro`en and one phosphorus"V# function 5[05[0[1[2 Carbonyl derivatives with one nitro`en and one arsenic function "carbamoylarsines# 5[05[0[1[3 Carbonyl derivatives with one nitro`en and one antimony function 5[05[0[1[4 Carbonyl derivatives with one nitro`en and one bismuth function 5[05[0[2 Carbonyl Derivatives with One Nitro`en and One Metalloid "B\ Si\ Ge# Function 5[05[0[2[0 Carbonyl derivatives with one nitro`en and one boron function 5[05[0[2[1 Carbonyl derivatives with one nitro`en and one silicon function "carbamoylsilanes# 5[05[0[2[2 Carbonyl derivatives with one nitro`en and one `ermanium function "carbamoyl`ermanes# 5[05[0[3 Carbonyl Derivatives with One Nitro`en and One Metal Function 5[05[0[3[0 Carbon monoxide insertion reactions 5[05[0[3[1 Nucleophilic attack on metal carbonyl complexes 5[05[0[3[2 Other methods 5[05[1 FUNCTIONS CONTAINING AT LEAST ONE PHOSPHORUS\ ARSENIC\ ANTIMONY OR BISMUTH FUNCTION "AND NO HALOGEN\ CHALCOGEN OR NITROGEN FUNCTIONS# 5[05[1[0 Carbonyl Derivatives with Two P\ As\ Sb or Bi Functions 5[05[1[1 Carbonyl Derivatives with One P\ As\ Sb or Bi Function To`ether with a Metalloid or Metal Function 5[05[2 FUNCTIONS CONTAINING AT LEAST ONE METALLOID FUNCTION "AND NO HALOGEN\ CHALCOGEN OR GROUP 4 ELEMENT FUNCTIONS# 5[05[2[0 5[05[2[1 5[05[2[2 5[05[2[3
Carbonyl Derivatives with Two Silicon Functions Carbonyl Derivatives with Two Boron Functions Other Carbonyl Derivatives with Two Dissimilar Metalloid Functions Carbonyl Derivatives with One Metalloid and One Metal Function
5[05[3 CARBONYL DERIVATIVES CONTAINING TWO METAL FUNCTIONS
499 499 499 495 400 400 400 401 402 402 402 403 403 404 404 405 405 406 406
406 406 408
408 408 419 419 419 410 410
5[05[3[0 Metal Carbonyl Complexes and Fluxionality
388
499
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en 411 411 411 411 412 412 413 414 414 414
5[05[3[1 Preparation of Metal Carbonyls 5[05[3[1[0 Metal carbonyls of titanium\ zirconium and hafnium 5[05[3[1[1 Metal carbonyls of vanadium\ niobium and tantalum 5[05[3[1[2 Metal carbonyls of chromium\ molybdenum and tun`sten 5[05[3[1[3 Metal carbonyls of man`anese\ technetium and rhenium 5[05[3[1[4 Metal carbonyls of iron\ ruthenium and osmium 5[05[3[1[5 Metal carbonyls of cobalt\ rhodium and iridium 5[05[3[1[6 Metal carbonyls of nickel\ palladium and platinum 5[05[3[1[7 Metal carbonyls of copper\ silver and `old 5[05[3[1[8 Mixed metal carbonyls
5[05[0 FUNCTIONS CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGENS OR CHALCOGENS# 5[05[0[0 Carbonyl Derivatives with Two Nitrogen Functions 5[05[0[0[0 Acyclic ureas "i# Synthesis of urea Urea "2#\ the parent compound of carbonyl derivatives with two nitrogen functions\ may be prepared by the action of ammonia "0# on hydrogen isocyanate "1# "Equation "0## or by using ammonia instead of a substituted amine in the reactions outlined in the subsequent sections ð72HOU"E3#223Ł[ Urea is an important starting material for the synthesis of substituted ureas[ As a weak base it can be used as a catalyst in chemical reactions[ O
+ O C NH
NH3
(1) NH2
H2N (1)
(2)
(3)
"ii# Reaction of amines:imines with phos`ene Phosgene "3# may be attacked by amines or imines to yield N!alkylated symmetrical ureas\ in all cases[ Primary amines require temperatures ×099>C to form substituted ureas successfully^ at temperatures ³099>C the isocyanate may be formed[ Equation "1# outlines the reaction of a secondary amine "4# with phosgene "3# to give the N\N\N?\N?!tetrasubstituted urea "5#[ The reaction takes place in inert solvents and the generated hydrogen chloride reacts with excess amine[ This equation applies equally for primary amines[ For R0 1!nitrophenyl\ R1 H a yield of 70) has been reported ð46JGU1489\ 46JGU1771\ 71JPR116Ł[ For tertiary amines "6# the reaction involves the loss of an alkyl chloride rather than hydrogen chloride[ Benzyl chloride is lost more easily than alkyl chloride but aryl chlorides are more di.cult to remove "Equation "2### ð23BSF133\ 35MI 505!90\ B!60MI 505!90\ 62OSC"4#190\ 70JOC2900Ł[ Imines "8# react similarly "Equation "3##\ usually involving the loss of hydrogen chloride\ which can be reacted with excess imine or an added tertiary amine "e[g[\ pyridine# ð68JPR716Ł[ O
+ R1
Cl
Cl
O
H N
–2[R1R2NH2]+Cl–
R2
R1
toluene, 100 °C, 35 min
N R2
O
+ 2R3N Cl
Cl (4)
R2
(2)
R1 (6)
(5)
(4)
N
O
–2RCl
(3) NR2
R 2N (7)
(8)
490
At Least One Nitro`en O
R1
NH
+ 2 R2
R1
Cl
Cl (4)
R1
O
CHCl3, pyridine
R2
–2HCl
N
N
(4)
R2
(10)
(9)
"iii# Reaction of amines with S!chlorothiocarbonyl chloride The reaction of 0H!benzotriazole "01# with S!chlorothiocarbonyl chloride "00# in dichloromethane at 19>C for 2 h results in the formation of 0!"0H!benzotriazolocarbonylthio#!0H!benzotriazole "02# which\ on heating at 29>C\ yields 0\0?!carbonyl!bisbenzotriazole "03# "51)# with loss of sulfur "Scheme 0# ð68LA0645Ł[
Cl
O
N
O S
Cl
+ 2
N
NEt3, CH2Cl2 –2HCl
N
N N
O S
N
N
∆
N N
N
N
–S
N
N
N N
H (11)
(13)
(12)
(14)
Scheme 1
"iv# Reaction of amines with carbamic acid chlorides This synthesis allows the possibility of forming unsymmetrical ureas[ Again the reaction involves the formation of hydrogen chloride which may be precipitated as an amine hydrochloride salt either by using an excess of base or by adding a tertiary amine "Equation "4## ð25JCS0162\ 56JMC430\ 69JOC732\ 61GEP1195255\ 71JOU0847Ł[ For R0 Et\ R1 Ph\ R2 H\ R3 H the reaction involves the bubbling of ammonia gas "05# "R2 R3 H# through a solution of N!ethyl!N!phenylcarbamic acid chloride "04# and results in the precipitation of ammonium chloride and ½099) yield of the urea "06# ð25JCS0162Ł[ The major drawback of this method is that compound "04# is carcinogenic\ so other synthetic pathways should be employed if possible[
O Cl
H N
R1
+ R3
N
R4
R2 (15)
O
base, 2:1 C6H6:EtOH
(16)
–HCl
R3
N
N
R1
(5)
R2 R4 (17)
"v# Reaction of amines with carbamic acid esters The sodium methoxide!catalysed reaction of amines "08# with carbamic acid esters "07# at 054>C results in the formation of N!substituted ureas[ For R0 Et\ R1 Ph\ R2 H\ R3 Bu\ R4 Bu the product N\N!dibutyl!N?!phenylurea has been isolated in 84) yield "Equation "5## ð57T1256\ 61CL860Ł[ This method works well if the ester group is a good leaving group such as phenoxy\
491
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
3!nitrophenoxy or 1\3\4!trichlorophenoxy[ Both symmetrical and unsymmetrical ureas can be syn! thesized by this method[ O R1
H R3
N
O
+
O dioxane, NaOMe, 165 °C
N
R4
R5
N
–R1OH
R2 (18)
R2
N
R5
(6)
R4 R3 (20)
(19)
"vi# Reaction of amines with carbonic acid esters High temperatures and pressures must be used to e}ect the reaction of diphenyl carbonate "10# with dimethylamine "11#\ but the yield of N\N\N?\N?!tetramethylurea "12# is 62) "Equation "6## ð52AG0948\ 55JMC333\ 62GEP1130360\ 67JHC0120Ł[
O
O
O
H
O Ph
Ph
+ Me
(21)
200 °C, ~200 atm., 4 h
N
Me
(7)
NMe2
Me2N
73%
(23)
(22)
"vii# Reaction of amines with 3\5!diphenylthienoð2\3!dŁ!0\2!dioxol!1!one 4\4!dioxide The following is a general method for the preparation of tetrasubstituted symmetrical or unsym! metrical ureas in very high yields in which the leaving group can be recovered for re!use[ The cyclic carbonate "13# was reacted in THF with an equimolar quantity of amine "14# at 19>C for 29 min[ Following addition of an equimolar quantity of the second amine "15# and re~ux for 19 min\ the tetrasubstituted urea "16# was isolated in overall 68Ð87) yield "Scheme 1# ð68CB616Ł[ NHR1R2 (25)
O O
R3
Ph
Ph
O
SO2
O
SO2
O
THF, 20 °C
Ph
R2
Ph N
R1
O
NHR3R4 (26)
Ph
+
O reflux 79–98%
HO
N R4 N R1
Ph
R2
(24)
SO2 O
(27) Scheme 2
"viii# Reaction of amines with urea This is a general method for the synthesis of N!mono! or N\N!disubstituted ureas[ Alkylamines "18# or hydrochloride salts of alkylamines "29# react with urea "17# in a replacement reaction involving the loss of ammonia or ammonium halide and yielding the required substituted urea "20# in high yield "Equation "7##[ The N\N!disubstituted urea contaminant can be removed by recrystallization[ The above reaction using cyclohexylamine yields N!cyclohexylurea in 85) yield ð72GEP2024000Ł[ O
+ RNH2 (or +NRH3 X–) NH2
H2N (28)
(or NH4X)
(29)
(30)
O
–NH3
(8) NH2
RHN (31)
"ix# Oxidation of thioureas Thioureas "21# may be oxidized to the corresponding ureas "22# by a variety of reagents] manga! nese dioxide in dichloromethane ð67BCJ0134Ł\ t!butyl hypochlorite in carbon tetrachloride ð72T0618Ł\
492
At Least One Nitro`en
sodium nitrite in 3 mol l−0 hydrochloric acid ð71T0052Ł\ or mercuric acetate in dichloromethane "Equation "8## ð89JHC1104\ 80TL3680Ł[ S R1
N
O
oxidation
R4
N
R1
R3 R2 (32)
N
(9)
R4
N
R3 R2 (33)
"x# Addition to isoureas Isoureas "23# may be cleaved by the addition of HX "where X OH\ OR\ NHR# in a nucleophilic fashion to yield substituted ureas "24# as shown "Equation "09## ð63YGK825\ 70ACH46Ł[ N
NMe2
NMe2
O
+HX
(10)
N
O H O
O X
(34)
X = OH, OR, NHR
(35)
"xi# Preparation from ortho!carbonic acid derivatives The hydrolysis of bis"dialkylamino#dichloromethanes "25# results in the isolation of ureas "26# "Scheme 2# ð67IZV119Ł[
CCl4
2RNH2, CuCl2
Cl H
–2HCl
O
Cl N
N
+H2O
H
–2HCl
R
R
H
N
N
R
R
(36)
H
(37)
Scheme 3
"xii# Addition of amines to carbon oxide sul_de This is a two!step reaction which is carried out in inert solvents such as benzene\ toluene\ methanol\ propanol or butanol and involves an intermediate which need not be puri_ed before the subsequent reaction[ N\N!Dimethyl!N?!phenylurea "31# was prepared by the action of dimethyl! amine "28# on carbon oxide sul_de "27# in toluene and the subsequent reaction of aniline "30# with the intermediate "39# formed[ The temperature was maintained at 19>C for 44 min then brought to 71>C over 09 min before maintaining it at 71Ð78>C for 3 h to e}ect complete reaction[ The isolated yield was 70) "Scheme 3# ð68GEP1631047Ł[
O O C (38)
S + 2HNMe2 (39)
+NH
Me2N
S– (40) Scheme 4
2Me2
PhNH2 (41) +
[Me2NH2] HS–
O NHPh
Me2N (41)
493
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
"xiii# Addition of amines\ imines or water to isocyanates or alkali metal cyanates For this reaction\ increasing the electron!withdrawing power on the isocyanate results in an increase in the reactivity towards the nucleophile[ N?!Cyclohexyl!N!ð"1!methoxycarbonyl#phenylŁ urea "34# can be prepared by the reaction of equimolar amounts of the methyl ester of 1!amino! benzoic acid "33# and cyclohexyl isocyanate "32# at re~ux for 19 min in petroleum ether "b[p[ 89Ð 099>C# using a catalytic amount of triethylamine[ The isolated yield was 83) "Equation "00## ð50JOC4127Ł[ This reaction type is known for a large variety of amines and isocyanates ð15JA0625\ 38JA1186\ 46JA4606\ 46LA"598#72\ 51JOC1511\ 52JMC558\ 68JMC17\ 68JOU0966\ 79JCED181\ 79JOC775\ 71CPB423\ 72CPB30\ 89H"20#0282\ 89JOC2588\ 80IZV1482\ 81S186Ł[
H N O
pet. ether (90–100)
+
O C N
H2N
N H
reflux, 20 min 94%
CO2Me
OMe
O
(11)
(44)
(43)
(45)
N\N?!Diphenyl!N!"0!phenyl!0!propenyl#urea "37# can be prepared by reacting equimolar amounts of propiophenone phenylimine "36# with phenyl isocyanate "35# for 1 h at ½029>C[ The reported yield is 66) "Equation "01## ð79CB1388Ł[ This reaction is also generally applicable ð75CB1442Ł[ The reaction of water with alkyl isocyanates "38# leads to the production of primary amines "49# which then react with excess alkyl isocyanate "38# in the usual way to form symmetrical disubstituted ureas "40# "Scheme 4#[ The yield of N\N?!didodecylurea made in this manner has been reported as 80) ð54MI 505!90Ł[ Ph N H
Et
Ph
130 °C, 2 h
+
O C N
Ph
N
Ph
Ph
O
(12)
N
77%
Ph (46)
(47)
(48) R
+H2O
R
H2NR
O C N
NHR
O C N
O
–CO2
NHR (50)
(49)
(51)
Scheme 5
Alkali metal cyanates "41# react with amines "42# to form ureas "43# "Equation "02##[ In the synthesis of N!heptylurea\ heptylamine\ ice\ ice!water and 4 mol l−0 hydrochloric acid were heated to 69Ð79>C before the sodium cyanate was added portionwise[ After 1Ð3 h two phases separated which\ following isolation\ yielded 75Ð77) of the desired monosubstituted urea ð52OSC"3#404Ł[ R1 H N
+ Na+ – NCO
(53)
(52)
(13)
O HCl
R2
NH2
H2O
NR1R2 (54)
"xiv# Hydrolysis of cyanamides Ureas "45# are also formed by the action of water on cyanamides "44# in a reaction which can be catalysed by either acids or bases "Equation "03## ð55CB1826\ 70GEP1744771Ł[ The cyanamides decom!
494
At Least One Nitro`en
pose to the corresponding amides on heating to 064>C with concentrated hydrochloric acid[ The best yields are obtained by using basic hydrogen peroxide under mild conditions[ NH2
H
H2O
N C N
O
(14)
N R
R
H (56)
(55)
"xv# Oxidative amination of carbon monoxide Two equivalents of amine may attack carbon monoxide to form ureas "46#\ provided an oxidation process also occurs "Equation "04##[ In the synthesis of N\N?!bis"ethoxycarbonylmethyl#urea\ carbon monoxide is bubbled through a solution of glycine ethyl ester\ triethylamine and catalytic selenium in THF at 19>C for 3 h[ The isolated yield was 87) ð68S624Ł[ 2 RNH2 + CO + 1/2 O2
NHR
Se
(15)
O –H2O
NHR (57)
"xvi# Reaction of amines with isocyanides Ureas may also be synthesized in a redox reaction of mercuric salts "47# and amine "48# on isocyanide "59# "Equation "05##[ For example\ N!butyl!N?!"1\5!dimethylphenyl#urea "50# is prepared as shown in 77) yield ð61TL3152Ł[ The order of decreasing reactivity of the mercuric salts is Hg"OCOMe2#1 ×Hg"NO2#1 ×HgCl1 ŁHg"CN#1[ O Hg(OCOMe)2 + 3BunNH2 +
–Hg,
BunHN
–2MeCONHBun
CN
N H
88%
(58)
(60)
(59)
(16)
(61)
"xvii# Hydroxyureas and alkoxyureas This class of compounds may be synthesized by the reaction of phosgene with hydroxylamine hydrochloride ð55JCS"C#249Ł\ with N!hydroxylamines ð64CZ134Ł or with O!methylhydroxylamine hydrochloride ð55JCS"C#249Ł in dioxane:water in the presence of potassium acetate to yield the symmetrical N\N?!dihydroxyurea or N\N?!dimethoxyurea[ Carbamic acid chlorides react with hydroxylamine in dioxane\ in the presence of triethylamine\ to form the corresponding N\N!dialkyl!N?!hydroxyurea derivatives[ The yield of N\N!diethyl!N?! hydroxyurea prepared by this method is 57)\ while the reported yield of the N\N!dimethyl derivative is 75) ð63AP"296#6Ł[ N!Hydroxyurea has been prepared by the reaction of ethyl carbamate "urethane# with hydroxyl! amine hydrochloride in alkaline solution at ½19>C with reported yields of 42Ð62) "Equation "06## ð62OSC"4#534Ł[ O Et
O
N H
H
H
+
N H
OH
O •HCl
~20 °C
HO
N
N
H
H
H
(17)
The addition reaction of isocyanates or alkali metal cyanates with hydroxylamine or hydroxyl! amine derivatives in benzene\ THF\ diethyl ether or dichloromethane solution occurs at ½19>C[
495
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
For example\ equimolar amounts of O!phenylhydroxylamine and methyl isocyanate react at 19>C over 0 h to yield 81) of the required N!methyl!N?!phenoxyurea "51# "Equation "07## ð72S360Ł[ H
Me N C O
+
N
O
O Ph
20 °C
Ph
H
O
N
N
H
H
Me
(18)
(62)
"xviii# Acylureas The N!acyl derivative of urea can be prepared by the synthesis of the O!acyl derivative followed by an internal O:N rearrangement of the acyl group ð68COC"1#0983Ł[ For example\ the O!acyl derivative is formed in the reaction of acryloyl chloride and urea[ The O:N rearrangement occurs in inert solvents such as dioxane\ THF or chloroform at 19Ð39>C in the presence of triethylamine or sodium carbonate to give N!acryloylurea in 42[4) yield ð57CB1308Ł[ The reaction of acetamide with half an equivalent of bromine in base gives an isocyanate intermediate which reacts further with acetamide to form N!acetyl!N?!methylurea in 79Ð73) yield ð32OSC"1#351Ł[ Other methods which may be employed in the synthesis of acylureas include the reaction of phosgene with acylamines ðB!54MI 505!91Ł\ the reaction of N!acylcarbamidic acid esters with amines ðB!54MI 505!91Ł\ the hydrolysis of N!acylcyanamides ð57USP2428458\ 57USP2464864Ł\ the reaction of isocyanides with N!bromosuccinimide or with N!bromoacetamide ð52BCJ0203Ł\ the hydrolysis of N!"0!chloro!0!alkenyl#urea ð61AG882Ł\ the addition of carboxylic acids to carbodiimides ð54JOC1738\ 55JA0913\ 56CRV096Ł and the reaction of N!hydroxyformamides with acyl chlorides ð68CZ064Ł[
"xix# Nitrosoureas The synthesis of nitrosoureas may be carried out\ in good yield\ by reacting an N!nitrosocarbamic acid ester with an amine under mild conditions ð71JMC067Ł[ N!Methyl!N!nitroso!N?!"1!phenylethyl#urea "52# has been prepared by the reaction of a solution of N!methyl!N?!"1!phenylethyl#urea in formic acid and water with an aqueous solution of sodium nitrite at 9Ð4>C over 29 min "Equation "08##[ The isolated yield of the N!nitrosourea derivative is reported as 73) ð52JMC558\ 55JA2687Ł[ O Me
O HCO2H, H2O, NaNO2
N H
N
Ph
H
0–5 °C, 30 min
Me
N
N
NO
H
Ph
(19)
(63)
"xx# Azodicarbonyl amides "bis"aminocarbonyl#diazines# Members of this class of compounds have been prepared by the oxidation of the corresponding N\N?!bis"aminocarbonyl#hydrazines or by the reaction of bis"alkoxycarbonyl#diazines with primary or secondary aliphatic amines ð55AG265\ 71AHC"29#0Ł[ The latter has been used to produce N\N\N?\N?! tetramethylazodicarboxamide in 68) yield ð62JOC0541Ł[
5[05[0[0[1 Cyclic ureas "i# Reaction of diamines with phos`ene Cyclic ureas are the products in this and subsequent reactions[ Diamines "53# do not react with phosgene "56# to form the required cyclic urea "58# directly but need to be activated[ Therefore\ the
496
At Least One Nitro`en
diamine "53# is treated with hexamethyldisilazane "HMDS# "54# under re~ux for 09 h to yield 77) "n 3# of the bis"trimethylsilylamino#alkane "55#[ The reaction of "55# with phosgene "56# occurs in toluene at 9>C in 0 h\ facilitated by triethylamine[ For n 2\ the yield is 59)^ for n 3\ the yield is 64)[ The 0\2!bis"trimethylsilyl#!1!oxo product "57# is readily hydrolysed in ½099) yield to form the cyclic urea product "58# "Scheme 5# ð59CB1709\ 64JCS"P0#101\ 66AJC344Ł[ Polymeric ureas may be formed even if the reaction mixture is very dilute[
TMS
H 2N ( )n H2N
H N
H TMS N ( )n TMS N H (66)
TMS (65)
reflux, 10 h 89%
(64)
TMS COCl2 (67), NEt3 toluene, 0 °C, 1 h
H
N ( )n
O
N
H2O, EtOH 100%
N
( )n
O N
TMS
H
(68)
(69)
Scheme 6
"ii# Reaction of imines with chloroformate esters The one!step synthesis of 1!oxo!0\2\3\4!tetraarylimidazolidine "61# has been reported via the reaction of two equivalents of arylaldehyde arylimine "69# with sodium in ether "2 h re~ux# followed by the addition of ethyl chloroformate "60# to the _ltrate of the _ltered initial reaction mixture and 0 h re~ux "Equation "19##[ The reaction yields 59) of a racemic mixture of d! and l! products and 17) of the meso!compound[ The diastereomers can be separated by recrystallization ð69JOC1988\ 60JOC1405\ 79IJC"B#542\ 79S0990Ł[
Ar1 2
i, Na, Et2O, reflux, 3 h
N
ii, ClCO2Et (71), reflux, 1 h
Ar2
Ar2 N
Ar1
N
Ar1
+
O
Ar1
N
Ar1
(20)
O
Ar2 (70)
Ar2 N
Ar2
meso
(72)
d-, l-
"iii# Reaction of diamines with dialkyl carbonates This reaction usually requires vigorous conditions but the reaction of 0\1!diaminoethane "63# with bis"succinimido#carbonate "62# occurs readily at 19>C in good yield "89)# to form 1!oxoimi! dazolidine "64# "Equation "10## ð71SC102Ł[ O H
N O
H2N
O
+
O O
O
20 °C
+ HO N
O H2N
90%
(21)
N H
N
O
N
O
O (73)
(74)
(75)
"iv# Pyrolysis of bis"carboxyalkylamino#alkanes An excellent yield "½099)# has been reported for the thermal conversion of 0\3!bis"carboxy! alkylamino#alkanes "65# into 0\2!dimethyl!1!oxoimidazolidine "66# "Equation "11## ð68AG"E#492Ł[
497
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en CO2– K+
Me
N
Me
N
pyrolysis, 350 °C, 20 torr
(22)
O
Me
–K2CO3 100%
N
N
CO2– K+
Me
(76)
(77)
"v# Reaction of urea with aldehydes and ketones The condensation of aldehydes and ketones with urea can lead to a large variety of mono! and polycyclic ureas[ Cyclic ureas such as 2\6!dioxo!1\3\5\7!tetraazabicycloð2[2[9Łoctane "79# may be synthesized by the reaction of two equivalents of urea "67# with aldehydes such as glyoxal "68# "Equation "12## ð0766LA"078#048\ 41USP1481454Ł[ H
H O
NH2
+
2O NH2
H2O, H2SO4
N
N
N
O
O
70 °C, 1 h 88%
O
N
H
H
(79)
(78)
(23)
(80)
"vi# Cyclization of N!"v!haloalkyl#ureas Ureas may be cyclized readily if there is a suitable leaving group on the N!alkyl chain[ The synthesis of 0\2!diphenyl!1!oxoimidazolidine "71# "R0 R1 Ph\ R2 R3 H# was carried out by reacting 09 mol l−0 sodium hydroxide in ethanol for 04 min at re~ux with 0!"1!chloroethyl#!0\2! diphenylurea "70# "R0 R1 Ph\ R2 R3 H#[ The yield was reported as 35) "Equation "13## ð62JHC528Ł[ This procedure is generally applicable for various R groups\ leading to a wide variety of cyclic ureas "71# ð40JOC0718\ 42CJC785\ 42JA0019\ 54CJC0687\ 69JOC732\ 60JHC446\ 68JOU0966Ł[ R4 R2 N
R3
N
NaOH, EtOH, reflux, 1.5 min
R3
O
R2
Cl
(24)
O –HCl
N
N H
R4
R1
R1 (81)
(82)
"vii# Addition of diamines to alkali metal cyanates Diamines "72# add to alkali metal cyanates "73# to yield cyclic ureas "74# "Equation "14## ð55JMC741Ł[ The reaction gives yields of 21Ð77) for various R groups "R H\ Me\ CF2\ SMe\ Cl\ Br# and is again applicable to other similar systems ð34JA1968\ 36JA2049\ 46JA4609\ 62JMC890Ł[ R
R i KOCN (84), H+
H
N
H2N (83)
ii, 215–225 °C
N
O N H
(85)
(25)
498
At Least One Nitro`en "viii# Cyclization of N!"1!propynyl#ureas
N!"1!Propynyl#ureas "75# are cyclized in good yield at mild temperatures by the action of base to form cyclic ureas "76# "Equation "15## ð51JOC2968\ 52JOC880\ 53JOC0740\ 67JOC50Ł[
O
R4
R4 N H R2
O 80–90%
R3
N
N
NaOEt, 20 °C, 1 h
R1
R1 (86)
(26)
R3
N R2
(87)
"ix# Cyclization of N!haloureas 2!Membered ring cyclic ureas can be synthesized in good yield from N!haloureas[ The cyclization is carried out by potassium in pentane or by potassium t!butoxide in t!butanol[ For example\ the reaction of bis"t!butyl#urea "77# in t!butanol with t!butyl hypochlorite yields the N!halourea "78#\ which may then be cyclized by the addition of potassium t!butoxide to form the cyclic urea "89# in an overall 89) yield "Scheme 6# ð58JOC1143Ł[ This reaction also works for other N!substituted ureas ð58JOC1152\ 61LA"654#83\ 67JOC811Ł[ But
But N H
O N H
ButOH, ButOCl
N Cl O
But ButO– K+
O
10 min
10 min
N H
But
N N But
But
(88)
(89)
(90)
Scheme 7
"x# Oxidation of cyclic thioureas Cyclic thioureas "80# can be oxidized to the corresponding cyclic ureas "81# by the action of a range of oxidizing agents such as potassium permanganate ð66BSB552Ł\ hydrogen peroxide ð45CB232\ 47JA5398\ 70JMC0978Ł or dimethyl selenoxide ð67JOC1021Ł "Equation "16##[ N S
oxidation
N
(27)
O
N
N
(91)
(92)
"xi# Addition of diamines to carbon oxide sul_de The synthesis of 1!oxo!perhydropyrimidine "84# involves the reaction of 0\2!diaminopropane "82# and carbon oxide sul_de in 49) ethanol at 56>C for 19 min followed by the addition of HCl and heating at 73>C for 0[4 h[ The isolated yield of "84# was 70) ð68USP3043820Ł[ The reaction goes through an intermediate "83# "Scheme 7#[
409
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en O –S
H2N
COS
NH2
H N
N
–H2S
H
O
+
N H (95)
H3N (93)
(94) Scheme 8
"xii# Reaction of isocyanates and aziridines The reaction of isocyanates "85# with aziridines "86# proceeds smoothly at 099>C in the presence of lithium halides to yield cyclic ureas "87#[ For R0 benzoyl and R1 1!phenylethyl the yield of 0!benzoyl!1!oxo!2!"1!phenylethyl#imidazolidine "87# has been reported as 48) "Equation "17## ð55LA"587#079Ł[ Alkyl and aryl isocyanates also trimerize in a competing reaction[ R1 R1 N C O
N R2
+
N
LiX
O
(28)
100 °C, 1–3 h
(96)
(97)
N R2 (98)
X = Cl, Br
"xiii# Reaction of carbodiimides and oxiranes This reaction is catalysed by alkali metal hydroxides\ tertiary amines or lithium chloride[ A cyclic urea "090# has been synthesized in the reaction of phenyl oxirane "099# with diphenylcarbodiimide "88# at 199>C under nitrogen for 6 h and in the presence of lithium chloride[ The reported yield was 82) "Equation "18## ð50CB2176Ł[ Ph Ph N C
+
N
N
LiCl, N2
O
(29)
O
Ph 200 °C, 7 h
Ph
Ph
N Ph
(99)
(100)
(101)
"xiv# Reaction of diamines with carbon monoxide The reaction of diamines "092# with carbon monoxide "091# takes place using various conditions\ depending on the chain length\ to yield the cyclic ureas "093#[ Either sulfur in methanol or selenium in THF can be used for the reaction and the conditions vary from 39Ð019>C\ and from 3Ð49 atm pressure to give yields of 47Ð87) "Equation "29## ð60JA5233Ł[ H N
H 2N CO + H 2N (102)
(103)
58–98%
(30)
O N H (104)
"xv# Rin` expansion of cyclic amidoximes The synthesis of 1!oxo!0\2!diazacyclododecane "095^ x 6# is carried out by Beckmann rearrange! ment on 1!hydroximinoazacycloundecane "094^ x 6# in phosphoric acid for 09 min at 019>C\ then
400
At Least One Nitro`en
49 min at 039Ð049>C[ The reported yield of the cyclic urea "095# was 65) "Equation "20## ð46LA"596#56\ 67JOC0433Ł[ This is a very good method for preparing cyclic ureas containing large rings[ H HO
N N
H3PO4, 120–150 °C
( )x
N O
( )x
76%
H
(31)
N H (106)
(105)
5[05[0[0[2 Carbamoyl azides Carbamoyl azides\ R0R1NCON2\ are most generally prepared by one of two routes[ The _rst of these is the displacement of chloride from the corresponding carbamoyl chloride\ R0R1NCOCl\ by reaction with sodium azide ð69JHC796Ł[ The second general route involves the diazotization of the hydrazides R0R1NCONHNH1 ð75T1566Ł[ The second method was used to prepare the highly unstable and explosive carbonic diazide\ CO"N2#1\ ð0784JPR"1#361Ł which has subsequently been shown to react with benzene to give N!"azidocarbonyl#azepine ð55CI"L#0155Ł[ Carbamoyl azides RNHCON2 can also be prepared directly from aldehydes RCHO by oxidation with pyridinium chlorochromate "pcc# in the presence of sodium azide[ This method probably involves the intermediacy of an acyl azide which undergoes Curtius rearrangement and further reaction with sodium azide ð77SC434Ł[
5[05[0[1 Carbonyl Derivatives with One Nitrogen and One P\ As\ Sb or Bi Function 5[05[0[1[0 Carbonyl derivatives with one nitrogen and one phosphorus"III# function The synthesis of carbonyl derivatives with one nitrogen and one phosphorus function\ the phosphorus being a secondary phosphine "098#\ is achieved by reacting a phosphine "096# with an isocyanate "097# "Equation "21##[ The reaction has been carried out with R0 R2 phenyl and R1 "CH1#n SH "n 1\ 2# at room temperature and resulted in an isolated yield of 51Ð64) ð62JPR360Ł[ The same reaction with R0 Ph or cyclohexyl\ R1 CHPhCH1COR3 "R3 Me\ Ph\ But#\ R2 Ph carried out in ethanol or acetone as solvents gave "098# in yields of 45Ð66) ð69JPR255Ł[ R1 P H R2 (107)
O
+
R3 N C O
R1
(108)
P
N
R2
H
R3
(32)
(109)
Tris"trimethylsilyl#phosphane "009# and isopropyl isocyanate "000#\ when stirred in diethylether for 2 days\ react to form a compound of the required type "001b#[ However\ compound "001b# is unstable and reacts further to form compounds with phosphorusÐcarbon triple bonds "Scheme 8# ð78AG"E#42Ł[
P(TMS)3 +
(110)
Pri N C O (111)
O-TMS 87%
(TMS)2P N Pri (112a)
O (TMS)2P N Pri
P
C compounds
TMS (112b)
Scheme 9
In an unusual reaction\ it has been reported that phosphiatriafulvene "002# and isocyanates "003# "R Me\ Ph# react in diethylether over 5 h to form imidoesters "005# and amides "006# via a betaine
401
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
intermediate "004# "Scheme 09# ð80S0988Ł[ If the phosphine does not have a hydrogen substituent\ the product of addition to isocyanates may be formed in very good yield and may also be stable ð66CB1257Ł[ But
O
But –
+
R
+
P
Et2O, 6 h
N C O
But
(114)
(115)
TMS
O
But
N P
R TMS
But
(113)
But
N P
–78–20 °C
TMS
–
+
R
TMS-O N
R
P
But
But
(117)
(116)
Scheme 10
5[05[0[1[1 Carbonyl derivatives with one nitrogen and one phosphorus"V# function These compounds "019# are formed when a phosphine oxide "007# reacts with an isocyanate "008# "Equation "22##[ This has been achieved with R0 R1 OMe and R2 SO1NCO[ The reaction in ether at 9>C gave the required product "019#[ However\ if the reaction is carried out at 19>C for 0 h a 1 ] 0 product is formed "i[e[\ ð"MeO#1P"O#NHŁ1SO1#[ This reaction is generally applicable and also works for R0 R1 Et\ Pr\ Pri\ Bu and Bui ð57USP2390103\ 58RZC0332\ 62JGU0908Ł[ The reaction has also been carried out with R0 R1 OMe and R2 Ts in benzene under re~ux for 4 h[ The required product "019# was isolated[ The same authors have synthesized several other compounds "019# bearing a variety of arenesulfonyl groups ð57USP2302271Ł[ O R1
P R2
H
R1
R3 N C O
+
R2
O
H
P
N
(33)
R3
O
(118)
(120)
(119)
The synthesis of compounds "013# has also been achieved by reacting compounds of type "TMS! O#PH"OR0# "010# with OCNCH1CO1R1 "011# in ether at ¾24>C for 0 h to give "012# in quantitative yield^ these reacted with aqueous sodium hydroxide at −4>C to give the desired products "013# "Scheme 00# ð76EGP131701Ł[ This method is applicable for R0 H\ TMS\ alkali metal and "sub! stituted# ammonium and R1 H\ alkyl and an alkali metal[
TMS-O
P H
(121)
H
O OR1
Et2O
+ O C N
TMS-O R1O
100%
OR2
N
P
(122)
CO2R2
NaOH (aq.) –5 °C
O (123)
R1O
O
H
P
N
H
CO2R2
O (124) Scheme 11
The synthesis of phosphine oxides "016# can be achieved by the reaction of the phosphonate esters "014# with amines "015# "Equation "23## ð68EUP2997Ł[ For R0 R1 Et\ R2 R3 H\ R4 Me the
402
At Least One Nitro`en
reaction involves the passing of ammonia into the reaction mixture at 39>C for 2 h to yield the required product "016#[ A similar reaction with R0 R1 R4 Me and 0\0\2\2!tetramethylguanidine as the amine "015# gave "MeO#1P"O#CON1C"NMe1#1 as the product ð65GEP1442036Ł[ O R2O R1O
R5
P
N
O
R5
R3
+
N
O
R4
R2O R1 O
H (126)
(125)
R4
P
N
O
R3
(34)
(127)
The reaction of trialkyl phosphite "017# and alkyl chloroformate "018# at 014>C yields the phosphonate "029#\ which with ammonia\ or other amines\ gives the required carbamoyl phos! phonates "020# "Scheme 01#[ This method works for R0\ R1 alkyl\ allyl\ haloalkyl\ alkoxyalkyl and alkenyl^ R2 Me^ R3 Me and R4 alkyl\ alkynyl and hydroxyalkyl ð60GEP1939256\ 63USP2738091\ 66GEP1527643Ł[ In an Arbuzov reaction\ trimethyl phosphite "022# has been incorporated into com! pound "021# to form "023# in 87) yield at 19Ð29>C "Equation "24## ð71EUP32867Ł[ OR2 R1O
P
O
OR3
+ O
Cl
R4
R1 O
125 °C
R2O
P
R1O
NH3
O
R4
R2O
O P
NH2
O (131)
O (130)
(129)
(128)
O
Scheme 12
O
O O Me
(MeO)3P (133)
MeO
20–30 °C 98%
MeO
O O
N
O
P
N
O
Me
Cl (132)
(35)
O O
(134)
5[05[0[1[2 Carbonyl derivatives with one nitrogen and one arsenic function "carbamoylarsines# The synthesis of carbamoylarsines "026# has been carried out by one of two methods^ the reaction of alkyl or aryl arsines "024# with phenyl isocyanate "025# in the presence of dibutyltinacetate to form N!phenylcarbamoyl arsines "Equation "25##\ or the reaction of lithium arsides "027# with cyclohexyl isocyanate "028# to form N!cyclohexylcarbamoyl arsines "039# "Scheme 02#[ The former reaction does not work for cyclohexyl isocyanate ð56LA"698#137Ł[ RnAsH3–n + (3–n) (135)
Bu2Sn(OAc)2, dioxane reflux, 5 h
Ph N C O
O (36)
RnAs
NHPh
60–89%
(136)
3–n
(137)
R = Ph, n = 2; c-C6H11, n = 2; Ph, c-C6H11; Ph, n = 1; Bu, n = 1
5[05[0[1[3 Carbonyl derivatives with one nitrogen and one antimony function No compounds of this type were found in the literature[ 5[05[0[1[4 Carbonyl derivatives with one nitrogen and one bismuth function The synthesis of compounds of this type was achieved by Mishra and Tandon _rst by forming a 0 ] 0 adduct of DMF "030# with bismuth trichloride "031# and then by reacting this with bases to
403
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
Li3–nAsRn + (3–n) (138)
c-C6H11
Li+
O
Et2O
RnAs
N C O
–
N
RT
c-C6H11 3–n
(139) H2O EtOH 41–71%
O LiOEt + RnAs
R = Ph, n = 2; c-C6H11, n = 2; Bu, n = 1
N
c-C6H11 3–n
H (140) Scheme 13
form the isolated compounds such as "032#[ The bases used were triethylamine\ diethylamine\ a! picoline and pyridine[ Scheme 03 gives an outline of the mechanism when pyridine is used ð60IC0785Ł[ O O
Cl N
Me
+ BiCl3
N
BiCl3•HCONMe2
Bi
NMe2
Cl–
N+
Me (141)
(142)
(143) Scheme 14
5[05[0[2 Carbonyl Derivatives with One Nitrogen and One Metalloid "B\ Si\ Ge# Function 5[05[0[2[0 Carbonyl derivatives with one nitrogen and one boron function Compounds of this type have been synthesized in many di}erent ways^ the reaction of H!Ala! OMe = HCl in dichloromethane with triethylamine\ Me2N = BH1CO1H and dicyclohexylcarbodiimide "dcc# gives L!Me2N = BH1CONHCHMeCO1H ð78EUP225661Ł[ Dipeptide and tripeptide esters can similarly be used ð89EJM290Ł[ Boron analogues of hydroxamic acids can be made by reacting hydroxylamine hydrochloride with Me2N = BH1CO1H in water to give an 74) yield of Me2N = BH1C"O#NHOH = HCl ð77IC291Ł^ Me2N = BH1CO1H reacts with R0R1NH in the presence of dcc in chloroform at room temperature to give Me2N = BH1CONR0R1 ð89BCJ2547Ł^ cyclic examples may be synthesized "e[g[\ a carbamoyl analogue "033# of the cyanoborane oligomer "BH1CN#x # by putting "EtO#1P"O#CH1NMe1 = BH1CONHEt on silica gel ð80IC1322Ł[ The reaction of phenylaniline methyl ester hydrochloride with trimethylamine!carboxyborane\ triphenylphosphine\ carbon tetrachloride and triethylamine in acetonitrile for 13 h yields Me2N = BH1CO!Ph!OMe ð81MI 505!90Ł[ H Et O
H H B N
O
N Et H H H B
(144)
A common way of making these compounds is exempli_ed by that reported by Sood et al[\ which involved the reaction of cyanoborane "034# with triethyl phosphite "035# to form the triethylphos! phite!cyanoborane adduct "036# followed by ethylation with triethyloxonium tetra~uoroborate to
404
At Least One Nitro`en
form the nitrilium ion "037#[ This was readily hydrolysed to triethyl phosphite!N!ethyl! carbamoylborane "038# "Scheme 04# ð80T5804Ł[ Many other papers make use of the same method on di}erent substrates ð65JA4691\ 68JINC0112\ 70JINC346\ 78CC899\ 89IC443\ 89IC2107\ 80IC0935\ 81IC3800Ł[ (EtO)3P (146), DME
(BH2CN)x
reflux, 48 h
RT, 4 d or reflux, 2 d 58%
(145)
Et3O+ BF4–, CH2Cl2
(EtO)3P•BH2CN (147)
O 1 mol l–1 NaOH to pH 11
+
(EtO)3P•BH2CNEt –BF4
NHEt
(EtO)3P•BH2
73%
(149)
(148) Scheme 15
5[05[0[2[1 Carbonyl derivatives with one nitrogen and one silicon function "carbamoylsilanes# Carbamoylsilanes may be made by the addition of hexamethyldisilathiane "040# to N\N!diethyl! carbamoylmercury "049# in ether[ The product\ N\N!diethylcarbamoylsilane "041#\ however\ can decarbonylate "Equation "26## ð58CC351Ł[ Hg(CONEt2)2 + (TMS)2S (150)
Et2O
(37)
TMS-CONEt2
(151)
(152)
Hydrosilylation of alkyl isocyanates with triethylsilane in the presence of palladized charcoal or palladium dichloride at 79Ð029>C for 5 h yields 39Ð89) of the desired product "RNHCOSiEt2# ð66JOM"039#86Ł[ Deoxygenation of cyclohexyl isocyanate with Ph1"Me2C#Si−Li¦ in an NMR tube at −49>C in THF resulted in the identi_cation and isolation of N!cyclohexyl!t!butyldiphenyl! silylcarboxamide "042# ð72T1878Ł[ A solution of "TMS#2SiLi"THF#2 in pentaneÐTHF "09 ] 0# added over 1 h to a solution of Me1NCOCl in dry pentane under dry nitrogen at −29>C then stirred at room temperature yields 64) of "TMS#2SiCONMe1 ð80JOM"392#182Ł[ Ph2(But)SiCONH (153)
5[05[0[2[2 Carbonyl derivatives with one nitrogen and one germanium function "carbamoylgermanes# Carbamoylgermanes may be synthesized by treating lithium t!butylamide "043# with carbon monoxide "044# to form "t!butylcarbamoyl#lithium "045#\ which reacts with trimethylgermyl chloride "046# to form the required product "047# "Scheme 05#[ Yields are in the region of 44) ð60AG"E#228Ł[ H But
N
Li
+ CO
H
C6H6, Et2O 50 °C
But
H
N
Li ..
But
N
Li –LiCl
O (154)
(155)
H
Me3GeCl (157)
(156)
But
N
GeMe3 O
(158)
Scheme 16
Another method for the preparation of carbamoylgermanes is the reaction of triethyl! germyllithium "048# with amides "059# in hexane at −29>C for 4 h followed by hydrolysis[ For
405
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
R Me\ the yield of N\N!dimethylamidetriethylgermylcarbonyl acid "050# is 34) "Equation "27## ð73IZV0786Ł[ Et3GeLi +
TMS
Et3GeCONR2 +
CONR2
(159)
R = Me, Et
(160)
(38)
TMS
(161)
5[05[0[3 Carbonyl Derivatives with One Nitrogen and One Metal Function 5[05[0[3[0 Carbon monoxide insertion reactions The insertion of carbon monoxide into a previously formed metalÐnitrogen bond is the most! studied method of synthesizing this type of compound ð76OM261\ 77AOC"17#028\ 77CRV0948\ 78CCR0Ł[ The _rst example of carbon monoxide insertion into a d! or f!element metal to di! alkylamide bond giving rise to carbamoyl insertion products was reported by Fagan ð70JA1195Ł[ The facile insertion of carbon monoxide into chlorobis"pentamethylcyclopentadienyl#uranium and thorium dialkylamido complexes "051# led to the formation of the h1!carbamoyl complexes Mðh! Me4C4Ł1ðh1!CONR1ŁCl "052# "Equation "28##[ Bis"dialkylamido# compounds "053# are more reactive toward carbon monoxide than the chloro analogues "051# "Scheme 06#[ The yield of bis"car! bamoyl#Mðh!Me4C4Ł1ðh1!CONR1Ł1 "055# is ½29)\ but when the solutions are maintained under vacuum at 099>C\ carbon monoxide loss occurs and the bis"carbamoyl# products "055# revert to the mono insertion products Mðh!Me4C4Ł1ðh1!CONR1ŁNR1 "054#[
Cp*
M
+ CO Cp*
Cp*
M Cp*
+ CO NR2
(164)
Cl
O
NR2
NR2
65 °C, 1 atm CO, 1.5 h
toluene 0 °C, 2 h 40%
Cp*
(163)
M = Th, U; R = Me, Et
O
NR2
(39)
M
Cp*
1 atm, 1.5–2.0 h 55%
Cl (162)
O
R 2N
toluene 95–100 °C
NR2
Cp*
M NR2
Cp*
vacuum, 100 °C
M
O
Cp* NR 2
Cp* (165)
(166)
M = Th, U; R = Me, Et Scheme 17
"dppe#PtMeðN"CH1Ph#"H#Ł "056# reacts with 2 atm of carbon monoxide at 14>C to give "dppe#PtMe"CONHCH1Ph# "057# in 79) yield "Equation "39## ð74OM828Ł[ Similarly\ the reaction of "dppe#PtMeNMe1 "generated in situ# with carbon monoxide leads to "dppe#PtMe"CONMe1# in 65) isolated yield[ Me (DPPE)
(DPPE) N Bn
H (167)
Me
3 atm CO, 25 °C
Pt
Bn
Pt
80%
(40)
N O
H
(168)
Metals in groups 7\ 8 and 09 bearing amide ligands are not well known[ Cowan and Trogler have reported the carbon monoxide insertion reaction into the platinumÐamide bond of Pt"Ph1PCH1 CH1PPh1#"Me#ðNH"CH1Ph#Ł to generate the carbamoyl metal complex Pt"Ph1PCH1CH1PPh1# "Me#ðCONH"CH1Ph#Ł ð76OM1340Ł[ Carbon monoxide can also be inserted into the rutheniumÐ amide bond[ When carbon monoxide is bubbled through a solution of h4!CpRu"NH1#"Cy1PCH1 CH1PCy1# "Cy cyclohexyl#\ the carbamoyl complex h4!CpRu"CONH1#"Cy1PCH1CH1PCy1# is iso! lated ð80OM1670Ł[ An unusual reaction has been reported involving the insertion of carbon monoxide into the iridiumÐnitrogen bond of Ir"CO#"NHAr#"PPh2#1 "058# "where Ar Ph\ p!C5H3Me# at
406
At Least One Phosphorus etc[
room temperature producing a 89) yield of the carbamoylÐmetal complex "069# "Equation "30## ð82OM1390Ł[ Ar
Ph3P
N
Ph3P O H N OC Ir Ph3P H
H CO (1 equiv.), RT
Ir
90%
CO PPh3
(169)
(170)
(41)
R
5[05[0[3[1 Nucleophilic attack on metal carbonyl complexes CarbamoylÐmetal complexes can also be made by nucleophilic attack on metal carbonyls[ The direct addition of a nucleophilic nitrogen anion "Nu−# to a coordinated carbon monoxide ligand "M Fe\ Ru\ Os\ Co\ Re\ Mo\ W# leads to the required compounds ð68JA0516\ 71IC0693\ 73JA0014\ 74JA1244\ 74M0092\ 74OM367\ 74OM0412\ 75JOM"201#C10\ 76IC415Ł[ The attack of the conjugate acid of a nitrogen nucleophile "NuH# on metal carbonyls "M Pt\ Ni\ Ir\ Fe\ Ru\ Os\ Mn# also results in the preparation of carbamoylÐmetal complexes[ This method is restricted to strongly activated\ usually cationic\ metal carbonyl complexes since NuH is always a much weaker nucleophile than Nu− ð64IC1037\ 65IC1235\ 68IC0054\ 79AOC"07#0\ 73OM0412\ 74OM489Ł[ The attack of the nitrogen nucleophile on metal carbonyls "M Fe\ Ni# can be aided by Y groups which make the nitrogen electron rich\ thus promoting nucleophilic attack "Y Li\ MgX "X Hal#\ HgR\ C"NMe2#2\ HB"OR#1\ B"OR#2# ð72OM0933Ł[
5[05[0[3[2 Other methods CarbamoylÐmetal complexes can be synthesized by using an electron!rich transition!metal com! plex to displace a halide from an organic carbamoyl halide[ For example\ FeCp"CO#1CONR1 "R Me\ Et# has been synthesized in this way ð52JA0807Ł[ WCp"CO#1CONHMe "062# has been made in the reaction of WCp"CO#1Me "060# with hydrogen isocyanate "061# "Equation "31## ð61JA2688Ł[ Trans!ðPt"PPh2#1"CNMe#CONHMeŁ¦ "064# has been made by the attack of hydroxide ion on trans!ðPt"PPh2#1"CNMe#1Ł1¦ "063# "Equation "32## ð60JA4313Ł[ Me Cp
W CO
HNCO (172)
CO
(171)
O
Cp
NHMe W CO
(42) CO
(173) O
CNMe MeNC
Pt
PPh3 PPh3
+ HO–
MeNC
(174)
NHMe Pt
(43)
PPh3 PPh3
(175)
5[05[1 FUNCTIONS CONTAINING AT LEAST ONE PHOSPHORUS\ ARSENIC\ ANTIMONY OR BISMUTH FUNCTION "AND NO HALOGEN\ CHALCOGEN OR NITROGEN FUNCTIONS# 5[05[1[0 Carbonyl Derivatives with Two P\ As\ Sb or Bi Functions Carbonyl bis"diphenylphosphide# "067# may be synthesized by adding a solution of diphenyl! "trimethylsilyl#phosgene "066# in diethyl ether dropwise to a solution of phosgene "065# in diethyl!
407
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
ether at −099>C under nitrogen[ The reported yield is 39) and involves the production of trimethylsilyl chloride "068# "Equation "33## ð62AG"E#731Ł[ O
+ 2 TMS-Cl
40%
Cl
Cl
O
Et2O, 100 °C
+ 2 TMS-PPh2 (176)
(177)
(44)
PPh2
Ph2P (178)
(179)
Treatment of Cl1P"O#CH1CHOEt "079# with NOCl "070# in carbon tetrachloride at 9>C gives a reported 74) yield of Cl1P"O#CH"NO#CH"OEt#Cl "071# which\ on ethanolysis\ gives a mixture containing Cl1CHOEt "072#\ EtO1CNHCH"OEt#1 "073#\ "EtO#1P"O#CONHCH"OEt#1 "074# and ð"EtO#1P"O#Ł1CO "075# "Scheme 07# ð79MI 505!90Ł[ Carbonylbis"phosphonates# "077# are prepared by alkaline hydrolysis of a salt of a dihalomethylenediphosphonic acid "076#[ Thus\ compound "076# and sodium hydroxide are re~uxed for 0Ð5 h in water to yield 52) of compound "077# "Equation "34## ð56JOC3000\ 69USP2386202Ł[ Cl
O P
Cl
+ NOCl
OEt (180)
Cl
85%
Cl
EtO
OEt
N
EtO
O
H
P
N
+ EtO
H (183)
O
Cl EtOH
P
OEt NO (182)
OEt
O
Cl
Cl
(181)
OEt
+
CCl4, 0 °C
O
(184)
OEt
EtO
+
EtO
O
O
P
P
OEt
OEt OEt
O (186)
(185) Scheme 18
HO
OH O P
O NaOH, H2O, pH > 10.5
Cl Cl
OH
P
–O
63%
–O
OH
O (187)
O–
P
P
O
O
4 Na–
(45)
O–
(188)
Metal carbonyl complexes have also been prepared containing phosphorus ligands bridged by carbonyl groups ð89JOM"272#184Ł[ The addition of Pr1i NPCl1 "089# to a solution of Na1Fe"CO#3 "078# in ether at −67>C\ followed by 13 h stirring at room temperature\ results in the isolation of a 24) yield of "Pr1i NP#1COFe1"CO#5 "080#[ The amine must be sterically hindered for this reaction to succeed "Equation "35## ð74IC3338\ 76JA6653Ł[ These compounds may also be prepared by inserting carbon monoxide into a P0P bond[ The reaction of the iron complex "081# with carbon monoxide at 79>C and 49 atm pressure results in the isolation of the phosphorus!bridging carbonyl derivative "082# as the major product "Equation "36## ð75AG"E#644\ 75ZN"B#172\ 76CB0310Ł[ OC CO OC Fe Na2Fe(CO)4 +
Pri
2NPCl2
Et2O
O
35%
COCO Fe CO
P
NPri2
P
(46)
NPri2 (189) OC CO OC Fe
(190)
P
COCO Fe CO
P But (192)
But
(191)
+ CO 80 °C, 50 atm
OC CO OC Fe O
P
COCO Fe CO
P But (193)
(47) But
408
At Least One Metalloid
Phosphoureas\ such as 0\2!bis"trimethylsilyl# substituted diphosphourea derivatives "083#\ may be cyclized to form 0\2!di!t!butyl!1!alkyl!0\1\2!triphosphetan!3!ones "087# in good yield[ The reac! tion takes place at room temperature in toluene over 01Ð25 h "Scheme 08# ð72CB1260Ł[ But
O But
P
P
O-TMS P
TMS
TMS
But
But
TMS
O
O P
P R
–TMS-Cl
(195)
O-TMS P
But
TMS
(194)
But
+RPCl2
P
But
P R
P
But
–TMS-Cl
But
P
P
Cl
(198)
(197)
R = Me, Ph, But
But
But
Cl
(196)
P P
Scheme 19
No references were found to carbonyl derivatives with two As\ Sb or Bi functions[
5[05[1[1 Carbonyl Derivatives with One P\ As\ Sb or Bi Function Together with a Metalloid or Metal Function No references were found for carbonyl derivatives either with one P\ As\ Sb or Bi function together with a metalloid function or with one As\ Sb or Bi function together with a metal function[ There are\ however\ reports of carbonyl derivatives with one phosphorus and a metal function[ They are made by carbon monoxide insertion into metalÐphosphorus bonds[ For example\ Cp HfCl1"PBut1# "088# "Cp h4!C4Me4# has been shown to react with 0 equivalent of carbon monoxide within minutes at 14>C to generate the insertion product "199# "Equation "37## ð74JA3569\ 76JCS"D#1928\ 77CRV0948Ł[ Cp* Cl Hf Cl
But
CO, 2 atm, 25 °C
But
73%
P
Cp* Cl Hf Cl
(199)
O (48) P(But)
(200)
5[05[2 FUNCTIONS CONTAINING AT LEAST ONE METALLOID FUNCTION "AND NO HALOGEN\ CHALCOGEN OR GROUP 4 ELEMENT FUNCTIONS# 5[05[2[0 Carbonyl Derivatives with Two Silicon Functions Bis"silyl# ketones may be prepared by the oxidation of the corresponding carbinol[ For example\ bis"triphenylsilyl# ketone "191# has been synthesized by oxidizing 0\0!bis"triphenylsilyl#methanol "190# with chromium trioxide and sulfuric acid in diethylether at room temperature for 34 min "25) yield#^ by reacting the methanol derivative "190# in ether successively with dcc\ pyridinium tri~uoroacetate and DMSO and stirring for 01 h at room temperature "15) yield#^ and by oxidizing the methanol derivative "190# in carbon tetrachloride solution with benzoyl peroxide and N!bromo! succinimide at 54>C "5) yield# "Equation "38## ð57CJC1008Ł[ SiPh3 Ph3Si (201)
OH
O
oxidation
(49) SiPh3
Ph3Si (202)
419
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
Bis"trimethylsilyl# ketone "194# has been prepared by the reaction of the bis!silylated ylide "192# with the freshly prepared adduct formed from ozone and triphenylphosphite "193# in toluene at −67>C for 4 h "Equation "49## ð74AG"E#0957\ 81AG"E#0953Ł[ PPh3
O
toluene, –78 °C, 5 h
(50)
+ O3•P(OPh)3 50%
TMS
TMS (203)
TMS
TMS
(204)
(205)
The oxidation of tris"trimethylsilyl#!methylthiomethane "195# with m!chloroperoxybenzoic acid "mcpba# leads to bis"trimethylsilyl# ketone "194# under very mild conditions[ A solution of mcpba in dichloromethane is added slowly\ under nitrogen\ to a solution of the thiomethane derivative "195# in dichloromethane at −67>C[ After 09 min stirring and workup\ the ketone "194# is isolated in 34) yield "Equation "40## ð75TL4874Ł[ TMS TMS
TMS S
O
CH2Cl2, mcpba (207), –78 °C
Me
(51) TMS
45%
(206)
TMS
(205)
5[05[2[1 Carbonyl Derivatives with Two Boron Functions No references were found to carbonyl derivatives with two boron functions[
5[05[2[2 Other Carbonyl Derivatives with Two Dissimilar Metalloid Functions Germyl silyl ketones have been prepared by hydrolysing the corresponding 1!substituted 0\2! dithianes[ For example\ triethylgermyl trimethylsilyl ketone "100# is synthesized by reacting 1!triethylgermyl!0\2!dithiane "197# with n!butyllithium in THF over 0Ð2 h at −19>C to form the carbanion which readily reacts with trimethylsilyl chloride at 9>C to form 1!triethylgermyl!1! trimethylsilyl!0\2!dithiane "198# in 68) yield[ Hydrolysis of the dithiane "198# with mercuric chloride "109# and cadmium carbonate in 09) water in methanolÐTHF at 14>C over 89 min yielded the required ketone "100# "Scheme 19# ð56JA320Ł[ S
i, BunLi
S
GeEt3
CdCO3
ii, TMS-Cl
S
TMS
HgCl2 (210)
GeEt3 S (208)
(209)
O TMS
GeEt3 (211)
Scheme 20
5[05[2[3 Carbonyl Derivatives with One Metalloid and One Metal Function Transition!metal acylsilanes have been of some interest since the preparation of the _rst transition! metal!bonded acylsilane\ fac!Re"CO#2"diphos#ðCOSiPh2Ł "104#[ It is prepared by adding a THF solution of Ph2SiLi to a slurry of ðRe"CO#3"diphos#ŁðClO3Ł "103# in THF at 14>C and reacting for 89 min[ The transition!metal!bonded acylsilane "104# was isolated as air!stable purple crystals in 14Ð29) yield "Scheme 10# ð65JA3567Ł[
410
Two Metals
Re(CO)5Cl
P OC Re P OC CO
diphos
(212)
P OC Re P OC CO
i, AlCl3, CO ii, HClO4
(213)
Ph3Si
+
CO
CO
CO OC Re CO OC CO
Ph3SiLi
ClO4–
O
(214)
(215)
Scheme 21
Reaction of Cp1Zr"TMS#Cl "105# with carbon monoxide "578 kPa# provides the silaacyl Cp1Zr "h1!CO!TMS#Cl "106# and the _rst observation of carbon monoxide insertion into a transition metalÐsilicon bond[ The complex "106# was isolated in 89) yield[ "Equation "41## ð76JA1938Ł[ Cl
Cl
Et2O, +CO, 689 kPa
Cp2Zr
(52)
Cp2Zr
–CO
TMS
O TMS (217)
(216)
Pentane solutions of Cp1ZrðSi"TMS#2ŁTMS "107# react rapidly with carbon monoxide "578 kPa# to give an orange solution from which the silaacyl Cp1Zr"h1!COTMS#ðSi"TMS#2Ł "108# can be crystallized in 64) yield "Equation "42##[ This reaction is generally applicable and the carbon monoxide insertion reaction of transition!metal silyl compounds has been widely reported ð74JA3973\ 74JA5398\ 75JA4244Ł[ TMS
Si(TMS)3
pentane, +CO, 689 kPa
Cp2Zr
(53)
Cp2Zr 75%
Si(TMS)3
O TMS (219)
(218)
5[05[3 CARBONYL DERIVATIVES CONTAINING TWO METAL FUNCTIONS 5[05[3[0 Metal Carbonyl Complexes and Fluxionality Carbon monoxide reacts with transition metals to form transition!metal carbonyl complexes[ Where two or more atoms of the transition metal are incorporated into the organometallic complex\ the carbonyls adopt either a terminal or a bridged con_guration[ The energy di}erence between terminal and bridging carbonyls is usually low\ so a ~uxionality exists between the con_gurations[ The compound "119# contains both terminal and bridging carbonyl ligands ð73AOC"12#108Ł[ In a simple C!bonded bridge\ the carbon monoxide ligand is perpendicular to the metalÐmetal axis and the carbon is equally bound to both metals\ whereas the CO ligand may also be preferentially bound to one or other of the metal atoms in the bridging carbonyl complex[ The carbon monoxide ligand is usually bound to two or more metal atoms in one of the ways shown in Figure 0[ In "a# the M0C bonds are of equal length^ in "b# the M0C bond lengths are signi_cantly di}erent^ in "c# and "d# the carbon monoxide ligand is triply bridging\ with the obvious di}erences between the bond lengths[ O Cp
Cp Ru
Ru CO
OC O (220)
M M
CO
(a)
M
M M
M
CO
M
(b)
(c) Figure 1
M CO
M M (d)
CO
411
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
If a metal carbonyl complex is synthesized in which there is more than one metal atom\ some or all of the carbon monoxide ligands may bridge between two or more of the metal atoms[ Some transition metals form only monomer complexes and so carbonyl bridging is impossible[ The carbonyl!bridged transition!metal complexes are polymers of metal carbonyls where polymerization is possible[
5[05[3[1 Preparation of Metal Carbonyls A large number of metal carbonyls is known and the following survey is intended to provide a brief summary of methods of preparation of the more common compounds[ For more information\ appropriate volumes of Comprehensive Or`anometallic Chemistry and a specialist monograph ðB!82MI 505!90Ł should be consulted[
5[05[3[1[0 Metal carbonyls of titanium\ zirconium and hafnium Titanium hexacarbonyl ðTi"CO#5Ł has been produced by condensation of titanium metal vapour with carbon monoxide in a matrix of inert gases at 09Ð04 K and identi_ed spectroscopically ð66IC711Ł[ The cyclopentadienyl derivative\ Ti"C4H4#1"CO#1\ has been prepared by treating TiCl1"C4H4#1 with sodium cyclopentadienide and carbon monoxide under pressure ð50JA0176Ł[ The _rst hafnium carbonyl\ "h4!C4H4#1Hf"CO#1\ was prepared and studied by Sikora et al[ ð68JA4968Ł[ None of the above transition metal carbonyl complexes contains bridging carbon monoxide ligands[
5[05[3[1[1 Metal carbonyls of vanadium\ niobium and tantalum Reduction of vanadium trichloride "VCl2# by sodium in pyridine under 199 atm of carbon monoxide yields\ following workup\ the vanadium hexacarbonyl ðV"CO#5Ł "an odd!electron tran! sition!metal carbonyl complex#\ which cannot be isolated[ The noble gas con_guration is attained in the isolable anionic intermediate ðV"CO#5Ł− or in the super!reduced 07!electron species ðV"CO#4Ł2− ð70JA5099Ł[ A direct synthesis of V"CO#5 and the dimer V1"CO#01 by condensation with carbon monoxide in a matrix of noble gases has been reported ð65IC0555Ł[ All the transition!metal carbonyl complexes of this group are extremely unstable[
5[05[3[1[2 Metal carbonyls of chromium\ molybdenum and tungsten This is the _rst group to be discussed in which metal carbonyls have been known for some time and are quite stable[ Molybdenum hexacarbonyl\ Mo"CO#5\ chromium hexacarbonyl\ Cr"CO#5\ and tungsten hexacarbonyl\ W"CO#5\ were all prepared for the _rst time in the early part of the twentieth century ð09JCS687\ 16BSF0930\ 17CR"076#453Ł[ The monomers have been made by the reaction of carbon monoxide at 199Ð149 atm and 199Ð299>C with the metals "M Mo\ W# ð29GEP420391\ 20GEP436914Ł by reacting anhydrous metal"III# chloride "M Cr# or metal"V# chloride "M Mo\ W# with phenyl! magnesium bromide and carbon monoxide at 3>C and 0 atm and hydrolysing the reaction products ð16BSF0930\ 24ZAAC"110#210\ 36JA0612\ 49IS045Ł by reacting the metal chlorides with carbon monoxide at 099 atm and 9Ð09>C in the presence of zinc or iron powders "M Mo\ W# ð39DOK"15#43\ 39DOK"15#46Ł[ Chromium hexacarbonyl has also been prepared using a metalÐpyridine system as the reducing agent[ The reaction of anhydrous pyridine\ magnesium powder and small amounts of iodine was used to carbonylate chromium"III# and chromium"II# salts at 029Ð079>C and 099Ð299 atm for 3Ð 01 h ð46JA2500\ 48G798Ł[ Lithium aluminum hydride has also been used as the reducing agent ð48MI 505!91Ł[ The most versatile method of preparing the hexacarbonyls of this group is the reductive car! bonylation with trialkylaluminum compounds\ for which yields of 81)\ 65) and 81) have been reported for Cr"CO#5\ Mo"CO#5 and W"CO#5\ respectively ð59JA0214Ł[ Reduction of the hexacarbonyls with a borohydride in liquid ammonia forms dimeric ðM1"CO#09Ł1−[ Chromium hexacarbonyl Cr"CO#5 forms chromocene Cr"h4!C4H4#1 on reaction with
412
Two Metals
sodium cyclopentadienide\ while under the same conditions the molybdenum and tungsten hexa! carbonyls form only ð"h4!C4H4#M"CO#2Ł1[ The chromium analogue of these dimers can also be formed ðB!73MI 505!90Ł[
5[05[3[1[3 Metal carbonyls of manganese\ technetium and rhenium Decacarbonyldirhenium\ Rh1"CO#09 was _rst prepared in 0830 by Hieber and Fuchs ð30ZAAC"137#145Ł[ Decacarbonyldimanganese\ Mn1"CO#09\ was prepared and fully characterized in 0843 by Brimm et al[ ð43JA2720Ł and the synthesis of decacarbonylditechnetium\ Tc1"CO#09\ was _rst described in 0850 ð50AG468\ 50JA1842\ 54ZN"B#0048Ł[
"i# Decacarbonyldiman`anese Decacarbonyldimanganese has been prepared by reacting carbon monoxide at 199 atm at room temperature for 04Ð06 h with a mixture of magnesium powder\ manganese iodide\ copper and copper iodide suspended in diethyl ether ð43JA2720Ł\ by the action of phenylmagnesium bromide or chloride and carbon monoxide at 29 atm on anhydrous MnCl1 in diethyl ether at −19 to 29>C ð47USP1711136Ł\ and by reducing manganese"II# salts with sodium benzophenone ketyl in THF\ carbonylating the resulting mixture with carbon monoxide at 199Ð699 atm and 54Ð199>C and hydrolysing and steam distilling the Mn1"CO#09 from the resulting mixture ð47JA5056Ł[ The reduction of an anhydrous manganese"II# salt with a trialkylaluminum compound dissolved in an ether or benzene in the presence of carbon monoxide under pressure results in a 59) yield of the required compound ð47IZV099\ 59JA0214\ 54IC182Ł[
"ii# Decacarbonylditechnetium This carbonyl has been prepared by the action of carbon monoxide at 149Ð249 atm on the heptoxide Tc1O6 at 119Ð164>C for 01Ð19 h ð50AG468\ 50JA1842\ B!53MI 505!90\ 54ZN"B#0048Ł[
"iii# Decacarbonyldirhenium and hi`her polymers of rhenium hexacarbonyl Rhenium heptoxide\ Re1O6\ is reduced by carbon monoxide at high temperature and pressure to give Re1"CO#09 "110# "Equation "43## ð30ZAAC"137#145Ł[ The reaction of ReCl4 or ReCl2 with carbon monoxide at 029>C and 149Ð179 atm for 7 h using sodium in THF as the reducing agent has yielded 69) of Re1"CO#09 ð52JCS0022Ł[ The polynuclear tetracarbonylrhenium\ ðRe"CO#3Łn\ has been prepared by reacting Re1S6 with carbon monoxide "74 atm# at 199>C in the presence of copper powder[ Re2O7
+ 17 CO
Re2(CO)10
+ 7 CO2
(54)
(221)
5[05[3[1[4 Metal carbonyls of iron\ ruthenium and osmium "i# Iron carbonyls The transition!metal carbonyls Fe1"CO#8 "111# and Fe2"CO#01 "112# are obtained by the action of sunlight on Fe"CO#4 in glacial acetic acid or in acetic anhydride in vacuo ð16CB0313\ 18MI 505!90Ł[ The trimer "112# may also be prepared by oxidizing alkaline solutions containing carbonylferrates with manganese dioxide\ MnO1\ followed by removal of excess MnO1\ acidi_cation and extraction of the carbonyl with petroleum ether ð46ZAAC"178#213Ł[ The cyclopentadienyl iron carbonyl dimer "113#
413
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en
has been prepared by reacting iron pentacarbonyl and dicyclopentadiene at 024>C in an auto! clave[ Prolonged reaction of the same reactants produces the tetrameric cluster compound\ ðFe"h4!C4H4#"CO#Ł3\ which involves CO groups which are triply bridging ðB!67MI 505!90Ł[ CO
O OC OC OC
CO
CO Fe CO OC CO CO Fe OC Fe CO CO OC CO CO
Fe
Fe
CO CO CO
O
Fe
O
CO Fe
OC
O
OC
OC
OC
CO Fe
Fe CO
CO
Fe CO
OC
OC
O (222)
OC
CO
O (223)
O (224)
"ii# Ruthenium carbonyls Both Ru"CO#4 and Ru2"CO#01 are formed when RuI2 is mixed with a large excess of silver powder and kept at 069>C for 13 h under carbon monoxide at about 349 atm in a rotating autoclave[ The trimer is prepared from the monomer by heating it in hydrocarbons or alcohols for a short time in the presence of light ð25ZAAC"115#274Ł[ When ruthenium"III# acetylacetonate reacts with carbon monoxide and hydrogen "2 ] 0# under pressure "049Ð199 atm# at 039Ð059>C in acetone\ benzene or methanol\ yields as high as 71) of Ru2"CO#01 are obtained ð53CI"M#195Ł[
"iii# Osmium carbonyls The carbonyls Os"CO#4 and Os2"CO#01 are formed when the halides "OsCl2 and Os1Br8# and an oxyiodide are mixed with powdered copper or silver and reacted with carbon monoxide at high pressure "199Ð299 atm# and temperature "049Ð299>C# ð32MI 505!90Ł[
5[05[3[1[5 Metal carbonyls of cobalt\ rhodium and iridium Mononuclear carbonyls are not formed with this group of transition metals as the elements of this group can only satisfy the 07!electron rule in their carbonyls if metalÐmetal bonds are present[ However\ multinuclear carbonyls such as Co5"CO#05\ Rh5"CO#05 and Ir3"CO#01 are readily formed ð39ZAAC"134#210\ 55JA0710\ 56CC339Ł[
"i# Cobalt carbonyls The octacarbonyl Co1"CO#7 has been prepared by the reaction of carbon monoxide at 29Ð39 atm and 049>C with _nely divided cobalt ð09JCS687Ł or by reacting cobalt halides and sul_des with carbon monoxide in the presence of reducing metals\ such as copper ð28ZAAC"139#150Ł[ By treating CoSO3 or CoCl1 in aqueous ammonia solution with carbon monoxide "84Ð009 atm# at 019Ð039>C for 05Ð07 h a yield of 59) of the required carbonyl may also be obtained ð42LA"471#005Ł[ Adkins and Krsek prepared solutions of Co1"CO#7 by reacting Raney cobalt suspended in diethyl ether with carbon monoxide at about 149 atm and 049>C ð37JA272Ł[ According to a Japanese patent\ Co1O2 suspended in benzene is transformed into the carbonyl by reaction with carbon monoxide and hydrogen at 199 atm and 009>C in the presence of some pyridine and preformed Co1"CO#7 ð45JAP09813Ł[ Another way to synthesize octacarbonyldicobalt is to use high pressures of carbon monoxide "099Ð199 atm# at high temperatures "039Ð299>C# with anhydrous cobalt salts of organic or inorganic acids dissolved or suspended in nonaqueous media\ using hydrogen as the reducing agent[ The reaction is accelerated by the addition of preformed Co1"CO#7 ð38USP1362882\ 38USP1365152\ 38USP1366442\ 38USP1366443\ 59CI"M#022\ 59CI"M#026Ł[ The carbonyl Co3"CO#01 "115# is prepared by heating Co1"CO#7 "114# to 59>C for 13 h in an inert atmosphere with the evolution of carbon monoxide "Equation "44## ð09JCS687Ł\ or by using hydrocarbons as solvents in the reaction ð44CI"M#5\ 44JA2840Ł[ A method has also been reported for
414
Two Metals
the preparation of Co3"CO#01 "116# from cobalt"II# ethylhexanoate or cobalt"II# and cobalt"III# acetylacetonates[ These are reacted with hydrogen at 29Ð49 atm and with Co1"CO#7\ giving yields of over 89) "Equation "45## ð48CI"M#021Ł[ 2 [Co2(CO)8]
60 °C
(225)
Co4(CO)12 + 4 CO
(55)
(226)
2 (RCO2)2Co + 3 Co2(CO)8 + 2 H2
Co4(CO)12 + 4 RCO2H
(56)
(227)
"ii# Rhodium carbonyls When rhodium metal is reacted at 199>C with carbon monoxide "349 atm# for 04 h\ the dimer Rh1"CO#7 can be isolated[ The reaction of anhydrous RhCl2 and carbon monoxide at 199 atm for 04 h in the presence of copper "or silver\ cadmium or zinc# results in the isolation of the other polymers[ At 49Ð79>C\ the tetramer Rh3"CO#01 is formed\ whereas at 79Ð129>C only Rh5"CO#05 is present ð32ZAAC"140#85Ł[
"iii# Iridium carbonyls The reaction of iridium halides\ IrX2\ with carbon monoxide at 249 atm for 13Ð37 h at 099Ð039>C in the presence of copper yields a mixture of Ir3"CO#01 and ðIr"CO#3Łn[ Separation is based on the solubility of ðIr"CO#3Łn in ether and carbon tetrachloride relative to that of Ir3"CO#01 ð39ZAAC"134#210Ł[
5[05[3[1[6 Metal carbonyls of nickel\ palladium and platinum The _rst transition!metal carbonyl to be discovered was nickel tetracarbonyl\ Ni"CO#3\ and it is used to produce metallic nickel[ Reduction of Ni"CO#3 leads to a number of polynuclear carbonylate anion clusters such as ðNi4"CO#01Ł1− and ðNi5"CO#01Ł1− ðB!73MI 505!90Ł[ Alkaline reduction of ðPtCl5Ł1− in an atmosphere of carbon monoxide yields a series of platinum carbonylate anion clusters\ ðPt2"CO#5Łn1−[ By re~uxing salts of the n 2 anion in acetonitrile\ the cluster anion ðPt08"CO#11Ł3− has been obtained ð68JA5009Ł[
5[05[3[1[7 Metal carbonyls of copper\ silver and gold Neutral binary carbonyls are not formed by these metals at room temperature\ but some have been synthesized by the condensation of copper or silver vapour and carbon monoxide at temperatures of 5Ð04 K "e[g[\ M1"CO#5# ð65JA2056Ł[
5[05[3[1[8 Mixed metal carbonyls These are prepared by reacting a halogenocarbonylmetal with carbonylmetallates of alkali metals "Equations "46#\ "47#\ "48#\ and "59##[ The reactions are carried out in an ether\ such as THF\ and occur very rapidly[ NaMn(CO)5
+ ReCl(CO)5
NaCl
+ (CO)5MnRe(CO)5
(57)
NaCo(CO)4
+ MnBr(CO)5
NaBr
+ (CO)4CoMn(CO)5
(58)
+ (CO)4CoFe(C5H5)(CO)2
(59)
NaCo(CO)4
+ Fe(C5H5)(CO)2I
NaI
415
Carbonyl and Two Heteroatoms Other Than a Halo`en or Chalco`en NaRe(CO)5
+ Fe(C5H5)(CO)2Cl
NaCl
+ (CO)5ReFe(C5H5)(CO)2
(60)
The anion ðFeCo2"CO#01Ł− has been prepared by reacting Co1"CO#7 with Fe"CO#4 in the presence of acetone ð59G0994Ł[ Ultraviolet radiation of a hexane solution of Fe"CO#4 and Mn1"CO#09 results in the formation of the mixed metal carbonyl ð"CO#4MnŁ1Fe"CO#3 ð54ZN"B#0295Ł[ Warming a THF solution of the salt ðMn"CO#5ŁðCo"CO#3Ł to room temperature results in the formation of "CO#4 MnCo"CO#3 ð53CB1178Ł[
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.17 Functions Containing a Thiocarbonyl Group and at Least One Halogen; Also at Least One Chalcogen and No Halogen ERICH KLEINPETER University of Potsdam, Germany and KALEVI PIHLAJA University of Turku, Finland 5[06[0 FUNCTIONS CONTAINING AT LEAST ONE HALOGEN 5[06[0[0 Thiocarbonyl Halides with Two Similar Halo`ens 5[06[0[0[0 Thiocarbonyl di~uoride 5[06[0[0[1 Thiocarbonyl dichloride "thiophos`ene# 5[06[0[0[2 Thiocarbonyl dibromide 5[06[0[0[3 Thiocarbonyl diiodide 5[06[0[0[4 Sulfoxides of thiocarbonyl halides "sul_nes# with two similar halo`ens 5[06[0[1 Thiocarbonyl Halides with Two Dissimilar Halo`ens 5[06[0[1[0 Thiocarbonyl chloride ~uoride 5[06[0[1[1 Thiocarbonyl bromide ~uoride 5[06[0[1[2 Thiocarbonyl bromide chloride 5[06[0[1[3 Sulfoxides of thiocarbonyl halides "sul_nes# with two dissimilar halo`ens 5[06[0[2 Thiocarbonyl Halides with One Halo`en and one Other Heteroatom Function 5[06[0[2[0 Fluorothioformates ROC"F#1S 5[06[0[2[1 Chlorothioformates ROC"Cl#1S 5[06[0[2[2 Fluorodithioformates RSC"F#1S 5[06[0[2[3 Chlorodithioformates RSC"Cl#1S 5[06[0[2[4 Bromodithioformates RSC"Br#1S 5[06[0[2[5 Fluoroselenothioformates RSeC"F#1S 5[06[0[2[6 Chloroselenothioformates RSeC"Cl#1S 5[06[0[2[7 Bromoselenothioformates RSeC"Br#1S 5[06[0[2[8 Sul_nes derived from CF2SeC"Cl#1S and CF2SeC"Br#1S 5[06[0[2[09 Thiocarbamoyl ~uorides R1NC"F#1S 5[06[0[2[00 Thiocarbamoyl chlorides R1NC"Cl#1S 5[06[0[2[01 Thiocarbamoyl bromides R1NC"Br#1S
416
417 417 417 418 418 429 429 420 420 421 421 421 422 422 422 423 424 425 425 425 426 426 426 426 439
417
Thiocarbonyl and Halo`en or Chalco`en
5[06[1 FUNCTIONS CONTAINING AT LEAST ONE CHALCOGEN FUNCTION "AND NO HALOGEN#
439 439 434 434 434 441 441 441 444 445 459 459 450
5[06[1[0 Thionocarbonates "O\O!Diesters of Thiocarbonic Acid# 5[06[1[1 Dithiocarbonates "O\S!Diesters of Dithiocarbonic Acid# 5[06[1[1[0 Salts of O!alkyl esters of dithiocarbonic acid 5[06[1[1[1 O\ S!Diesters of dithiocarbonic acids 5[06[1[2 Derivatives of Trithiocarbonic Acid 5[06[1[2[0 Salts of monoesters of trithiocarbonic acid 5[06[1[2[1 Diesters of trithiocarbonic acid 5[06[1[3 Derivatives of Thiocarbamic Acid 5[06[1[3[0 O!Esters of thiocarbamic acids 5[06[1[4 Derivatives of Dithiocarbamic Acid 5[06[1[4[0 Salts of dithiocarbamic acids 5[06[1[4[1 Esters of dithiocarbamic acids
5[06[0 FUNCTIONS CONTAINING AT LEAST ONE HALOGEN Functions containing at least one halogen have been described in a volume of Houben!Weyl ð72HOU"E3#396Ł published in 0872[ Thus the literature search for related compounds in Chapter 5[06 is based on Chemical Abstracts from 0879 to February 0883[ The present text concentrates on literature from the mid 0879s^ original references to synthetic methods given in Volume E3 of Houben!Weyl are mentioned only in order to locate them in cases of need[ Volume E3 of Houben! Weyl can be strongly recommended because it includes detailed synthetic procedures ð72HOU"E3#396\ 72HOU"E3#319Ł[ A number of clathrate compounds have proved useful for facilitating the handling of thiophosgene and similar reactive reagents ð81TL150Ł[
5[06[0[0 Thiocarbonyl Halides with Two Similar Halogens 5[06[0[0[0 Thiocarbonyl di~uoride "i# From 1\1\3\3!tetra~uoro!0\2!dithietane Middleton et al[ ð50JA1478\ 54JOC0264Ł prepared thiocarbonyl di~uoride F1C1S "a colorless gas boiling at −43>C# ð54JOC0264Ł in high purity and yield "×89)# by a three!step procedure^ _rst thiophosgene was dimerized and the dimer ~uorinated with SbF2[ Pyrolysis of the resulting 1\1\3\3! tetra~uoro!0\2!dithietane at 364Ð499>C led to thiocarbonyl di~uoride in nearly quantitative yield "Scheme 0#[ Cl
Cl
S
Cl
F
S
Cl
F
F
S
2
S
2 Cl
S
Cl
F
S
F
F
Scheme 1
"ii# Other methods Thiocarbonyl di~uoride was also obtained as a by!product of the reaction of bis"tri~uoromethyl# trisul_de with Grignard reagents RMgX "R Et\ Pri# ð81JFC"48#80\ 82JFC"59#74Ł[ Middleton et al[ ð54JOC0264Ł also obtained thiocarbonyl di~uoride from tetra~uoroethylene by reaction with sulfur at 349Ð499>C[ It was obtained in even higher yield "85)# by Marquis ð59USP1851418Ł from chloro! di~uoromethane by bubbling it through sulfur at 259>C[ Further F1C1S was obtained from the sulfenyl chloride FCl1CSCl by reduction with tin and concentrated HCl but in lower yield "36[4)# ð48ZOB2681Ł[
418
At Least One Halo`en 5[06[0[0[1 Thiocarbonyl dichloride "thiophosgene#
"i# From trichloromethanesulfenyl chloride and other perchloromethyl derivatives containin` sulfur One of the most useful methods for the synthesis of thiophosgene is the reduction of perchloro! methyl sulfenylchloride with H1S at 009Ð003>C^ this gives thiophosgene in 85) yield ð63S15Ł[ A number of other reducing agents have been used ð72HOU"E3#396Ł\ including tin and concentrated HCl "Equation "0## ð78JAP92959307Ł[ Cl3C
SCl
Cl
red.
(1)
S Cl
Alternatively\ perchloromethyl derivatives containing sulfur can be thermally decomposed ð54GEP0108344Ł[ A number of synthetic procedures are published which optimize the thiophosgene yield^ in particular\ aqueous H1SO2 in the presence of catalysts "S1Cl1\ SCl1\ alkali metal iodide and:or I1# proved useful ð78JAP92926009\ 78JAP92959306\ 78JAP92959307\ 78JAP92086209\ 80JAP92959308Ł[
"ii# From trichloromethyl thiol Thiophosgene\ a red liquid boiling at 62[4>C ð72HOU"E3#396Ł was also prepared by reducing trichloromethyl thiol with SO1 in the presence of KI and S1Cl1 ð74JAP51002601\ 77JAP90146005Ł[ When H1S was used in place of S1Cl1\ the yields obtained were higher than 86) "Equation "1## ð75JAP51065809Ł[
Cl3C
SH
SO2
Cl (2)
S Cl
"iii# From carbon monosul_de Thiophosgene can be obtained from carbon monosul_de CS "continuously produced by dis! sociation of CS1 in a high!frequency discharge at 9[0 torr "mm Hg## ð63IC0667Ł by reaction with Cl1 at room temperature ð56AG538\ 57ZAAC"250#079Ł[
5[06[0[0[2 Thiocarbonyl dibromide "i# From carbon monosul_de Carbon monosul_de\ continuously produced by dissociation of CS1 in a high!frequency discharge "9[0 torr "mm Hg##\ ð63IC0667Ł reacts at room temperature with Br1 giving thiocarbonyl dibromide ð56AG538\ 57ZAAC"250#079Ł[ This compound is an orangeÐred liquid boiling at 031Ð033>C ð54JOC0264Ł[
"ii# Other methods Thiocarbonyl dibromide was obtained from F1C1S in 86) yield ð54JOC0264Ł by addition of anhydrous hydrogen bromide^ thiol intermediates eliminate the hydrogen ~uoride "Equation "2##[ Thiocarbonyl dibromide could also be obtained from thiophosgene but only in 20) yield ð70CB718Ł^ the halogens were exchanged in this case with BBr2 at 59Ð54>C[
429
Thiocarbonyl and Halo`en or Chalco`en F
Br
+2HBr
S
(3)
S –2HF
F
Br
5[06[0[0[3 Thiocarbonyl diiodide "i# From carbon monosul_de Thiocarbonyl diiodide can be synthesized in a similar way to thiophosgene and thiocarbonyl dibromide\ from carbon monosul_de by reaction with I1 ð56AG538\ 57ZAAC"250#079Ł[ Although the diiodide could not be isolated\ it was identi_ed by IR spectroscopy "nC1S 0951 cm−0^ nC0I 591 cm−0# ð56AG538\ 57ZAAC"250#079Ł[
5[06[0[0[4 Sulfoxides of thiocarbonyl halides "sul_nes# with two similar halogens "i# Di~uorosul_ne\ F1C1SO "a# From 0\0\3\3!tetra~uorodithietane[ It was much more di.cult to obtain this compound than the corresponding dichlorosul_ne Cl1C1SO "see below#[ 1\1\3\3!Tetra~uoro!0\2!dithietane was easily oxidized with tri~uorotriacetic acid "in dichloromethane at 9>C# to 1\1\3\3!tetra~uoro!0\2! dithietane!0!oxide^ however\ to get the corresponding 0\2!dioxide\ Henn and Sundermeyer ð77JFC"28#218Ł only succeeded by employing tri~uoromethanetrisulfonic acid as a new oxidizing agent "Scheme 1#^ pyrolysis at 379>C and 9[90 torr "mm Hg# yields F1C1SO quantitatively[ Di~uorosul_ne was detected only by mass spectrometry and decomposes spontaneously at −099>C to F1C1O and sulfur[ O F
S
F
F
S
F
O
MeCO3H, CH2Cl2, 0 °C
F
S
F
63%
F
S
F
F3CSO4H, 0 °C
F
S
F
39%
F
S
F
∆
F S O F
O Scheme 2
"b# From allyl di~uorochloromethyl sulfoxide[ F1C1SO could also be obtained by pyrolysis of F1ClCS"O#CH1CH1CH1 at 299Ð399>C ð75CB158Ł^ again\ it was identi_ed by mass spectrometry[
"ii# Dichlorosul_ne Cl1C1SO The synthesis\ structure\ analysis\ and chemistry of thiophosgene!S!oxide "dichlorosul_ne# have been reviewed ð81SUL164Ł[ "a# From 1\1\3\3!tetrachloro!0\2!dithietane[ 1\1\3\3!Tetrachloro!0\2!dithietane was oxidized with trichlorotriacetic acid "in dichloromethane at 9>C#\ and the 0!oxide thus obtained further oxidized to the corresponding 0\2!dioxide ð72CB0512Ł[ The latter compound is cleaved quantitatively to dichlorosul_ne by means of vacuum pyrolysis at 379>C and 9[4 torr "mm Hg# "Scheme 2#[
O Cl
S
Cl
MeCO3H, CH2Cl2, 0 °C
Cl
S
Cl
Cl
S
Cl
51%
Cl
S
Cl
O Scheme 3
∆
Cl S O Cl
420
At Least One Halo`en
"b# From thiophos`ene[ Thiophosgene!S!oxide was synthesized from thiophosgene in 21) yield by oxidation with mcpba "Equation "3## ð58TL3350Ł[ It is obtained as a yellow liquid "b[p[ 23Ð25>C at 14 torr "mm Hg##[ Cl
Cl
PhCO3H, 0 °C
S
S O
Cl
(4)
Cl
"c# From trichloromethanesulfenyl chloride[ Cl1C1SO was also obtained by hydrolysis of trichloromethanesulfenyl chloride Cl2CSCl in ca[ 29) yield "slightly dependent on the reaction conditions# and was found to be a thermally unstable compound ð58CC767Ł[ "d# From allyl trichloromethyl sulfoxide[ Cl1C1SO was obtained in 38) yield by pyrolysis of Cl2CS"O#CH1CH1CH1 at 299Ð399>C ð75CB158Ł[
"iii# Dibromosul_ne Br1C1SO Dibromosul_ne "a reddish liquid# was described for the _rst time by Schork and Sundermeyer ð74CB0304Ł[ Tetrabromo!0\2!dithietane was oxidized with tri~uorotriacetic acid in dichloromethane in two steps to the corresponding 0\2!dioxide^ the pyrolysis of this 0\2!dioxide gave dibromosul_ne in 69) yield "Scheme 3#[ O
O
Br
S
Br
F3CCO3H, CH2Cl2, 0 °C
Br
S
Br
F3CCO3H, 0 °C
Br
S
Br
Br
S
Br
24.6%
Br
S
Br
44.7%
Br
S
Br
∆
Br S O Br
O Scheme 4
The IR spectra of F1C1SO\ Cl1C1SO and FClC1SO "Section 5[06[0[1[3# were obtained at 09Ð 14 K in an argon matrix on a CsI window ð75SA"A#0170Ł in order to di}erentiate the sulfoxides from the corresponding dihalocarbonyls and thiocarbonyl compound[ Characteristic vibrations are given in Table 0 ð75SA"A#0170Ł[ Table 0 Characteristic frequencies of halocarbonyls\ thiocarbonyls\ and the corresponding sulfoxides "wavenumbers in cm−0#[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * X 0X 1C1O X 0X 1C1SO X 0X 1C1S ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * X0 X1 Cl 0029"nC0S# 0706"nC0O# 0058"nC0S# 674"nassCCl1# 726"nassCCl1# 835"nassCCl1# 0146"nC0S# 0757"nC0O# 0186\ 0135"nC0S# X0 F\ X1 Cl 0903"nC0F# 0984"nC0F# 0020\ 0034"nC0S# 501"nC0Cl# 665"nC0Cl# 539"nC0Cl#< 0949\ 0971"nS0O# X0 X1 F 0243"nC0S# 0829"nC0O# 0262"nC0S# 0079"nassCF1# 0133"nassCF1# 0185"nassCF1# 0007"nS0O# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
5[06[0[1 Thiocarbonyl Halides with Two Dissimilar Halogens 5[06[0[1[0 Thiocarbonyl chloride ~uoride "i# From dichloro~uoromethanesulfenyl chloride Thiocarbonyl chloride ~uoride FClC1S "a yellow liquid boiling at 6>C# can be readily synthesized from the sulfenyl chloride FCl1CSCl in 76) yield by reduction with tin and concentrated HCl ð48ZOB2681Ł[
421
Thiocarbonyl and Halo`en or Chalco`en
"ii# Other methods FClC1S was obtained as a by!product of the F1C1S synthesis via the pyrolysis of 1!chloro! 1\3\3!tri~uoro!0\2!dithietane and could be readily separated from F1C1S by distillation ð54JOC0264Ł[ Also\ benzenethiosulfonic acid S!dichloro~uoromethyl ester can be thermally decom! posed "at 069Ð149>C# "Equation "4##^ the yields obtained were satisfactory ð72HOU"E3#396Ł[ Cl PhO2S
S
Cl
–C6H5SO2Cl
Cl
S
F
(5) F
5[06[0[1[1 Thiocarbonyl bromide ~uoride Thiocarbonyl bromide ~uoride\ FBrC1S\ a yellow liquid boiling at 3Ð7>C and 099 torr "mm Hg#\ can be obtained in 23) yield from thiocarbonyl chloride ~uoride by halogen exchange with BBr2 at 59Ð54>C ð70CB718Ł[ FBrC1S spontaneously decomposes at room temperature[
5[06[0[1[2 Thiocarbonyl bromide chloride Thiocarbonyl chloride bromide\ ClBrC1S\ a red liquid boiling at 36>C and 79 torr "mm Hg#\ has been obtained from thiophosgene in 03) yield by halogen exchange with BBr2 ð65CB2321\ 70CB718Ł[
5[06[0[1[3 Sulfoxides of thiocarbonyl halides "sul_nes# with two dissimilar halogens "i# Chloro~uorosul_ne ClFC1SO Chloro~uorosul_ne was synthesized from 1\3!dichloro!1\3!di~uoro!0\2!dithietane by oxidation with tri~uoroperacetic acid at −09>C to the 0\2!dioxide^ pyrolysis at 349>C of the latter compound gives ClFC1SO nearly quantitatively[ This could not be isolated but was identi_ed by on!line mass spectrometry and photoelectron spectroscopy\ respectively "Scheme 4# ð76CB0388\ 77JFC"28#218Ł[ The isomerism of the chloro~uorodithietanes was studied by 08F NMR spectroscopy and x!ray structure analysis ð76CB0388Ł[ The two isomers of chloro~uorosul_ne "Equation "5## were identi_ed by IR and PE spectroscopy and\ synthetically\ by cycloaddition to 0\2!cyclopentadiene ð76CB0388Ł[ O Cl
S
Cl
F
S
F
MeCO3H, –10 °C
Cl
S
Cl
F
S
F
∆
Cl S O F
O Scheme 5
O
F
F S
S Cl
Cl
(6) O
ClFC1SO was also obtained by pyrolysis of FCl1CS"O#CH1CH1CH1 at 299Ð399>C^ it was identi_ed by means of mass spectrometry ð75CB158Ł[
422
At Least One Halo`en 5[06[0[2 Thiocarbonyl Halides with One Halogen and one Other Heteroatom Function 5[06[0[2[0 Fluorothioformates ROC"F#1S
Thiocarbonyl chloride ~uoride reacts with alcohols at low temperature but without any solvent leading selectively to the alkyl ~uorothioformates ROC"F#1S "R Me\ Et\ Pri\ Ph# ð48ZOB2681Ł[
5[06[0[2[1 Chlorothioformates ROC"Cl#1S "i# From phenols and naphthols Phenols and naphthols readily react with thiophosgene in the presence of a base to give aryl chlorothioformates in good yield "Equation "6## ð51JOC3498\ 54CB1952\ 54LA"570#53\ 56AG"E#170\ 72HOU"E3#396Ł[ Aryl chlorothioformates "in addition to those given in ð72HOU"E3#396Ł# which were synthesized in this way are listed in Table 1[ Hydrocarbons and chlorohydrocarbons were used as solvents[ Phenyl chlorothioformate is a yellow liquid boiling at 80>C and 09 torr "mm Hg# ð48ZOB2681Ł[ In a number of cases\ the aryl chlorothioformates were not isolated but used for the synthesis of thiocarbonic acid derivatives ð70JA821\ 71EUP51723\ 72JA3948\ 76USP3643961Ł[ In some cases thiophosgene was produced directly in the reaction mixture "see above# "a# by chlorination of CS1 ð74JAP51019247\ 89JAP92119062Ł from which the corresponding phenyl chlorothioformates were obtained in 82Ð85) yield^ "b# by reduction of CCl2CSCl ð74JAP50118759\ 74JAP50118750\ 77JAP1998747Ł\ the aryl chlorothioformates being obtained in 52) yield and the corresponding naphthyl derivatives in 63) yield^ and "c# by reducing CCl2SH with SO1 ð75GEP2505998Ł[ Cl
Cl OH
+
NaOH
S –HCl
Cl
S O
(7)
Table 1 Aryl chlorothioformates synthesized from thiophosgene and phenols or napthols[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Aryl0OH Base Yield Ref[ ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 84[9 80JAP92107225 Phenol NaOH:H1O 80JAP92082648 m!tert!butyl!phenol NaOH:H1O 82JAP94947889 87[8 77JAP90290543 m!tert!butyl!phenol NaOH:H1O 0 m!R !p!R!phenol NaOH:H1O 72JAP59044041 R0 halogen^ R alkyl − 1 4\5\6\7!tetrahydro!naphthol!1 NaOH:H1O 78[8 89JAP93955455 79[8 89JAP93017152 4\5\6\7!tetrahydro!naphthol!1 NaOH:H1O 89JAP94921505 76JAP90091947 4\5\6\7!tetrahydro!naphthol!1 NaOH:H1O:Na1S1O3 70[9 76JAP90964351 NaOH 88[9a 74SUL50 C5Cl40OH b 1\3\5!Trimethyl!phenol NaOH 70[9 74SUL50 37c 89CL72 1\5!di!OMe0C5H2ONa ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * a
Colorless solid^ m[p[ 097Ð001 >C[
b
Oily product^ m[p[ 39Ð32 >C[
c
In THF at 9 >C[
The esters ROC"Cl#1S "R succinimido\ phthalimido\ norborn!4!ene!1\2!dicarboximido# proved to be useful reagents for introducing the thiocarbonyl group into organic compounds ð77EGP162721Ł[
"ii# From alcohols\ alcoholates\ and alkoxytrimethylsilanes Propargyl chlorothioformate "a light yellow liquid boiling at 30>C and 7 torr "mm Hg# was obtained "41) yield# as above from propargyl alcohol and thiophosgene with sodium hydride as the base "Equation "7## ð81AG"E#755Ł^ the corresponding allene\ CH11C1CHCH1OC"Cl#1S\ could
423
Thiocarbonyl and Halo`en or Chalco`en
not be isolated owing to spontaneous ð2\2Ł!sigmatropic rearrangement to CH11C"CH1CH1# SC"Cl#1O ð81AG"E#755Ł[ Cl
+
OH
S
S
NaH
(8) O
Cl
Cl
Alkyl chlorothioformates have been synthesized in two di}erent ways[ The _rst is the reaction of thiophosgene with a potassium alkoxide in the corresponding alcohol ROH "or in tetrahydrofuran# between −54>C and 04>C ð75S659Ł[ EtOC"Cl#1S was prepared from thiophosgene in 82) yield when the reaction mixture was kept for 0 h at −59>C in ethanol and tetrachloromethane "Equation "8## and other alkyl chlorothioformates were similarly isolated in high yield[ When sodium alkoxides RONa "R Et\ Prn# were used\ the corresponding alkyl chlorothioformates "R Et\ Prn# were obtained in approximately 49) yield ð73ZAAC"497#025Ł[ As an alternative\ the reaction of alkoxytrimethylsilanes with thiophosgene\ which does not require basic media\ was tried ð75S659Ł^ the yields\ were\ however\ no higher than 24) "Equation "09##[ Cl ROH
+
S
EtOK
(9)
S –KCl, –EtOH
Cl Cl EtO-TMS +
S
RO
solv./cat. at 80 °C
Cl S
EtO
Cl
(10) Cl
The second method is the chlorolysis of bis"alkoxythiocarbonyl# disul_des with Cl1 or SOCl1 ð46GEP0907943\ 54CB1948\ 72JOC3649Ł[ However\ the alkyl chlorothioformates are obtained in lower yield than from the _rst method\ the reagents must be very clean\ and the products are di.cult to purify by distillation "Equation "00## ð75S659Ł[ S
S
RO
OR S
S
Cl2
S (11)
2 RO Cl
5[06[0[2[2 Fluorodithioformates RSC"F#1S "i# From chlorodithioformates The alkyl ~uorodithioformates RSC"F#1S "R Et\ Prn# have been synthesized in yields of 39) and 59)\ respectively\ from the corresponding chlorodithioformates with KF under solidÐliquid phase!transfer catalysis conditions "07!crown!5 in acetonitrile under argon#^ spectroscopic data was obtained ð73ZAAC"498#56Ł[
"ii# Other methods The reaction of thiols RSH "R Me\ Et# with FClC1S\ but without any solvent\ is an alternative for the synthesis of alkyl ~uorodithioformates ð48ZOB2681Ł[ Per~uoromethyl ~uorodithioformate CF2SC"F#1S can be synthesized from tri~uoromethyl thiol CF2SH with anhydrous NH2 ð44JCS2760Ł "yield 39)# or with KF ð57CB1598Ł "yield 47)# as HF acceptors[ The yield increases to ca[ 85) if FClC1S and Hg"SCF2#1 are used at room temperature ð61CB719Ł^ CF2SC"F#1S is obtained in this way as a yellow liquid boiling at 32>C ð57CB1598Ł and it can be readily converted into CF2SC"Cl#1S "yield 76)# with BCl2 ð65CB0865Ł[
424
At Least One Halo`en 5[06[0[2[3 Chlorodithioformates RSC"Cl#1S "i# From thiols
Alkyl chlorodithioformates RSC"Cl#1S "R Et\ Prn\ Pri\ Bun# were synthesized in yields of 44) to 69) from the corresponding thiols RSH and thiophosgene in dry CS1 at room temperature ð73ZAAC"497#025Ł[ The compounds could be readily stored at −19>C under argon^ spectroscopic data was obtained[
"ii# From carbon monosul_de The insertion of carbon monosul_de into the SCl bond of sulfenyl chlorides was used for the synthesis of alkyl and aryl chlorodithioformates[ However\ the production of CS needs special care and equipment ð63IC0667Ł[ In this way\ trichloromethyl chlorodithioformate "an orange oil boiling at 87Ð099>C and 03 torr "mm Hg## was obtained from trichloromethanesulfenyl chloride in 64) yield "Equation "01## ð73JOC2743Ł and phenyl chlorodithioformate PhSC"Cl#1S from phenyl chloro! dithioformate in 62) yield ð73JA152Ł[ Chlorodithioformates which have been prepared by this method are S1C"Cl#SSC"Cl#1S "49) yield#\ Cl2CSCCl1SC"Cl#1S "38)# ð75SUL192Ł\ and a num! ber of other RSSC"Cl#1S derivatives ð75ACS"B#598Ł] R COMe\ an orange oil "49)#\ R COCl\ a dark red oil boiling at 44Ð45>C and 9[93 torr "mm Hg# "42)#\ R CCl2\ an orange oil boiling at 67Ð79>C and 9[93 torr "mm Hg# "46)#\ and R C1Cl4\ an orange oil boiling at 097Ð098>C and 9[92 torr "mm Hg# "08)# ð75ACS"B#598Ł[ S Cl3C
SCl
+ CS
(12)
Cl3CS Cl
S1C"Cl#CH1CH1SC"Cl#1S "a light yellow oil\ 27) yield# and 1\4!bis"chlorothiocarbonylthio#! 0\2\3!thiadiazole "yellow needles melting at 58>C\ 099)# were obtained in the same way "Equation "02## ð80SUL032Ł[ S
N N ClS
S
Cl
SCl
S
N N
2 CS
S
S
S
(13)
Cl
"iii# Other methods Methyl chlorodithioformate MeSC"Cl#1S was obtained as the major product from "MeS#1C"Cl#SCl "with H1O\ 47)^ with aq[ KI\ 44)^ with MeSH\ 36)#\ from MeSCCl1SSMe "with H1O\ 70)^ with aq[ KI\ 61)^ with MeSH\ 59)# and from MeSCCl1SCl "with MeSH\ 25)#\ respectively ð73SUL130Ł[ Alkali metal chlorodithioformates MSC"Cl#1S were prepared from the alkali metal chlorides "yields] M Na\ 34)\ K\ 12)\ Rb\ 24)\ and Cs\ 20)# and CS1 in the presence of NaOH pellets ð72ZAAC"491#6Ł[ Ethyl chlorodithioformate EtSC"Cl#1S was obtained from KSC"Cl#1S and EtI but only in 01) yield ð72ZAAC"491#6Ł[ Diazocarbonyl compounds can also give chlorodithioformates with thiophosgene "Equation "03## ð53LA"563#013Ł[ O
O N2+ –
Cl
+ 2
S Cl
MeO
S –N2
MeO
S
(14)
CCl3 Cl
"iv# Speci_c methods for aryl chlorodithioformates The reaction of pentachlorobenzenesulfenyl chloride and sodium trithiocarbonate gave the pentachlorophenyl chlorodithioformate in 35) yield "Equation "04## ð74T4034Ł[
425
Thiocarbonyl and Halo`en or Chalco`en Cl C6Cl5
S
S
Na2CS3
Cl
–2Cl–
SCl
(15)
C6Cl5
S
Cl
Aryl chlorodithioformates were also obtained by the reaction of arenediazonium chlorides with CS1 under Sandmeyer conditions "copper powder or Cu"I#Cl at room temperature# "Equation "05## ð68ZC178Ł and\ in the usual manner\ from thiophosgene and arenethiols "Equation "06## ð74SUL50Ł[ This last method gave 3!nitrobenzenethio! ð62CB0376Ł and 1!naphthalenethio! derivatives ð64JCS"P1#805Ł[ Penta~uorobenzenethiocarbonic acid chloride was obtained "59)# by Haas and Kempf ð73T3852Ł from bis"penta~uorobenzenethio#mercury and thiophosgene "Equation "07##[ Cl +
S
CuCl
N N Cl– + CS2
S
X
(16)
X Cl ArSH +
Cl S Cl
S
–HCl
Cl
Hg(SC6F5)2 +
Cl
NaOH, CHCl3
S
Cl
pentane, 12 h
S
2 c. 60%
(17)
ArS
C6F5
S
+ HgCl2
(18)
5[06[0[2[4 Bromodithioformates RSC"Br#1S "i# From thiols Alkyl bromodithioformates RSC"Br#1S were obtained in 20) yield "R Et# and 33) yield "R Prn# by treating the corresponding thiol RSH with Br1C1S in ether at room temperature under argon[ The deep red liquids could be stored at −19>C under argon ð73ZAAC"498#50Ł^ spec! troscopic data was obtained[
"ii# Other methods Tri~uoromethyl bromodithioformate F2CSC"Br#1S\ a red liquid boiling at 56>C and 049 torr "mm Hg#\ was obtained in 72) yield from F2CSC"F#1S by halogen exchange with BBr2 at 24Ð 39>C^ IR\ 08F NMR\ UV\ and MS data was obtained ð65CB2321Ł[
5[06[0[2[5 Fluoroselenothioformates RSeC"F#1S Tri~uoromethyl ~uoroselenothioformate F2CSeC"F#1S\ a liquid boiling at 46Ð47>C\ was pre! pared from Hg"SeCF2#1 and FClC1S at −67>C^ the 08F chemical shifts "25[2 and −096[5 ppm#\ the IR and MS data of the compound were measured ð65ZAAC"316#003Ł[
5[06[0[2[6 Chloroselenothioformates RSeC"Cl#1S "i# From alkaneselenols In a similar way to the corresponding alkyl chlorodithioformates\ the selenoesters RSeC"Cl#1S "R Et\ Prn\ yellow viscous oils# were synthesized from the corresponding alkaneselenols and thiophosgene in dry CS1 as the solvent at room temperature in yields of 52Ð65) ð73ZAAC"498#50Ł[
426
At Least One Halo`en "ii# Other methods
F2CSeC"Cl#1S was synthesized from F2CSeC"F#1S in 86) yield by halogen exchange with BCl2 ð65ZAAC"316#003Ł[
5[06[0[2[7 Bromoselenothioformates RSeC"Br#1S F2CSeC"Cl#1S\ a liquid boiling at 43>C and 49 torr "mm Hg#\ was synthesized photochemically "UV irradiation for 3 h# from F2CSeBr in 40) yield and by halogen exchange with BBr2 from F2CSeC"F#1S at 39>C in 63) yield ð75ZN"B#302Ł[
5[06[0[2[8 Sul_nes derived from CF2SeC"Cl#1S and CF2SeC"Br#1S Fockenberg and Haas ð75ZN"B#302Ł obtained the S!oxides of CF2SeC"Cl#1S and CF2SeC"Br#1S\ respectively\ by oxidation with mcpba[ CF2SeC"Cl#1SO\ a yellow liquid boiling at 36>C and 09 torr "mm Hg#\ was obtained in 45) yield and CF2SeC"Br#1SO\ a yellow liquid boiling at 59>C and 09 torr "mm Hg#\ in 14) yield[
5[06[0[2[09 Thiocarbamoyl ~uorides R1NC"F#1S N\N!Diethylthiocarbamoyl ~uoride Et1NC"F#1S was obtained from diethylamine and thio! carbonyl chloride ~uoride in 34) yield ð52CJC0532\ 53LA"489#012\ 69LA"622#084\ 69LA"624#047\ 64LA0914Ł[ N\N!Dimethylthiocarbamoyl ~uoride Me1NC"F#1S was also prepared by treating CF11CFR "R F\ Cl\ CF2# with tetramethylthiuramide sul_de at 029Ð024>C ð70URP793523Ł[ N!"Fluo! rothiocarbonyl#imidosulfuryl di~uoride F1S1NC"F#1S was synthesized by reaction of Si"NCS#3 with SF3 ð66MIP42425Ł[
5[06[0[2[00 Thiocarbamoyl chlorides R1NC"Cl#1S "i# From secondary amines and related compounds Thiocarbamoyl chlorides can be synthesized from thiophosgene and secondary amines "Equation "08## ð52CJC0532\ 53LA"489#012\ 69LA"624#047\ 64LA0914Ł[ Data published after 0879 is given in Table 2[ In two cases ð74JAP50122551\ 74JAP50122552Ł\ thiophosgene\ which is added to aromatic amines\ was produced directly in the reaction mixture from trichloromethyl thiol and SO1 ð74JAP50122551Ł or NaHSO2 ð74JAP50122552Ł[ Higher yields were obtained by replacing secondary amines with trimethylsilylamines "Equation "19## ð79T428Ł and the chlorothiocarbamates produced in this way proved easier to purify[ The TMS derivative RN"TMS#C"Cl#1S was also obtained ð75ZOB0436Ł[ R1 N H
Cl
+ Cl
R2
R1 N TMS R2
S
–HCl
Cl
+
S Cl
–TMS-Cl
R1 N
S
R2
Cl
(19)
R1 N
S
R2
Cl
(20)
Triphenylphosphine N!trimethylsilylimide and triphenylphosphiniminium chloride were similarly added to thiophosgene "Scheme 5# ð76UKZ284Ł[
427
Thiocarbonyl and Halo`en or Chalco`en Table 2 Chlorothiocarbamates as synthesized from secondary amines or amides and thiophosgene[
Chlorothiocarbamate
Solvent
m.p.
Yield (%)
Ref.
dry ether
170 °C
62.5
80CB1898
S O
N Cl
colorless crystals R2 N R1
N
Cl
pat.
83JAP60056958
ether
85EGP256705
S
R1 = lower alkyl R2 = halogen, lower alkyl, lower alkoxy S
N N Cl O S
62–64 °C
THF/benzene
N
88EGP273832
Cl O (succinimido, phthalimido and norborn-5-ene-2,3-dicarboximido analogues have also been synthesized) N,N'-Me,Ph–C(Cl)=S
SO2/CCl3SH/CCl4/KI
45.1
85JAP61233662
NaHSO3/CCl3SH/CCl4/KI
30
85JAP61233663
S MeO
N
N
Cl
Me
Cl
Ph3P
S
N–TMS
S
Cl
Ph3P
Ph3P
N
Cl b.p. 182–184 °C
NH2+ Cl– Scheme 6
"ii# From tetraalkylthiuramide disul_des Another generally used method for the preparation of thiocarbamoyl chlorides is the chlorination of tetraalkylthiuramide disul_des "Table 3 and Equation "10##[ Chlorine ð78JAP2919145\ 81MI 506!90Ł\ SO1Cl1 ð72JOC0338\ 77ZOB0378\ 78IZV898\ 89SC1658Ł and S1Cl1 ð78EUP244467Ł have been used as the chlorinating agent[ N\N!Dimethylthiocarbamoyl chloride was also synthesized from the monosul_de by reaction with phosgene "Equation "11## ð81MI 506!91Ł[ S
S
R 2N
Cl2
NR2 S
S 2 R 2N
(21) Cl
S
Cl
S Me2N
O
S S
Cl
NMe2
S 2 Me2N
(22) Cl
428
At Least One Halo`en Table 3 Chlorothiocarbamates synthesized by chlorination of thiuramide disul_des[ Chlorothiocarbamate
Chlorination
b.p. (°C)
Yield (%)
SO2Cl2
96/17 torr
Ref.
S 83.2
89IZV909 88ZOB1489
94
83JOC1449
97
90S2769
S2Cl2
99
89EUP355578
Cl2
92
92MI-617-01
87
89IZV909 88ZOB1489
Cl
Me2N S
SO2Cl2 Cl
Me2N S
SO2Cl2
43 (m.p.)
Cl
Me2N S
Cl
Me2N S
Cl
Me2N S
SO2Cl2
70/13 torr
Cl2
pat.
Cl
Et2N
S Me
N
Cl 89JAP03020256
"iii# From thioformamides The third synthetic method\ which is a general one for thiocarbamoyl chlorides\ is the chlorination of thioformamides "Equation "12## ð72HOU"E3#396Ł[ SCl1 ð69LA"622#084\ 78CB002Ł\ Cl1 ð69LA"622#084Ł and SO1Cl1 have been used as the chlorinating agent[ The thioformamides can be synthesized from the corresponding formamides with Lawesson|s reagent "Scheme 6# ð74JAP51003855Ł[ R1 N
S
Hal2
R2
MeO
N
N
R1 N
S
R2
Hal
+ HHal
HCO2H/(MeCO)2O
Me
MeO
N
H
MeO
N
(23)
Lawesson's reagent
Me O
N
N
Me
SO2Cl2/Et3N, CCl4
MeO
S
N
N Cl
Me S
Scheme 7
"iv# Other methods N\N!Dimethylthiocarbamoyl chloride was obtained as a by!product in the synthesis of alkyl iso! cyanates RN1C1O from RNHC"OR?#1S and Cl1C1N¦Me1Cl− ð81ZOR596Ł[ The stable gold
439
Thiocarbonyl and Halo`en or Chalco`en
chloride complexes ClAuS1C"Cl#NMe1 and Cl2AuS1C"Cl#NMe1 have been isolated and char! acterized ð81POL782Ł[
"v# Methods for thiocarbazic acid chlorides "R10NNR1C"Cl#1S# Thiocarbazic acid chlorides R0R1NN"R2#C"Cl#1S were prepared from the corresponding tri! alkylhydrazines and thiophosgene ð61CB1743\ 80AP"213#806Ł "Table 4 and Equation "13##[ Thiocarbazic acid chlorides were employed for the thiocarbazoylation of thiazine!1!ones and thiazolidine!1!ones ð80LA394Ł[ Table 4 Thiacarbazic acid chlorides\ R0R1N0N"R2#0C"Cl#1S\ obtained from thiophosgene and the corresponding trialkyl hydrazine[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0 R1 R2 m[p[ Yield Ref[ ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me Me Me 53Ð54 >C 58 61CB1743 morpholino Me 82 >C 43 80AP"213#806 piperidino Me 30Ð31 >C 02 80AP"213#806 Me Me cyclohexano 29 >C 18 80AP"213#806 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
R1 H N N R3 R2
Cl
+
S R1 N N
CH2Cl2, –30 °C to –15 °C
S
–HCl
Cl
Cl (24) R3
R2
5[06[0[2[01 Thiocarbamoyl bromides R1NC"Br#1S Thiocarbamoyl bromides can be synthesized from the corresponding thioformamides by reaction with bromine "Equation "12## ð69LA"622#084\ 61LA"644#034Ł[ For example\ MePhNC"Br#1S was formed in 67) yield and EtPhNC"Br#1S in 72) yield[ 5[06[1 FUNCTIONS CONTAINING AT LEAST ONE CHALCOGEN FUNCTION "AND NO HALOGEN# 5[06[1[0 Thionocarbonates "O\O!Diesters of Thiocarbonic Acid# The direct reaction of alcohols and phenols with thiocarbonylating agents usually leads to thionocarbonates in good yield ð72HOU"E3#319Ł[ Thiophosgene and chlorothionoformates are most often used for thiocarbonylation^ several other reagents are used in speci_c cases[
"i# From thiophos`ene In these reactions thiophosgene is allowed to react with a hydroxy compound in the presence of a base "Equation "14##^ bases used include potassium carbonate ð58JOC2900Ł\ pyridine ð44JA1368\ 51JOC3498\ 79CB649Ł and 3!dimethylaminopyridine "dmap# ð71TL0868\ 72TL754Ł[ 0\1!Diols "Equation "15## ð71TL0868Ł and enols also react easily ð79CB649\ 72HOU"E3#319Ł[ Cl 2ROH
+
RO
base
S
Ph
OH
Ph
OH
RO
Cl
+
Ph dmap
O
95%
Ph
O
S
S Cl
(25)
S
Cl
(26)
430
At Least One Chalco`en
The above method is successful with 1!~uoroalcohols\ an example being the formation of bis"1! ~uoro!1\1!dinitroethyl# thionocarbonate "Equation "16##^ it is unsuitable for nitroalcohols such as 1\1!dinitropropanol and 1\1\1!trinitroethanol ð72HOU"E3#319\ 72JCED020Ł[ O2N O2N Cl
O2N 2
OH
O2N
+
F
F O
HO–
S
S
(27)
O
Cl O2N O2N
F
"ii# From chlorothionoformates This is the most general method for the preparation of mixed thionocarbonates ð72HOU"E3#319Ł[ After protection of the 2! and 4!hydroxyl groups of methyl shikimate\ the 3!hydroxyl group can be transformed into a thionocarbonate by reaction with phenyl chlorothionoformate in the presence of an equivalent amount of dmap "Equation "17## ð74TL3830Ł[ Similarly the 1?!hydroxy group of 0!"2?\4?!O!"0\0\2\2!tetraisopropyldisiloxane!0\2!diyl#!b!D!ribofuranosyl#!0H!benzimidazole was transformed into a thionocarbonate by reaction with dmap and p!tolyl chlorothionoformate "Equa! tion "18## ð76HCA027Ł[ CO2Me CO2Me Cl
dmap
+ TBDMS-O
S
TBDMS-O
O-TBDMS
PhO
O-TBDMS
(28)
S
O
OH OPh N
N
Pri
2Si
N
O
Cl
+
O
dmap
S
Si O Pri2
O
(29)
O
4-MeC6H4O
O
N
O
Pri2Si
Si O O Pri2 4-MeC6H4O
OH
S
Sometimes a hydroxy derivative is metallated before treatment with an aryl "or alkyl# chloro! thionoformate^ for example\ by adding methyllithium and then ClC"1S#OPh to a solution of 0!O! benzyl!1\2!isopropylidene!L!lyxose in THF at −67>C\ the corresponding thionocarbonate was obtained in 89) yield "Equation "29## ð74T3968Ł[ O
Cl
O
OBn
+
O
O
S PhO
HO
O
MeLi, –78 °C
OBn
S
90%
PhO
O
(30)
O
The reaction of pyranosides which do not possess cis!vicinal hydroxyl groups "e[g[ Me a!D!glc\ Me b!D!xyl# with dibutyltin oxide and then with phenyl chlorothionoformate gives mono! thionocarbonates in good yield "Scheme 7# ð75CPB329Ł[ They\ in turn\ can be used for preparing the deoxy compounds[ Pyranosides with cis!vicinal hydroxyl groups "e[g[ Me a!D!gal\ Me!b!D!ara# give cyclic thionocarbonates instead "Scheme 7#[ The reaction of a sulfone with butyllithium and then with an aldehyde at −39>C gives the lithium salt of a b!hydroxysulfone\ which can be used in situ for the synthesis of the corresponding thionocarbonate "Scheme 8# ð80TL1692Ł[ When diethyl di~uoromethylphosphonate is metallated
431
Thiocarbonyl and Halo`en or Chalco`en S
OH
O
Bu2SnO
Bu Sn
OH
O
OH
OH
OH
PhO
O
Cl
S
Bu
i, Ac2O, py
S
O
O
OPh
deoxy compounds
ii, Bu3SnH
Scheme 8
with lithium diisopropylamide "LDA# in THF at −67>C and then reacted with a series of aldehydes\ intermediate alkoxy adducts are obtained which give thionocarbonates in 60Ð89) yield with phenyl chlorothionoformate "Equation "20## ð81TL0728Ł[ These thionocarbonates can then be used for the synthesis of 0\0!di~uoroalkylphosphonates[ S
( )7
i,
SO2Ph
BunLi,
LiO
THF, –40 °C
ii, RCHO, THF, –40 °C
SO2Ph
R
n-C7H15
4-FC6H4O
S Cl
O
SO2Ph
R
n-C7H15
4-FC6H4O
THF, –40 °C
Scheme 9
S O
i, LDA, THF, –78 °C ii, RCHO, THF, –78 °C
F
(EtO)2P
iii, PhOCSCl, –78 °C
F
O
O
(EtO)2P
OPh
(31)
R
F
F
Diol monothionocarbonates can be prepared as illustrated in Scheme 09[ 4!Oxopentyl phenyl thionocarbonate ð80CPB0548\ 81TL1432Ł and 4!oxohexyl phenyl thionocarbonate ð81T8322Ł were pre! pared in the usual manner by treating the respective hydroxy compound with phenyl chloro! thionoformate[
R1
R1
O
R3
+
R4
( )4
R2
M M = Li or MgBr
O
OPh
R3
R2 R4
S
( )4 OH O
S OPh S
PhO
O R1
+ R2
R1
R3 R4
( )4
Cl
R3
OH R2 R4
MgBr
( )4 OH OH
R4 = H or Me Scheme 10
Very often\ the thionocarbonate group serves as a reactive intermediate or as a protective group^ further examples of their formation from chlorothionoformates are given in Table 5[
432
At Least One Chalco`en
Table 5 Further examples of thionocarbonates prepared by treating a hydroxy compound with a chlorothionoformate[ Thionocarbonate
Chlorothionoformate
S
Base
Yield (%)
Ref.
MeONa
72
83JOC4750
EtONa
40–46
83JOC4750
MeONa
28
83JOC4750
pyridine
84
88S226
pyridine
62
91T121
pyridine
43
91T6381
dmap
89
91JCS(P1)787
pyridine
92
92JOC6803
S OMe
MeO
Cl
MeO
S
S OEt
EtO
Cl
EtO
S
S OEt
MeO
Cl
EtO S
O
S
OPh OMe
O
Cl
PhO
O
O
S OPh
O
Cl
PhO
S O O O
PhO
OMe O
S
OPh
S Cl
PhO
S O
CN O
TBDMS-O
S
S Cl
PhO OPh
Ph S OPh O
PhO
Cl
S
"iii# From thiocarbonylbis"azoles# Thiocarbonylbis"azoles# react with two alcohol molecules or with diols forming acyclic or cyclic thionocarbonates\ respectively ð72HOU"E3#319Ł[ Thiocarbonyldiimidazole is most often used but 0\0?!thiocarbonylbis"0\1\3!triazole# can also serve as the thiocarbonylating reagent ð72HOU"E3#319Ł[ The latter proved to be very e}ective in preparing thionocarbonates from 1\1!dinitropropanol and from 1\1!di~uoro!1!nitroethanol[ The same approach can also be applied to the preparation of unsymmetrical thionocarbonates "Scheme 00# ð72JCED020Ł[ An example of the formation of a thionocarbonate from a 0\1!diol and thiocarbonyldiimidazole is shown in Equation "21#[ Several cyclic thionocarbonates were prepared from various 0\1!diols and thiocarbonyldiimidazole in order to be used as initiators for radical!based cyclization reactions ð76TL4862Ł[ Catechol has also been used as a diol with thiocarbonyldiimidazole\ the thionocarbonate "0\2!benzoxadiole!1!thione# being formed in 71) yield ð77JOC1152Ł[ Mixed thionocarbonates have been prepared by the successive displacement of imidazole from thiocarbonyldiimidazole by two di}erent alcohols ð81JOC5792Ł[
433 O 2N O2N
Thiocarbonyl and Halo`en or Chalco`en N
F
N
+
OH
N
N
N
N
O 2N O2N
pyridine, CH2Cl2
F
N O
N
N
F3CCH2OH
S
S O 2N O2N
F O
O
CF3
S Scheme 11
O O O HO
N
+
N
N
N
O
toluene, heat
(32)
O
O
72%
OH
S S
"iv# Other methods Several cyclic thionocarbonates have been prepared by cyclization reactions^ two examples are shown in Equations "22# and "23# ð81CPB1168\ 82JOC1783Ł[ The reaction shown in Equation "23#\ and the substitution process shown in Equation "24# ð81T5772Ł\ involve intermediate thioacyl radicals[ By adding NaSH to a stirred mixture of methyl 1!O!methyl!b!L!arabinopyranoside and Viehe|s salt\ methyl 1!O!methyl!2\3!O!thiocarbonyl!b!L!arabinopyranoside was isolated in 62) yield "Equation "25## ð71AJC0698Ł^ other diols were similarly converted into thionocarbonates[ An interesting route to diaryl thionocarbonates proceeds via CuI complexes which react with carbon disul_de "Scheme 01# ð77TL716Ł[ OH ( )4
Et
O
(TMS)2NLi, THF, RT, <5 min
OPh
O
+ PhOLi
S
S
O
O HO
(33)
76%
O
H O
H O O
(34)
15%
SMe
O
O
Bu3SnH, AIBN, toluene, reflux
O
O S
S
S O
S Im
Bu3SnOMe, AIBN, toluene
O
O
OMe
(35)
O
R
R
OH +
O
+
HO MeO
Cl–
Me2N Cl
OMe
O
S
Cl
O
NaSH
(36)
O MeO
OMe
434
At Least One Chalco`en Ar O 2CuCl + 4Et3N + 2NaOAr
[Et3N]2Cu
S
CS2
Cu[NEt3]2
+ Cu2S
40–98%
O
ArO
OAr
Ar Scheme 12
5[06[1[1 Dithiocarbonates "O\S!Diesters of Dithiocarbonic Acid# Dithiocarbonic acid itself is unstable and decomposes spontaneously to H1S and COS[ However\ its O!alkyl esters "xanthates# and their salts are relatively stable[
5[06[1[1[0 Salts of O!alkyl esters of dithiocarbonic acid The potassium salts can be easily prepared from alcohols\ carbon disul_de and KOH using the appropriate alcohol as the solvent "Equation "26## ð59CB2945\ 66S762\ 72HOU"E3#319Ł[ These salts are very often used to synthesize other derivatives of dithiocarbonic acids[ For example\ the reaction of 2!"1!hydroxyethyl#! or 2!"2!hydroxypropyl#benzothiazolin!1!ones with potassium hydroxide and excess carbon disul_de a}orded the corresponding dithiocarbonates "Scheme 02# ð77JHC0590Ł which were converted by aqueous ammonium persulfate to the corresponding disul_des or by chloro! alkanes to the S!alkyl derivatives[ S ROH + CS2 + KOH RO
S – K+
+ H2 O
(37)
S O N ( )n O
RX
S
SR O
S O N
S
N
+ CS2 + KOH
( )n O
( )n OH
S– K+ S S (NH4)2S2O8
O N ( )n O S S
2
Scheme 13
5[06[1[1[1 O\S!Diesters of dithiocarbonic acids "i# From salts of O!esters of dithiocarbonic acids A salt M¦−SC"1S#OR "M K or Na# can be converted into the corresponding O\S!diester by reaction with a chloroalkane or a similar reagent[ This is exempli_ed in Scheme 02^ further examples are shown in Equations "27# and "28#[ By heating equimolar amounts of 1!chloromethylpyridine or 1!chloromethylquinoline with potassium O!ethyl dithiocarbonate for 1 h the corresponding dithiocarbonates were obtained "Equation "27## ð78JPR328Ł[ Similarly\ the reaction of 2!chloro!
435
Thiocarbonyl and Halo`en or Chalco`en
methylbenzothiazolin!1!thione with sodium O!alkyl dithiocarbonates "alkyl Me\ Et# gave the corresponding esters "Equation "28## ð78JHC0134\ 78JPR328Ł[ The preparation of 30 compounds of the type "EtOC"S#SCH1C5H3#1Z "Z "CH1#0Ð5\ O\ S or SO1# from potassium O!ethyl dithiocarbonate and the corresponding chloro compound has been described ð89MI 506!92Ł[ The reaction of bromo! triphenylmethane with potassium O!ethyl dithiocarbonate in various conditions a}ords O!ethyl S!triphenylmethyl dithiocarbonate in 68Ð83) yield ð89JCS"P0#1998Ł[ S!Methyl O!trimethylsilyl dithiocarbonate was obtained "27)# from sodium O!trimethylsilyl dithiocarbonate and chloro! methane ð73ZAAC"404#071Ł[ The corresponding S!ethyl derivative was obtained similarly in 30) yield with iodoethane[ K+ –S R
Cl
R
OEt
S
OEt
+
+ KCl
(38)
S
S R = 2-pyridyl, 2-quinolyl
S S
S S N
Na+ –S
OR
N
+
+ NaCl
S
S Cl
RO
(39)
S
Protected glycosyl bromides and chlorides can be converted into the corresponding S!glycosyl O! ethyl dithiocarbonates with complete anomeric inversion in high yield ð80TL6342\ 81MI 506!93Ł^ an example ð81MI 506!93Ł is shown in Equation "39#[ OAc OAc
AcO
X O
AcHN
S CO2Me
AcO
+ K+ –S
AcO
OAc OAc
+ KX
S
O
AcHN
OEt
CO2Me
AcO S
(40)
OEt
a!Haloketones and a!haloketoximes undergo displacement easily[ For example\ the reaction of 1!chlorocyclopentanone with potassium O!isopropyl dithiocarbonate in acetone led to the formation of the corresponding dithiocarbonate ð82H"24#66Ł\ and 2!bromo!4!methylhexan!1!one reacted with potassium O!ethyl dithiocarbonate in acetone to give the dithiocarbonate in 75) yield ð76JHC470Ł[ Chloroacetaldehyde reacts with potassium O!ethyldithiocarbonate in an analogous way to give the dithiocarbonate in 54) yield ð81HCA896Ł[ There are many other examples of displacement of halide from a!halocarbonyl compounds ð71JIC771\ 73MI 506!90\ 74JIC053\ 75MI 506!93\ 77MI 506!90Ł[ Sodium O! methyl dithiocarbonate and a!chloroacetophenone oxime reacted to give the displacement product "as a mixture of syn and anti isomers# in 76) yield ð76S238Ł[ This was converted into 2!phenyl!3H! 0\4\1!oxathiazine!5!thione by heating with tosyl isocyanate "Scheme 03#[ Related reactions of a! haloketoximes have been described ð74TL4832Ł[ S Ph
Cl N
S
+ OH
Na+ –S
OMe
87%
MeO
Ph
S N
OH
Ph
S
TsNCO
S
O
N
Scheme 14
Carboxylic acid chlorides react readily with potassium O!alkyl dithiocarbonates[ Acetyl chloride reacts with potassium O!ethyl and O!methyl dithiocarbonate to give the corresponding anhydrides MeCOSC"1S#OR in high yield ð70LA0133Ł[ Similar reactions of 1!furoyl chloride ð74MI 506!92Ł and of phthaloyl chloride "Equation "30## ð76JIC083Ł have been described[ Alkyl chloroformates can be used to prepare anhydrides of dithiocarbonic acids ð67JOC1829Ł[ Thus\ O!butyl S!ethoxycarbonyl dithiocarbonate was prepared by slow addition of potassium O!butyl dithiocarbonate to an excess of ethyl chloroformate in acetone at 9>C ð72JCS"P0#1530Ł[ Phthaloylglycyl chloride reacted with potassium O!alkyl dithiocarbonates to give the corresponding O!alkyl S!phthaloylglycyl dithio! carbonates[ Irradiation of the latter in benzene with a mercury lamp gave the corresponding alkyl
436
At Least One Chalco`en
dithiocarbonates "Scheme 04# ð74IJC"B#574Ł[ Analogous reactions\ involving the extrusion of COS from dithiocarbonic anhydrides\ have been reported ð78TL3256Ł[ O O
O
+ 2
O
Cl
K + –S Cl
O
S
O
S
Cl
OR
Cl
(41)
OR
S
S
S RO
O
O
O Cl
S N
+
N
O
S K+ –S
hν, C6H6
OR
OR
S O
O O
S S
N
OR
O Scheme 15
An alcohol can be converted to a dithiocarbonate by allowing it to react with phosgene and potassium O!ethyl dithiocarbonate[ The products have been used as condensing agents for the preparation of peptides ð74KPS733Ł[ When irradiated with visible light\ these compounds give the corresponding S!alkyl dithiocarbonates "Scheme 05# ð89JA1923Ł[ The radical intermediates in these reactions can also undergo cyclization\ as shown in Scheme 06[ Irradiation of S!4!hexenyloxy O! ethyl dithiocarbonate converted it smoothly in re~uxing heptane into S!cyclopentylmethyl O!ethyl dithiocarbonate whereas S!2!butenyloxy O!ethyl dithiocarbonate gave a lactone[ S
O
O
K+ –S
ROH + Cl
Cl
RO
O
OEt
RO
Cl
S S
S
hν
RS
OEt
OEt
Scheme 16
S
S
O
hν, n = 3
S
OEt
87%
( )n
O
S S
hν, n = 1
OEt
84%
S O
OEt
O
Scheme 17
Several other types of activated halides have been shown to react with O!alkyldithiocarbonate salts[ 1!Chloro!3\4!dihydroimidazole reacts with two moles of potassium O!alkyl dithiocarbonates giving the corresponding diesters ðROC"1S#Ł1S and imidazoline!1!thione ð81JCS"P0#36Ł[ Dis! placement of chloride from 0!chloro!0\2\2!triphenylallene by potassium O!ethyl dithiocarbonate has also been reported ð78BCJ856Ł[ The reaction of triphenyltelluronium chloride with the equivalent amount of sodium O!alkyl dithiocarbonate gives the corresponding triphenyltelluronium dithio! carbonate "Equation "31##[ The same product can be obtained by reacting a triphenyltelluronium alkoxide with carbon disul_de[ The reaction of freshly prepared dimethyltellurium diiodide with a sodium O!alkyl dithiocarbonate leads to dimethyltellurium bis"O!alkyl dithiocarbonates# "Equation "32##\ which can also be obtained by inserting carbon disul_de into dimethyltellurium bis"alkoxides# ð74ZAAC"414#016Ł[ S!"Alkoxycarbonyl# O!alkyl dithiocarbonates have been prepared by the addition of a solution of a potassium O!alkyl dithiocarbonate to that of an O!alkyl chlorothiocarbonate "Equation "33## ð79AQ072\ 72JCS"P0#1530Ł[
437
Thiocarbonyl and Halo`en or Chalco`en Na+ –S
Ph3TeS
OR
OR
Ph3TeCl +
+ NaCl
S Me
S Me2TeI2 +
R1O
Me S
2 Na+ –S
RO
OR
K+ – S
Cl
(42)
S
S
OR2
(43)
+ 2NaI
Te
S
S
R1O
OR OR2
S
+
(44)
+ KCl
S
S
S
S
Bis"methoxythiocarbonyl#sulfanes have been prepared by a variety of di}erent methods as shown in Scheme 07 ð76ZAAC"441#070Ł[ Several analogous preparations have been reported ð75JOC0755Ł[ Methoxydichloromethanesulfenyl chloride\ when added to a suspension of potassium O!methyl dithiocarbonate in CDCl2 at 4>C\ gave the dithiocarbonate which underwent a further displacement reaction with N!methylaniline "Scheme 08# ð89JOC0364Ł[ ðMethoxy"thiocarbonyl#Ł"chloro! carbonyl#disulfane\ MeOC"1S#S1COCl\ is obtained "30)#\ together with bisðmethoxy "thiocarbonyl#Łsulfane\ when ClSCOCl is added to a suspension of potassium O!methyl dithio! carbonate in chloroform ð75JOC0755Ł[ S S
MeO
OMe S
S
S
MeO
O
S
OMe S
Cl OMe (0.5 mol.) I2 80%
85%
K+ –S
OMe S SCl2
S2Cl2
93%
97%
MeO
S
MeO
S S
S
S
S
OMe
S
S
OMe S
S
S Scheme 18
MeO Cl Cl
K+ –S SCl
S
OMe
MeO
+
Cl
S
S
PhNHMe
S
OMe
39%
Cl
Me
N Ph
S
OMe S
Scheme 19
Salts of O!alkyl dithiocarbonates can act as nucleophiles towards a variety of reagents other than halides[ Methoxythiocarbonyl methylsulfane can be synthesized by the reaction of potassium O! methyl dithiocarbonate with the S!methyl ester of methanethiosulfonic acid "Equation "34## ð76ZAAC"449#098Ł[ In basic conditions\ and in the presence of excess KSC"1S#OMe\ a further reaction can occur leading to the formation of a symmetrical disulfane[ When potassium O!isopropyl dithiocarbonate reacts with "Z#!3!phenylbut!2!enyl methanesulfonate in the presence of a phase transfer catalyst O!isopropyl "Z#!S!3!phenylbut!2!enyl dithiocarbonate is obtained "Equation "35## ð77JCS"P0#0406Ł[ K+ –S MeSO2SMe
OMe
+ S
MeS
S
OMe
+ MeSO2K S
(45)
438
At Least One Chalco`en Ph
Ph K + –S
OPri
Bu4N+ Cl–
+
+ MeSO3K
OPri
S OSO2Me
(46)
S
S
A mixture of 2!O!acetyl!1!azido!3!"benzyloxycarbonyl#amino!1\3\5!trideoxy!D!galactopyranosyl nitrate and the minor talopyranoside was obtained by treating a D!galactal with sodium azide and cerium"IV# nitrate in acetonitrile at −14>C ð81MI 506!94Ł[ A reaction of the above mixture with potassium O!ethyl dithiocarbonate in acetonitrile in turn gave O!ethyl S!"2!O!acetyl!1!azido!3! "benzyloxycarbonyl#amino!1\3\5!trideoxy!b!D!galactopyranosyl# dithiocarbonate "Scheme 19# ð81MI 506!94Ł[ Several similar reaction sequences have been reported ð77LA64\ 80T4038\ 82HCA884Ł[ ZHN
ZHN
O
ZHN
NaN3, (NH4)2Ce(NO3)6
O
71%
AcO
ONO2
AcO
N3 O
+ AcO
N3
ONO2
S 58%
K+ – S
OEt
ZHN
ZHN O
AcO
OEt
S
N3
+
N3 O
OEt
S
AcO
S
S
Scheme 20
The addition of V[ harveyi oxidoreductase "NADH oxidized by ribo~avin# to an anaerobic solution of potassium O!ethyl dithiocarbonate\ 00!deoxydaunomycin\ and NADH led to two dithio! carbonates "6S and 6R# in an 74 ] 04 ratio "Equation "36## ð72JA6076Ł[ The cyclization shown in Equation "37# is initiated by nucleophilic opening of the three!membered ring by potassium O!ethyl dithiocarbonate ð77ZOR006Ł[ O
O
O
O
OH
S OH
+ K+ –S
OEt
87%
OH
(47)
OEt
S OMe O
OH
+ OEt
S
OR S 7-(S)
R = daunosamine
S 7-(R)
85:15
S O Me O
S
O
S
N
N
X N
+
reflux
K+ –S
Me
OEt
N
O
Me
S N
N N
S
OEt (48)
N
Me X = Cl, Br
"ii# From carbon disul_de It is possible to prepare O\S!dialkyl dithiocarbonates directly from alcohols by reaction with a base\ carbon disul_de and a haloalkane[ This is mechanistically equivalent to using salts of O!esters of dithiocarbonic acids "5[06[1[1[1"i##\ but experimentally more convenient\ and the procedure has
449
Thiocarbonyl and Halo`en or Chalco`en
been widely used[ In a typical procedure\ the sodium salt of the alcohol is produced by its reaction with sodium hydride and a catalytic amount of imidazole in THF^ carbon disul_de and a haloalkane are then added sequentially[ An example is shown in Equation "38# ð81JA3000Ł^ many others\ encompassing a wide range of primary alcohols ð71JOC021\ 78CC0154\ 80JOC1738\ 81JOC5792Ł\ secondary alcohols ð68JA5005\ 70CC645\ 70JCS"P0#1252\ 71HCA260\ 71YGK241\ 72JOC3649\ 76CC0117\ 77CAR"070#142\ 89TL3820\ 80T010\ 80T5270\ 81TL4150\ 82CAR"131#170\ 82CAR"135#008\ 82JOC1783\ 82JOC2687Ł\ tertiary alcohols ð82TL1622Ł and phenols ð75T1218Ł\ have been described[ SMe
i, NaH ii, CS2 iii, MeI
OH NC
O
S
NC
(49)
61%
O2S
O2S
Sometimes butyllithium is used in place of sodium hydride for the preparation of dithiocarbonates directly from alcohols[ An example is shown in Equation "49# ð74T3968Ł^ other examples have been described ð76BCJ0742\ 77M016Ł[ Phase!transfer catalysts have also been used with aqueous sodium hydroxide as the base ð77M016\ 78SC436Ł[
O
i, BuLi ii, CS2 iii, MeI
O
HO
O O
88%
OBn
O
MeS
O
(50)
OBn O
S
An extension of the methodology involves the generation of a carbanion using butyllithium and its aldol addition to an aldehyde^ the lithium salt of the aldehyde then reacts further with carbon disul_de and iodomethane ð77TL5014\ 80TL1692Ł[ An example of the reaction sequence is shown in Scheme 10 ð80TL1692Ł[ LiO
i, BuLi
( )6
SO2Ph
ii, RCHO
R
S
SO2Ph n-C7H15
i, CS2
O
SO2Ph
R
n-C7H15
MeS
ii, MeI
Scheme 21
By treating carboxylic esters with lithium diisopropylamide "LDA# at 9>C\ lithium enolates were generated[ The latter were treated with carbon disul_de followed by a haloalkane to produce O!"0! alkoxy!1\1!dialkylvinyl# S!alkyl dithiocarbonates in very good yield "Scheme 11# ð78CC573\ 78JOC4592Ł[ R1 R2
OR3 O
LDA, 0 °C
R1 R2
OR3
R1
OR3
CS2, –78 °C
S R2
OLi
O SLi
R1
OR3
R2
O
R4X
S SR4
Scheme 22
"iii# From thiocarbonyl chlorides O\S!Dialkyl dithiocarbonates can be prepared by the displacement of chloride from alkoxy! thiocarbonyl chlorides by thiolate anions[ For example\ S!ethyl O!methyl dithiocarbonate was obtained by adding sodium ethanethiolate to a solution of methoxythiocarbonyl chloride in ether at a rate to maintain a mild re~ux "Equation "40## ð72JOC3649Ł[ Silver salts have also been used for preparations of this type ð75JOC3377Ł\ and imidazolides ROC"1S#Im "Im 0!imidazolyl# have been used in place of alkoxythiocarbonyl chlorides ð75T1218Ł[
440
At Least One Chalco`en S
S
+ NaSEt MeO
+ NaCl MeO
Cl
(51)
SEt
S!"Alkoxycarbonyl# O!alkyl dithiocarbonates have been prepared in high yield by the addition of a solution of a potassium O!alkyl monothiocarbonate to that of an O!alkyl chlorothiocarbonate in aqueous acetone "Equation "41## ð74PS"14#80Ł[ In the presence of a phase transfer catalyst and aqueous sodium thiosulfate\ methoxythiocarbonyl chloride gives bis"methoxythiocarbonyl# sul_de "63)# "Equation "42## ð72JOC3649Ł[ S
S
S
O
+ KCl
(52)
+ 2NaCl + SO3
(53)
+ R1O
Cl
K+ –S
S
+
2 MeO
R1O
OR2
S
Bu4NI
Na2S2O3
74%
Cl
OR2
S S
MeO
S
OMe
An alternative procedure is to displace chloride from dithiocarbonyl chlorides such as PhSC"1S#Cl with alkoxide anions ð80T010Ł[ "iv# By radical addition to alkenes Examples of intramolecular addition of radicals ROC"1S#S= to carbonÐcarbon double bonds have already been illustrated in Scheme 06[ Intermolecular radical addition reactions have also been reported ð77CC297\ 78H"17#060Ł^ two examples are shown in Equations "43# and "44#[ O
O Ph
Ph
OMe
S
hν
+
N Me
N Me
(54)
S
40%
S
O
O
S
MeO
OEt
But
OEt
S
hν
+ O
SO2Ph
S
S
45%
(55)
S SO2Ph
But
"v# From other dithiocarbonates The radical reaction of bromoalkanes with O!ethyl triphenyltin dithiocarbonate was initiated by tributyltin hydride and 1\1?!azobisisobutyronitrile "AIBN# or by visible light[ Dithiocarbonates were obtained in good yield ð81JA6898Ł[ The reaction sequence is illustrated in Scheme 12 for a radical which undergoes cyclization before capture^ the sequence depends on the ability of triphenyltin radicals to add reversibly to dithiocarbonates[ Ph3SnS
OEt
Bu3SnH, AIBN or hν
Ph3Sn•
RBr
R• + Ph3SnBr
S Ph3SnS R•
OEt
Ph3SnS
• OEt
S
OEt
+ Ph3Sn•
R*• + S
SR* S
H
Br e.g.
SR*
S
88%
O
O
O Scheme 23
OEt
O H
441
Thiocarbonyl and Halo`en or Chalco`en
O!Ethyl S!"1!hydroxy!3!oxo!3!phenylbutyl# dithiocarbonate and related esters were prepared by allowing lithium enolates of ketones to react with O!ethyl S!"1!oxoethyl# dithiocarbonate ð81HCA896Ł[ An example is shown in Equation "45#[ S Pr
i, LiN(TMS)2 ii, ZnCl2
O
S
iii, O
Et
Pr S
O
OEt
S
(56)
Et
OEt
OH
5[06[1[2 Derivatives of Trithiocarbonic Acid Trithiocarbonic acid\ "HS#1C1S\ can be generated from barium trithiocarbonate by reaction with dilute HCl at 9>C ð52ZAAC"210#032Ł[ It is\ however\ stable only at −67>C^ otherwise it decomposes to hydrogen sul_de and carbon disul_de[ Salts of trithiocarbonic acid are obtained by the reaction of carbon disul_de with metal sul_des or metal hydrogen sul_des ð72HOU"E3#319Ł[ A 0\4!diazabi! cycloð4[3[9Łundec!4!ene "dbu# salt was obtained by heating a mixture of water\ CS1\ and dbu in molar ratios 1 ] 2 ] 3 ð75CE200\ 76NKK0397Ł[
5[06[1[2[0 Salts of monoesters of trithiocarbonic acid The reaction of aliphatic or aromatic thiolate salts with carbon disul_de gives salts of the monoesters of trithiocarbonic acid "Equation "46## ð69JA2231\ 69MI 506!90\ 61JA0452\ 79JOC064\ 82POL02Ł[ In a few cases lithium salts have been generated by fragmentation of 0\2!dithiole derivatives ð70TL4084\ 71BCJ228Ł^ an example ð70TL4084Ł is shown in Scheme 13[ S– M+
RS S
•
(57)
+ RS– M+
S
S
S S
S
S
S
Li+ 2BuLi
–
S
S
S
S
S
–
S
Li+
S S Li+ –S
S
S
S– Li+
+ 2C2H4
S Scheme 24
5[06[1[2[1 Diesters of trithiocarbonic acid "i# From thiophos`ene Diesters of trithiocarbonic acid can be prepared in very good yield from thiophosgene and salts of thiols and thiophenols "Equation "47## ð50JOC3936\ 72HOU"E3#319Ł[ The reaction of thiophosgene with dithiolates gives cyclic trithiocarbonic acid esters "Equation "48## ð66CC559\ 72HOU"E3#319Ł[
442
At Least One Chalco`en S
S
+ 2RS– M+ Cl
+ 2MCl RS
Cl
(58)
SR S
M+ –S
S
S– M+ S
+ Cl
Cl
R
S
+ 2MCl
(59)
R R
R
"ii# From S!esters of dithiocarbonic acid chloride The starting acid chlorides can be isolated as intermediates from the reaction of thiophosgene with thiols or thiophenols ð72HOU"E3#319Ł^ they form mixed esters when allowed to react further with another alkanethiol or thiophenol "Equation "59## ð50JOC3936\ 60CC203Ł[ S
S
+ R2S– M+ R1S
+ MCl R1S
Cl
(60)
SR2
"iii# From salts of monoesters of trithiocarbonic acid The salts are excellent nucleophiles\ and they are alkylated by haloalkanes and a range of other alkylating agents ð72HOU"E3#319Ł[ The reaction can also be conveniently carried out by generating the salt in situ from a thiol\ carbon disul_de\ and a base ð75S783Ł[ Phase transfer catalysts have been used to achieve one!pot conversions of thiols to dithiocarbonates ð76BCJ324Ł[ An example of the alkylation reaction "which was used as a step in a penem synthesis# is shown in Equation "50# ð70TL2374Ł[ There are several other similar examples of the preparation of trithiocarbonates derived from azetidinones ð70CPB2047\ 76H"14#012\ 81JOC3241Ł[ A reaction of pot! assium 0\1!ethanebis"trithiocarbonate# with HCl gave 0\1!ethanebis"trithiocarbonic acid#\ HSCSSCH1CH1SCSSH[ Further reaction with iodoalkanes gave RSC"1S#SCH1CH1SC"1S#SR "R Me\ 75)^ R Et\ 71)# ð74ZAAC"429#090Ł[ An example of the use of a leaving group other than a halide is provided by the reaction of potassium S!methyl trithiocarbonate with the S! methyl ester of methanethiosulfonic acid\ MeSO1SMe\ which gave methyl methylthiothiocarbonyl disulfane\ MeSC"1S#S1Me ð76ZAAC"449#098Ł[ O
O Cl3C
O
Cl3C O K + –S
Cl N O MeO2C
O
O
SEt S
O
S
S
+ N O
+ KCl
(61)
SEt O
MeO2C
Many electrophiles other than alkylating agents have also been used\ and some of these are illustrated in Scheme 14[ Reactions of the salts are shown with 1!chloro!2\4!dinitropyridine ð70JHC0470Ł\ methyl chlorodithioformate\ iodine\ sulfur monochloride\ and sulfur dichloride ð76ZAAC"434#014\ 76ZAAC"443#061Ł and trichloromethanesulfenyl chloride ð74T4034Ł[ The reaction of RPCl1 or R1PCl "R Me\ Pri\ Ph# with NaSCSSR0 "R0 Et\ Pri# gave RP"SCSSR0#1 and R1PSCSSR0\ respectively ð77PS"24#82Ł[ Triphenyltellurium chloride reacted with sodium S!alkyl trithiocarbonates giving the corresponding S!alkyl S!triphenyltellurium trithiocarbonates in high yield ð77ZAAC"445#078Ł[
443
Thiocarbonyl and Halo`en or Chalco`en S
MeS
S
S
S
S
SMe MeS
S
S
S
S– M+
RS
81%
S
S
N Cl R = But, M = Na
SMe
NO2 S
O 2N
92% MeS
N
S
SBut
Cl
S R = Me, M = K 79%
S S
S
NO2
S
I2 R = Me, M = K 85%
MeS
S
S
O 2N
ClSCCl3 R = PhCH2, M = Na
SCCl3
S
S2Cl2 R = Me, M = K 97%
SCl2 R = Me, M = K 86%
Ph
S
S
MeS
SMe
S
S
SMe S
Scheme 25
"iv# From trithiocarbonate salts Sodium\ potassium\ and barium salts of trithiocarbonic acid react with alkylating agents giving symmetrical dialkyl trithiocarbonates "Equation "51## ð79CPB009\ 71BCJ0063\ 72HOU"E3#319Ł[ These esters were also synthesized in high yield in the presence of a phase transfer catalyst ð75S783\ 77S11\ 77SC0420Ł[ For example\ carbon disul_de and 22) aqueous sodium hydroxide were stirred together\ and haloalkanes were then added in the presence of tetrabutylammonium hydrogensulfate "Scheme 15# ð77SC0420Ł[ The dbu trithiocarbonate salt also reacts with alkylating agents to give dialkyl trithiocarbonates in good yields ð75CE200\ 76NKK0397Ł[ The method can be used to prepare cyclic trithiocarbonates^ for example\ cis!2\4!dibromocyclopentene reacted with sodium trithiocarbonate in DMF to give the cis!2\3!cyclopenteno!0\2!dithiolane!1!thione "Equation "52## ð82H"24#66Ł[ –S
S–
RS
SR
+ 2X–
2RX +
S
•
Na+ –S
NaOH (aq.)
S
(62)
S
S
S– Na+
RS
i, Bu4NHSO4 (cat.) ii, 2RX
S
SR S
Scheme 26
Br Na+ –S
S
S– Na+
+ S
58%
S
+ 2NaBr
(63)
S
Br
Other types of electrophile can be used to functionalize the trithiocarbonate salts[ For example\ the reaction of sodium trithiocarbonate with trichloromethanesulfenyl chloride gave the crystalline "Cl2CS1#1CS\ which on oxidation gave the sul_ne "Cl2CS1#1CS1O ð73SUL74Ł[ The compounds "RS1#1C1S can be prepared by treating a sulfenyl chloride "R CCl2\ CCl2CCl1\ CCl1FCCl1 or CClF1CCl1# with an excess of freshly prepared aqueous sodium trithiocarbonate in dichloromethane\ or with anhydrous barium trithiocarbonate suspended in acetonitrile ð74T4034Ł[ Oxidation of these compounds with mcpba gave the sul_nes "Scheme 16#[ When thioureas are prepared by three!component reactions of amines\ carbon tetrachloride\ and sodium sul_de\ the reactions proceed exothermically in the presence of a phase!transfer catalyst ð72LA0728Ł[ Thiophosgene is an intermediate in this conversion\ and its phase!transfer catalyzed transformation into carbon disul_de and trithiocarbonate can be demonstrated[ When the amine
444
At Least One Chalco`en RSS
BaCS3 or Na2CS3
RSCl
SSR
RSS
mcpba
SSR S
S
O
Scheme 27
was replaced by dibromomethane\ benzyl chloride or a\b!dibromostyrene\ the products included 0\2! dithietane!1!thione "4)#\ dibenzyl trithiocarbonate "34)#\ and 3!phenyl!0\2!dithiolane!1!thione "49)#\ respectively ð72LA0728Ł[ An analogous reaction\ in which 3!chloromethyl!0\2!dioxolane is the electrophile\ has been reported ð80JPR028Ł[
"v# Methods leadin` to cyclic trithiocarbonates Five!membered cyclic trithiocarbonates are accessible by a variety of routes ð54JA823\ 64JOC2941\ and several of the general routes described above can be used "e[g[ those in Equations "48# and "52##[ The following are some speci_c methods[ Several cyclic trithiocarbonates have been prepared from the corresponding dithio!N\N!dimethyl! iminium salts by reaction with hydrogen sul_de or with sodium hydrogensul_de ð81CC0309\ 81KGS0006\ 82H"24#66Ł[ An example of the process is shown in Equation "53# ð82H"24#66Ł[ A di}erent route to cyclic trithiocarbonates is shown in Equation "54#[ A suspension of tetraethylammonium tetrathiooxalate in acetonitrile was stirred with carbon disul_de at ambient temperature until the former had dissolved[ Chloromethane was then bubbled through the solution[ The precipitate obtained consisted of 64Ð89) of 3\4!bis"methylthio#!0\2!dithiole!1!thione and 09Ð14) of dimethyl trithiocarbonate ð75ACS"B#482Ł[ 65JOC515\ 70TL4084Ł
S
S– Et4N+ S– Et4N+
S
S
86%
S S
S
H2S, –40 °C
+
NMe2 BF4–
MeS
S
i, CS2
MeS S
ii, MeCl
S
MeS
(64)
S
+
(65)
S MeS
1!Pyridyl! and 1!quinolyl dithiocarbonates cyclocondense with carbon disul_de to yield 3\4! disubstituted 0\2!dithiole!1!thiones in 04 to 59) yield "Scheme 17# ð78JPR"220#328Ł[ K+ –S R1
Cl
OEt
R1
S
OEt
i, NaH
R1
S
–S
S–
OEt
+ S
ii, CS2
S R1
S
R2S
S
R 2I
S
S R1 = 2-pyridyl, 2-quinolyl Scheme 28
5[06[1[3 Derivatives of Thiocarbamic Acid Thiocarbamic acid has the structure H1NC"1S#OH[ The free acids R0R1NC"1S#OH decompose to COS and the corresponding amine when their preparation is attempted\ but their salts can be prepared by treating COS with amines in the presence of an alkali metal hydroxide[ Alkylation or acylation of these salts usually gives S!esters of thiocarbamic acid ð70S511\ 70ZAAC"370#015Ł[ The O! esters are isolable but when heated those bearing a dialkylamino group can isomerize to S!esters ð55JOC2879\ 58JOC2593\ 62JOC1095Ł^ those with a monoalkylamino function can decompose to iso! thiocyanates and alcohols ð72HOU"E3#319Ł[
445
Thiocarbonyl and Halo`en or Chalco`en
5[06[1[3[0 O!Esters of thiocarbamic acids "i# From O!alkyl or O!aryl chlorothioformates The reaction of O!alkyl or O!aryl chlorothioformates with amines is a general method for the preparation of O!esters of thiocarbamic acids ð72HOU"E3#319Ł^ the following are examples of the method[ N\N\O!Trimethyl thiocarbamate was prepared from dimethylamine and O!methyl chloro! thioformate "Equation "55## ð76CB876Ł[ 0\1\2\3!Tetrahydro!1!"methoxythiocarbonyl#!b!carboline! 2!carboxylic acid was obtained by adding an ethereal solution of O!methyl chlorothioformate and aqueous sodium hydroxide to an aqueous solution of sodium 0\1\2\3!tetrahydro!b!carboline!2! carboxylate "Equation "56## ð76CPB1739Ł[ 3!"Nitrophenylamino#aniline reacted with O!phenyl chlorothioformate and pyridine in acetone to give the corresponding O!phenyl thiocarbamate ð77MI 506!91Ł[ The amino group of 3!cyano!2!methylthiopyrazol!4!amine was similarly substituted ð81PHA140Ł[ MeO
Cl
MeO
NMe2
+ Me2N+H2 Cl–
+ 2Me2NH
(66)
S
S
CO2Na
CO2Na MeO
Cl
NaOH
+
NH
N 35%
S
N H
N H
OMe
+ NaCl
(67)
S
The reaction of an O!aryl chlorothioformate "one equivalent# with an alkyl or aryl bis"tri! methylsilylamine# "three equivalents# in ether at room temperature gave the corresponding thi! ocarbamate in good yield "Scheme 18# ð74PS"10#180Ł[ If the chlorothioformates were used in excess\ the products were the corresponding N!alkyl or N!aryl bis"O!arylthionocarbonates# "Scheme 18#[ R ArO ArO
N
TMS
S
Cl
+ RN(TMS)2 R
S ArO
N S
OAr S
Scheme 29
"ii# From N\N!dialkylthiocarbamoyl chlorides This general method is exempli_ed by the preparation of N\N!diethyl O!phenyl dithiocarbamate from phenol "Equation "57##[ A solution of phenol in DMF was poured into a suspension of sodium hydride in DMF and stirred at 9>C[ After hydrogen evolution was over\ N\N!diethylthiocarbamoyl chloride was added and the mixture was heated for 0 h at 79>C[ After separation\ 65) of N\N! diethyl O!phenyl thiocarbamate was obtained ð55JOC2879\ 81S001Ł[ Similar preparations have been reported from N\N!dialkylcarbamoyl chlorides and the following] substituted phenols ð48JA603\ 80CPB0828Ł\ 0!naphthol ð81S001Ł\ 2!hydroxypyridine ð81S001Ł\ methyl 2!hydroxythiophene!1!carb! oxylate ð73S061Ł\ "R#!"¦#!0\0?!binaphthol ð82JOC0637Ł\ other binaphthols ð80PS"52#40Ł and calix! ð3Łarenes ð89CC0321Ł[ Et2N
Et2N
Cl
+ S
PhO– Na+
76%
OPh
+ NaCl
(68)
S
2!Methyl!1!ð"dimethylthiocarbamoyl#oxyŁ!2!methylcyclopent!1!en!0!one and related compounds
446
At Least One Chalco`en
ð75JOC3630Ł can be prepared by adding lithium hydroxide solution at room temperature to a stirred solution of the ketone in chloroform\ and then a solution of N\N!dimethylthiocarbamoyl chloride in chloroform "Equation "58## ð76JOC4529Ł[ Cyclohexane!0\1!diones have been used as the starting materials for similar preparations ð77JOC0009Ł[ O Me2N
Cl
O
Me2N
HO
O
+
(69) S
S
The thiocarbamoyl chloride can be generated in situ and then reacted with the appropriate alcohol or phenol] an example of this approach is shown in Scheme 29 ð89OPP017Ł[ Me Ar
N
S
S
N
S
Me
Me
S Cl2
Ar
N
Ar
Cl
2-naphthol
Ar 80%
O S
S
Me
N
Ar = 3-MeC6H4 Scheme 30
"iii# From N\N?!thiocarbonyldiimidazole and related compounds A mild procedure for the functionalization of alcohols is to heat the alcohol with N\N?!thio! carbonyldiimidazole in a solvent such as dichloromethane or THF "Equation "69##[ This procedure was used to convert several epoxyalcohols into the thiocarbonylimidazolides in high yield ð70JCS"P0#1252Ł\ and there are several other examples of similar procedures ð64JCS"P0#0463\ 74T3968\ 76JA598\ 81JOC5792\ 81T5772\ 81T7920\ 81TL4150Ł[ N
N
N
N
+ ROH
N
N
OR
+ HN
(70)
N
S
S
O\N!Dibenzyl N!methyl thiocarbamate was prepared by adding sodium hydride to a solution of 0!"N!benzyl N!methyl thiocarbamoyl#imidazole and benzyl alcohol in acetonitrile "Equation "60## ð77JOC1152Ł[ 0!ð"Benzyloxy#thiocarbonylŁimidazole was obtained from N\N?!thiocarbonyl! diimidazole\ benzyl alcohol\ and sodium hydride^ this compound also gave O\N!dibenzyl N!methyl thiocarbamate when benzylamine was added ð77JOC1152Ł[ Me Ph
Me
N
N
N
+ PhCH2OH
Ph
N
S
O
Ph
+ HN
N
(71)
S
"iv# From aminoalcohols and carbon disul_de and related methods Several fused tetrahydro!0\2!oxazine!1!thiones were prepared from aminoalcohols "as in the example shown in Scheme 20# by cooling a solution of the aminoalcohol in aqueous potassium hydroxide to 9>C\ and then mixing the solution with a solution of carbon disul_de in dioxane[ Aqueous lead"II# nitrate was then added and lead sul_de precipitated[ The oxazine!1!thiones were obtained by extraction with ethanol ð72T0718Ł[ An alternative procedure is to add thiophosgene to a solution of the aminoalcohol and triethylamine ð72T0718Ł[ There are other reports of the prep!
447
Thiocarbonyl and Halo`en or Chalco`en
aration of a variety of oxazine!1!thiones from aminoalcohols by similar methods ð71H"08#0080\ 72JHC0070\ 73JHC0262\ 74S0038\ 74T0242\ 89MRC0934Ł[ i, KOH (aq.) ii, CS2 iii, PbNO2
NH2
H N
42% (R = H)
OH
NHMe
Cl2CS, Et3N 23% (R = Me)
S
O
H
R
OH
Scheme 31
0\2\3!Oxadiazole!1!thiones were obtained by reacting the respective hydrazides with carbon disul_de in the presence of potassium hydroxide "Equation "61## ð82JMC0989\ 82JMC0791Ł[ R
H
NHNH2
+
S
•
KOH
S
O
N N R
O
(72) S
"v# From isothiocyanates The addition of alcohols to isothiocyanates "Equation "62## is a general method for the preparation of O!alkyl thiocarbamates^ many examples of the procedure have been reported ð72JHC0112\ 72ZOR81\ 73CCC0466\ 73ZOR1047\ 74JPR0996\ 74KGS228\ 74MI 506!90\ 74S312\ 75MI 506!91\ 76CCC0653\ 78CPB0138\ 78MI 506!90\ 89JHC396\ 89JHC532\ 89JOC4129\ 89MI 506!91\ 89ZOR0311\ 80S154\ 82OPP72\ 82TL2634Ł[ Others
include the preparation of the N!penta~uorosulfanyl derivative SF4NHC"1S#OMe "76)# ð73CB0696Ł and the reaction of hydroxypyridones with alkyl isothiocyanates ð76MI 506!91\ 80PJS311Ł[ A cyclic trimeric isothiocyanato phosphazene reacts with alcohols "R Me\ Et\ Pr\ Bu\ Pri# giving _rst "at 14>C# a species in which three of the six thiocyanato groups have reacted\ a higher temperature "55>C# being necessary to bring about reaction of all the isothiocyanato groups "Scheme 21# ð80IC0665Ł[ Butadien!0!yl thiocyanate undergoes a DielsÐAlder reaction with dienophiles\ and the cycloadducts were intercepted by reaction with ethanol "Equation "63## ð75HCA0787Ł[ The hydroxyl group of ~uorenone oxime adds to benzoyl isothiocyanate to give the thiocarbamate ð74CC0394Ł[ O\O!Dialkyl imidodicarbonothioates R0OC"1S#NHC"1S#OR1 can be obtained by reaction of O!alkyl carbonochlorodithioates R0OC"1S#Cl with sodium isothiocyanate and treat! ment of the resultant alkoxythiocarbonyl isothiocyanates with alcohols R1OH ð74S864Ł[ H R1 N
•
+
S
R2OH
R1
OR2
N
(73)
S
S
S
Z
N N P N • S
N
H N
N
N P N N
•
S
25 °C
S
P
ROH
S
N N OR S • • N P P N N S S NH HN
• S
N H
S
•
N P
(74) EtO
S
• N
•
+ N
S •
S
•
Z
S
EtOH, 110 °C
OR
RO Scheme 32
ROH 66 °C
S H N
H N
P S RO N N H H N P P N N RO NH HN S
ORRO
OR S OR S
448
At Least One Chalco`en
The reaction of phosgene with one or two equivalents of ammonium thiocyanate gives thio! carbonyl chloride thiocyanate "8)# or thiocarbonyl dithiocyanate "62)#\ respectively ð70CB0021Ł[ The latter compound reacts with alcohols to give O!alkyl imidodi"thiocarbonic acids#\ ðROC"1S#Ł1NH[ Carbonyl isocyanate isothiocyanate\ SCNC"1O#NCO can be obtained by con! densing carbonyl chloride isocyanate with ammonium thiocyanate ð70CB1953Ł[ This reacts further with an alcohol giving O!alkyl "isothiocyanatocarbonyl# carbamates\ ROC"1O#NHC"1O#NCS[ These can react further with a second equivalent of an alcohol "which can be the same alcohol or a di}erent one# to give the esters ROC"1O#NHC"1O#NHC"1S#OR ð70CB1953Ł[
"vi# From O!alkyl thiocarbamic acids and their salts O!Methyl thiocarbamic acid\ MeOC"1S#NH1\ can be obtained in 56) yield by treating the corresponding potassium salt in water with chloroacetic acid ð70ZAAC"370#015Ł[ O!Ethyl thio! carbamic acid\ EtOC"1S#NH1 was obtained "35Ð49)# from dry ammonium thiocyanate in ethanol at 01Ð04>C after adding sulfuric acid ð71CB0141Ł[ It reacts with oxalyl chloride giving a mixture of ethoxy"thiocarbonyl# isocyanate\ EtOC"1S#NCO and its dimer "Scheme 22#[ Ethoxy"thiocarbonyl# isocyanate reacts further with alcohols and amines as shown in Scheme 22 ð71CB0148Ł[ O EtO
NH2
EtO
(COCl)2
N
•
S
S
+
O
N EtO
ROH
H N
EtO S
S N
OEt O
S
R2NH
OR
H N
EtO S
O
NR2 O
Scheme 33
"vii# Other methods O!Ethyl thiocarbamates were prepared by the reaction of potassium O!ethyl dithiocarbonate with amines ð78JOC1867Ł[ When N!arylbenzimidoyl chlorides were added to various potassium O!alkyl dithiocarbonates\ O!alkyl esters of the corresponding N!aryl!N!thiobenzoyl thiocarbamic acids were obtained "Equation "64## ð70ZC327Ł[ Other imidoyl chlorides reacted similarly ð74ZC108Ł[ A rearrangement is also involved in the alkylation of some dithiocarbamates "Equation "65## ð77JCS"P0#702Ł[ Alkylation of the potassium salts K¦−SC"1S#O"CH1#nOC"1S#S− K¦ gave dialkyl bis"dithiocarbonates#\ which on reaction with amines RNH1 gave the bis"thiocarbamates# RNHC"1S#O"CH1#nOC"1S#NHR ð71MI 506!92Ł[ Ph
Ar
K+ –S
Cl
OR
+ NAr
Ph
S
N S
OR
+ KCl
(75)
S O
O Ph
O S
N
+ PhCH2Cl
base
N
96%
O
S Ph
(76) S S
Ph
N\N!Dimethyl!N?!phenylthiourea\ PhNHC"1S#NMe1\ reacts with ethyl bromocyanoacetate to give O!ethyl N!phenylthiocarbamate\ EtOC"1S#NHPh ð71JCS"P0#542Ł[ The reaction of 1\2!dihydro!
459
Thiocarbonyl and Halo`en or Chalco`en
5!methoxy!1!thioxo!3H!0\2\4!thiadiazine!3!one with dibenzylamine resulted in the formation of a dithiocarbamate by ring cleavage "Equation "66## ð70CB1964Ł[ O HN
Ph
+
N
–HSCN
H N
Ph
Ph
Ph
H N
N
OMe
(77)
87%
S
OMe
S
O
S
Several routes to dithiocarbamates involve the displacement of sulfur functions by amino func! tions[ Some of these are illustrated in Equation "67# ð89ZC89Ł\ Equation "68# ð76CPB045Ł\ Equation "79# ð72JCS"P0#1900Ł\ and Equation "70# ð75JOC0755Ł[ The reaction of dithiocarbonate esters with N\N!dimethylhydrazine leads to mixtures of thionocarbamates and thionocarbazates whereas alkoxythiocarbonylimidazoles give cleanly the latter ð73JCS"P0#0994Ł[ R1O
S
R1O
OEt
+ S
NHR2
R2NH2
+ EtOH + COS
(78)
S
O
RS
+
OEt
+
N NH2
+
base
N –
S
I–
(79) OEt
N S
EtO
SMe
EtO
+
H2NNH2
S
MeO
S
(80) S
Me
OMe
+ S
93%
NHNH2
S
PhNHMe
MeO
N
89%
Ph
(81)
S
5[06[1[4 Derivatives of Dithiocarbamic Acid The parent compound\ dithiocarbamidic acid\ can be obtained as an unstable crystalline solid from the reaction of ammonium dithiocarbamate and concentrated HCl at 9>C[ Other dithio! carbamic acids\ R0R1NC"1S#SH\ are also unstable compounds which can be generated from their salts with HCl ðB!51MI 506!90\ B!66MI 506!90Ł^ they decompose to amines R0R1NH and carbon disul_de ð72HOU"E3#319Ł[
5[06[1[4[0 Salts of dithiocarbamic acids Alkylammonium dithiocarbamates are prepared from carbon disul_de and two moles of the amines in solvents such as acetone or ethanol ðB!51MI 506!91\ 68JINC0166\ 79ZC090\ 72HOU"E3#319Ł[ When the reaction is carried out in aqueous sodium hydroxide or potassium hydroxide\ the sodium or potassium dithiocarbamates are formed ð40RTC806\ 40RTC838\ 54JMC063Ł[ Formamide reacts with carbon disul_de in the presence of sodium hydroxide to give sodium N!formyl dithiocarbamate\ Na¦−SC"1S#NHCHO ð74ZAAC"411#034Ł[ The reaction of hydrazine hydrate with carbon disul_de and methanolic potassium hydroxide gives potassium dithiocarbazate\ K¦−SC"1S#NHNH1 ð74ZAAC"420#090Ł[ With a 1 ] 0 ratio of carbon disul_de to hydrazine\ the product is the salt 1K¦−SC"1S#NHNHC"1S#S− ð74ZAAC"420#71Ł[ Carbon disul_de reacts with methylhydrazine at the substituted nitrogen atom ð78S812Ł whereas it reacts with arylhydrazines at the unsubstituted nitrogen atom ð81CCC0588Ł[ Lithium dithiocarbamates were obtained from secondary amines by deprotonation of the amine using butyllithium in THF at 9>C followed by the addition of carbon
450
At Least One Chalco`en
disul_de in THF at 9>C ð80S526Ł[ This procedure is particularly useful with cyclic secondary amines such as indoline since the salt can be further deprotonated at C!1 by s!butyllithium ð83S872Ł and this allows electrophiles to be introduced at C!1[
5[06[1[4[1 Esters of dithiocarbamic acids "i# From dithiocarbamates The S!alkylation of alkali metal or ammonium dithiocarbamates by haloalkanes and related compounds is the most general method for the preparation of esters of N!alkyl or N!aryl dithio! carbamates "Equation "71##[ The method is fully documented in earlier reviews ðB!51MI 506!90\ B! 51MI 506!91\ 72HOU"E3#319Ł\ and there are many more recent examples[ A wide range of electrophiles has been used^ these include haloalkanes\ alkyl nitrates\ a!haloketones\ a!haloesters\ activated heteroaryl halides\ aromatic diazonium salts\ acyl halides\ and activated alkenes[ A selection of examples from the 0879s is given below[ R1R2N
R1R2N
S – M+
+
SR3
R3X
+
MX
(82)
S
S
The standard method for S!methyl esters is the reaction of dithiocarbamate salts with iodo! methane ð71ZAAC"377#83Ł[ S!Alkyl esters\ "H1N#1C1NC"1S#SR\ of guanidinothioformic acid were prepared from its potassium salt and iodoalkanes "e[g[\ R Me\ 72)^ R Bn\ 32)# ð71ZAAC"374#192Ł[ S!Alkyl!N!formyl!N!methyl dithiocarbamates\ OHCN"Me#C"1S#SR\ were obtained from the potassium salt of the corresponding acid in an analogous manner ð74ZAAC"416#029Ł[ The S!alkyl esters\ S1CHNHC"1S#SR\ of N!thioformyl dithiocarbamic acid were prepared by reaction of iodoalkanes with tetra!n!butyl N!thioformyl dithiocarbamate ð74ZAAC"414#001Ł[ Several examples of the formation of dithiocarbamates from disaccharides by displacement of bromide have been described ð80CAR"105#160Ł^ one of these is shown in Equation "72#[ 1!Chloromethylquinoline and other halomethyl!substituted heterocycles have also been con! verted into dithiocarbamates by displacement of halide ð76BCJ0796\ 78JPR"220#328Ł[ OAc
OAc AcO O
OMe O
O AcO
O
Na+ –S
NMe2
+
OMe OS
O
58%
S
Br
AcO O O
AcO
(83)
S NMe2
+ NaBr
There are many examples of the displacement of halide from a!halocarbonyl compounds by dithiocarbamate anions[ These include reactions of 0!"chloroacetyl#piperidine ð70UKZ15Ł\ 1!"chloro! acetamido#benzothiazole ð71FES194Ł\ 1!"chloromethyl#benzimidazole ð74IJC"B#0187Ł\ and of several chloroacetyl substituted heterocycles ð74MI 506!93\ 74IJC"B#479\ 75MI 506!91\ 76MI 506!90\ 78JIC59\ 81AF0342Ł[ The reaction of chloroacetonitrile with sodium N\N!dimethyl dithiocarbamate in the presence of a phase!transfer catalyst\ tetrabutylammonium iodide\ has been reported ð77BCJ1192Ł[ The reaction of a!bromocarboxylic acids with sodium or potassium N\N!dialkyl dithiocarbamate is illustrated in Equation "73# ð80JOC4573Ł[ The ester "−#!menthyl chloroacetate ð74MI 506!90Ł\ a! chloroalkylnitrosamines "RN"NO#CH1Cl# ð76LA472Ł\ and chloromethyl oximes ð76S238Ł have been used in similar displacement reactions[ a!Haloketones undergo displacement of halide easily ð74H"12#2988Ł\ and some of the dithiocarbamates formed in this type of process have been reduced by baker|s yeast to chiral alcohols\ as illustrated in Scheme 23 ð77BCJ2194Ł[ CO2H –S
CO2H
NMe2
+ Br
S
73%
S
NMe2 S
+ Br–
(84)
451
Thiocarbonyl and Halo`en or Chalco`en Cl
S
Na+ –S
S
NMe2
+
O
baker's yeast
S
88%
S
NMe2
S
91%, >96% ee
O
NMe2
OH
Scheme 34
Carbon electrophiles other than halides can be used] there are examples of the formation of dithiocarbamates from epoxides ð73AP"206#0931Ł and from tosylates ð77S113\ 81JA09462Ł[ Dithio! carbamates can also be formed by conjugate addition reactions or by conjugate additionÐelimination reactions with activated alkenes ð73MI 506!91Ł[ An example of conjugate addition followed by cyclization is illustrated in Scheme 24 ð80M0936Ł\ and related reactions of 3!benzylideneoxazolones have been described ð81S808Ł[ 3!Chloro!2!nitrocoumarin reacts with potassium N\N!dialkyl dithio! carbamates in acetone by displacement of the nitro group\ whereas chloride is displaced in the reaction with potassium N!phenyl dithiocarbamate "Scheme 25# ð81JHC272Ł[ Examples of additionÐ elimination reactions of a\b!unsaturated sulfones ð70KGS896\ 73ZOR1003Ł include the preparation of sulfolene derivatives "Equation "74## ð70KGS896Ł[ Ar Ar
H N
HS
+
Ph
HCl, –5 °C
S
H
N
S
20 °C
N
S
O
S
Ar
S
Ph
O
Ph Scheme 35
S K+ –S
Cl S
NR2
NR2
K + –S
Cl NO2
S
NHPh
S
S
NHPh NO2
O
O
S
O
O O
O
Scheme 36
NR2
Cl –S
S
NR2
S
+ S
S O2
+ Cl–
(85)
S O2
Acid chlorides react readily with dithiocarbamate salts ð70LA0277\ 73MI 506!93\ 77ZOR1908Ł[ Aryl a! chlorooxime O!methanesulfonates also react to give isolable but unstable dithiocarbamates which can be cyclized to dithiazolium salts with ~uoroboric acid "Scheme 26# ð74CC0530Ł[ Acetylene reacts with amines and carbon disul_de to give either mono! or bis"dithiocarbamates# "Scheme 27# depending upon the temperature and the reaction conditions ð70ZOR1158Ł[ S!Aryl dithiocarbamates have been prepared from sodium dithiocarbamates and diaryliodonium salts "Equation "75## ð76JCS"P0#1648\ 76JOC3006Ł[ Cl
Ar N
Na+ –S
NR2
Ar
+ OSO2Me
S
MeO2SO
NR2
S N
Scheme 37
S
N S
HBF4
+
Ar
S
NR2 BF4–
452
At Least One Chalco`en R 2N 2H
H + R2NH +
S
•
S
S
R2N
S
S
S S NR2
S Scheme 38
Na+ –S
ArS
NR2
Ar2I+ X– +
NR2
+ ArI + NaX
(86)
S
S
There are several examples of the use of heteroatomic electrophiles for the substitution of dithiocarbamate salts[ For example\ salts M¦−SC"1S#NMe1 react with iodine to give "SC"1S#NMe1#1 and with SCl1 and S1Cl1 to give the corresponding tri! and tetrasulfanes\ respectively ð77ZAAC"445#030Ł[ Other iodine coupling reactions are reported ð74ZAAC"413#000\ 74ZAAC"416#014Ł[ Reaction with MeSO1SMe gives MeS1C"1S#NMe1 ð76ZAAC"440#080Ł[ Substitution reactions using phosphorus halides ð70ZOB429\ 71MI 506!91\ 72JIC795Ł and tellurium halides ð77JCS"D#1252Ł have also been reported[ TMS esters are formed with TMS!Cl ð77JOC1152Ł[
"ii# From carbon disul_de The reaction between amines and carbon disul_de to give dithiocarbamates was described in "i# above[ Procedures in which dithiocarbamate S!esters are made in one pot from carbon disul_de\ an amine\ and an electrophile are therefore not essentially di}erent from those already described[ However\ examples of the procedure are given here since the method is experimentally convenient[ A typical procedure is described for the preparation of N!aryl S!methyl dithiocarbamates from anilines ð70S850Ł[ The compounds were obtained by adding aqueous sodium hydroxide and carbon disul_de to a vigorously stirred solution of the aniline derivative in DMSO at room temperature[ Iodomethane was then added a with ice cooling[ The mixture was poured into water\ and the precipitated product was isolated and recrystallized from ethanol[ Similar procedures have been described for N!aryl S!nonyl dithiocarbamates ð71JMC446Ł and for S!allyl N!aryl dithiocarbamates ð80S036Ł[ Other procedures have been described for the preparation of N\N\S!trialkyl dithio! carbamates ð73MI 506!92\ 77S664\ 80S526Ł and for the formation of dithiocarbamates from chloroacetic acid and carbon disul_de ð71MI 506!90Ł[ The reaction of sodium N!formyl dithiocarbamate\ Na¦−SC"1S#NHCHO\ obtained from for! mamide\ carbon disul_de and sodium hydride\ with iodomethane or iodoethane in ether gives the respective S!alkyl N!formyl dithiocarbamates ð74ZAAC"413#006Ł[ Acyl dithiocarbazates RC"1O#NHNHC"1S#SR were prepared from acylhydrazines by reaction with carbon disul_de and aqueous potassium hydroxide\ followed by alkylation with an iodoalkane ð71JMC446Ł[ Methylhydrazine has also often been used in this type of preparation ð61ICA00\ 67JINC340\ 77S589Ł[ The reaction of methylhydrazine\ carbon disul_de and potassium hydroxide with 0\1!bis"bromo! methyl#benzene gave the bis"N!methyl dithiocarbazate# "Equation "76## ð80POL712Ł[ Dibromo! methane has been used as the electrophile in the formation of 0\0!bis"dithiocarbamates# ð80ANC0184Ł[ S Br Br
+ 2S
•
S
+ 2MeNHNH2
KOH
S
N(Me)NH2
S
N(Me)NH2
+ 2KBr
(87)
S
A large number of heterocycles containing the NC"1S#S function are known\ and many of them are prepared using carbon disul_de[ A few representative examples are given below[ Reactions of b!lactones with dithiocarbamates\ generated in situ from amines and carbon disul_de in the presence of a base\ lead to 0\2!thiazine!1!thiones by way of intermediate dithiocarbamates
453
Thiocarbonyl and Halo`en or Chalco`en
"Scheme 28# ð70AP"203#476\ 71AP"204#092\ 73AP"206#186\ 74AP"207#737\ 75AP"208#0953\ 78IJC"B#328Ł[ 0\2!Thia! zoline!1!thiones were prepared in high yield by the route shown in Equation "77# ð78M760Ł[ R2 R3
R3 R4
R1
+ R5NH2
+
S
•
base
S
R5HN
O
S S
O
R1
R2
O R4
O/H+
Ac2
R5
CO2– S
R3
N
R4 R1 S
R2
Scheme 39
R2S
S i,
EtO2C
N
+
SEt
S
•
S
NaOBut
S
EtO2C
ii, R2X
R1
S
N
(88)
R1
The oxidation by iodine of potassium N!methyl N!thioformyl dithiocarbamate\ K¦−SC"1S#NMeC"1S#H\ obtained in 79) yield from N!methylthioformamide\ carbon disul_de\ and potassium hydroxide at −04>C\ gives N!methyl!0\1\3!dithiazol!2\4!dithione "Equation "78## ð74ZAAC"417#057Ł[ Similarly\ 0\2\3!oxadiazol!1!ylmethyl N!aryl dithiocarbamates undergo oxidative cyclization with thionyl chloride or iodine to yield 4!aryl!0\2\3!oxadiazoloð2\1!dŁð0\2\3Łthiadiazine! 5"4H#!thiones "Equation "89## ð78IJC"B#328Ł[ Various 0\2\3!thiadiazole!1"2H#!2!thiones have been prepared from hydrazine derivatives and carbon disul_de ð82JMC0989\ 82JMC0791Ł[ 4!Phenyl!0\1\3! dithiazole!2!thione was obtained from its sodium salt formed from sodium hydride\ thiobenzamide\ and carbon disul_de in dry pyridine after treating the latter with HCl ð74ZAAC"414#001Ł[ The reaction of a primary alkylamine and carbon disul_de with 0\3!dibromobutane!1\2!dione also results in the formation of a heterocycle\ 3\3?!bis"2!alkyl!3!hydroxy!thiazolidine!1!thione# ð78SUL012Ł[ S
S
S I2
S– K+
N
S
S S
N
32%
Me
(89)
Me Ar
N N R
S
NHAr
I2 or SOCl2
O
N N N
R S
S
(90)
S
O
Many heterocyclic amines have been functionalized on nitrogen by reaction in basic conditions with carbon disul_de and an alkylating agent[ For example\ carbon disul_de was reacted with the lithium salt of imidazoline 1!thione in THF\ and iodomethane was then added to give S!methyl 1!methylthio!3\4!dihydroimidazole!0!carbodithioate "Equation "80## ð70JCS"P0#1388\ 70S897Ł[ The re! action of 4!amino!0\1\3!triazoles with carbon disul_de "9[0 mole#\ potassium hydroxide "9[0 mole#\ and alkylating agents results in substitution of either the exocyclic amino group or a ring nitrogen atom\ depending on the amount of base used ð89JHC0138Ł[ 1!Aminothiazole has similarly been converted into a dithiocarbamate ð70ZOR080Ł[ The reactions of pipecolic acid\ 0\1\2\3!tetra! hydroisoquinoline!2!carboxylic acid\ and 0\1\2\3!tetrahydro!b!carboline!2!carboxylic acid with car! bon disul_de in the presence of sodium hydroxide followed by alkylation with methyl iodide readily gave the corresponding dithiocarbamates ð76CPB1739Ł[ N
H N S N –
Li+
+ S
•
S + 2MeI
N
79%
S
SMe
(91)
SMe
Carbon disul_de inserts into the P0N bonds of 1!dimethylamino! or 1!diethylamino!2!phenyl! 0\2\1!oxazaphospholanes "Equation "81## ð70ZOB17Ł[ Analogous insertion reactions of carbon dis! ul_de into P0N bonds ð72ZOB674Ł and into As0N bonds ð78ZOB1419Ł have been reported[
454
At Least One Chalco`en
Formamide reacts with carbon disul_de in the presence of sodium hydroxide to yield crude sodium N!formyl dithiocarbamate\ NaSC"1S#NHCHO ð74ZAAC"11#034Ł[ S NR2 Ph
P N
O
+ S
•
S
S
94% (R = Me) 86% (R = Et)
Ph
NR2
(92)
P N
O
Dithiocarbamic acids derived from amines and carbon disul_de add to vinyl ethers and thioethers "Equation "82## ð75ZOR1034\ 76ZC13Ł[ Additions to alkoxyallenes have also been reported ð89ZOR0253Ł[ Hydroxybenzyl dialkyldithiocarbamates were prepared in 34Ð78) yields from the corresponding phenols by aminomethylation with formaldehyde and secondary amines followed by thiocarbamoylation with carbon disul_de ð75MI 506!92Ł[ Bis"dithiocarbamates# have been prepared by treating diamines with CS1[ Thus the reaction of m!phenylenediamine with carbon disul_de and ammonium hydroxide gave the bis"dithiocarbamate# in 69) yield ð75MI 506!94Ł[ Dialkylamines react similarly ð76ZPK0718Ł[ The reaction of ethynyl ketones\ ArCOC2CTMS\ with amines and carbon disul_de in MeCN gave the adducts ArCOCH1C"TMS#SC"1S#NR1 ð89ZOB591Ł[ R12NH
+ S
•
S
R12N
XR2
+
XR2
S
(93) S
X = O, S
"iii# From isothiocyanates Two general procedures for obtaining dithiocarbamates from isothiocyanates are outlined in Equation "83# and in Scheme 39[ The addition of thiols to isothiocyanates is represented by the reaction of benzenethiol and phenyl isothiocyanate to give 62) of S!benzyl N!phenyl dithio! carbamate ð70CCC0869\ 73CCC0466Ł and by the addition of methanethiol to penta~uorosulfanyl isothiocyanate ð73CB0696Ł[ The general procedure of Scheme 39 is illustrated by the reaction of benzoyl chloride\ potassium isothiocyanate\ and alkanethiols ð70ZAAC"365#6\ 71JMC446Ł[ The addition of potassium isothiocyanate and benzenethiol or methanethiol to a solution of 2!chloro! benzoðbŁthiophene!1!carbonyl chloride similarly gives the dithiocarbamates ð73JPR522Ł[ In an analogous reaction\ S!ethyl and S!propyl isothiocyanodithioformic acids are obtained from RSC"1S#Cl "R Et\ Pr# and potassium isothiocyanate in the presence of phase!transfer catalyst\ 07!crown!5 ð73ZAAC"401#120Ł[ R1HN R1N
•
SR2
S + R2SH
(94) S
R1
R1
Cl
N
+ KNCS O
O
•
R2SH
H N
R1
R2
S O
S
Scheme 40
Carbonyl diisothiocyanate reacts with a range of nucleophiles to give cyclic dithiocarbamates "Scheme 30# ð70CB0021\ 70CB1964Ł[ Analogous reactions of carbonyl isocyanate isothiocyanate have been described ð70CB1953Ł[ N!"1\5!Dimethylphenyl#!N!isothiocyanatomethyl chloroacetamide reacts with aqueous sodium hydrogen sul_de giving\ after stirring for 0 h\ 1!"1\5!dimethylphenyl#! 5!oxo!1!thioxo!hexahydro!0\2\4!thiadiazepine in 75) yield ð75S706Ł[ Several 0\2!thiazolidine!1!thiones were prepared from 0!iodo!1!isothiocyanatocycloalkane and sodium sul_des^ an example is shown in Equation "84# ð70JCS"P0#41Ł[ 0\2!Thiazine!1!thiones are formed by the cyclization of appropriate dithiocarbamates[ For instance\ treatment of PhCH! 1CRC"1O#NCS "R H\ Me\ Ph# with NaSH in methanol gave dithiocarbamates H1NC"1S#SCHPhCHRCO1Me which then cyclized to 1!thioxo!0\2!thiazin!3!ones ð89MI 506!90Ł[
455
Thiocarbonyl and Halo`en or Chalco`en O HN
NH
S
H2O or H2S
S
X
O S
O •
N
N
•
ROH or RSH
S
HN
N
S
XR
S
R2NH
O HN
N
S
X = O, S
S
NR2
Scheme 41
Similarly\ the condensation of RCOCHR0CR1R2NCS with NaHS gave RCOCHR0CR1R2NHC "1S#S−Na¦ which reacted with iodomethane to a}ord the corresponding S!methyl dithio! carbamates[ With mineral acids the latter give the corresponding dithiocarbamic acids and their ring tautomers\ thiazinethiones ð80KGS305Ł[ 1!Thioxo!5!nitro!1\2!dihydro!3H!0\2!benzothiazin!3! one can be obtained by the reaction of 1!chloro!4!nitrobenzoyl isothiocyanate with sodium hydrogen sul_de ð81MI 506!92Ł[ S
I N
•
Na2S
S
S
(95)
N H
"iv# From thiocarbamoyl chlorides Several dithiocarbamates were prepared by stirring a mixture of a thiophenol\ dimethyl! thiocarbamoyl chloride\ potassium t!butoxide\ and DMF at room temperature\ as illustrated in Equation "85# ð80CPB0828Ł[ The reaction of benzimidazole!1!thiol with N\N!diethylthiocarbamoyl chloride in the presence of anhydrous potassium carbonate in re~uxing THF a}orded the cor! responding dithiocarbamates ð74JHC0158Ł[ Reactions of thiazolidine!1!thione with thiocarbamoyl or thiocarbazic acid chlorides led to S!substitution products "Scheme 31# ð81AP"214#062Ł[ Me2N
Cl
Me2N
KOBut
+ PhSH
SPh
+ KCl
S
Me2N
S Me2N
N S
(96)
S
Me2N(Me)N
Cl S
HN
S
S S
Cl
S
S
Me2N(Me)N
N S
S
Scheme 42
"v# From thiuram disul_des N\N!Dimethyl dithiocarbamates can be prepared from thiuram disul_des as shown in Equation "86# ð82S372Ł[ This approach has been used with other aryllithium derivatives ð76JHC638Ł[ Com! pounds of the type R01TeðSC"1S#NR11Ł1 were obtained by reaction of dimethyltellurium with
456
At Least One Chalco`en
thiuram disul_des ð77ZAAC"445#068Ł[ Sodium cyclopentadienide cleaves thiuram disul_des] after acidi_cation\ a mixture of tautomeric S!cyclopentadienyl dithiocarbamates was isolated ð82H"24#66Ł[ S Me2N
S
S
NMe2 S
S
RLi
(97) Me2N
SR
"vi# Other methods S!Methyl N\N!dimethyl dithiocarbamate was prepared from dimethylamine and MeSC"1S#Cl ð76CB876Ł[ Similarly\ condensation of the latter with methylphenylamine gave the N!methyl!N! phenyldithiocarbamate ð72JOC3649Ł[ A few thiazolidine!1!thiones were prepared from vic!iodoal! kanecarbamates\ potassium S!ethyl dithiocarbonate\ and aqueous sodium hydroxide ð74H"12#0070Ł[ A method of preparing N!hydroxydithiocarbamates is illustrated in Equation "87# ð74TL4832Ł[ 7!Hydrazino!4!chloro!2\3!dihydro!1\5!dimethylbenzopyran reacts readily with allyl chloro! dithioformates in the presence of diisopropylethylamine "Hunig|s base# to give the corresponding allyl hydrazinecarbodithioates ð77JOC27Ł[ PhS
Cl
PhS
NHOH
+ MeNHOH S
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
(98) S
Comprehensive Organic Functional Group Transformations
6.18 Functions Containing a Thiocarbonyl Group Bearing Two Heteroatoms Other Than a Halogen or Chalcogen JOSE´ BARLUENGA, EDUARDO RUBIO and MIGUEL TOMA´S Universidad de Oviedo, Spain 5[07[0 THIOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGEN OR CHALCOGEN FUNCTIONS# 5[07[0[0 Thiocarbonyl Derivatives with Two Nitro`en Functions 5[07[0[0[0 From isothiocyanates 5[07[0[0[1 From carbon disul_de 5[07[0[0[2 From thiophos`ene 5[07[0[0[3 From thiocarbonyl transfer rea`ents 5[07[0[0[4 From ureas 5[07[0[0[5 Miscellaneous methods 5[07[0[1 Thiocarbonyl Derivatives with One Nitro`en and One Phosphorus Function 5[07[0[1[0 From isothiocyanates 5[07[0[1[1 From halothioamides 5[07[0[1[2 From thiophosphinoyldithioformates 5[07[1 FUNCTIONS CONTAINING AT LEAST ONE METALLOID FUNCTION
458 458 458 463 465 466 467 479 479 470 473 473 473
5[07[0 THIOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGEN OR CHALCOGEN FUNCTIONS# 5[07[0[0 Thiocarbonyl Derivatives with Two Nitrogen Functions The synthesis of thioureas and their derivatives have been reviewed previously ð68COC"2#262\ This chapter has been organized according to the principal reagents used as primary sources for the synthesis of these compounds[ 72HOU"E3#396Ł[
5[07[0[0[0 From isothiocyanates Isothiocyanates are\ probably\ the most powerful starting materials for preparing thioureas and derivatives[ Thus\ in a general manner\ alkyl or aryl isothiocyanates react with ammonia\ primary amines\ and secondary amines to give 0!substituted\ 0\2!disubstituted and trisubstituted thioureas\ respectively ð44CRV070Ł[ This reaction generally takes place with good yields and works better in polar solvents such as diethyl ether\ ethanol\ water\ or acetone "Equation "0##[ One of the main 458
469
Thiocarbonyl and Two Other Heteroatoms
advantages of the method is its versatility\ allowing the use of reagents with a wide range of substitutents\ both in the amine and in the isothiocyanate components[ S
H
R1 N
•
+
S
R2
N
R3
(1)
35–100%
NR2R3
R1HN
R1 = alkyl, Ar R2, R3 = H, alkyl, Ar
The amine component can be extensively functionalized[ Thus\ v!aminoalcohols and amino! phenols react chemoselectively in boiling chloroform with isothiocyanates through the amino group exclusively "Equation "1## ð64JMC89Ł[ Aminothiols also react with phenyl isothiocyanate through the amino group\ while alkyl isothiocyanates produce a 0 ] 0 mixture of isomers "0# and "1# resulting from competitive addition of the amino and the thiol group[ If the hydrochloride derivative is used instead of the free amine\ the reaction leads to the exclusive formation of the dithiocarbamate derivative "1# "Scheme 0# ð52JOC2039Ł[ R1 N
H •
S
+ R2
N
S
CHCl3
( )n
OH
reflux
R1HN
( )
N
n
(2) OH
R2
S R1 = Ph
R1HN
47–66%
R1 N
N
H •
S
+ R2
N
( )
n
SH
R2 ( )n
SH S
S
R1 = alkyl
R1HN
( )
N
n
SH
+
R1HN
S
( )
n
NHR2
R2 (1)
(2)
Scheme 1
Hydroxylamine and substituted hydroxylamines react with alkyl and aryl isothiocyanates to give the corresponding hydroxythiourea derivatives "2# in variable yields^ the best results are obtained with aromatic isothiocyanates and N! or O!alkylhydroxylamines\ while isothiocyanates having bulky substituents\ such as t!butyl\ give rise to lower yields "Equation "2#\ Table 0# ð0786JPR60\ 55PHA12\ 58ACS213Ł[ R1 N
S
H •
S
+ R2
N
OR3
31–97%
R1HN
N
OR3
R2
Table 0 Thioureas "2# from hydroxylamines and isothio! cyanates[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0 R1 R2 Yield Ref[ ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Me H Me 41 55PHA12 Bun H H 37 55PHA12 But H H 20 69JMC266 Ph Me H 86 50AP654 Ph H Et 59 58ACS213 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
(3)
460
At Least One Nitro`en
Steroids containing fused heterocycles\ such as the thiazole ring\ have been the subject of attention due to the in~uence exerted by the heterocyclic component on their pharmacological behavior[ This type of compound has been prepared stereospeci_cally by employing a general method of ring expansion of N!thioacylaziridines[ Thus\ steroidal 1\2!aziridines react with phenyl isothiocyanate to give unstable thiourea intermediates which\ with sodium iodide\ undergo ring expansion to give the _nal derivatives "3# and "4# "Scheme 1# ð79JCS"P0#655Ł[ O
O PhNCS
PhHN
S
NaI
N
PhHN 66%
S
HN
N (4)
O
O PhNCS
PhHN
S
NaI
PhHN
N 78%
S
HN
N (5)
Scheme 2
The N0Si bond of trimethylsilylamines has also been found to insert into the C1N bond of isothiocyanates[ The reaction takes place in ether at room temperature to give N!silylated thioureas\ which can in turn be easily hydrolyzed to the corresponding derivatives "Scheme 2# ð68LA152Ł[ S R1 N
TMS •
S
+ R2
N
R2
R2
S
N
N
R2
R1
R2
TMS
N
R1 = Me, R2 = Et, 75%
NHR1
R2
Scheme 3
In a similar way\ trimethylstannylthioureas have been prepared in essentially quantitative yield from phenyl isothiocyanate and stannylamines ð54JCS1046Ł[ This aminostannylation reaction is e}ected under mild conditions and appears to involve a cyclic transition state as suggested by the low activation parameters found "Scheme 3#[ Me SnMe3
Ph N
•
S
+ Me
N
Me3Sn
N Me
Me
N
•
S
S Ph
N
NMe2
SnMe3
Ph Scheme 4
The N0H bond of imines also reacts with isothiocyanates[ For instance\ diphenylmethyleneamine reacts with phenyl isothiocyanate to give methylenethioureas "5#\ which have the structure of 1! amino!2!aza!0!thiabutadienes ð89JOC0610Ł[ The same compounds are obtained by reacting methyl and phenyl isothiocyanate with N!tributylstannyldiphenylmethyleneamine ð61JCS"P0#029Ł[ The N!phenyl derivative is stable and may also be prepared from bis"tributyltin# oxide and N!phenyl!N?! diphenylmethyleneaminothiourea in boiling benzene[ Methyl isothiocyanate\ however\ undergoes addition at the carbonÐsulfur double bond and requires hydrolysis to yield the thiourea derivative[ The related reaction of N!silylated methyleneamines is also known and represents a more general entry into this type of compound ð61JCS"P0#0567\ 78S117Ł[ Another approach to these compounds involves the reaction of secondary amines with 0!bromoalkyl isothiocyanates^ the reaction takes place in ether at low temperature\ and the brominated intermediate is transformed with loss of hydrogen bromide into the azathiabutadiene "Scheme 4# ð68CB0845Ł[ An interesting example of the insertion of a nitrogenÐmetalloid bond into isothiocyanates is the
461
Thiocarbonyl and Two Other Heteroatoms Ph
Ph
R N
•
S
+
N
N
S
59–92%
Ph
H
Ph NHR (6) H2O
(Bu3Sn)2O
Ph R N
•
S
Ph
+
N
N
S
Bu3Sn
Ph
N
Ph
Ph
S
50%
N R
S
Ph SnBu3
Bu3Sn
R = Me, Ph
R2 R1 N
R2 •
S
+
N
N
R3 N R1
S R3
TMS
TMS
R3 = H, Ar
R1 R2
R1 N
•
S
+
H N
N
–HBr
S
R2
Br
N R2 R2
R1 = c-C6H11; NR22 = piperidino, 90% Scheme 5
reaction of diazaboracyclohexane with phenyl isothiocyanate which results in the formation of the rare eight!membered boratriaza heterocycle "6# "Equation "3## ð65JOM"009#04Ł[ H N N
B
H
N Ph
+
Ph
N
•
S
CCl4
B
90%
N N
H H
Ph (4) Ph
S (7)
Functionalized isothiocyanates appear to be adequate starting materials for the synthesis of N!unsubstituted thioureas for which the preparation seems to be otherwise di.cult or requires cumbersome procedures[ For instance\ alkanoyl isothiocyanates\ easily available from acid chlorides and lead"II# thiocyanate\ react with secondary amines in acetone to yield N!alkanoylthioureas which are in turn deprotected with aqueous base ð44OSC"2#662\ 76JCS"P0#0042Ł[ Thioureas of this sort are also available by reaction of alkoxycarbonyl isothiocyanates with amines followed by acid hydrolysis of the carbamate moiety "Scheme 5# ð62JPR033Ł[ Silicon"IV# isothiocyanate reacts in benzene with secondary amines to give\ after solvolysis with a mixture of water and isopropanol\ 0\0!disubstituted thioureas ð62OSC"3#790Ł[ Phosphorus derivatives\ such as 1!isothiocyanatobenzo!0\2\1!dioxophosphole\ react with secondary amines to furnish the corresponding addition compounds "7#^ further treatment with aqueous sodium hydrox! ide allows the removal of the phosphorus group yielding 0\0!disubstituted thioureas "Scheme 6# ð60LA"632#056Ł[ In what constitutes a special reaction\ aliphatic and aromatic isothiocyanates dimerize on heating in DMSO to a}ord N\N?!symmetrically substituted thioureas "Equation "4## ð63S178Ł[ NHR
DMSO, heat
R N
•
S
(5)
S 32–87%
R = Me, Tol, 4-Cl-C6H4
NHR
462
At Least One Nitro`en H R2
R1
+
O N
•
N COR1
H N
30–99%
R2
S
S
OH–
N R2 R2
NH2 S
H R2
OR1
+
O N
•
N CO2R1
H N
42–63%
R2
S
N R2
H3O+
R2
S N R2 R2 Scheme 6
H
R Si
N
•
S
+
4
Si
H N
NH2
N
PriOH, H2O
R N
R
S
S N R
–SiO2
R
R 4
O P
N
•
S
R
O
R
O
+ H N
O
NH2
H R
P N
S N R
40%
N S
NaOH
R
R
(8) Scheme 7
The synthesis of heterocyclic derivatives of thioureas has been reviewed by Mukerjee and Ashare ð80CRV0Ł[ The strategies developed are based on the idea of the counter!attack reagent\ since the thiourea adduct resulting from the addition of one equivalent of amine to an isothiocyanate might still undergo a subsequent intramolecular cyclization if adequate functionalization is present[ Amino acids and their derivatives\ amino aldehydes\ amino ketones\ amino oximes\ hydrazines\ and hydra! zides are among the many reagents employed for this purpose[ Thus\ a wide variety of _ve! and six! membered heterocycles has been easily prepared "Equation "5##[ R N
•
S
+
H2N ( )n X
H n = 1, 2
X = CHO X = RC=O X = CO2H, CO2R
S
N ( )n N Y R Y = CH(OH) Y = CR(OH) Y = C =O
(6)
n = 1, 19–49%; n >1, 15–85%
Thiosemicarbazides are also prepared in a general manner from isothiocyanates[ Thus\ alkyl and aryl isothiocyanates react exothermically with mono!\ di!\ or trisubstituted hydrazines\ as well as with hydrazine itself\ to give thiosemicarbazides in good yield[ When unsymmetrical mono! and disubstituted hydrazines are employed both of the two possible regioisomers "8# and "09# are actually obtained\ although the thiosemicarbazides resulting from the attack of the less!substituted nitrogen predominate in the case of monosubstituted hydrazines "Scheme 7# ð50ZOB2615\ 69MI 507!90Ł[ Another entry into thiosemicarbazides is provided by the reaction of isothiocyanates\ prepared from azides and carbon disul_de\ with triphenylphosphine and hydrazine[ However\ the yields obtained through this method are only moderate "Scheme 8# ð81T6494Ł[ Functionalized hydrazines have also been used as suitable precursors of thiourea derivatives[ For instance\ acylhydrazines ð57JOC740\ 61TL1828\ 79JHC0258Ł and sulfonylhydrazines ð69JMC223Ł react regioselectively through the free amino group with isothiocyanates in ethanol to give thiosemi! carbazides in good yields "Equation "6##[
463
Thiocarbonyl and Two Other Heteroatoms NHR1 S R3 N N R4 R2
R2, R3, R4≠ H or R2 = R3 56–100%
R3
R2
R1N N
•
S
+
N N R4
H
NHR1
R2 ≠ R3, R4= H
NHR1
S
S
+
N NHR3
N NHR2
R2
R3 (10)
(9) Scheme 8
Ar
i, Ph3P
N3
N
Ar
•
ii, CS2
H2N–NH2•H2O
S
Ar
26%
H
H
N
N
NH2
S
Ar = Ph Scheme 9
NHR
H
R N
•
+ H2N N
S
S
EtOH
H
X = COR2, SO2R2 R = Ph, X = O2S
(7)
N NHX
X
88%
OMe
Thiosemicarbazides are also available from amino isothiocyanates[ In this case\ reaction of 2!aminopyridine with substituted amino isothiocyanates represents another route to 0\0\3!tri! substituted thiosemicarbazides "Equation "7## ð57ACS0787Ł[ H
R N N
R
H2N
R N
S
EtOH
R
+ N
•
(8)
N H
S
N
40%
N R = Pri
It is also possible to obtain cyclic derivatives of thiosemicarbazides from properly functionalized isothiocyanates following the same pattern described above for thioureas[ Thus\ hydrazine reacts with 1!acetoxyvinyl isothiocyanate in re~uxing ether to give 3\4!dihydro!0\1\3!triazine!2"1H#!thione "00# "Equation "8## ð68JCR"S#139Ł[ H N
•
S
N
S ether, reflux
O O
+ H2N NH2
57%
H
N
N (9)
(11)
5[07[0[0[1 From carbon disul_de Symmetrical thioureas are synthesized inexpensively by reacting primary amines with carbon disul_de in the presence of a catalyst\ such as sulfur\ hydrogen peroxide\ hydroxide ion\ iodine\ or pyridine[ The reaction appears to involve an ammonium dithiocarbamate intermediate which upon
464
At Least One Nitro`en
loss of hydrogen sul_de and addition of a second equivalent of amine yields 0\2!disubstituted thioureas[ This reaction pathway is supported by the formation of unsymmetrical thioureas when the reaction is carried out in the presence of ammonia or other amine "Scheme 09# ð44CRV070Ł[
S
NHR1
cat.
S + R1NH2
•
S
–SH2
SH
R1NH2
R1 S
•
N
NHR1 S
or R2NH2 ~100%
NHR1(R2)
Scheme 10
Trisubstituted thioureas are synthesized from carbon disul_de\ aliphatic or aromatic primary amines and hexaalkylphosphorus triamides\ which transfer one of their dialkylamino groups[ The reaction takes place in pyridine giving the thioureas in almost quantitative yield "Equation "09## ð64S273Ł[ NR12
pyridine
S
S + (R12N)3P + R2NH2
•
S ~100%
(10) NHR2
R2 = Ph, Bn, c-C6H11
Carbon disul_de condenses with three molar equivalents of dialkylcyanamides at 099>C and high pressure to give substituted thiocarbamoylimino!0\2\4!thiadiazines "01# in good yields[ The reaction is thought to proceed through a repeated ð1¦1Ł cycloadditionÐretroaddition cycle "Scheme 00# ð89JCS"P0#0107Ł[ S
•
S + R2N
NR2
500 MPa
2 R2N
S
N 100 °C
N
•
NR2
N
S
S
NR2 N S
N N
NR2 = NMe2, pyrrolidine, piperidine, 55–84%
(12)
NR2
Scheme 11
Hydroxylamines show anomalous behavior towards carbon disul_de in DMF since the formation of monohydroxythioureas "02# instead of the expected N\N?!dihydroxy derivatives has been reported to occur "Equation "00## ð69LA"620#060Ł[ NHR S
•
S +
DMF
RNHOH 82%
R = c-C6H11
S N OH
(11)
R (13)
As expected\ a\v!diamines react with carbon disul_de in ethanol to give cyclic thioureas ð52FCF443Ł[ The method allows the preparation of heterocycles of various ring sizes\ including medium ring\ macrocyclic\ and benzocondensed products as is exempli_ed in Scheme 01 by the reaction of 0\7!diaminooctane ð79TL202Ł and 1!aminobenzylamine ð58JOC2593\ 60ZC01Ł with carbon disul_de[ Substituted pyrimidine!1"0H#!thiones "03# are available in a regioselective fashion by re~uxing 3!amino!0!azabutadienes in carbon disul_de "Scheme 01# ð68CC564\ 71JCS"P0#1038Ł[ 1!Thiohydantoins are immediate precursors of imidazothiazoles\ potential central nervous system antitumor agents[ These thiohydantoins are generally prepared in good yields from a!amino acids or a!amino esters and isothiocyanates[ Alternatively\ they can be obtained in one pot by reaction of dithiocarbamic esters\ generated in situ from a primary amine\ carbon disul_de and methyl iodide\ and a!amino acids "Scheme 02# ð72S280Ł[ The Schi} bases derived from aromatic aldehydes and arylamines are precursors of imidazole!1! thione in a reaction sequence that comprises three steps^ thus\ the sodium cyanide promoted dimerization of the imines in DMF giving the benzil dianil is followed by reduction with sodium in ether and cyclization with carbon disul_de[ This method is restricted to all!aryl substituted com!
465
Thiocarbonyl and Two Other Heteroatoms S H R
N
R
H ( )n
N
+ S
•
EtOH/H2O
S
N
13–72%
R
R
N ( )n–2
n = 1, 2, 6 H N
NH2 NH2
+ S
•
S N
∆
S
R2 R3
R2 R3
∆
NHR1
+ S R4
H
•
N
R1
S 80–95%
NH
R4
N
S
(14) Scheme 12
O RNH2 + MeI +
S
•
S
NHR
EtOH
S
DL-alanine/Et3N
SMe
H
76–97%
N
N
R
S Scheme 13
pounds since only aromatic aldimines undergo cyanide!catalyzed dimerisation to form dianils "Scheme 03# ð79S0990Ł[ Ar2 NaCN
Ar1 NAr2
DMF
Ar1
N
Ar1
N Ar2
Ar1 = Ar2 = Ph
Ar2 i, Na, ether ii, CS2
Ar1
N
Ar1
N
S Ar2 65%
Scheme 14
Carbon disul_de also inserts into the N0Si bond of siladiazoles to give an unstable intermediate "04# which readily decomposes to the corresponding thiourea[ The reaction takes place at or below room temperature and sometimes requires the use of a high excess of carbon disul_de ð80JOM"308#8Ł[ Other reactive amines such as bis"tributyltin#ethylene diamine have also been reported to a}ord cyclic thioureas "Scheme 04# ð69MI 507!91Ł[
5[07[0[0[2 From thiophosgene Substituted thioureas can also be prepared by reaction of thiophosgene with primary and sec! ondary amines[ This method is closely related to the one described in Section 5[07[0[0[0\ and involves the formation of isothiocyanates and thiocarbamoyl chlorides as the intermediates in the reaction with primary or secondary amines\ respectively ð44CRV070\ 62RCR476Ł[ Accordingly\ when the reac! tion is carried out using equimolecular amounts of thiophosgene and secondary amine\ the cor! responding thiocarbamoyl chloride is isolated^ this intermediate can in turn react with another equivalent of a di}erent amine\ thus allowing the synthesis of unsymmetrically substituted thioureas "Scheme 05#[
466
At Least One Nitro`en S
R2 N
R1
CS2 (1–10 equiv.) 25 °C
N
N
R2
S Si
N
R1
S
Si R1 N
Si R1
S
R1
R1 –
R2
83–87%
N
R3
R3
R3
(15) H Bu3Sn
N
N
H
H
N
SnBu3
+ S
•
S
S
N H Scheme 15
NR1R2
HNR1R2
Cl
NR1R2
HNR1R2
S
S
S
Cl
NR1R2 77–87%
Cl
NR1R2
HNR3R4
S NR3R4
Scheme 16
Thiophosgene also reacts with nitrogen heterocycles to give bis"heterocyclic# thiocarbonyl com! pounds which have found utility as thiocarbonyl transfer reagents in other syntheses of thiourea derivatives "see Section 5[07[0[0[3#[ The synthesis of these compounds can be achieved either from N0H containing heterocycles\ mostly azoles\ or activated derivatives thereof[ For instance\ N! trimethylsilylimidazole reacts with thiophosgene in carbon tetrachloride at room temperature to furnish N\N?!thiocarbonylbis"imidazole# "Equation "01## ð67JOC226\ 68LA0645Ł[ Cl
Het
+ Het–R
S
(12)
S
Cl
Het R = H, TMS
N
N Het =
N
, N
N
N N ,
N,
, N
,
N
N
N
As in the case of carbon disul_de\ aliphatic diamines produce cyclic thioureas ð64JCS"P0#101\ 0\2!Dimethyl!1\1!diethyl!0\2!diaza!1!germacyclopentane reacts with thio! phosgene at room temperature to give 0\2!dimethylimidazolidine!1!thione "05# in 67) yield "Equa! tion "02## ð64JOM"77#C24\ 80JOM"308#8Ł[ 64JMC802\ 79JMC0150Ł[
Me Cl
+
S Cl
Me
N Et2Ge
N S
N Me
78%
(13) N Me (16)
5[07[0[0[3 From thiocarbonyl transfer reagents As has been indicated above\ heterocyclic thiocarbonyl transfer reagents have been used increas! ingly for the synthesis of thiourea derivatives[ For instance\ N\N?!thiocarbonyl!bis"imidazole# reacts
467
Thiocarbonyl and Two Other Heteroatoms
with two equivalents of aliphatic or aromatic primary amines in CH1Cl1 or chloroform at room temperature to give 0\2!disubstituted thioureas in nearly quantitative yield ð67JOC226\ 79JCS"P0#655Ł[ Secondary amines such as diethylamine expel just one imidazole group to furnish the mixed thiourea "06# "Scheme 06# ð51LA"546#87Ł[ The other azoles studied\ while usually less reactive\ may in certain situations o}er some advantages due to their higher stability to moisture and the low solubility of the free heterocycle recovered "Scheme 06# ð67JOC226Ł[ NHR
RNH2
N
90–100%
N N
S NHR
N
NR2 S
S
R2NH
N N (17)
Scheme 17
N\N?!Thiocarbonylbis"2\4!dimethyl#pyrazole has been reported to give N\N?!diphenylthiourea and benzimidazoline!1!thione on reaction with aniline and 0\1!diaminobenzene\ respectively[ When 0\3!diaminobenzene is used the reaction results in the formation of a thiourea derived polymer[ Aliphatic primary diamines show di}ering behavior depending on the length of the methylene chain[ Thus\ while 0\2!diaminopropane and 0\3!diaminobutane form the bis"2\4!dimethyl!0!pyra! zolylthioformyl#diamines "DMP 2\4!dimethylpyrazolyl#\ 0\4!diaminopentane produces a thermo! plastic polymer "Scheme 07# ð50LA"535#85Ł[ NHPh
PhNH2
S
70%
NHPh
NH2
H N
NH2
S
70%
N H
N
N
N
N S
H2N
NH2
polymer H2N
( )n
n = 3, 70% n = 4, 80% H2N
( )5
H
NH2
DMP
N
H ( )n
N
S
DMP S
NH2
polymer
Scheme 18
A particularly useful preparation of thiourea derivatives takes advantage of the in situ formation of thiocarbonylbis"imidazole# from imidazole\ carbon disul_de and a 1!halothiazolium salt "molar ratio 1 ] 1 ] 0#\ thus avoiding the use of thiophosgene[ The utility of this in situ generated thiocarbonyl! bis"imidazole# has been demonstrated in the preparation of unsymmetrical thioureas "07# and thiosemicarbazides "08# by stepwise addition of two di}erent amines or an amine and hydrazine hydrate\ respectively "Table 1\ Scheme 08# ð77JOC1152Ł[ 5[07[0[0[4 From ureas The direct conversion of the carbonyl moiety into a thiocarbonyl function is possible in general with some phosphorus derivatives\ such as P3S09 and the popular Lawesson|s reagent[ Some examples
468
At Least One Nitro`en Table 1 Thioureas "07# and thiosemicarbazides "08# from thiocarbonylbis"imidazole#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0R1NH R2R3NH Yield ")# ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * PhCH1MeNH NH2 47 64 PhMeNH NH2 Morpholine NH2 37 NH1NH1 = xH1O 30 PhCH1MeNH 63 PhMeNH NH1NH1 = xH1O Morpholine NH1NH1 = xH1O 41 PhMeNH Piperidine 77 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
X
R
+
N
HN
N
N THF, 0 °C
N
N
S NR3R4 (18)
S 48–88%
N i, R1R2NH ii, NH2NH2
N
N
–CS2
N
NR1R2
i, R1R2NH ii, R3R4NH
N
S
N
X = Br, Cl Y = BF4–, FSO3
SNa
S
S
Ph (0.5 equiv.)
S
N
NaH, CS2
Y– S
NR1R2 S
41–74%
NHNH2 (19) Scheme 19
involving P3S09 and tetrasubstituted thioureas have been described[ The yields vary from moderate to poor ð60LA"635#81Ł\ a notable exception being the transformation of imidazolidin!1!one into the thione "19# which has been achieved in nearly quantitative yield "Equation "03##[ P4S10
R
N
N
R
~100%
R
N
N
O
(14)
R
S (20)
High yields are obtained with some heterocyclic derivatives[ Thus\ 0\3\5!trisubstituted 1"0H#! pyrimidones are converted into the corresponding pyrimidine!1!thiones "10# by re~uxing in benzene with Lawesson|s reagent[ In this case the yields vary from poor to quantitative "Equation "04## ð71H"08#1172Ł[ R2
R2 N
R3
N
R1 O
Lawesson's reagent benzene, reflux 15–100%
R1 R2 R3
= H, Me, Ar = Me, Ar = Me, Ar
N R3
N (21)
R1 (15) S
479
Thiocarbonyl and Two Other Heteroatoms
5[07[0[0[5 Miscellaneous methods A nearly quantitative conversion of symmetrical thioureas into unsymmetrical thioureas\ by exchange of one amino group\ has been described ð82TL5336Ł[ The process is accomplished by re~uxing 0\2!diphenylthiourea with di}erent types of amines and triethylamine in acetonitrile giving high yields of 0!phenylthiourea derivatives "11#^ the reaction also works\ though in lower yields\ in other polar solvents such as methanol\ ethanol\ THF\ or DMF[ The procedure has also been shown to take place under phase transfer catalysis\ thus allowing aqueous solutions of low boiling point amines to be used "Equation "05##[ Sodium cyanothioformate reacts with primary diamines in re~uxing butanol to a}ord heterocyclic derivatives "12# in good yields "Equation "06## ð44MI 507!90\ 70JPR30Ł[ NHPh
NHPh
Et3N, MeCN
+ R1R2NH
S
(16)
S reflux 70–90%
NHPh
NR1R2 (22)
H CN
BunOH
N
+ H2N(CH2)nNH2
S
S
reflux 81–89%
SNa
( )n
(17)
N H (23)
n = 1, 2
Thiourea S\S!dioxide derivatives have found application in the reduction of di}erent compounds\ such as dinitrodiaryl derivatives ð77AJC884Ł\ organoselenium and tellurium halides\ and oxides ð77SC290Ł as well as azobenzenes ð77MI 507!90Ł[ Thiourea itself can be quantitatively converted into its dioxide by treatment with H1O1 and sodium acetate in water at 4>C ð89MI 507!90Ł[ The S\S! dioxides derived from monosubstituted thioureas are stable and can be obtained in a similar way by treatment with two equivalents of hydrogen peroxide in ethanol at low temperature ð58LA"611#79Ł[ When the thiourea bears bulky substituents at both nitrogen atoms\ the oxidation process stops at the S!oxide stage ð58LA"611#41Ł[ The oxidation of the thioxo function of 0!aryl thiosemicarbazides with hydrogen peroxide leads to the S!oxide derivative but it is also accompanied with the additional oxidation of the hydrazo group to the azo function "Scheme 19# ð55TL2584Ł[ NH2 S NH2 NH2 S NHR
H2O2, NaOAc, H2O
NH2 O2S
97%
H2O2, EtOH
NH2 NH2 O2S
48%
NHR
R = Prn NHBut
NHBut 30% H2O2, EtOH
S N
OS N
64%
Et
H NH2 S
H
H2O2
N NHAr
Et
NH2 OS N NAr
H Scheme 20
5[07[0[1 Thiocarbonyl Derivatives with One Nitrogen and One Phosphorus Function Phosphinothioformamides\ also named thiocarbamoylphosphines\ are generally used as ligands in organometallic chemistry[ The related compounds containing nitrogen and one atom of group 04 other than phosphorus "As\ Sb\ Bi# are not known[
470
At Least One Nitro`en 5[07[0[1[0 From isothiocyanates
Isothiocyanates are the most valuable source for preparing phosphinothioformamides[ Typically\ the P0H bond of phosphines adds to isothiocyanates to give the title compounds "Equation "07## ð76ZN"B#66Ł[ Thioalkyl phosphines\ prepared from sodium phosphines and chloroalkyl thiols\ react with PhNCS to give the thioalkylphosphinothioformamide derivatives which can undergo a sub! sequent intramolecular cyclization to the thiocarbonylphosphazine "13# "Scheme 10# ð62JPR360Ł[ Bis"ethylthio#alkylphosphines undergo reduction of the phosphorusÐsulfur bond with dibutyltin dihydride giving rise to the corresponding species with a P0H bond\ which yields alkylthiophos! phinothioformamides upon reaction with phenyl isothiocyanate "Scheme 11# ð77ZOB0357Ł[ The reaction of phosphonate and thiophosphonate isothiocyanates with secondary phosphines results in the formation of the corresponding phosphonates and thiophosphonates "Equation "08## ð81PS"62#70Ł[ NHR2
Ph
R2 P H +
N
S •
S
P
R1
(18)
Ph
R1
NHPh
Ph
Ph P H +
P
S N
•
S
P
–H2S
N
Ph
HS
NHPh
H P
R1
+ Bu2SnH2
P
EtS
S
Ph (24)
SH Scheme 21
EtS
Ph
EtS
R1
PhNCS
S P
49–67%
SEt
R1 R1 = But, Et, SEt
Scheme 22
(PriO)2(X)P
+ N
•
S
R1 P H
PR12 S N P(X)(OPri)2
R1
(19)
H X = O, S
The P0H bond of phosphorus"V# derivatives also adds to isothiocyanates to yield phos! phinothioformamides "Equation "19## ð58BCJ1864\ 76ZN"B#759Ł[ Chiral phosphinothioformamides "14# are obtained when using isothiocyanates prepared from optically active amines\ such as "S#! and "R#!phenylethylamine "Equation "10## ð75ZN"B#0031Ł[ "N!Alkylthiocarbamoyl#phosphonic acid esters "15# have been prepared and shown to be versatile precursors of a!substituted methyl phos! phonate derivatives which display interesting biological activity[ Their preparation cannot be achieved by the Arbuzov!type reaction of trialkyl phosphites and isothiocyanates[ However\ when dialkyl phosphates are used instead\ the reaction works well and addition of the P0H bond to the C1N double bond of the isothiocyanate takes place[ The process is base catalyzed and the reaction is usually run in the presence of alkoxide ion\ except for compounds sensitive to these reagents such as phosphonates^ in these cases\ triethylamine is a good alternative "Equation "11## ð64ZOB0373\ 71JOC2901Ł[ The related "N!alkylthiocarbamoyl#thiophosphonic acid esters have been prepared in a similar way by starting from the corresponding thiophosphonic esters "Equation "12## ð72JOC2855Ł[ O
R R
+ N
•
S
P H Ph Ph
S
P(O)Ph2 R N R H
(20)
471
Thiocarbonyl and Two Other Heteroatoms P(O)Ph2
O Ph
*
+ N
•
S
S
P H Ph Ph
N
+ •
S
P(O)(OR2)2 base
P H R2O 2 RO
S H (26)
P(S)(OR2)2
S N
+ •
S
(22)
N R1
25–85%
R1 = Me, Bn R2O = OMe, OPh (R2O)2 = O(CH2)3O
R1
Ph
H (25)
O R1
(21)
N *
S
P H R2O 2 RO
(23)
N R1
30–70%
H
Trimethylsilyl tetraethylphosphorodiamidite reacts with phenyl isothiocyanate yielding\ after hydrolysis of the N0Si bond\ the thiocarbamoylphosphonate derivative "16# "Scheme 12# ð65IZV344Ł[ Thiocarbamoylphosphonic acids have also been prepared by reaction of tris"trimethyl! silyl# phosphite with alkyl and aryl isothiocyanates[ The exothermic reaction takes place very rapidly at room temperature to give an adduct which upon treatment with aniline in methanol furnishes the monoanilinium salt of thiocarbamoylphosphonic acid "17# in almost quantitative yield "Scheme 13# ð68TL2902Ł[ P(O)(NEt2)2 Ph N
•
S
+ (Et2N)2P–OTMS
P(O)(NEt2)2 H3O+
S N TMS
S N H
87%
Ph
Ph (27)
Scheme 23
O R N
•
S
+ P(O-TMS)3
RN
O
P O-TMS O-TMS S
TMS
P OH O– +NH3Ph
PhNH2, MeOH
S 90–98%
N H R (28)
Scheme 24
Alkyl and aryl isothiocyanates react with trimethylsilyldiphenylphosphine at 79>C to give the expected N!silylated derivatives arising from addition of the P0Si bond\ which undergo easy methanolysis producing diphenylphosphinothioformamides "18# "Scheme 14# ð57JCS"A#0094Ł[ The insertion of isothiocyanates into the P0Si bond has also been described in several other phosphorus derivatives^ thus\ bis"trimethylsilyl#phosphines give similar insertion products with phenyl iso! thiocyanate "Equation "13## ð74ZAAC"419#019\ 74ZAAC"419#028Ł[ The P0Si bond of trimethylsilyl phosphatriafulvenes also inserts into the C1N bond of isothiocyanates yielding compounds "29# through the betaine intermediate shown "Scheme 15# ð80S0988Ł[ Silylphosphines and germylphos! phines react at room temperature\ in almost quantitative yield\ with equimolar amounts of phenyl isothiocyanate to give the corresponding phosphinothioformamide derivatives "20#[ The reaction proceeds with retention of the con_guration at the silicon or germanium centers suggesting a four! center mechanism "Equation "14## ð68TL2496Ł[
472
At Least One Nitro`en PPh2 R N
•
S
PPh2 MeOH
S
+ Ph2P-TMS
N TMS
S N H
67–70%
R
R (29)
R = alkyl, aryl Scheme 25 R P
Ph N
•
+ RP(TMS)2
S
TMS
S
(24) N TMS Ph
R = Me, Ph, But, mesityl
TMS
But
But R
+
P-TMS
N R
TMS N
•
S
S
P
+
65–73 %
S
But
But
R N
But
P
–
But (30)
Scheme 26
Ph N
•
S
M
+
S
PEt2
Me
Et2P
Me
N M
(25)
Ph (31)
M = Si, Ge
Phosphorus"III# acid amides react rapidly with isothiocyanates to form an addition intermediate which\ upon hydrolysis\ furnishes phosphinothioformamides "21# "Equation "15## ð66IZV0066Ł[ Also\ phosphorus"V# acid t!butyl esters and amides react with phenyl isothiocyanate to give phos! phinothioformamides "Equation "16## ð89ZOB452Ł[ O P(OR)NHPh
i, PhNCS
(RO)2PNHPh
(26)
S ii, H2O
N H Ph (32)
O O P
R
But
+
PR2
Ph N
•
S
(27)
S
62–82%
N H
R Ph R = EtO, Me2N
N!Thiophosphonate phosphinothioformamides "22# can be prepared by reaction of dialkoxythiophosphoryl isothiocyanates with sodium dialkylphosphites in ethanol[ However\ the yield in this reaction is very low\ and heating in benzene does not improve the synthesis of "22#\ but results in phosphonateÐthiophosphate rearrangement "Equation "17## ð82ZOB522Ł[ O S
P(OEt)2
+
(PriO)2P N
•
S
(EtO)2PONa
18%
(28)
S N P(S)(OPri)2 H (33)
473
Thiocarbonyl and Two Other Heteroatoms
5[07[0[1[1 From halothioamides Chlorothioamides are the main alternative to isothiocyanates for preparing thiocarbonyl deriva! tives containing nitrogen and phosphorus atoms[ Thus\ lithium diphenylphosphide reacts with N!alkyl! and N!arylthioformamidoyl chlorides to give diphenylphosphinothioformamides "23# in 43Ð62) yield ð74CB116Ł[ Good yields are also obtained in the reaction of lithium trimethyl! silylphosphides with thioformamidoyl chlorides to give the trimethylsilylphosphinothioformamide derivatives "24# ð73ZAAC"407#10Ł[ Phosphorus"III# esters react with dialkylamides of chloro! thioformic acid to give phosphinothioformamides "25# in moderate to good yields "Scheme 16# ð77ZOB0378Ł[ R1 N R1
Ph2PLi
S
R1
= Me, Ph 57–73%
R1 N R1
P Ph Ph (34) R1 N R1
R2P(TMS)Li
S
S
R1 = Me R2 = Me, But, Ph, TMS 77–89%
Cl
P
TMS
R2 (35) R1 N R1
R2P(OR3)2
S
R2 = Me, Et R3 = Et, Pr, Bu 45–83%
P OR3 R2 (36)
Scheme 27
5[07[0[1[2 From thiophosphinoyldithioformates Substituted thiophosphinoylthioformamides "26# are obtained by aminolysis reaction of thiophos! phinoyldithioformates[ The reaction works well for ammonia and primary aliphatic amines with moderate steric hindrance "Equation "18## ð69ACS0983Ł[ SR3
R4
NHR4 R4NH2
S
S
PR1R2
PR1R2
S
S
= H, alkyl
(29)
(37)
5[07[1 FUNCTIONS CONTAINING AT LEAST ONE METALLOID FUNCTION Thiocarbonyl compounds bearing metalloid functions are almost unknown[ Two di}erent approaches for the synthesis of bis"trimethylsilyl#thioketone have been described up to now\ and some controversy has been generated concerning the stability of this compound[ Block et al[ proposed in 0874 the intermediacy of bis"trimethylsilyl# thioketone "27# in the serendipitous synthesis of alkyltrimethylsilyldithioformates from alkanesulfenic acids[ This bis"trimethylsilyl# thioketone was prepared by pyrolysis of the corresponding thiosul_nate and trapped in situ with 1\2!dimethyl!
474
At Least One Metalloid
butadiene to give the corresponding DielsÐAlder cycloadduct[ In the absence of the trapping agent\ the major product is the trimethylsilyldithioformate "28# "Scheme 17# ð74TL1148\ 77T170Ł[ Et
TMS SH +
S TMS
Cl
TMS
Et
TMS
pyridine
S O
heat
S 46%
O
S
2,3-dimethylbutadiene
TMS TMS
22%
TMS S
+ EtSOH
TMS
TMS
(38)
–TMS-OH
S EtS (39)
Scheme 28
Ricci et al[ almost simultaneously reported the _rst synthesis of bis"trimethylsilyl# thioketone "27# starting from tris"trimethylsilyl#methane[ Thus\ the treatment of the latter with one equivalent of MeLi followed by addition of elemental sulfur and acidic hydrolysis leads to tris"trimethyl! silyl#methanethiol which is transformed into tris"trimethylsilyl#methanesulfenyl bromide by reaction with MeLi and bromine[ Finally\ heating of the sulfenyl bromide results in loss of bromo! trimethylsilane and formation of the target compound "27# "Scheme 18# ð74TL0980Ł[ TMS TMS TMS
i, MeLi ii, S8 iii, H3O+
TMS TMS TMS
SH
i, MeLi ii, Br2
TMS TMS TMS
heat
TMS
–Br-TMS 50%
TMS
SBr
S (38)
Scheme 29
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.19 Functions Containing a Selenocarbonyl or Tellurocarbonyl Group— SeC(X)X? and TeC(X)X? FRANK S. GUZIEC, Jr. and LYNN JAMES GUZIEC New Mexico State University, Las Cruces, NM, USA 5[08[0 OVERVIEW
476
5[08[1 SELENO! AND TELLUROCARBONYL FUNCTIONS CONTAINING AT LEAST ONE ATTACHED HALOGEN
477
5[08[2 SELENOCARBONYL FUNCTIONS CONTAINING AT LEAST ONE ATTACHED CHALCOGEN "AND NO HALOGENS#
477
5[08[2[0 5[08[2[1 5[08[2[2 5[08[2[3 5[08[2[4 5[08[2[5
Dialkoxy!substituted Selenocarbonates\ "RO#1C1Se Dithio!substituted Selenocarbonates "RS#1C1Se Selenocarbonyl Functions Flanked by Two Selenium Atoms\ "RSe#1C1Se Selenocarbonyl Functions Flanked by Two Different Chalco`en Atoms\ RX"C1Se#YR Selenocarbamates RO"C1Se#NHR\ RS"C1Se#NHR\ and RSe"C1Se#NHR Phosphorus!substituted Selenocarbonyl Derivatives
5[08[3 FUNCTIONS CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGEN OR CHALCOGEN FUNCTIONS#
477 478 489 481 482 485 485 485 488
5[08[3[0 Selenoureas "R1N#1C1Se 5[08[3[1 Telluroureas "R1N#1C1Te
5[08[0 OVERVIEW Initially it should be noted that examples of selenocarbonyl analogues of well!known carbonyl! based functional groups are much less common than the corresponding oxygen and sulfur compounds[ The related tellurocarbonyl compounds are even more rare[ This scarcity is probably due to a number of factors[ Selenocarbonyl and tellurocarbonyl compounds are much less stable than their oxygen and sulfur analogues\ presumably owing to poor overlap in the p bonds of the selenium and tellurium compounds[ These compounds are also prone to lose volatile selenium and tellurium species and are therefore often unpleasant to work with and potentially toxic[ The early literature associated with selenocarbonyl or tellurocarbonyl compounds is fraught with errors[ Even the nomenclature describing these analogues is often inconsistent\ leading to di.culties in searching the literature "e[g[\ the term {selenone| is often used incorrectly to designate a carbonÐselenium double bond instead of the accepted term {selone|#[ A number of reports dealing with these problems have been published ðB!62MI 508!90\ B!62MI 508!91\ B!75MI 508!90\ B!76MI 508!90\ B!76MI 508!91Ł[ On a 476
477
Selenocarbonyl or Tellurocarbonyl
positive note it should also be stated that advances in the availability of novel reagents for the introduction of selenium and tellurium into organic molecules and progress in spectroscopic charac! terization may make further examples of these compounds more common in the near future[
5[08[1 SELENO! AND TELLUROCARBONYL FUNCTIONS CONTAINING AT LEAST ONE ATTACHED HALOGEN Compounds containing a halogen directly attached to a selenocarbonyl or tellurocarbonyl moiety are quite rare[ In addition\ very little has been reported on the reactions of these compounds[ Selenocarbonyl di~uoride "0# is quite unstable to dimerization in solution and to polymerization in the presence of Lewis acids[ It can be obtained by pyrolysis of the dimer at 259>C "Equation "0##\ or on a preparative scale by treatment of aluminum triiodide with Hg"SeCF2#1 "Equation "1## ð79ZN"B#415Ł[ Its tellurium analogue "1# can be prepared similarly using diethylaluminum iodide as a Lewis acid "Equation "2## ð80CC0267Ł[ This compound is also highly reactive and prone to dimerization[ F F
Se Se
F F
360 °C hν
F (1)
2 Se F (1) F
Hg(SeCF3)2 + AlI3
(2)
2 Se F
F Hg(TeCF3)2 + Et2AlI
(3)
2 Te F (2)
Selenophosgene "2# can be prepared by vacuum pyrolysis of 1\1\3\3!tetrachloro!0\2!diseletane "Equation "3##\ but is stable only below −029>C ð70ZN"B#0150Ł[ Cl Cl
Se Se
Cl
>300 °C
Cl (4)
2 Se
Cl
Cl (3)
A single example of a monosubstituted selenoacyl halide has been reported[ It is prepared starting from selenocarbonyl di~uoride "Equation "4## ð79ZN"B#415Ł[ F
F
+ B(SeCF3)3
Se F
Se
(5) SeCF3
5[08[2 SELENOCARBONYL FUNCTIONS CONTAINING AT LEAST ONE ATTACHED CHALCOGEN "AND NO HALOGENS# Note that no tellurocarbonyl compounds of this class have been reported to date[
5[08[2[0 Dialkoxy!substituted Selenocarbonates\ "RO#1C1Se Oxygen!substituted selenocarbonates are not particularly well represented in the literature\ and generally appear only as minor by!products in the preparations of selenium!containing compounds
478
At Least One Chalco`en
ð77AJC438Ł[ Treatment of sugar!derived cis!vicinal diols with phosgeneiminium chloride "3#\ fol! lowed by sodium hydrogen selenide treatment\ a}orded the corresponding cyclic selenocarbonates "4# in good yield "Equation "5## ð77AJC438Ł[ This reaction is reported to fail in the case of catechol\ a}ording instead the open!chain selenourethane "5# "Equation "6## ð77AJC438Ł[ R R
R
+
+ HO
Cl
CH2Cl2
Cl–
Me2N
NaHSe
O
(6)
O
Cl
OH
Se (5)
(4)
OH
OH
Cl
+
+
R
CH2Cl2
Cl–
Me2N
Se
NaHSe
(7)
Cl
OH
O (6)
(4)
NMe2
5[08[2[1 Dithio!substituted Selenocarbonates "RS#1C1Se Cyclic dithio!substituted selenocarbonates are important intermediates in the preparation of tetrathiafulvalenes[ A general route to these compounds involves alkylation of dithiocarbamate anions "6#\ readily obtained by reaction of secondary amines with carbon disul_de in the presence of base\ followed by cyclization in strong acid to the corresponding iminium salts "7#[ Treatment of this isolable salt with NaHSe or H1Se a}ords the desired cyclic selenocarbonate "8# "Scheme 0# ð78JCS"P0#0957Ł[ S OMe
+
N H
KOH
CS2
S– K+
N
Br
OMe
(7) S N
S
OMe
Ph4B– S
i, H2SO4, 60 °C
OMe
N+
ii, NaBPh4
NaHSe
S Se
S
S (9)
(8) Scheme 1
The previously mentioned phosgeneiminium chloride route to dialkoxy!substituted seleno! carbonates can also be used in the preparation of dithio!substituted derivatives[ Treatment of butanethiol with Viehe|s salt "3#\ followed by addition of sodium hydrogen selenide\ a}orded the dithioselenocarbonate "09# in good yield "Scheme 1#[ Cyclic dithioselenocarbonate derivatives "00# and "01# have also been prepared using this method ð77AJC438Ł[
BuSH
+
+
Cl
SBu
+
Cl–
Me2N
Me2N
Cl
SBu Cl–
(4) Scheme 2
S
S
Se
Se S (11)
S (12)
NaHSe 73%
SBu Se SBu (10)
489
Selenocarbonyl or Tellurocarbonyl
Complex selenocarbonates can be prepared by direct metallation of 3\4!unsubstituted seleno! carbonates[ For example\ consecutive treatment of the cyclic unsaturated dithioselenocarbonate "8# with lithium diisopropylamide "LDA#\ selenium\ zinc chloride\ and tetrabutylammonium bromide a}ords a diselenolate salt that can be acylated to the complex selenocarbonate "02# "Scheme 2# ð81JOM"316#102Ł[ Similar metallation reactions have been reported for other selenocarbonate derivatives[ i, LDA, THF, –78 °C ii, Se
S Se S (9)
Se (Bu4N)2
S
Zn
iii, ZnCl2 iv, Bu4NBr
Se
PhCOSe
S
PhCOSe
S
PhCOCl
Se S 2
Se (13)
Scheme 3
5[08[2[2 Selenocarbonyl Functions Flanked by Two Selenium Atoms\ "RSe#1C1Se Compounds of this type are generally referred to as triselenocarbonates in the literature[ A variety of preparations of this class of compounds\ particularly the cyclic triselenocarbonates\ have been reported owing to their importance as intermediates in the preparation of tetraselenafulvalenes[ The parent acid\ triselenocarbonic acid "03#\ can be prepared by acidi_cation of barium tri! selenocarbonate "Equation "7##[ It is unstable even at low temperatures\ liberating hydrogen selenide and polymeric selenium!containing materials[ The chemistry of this and related selenium!substituted carbonic acids has been reviewed ð57AG"E#757\ B!62MI 508!92Ł[ SeH
H+
BaCSe3
(8)
Se SeH (14)
A number of triselenocarbonate preparations begin with carbon diselenide as a starting material[ "It should be noted that carbon diselenide is a remarkably unpleasant reagent and should be used only with great care ðB!62MI 508!93Ł[# Reaction of sodium acetylide with carbon diselenide in the presence of selenium\ followed by acidi_cation\ a}ords the cyclic unsaturated triselenocarbonate "04# "Scheme 3# ð66JA4898Ł[ Electrochemical reduction of carbon diselenide\ followed by alkylation of the intermediate dianion\ can be used to prepare complex selenium!substituted tri! selenocarbonates such as "05# "Scheme 4# ð65CC037\ 72CC124Ł[ Heating 0\1\2!benzoselenadiazole in re~uxing xylene in the presence of a two!fold excess of carbon diselenide a}ords benzo!0\2!diselena! 1!selone "06# in 58) yield "Equation "8## ð72CC184Ł[ Se NaC CH
+
+ Se
CSe2
Se
Se
H+
Se
Se– Na+
Se (15)
Scheme 4 –Se
CSe2
Se
e–
Br
Se
Se
Se
Se (16)
Se
Se
–Se
Se Br
Scheme 5 N N Se
CSe2 ∆
Se Se Se (17)
(9)
480
At Least One Chalco`en
Treatment of alkyl halides with carbon diselenide and potassium hydroxide in dimethyl sulfoxide a}ords a variety of both cyclic and acyclic triselenocarbonates "07# in moderate yields "Equation "09## ð56ACS0870Ł[ It should be noted that the expected direct preparation of acyclic triseleno! carbonates via reaction of a selenolate with carbon diselenide\ followed by alkylation\ fails to a}ord the desired product "Equation "00## ðB!62MI 508!94Ł[ +
RX
CSe2
+
Se
DMSO
KOH
(10) SeR
RSe (18) R = –(CH2)2–, –(CH2)3–, –CH2Ph, –CH2CO2H, –Me
Se
Se
+
RSe–
(11)
CSe2 Se–
RSe
SeR
RSe
Reaction of cyclic iminium intermediates such as "08# with hydrogen selenide provides a con! venient route to substituted unsaturated triselenocarbonates "Scheme 5 ð64JOC635Ł\ Scheme 6 ð73CC78Ł\ Scheme 7 ð66CC494Ł and Scheme 8 ð79CC755A\ 79CC755BŁ#[ The required iminium salts can be obtained by cyclization of diselenocarbamates[ The latter two approaches have the advantage that they avoid the use of carbon diselenide as a source of selenium[ Se
R
R
+
Se–
N
Se
Br
Se
+
H2Se
ClO4–
N
N
R
Se
R
Se
Se
Se
R
H2SO4 HClO4
O
O
R
Se
R
R
(19) Scheme 6
Se
Se
O
N
+
Se
H+
Se
N
Se O
2
2
H2SO4, 0°C
+
Se
Se
H2Se
N
Se
Se
Se (15)
Scheme 7
R R
Se
R
Se
NMe2
Me2N
O O
O
R
Se
+
Br
R
R
R Se
H+
NMe2
Se
Me +
N
R
Se Scheme 8
Me
+
H2Se
NMe2 NMe2 R
Se
R
Se
H2Se
Se
481
Selenocarbonyl or Tellurocarbonyl O
+
Cl Cl–
Me2N
Et3N
Cl
R
Se
+ N
Se
R
R
Se
Br
Se–
Me2N
R
R
Se
H2Se
Me2N
+
Et3NH
CF3CO2H
R
Se
H2SO4
O
Me
R
Se
R
Se
H2Se
Se
Me Scheme 9
Thiocarbonyl compounds can similarly be converted to the corresponding selenocarbonyl deriva! tives by alkylation followed by hydrogen selenide treatment "Scheme 09# ð72CC183Ł[ The tri! selenocarbonate moiety has been incorporated into more complex structures by an extrusionÐ cycloaddition sequence "Equation "01## ð78CC0419Ł[ The previously described metallation route to other selenocarbonates "Scheme 2# has also been used for functionalization of cyclic 3\4!unsaturated triselenocarbonates ð81JOM"316#102Ł[ Se
Se
(MeO)2+ CHBF4–
S
Me +
S
Se
Se
H2Se
Se Se
Se Scheme 10
OEt
Se Se
reflux
Se
OEt
OHC
toluene
+
OHC
Se Se
EtO
(12)
Se
EtO
Bis"tri~uoromethyl# triselenocarbonate "19# has been prepared from 1\1\3\3!tetra~uoro!0\1! selenetane and B"SeCF2#2 "Equation "02## ð79ZN"B#415Ł[ Another less general triselenocarbonate preparation involves the alkylation of barium triselenocarbonate "Equation "03## ð60CB0318Ł^ however\ whether the structure of the product obtained is in fact a triselenocarbonate appears to be questionable ðB!62MI 508!92Ł[ Se
F
Se
F
+ F
Se
B(SeCF3)3
(13)
F
SeCF3
F3CSe (20)
SeMe BaCSe3 + 2 MeI
(14)
Se SeMe
5[08[2[3 Selenocarbonyl Functions Flanked by Two Different Chalcogen Atoms\ RX"C1Se#YR Compounds of this type are best prepared from intermediate diselenoxanthate salts[ For example\ treatment of carbon diselenide with alkoxides and alkylation a}ords O!alkyl diselenocarbonates "10# "Scheme 00# ð69ACS1950Ł[ S!Alkyl derivatives "11# can be similarly prepared using thiolates "Scheme 01# ð69ACS1944Ł[ Se RO–
+
RO
Se
RX
CSe2 Se–
SeR
RO (21)
Scheme 11
482
At Least One Chalco`en Se RS–
+
RS
Se
RX
CSe2 Se–
SeR
RS (22)
Scheme 12
The cyclic selenocarbonate "12# can be prepared by treatment of 1!hydroxythiophenol with Viehe|s salt\ followed by addition of sodium hydrogen selenide "Equation "04##[ The acyclic derivative "13# could be similarly prepared by consecutive treatment of Viehe|s salt with phenol and butanethiol\ followed by sodium hydrogen selenide treatment "Equation "05## ð77AJC438Ł[ OH +
+
Me2N
CCl2 Cl–
O
NaHSe
Se
(15)
Se
SH
(23)
+
CCl2 Cl–
Me2N
i, PhOH ii, BuSH iii, NaHSe
Se (16) SBu
PhO (24)
Heterocyclic organometallic selenocarbonate derivatives such as "14# have been prepared by addition of osmiumÐformaldehyde complexes to carbon diselenide "Equation "06## ð72JOM"133#C42Ł[ Mixed selenocarbonates can also be metallated to more complex derivatives as previously described "Scheme 2# ð81JOM"316#102Ł[ L2(CO)2Os
CSe2
O
O
L2(CO)2Os Se (25)
(17) Se
5[08[2[4 Selenocarbamates RO"C1Se#NHR\ RS"C1Se#NHR\ and RSe"C1Se#NHR Monoselenocarbamates can be prepared by a variety of methods[ Treatment of an alcohol with an isoselenocyanate a}ords the corresponding selenourethane "15# in good yield "Equation "07## ð61BCJ1826Ł[ Addition of hydrogen selenide to an alkyl cyanate a}ords primary mono! selenourethanes "16# "Equation "08## ð55ACS1980Ł[ These compounds can also be prepared by ammonolysis or hydrazinolysis of diselenocarbonates "Equations "19#\ "10## ð53ACS1306\ 69ACS1950\ 61ANY"081#090Ł[ Se RNCSe + R1OH
OR1 RHN (26)
(18)
Se ROCN + H2Se
NH2
RO
(19)
(27) Se
Se RO
(20)
Se
NH2NH2
SeR1
NH2
RO
SeR1
RO
Se
NH3
(21) RO
NHNH2
An aryl selenocarbamate "5# was the unexpected major product in the previously described attempt to prepare a cyclic dioxygen!substituted selenocarbonate "Equation "6##[
483
Selenocarbonyl or Tellurocarbonyl
Selenothiocarbamates "17# can readily be prepared by alkylation of thioureas\ followed by treat! ment of the intermediate salts with sodium hydrogen selenide under slightly acidic conditions "Scheme 02# ð58JOC2438Ł[ Under basic conditions the corresponding selenoureas are obtained "see below\ Equation "17##[ S
SMe
MeI
NR2
R2N
Se
HSe–
+
NR2
R2N
SMe
R2N
pH 5–6
(28) Scheme 13
Reactions of carbon diselenide with secondary amines a}ord salts of diselenocarbamic acids "18# "Equation "11## ð56ACS1893\ 57ZC129\ 69ACS240\ 61IJS"A#022Ł[ Related salts can be prepared by the reaction of phosgeneiminium chloride with hydrogen selenide in the presence of triethylamine "see above\ Scheme 8#[ This route avoids the use of carbon diselenide ð79CC755A\ 79CC755B\ 75BCJ0630Ł[ Such salts can readily be alkylated to the corresponding diselenocarbamates "29# "Equation "12## ð50JCS1811\ 75BCJ0630Ł[ R2NCSe2– R2NH2+
2 R2NH + CSe2
(22)
(29)
Se Se–
N
Se
R O
+
R
Se
Br
R
N
(23)
O R
(30)
Salts of dialkyl selenocarbamates under mild oxidative conditions a}ord mixtures of bis"seleno! carbamoyl# selenides "21# and the corresponding triselenides "22# "Scheme 03# ð50JCS1811\ 69ACS848\ 71S660Ł[ This reaction proceeds through an intermediate unstable diselenide "20# that is in equilibrium with these species[ The monoselenide "21# can be converted to the triselenide "22# upon treatment with elemental selenium[ Conversely\ treatment of the triselenide with triethyl phosphite a}ords the monoselenide "Equation "13## ð71S660Ł[ Se [O]
2 R2NCSe2– R2NH2+
2
R2N
Se
NR2
Se Se
(31) Se
Se
Se R2N
NR2
Se
NR2
Se
Se
R2N
+
Se
Se
(32)
(33) Scheme 14
Se
Se R2N
Se (32)
Se
Se8
NR2
P(OEt)3
R2N
Se NR2
Se Se (33)
(24)
Se
Hydrazines react with carbon diselenide to a}ord diselenocarbazate salts "23# "Equation "14## ð55ACS1631Ł[ Nickel complexes of these compounds can be prepared but appear to have eneselenolate structures such as "24# ð55ACS1631Ł[ The free diselenocarbazic acids "25#\ which can be prepared by
484
At Least One Chalco`en
acidi_cation of the simple salts "Scheme 04#\ are reported in some cases to be more stable than the corresponding dithiocarbazic acids ð69ACS848Ł[ Se +
Me2HN
Me2NNH2 + CSe2
(25)
Se–
N H (34)
SeH Me2NN Se
Ni 2
(35)
Se MeNHNHMe + CSe2
+
Se
HCl
Se–
MeNH2NMe
SeH
MeNHNMe (36)
Scheme 15
Heterocyclic selenocarbamate derivatives*oxazolidine!1!selones "26#*have been prepared by a variety of routes[ Mercuric chloride!promoted reaction of 0\1!amino alcohols with carbon diselenide readily a}ords this class of compounds in moderate yields "Equation "15## ð79JHC460\ 78H"17#158Ł[ Another route to these compounds that avoids the problems associated with the use of carbon diselenide is outlined in Scheme 05 ð80JCS"P0#1384Ł[ This route allows a large!scale preparation of chiral oxazolidineselones such as "27#\ useful as NMR shift reagents[ A more direct route to these compounds involves metallation and direct selenation of the corresponding readily available oxazolines "28# "Equation "16## ð80JOC5622Ł[
R1 R HO
H
R3
R2 R3 NH2
HgCl2
+ CSe2
N
R2 R1
MeCN
Se
(26)
O R (37)
OHC HO
NH2
TBDMS-O
TBDMS-Cl TEA
Ph
NH2
TBDMS-O
HCO2H
Ph
NH
Ph
C– TBDMS-O
POCl3
Se
N+
TBDMS-O
Se0
Ph
N
•
Se
tbaf
Ph
O
NH
Ph (38)
TBDMS = t-butyldimethylsilyl Scheme 16
Se N
O
i, base ii, Se0
HN
O (27)
R
R1
iii, citric acid
R
R1
485
Selenocarbonyl or Tellurocarbonyl
5[08[2[5 Phosphorus!substituted Selenocarbonyl Derivatives Reaction of trialkylphosphines with carbon diselenide a}ords moderately stable zwitterionic selenocarbonyl compounds "39# "Equation "17## ð52ACS438\ 69QRS34Ł[ Complex reaction mixtures were obtained using triphenylphosphine[ Se R3P + CSe2
(28)
+
Se–
R3P R=Me, Et, Pr
(40)
5[08[3 FUNCTIONS CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGEN OR CHALCOGEN FUNCTIONS# 5[08[3[0 Selenoureas "R1N#1C1Se Selenoureas are probably the most widely studied selenocarbonyl derivatives[ The early chemistry associated with the preparation and reactions of this class of compounds has been reviewed ðB!62MI 508!95Ł[ Selenoureas can be prepared using a variety of general methods[ Thioureas can be converted to selenoureas "30# via an alkylationÐdisplacement sequence\ provided the pH is kept in the range 7Ð8 "Scheme 06# ð52BSB038\ 58JOC2438Ł[ Reaction at a more acidic pH a}ords the selenocarbamate instead "see Scheme 02#[ This route provides a convenient method for the preparation of both tri! and tetrasubstituted selenoureas[ S
SMe MeI
Me2N
NMe2
+
Se I–
NMe2
Me2N
NaHSe
NMe2
Me2N
pH 8–9
(41) Scheme 17
Reaction of isoselenocyanates with ammonia\ primary amines\ or secondary amines provides another general route to mono!\ di!\ or trisubstituted selenoureas "Equation "18## ð48M30\ 52JOC0531\ 52ZC237\ 56CB0262\ 56CB0348\ 79S59Ł[ Reaction of a primary ammonium salt with selenocyanate ion also a}ords the monosubstituted selenourea "Equation "29## ð48G582Ł[ Se RNCSe + R12NH
RHN
(29)
NR12 Se
+
PhCH2NH3
Cl–
+ KSeCN
Ph
NH2
N H
(30)
Carbodiimides react with hydrogen selenide to a}ord 0\2!disubstituted selenoureas "Equation "20## ð42JOC181Ł[ Cyanamides also react with H1Se to a}ord unsubstituted\ mono! or 0\0!di! substituted selenoureas "Equation "21## ð36JA0722\ 40JA0753\ 42JOC181\ 52OSC"3#248Ł[ Se RN
•
+ H2Se
NR
(31) NHR
RHN Se R2N
N
+ H2Se
(32) R2N
NH2
Cyanamide and cyanamide salts are reported to react with phosphorus pentaselenide in aqueous solution\ presumably via formation of H1Se\ to a}ord selenourea "Equation "22## ð80EGP180641Ł[ Phosphorus pentaselenide is reported to convert urea into selenourea in only poor yield "Equation
486
At Least One Nitro`en
"23## ð55ACS170Ł[ N\N!Dimethylcyanamide is also reported to react with another selenating reagent\ bis"trimethylsilyl# selenide\ to a}ord 0\0!dimethylselenourea in low yield "Equation "24## ð89CL0392Ł[ Se
H2O
N +
H 2N
(P2Se5)n
Se
O
+
(P2Se5)n
(34) NH2
H2N
NH2
H2N
(33)
NH2
H 2N
50–100 °C
Se Me2N
+ (TMS)2Se
N
(35) NH2
Me2N
Treatment of dibenzyl triselenocarbonate "31# with excess primary amine a}ords symmetrical 0\2!disubstituted selenoureas\ presumably via an isoselenocyanate intermediate "32# "Scheme 07# ð61ANY"081#090Ł[ Treatment of carbon diselenide with excess primary amine also a}ords a 0\2!di! substituted selenourea ð25CB0245Ł[ This reaction also probably involves an isoselenocyanate inter! mediate "Scheme 08#[ Se Ph
Se Se (42)
Se
+
Ph
RNH2
RN
•
Se
NHR
Se
Ph
–PhCH2SeH
Se
RNH2
RHN
NHR
(43) Scheme 18
Se RNH2 + CSe2
RN
RHN
•
Se
+
–
–RNH3SeH
+
Se– RNH3 Se
RNH2
RHN
NHR
Scheme 19
Tetrasubstituted selenoureas can be prepared from selenocarbamoyl selenides or triselenides "33# "see Scheme 03# by treatment with secondary amines at elevated temperature in the presence of oxygen "Equation "25## ð71S660Ł[ Se
+ R2N
Se
O2
(36)
2 R2NH 70 °C
Sen
NR2
R2N
2
(44)
n = 1, 3
Selenobiurets "34# can be prepared from the corresponding thiocarbonyl analogs by an alkylationÐ selenation procedure similar to that used for the preparation of simple selenoureas "Equation "26##[ X
S
X
Se
i, MeI
(37) H 2N
N H (45)
NH2
ii, NaHSe
X = O, S, Se
H2N
N H
NH2
487
Selenocarbonyl or Tellurocarbonyl
Heterocyclic selenoureas such as selenopyrimidines "35# and selenobarbiturates "36# have been prepared from selenourea and b!dicarbonyl compounds "Equations "27# and "28## ð45JA4181\ 48JA5169Ł[ O EtO2C R
R
HN
selenourea
ONa
(38)
Se
N H (46)
O R HN
selenourea
(EtO2C)2CR2
Se
R N H
(39)
O
(47)
Metallation of N!methylimidazole at low temperature followed by selenation with elemental selenium a}ords the selenium analogue "37# of the antithyroid drug MMI "Equation "39## ð83JOC3580Ł[ Me
Se
N
Me
i, BuLi, –78 °C
N
NH
(40)
Se0
ii, iii, H+
N
(48)
Selenosemicarbazides "38# can be prepared by reaction of an isoselenocyanate with a hydrazine "Equation "30## ð51BSB430\ 55ACS167\ 56CB0262Ł[ These compounds can be converted to the cor! responding selenosemicarbazones ð45JA86\ 51BSB430\ 55ACS167\ 56CB0262Ł[ Se RNCSe + R1NHNH2
N H (49)
RHN
H N
R1
(41)
Other biologically interesting complex selenocarbonyl derivatives have also been prepared via displacements using selenourea[ These include the selenium analogue of the benzodiazepin drug {{TIBO|| "49# "Equation "31## ð80JMC2076Ł and selenoguanosine derivatives "40# and "41# "Scheme 19# ð80TL3712Ł[ The latter compound is formed via a novel polyhetero!Claisen rearrangement[ Finally\ tris"methylphenylamino#methane "42# reacts with elemental selenium to a}ord the cor! responding selenourea in good yield "Equation "32## ð76CB0470Ł[ Cl N
Se
N H2N
Se
H N
N NH2
(42) N H
N H (50)
Se
Me HC
220 °C
+ Se°
N Ph (53)
melt 3
Ph
N
N
Me
Me
Ph
(43)
488
At Least One Nitro`en O
O N
HN H2N
Br N
H N
HN Se
N
+
OH
Br
OH
NH2
H2N
O
Se N
N
H2N
O OH
OH HO (51)
HO
O N
HN
N
HN
Se N
H2N
O
heat
N
Se N
H2N
OH
N OH
O
O OH
OH
HO
HO (52) Scheme 20
5[08[3[1 Telluroureas "R1N#1C1Te Cyclic telluroureas "44# have been prepared by tellurium!promoted cleavage of the tetra! aminoethylene derivatives such as "43# "Equation "33## ð79CC524Ł[ A variety of metal penta! carbonyl complexes of these compounds "46# have also been prepared by treatment of the telluroureas with the metal isonitrile pentacarbonyl complex "45# "Equation "34## ð79CC524Ł[ R
R
R
N
N
2 Te
N
N
N
∆
N
R R (54)
R (55)
R = Me, Et Et
Et
N
N Te N
(44)
Te
Te
+ M(CO)5(NCMe)
M(CO)5
(45)
N
M = Cr, W, Mo
Et
Et
(57)
(56)
Tellurium is also reported to react with 0\2!dimethylbenzimidazoline at elevated temperature to a}ord the corresponding cyclic tellurourea "47# "Equation "35## ð58ZOB830Ł[ Me
Me N
2 Te
N
N
∆
N
Te
(46)
Me
Me (58)
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.20 Functions Containing an Iminocarbonyl Group and at Least One Halogen; Also One Chalcogen and No Halogen THOMAS L. GILCHRIST University of Liverpool, UK 5[19[0 FUNCTIONS CONTAINING AT LEAST ONE HALOGEN 5[19[0[0 Iminocarbonyl Halides with Two Similar Halo`en Functions 5[19[0[0[0 Carbonimidic di~uorides\ F1C1NR 5[19[0[0[1 Carbonimidic dichlorides\ Cl1C1NR 5[19[0[0[2 Carbonimidic dibromides\ Br1C1NR 5[19[0[0[3 Carbonimidic diiodides\ I1C1NR 5[19[0[1 Iminocarbonyl Halides with Two Dissimilar Halo`en Functions 5[19[0[1[0 Carbonimidic chloride ~uorides\ ClFC1NR 5[19[0[1[1 Carbonimidic bromide ~uorides\ BrFC1NR 5[19[0[1[2 Carbonimidic bromide chlorides and carbonimidic chloride iodides\ ClXC1NR "X Br or I# 5[19[0[2 Iminocarbonyl Halides with One Halo`en and One Other Heteroatom Function 5[19[0[2[0 Iminocarbonyl ~uorides with one other heteroatom function 5[19[0[2[1 Iminocarbonyl chlorides with one other heteroatom function 5[19[0[2[2 Iminocarbonyl bromides and iodides with one other heteroatom function 5[19[1 FUNCTIONS CONTAINING AT LEAST ONE CHALCOGEN "AND NO HALOGENS# 5[19[1[0 Iminocarbonyl Compounds with Two Similar Chalco`en Functions 5[19[1[0[0 Iminocarbonyl compounds with two oxy`en functions 5[19[1[0[1 Iminocarbonyl compounds with two sulfur functions 5[19[1[0[2 Iminocarbonyl compounds with two selenium functions 5[19[1[1 Iminocarbonyl Compounds with Two Dissimilar Chalco`en Functions 5[19[1[1[0 Iminocarbonyl compounds with one oxy`en and one sulfur function 5[19[1[1[1 Iminocarbonyl compounds with one oxy`en or sulfur and one selenium or tellurium function 5[19[1[2 Iminocarbonyl Compounds with One Chalco`en and One Other Heteroatom Function 5[19[1[2[0 Iminocarbonyl compounds with one oxy`en and one nitro`en function 5[19[1[2[1 Iminocarbonyl compounds with one oxy`en and one phosphorus function 5[19[1[2[2 Iminocarbonyl compounds with one oxy`en and one metalloid or metal function 5[19[1[3 Iminocarbonyl Compounds with One Sulfur and One Other Heteroatom Function 5[19[1[3[0 Iminocarbonyl compounds with one sulfur and one nitro`en function 5[19[1[3[1 Iminocarbonyl compounds with one sulfur and one phosphorus function 5[19[1[3[2 Iminocarbonyl compounds with one sulfur and one metalloid or metal function 5[19[1[4 Iminocarbonyl Compounds with One Selenium and One Other Heteroatom Function
590
591 591 591 593 509 501 501 501 502 502 503 503 505 512 512 512 512 515 517 517 517 529 520 520 523 523 523 523 525 526 526
591
Iminocarbonyl and Halo`en or Chalco`en
5[19[0 FUNCTIONS CONTAINING AT LEAST ONE HALOGEN 5[19[0[0 Iminocarbonyl Halides with Two Similar Halogen Functions In the mid!0889s these iminocarbonyl halide compounds XYC1NR "X\ Y halogen# are named in Chemical Abstracts as carbonimidic dihalides^ they are also commonly called isocyanide dihalides[ Methods of synthesis of compounds of this type have been reviewed previously[ The most important of these reviews are by Ulrich ðB!57MI 519!90Ł\ by Ulrich and Richter ðB!66MI 519!90Ł\ by Kuhle et al[ ð56AG"E#538\ B!60MI 519!90Ł and by Kuhle ð72HOU"E3#411Ł[ The reviews by Ulrich and those by Kuhle and colleagues all contain experimental details for the preparation of some compounds of this class[ Several speci_c compounds containing ~uorine are covered in appropriate sections of the Gmelin Handbooks on per~uorohaloorganic compounds ðB!68MI 519!90\ B!79MI 519!90\ B!70MI 519!90Ł[
5[19[0[0[0 Carbonimidic di~uorides\ F1C1NR Carbonimidic di~uoride compounds have been reported with R H\ D\ alkyl\ perhaloalkyl\ aryl\ hetaryl\ acyl! and with a variety of heteroatomic substituents on nitrogen[ No methods exist which can be used to prepare all these types of compound but there are methods which have some generality\ these are listed below[ Methods which are speci_c to derivatives of one type are described for the compounds concerned[
"i# From tri~uoromethylamines\ F2CNHR Tri~uoromethylamines serve as precursors to carbonimidic di~uorides of various types\ including the parent compound "R H#[ Conditions and reagents used to bring about the dehydro~uorination vary depending upon the substituent\ but low temperatures are desirable because several types of carbonimidic di~uoride dimerise easily at ambient temperatures[ Triethylamine and potassium ~uoride have been used most often as co!reagents[ Examples of carbonimidic di~uorides which have been prepared by this method are listed in Table 0[ Table 0 Carbonimidic di~uorides formed by dehydro~uorination of tri~uoramines\ F2CNHR[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R Rea`ents and conditions ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * H NEt2\ 084Ð152 K 77CC094 NaF\ 039>C 69 48JGU1551 CF2 Ph KF\ 039>C 48JGU1551 B!60MI 519!90 C5H3Cl!3 NEt2\ MeCOCl\ 39>C 27 B!60MI 519!90 OMe\ OBut\ OCF2 KF\ −085Ð13>C 70JFC"07#330 KF\ −085Ð13>C 81 89EUP242632 OCF1CF2 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
"ii# From carbonimidic dichlorides Some carbonimidic dichlorides have been converted into the corresponding di~uorides[ Tri! ~uoroamines can be intermediates\ so that in such examples the method is an extension of method "i#[ This is illustrated by the reaction of N!arylcarbonimidic dichlorides with hydrogen ~uoride to give N!aryltri~uoroamines which are then dehydro~uorinated by heating with potassium ~uoride "Scheme 0# ð55AG"E#737\ B!60MI 519!90Ł[ Aromatic carbonimidic dichlorides can also be converted into the di~uorides by heating with an alkali metal ~uoride in a high boiling inert solvent^ for example\ N!pentachlorophenylcarbonimidic di~uoride is obtained from the dichloride and pot! assium ~uoride in 57) yield ðB!60MI 519!90Ł[ Related preparations of compounds F1C1NXF4 "X S or Te# have been described starting from the corresponding carbonimidic dichlorides "Scheme
592
At Least One Halo`en
1# "X S] ð65IC03\ 77IC469Ł\ X Te] ð74IC3060Ł# and the azine F1C1NN1CF1 has been prepared by heating the corresponding tetrabromide with silver ~uoride ð51JOC1478Ł[ F1C1NCF2 is prepared in good yield by heating Cl1C1NCCl2 with an excess of sodium ~uoride in sulfolane ð61GEP1090096Ł[ Cl
F
F
HF
NR
F
Cl
NR
NHR F
F Scheme 1
Cl
HgF2
NXF5 Cl
CF3
F
XF5
F
Hg N heat
NXF5 2
Scheme 2
"iii# From isothiocyanates The conversion of several aryl isothiocyanates into carbonimidic di~uorides has been achieved by reaction with mercury"II# ~uoride and other metal ~uorides ð54JA3227Ł[ N!Ethylcarbonimidic di~uoride was also prepared "26)# by this method[
"iv# From isocyanides The reaction of isocyanides RNC "R But\ Ph\ 1!ClC5H3\ and 1!FC5H3# with ~uorine at −67>C leads to the formation of the corresponding carbonimidic di~uorides ð79TL3782Ł[
"v# Dehalo`enation methods The best methods for the preparation of the N!halocarbonimidic di~uorides start from nitriles[ An e.cient synthesis of the N!chloro compound is shown in Scheme 2 ð72JOC3733Ł and the N!~uoro analogue can be prepared in a related way by dechlorination of ClCF1NClF with mercury in tri~uoroacetic anhydride ð70JOC0166\ 73IC1077Ł[ Several N!per~uoroalkyl compounds\ including F1C1NCF2 and F1C1NCF1CF1N1CF1\ have been made by a related photochemical dechlori! nation method ð89IC460Ł[ N!Bromocarbonimidic di~uoride is prepared from cyanogen ~uoride\ bromine and potassium ~uoride ð73JA3155\ 77JOC3332Ł[ The reaction of "CF2#1NX "X Br or Cl# with iron pentacarbonyl leads to the formation of F1C1NCF2 in high yield ð54JCS4663Ł[ A related reductive method has provided a route to carbonimidic di~uorides "0# "Equation "0##[ The reaction of chlorodi~uoronitrosomethane with diethyl phosphite gave "0# "31)# ð58JGU0583Ł[ Cl
N
ClF 85%
Cl F F
135 °C
F
85%
F
NCl2
NCl
Scheme 3
Cl F F
N O
+
H EtO P O EtO
F 42%
N F
O O P OEt OEt
(1)
(1)
"vi# Speci_c methods Some methods which are useful for speci_c derivatives or for speci_c groups of compounds are discussed under this heading[
593
Iminocarbonyl and Halo`en or Chalco`en
The hydrolysis of tri~uoromethyl isocyanate in triethylamine has been used to prepare car! bonimidic di~uoride^ F1C1ND has also been made in this way ð81ZN"B#240Ł[ Among the many methods which can be used to prepare N!tri~uoromethylcarbonimidic di~uoride ðB!68MI 519!90Ł\ several involve the vapour phase pyrolysis of copolymers of tri~uoronitrosomethane and per! haloalkenes ð44JCS0770\ 53JCS0240\ 54JCS5198\ 80MI 519!90Ł[ The compound can also be formed by decomposition of "CF2#1NOSN ð75JFC"23#35Ł[ The vapour phase pyrolysis of oxazetidines "1#^ R CF2\ C1F4 and C2F6# also provides a route to the corresponding per~uoroalkylcarbonimidic di~uorides "Equation "1## ð45JCS2305\ 53JCS0240\ 53JCS3955Ł[ The imine "CF2#1C1NCF2 is isomerised to F1C1NCF"CF2#1 by heating with caesium ~uoride as a catalyst ð80JFC"42#070Ł[ F
F
F
F
F
(2)
NR
O N
F
R (2)
The pyrolysis of di~uorodiazirine provides a route to F1C1NN1CF1 ð57JHC30\ 73USP3335957Ł[ Perhaloalkenes can be inserted into the N0N bond of this azine by irradiation of the mixture to give new carbonimidic di~uorides "for example\ the compound F1C1NCF1CF1N1CF1 from tetra~uoroethylene# ð56JA2757Ł[ The hydrazone "2# has been isolated from the photolysis of the azoalkane "3#^ the reaction sequence shown in Scheme 3 can account for its formation ð89JOC0492Ł[ F
F N
F F
F N
F
F
• N
RH
F
N
F •
F
H N
N N
F
N
Et
Et (3)
(4) Scheme 4
5[19[0[0[1 Carbonimidic dichlorides\ Cl1C1NR The dichlorides are by far the most numerous of the carbonimidic dihalides^ a few compounds of this class have been identi_ed as natural products ð66JA6256\ 67TL0280\ 67TL0284Ł and there are several well!established methods of synthesis of dichlorides bearing a wide variety of functional groups on nitrogen[ The review by Kuhle ð72HOU"E3#411Ł provides a valuable survey of the literature up to 0871^ this and the earlier review by Kuhle et al[ ðB!60MI 519!90Ł contain experimental details of preparations and tables of examples which are not readily accessible from other sources[ The major methods of preparation are detailed below and\ where appropriate\ examples of their use are quoted\ particularly when the original paper gives experimental details[ "i# From isothiocyanates The oldest method of preparation is from isothiocyanates] it is known for alkyl!\ aryl!\ acyl!\ phosphoryl! and sulfonyl!substituted carbonimidic dichlorides[ The chlorination of alkyl and acyl isothiocyanates is usually carried out with chlorine in an inert solvent and the products can sometimes be isolated in good yield\ for example R Me\ 74) ð48JGU1020Ł^ R Ph\ 85) ðB!60MI 519!90Ł^ R b!tetraacetylglucosyl\ 81) ð76AG"E#248Ł[ The method is not completely general] the products can be unstable "as with 1!nitrophenyl isothiocyanate# or they can undergo further reaction with chlorine "e[g[\ reaction of phenyl isothiocyanate with an excess of chlorine in chloroform results in further chlorination at the 3!position of the ring ð53JOC0502Ł#[ The course of the reaction of chlorine with isothiocyanates is shown in Scheme 4\ the intermediate sulfenyl chlorides "4# having been isolated in a few cases[
RN
•
S
Cl2
ClS
Cl NR
Cl
NR Cl
(5) Scheme 5
594
At Least One Halo`en
Acyl isothiocyanates can be chlorinated in much the same way\ with chlorine in an inert solvent ðB!60MI 519!90\ 64JCS"P1#0935Ł[ A Lewis acid catalyst facilitates the reaction and both aluminium"III# chloride and titanium"IV# chloride have been used[ An example of the e}ect of a catalyst is shown in Scheme 5[ Chlorination of carbonyl diisothiocyanate "5# in the absence of a catalyst gave the carbonimidic dichloride "6# but in the presence of iodine both functional groups were chlorinated to give "7# ð71CB2476Ł[ The thiocyanato group of carbonyl isocyanate isothiothiocyanate "8# has also been selectively chlorinated to give compound "09# in good yield^ the isocyanate function can then be selectively hydrolysed ð70CB1953Ł[ N O N
•
S
N
•
S
O
Cl2
N
68%
(7)
S Cl Cl
Cl
Cl2, I2(cat.) 78%
(6)
•
N
Cl
O
Cl
N
Cl (8) N
•
O
Cl2
O N
•
N
82%
S
•
O
O Cl
O quant.
N (10)
(9)
NH2
H2O
Cl N
Cl
Cl
Scheme 6
Phosphoryl isothiocyanates are similarly readily chlorinated but the chlorination of sulfonyl isothiocyanates is more sluggish[ An alternative is to use related reagents such as the dithiocarbamate salts "00# ðB!60MI 519!90Ł or the corresponding bismethyl compounds "01# ð72AQ"C#004Ł\ both readily available from the corresponding sulfonamide[ Both are more readily chlorinated than the iso! thiocyanate[ The benzothiazolyl!substituted carbonimidic dichloride "02# has been obtained "54)# in an analogous manner by chlorination of the corresponding bis"methylthio# compound ð73S419Ł[ The _nal product of chlorination of trimethylsilyl isothiocyanate is the sulfenyl chloride Cl1C1NSCl ðB!60MI 519!90Ł[ Cl N Cl Na+ –S
Cl
NSO2Ar
NSO2Ar Na+ –S
N S
MeS MeS (11)
(12)
(13)
"ii# From isocyanides The addition of chlorine to isocyanides in the cold is also a long!established method for the preparation of carbonimidic dichlorides[ It has been used mainly for alkyl derivatives\ for example R But\ 41) ðB!60MI 519!90Ł\ R TsCH1\ 56) ð70JHC0016Ł and R PhCH1\ 57) ð75T1566Ł[ Aryl derivatives can also be prepared by this method and because of the mild reaction conditions it can be useful for the preparation of compounds which are sensitive to further chlorination ð76CB310Ł[ A speci_c preparation based on an isocyanide is the formation of chromium carbene complexes by
595
Iminocarbonyl and Halo`en or Chalco`en
reaction of coordinated trichloromethyl isocyanide with secondary amines "Equation "2## ð77AG"E#0233\ 78CB0896Ł[ Cl R2NH
Cl3CNCCr(CO)5
N Cl
17–73%
(3)
: Cr(CO)5 R2 N
"iii# From formanilides Many N!arylcarbonimidic dichlorides have been prepared in good yield from the corresponding formanilides by chlorination in thionyl chloride as a solvent "Equation "3## ð51AG"E#536\ B!60MI 519! 90Ł[ Sulfuryl chloride is most often used as the chlorinating agent[ The method is most e.cient for aryl derivatives with deactivating groups on the ring which inhibit ring chlorination[ Examples from more recent literature include preparation of the 2!tri~uoromethylphenyl derivative ð76JCS"P0#0958Ł\ the 3!cyanophenyl derivative ð81SC0080Ł and the 1\5!dichloro!3!nitrophenyl derivative ð76JMC0130Ł[ SO2Cl2, SOCl2
ArNHCHO
Cl (4)
ArN Cl
An example of the use of an analogous procedure for the preparation of an aliphatic carbonimidic dichloride is the preparation of Cl1C1NCH1CH1CN by chlorination of the corresponding for! mamide ð68GEP1642193\ 68GEP1643593Ł[
"iv# From isocyanates The reaction of several aliphatic isocyanates with chlorinating agents such as phosphorus penta! chloride is reported to give N!alkylcarbonimidic dichlorides[ For example\ methyl isocyanate ðB! 57MI 519!90Ł and butyl isocyanate ðB!60MI 519!90Ł have been converted into the corresponding dichlorides "in 72) and 49) yields# by reaction with a mixture of phosphorus pentachloride and phosphorus oxychloride[ The method is not a useful one for aryl derivatives because at the temperatures required for reaction phosgene is eliminated[ However\ there are examples of successful chlorination of phosphoryl and sulfonyl isocyanates ðB!57MI 519!90Ł[ Some a!chloroalkyl isocyanates exist in tautomeric equilibrium with carbonimidic dichlorides[ For example\ trichloromethyl isocyanate is in equilibrium with the chloroformyl derivative "03# "Scheme 6# and reaction of the mixture with antimony penta~uoride gave the ~uoride "04# as the major product ð77ZOB0405Ł[ Compound "03# is reported as the product of radical chlorination of methyl isocyanate ð74GEP2226828Ł^ it can be prepared in the laboratory by Curtius rearrangement of trichloroacetyl azide ð82T2116Ł[ Cl Cl
Cl N
Cl •
O
Cl SbF5
N Cl
O Cl (14)
65%
N Cl
O F (15)
Scheme 7
"v# From cyano`en chloride Cyanogen chloride is a very useful starting material for the preparation of a variety of car! bonimidic dichlorides[ Examples of several types which can be prepared from cyanogen chloride are given in Table 1[ Reaction of cyanogen chloride with chlorine in the presence of alkenes leads to the formation of N!"b!chloroalkyl#carbonimidic dichlorides "Equation "4## ð58JPR04\ 69S19Ł[ These {three component| reactions may go by way of Cl1C1NCl since this compound has been
596
At Least One Halo`en
shown independently to add to the double bond of alkenes ð58AG"E#595Ł[ A tetramer of cyanogen chloride\ prepared in the presence of hydrogen chloride and DMF\ has also been shown to be a carbonimidic dichloride "05# ðB!60MI 519!90Ł[ Cl N Cl
N N
Cl N
Cl (16)
Cl2,
Cl
N
Cl N
R
(5)
Cl Cl
R
Table 1 Carbonimidic dichlorides prepared from cyanogen chloride\ ClCN[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R Rea`ents and conditions ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * MeOCH1Cl\ 49>C\ 4 atm 09 55AG"E#734 CH1OMe Cl1\ H1C1CH1\ 9>C 08 58JPR04 CH1CH1Cl Cl1\ H1C1CHCl\ FeCl2 89 69S19 CH"Cl#CH1Cl Cl1\ ButCl\ FeCl2 80 62T186 But 59 69S19 MeC1CHCl Cl1\ H1C1C"Cl#Me\ FeCl2 ClCH1COCl\ 49>C\ 4 atm 53 55AG"E#734 COCH1Cl COPh PhCOCl\ 49>C\ 4 atm 19 55AG"E#734 62 58AG"E#595\ 76JFC"26#18 Cl Cl1\ 59>C\ carbon 16 47JCS653 SCl SCl1\ 9>C CF2SF3Cl\ hn 39 65IC03 S"CF2#SF3 TeF4Cl\ hn 21 74IC3060 TeF4 "CF2#1NCl\ hn 099 55JCS"A#822\ 81IC377 N"CF2#1 CF2"C1F4#NCl\ hn 59 78IC2234 N"CF2#C1F4 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
"vi# Other chlorination methods There are several useful examples of the formation of carbonimidic dichlorides by chlorination of amines and amides\ but none of the reactions is general[ Reaction of N\N!dimethylaniline with chlorine under carefully controlled conditions leads to the formation of the carbonimidic dichloride "06# in high yield ð51AG"E#521Ł[ Other examples of chlorination routes are shown in Scheme 7 ð58LA"629#022\ 67CB0508\ 72MI 519!90Ł[ Cl N
Cl
Cl Cl Cl (17)
MeHN
O
Cl Cl2, hν
N Cl
R
O R
Me2N
O
Cl Cl2, heat
N Cl
Cl Scheme 8
CCl3
597
Iminocarbonyl and Halo`en or Chalco`en
An important chlorination reaction is the reaction of glyoxylic acid aldoxime to give N!hydroxy! carbonimidic dichloride "Scheme 8#[ The chlorination has been carried out with chlorine ð77SC0060Ł and also with N!chlorosuccinimide or t!butyl hypochlorite ð78LA874Ł[ "This oxime can also be prepared by reductive methods ðB!60MI 519!90Ł^ e[g[\ it has been prepared by the reduction of trichloronitromethane with tin and HCl ð74USP3447059Ł[# The chlorination of glyoxylic acid aldoxime has an analogy in the formation of the hydrazone "07#\ a possible mechanism for which is shown ð61JOC1994Ł[
HO2C
Cl N
N OH
Cl
OH
Cl
HO2C
Cl2
N Cl
Cl
Cl N
O
NHAr
N N Ar
Cl
NHAr
O H
Cl Ar =
(18)
Cl Cl
Scheme 9
"vii# Methods involvin` introduction of the CCl1 fra`ment Dichlorocarbene can be transferred to a variety of nitrogen compounds to produce carbonimidic dichlorides ð61TL2716\ 62ZOR0648\ B!66MI 519!90Ł[ Some of these reactions are outlined in Scheme 09 ð57CC857\ 60JOC0675\ 62JA1871\ 72JPR676\ 81TL1228Ł[ The reaction of azidooctane with dichlorocarbene appears to be capable of extension to the preparation of other carbonimidic dihalides[
PriN
NPri
•
PhHgCCl2Br
Cl
Cl
+
PriN
NPri
NPri
63%
Cl
–
Cl Cl
PhHgCCl3
N
Cl
Ph
+
N
–
N
41%
Cl
Ph
Ph
Cl
n-C8H17N3
CHCl3, KOBut 89%
C4F9(CH2)2N3
CHCl3, NaOH 39%
Cl N Cl
C8H17
Cl Cl
N (CH2)2C4F9
Scheme 10
There are also some useful speci_c syntheses based on the formal transfer of CCl1 from tetra! chloromethane[ The hydrazone "08# has been synthesised by methods involving the low temperature reaction of tetrachloromethane with the azosilane "19# and with salts of silylated hydrazines ð60CB2878\ 65ZN"B#0206\ 75JOM"290#04\ 80ZAAC"594#020Ł[ These reactions probably involve
598
At Least One Halo`en
dichlorocarbene as an intermediate since compound "08# is also formed from "19# and a di}erent source of dichlorocarbene "Equation "5##[ TMS N N
CCl4, –78 °C or CHCl3, (TMS)2N–Na+
Cl
70%
Cl
TMS
(6)
N N(TMS)2
(20)
(19)
Some per~uoroaryl! and perchloroaryl!carbonimidic dichlorides can be synthesised by the reac! tion of the perhaloamine with tetrachloromethane and aluminium"III# chloride ð72JFC"11#328\ 72KGS687Ł and the same procedure has been used to convert penta~uorophenylhydrazine into the hydrazone "10# "Equation "6## ð75ZOR0186Ł[ N!Phenylcarbonimidic dichloride is one of the products of photolysis of mixtures of aniline and tetrachloromethane or chloroform ð78ZN"B#0478Ł and penta~uorophenylcarbonimidic dichloride is produced by the vapour phase pyrolysis of chloroform with penta~uoroaniline ð66JFC"8#494Ł[ Cl C6F5NHNH2
CCl4, AlCl3
N Cl
49%
(7)
N C6F5 Cl3C (21)
"viii# From other carbonimidic dichlorides Carbonimidic dichlorides with reactive functional groups attached to nitrogen can be converted into other carbonimidic dichlorides and in some cases this provides the best route to the new species[ The addition of N!chlorocarbonimidic dichloride to carbonÐcarbon double bonds has been referred to earlier^ this compound also reacts with sulfur\ in a process catalysed by chloride ions ð63TL0576Ł and with dimethyl or diphenyl disul_de "Scheme 00# ð63TL0580Ł[ The sulfenyl chloride Cl1C1NSCl\ like other sulfenyl halides\ adds readily to alkenes] the adduct with cyclohexene has been isolated in 79) yield ð47JCS653Ł[ New acylcarbonimidic dichlorides can also be formed from Cl1C1NCOCl\ an example being the generation of the phosphorus!containing species "11# "Equation "7## ð67JGU0401Ł[ Cl Cl
N NSCl
S8, Cl–
Cl
S N
Cl
Cl NCl
+ Cl
Cl 50%
Cl 30%
PhSSPh 90%
Cl NSPh Cl Scheme 11
Cl N Cl
Cl O
Cl3C + Cl3C P Cl
Cl
Cl NH
P
N Cl
N
CCl3 CCl3
(8)
O (22)
"ix# Methods for dichloroiminium cations Salts of the type "12^ R0\ R1 alkyl# are very useful synthetic intermediates[ The methods of preparation and their chemistry have been reviewed by Janousek and Viehe ðB!65MI 519!90Ł and
509
Iminocarbonyl and Halo`en or Chalco`en
by Marhold ð72HOU"E3#544Ł[ No new general preparative methods have been reported since the publication of these reviews[ The most important methods are all of a similar type\ involving the chlorination of compounds of general structure "13^ X H\ Cl\ SR or SO1R# "Equation "8## ð60ZOR1973\ 62ZOR28\ B!65MI 519!90Ł[ Salts derived from cyclic secondary amines have been synthesised by reaction with carbon disul_de followed by chlorination ð78SC1714Ł[ On heating to 039>C they undergo ring opening to carbonimidic dichlorides "Equation "09##[ R1R2N
X
R1 + N
Cl2, PCl5
S (24)
+
X
Cl Cl–
(9)
Cl
R2 (23)
Cl
Cl
140 °C
N
Cl
77–86%
Cl
X
N
Cl
(10)
Cl–
There are a few examples of the preparation of dichloroiminium salts "12# by N!alkylation of carbonimidic dichlorides ðB!65MI 519!90\ 81ZAAC"506#025Ł but this is not a general method since the carbonimidic dichlorides are poor nucleophiles[ The compound Cl1C1NCl can be protonated in a superacid medium ð81ZAAC"506#025Ł[ The parent dichloroiminium cation Cl1C1NH1¦ has been generated from cyanogen chloride and hydrogen chloride and both tetrachloroferrate and hexa! chloroantimonate salts have been isolated ð62T186Ł[ A review of conjugated iminium salts "14#\ which are prepared from a variety of chloroiminium salts and nitriles R0CN\ includes examples of dichloroiminium salts "14^ R0 Cl# ð77S544Ł[ R1 Cl
R2 N
+
NR32 X–
(25)
A compound which can formally be regarded as a coordinated dichloroiminium cation is the dichlorodiazomethane complex "15#\ which has been generated from a structurally related diimide complex by CCl1 transfer ð79CC768\ 70JCR"S#165Ł[ The salt ð"CO#4Cr1C1N¦1CCl1Ł AlCl3− has been isolated from the reaction of the isocyanide complex "CO#4CrCNCCl2 with aluminium trichloride ð75OM1076Ł[ Cl Cl
N N+ P P
W
P
P
P
P
= dppe
Br (26)
5[19[0[0[2 Carbonimidic dibromides\ Br1C1NR The methods available for the synthesis of carbonimidic dibromides are nearly all analogous to methods used for the corresponding dichlorides\ but with fewer examples[ The most straightforward method of preparation is the addition of bromine in the cold to isocyanides\ a method which was _rst described in 0767 ð0767BSF"1#074Ł[ Experimental details have been given for the preparation "65)# of N!phenylcarbonimidic dibromide by this method ðB!60MI 519!90Ł and the thermally unstable N!cyclohexyl analogue has been prepared in the same way[ The low stability of simple N!alkyl derivatives can preclude their full characterisation[ Similarly\ Br1C1NCN\ prepared by the addition of bromine to isocyanogen\ is unstable and polymerises easily ð82JOC5829Ł[ N!3!Bromophenylcarbonimidic dibromide is reported to be formed by bromination of phenyl!
500
At Least One Halo`en
thioformamide "Scheme 01# ð50MI 519!90Ł[ Other methods for the formation of N!aryl derivatives which are analogous to those used for carbonimidic dichlorides are also illustrated in Scheme 01 ð68BSF"1#419\ 77CB0334Ł[ Br N
NHPh
Br
S Br Br
CBr4, AlBr3
C6F5NH2
NC6F5
21%
Br
Cl +
N
MeO
•
Br
–
PhNMe3, Br3
O
NAr Br
Cl Scheme 12
The bromination of methyl isocyanate with N!bromosuccinimide leads to the formation of tribromomethyl isocyanate "16a# "59)# ð71CB759Ł[ Like the corresponding trichloromethyl iso! cyanate this compound exists in equilibrium with a carbonimidic dihalide isomer "16b# "Equation "00##[ N!Tri~uoromethylcarbonimidic dibromide has been prepared by the reaction of the amine "CF2#1NH with boron tribromide ð73JFC"13#412Ł[ Br
O Br Br Br
N
• Br
N
(11)
O Br (27b)
(27a)
The best route to the oxime "17#\ a useful precursor to bromonitrile oxide\ is the bromination of glyoxylic acid aldoxime "Equation "01##[ This reaction has been carried out using N!bromo! succinimide ð78LA874Ł and with bromine in water ð89JOC2934\ 81TL2002Ł[ The preparation has been performed on a 499 g scale ð73TL376Ł[ The oxime can be acylated on oxygen to give other car! bonimidic dibromides ð76EUP121901Ł[ There are also related bromination routes to the arylhy! drazones "18# ð61JOC1994\ 65CI"L#053Ł and to the N\N!dimethylhydrazone ð80ZOR422Ł[ HO2C
Br2, H2O
N
47%
OH
Br (12)
N Br
OH (28)
Br N Br
NH Ar (29)
The bromination of tetrazolylhydrazones "29# has provided a route to several azines "20# which have been isolated in moderate to good yield "Equation "02## ð53CI"L#0646\ 68JCS"P0#613Ł[ The tetra! bromoazine "21# has been prepared by an analogous route ðB!60MI 519!90Ł[ Br
N N N
N N H
N H (30)
Ar
N
Br2, AcOH
Br
(13)
N Ar (31)
501
Iminocarbonyl and Halo`en or Chalco`en Br N Br
Br N Br
(32)
Dibromoiminium salts Br1C1NR1¦Br− "R Me or Et# have been prepared by routes analogous to those used for the dichloroiminium salts ð63ZOR338\ 77AJC452Ł[ Thus\ the dimethyliminium salt was formed by bromination of the disul_de "22# "Equation "03##[ S Me2N
S
Br2
S
NMe2
Br
+
NMe2 Br–
(14)
Br
S (33)
5[19[0[0[3 Carbonimidic diiodides\ I1C1NR Isolable examples of this class of compounds are virtually unknown[ The likely reason is their tendency to dissociate to iodine and the isocyanide[ For example\ N!alkylcarbonimidic dichlorides react with potassium iodide with the liberation of iodine ð48JGU1020Ł^ the probable explanation is that carbonimidic diiodides are formed as intermediates but then dissociate "Scheme 02#[ Cl NR
I
KI
NR
Cl
I2 + RNC
I Scheme 13
Diiodoformaldoxime "23# has been isolated in good yield from the reaction of mercury or sodium fulminate with iodine ð20LA"378#6\ 21CB54Ł[ The iminium salt I1C1NMe1¦I− has been prepared "79)# by the reaction of the corresponding dichloroiminium chloride with iodomethane ð68ZOR104\ 70ZOR079Ł[ I N I
OH (34)
5[19[0[1 Iminocarbonyl Halides with Two Dissimilar Halogen Functions There are relatively few examples of carbonimidic dihalides with di}erent halogens attached to carbon[ Most contain ~uorine\ with chlorine present as the second halogen[
5[19[0[1[0 Carbonimidic chloride ~uorides\ ClFC1NR ClFC1NH has been suggested as an intermediate in the reaction of HF with cyanogen chloride\ but it has not been detected directly ð58HCA701Ł[ Several methods of preparation of ClFC1NF
502
At Least One Halo`en
have been described and the "E#! and "Z#!isomers have been identi_ed ð69JA2554Ł[ The methods of preparation are summarised in Scheme 03 ð56JGU0232\ 58JGU0290\ 69JA2554\ 62JOC0964Ł[ Cl Cl F
Cl
i or ii
NF2
NF
H2NCONHNH2•HCl
F
F2N NF F2N
i, Hg, 100 °C, 52%(E), 39%(Z); ii, Fe(CO)5, 10 °C, 43% Scheme 14
ClFC1NCF2 has been produced by the high temperature pyrolysis of 1\2!dichloroper~uoro!N! methylazetine and of copolymers of tri~uoronitrosomethane with chloro~uoroalkenes such as tri~uorochloroethylene ð54JCS5198\ 61GEP1090096Ł[ This compound is also one of the products obtained from the reaction of tri~uoromethyl isocyanide with chlorine ~uoride ð74IC3554Ł[ Reductive routes to the azine "24# ð60ZOR1156Ł and to the oxime "25# ð59JGU3918Ł have been described and these are outlined in Scheme 04[ Cl F F
N
N
Cl F F
F
N
HI
F
N Cl
Cl
F Cl Cl
N O
H2S
Cl N F
(35)
OH (36)
Scheme 15
Chloro~uoroformaldoxime "25# is not isolable^ it is converted into a crystalline polymer when the solution is concentrated[ However\ several series of phosphorus!substituted oximes have been isolated and characterised from the reaction of dichloro~uoronitrosomethane with phosphites and other phosphorus"III# reagents[ Two examples\ one resulting from oxidative addition to a cyclic phosphorus"III# reagent without ring opening ð61JGU182Ł and the other resulting from ring opening ð58JGU0124Ł\ are shown in Scheme 05^ many related reactions have been described ð58JGU0581\ 69JGU439\ 61JGU688\ 61JGU792\ 77KFZ032\ 78ZOB0344Ł[ Cl O P NEt2
F 83%
S
Cl
S
N
CFCl2NO
O P NEt2 O
Cl
O P OMe N
CFCl2NO 96%
N F
O O P N O
Me
Me
Scheme 16
5[19[0[1[1 Carbonimidic bromide ~uorides\ BrFC1NR A few of these compounds have been described[ Photolysis of a mixture of N1F3 and ~uoro! tribromomethane gave BrFC1NF as a mixture of "E#! and "Z#!isomers ð55IC0684Ł[ Reaction of tetrabromoformaldazine "21# with silver ~uoride gave a mixture containing BrFC1NN1CF1 "the major component#\ BrFC1NN1CBrF and BrFC1NN1CBr1 ð55JOC2722Ł[
5[19[0[1[2 Carbonimidic bromide chlorides and carbonimidic chloride iodides\ ClXC1NR "X Br or I# There are a few salts which contain these functional groups[ The salts ClXC1NH1¦SbCl5− "X Br and I# have been isolated from the reaction of cyanogen bromide and cyanogen iodide with antimony"V# chloride and HCl ð53CB0175Ł and the crystal structure of the salt formed from cyanogen bromide has been determined ð82ZN"B#08Ł[ There are also examples of salts of the type "14^ R0 Br# ð77S544Ł[
503
Iminocarbonyl and Halo`en or Chalco`en
5[19[0[2 Iminocarbonyl Halides with One Halogen and One Other Heteroatom Function Compounds having this general structure are known with ~uorine\ chlorine\ bromine and iodine as the heteroatom[ The second heteroatom is most commonly oxygen\ sulfur or nitrogen[ The methods of preparation of the oxygen\ sulfur and nitrogen compounds have been reviewed by Ulrich ðB!57MI 519!90Ł and by Kuhle ð58AG"E#19\ 72HOU"E3#432Ł[ Similar displacement reactions of dihaloiminium ions are reviewed by Janousek and Viehe ðB!65MI 519!90Ł and by Marhold ð72HOU"E3#544Ł[
5[19[0[2[0 Iminocarbonyl ~uorides with one other heteroatom function "i# Iminocarbonyl ~uorides with an oxy`en function\ F"R0O#C1NR1 The parent compound of this type "R0 R1 H# is named in Chemical Abstracts as car! bono~uoridoimidic acid[ A few of these compounds have been prepared by the selective displacement of ~uoride from carbonimidic di~uorides by oxygen nucleophiles[ The reaction can be carried out on N!per~uoroalkylcarbonimidic di~uorides with alkoxides "Scheme 06# ð65IZV1270\ 81JFC"46#182Ł[ Nitric acid has also been used as the nucleophile^ dropwise addition of concentrated nitric acid at −67>C gave the nitrate "26# ð57JGU26Ł[ An example of a related method in which the oxygen nucleophile is generated in situ is shown in Scheme 07 ð71POL018Ł[ Two speci_c methods based on di}erent approaches are also shown[ Thermolysis of the diazirine "27# at 79>C gave the carbene dimer as the major product\ but the azine "28# as a minor product "02)# "Equation "04## ð75TL308Ł[ Compounds of this class have also been formed by thermal rearrangement of per~uorinated oxazi! ridines^ a C!per~uoroalkyl substituent of the oxaziridine migrates to oxygen in the rearrangement ð82JCS"P0#494Ł[ A reductive dechlorination method provided a route to compound "39# "as a mixture of the two isomers# in 68) yield "Equation "05## ð76AG"E#023Ł[ RO NCF3
F
NaOR
NCF3
F
O2NO
HNO3, –78 °C
NCF3
60%
F
F (37)
Scheme 17
F3C
F3C
F
F
F
F
CsF
NF
F3CF2CO
F
O–
O
NF
55%
F
Scheme 18
MeO MeO F
N
F
N
F
(15)
N OMe
(38)
F5SOCFClNCl2
N
80 °C
(39)
Zn, 50 °C
F5SO NCl
(16)
F (40)
"ii# Iminocarbonyl ~uorides with a sulfur function\ F"R0S#C1NR1 Such compounds can be prepared in a manner analogous to those with an oxygen function\ by displacement of one ~uoride of carbonimidic di~uorides using a thiol as the nucleophile ð58JGU072Ł[
504
At Least One Halo`en "iii# Iminocarbonyl ~uorides with a nitro`en function\ F"R0R1N#C1NR2
These compounds are described in Chemical Abstracts as carbamimidic ~uorides[ The addition of ammonia ð72IZV583Ł or primary alkylamines ð79JFC"04#058Ł to F1C1NCF2 leads to compounds of this type having the general structure "30# in good yield[ With an excess of the carbonimidic di~uoride 1 ] 0 adducts "31# can be isolated ð72MI 519!91Ł[ Trimethylsilyl azide reacts with F1C1NCF2 to give the a!azidoimide F"N2#C1NCF2 which shows no tendency to cyclise to the corresponding tetrazole ð74IZV699Ł[ The carbonimidic di~uoride F1C1NCF2 also reacts with antimony"V# ~uoride\ either to give a cyclic trimer ð72JFC"11#064Ł or\ in liquid sulfur dioxide\ to give the salt "CF2#1NC"F#1N¦1CFN"CF2#1SbF5− ð73JFC"15#210Ł[ F NCF3 R N
RHN
NCF3
NCF3
F (42)
F (41)
The most numerous examples of compounds of this class are formal dimers "32# of carbonimidic di~uorides[ In the presence of ~uoride ions the carbonimidic di~uorides can dimerise by the route shown in Scheme 08[ This is in e}ect a special case of nucleophilic displacement of ~uoride[ Some examples of dimers formed in this manner are listed in Table 2[ Related reactions are the combination of F1C1NF with F1C1NBr to form a {mixed dimer| "33# ð77JOC3332Ł and with F3S1NF to give Table 2 Dimers "32# of carbonimidic di~uorides F1C1NR[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * F 71POL018\ 72JOC660\ 89JA617 But 79TL3782 76JFC"26#148\ 65IZV101 CF2 Ph 55AG"E#737\ 79TL3782 OCF2 70JFC"07#330 TeF4 74IC3060 78IC2234 N"CF2#C1F4 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
F
F
F NR
F–
F F
F
NR F
–
NR
F
NR F
F
NR F (43)
Scheme 19
F
F
F3CN
F5SN NBr
F (44)
NF F (45)
the 0 ] 0 adduct "34# ð73IC1077Ł[ Some useful speci_c preparations of compounds of this class have been described[ The N! bromoimide "35# has been prepared in 89) yield from "CF2#1NCN\ bromine and caesium ~uoride ð89JA617Ł and compound "36# in 73) yield from ~uorocyclohexane\ cyanogen chloride and hydro!
505
Iminocarbonyl and Halo`en or Chalco`en
gen ~uoride ð58HCA701Ł[ The reaction of TeF4NHCF2 with potassium ~uoride gives the imide "37# "38)# ð74IC3060Ł[ The azoimide "38^ R CF1NF1# has been obtained in low yield by thermolysis of per~uoroaminodiazirine ð56JHC278Ł and the related compound "38^ R C"F#1NF# by reaction of the azo compound "49# with carbon monoxide at 079>C ð61IC307Ł[ The per~uoro compound F1NCF1NF is produced in low yield by ~uorination of guanylurea ð56JOC2748Ł[ A potentially more general method of synthesis of this class of compounds which has not been exploited is the exchange of the chlorine of the corresponding imidoyl chlorides for ~uorine by the action of hydro~uoric acid ð58AG"E#19Ł[ H N
(CF3)2N
F5TeHN
NCF3
NBr
NCF3
F (47)
F (46)
F2N F2N
R
F (48)
F N N
N N
NF2 F NF2
NF F (49)
(50)
"iii# Iminocarbonyl ~uorides with a phosphorus function The reaction of triethyl phosphite or trimethyl phosphite with F1C1NCF2 leads to the formation of the adducts "RO#2P"F#C"F#1NCF2 in good yield ð66IZV1268\ 70IZV1521Ł[
5[19[0[2[1 Iminocarbonyl chlorides with one other heteroatom function "i# Iminocarbonyl chlorides with an oxy`en function\ Cl"R0O#C1NR1 There are two principal methods for the preparation of compounds of this type "named in Chemical Abstracts as derivatives of carbonochloridoimidic acid#[ The _rst\ and older\ method is the selective displacement of one chloride from a carbonimidic dichloride by an oxygen nucleophile\ usually an alkoxide or a phenoxide ion[ Several examples of reactions of this type are described by Kuhle ð58AG"E#19\ 72HOU"E3#432Ł[ The method recommended for reaction of alkoxides with N! arylcarbonimidic dichlorides is to use a two!phase system of chlorobenzene and aqueous alkali^ this prevents further displacement of chloride[ Examples of this method of preparation include those for R1 alkyl ð71TL2428Ł\ aryl ð64CB1189\ 71TL2428\ 73ZOR0086Ł and SF4 ð71JFC"08#300Ł[ Reaction with phenoxides has been performed with equimolar quantities of reagents in a polar solvent such as dioxane ð58AG"E#19Ł[ An example is the selective displacement of chloride from the dichloride "40# with phenol in the presence of triethylamine "Equation "06## ð64JCS"P1#0935\ 66ZC061Ł[ Cl
PhO N
N
PhOH, NEt3
Cl
Cl O
Cl
Cl
(17)
O (51)
The second general method of preparation of these compounds is the reaction of aryl cyanates with acyl chlorides "Equation "07## and with other active chlorine compounds such as sulfenyl chlorides[ Several examples of this reaction are described in a review by Grigat ð61AG"E#838Ł[ The range of examples has subsequently been extended[ With phosphorus pentachloride at −49>C the salts "41# were formed in high yield ð61JGU86Ł[ The pyrone derivatives "42# have been isolated in low yield from the reactions of aryl cyanates with malonyl chloride "which behaves as the pyrone acid chloride# ð74CB0260Ł and the {mixed| imidoyl chlorides "43# were isolated in moderate yield
506
At Least One Halo`en
from the reaction of Cl1C1NCOCl with aryl cyanates ð70ZOR287Ł[ Cyanates also react with chloroiminium salts to give salts of the type "14# ð77S544Ł[ ArO N
RCOCl
ArOCN
Cl
(18)
R O
ArO +
ArO
O N
ArO
O
N
Cl
N PCl PCl6–
Cl
Cl
O
Cl 3
N
HO
(52)
Cl
O Cl (54)
(53)
In principle the reaction of carbamate esters R0NHCO1R1 with phosphorus pentachloride could provide a third general method of synthesis\ but such reactions normally go further and yield isocyanates[ In the reaction of F4SNHCO1Ph with phosphorus pentachloride some of the imidoyl halide F4SN1C"Cl#OPh was isolated as well as the isocyanate ð72JFC"12#482Ł[
"ii# Iminocarbonyl chlorides with a sulfur function\ Cl"R0S#C1NR1 These compounds have also been called 0!halothioformimidates[ The parent compound "R0 R1 H# is named as carbonochloridimidothioic acid in Chemical Abstracts[ The four principal methods of preparation are exempli_ed below[ "a# From carbonimidic dichlorides[ The displacement of chloride from carbonimidic dichlorides by sulfur nucleophiles has been used as a method of preparation for a few types of compounds of this type\ including N!aryl\ aroyl and phosphoryl derivatives ð58AG"E#19\ 64CB1189\ 64JCS"P1#0935\ 73JOC417Ł[ For example\ the imidoyl chloride "44# was isolated "59)# from the reaction of the corresponding carbonimidic dichloride with phenylmethanethiol and triethylamine ð73JOC417Ł[ A related reaction is the preparation of the heterocycle "45# from the imidoyl chloride "46# and sulfur "Equation "08## ð65GEP1340524Ł[ PhCH2S NCOPh Cl (55)
Cl
N
N
Cl S8
Cl
Cl Cl
Cl (57)
N
N
S
S
Cl
Cl
(19)
(56)
"b# From isocyanides[ The addition of sulfenyl chlorides to isocyanides provides a general route to compounds of this class ð51AG"E#536\ 73T0964\ 74JOC660Ł[ With bis"trimethylsilyl#amino isocyanide a range of sulfenyl chlorides has been used "Scheme 19# ð66ZN"B#0992Ł[ The addition of methanesulfenyl chloride to isocyanides XCH1NC "X EtO1C or "EtO#1PO# gives the compounds MeSC"Cl#1NCH1X which are useful precursors to nitrile ylides ð81TL5044Ł[ "c# From isothiocyanates and related compounds[ As shown in Scheme 4 the preparation of carbonimidic dichlorides by chlorination of isothiocyanates goes by way of sulfenyl chloride inter! mediates and some of these intermediates are isolable ðB!60MI 519!90Ł[ For example\ the sulfenyl chlorides "47# have been isolated in good yield from the reaction of the isothiocyanates with chlorine ð67CB587Ł[ Chlorination of aryl isothiocyanates in the presence of thiols RSH leads to the formation of the compounds "48# ð89JHC0080Ł[ A related high yielding preparative method is the reaction of compounds "59^ X COAr or SO1Ar# with sulfuryl chloride to give the chlorides "50# ð64AP"297#268\ 73CZ393\ 80JPR076Ł[ Thio! and dithiocarbamic esters PhNHCXSR "X O or S# have also been
507
Iminocarbonyl and Halo`en or Chalco`en Cl3CS
Me2NS NN(TMS)2
NN(TMS)2 Cl
Cl Me2NSCl
Cl3CSCl
68%
93%
(TMS)2NNC S2Cl2
SCl2
Cl
96%
93%
S
S (TMS)2NN
)2
(TMS)2NN
NN(TMS)2
Cl
Cl Scheme 20
chlorinated in high yield by means of the Appel reagent "triphenylphosphine and tetra! chloromethane# to give compounds of this type ð65CB709Ł[ ClS
RS
RS
NCOAr
RS
NAr
Cl
NX
Cl
NX
RS
(58)
(59)
Cl (60)
(61)
"d# From thiocyanates[ The reaction of cyanates with acyl chlorides described by Grigat ð61AG"E#838Ł has an analogy in the reaction of methyl or ethyl thiocyanate with oxalyl chloride ð67LA0693Ł[ With 1 mol of methyl thiocyanate and in the presence of boron tri~uoride the imidoyl chloride "51# was formed "55)#[ The N!chloro compounds "52# have been isolated from the reaction of thiocyanates with iodine monochloride ð71MI 519!91Ł[ By analogy with the reaction shown in Equation "4# the three!component reaction of alkyl thiocyanates with chlorine and alkenes gave the adducts "53# in moderate yield ð58JPR04Ł[ Ethyl thiocyanate is also reported to react with hydrogen chloride to give the 1 ] 1 adduct "54# "39)# ð62BCJ292Ł[ Salts of the type "14# are formed from thiocyanates and imidoyl chlorides ð77S544\ 81T7160Ł[ The methods of preparation of salts R0SC"Cl#1NR11¦X− have been reviewed by Kantlehner ð68MI 519!91Ł[ MeS
R1S
O
N Cl
Cl O
N
N
R2 (64)
Cl (63)
Cl
+
NH2 Cl–
Cl
Cl
NCl SMe
(62)
EtS N
RS
EtS (65)
"iii# Iminocarbonyl chlorides with a selenium function\ Cl"R0Se#C1NR1 An example of a compound with this functional group is the selenazinone "56#\ which was formed by cyclisation of the selenocyanate "55# with HCl ð57AG"E#353Ł[ O Cl SeCN (66)
O N Se (67)
Cl
508
At Least One Halo`en "iv# Iminocarbonyl chlorides with a nitro`en function\ Cl"R0R1N#C1NR2
The current Chemical Abstracts name for the parent compound "R0 R1 R2 H# is car! bamimidic chloride[ This compound is still unknown but its salts and many substituted carbamimidic chlorides have been described[ There are _ve principal methods of preparation[ "a# From carbonimidic dichlorides and dichloroiminium salts[ In principle the reaction of car! bonimidic dichlorides with amines provides a general route to carbamimidic chlorides\ but the reaction must be carried out under carefully controlled conditions in order to be a useful synthetic method[ For example\ displacement of chloride from N!aroylcarbonimidic dichlorides takes place in high yield with dialkyltrimethylsilylamines at low temperature "Equation "19## ð78LA820Ł[ There are several other useful examples of displacement of chloride from carbonimidic dichlorides by secondary amines ð79CC768\ 72KGS687\ 77AG"E#0233\ 77JFC"39#106\ 78CB0896Ł one of which was shown to lead speci_cally to the "Z#!isomer ð82JPO208Ł[ Primary amines tend to react further to give guanidines[ N!Phenylcarbonimidic dichloride reacts with cyclic tertiary amines to give quaternary ammonium salts "Scheme 10# which either demethylate "n 4 and 5# or undergo ring opening "n 1Ð3# above room temperature ð63TL2654Ł[ Triazinones "57# have been prepared by the reaction of the carbonimidic dichloride "7# with arylamines ð71CB2476Ł[ (CH2)n
(CH2)n Me PhN
N PhN
Me
N+
N(CH2)nCl
Cl– PhHN
Cl
O
Cl Scheme 21
Cl NCOAr
R2N-TMS, –45 °C
Cl
R 2N (20)
NCOAr Cl
O N Cl
N N
Cl
Ar (68)
The major route to N\N!dimethylcarbamimidic chlorides "58# is provided by the displacement of chloride from the iminium salt "69# by amines\ dichloroamines and other nitrogen nucleophiles "Scheme 11# ðB!65MI 519!90Ł[ This reaction provides a wide range of compounds having the general structure "58#[ Many of these compounds are described in the review by Janousek and Viehe ðB!65MI 519!90Ł^ representative examples of reactions of the salt "69# with reagents of the general type RNH1 from this review and from later references are given in Table 3[ Cl
+
NMe2 Cl– Cl
RNH2
RHN
+
NMe2 Cl– Cl
(70)
–HCl
RN NMe2 Cl (69)
Scheme 22
N\N!Dichlorourethanes ð64ZOR60Ł and N\N!dichlorosulfonamides ð62ZOR32\ 67ZOR0730Ł also both react with the iminium salt "69# to give compounds of general structure "58#\ with the elim! ination of chlorine[ A variety of other nitrogen compounds react with the salt "69#] some examples are shown in Scheme 12 ð63ZOR25\ 64C198\ 67BSB280\ 68AG"E#222\ 73ZOB0009\ 75T5534Ł[ "b# From thioureas[ Several types of thiourea can be converted in good yield into carbamimidic chlorides by reaction with an equimolar amount of phosgene ðB!57MI 519!90Ł[ An example is the preparation of the N!p!toluenesulfonylimide "60# "77)# from the thiourea[ A variant of this method is provided by the reaction of N!acetylthiourea with phosphorus pentachloride\ which gave the imide "61# "60)# ð89ZOB695Ł[ N!Sulfonylcarbamimidic chlorides have also been obtained by chlori! nation of S!methylisothioureas ð64ZOR1132\ 79CP0965021Ł[
519
Iminocarbonyl and Halo`en or Chalco`en Table 3 Carbamimidic dichlorides "58# from the iminium salt "69# and RNH1[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 79 60AG"E#462 C5H3NO1!3 C5H3CN!1 quant[ 73TL0446 61 B!65MI 519!90 CO1Et CH1C"CN#1 71UKZ284 OCH1Ph 80 B!65MI 519!90 57 71LA1094 SO1Ph N"Me#C5H2"NO1#1!1\3 77 79JCS"P1#756 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
Me +
Me2N
N Cl
Me2N
Cl– F
N
Cl
Cl
Cl
Cl
Cl F
Cl
Cl
Cl
NCO
CONHMe 86%
CN
Me2N
Cl
N
N Cl Cl3C
Cl CN
+
CCl3
TMS
NC
NMe2 Cl–
62%
–
CHC(CN)2 K+
Cl
NC
(70) 70%
TMS-N3
O-TMS
CN Me2N
N
CN
+
Me2N
N
70%
N3 Cl– Cl Me2N
+
N
N
TMS-O SbCl5
N
O
SbCl6–
•
Cl
CN
Cl
O-TMS
Cl Scheme 23
H BuHN NTs
Cl Cl
N NPOCl2 Cl
Cl (71)
(72)
"c# From ureas[ Ureas can also be chlorinated with phosgene\ but attack on oxygen\ rather than on nitrogen\ which is the favoured reaction only with ureas having secondary or tertiary alkyl substituents on nitrogen ðB!57MI 519!90Ł[ An example of the reaction is shown in Equation "10# ð75JOC0608Ł[ There are also several examples of chlorinations of this type which have been carried out with the triphenylphosphineÐtetrachloromethane reagent ð62CB1982\ 63CB587\ 65CB0532\ 65CB1810\ 68CB539\ 79CB0984Ł and with phosphorus"V# chloride ð80ZOB532\ 81ZOB295\ 81ZOB213Ł[ Me2N NHPri O
COCl2, 0 °C 99%
Me2N NPri
(21)
Cl
"d# From cyanamides[ Dialkylcyanamides add to electron de_cient aroyl chlorides to give car! bamimidic chlorides\ generally in good yield[ The reaction was _rst described by Bredereck and Richter ð55CB1343Ł but was later greatly expanded\ especially by Ried et al[ ð79S508Ł[ The method
510
At Least One Halo`en
is exempli_ed by the preparation of the imidoyl chloride "62# "85)# from 3!nitrobenzoyl chloride and N!cyanopyrrolidine "Equation "11##[ The reaction has been performed with a variety of aroyl chlorides ð79CB1472\ 79S508Ł and other activated acyl chlorides ð79S508\ 70MI 519!91\ 75LA0886Ł[ Other activated halogen compounds also react with dialkylcyanamides to give carbamimidic chlorides] examples of reaction with sulfenyl chlorides ð79S508\ 76CZ228Ł\ sul_nyl chlorides ð79S508Ł\ di! arylimidoyl chlorides ð76CC88Ł\ chloroiminium salts ð73CC0094\ 77S544\ 78S807\ 81T7160\ 81JHC0440\ 82H"25#0410Ł\ thionyl chloride ð63ZOR0999Ł\ sulfur dichloride ð74IC1342Ł\ sulfuryl chloride ð62ZOR522Ł and phosphorus trichloride ð67JGU0967Ł are known[ Some of these are illustrated in Scheme 13 ð78S807Ł[
N N
N
+
O 2N
COCl
(22)
N Cl
NO2 O (73)
Me2N
+
N Cl R 2N
SbCl6–
R 2N N
Ar2CCl+ SbCl6–
N Cl
NMe2 Ar N Ar
Ph
R = Me
SAr
N
ArSCl
+
N
NMe2 Cl– Cl
ArSOCl
R 2N
R2N
N Cl
NAr Ph
Cl
Ar
R2N
Cl
N S O
SOCl2
Ar
PCl3
R 2N
Cl
R2N
N Cl
+
NMe2 Cl–
Cl
N
S O
Cl
Cl
PCl2
Scheme 24
Cyanamide itself has long been known to add to dry hydrogen chloride to give iminium salt "63# ðB!57MI 519!90Ł[ The salt is a solid which can be stored for short periods in anhydrous conditions ð89JMC323Ł[ Cyanamide is also chlorinated by hypochlorous acid to give the perchloro compound "64# ð70MI 519!92Ł[ The N!chloroimide has been prepared by the reaction of thionyl chloride with salts of dicyanamide ð69JCS"C#764Ł and several other carbamidic chlorides have been derived from it by reaction with nucleophiles[ H2N
+
Cl2N
NH2 Cl– Cl
NCl Cl
(74)
(75)
"e# From carbodiimides[ Diisopropylcarbodiimide and other carbodiimides with secondary alkyl substituents have been shown to react with activated halogen compounds to give carbamimidic
511
Iminocarbonyl and Halo`en or Chalco`en
chlorides[ The reaction has been described with phosgene and thiophosgene by Ulrich ðB!57MI 519!90Ł[ The reaction with trichlorotriazine is shown in Equation "12# ð71KGS010Ł^ the same type of reaction takes place with benzoyl chloride ð74AP"207#0946Ł\ aliphatic acid chlorides including chloroacetyl chloride ð55CB2044\ 66JOC2119Ł\ squaric acid dichloride ð74AP"207#881Ł and hydrogen chloride ð78TL1268Ł[ The reaction with phosphorus pentachloride leads to the formation of six! coordinate phosphorus species "65# with partial CN double bonds and with two equivalent phos! phorusÐnitrogen bonds ð57AG"E#188\ 58AG"E#344\ 89IC4970Ł[ Cl Cl PriN PriN
•
NPri
N
+
N
N Cl
NPri
85%
(23)
N
Cl
N
Cl
R Cl N Cl P Cl Cl N
N
Cl
Cl
R (76)
"v# Iminocarbonyl chlorides with a phosphorus function There are a few compounds containing this functional group[ The phosphonates "66# are formed in good yield by the reaction of the isocyanate Cl1P"O#CCl1NCO with alcohols ð60ZOB1044Ł[ The chlorooxime "67# is the major product of the nitrosation of compound "68# ð89ZOB112Ł^ it is a precursor to the phosphorus substituted nitrile oxide "79# ð82ZOB526Ł[ RO O RO P
PriO O PriO P N
Cl
PriO O PriO P
OH
N CO2R
(77)
Cl
OH
Cl (79)
(78)
O PriO P PriO
N + O– (80)
"vi# Iminocarbonyl chlorides with a metalloid or a metal function The insertion of alkyl isocyanides into boronÐhalogen bonds of BX2 or into metalÐchlorine bonds has provided a route to compounds of this type[ The reactions are summarised in Scheme 14 ð58M0712\ 64JOM"090#C0\ 66JCS"D#1904\ 68JOM"070#58Ł[ The unstable adducts formed with titanium"IV# chloride are useful synthetic intermediates ð77CB496Ł[
R
+N
X
–
BX3
–
X3B
+
X
N R BX3
[MCl4{C(Cl)=NR}CNR]
MCl5
R N C
M = Ta, Nb; R = Me, But
MCl4
[MCl3{C(Cl)=NR}CNR]2 M = Ti, Hf, Zr; R = But
Scheme 25
512
At Least One Chalco`en 5[19[0[2[2 Iminocarbonyl bromides and iodides with one other heteroatom function
Several examples of compounds of this type have been described with either sulfur or nitrogen as the second heteroatom attached to carbon[ The synthetic methods are analogous to some of those used for the corresponding iminocarbonyl chlorides[ Alkyl thiocyanates RSCN have been found to react with bromine and with iodine to give 0 ] 0 adducts having the structure "70^ X Br or I# ð71MI 519!90\ 71MI 519!91Ł[ The addition of SF4Br to tri~uoromethyl isocyanide gave the imidoyl bromide "71# "51)# ð74IC3554Ł[ Compounds of this type which have been prepared by nucleophilic displacement are the hydrazones "72#\ which are derived from the corresponding dibromo compounds by reaction with thiophenolate anions ð61JCS"P1#0949Ł and the iminium salt "73#\ which is formed from the chloroiminium salt by reaction with iodomethane ð70ZOR079Ł[ RS
Ar1S
F5S NX
X (81)
Me2N
+
NMe2 I–
NNHAr2
NCF3 Br
I
Br
(82)
(84)
(83)
Addition reactions of cyanamides have also been used to prepare carbamimidic bromides and iodides[ Cyanamide reacted with hydrogen bromide and hydrogen iodide to give the salts "74# in good yield ð69GEP0804557Ł and the addition of hydrogen bromide to diethylcyanamide or to N! cyanopyrrolidine also gave the corresponding bromoiminium salts ð77JCS"P0#788Ł[ Similarly the iminium salts "75^ X Br and I# were formed from the sodium salt of the corresponding cyanamide by addition of hydrogen bromide or hydrogen iodide ð65CPB15Ł[ The squaric acid derivatives "76^ X Br and I# have been prepared by addition of the corresponding halides to N!cyanopyrrolidine ð79S508Ł[
N
H 2N
+
NCCH2CONH
NH2 X–
+
Ph
X
NH2 X–
X (85) X = Br or I
N
O (87)
X (86)
O
Examples of imidoyl halides with a phosphorus function are provided by the hydrazone "77# "which is prepared by a method analogous to that used for the oxime "67## ð78ZOB603Ł and by the diazo compounds "78^ X Br and I\ R Ph and OMe# which are prepared by halogenation of the corresponding "78^ X H# ð68LA0991Ł[ PriO O PriO P
O
R R
P N2
NNHAr Br (88)
X (89)
5[19[1 FUNCTIONS CONTAINING AT LEAST ONE CHALCOGEN "AND NO HALOGENS# 5[19[1[0 Iminocarbonyl Compounds with Two Similar Chalcogen Functions 5[19[1[0[0 Iminocarbonyl compounds with two oxygen functions The parent compound of this class\ "HO#1C1NH\ is named in Chemical Abstracts as carbonimidic acid[ Derivatives are also called iminocarbonates[ The most extensive review of the methods of preparation of these compounds is by Kuhle ð72HOU"E3#450Ł[
513
Iminocarbonyl and Halo`en or Chalco`en
"i# From carbonimidic halides and related compounds The reaction of carbonimidic dichlorides with sodium alcoholates or phenolates in a 0 ] 1 molar ratio\ and sometimes with alcohols in excess\ provides a general route to carbonimidic diesters "89# "Equation "13## ð58AG"E#19Ł[ Examples include the formation of the diethoxyiminium salt "80# from the corresponding dichloroiminium salt and ethanol ð55ZAAC"233#002Ł\ the diester "81# from the carbonimidic dichloride and sodium methoxide ð70JHC0016Ł\ dimethyl N!cyclohexyliminocarbonate from the carbonimidic dichloride and sodium methoxide ð76CB228Ł and the polymer "82# from N! phenylcarbonimidic dichloride and bisphenol A ð80MM1291Ł[ N!Arylcarbonimidic dichlorides have also been used to trap the intermediates formed in the electrochemical reduction of diaryl!0\1! diketones\ giving the cyclic iminocarbonates "83# ð83TL1254Ł[ Cl
R2O
2 R2O–Na+
NR1
NR1
(24)
R2 O
Cl
(90)
PhN EtO
O
MeO NH2+ SbCl6– (91)
O
Ar2
O
NAr1
O
NCH2Ts
n
MeO
EtO
Ar2
(93)
(92)
(94)
Carbonimidic diesters have also been prepared by displacement of ~uoride from the corresponding carbonimidic di~uorides ð89JFC"37#284\ 81JFC"46#182Ł[ For example\ compound "84# was isolated "69)# from the reaction of the corresponding di~uoride with lithium 1\1\1!tri~uoroethoxide ð89JFC"37#284Ł[ Instead of halide\ 0\1\3!triazolide can also act as a leaving group for the preparation of carbonimidic diesters ð62JPR539Ł[ CF3CH2O N CF3CH2O
N(CF3)2 (95)
"ii# From cyano`en halides\ cyanates and isothiocyanates N!Unsubstituted carbonimidic esters have been prepared by nucleophilic addition of alcohols to cyanogen chloride\ to cyanogen bromide or to cyanate esters ð72HOU"E3#450Ł[ The addition to cyanate esters allows esters to be prepared which have two di}erent oxygen substituents "Equation "14##[ An example is the preparation of the methyl 3!tolyl ester "R0 Me\ R1 3!MeC5H3# "84)# from 3!tolyl cyanate and methanol ð62JPR178Ł[ A useful method for the preparation of "PhO#1C1NH is the reaction of potassium cyanide with two equivs[ of phenyl cyanate] cyanide displaces phenoxide from one mole of phenyl cyanate and this then adds to the second mole to give the iminocarbonate in high yield ð54CB2551Ł[ Iminocarbonates can also be obtained from isothiocyanates\ an example being the preparation of 1!"N!phenylimino#!0\2!dioxolane "82)# from phenyl isothiocyanate and Bu1Sn"OCH1CH1O# ð66BCJ2160Ł[ R2O
N
R1OH
R1O NH
(25)
R2O
"iii# From dichlorobis"aryloxy#methanes and orthocarbonates Dichlorodiphenoxymethane is a useful intermediate for the preparation of carbonimidic acid diphenyl esters "Equation "15##[ It has been shown to react with cyanamide to give the N!cyano
514
At Least One Chalco`en
compound "R CN# "89)# ð71JHC0194Ł[ An analogous route has been used to prepare the amino! sulfonyl compound "R SO1NH1# "56)# ð80S642Ł[ PhO
Cl
PhO
Cl
RNH2
PhO NR
(26)
PhO
Reactions of primary amines with tetraethyl orthocarbonate and with trialkyl orthoformates have also been used to prepare iminocarbonates ð69BCJ076\ 66MI 519!91Ł[ Triethyl orthocarbonate also reacts with arenesulfonamides to give the N!arenesulfonyl iminocarbonates in good yield ð52JOC1891Ł[
"iv# By functional `roup interconversion on nitro`en For several types of N!substituted carbonimidic diesters the most convenient method of prep! aration is from another carbonimidic diester "Equation "16##[ Examples of these reactions are summarised in Table 4[ The simplest type is from N!unsubstituted compounds which are halo! genated\ alkylated or acylated\ but in other cases the imidoyl nitrogen of the product is derived from the reagent[ Thus\ the conversion of dimethyl N!phenyl carbonimidate into the N!tosyl compound takes place by a ð1¦1Ł cycloadditionÐcycloreversion process ð76CB228Ł[ R1O
R1O NR2
R1O
NR3
(27)
R1O
Table 4 Carbonimidic diesters prepared by exchange of N!substituents "Equation "16##[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Yield R0 R1 R2 Rea`ent ")# Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Et H Cl Cl1 47 25CB1247 Et H CHPh1 Ph1CHNH2¦Cl− 22 76CB0160 ClCH1OMe 49 76CB0160 Ph H CH1OMe Me H "CF1Cl#1COH "CF1Cl#1CO 72 51USP2004402 Et H COMe MeCOCl 76 66ACH66 Et H !COCO! "COCl#1 77 66ACH66 ClCO1Et 57 75CB2125 Et H CO1Et Et H CSNHPh PhNCS 11 64ZOR1112 Et H PPh1 Ph1PCl ×79 60CB0088 1!NO1C5H3 H SO1NHMe ClSO1NHMe 71 74TL3038 H !SO! SOCl1 66 76S069 1!NO1C5H3 Et H NHTs TsNHNH1 43 52PCS269 62 79EUP03953 Me H CN H1NCN Et Cl OH NH1OH 79 02CB1336 3!NO1C5H3SCl 72 74ZOR0170 Et Cl 3!NO1C5H3SCl1 Me Ph Ts TsNCO 80 76CB228 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
"v# By O!alkylation of alkoxycarbonyl functions Carbamate esters can be alkylated on oxygen with trialkyloxonium tetra~uoroborates\ and this reaction provides a route to some carbonimidic diesters ð76CB228Ł[ Thus\ ethyl N!methyl! carbamate\ EtO1CNHMe\ gave diethyl N!methyliminocarbonate "42)# when alkylated with tri! ethyloxonium tetra~uoroborate[ Cationic species can also be produced by this method] some examples are shown in Scheme 15 ð76CB0160\ 81CB1376Ł[ There are also examples of N!"tri! methylsilyl#carbamates which exist in equilibrium with O!trimethylsilyl isomers ð65IZV1436Ł[
515
Iminocarbonyl and Halo`en or Chalco`en But
But
Et3O+BF4–
NCO2Et 72%
But
Ph3P
NCO2Et
+
But
Et3O+SbCl6–
Ph3P
NCO2Et MeO
BF4– OEt
+
OEt
N
91%
MeO
OEt
N
SbCl6– OEt
MeO
Et3O+BF4–
+
OEt
N quant.
MeO
BF4– OEt
Scheme 26
"vi# Other methods Azodicarboxylic esters are useful partners in DielsÐAlder reactions[ They normally act as dieno! philes but they can sometimes act as heterodienes ð72CJC0102\ 78JA1884Ł^ for example\ 2\3!dihydro! 1H!pyran and dibenzyl azodicarboxylate reacted to give the cycloadduct "85# "69)# ð78JA1884Ł[ CO2Bn N O
O
N OBn
(96)
Hydrazine sulfate is reported to react with bis"trimethylsilyl#amine and carbon dioxide to give the compound "86# as a separable component of a mixture with N!trimethylsilyl isomers ð77ZOB282\ 80ZOB0191Ł[ TMS-O N TMS-O
O-TMS N O-TMS
(97)
5[19[1[0[1 Iminocarbonyl compounds with two sulfur functions The parent compound of this class\ "HS#1C1NH\ is named in Chemical Abstracts as car! bonimidodithioic acid[ The compounds are also often referred to as iminodithiocarbonates[ Methods of preparation have previously been reviewed by Kuhle ð72HOU"E3#468Ł[ Most of the methods of preparation of these compounds are analogous to those used for iminocarbonates^ however\ because of the relative ease with which sulfur can be alkylated\ alkylation methods are more important than for the oxygen compounds[
"i# From carbonimidic halides This method of preparation has not been used extensively[ Carbonimidic dichlorides react with thiols or thiolate anions with displacement of one "Section 5[19[0[2[1# or both chloride ions "Scheme 16#[ The reaction is successful with carbonimidic dichlorides bearing a range of substituents on nitrogen ð72HOU"E3#468Ł[ Di}erent sulfur substituents can be introduced by successive displacement^ for example\ compound "87^ R2 Ph# was prepared "57)# from the intermediate "88^ R0 Ts\ R1 Me# and sodium thiophenolate ð75ZC193Ł[ Successive displacement of bromide by di}erent sulfur nucleophiles has also been carried out with a carbonimidic dibromide Br1C1NN1CHAr
516
At Least One Chalco`en
ð61JCS"P1#0949Ł[ The carbonimidic di~uoride F1C1NCF2 reacts in an analogous way with thiols ð58JGU072Ł[ R2S
Cl
R 2S
NR1
NR1
Cl
NR1 R3S (98)
Cl (99) Scheme 27
"ii# From cyano`en chloride and thiocyanates Cyanogen chloride reacts with dithiols such as ethane!0\1!dithiol and benzene!0\1!dithiol in the presence of HCl to give hydrochloride salts of N!unsubstituted iminodithiocarbonates^ an example is the salt "099# derived "53)# from propane!0\2!dithiol ð72HOU"E3#468Ł[ Alkyl thiocyanates also react with thiols to give compounds of this type\ including those in which the sulfur substituents are di}erent ð72HOU"E3#468Ł[ S NH2+ Cl– S (100)
"iii# Methods involvin` S!alkylation A variety of activated amino compounds can be converted into S\S!dialkyl iminodithiocarbonates by reaction with a base\ carbon disul_de and a haloalkane "usually iodomethane# "Scheme 17# ð72HOU"E3#468Ł[ The method was used initially to convert sulfonamides into the dithioesters RSO1N1C"SMe#1 ð55CB1774\ 80S119Ł but it also works well with cyanamides ð66ZAAC"323#004\ 73CCC1174Ł\ with aromatic primary carboxamides ð68S443Ł and with heteroaromatic amines includ! ing 1!aminothiazoles ð80JCR"S#059Ł and 1!aminobenzothiazoles ð71S489Ł[ S!Alkylation and S!acyl! ation of the intermediates shown in Scheme 17 can also be used as a method of preparation[ Dithiocarbamates R0NHCS1R1 can be alkylated in high yield to give iminodithiocarbonates bearing either identical or di}erent substituents on sulfur ð71LA120\ 72HOU"E3#468\ 72S264\ 74S780Ł[ Dithio! carbamates R01NCS1R1 can also be alkylated on sulfur to give salts[ The salt "Me1S#1C1NMe1¦I− has been prepared "79)# in this way^ it can also be made by N!alkylation of "Me1S#1C1NMe ð55CB2157Ł[ The tosylhydrazones "090#\ which are useful as precursors to bis"alkylthio#carbenes\ can similarly be made by alkylation of TsNHNHCS1Me ð61CC243\ 76S156Ł or of the potassium salt TsNHNHCS1−K¦ ð55LA"583#33Ł[ Reaction of this salt with a!chloroketones results in the formation of the cyclic iminodithiocarbonates "091# in good yield ð78S021Ł[ An intramolecular S!alkylation occurs when the dithiocarbamate "092# is treated with isocyanates^ the thiadiazoles "093# are formed in high yield ð73JOC0692Ł[ Similarly\ attempts to prepare compound "095# by S!methylation of the salt "094^ X NHCS1Me# resulted in its formation in poor yield\ the major product being 1\4! bis"methylthio#!0\2\3!thiadiazole resulting from intramolecular S!acylation ð75ZAAC"422#88Ł[
XNH2
CS2, base
S NHX
S
RHal
NHX
–S
RHal
RS
NNHTs RS (101)
R1
S
R2
S
NNHCS2Me
(102)
(103)
NNHTs
NX RS
Scheme 28
MeS
RS
517
Iminocarbonyl and Halo`en or Chalco`en MeS
SMe N
S
N
K+ –S
MeS
N N
NX
CONHR K+ –S
(104)
SMe
MeS (106)
(105)
The salt "094^ X CN# can also be protonated by treatment with HCl in ether at −19>C^ however\ protonation occurs predominantly on nitrogen to give a zwitterionic product ð66ZAAC"323#009Ł[
"iv# By functional `roup interconversion on nitro`en The NH group of iminodithiocarbonates can be substituted by a variety of electrophiles ð72HOU"E3#468Ł\ including isocyanates\ acyl chlorides\ sulfamoyl chlorides ð74TL0094Ł and aromatic sulfenyl chlorides[ N!Hydroxyiminodithiocarbonates can be made using hydroxylamine[ The reac! tions are analogous to those of iminocarbonates shown in Equation "16# and Table 4[
"v# Other methods Diazosulfones "R Ph\ Ar or Et# have been prepared by diazo transfer "Equation "17## using tosyl azide and a base ð53CB624\ 83T2084Ł[ RO2S
TsN3, base
RO2S
RO2S N2
(28)
RO2S
5[19[1[0[2 Iminocarbonyl compounds with two selenium functions A few compounds with this functional group are known ð60JPR793\ 61BCJ378\ 79CC755Ł[ One example is the salt "096#\ which was prepared from Cl1C1NMe1¦Cl− by successive reaction with hydrogen selenide and triethylamine\ then 2!bromobutan!1!one and tri~uoroacetic acid ð79CC755Ł[ Se NMe2+ –OCOCF3 Se (107)
5[19[1[1 Iminocarbonyl Compounds with Two Dissimilar Chalcogen Functions 5[19[1[1[0 Iminocarbonyl compounds with one oxygen and one sulfur function The parent compound of this class\ HO"HS#C1NH\ is named as carbonimidothioic acid in Chemical Abstracts[ Most of the methods for the preparation of derivatives are analogous to those used for compounds with two oxygen or two sulfur functions[
"i# From carbonimidic halides Carbonimidothioic esters "097# bearing a variety of substituents have been prepared by dis! placement of chloride from carbonimidic chlorides and appropriate oxygen or sulfur nucleophiles "Scheme 18# ð53JGU3038\ 72HOU"E3#450Ł[ Both chloride functions of N!benzenesulfonylcarbonimidic dichloride can be displaced by 1!thiolethanol and similar bidentate nucleophiles^ thus\ the oxathi!
518
At Least One Chalco`en
olane "098# is prepared in good yield ð56AP"299#442Ł[ The reaction is probably a general one] it has also been reported for the N!phenyl! ð53JGU3038Ł and the N!benzoyl! ð55CB0801Ł carbonimidic dichlorides[ R1O NR3
R2S–
R1O NR3
R1O–
R2S (108)
Cl
Cl NR3 R2S
Scheme 29
O NSO2Ph S (109)
"ii# From cyanates and thiocyanates N!Unsubstituted compounds of this class are most easily prepared either by the addition of thiols to cyanates or from alcohols and thiocyanates "Scheme 29# ð53CB2911\ 72HOU"E3#450Ł[ Cyanogen chloride can also be used as a starting material\ with 1!thiolethanol and related compounds\ for the preparation of cyclic derivatives such as "009#[ An alternative method of preparation of the salt "009# is the reaction of HSCN with ethylene oxide and HCl ð47HCA266Ł[ R 1O
N
R2SH
R1O NH
R1OH
R 2S
N
R2S Scheme 30
O NH2+Cl– S (110)
"iii# S!Alkylation methods A simple method for the preparation of compounds of this class is\ in principle\ the S!alkylation of anions "000# derived from O!alkyl thiocarbamates ð62JCS"P0#1533Ł[ In practice the most e.cient way of bringing about the reaction is often to generate the anions in situ from isothiocyanates and alkoxide ions "Scheme 20# ð64ZOR0517\ 81TL0914Ł[ A variant of this reaction is the reaction of acyl isothiocyanates with propargyl alcohol] the intermediates "001# undergo spontaneous cyclisation to give the cyclic iminothiocarbonates "002# ð62CPB51Ł[ An intramolecular alkylation also accounts for the formation of the dihydrothiazole "003# "61)# from Br"CH1#1NCS and phenoxide anions ð73CCC184Ł[ Oxiranes ð67JOC2621Ł and nitrile oxides ð54T0426Ł can also add across the C1S bond of isothiocyanates[ S
•
NR3
R1O–
R1O NR3 –S
R2Hal
R1O NR3 R2S
(111) Scheme 31
The procedure illustrated in Scheme 17 for the preparation of iminodithiocarbonates has been applied to the preparation of compounds such as "004# by using the sodium salt of cyanamide and
529
Iminocarbonyl and Halo`en or Chalco`en PhO
O
O
NCOR
NCOR S
HS
(113)
(112)
N S (114)
COS in place of CS1 ð72ZAAC"490#046\ 72ZAAC"490#065Ł[ O!Acyl compounds can also be prepared by successive S!alkylation and O!acylation of the intermediate formed from sodium cyanamide and COS ð72ZAAC"490#058Ł[ MeO NCN MeS (115)
"iv# By functional `roup interconversion on nitro`en Reactions of the type shown in Equation "16# and Table 4 are also possible with this class of compounds\ although fewer examples have been reported ð72HOU"E3#450Ł[ N!Acylation can be carried out using acyl chlorides and sulfonation by sulfonyl chlorides ð89GEP2730074Ł[ Hydroxyl! amine reacts with salts such as "009# to give the corresponding hydroxyimino derivatives\ and potassium cyanate introduces the CONH1 group on to nitrogen ð47HCA266Ł[
"v# Other methods The diester "005# has been prepared "69)# by heating phenyl isothiocyanate with dimethyl formamide diethyl acetal\ Me1NCH"OEt#1 ð66CB26Ł[ A good route to compounds "097^ R2 CN# is the reaction of the dithioesters "006# with cyanamide and a base\ followed by S!alkylation ð69AP"292#514\ 73JHC50Ł[ The salts "007# have been obtained from the iminodithiocarbonates "008# and potassium hydroxide ð76PS"18#0Ł[ EtO
K+ –O
R 1O
NPh EtS (116)
EtS (117)
RS NCN
NCN
S RS (118)
RS (119)
5[19[1[1[1 Iminocarbonyl compounds with one oxygen or sulfur and one selenium or tellurium function Several cyclic structures incorporate functional groups of these types[ The salts "019# have been prepared by acid catalysed cyclisation of a!selenocyanoketones\ R0COCH1R1SeCN ð78EGP169429Ł[ Analogous thiaselenoliminium salts\ such as "010#\ are formed when the thiaselenazines "011# are treated with HI ð73S556Ł[ The imines "012^ X NPh or NCO1Et# are conveniently prepared from the corresponding thiones "X S# by reaction with azidobenzene or with ethyl azidoformate ð79JHC006Ł[
520
At Least One Chalco`en
Compound "012^ X NPh# has also been prepared from phenyl isothiocyanate and the anion PhC2CSe− ð60JPR793Ł[ Reaction of the tellurium compound "013# with bromine gave a solid product which was formulated as "014# but it was too unstable to characterise fully ð70JOM"106#218Ł[ R1
Ph
O
R2
S
Ph
S NH2+ I–
NH2+X– Se
Se
(120)
(121)
SEt
N Se (122)
S Ph
S
S
NMe2+Br3–
Br Te
X
Te
Se (123)
NMe2
Br
(124)
Br
(125)
5[19[1[2 Iminocarbonyl Compounds with One Chalcogen and One Other Heteroatom Function 5[19[1[2[0 Iminocarbonyl compounds with one oxygen and one nitrogen function These compounds\ commonly called isoureas and named in Chemical Abstracts as derivatives of carbamimidic acid\ H1N"HO#C1NH\ are widely represented in the literature[ The most com! prehensive survey of methods of preparation is by Kuhle ð72HOU"E3#476Ł[ A review by Mathias ð68S450Ł on isoureas as alkylating agents also contains a survey of methods for their preparation[
"i# From carbonimidic halides\ esters and thioesters One of the most general methods of preparation of isoureas "015# is the displacement of a leaving group on the imidoyl carbon of carbonimidic halides\ esters and thioesters by a nucleophile[ The types of reaction which have been used are outlined in Scheme 21[ Hal NR4 R2R3N C R1O–
R1O NR4
Hal
R1O B
NR4
HOCH2CH2NH2*
R2R3NH
D
R1O
Hal
NR4 R2R3NH A
R1O
R2R3N
HOCH2CH2NH2*
(126)
E
R 1S
NR4
NR4 R1S
Hal * Methods D and E require this or a similar bidentate nucleophile Scheme 32
Method A\ the displacement of halide from haloformamidic esters\ is a useful one when appro! priately substituted starting materials are available[ An example is the formation of "015^ R0 R1 R2 Me\ R3 Ph# in high yield from methyl N!phenylchloroformamidate and di! methylamine ð72HOU"E3#476Ł[ The zwitterionic triazolones "016# are also formed by a reaction of this type from PhO"Cl#C1NCOCl and 0\0\disubstituted hydrazines ð73JOC1393Ł[ The displacement of an oxygen function by an amine "method B# has been used more widely[ Several iminocarbonates\ especially those with an electron!withdrawing substituent R3 on nitrogen\ participate in this reaction
521
Iminocarbonyl and Halo`en or Chalco`en
readily[ Some compounds of this type which react with primary and secondary amines are listed in Table 5[ Table 5 Carbonimidic diesters "R0O#1C1NR3 useful for preparation of isoureas "method B in Scheme 21#[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ R0 R3 Ref[ ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Et Ts 52JOC1891 Et CN 56CB1593 Me CN 74OPP145\ 80OPP610 Ph CN 76AF0997\ 76JHC164\ 77AF6\ 78JOC0951 Ph COPh 76AF0992 80S642 Ph SO1NH1 Ph SO1C5H3Cl!1 77GEP"O#2523818 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
PhO N –N
+
O
N R
R
(127)
Formamidinium chlorides bearing a variety of substituents on nitrogen react with alcoholates or phenolates to give isoureas "method C# ð72HOU"E3#476\ 75GEP"O#2493342Ł[ Fluoride can also be displaced\ as in the formation of the isourea "017# from the corresponding formamidinium ~uoride ð73JFC"15#210Ł[ Methods D and E require the introduction of both nitrogen and oxygen functions^ both are therefore essentially restricted to the formation of cyclic isoureas from 1!aminoethanol and related nucleophiles ð72HOU"E3#476\ 74BCJ2268Ł[ EtO NCF2N(CF3)2 (F3C)2N (128)
"ii# From cyano`en halides\ cyanates and cyanamides The reaction of cyanate esters with amines leads to isoureas\ as shown in Scheme 22[ Strongly basic aliphatic primary and secondary amines give 0 ] 0 adducts ð72HOU"E3#476Ł although in the presence of an excess of the cyanate\ primary amines can give 1 ] 0 adducts ð53CB2916Ł[ Hydroxyl! amine adds to phenyl cyanate to give a 0 ] 0 adduct ð71JOC3066Ł[ Cyanogen chloride and cyanogen bromide can give isoureas with suitable bidentate nucleophiles such as 1!aminophenols[ A more widely used method is the addition of alcohols to cyanamides[ This approach is illustrated by the formation of the isourea "018# "57)# from dimethylcyanamide and but!2!en!1!ol ð80S75Ł and of "029# "70)# from benzyl alcohol\ cyanamide and p!toluenesulfonic acid ð76TL0858\ 89TL3604Ł[ A related reaction is the conversion of the nitrilium salt "020# "Ad 0!adamantyl# into the isouronium salt "021# by reaction with methanol ð73CB491Ł[
R1O R1O NH
R22NH
R1O
N
R3NH2
NH R3N
R22N
NH Scheme 33
R1O
522
At Least One Chalco`en Ph
O
O NH2+ –OTs
NH Me2N (129)
H2N (130)
MeO Ph
NHAd+ SbCl6–
Ph
Ph
N NAd+ SbCl6–
N
Ph (132)
(131)
"iii# From carbodiimides N\N?!Disubstituted isoureas can be formed by the addition of alcohols or phenols to carbodi! imides[ The reaction can be catalysed by bases but also goes well in the presence of copper"I# chloride\ which allows even hindered alcohols to react[ Thus\ a range of alcohols can be added to diisopropylcarbodiimide in the presence of CuCl to give the isoureas ROC" NPri#NHPri in high yield ð76TL3334Ł[ The reaction is useful because it converts the oxygen function into a good leaving group[ This application is illustrated by the reaction of "S#!octan!1!ol and dcc\ which gave the isourea with retention of con_guration "Scheme 23#^ the leaving group can then be displaced with inversion of con_guration ð80S354Ł[ H C6H13
OH
dcc, CuCl 90%
C6H13
H NHC6H11
i, AcOH
O
ii, NaOH
NC6H11
H C6H13
OH
Scheme 34
"iv# By functional `roup interconversion on nitro`en Isoureas with one or more hydrogen atoms attached to nitrogen can be functionalised using acyl chlorides and alkanesulfonyl chlorides ð72HOU"E3#476Ł[ Other types of electrophilic substitution have been reported^ thus\ MeOC"1NH#NH1 can be selectively mono! and dichlorinated by reaction with sodium hypochlorite ð70JOC4937Ł and the isourea "022# reacted with thionyl chloride to give thiatriazine S!oxide "023# ð74TL0094Ł[ There are also several examples of intramolecular N!alkylation of isoureas ð77CC0064\ 78CC341Ł[ O
TMS-N ArO
N
N-TMS N
OAr
Me (133) Ar = 4-MeC6H4
ArO
S N
N OAr
Me (134)
"v# Other methods Isoureas can be prepared by O!alkylation of ureas using trialkyloxonium tetra~uoroborates ð76CB228Ł[ Some examples of intramolecular O!alkylation have also been reported ð72HOU"E3#476\
523
Iminocarbonyl and Halo`en or Chalco`en
78CC341Ł[
Dimethyl formamide diethyl acetal reacts with N!chloroamides to give isoureas RCON1C"OMe#NMe1 ð69CB145Ł[ A series of cyclic isoureas has been prepared using a 0\2! dipolar cycloaddition route "Scheme 24# ð80TL4876Ł[ SMe
Ar –
CsF
TMS
N
NR1
+
N
R2
ArCHO
O NR1
NR1
N
R2
R2
Scheme 35
5[19[1[2[1 Iminocarbonyl compounds with one oxygen and one phosphorus function Compounds of this class have been prepared by nucleophilic displacement of chloride from carbonimidic chlorides with a phosphorus function ð60ZOB1044\ 89ZOB111Ł[ An example is the arylhydrazone "024#\ which was prepared from the corresponding chloro compound\ sodium sul_te and HCl ð89ZOB111Ł[ HSO2O NNHC6H4Br-4 (PriO)2P O (135)
5[19[1[2[2 Iminocarbonyl compounds with one oxygen and one metalloid or metal function Oxazoles bearing a trimethylsilyl or a trimethylstannyl function at the 1!position are rep! resentatives of this type ð76JOC2302Ł[ The dihydrooxazole "025# was prepared "69)# from the oxazolinyllithium intermediate "026# and trimethyltin chloride\ but attempts to form the cor! responding trimethylsilyl derivative led only to opening of the ring ð76S582Ł[ The corresponding boron substituted species "027# were generated as intermediates when "026# was treated with tri! alkylboranes ð72SC256Ł[ N
N SnMe3
O (136)
N BR3–
Li O
O
(137)
(138)
5[19[1[3 Iminocarbonyl Compounds with One Sulfur and One Other Heteroatom Function 5[19[1[3[0 Iminocarbonyl compounds with one sulfur and one nitrogen function Compounds of this class are usually referred to as isothioureas^ the parent compound "HS#"H1N#C1NH is named as carbamidothioic acid in Chemical Abstracts[ There are many com! pounds of this type in the literature and by far the most common method of preparation is from thioureas\ by alkylation or other electrophilic substitution on sulfur[ More highly functionalised compounds can be obtained from thioureas by successive substitution on sulfur and on nitrogen[ A review by Kuhle ð72HOU"E3#486Ł provides a comprehensive survey of methods of preparation[ The major methods are summarised below[
524
At Least One Chalco`en "i# From carbonimidic halides
Carbonimidic dichlorides have been used only infrequently as starting materials for isothioureas\ because of the problems associated with introducing two nucleophiles successively[ Compounds of the type RS"PhNH#C1NSO1Ph have been prepared in moderate yield by successive displacement of chloride by thiols and by aniline ð74M540Ł[ When both nucleophiles are in the same molecule\ as with 1!aminothiophenol\ the method works well[ If the precursor imidoyl chloride already contains the sulfur function\ replacement of chloride by a nitrogen nucleophile occurs readily ð80JPR076Ł[ The nucleophile is normally a primary or secondary amine but sodium thiocyanate has been used to prepare compound "028# from the corresponding chloride ð75JOC3932Ł^ benzophenone imine\ Ph1C1NH\ has also been used in this type of displacement ð78JOC0074Ł[ The chloride of chloro! formamides is similarly readily replaced by sulfur nucleophiles to give isothioureas[ MeS NBut SCN (139)
"ii# From cyanamides\ carbodiimides or thiocyanates The addition of sulfur nucleophiles\ usually thiols\ to cyanamides or to carbodiimides produces isoureas "Scheme 25#[ The sulfur function of thiophosphoric diesters "RO#1P"1S#OH also adds to carbodiimides but the isothioureas so formed are unstable and readily rearrange to thioureas ð66JOC2518Ł[ Isothioureas unsubstituted on nitrogen can also be prepared by the addition of amines to thiocyanates "Scheme 25#[ R2N
NR4
•
R1SH (R2 = R4, R3 = H)
R2R3N
R1SH
R 1S NR4
N (R4 = H)
R2R3NH
R1S
N
(R4 = H)
R2R3N Scheme 36
"iii# From thioureas A wide range of alkylating agents has been used to convert thioureas bearing one or more hydrogen atom on nitrogen into isothioureas ð72HOU"E3#486Ł[ Alkyl halides are most commonly used ð77S359Ł but there are many examples of the use of other types of alkylating agent[ Even the tertiary bromide 0!bromoadamantane reacted with thiourea to give the isothiourea "039^ Ad 0! adamantyl# in 10) yield ð81CCC0836Ł[ It is also possible to introduce aryl substituents on sulfur by using activated aryl halides or arenediazonium salts as electrophiles[ Thioureas can be phos! phorylated on sulfur by reaction with a variety of phosphorus electrophiles ð89ZOB687\ 81IZV314Ł[
AdS NH2+Br– H2N (140)
525
Iminocarbonyl and Halo`en or Chalco`en
"iv# From iminodithiocarbonates Compounds of the type "MeS#1C1NX "X CN\ COR\ SO1R\ etc[# react readily with nitrogen nucleophiles "including amines and sulfonamides#[ Usually one of the sulfur functions can be displaced selectively to give an isothiourea\ although the use of nucleophilic amines in excess can lead to the formation of guanidines[ Diamines can give either guanidines or bis"isothioureas# "030#\ depending on the dilution ð82BCJ037Ł[ The reaction has proved to be widely used for the preparation of N!cyano substituted thioureas ð73CPB3782\ 77JOC2019Ł[ SMe
SMe N H
ArSO2N
( )
n
NSO2Ar
N H
(141)
"v# By substitution on nitro`en Isothioureas with a free NH group can be acylated by a wide range of reagents including acyl chlorides\ isocyanates and isothiocyanates ð72HOU"E3#486Ł[
"vi# Cycloaddition methods A ð1¦1Ł cycloadditionÐcycloreversion method of preparing isothioureas from arenesulfonyl isocyanates and dithiocarbamates is illustrated in Scheme 26[ Conjugated isothioureas "031# ð77CPB3644Ł act as dienes and undergo ð3¦1Ł cycloaddition to sulfene "H1C1SO1Ł to give the thiadiazine dioxides "032# ð76TL1530Ł[ ArSO2
R3S ArSO2
N
•
O
+
O N
S
S
R1R2N
R1R2N
–COS
R3S NSO2Ar R1R2N
SR3 Scheme 37
Ar
Ar
N
MeS
N
MeS
N
SO2
N NMe2
(142)
NMe2 (143)
5[19[1[3[1 Iminocarbonyl compounds with one sulfur and one phosphorus function Diazo compounds "033# ð71JOC0173Ł and "034# ð83T2084Ł bearing a sulfur and a phosphorus substituent have been prepared in good yield from the corresponding methylene compounds by diazo transfer using tosyl azide and a base[ Et2NSO2
PhSO2 N2
(MeO)2P
N2 (EtO)2P
O (144)
O (145)
526
At Least One Chalco`en 5[19[1[3[2 Iminocarbonyl compounds with one sulfur and one metalloid or metal function
1!Trimethylsilylthiazole "035# provides an example of this class of compounds ð89PAC532Ł[ Dihy! drothiazoles bearing both trimethylsilyl and trimethylstannyl substituents are also known ð89H"20#0102\ 82H"25#362Ł[ The route to these compounds is illustrated in Scheme 27[ The boron containing species "036# has been generated from methyl isocyanide ð61LA"644#56Ł but it is unstable and reacts further to give a zwitterionic 1 ] 0 adduct "Scheme 28#[ N TMS S (146)
R
R R
N
R
BuLi
R
N S
S
R
NC
R
R
Li
SLi
S-TMS
Me3SnCl R = H, 44%
R = H, 42% R = Me, 53%
120 °C
R
R R
NC
TMS-Cl
R
N
N
SnMe3
S
TMS
S Scheme 38
PhS PhS MeNC
+ Et2BSPh
NMe
91%
Et2B (147)
+
R
N
Et2BSPh
–
Et2B
–
BEt2
+
S Ph
Scheme 39
5[19[1[4 Iminocarbonyl Compounds with One Selenium and One Other Heteroatom Function Compounds of the type R0Se"R1R2N#C1NR3 are isoselenoureas[ Although not as numerous as isothioureas\ they can be prepared by analogous methods[ The most common method of preparation is the alkylation of selenoureas ð51JOC1788\ 67JHC362\ 75NJC40\ 78MI 519!90Ł[ An intramolecular addition of an amine to a selenocyanide leads to the formation of a cyclic selenourea "Scheme 39#[ The selenocyanide was generated in situ from 1!aminoethylselenosulfuric acid and cyanide ð54JOC1343Ł[ An intermediate isoselenocyanate is formed by the ring opening of the azirine "037# by carbon diselenide "Scheme 30# and its reaction with dimethylamine then iodomethane gives the isoselenourea "038# ð71CB1405Ł[ CN–
H2N
SeSO3H
Se H2N
NH2
SeCN
N
Scheme 40
Se–
Se N
CSe2
NMe2
N
N +
NMe2
•
Se
SeMe i, Me2NH ii, MeI
N NMe2
Se Me2N
(148)
O Me2N (149)
Scheme 41
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.21 Functions Containing an Iminocarbonyl Group and Any Elements Other Than a Halogen or Chalcogen IAN A. CLIFFE Wyeth Research (UK), Taplow, UK 5[10[0 IMINOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGEN OR CHALCOGEN FUNCTIONS# 5[10[0[0 Iminocarbonyl Derivatives with Two Nitro`en Functions 5[10[0[0[0 N!Unsubstituted iminocarbonyl derivatives 5[10[0[0[1 N!Alkyliminocarbonyl derivatives 5[10[0[0[2 N!Alkenyliminocarbonyl derivatives 5[10[0[0[3 N!Aryliminocarbonyl derivatives 5[10[0[0[4 N!Alkynyliminocarbonyl derivatives 5[10[0[0[5 N!Acyliminocarbonyl derivatives 5[10[0[0[6 N!Cyanoiminocarbonyl derivatives 5[10[0[0[7 N!Haloiminocarbonyl derivatives 5[10[0[0[8 N!Chalco`enoiminocarbonyl derivatives 5[10[0[0[09 N!Aminoiminocarbonyl derivatives 5[10[0[0[00 N!P\ N!As\ N!Sb and N!Bi iminocarbonyl derivatives 5[10[0[0[01 N!Si\ N!Ge and N!B iminocarbonyl derivatives 5[10[0[1 Iminocarbonyl Derivatives with One Nitro`en and One P\ As\ Sb or Bi Function 5[10[0[1[0 N!Alkylimino derivatives with one P or As function 5[10[0[1[1 N!Arylimino derivatives with one P function 5[10[0[1[2 N!Acylimino derivatives with one P function 5[10[0[1[3 Hydrazono derivatives with one P function 5[10[0[1[4 Diazonium derivatives with one P function 5[10[0[1[5 N\N!Dialkyliminium derivatives with one P function 5[10[0[2 Iminocarbonyl Derivatives with One Nitro`en and One Metalloid Function 5[10[0[2[0 Silicon derivatives 5[10[0[2[1 Boron derivatives 5[10[0[3 Iminocarbonyl Derivatives with One Nitro`en and One Metal Function 5[10[0[3[0 Group 07 transition!metal derivatives 5[10[0[3[1 Other metal derivatives 5[10[1 IMINOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE P\ As\ Sb OR Bi FUNCTION "AND NO HALOGEN\ CHALCOGEN OR NITROGEN FUNCTIONS# 5[10[1[0 Iminocarbonyl Derivatives with One P\ As\ Sb or Bi Function and One P\ As\ Sb or Bi Function 5[10[1[0[0 Iminocarbonyl derivatives with one P function and one P\ As\ Sb or Bi function 5[10[1[0[1 Iminocarbonyl derivatives with one As\ Sb or Bi function and another As\ Sb or Bi function 5[10[1[1 Iminocarbonyl Derivatives with One P\ As\ Sb or Bi Function and One Si\ Ge\ or B Function 5[10[1[1[0 Iminocarbonyl derivatives with one P function and one Si\ Ge or B function 5[10[1[1[1 Iminocarbonyl derivatives with one As\ Sb or Bi function and one Si\ Ge or B function 5[10[1[2 Iminocarbonyl Derivatives with One P\ As\ Sb and Bi Function and One Metal Function
528
539 539 539 531 533 533 535 535 536 537 549 542 544 545 545 546 546 547 548 559 559 550 550 551 552 552 553
554 554 554 557 557 557 558 569
539
Iminocarbonyl and Any Other Elements 5[10[1[2[0 Iminocarbonyl derivatives with one P function and one metal function 5[10[1[2[1 Iminocarbonyl derivatives with one As\ Sb and Bi function and one metal function
569 560
5[10[2 IMINOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE METALLOID FUNCTION "AND NO HALOGEN\ CHALCOGEN\ OR GROUP 4 ELEMENT FUNCTIONS# 5[10[2[0 Iminocarbonyl Derivatives with Two Metalloid Functions 5[10[2[0[0 N!Unsubstituted iminocarbonyl derivatives 5[10[2[0[1 N!Alkyl! and N!aryliminocarbonyl derivatives 5[10[2[0[2 N!Haloiminocarbonyl derivatives 5[10[2[0[3 N!Aminoiminocarbonyl "diazomethane# derivatives 5[10[2[0[4 N!Silyliminocarbonyl derivatives 5[10[2[1 Iminocarbonyl Derivatives with One Metalloid Function and One Metal Function 5[10[2[1[0 N!Alkyl! and N!aryliminocarbonyl derivatives 5[10[2[1[1 N!Aminoiminocarbonyl "diazomethane# derivatives
560 560 560 560 561 561 562 563 563 563
5[10[3 IMINOCARBONYL DERIVATIVES CONTAINING TWO METAL FUNCTIONS
564
5[10[0 IMINOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE NITROGEN FUNCTION "AND NO HALOGEN OR CHALCOGEN FUNCTIONS# 5[10[0[0 Iminocarbonyl Derivatives with Two Nitrogen Functions Iminocarbonyl derivatives with two nitrogen functions are called guanidines[ Common methods of preparation of this class of compounds are shown in outline in Scheme 0[ The following sections are ordered by type of substituent on the imino N1!atom[ NR2R3
MeI (or Me2SO4) or COCl2
NR4R5
X = MeS, Cl
S
+
NR2R3 X NR4R5
(1)
MeI or COCl2 or POCl3
NR2R3 O
X = MeO, Cl, Cl2PO2
NR4R5
(2)
(3)
i R1NH2
R1 N
NHR3
R2Hal
NR4R5
v
R1 N
NR2R3
R2 = H
NR4R5 (5a)
(4)
R1 N H
i, R2R3NH ii, R4R5NH
NR3
ii
NR4R5
R1 N
(5b)
R4R5NH
Cl Cl
(6)
R4R5NH iv
iii
R2
R1 N
N C N
•
R3
N R2
(7)
(8)
i, S -methylisothiouronium, O-methylisouronium, O-phosphorylisouronium or chloroformamidinium salts; ii, carbonimidic dichlorides; iii, carbodiimides; iv, cyanamides; v, guanidines Scheme 1
5[10[0[0[0 N!Unsubstituted iminocarbonyl derivatives The preparation of guanidine "4a^ R0ÐR4 H# ð72HOU"E3#597\ 80MI 510!90Ł and biguanide "4a^ R0Ð R H\ R4 C"1NH#NH1# ð48JA2617\ 50CRV202Ł will not be discussed here[ 3
530
At Least One Nitro`en "i# N!Unsubstituted iminocarbonyl derivatives from amidinium salts and urea derivatives
The reaction of amines with S!methylisothiouronium salts "1^ X MeS# produces guanidinium salts in high yields "Scheme 0\ i#[ Common variants of this classic reaction\ known as the Rathke guanidine synthesis ð0773CB186Ł\ involve the use of O!methylisouronium\ O!phosphorylisouronium and chloroformamidinium "Vilsmeier# salts in place of S!methylisothiouronium salt[ The method produces a wide range of substituted guanidines and is particularly suitable when ammonia and primary alkylamines are used as nucleophiles ðB!82MI 510!90Ł[ The reaction with secondary amines is generally less facile than with primary ð52JMC164Ł\ whilst hindered amines such as t!butylamine fail to react ð53CPB835Ł[ 0!t!Butylguanidine "4b^ R0 But\ R2ÐR4 H# may\ however\ be prepared in 49) yield by using the more reactive zwitterionic aminoiminomethane sulfonic acid "1^ X SO2−\ R1ÐR4 H# as the electrophile[ This reagent converts primary amines to guanidine derivatives in high yields under mild conditions at room temperature ð77TL2072\ 81JCS"P0#2068Ł and has the advan! tage over the Rathke procedure of not producing unpleasant methanethiol as a by!product[ Ther! mally stable N!substituted aminoiminomethanesulfonic acids "1^ X SO2−\ R1 alkyl\ R2ÐR3 H\ alkyl# are prepared by direct oxidation of thioureas "0^ R1 alkyl\ R2ÐR3 H\ alkyl# with peracids in the absence ð75S666Ł or presence ð75JOC0771Ł of sodium molybdate as catalyst[ Vilsmeier salts are also more reactive than isothiouronium salts and the highly hindered 0\0\2\2!tetra! isopropylguanidine "4a^ R0 H\ R1ÐR4 Pri# is obtained in 70) yield by treating the Vilsmeier salt "1^ X Cl\ R1ÐR4 Pri# with ammonia ð71JCS"P0#1974Ł[ Other variants of the Rathke synthesis utilise heteroaromatic species as leaving groups[ 2\4!Dimethyl!0H!pyrazole!0!carboxamidine nitrate "1^ X 2\4!Me1!pyrazol!0!yl\ R1ÐR4 H# ð42JA3942\ 47CJC0430Ł and 0H!pyrazole!0!carboxamidine hydrochloride "1^ X pyrazol!0!yl\ R1Ð R4 H# ð81JOC1386Ł both appear to be superior to S!methylisothiouronium sulfate as guanylating agents for the preparation of monoalkylguanidines "4b^ R0 alkyl\ R2ÐR4 H#[ The second reagent is the more reactive of the two\ producing products which can be puri_ed by simple crystallisation\ but both reagents are poor for preparing guanidine derivatives of sterically hindered\ more basic secondary amines[ However\ the use of heteroaromatic leaving groups has been extended by the _nding that N\N?!bisurethane!protected carboxamidines are a very reactive species "Scheme 1^ R0 t!butoxycarbonyl "t!BOC# PhCH1OCO#] in reactions with weak nucleophiles such as 1\1\1! tri~uoroethylamine or aniline they give high yields of guanidines after deprotection "using TFA for R0 t!BOC and catalytic hydrogenation for R0 PhCH1OCO#[ This observation indicates that the electrophilicity of neutral diacylated derivatives is greater than that of protonated unacylated analogues ð82TL2278Ł[ Pyrazole!containing guanylating agents show utility as reagents for the conversion of ornithine to arginine in solid!phase peptide synthesis ð82SC546Ł[
R1 N
N N
R1 N
R2NH2, THF, 22 °C
R2 N H
N R1
deprotect
R2 N H
H N
N R1
N H
H
H
H
Scheme 2
N!Unsubstituted iminocarbonyl derivatives may be prepared directly and in good yields by the treatment of thiourea derivatives "0# with ammonia in the presence of zinc"II# or preferably lead"II# salts "e[g[\ PbO# with concomitant formation of metal"II# sul_des ð57JMC0157Ł[ 0\2!Dialkylguanidines are prepared from 0!alkylthiourea derivatives by formation of a 0!alkyl!2! t!BOC!thiourea\ reaction with an alkylamine in the presence of a water!soluble carbodiimide "WSC#\ and deprotection "Scheme 2# ð81TL4822Ł[ 0!Alkylguanidines are obtained in an analogous fashion from 0\2!di!t!BOC!thiourea[
NHR1 S NH2
NaH, BOC2O >82%
NHR1 S NHBOC
Tf = trifluoromethanesulfonyl Scheme 3
i, R2NH2, WSC, DMF >80% ii, HCl or TMS-OTf
NHR1 HN NHR2
531
Iminocarbonyl and Any Other Elements
"ii# N!Unsubstituted iminocarbonyl derivatives from cyanamides The preparation of 0!alkyl! and 0\0!dialkylguanidines "4a^ R0ÐR2 H\ R3\ R4 H\ alkyl# by the reaction of amine salts with cyanamide "6^ R1 R2 H# in aqueous or alcoholic solution gives low yields "9Ð19)# of products "Scheme 0\ iv#[ The reaction only works well when metal "e[g[\ calcium# cyanamides are fused with alkylammonium salts ð47CJC0430Ł[ A far more important and widely used preparative reaction is that of a mono! or dialkylamine base or salt with a monoalkylcyanamide "6^ R1 H\ R2 alkyl#\ which gives 0\0!di and 0\0\1!trialkylguanidines "4a^ R0 R1 H\ R2 R3 alkyl\ R4 H\ alkyl# in high yields over a wide temperature range "9Ð079>C# ð57JMC0018\ 72HOU"E3#597Ł[ 0!Cyano!2H!guanidines such as 0!cyano!0\2\2!triethylguanidine are obtained when N!alkyl! dicyanamides are treated with dialkylamines at room temperature "Scheme 3^ R0 R1 Et# but\ on standing\ they decompose into a mixture of mono! and dialkylcyanamides ð62TL2542Ł[ NC
CN
N
R1 N CN
H
R22NH, Et2O
R2
slow decomposition
+
NC N
N
R1
R2
N R2
R1 N CN H
R2 Scheme 4
"iii# N!Unsubstituted iminocarbonyl derivatives from `uanidines The alkylation of unsubstituted guanidine with simple alkyl halides usually gives multicomponent mixtures "Scheme 0\ v#[ The few reports of good yields of monoalkylated products include the reaction of guanidine with tosylates in the presence of sodium hydride "Equation "0## ð54JMC335Ł and the reaction of 1!"arylamino#imidazolines with alkyl halides "Equation "1##\ which gives exocyclic N!alkylation with Na1CO2 or NEt2 as base\ and endocyclic N!alkylation with NaH ð79JMC0106Ł[ NH2+ Cl– H2N
TsO
+
N NH2
NH2
O 2 NaH,
ButOH,
reflux
N
HN
O
H
H
R N Ar
RHal
N
H
O
N Ar
+
N N
(1)
H N Ar
N
O
(2)
N N
H
R
The reaction of guanidines with aryl halides occurs only when the aromatic group is either activated by electron!withdrawing substituents ð53RTC0294Ł or is itself an electron!de_cient hetero! cycle ð51JOC1493Ł "Scheme 0\ v^ R0\ R2ÐR4 H\ R1 1\3!"NO1#1C5H2 or 2!NO1!pyridin!1!yl\ respec! tively#[ An alternative method involving the electrophilic substitution of benzene with hydroxyguanidine!O!sulfonate requires Lewis acid catalyst activation "Equation "2## ð56ZN"B#719Ł[ +
H
NHOSO3–
+
H2N NH2
AlCl3
PhH
N Ph HN
(3)
NH2
5[10[0[0[1 N!Alkyliminocarbonyl derivatives "i# N!Alkyliminocarbonyl derivatives from amidinium salts and urea derivatives There are many examples of the Rathke synthesis of N!alkylguanidines from S!alkyl! isothiouronium salts "1^ X SMe\ SEt# and product yields are usually excellent "Scheme 0\ i# ð72HOU"E3#597\ 82MI 510!90Ł[ Preparation from ureas may also be carried out conveniently via
532
At Least One Nitro`en
O!alkylisouronium "1^ X OMe# ð47CJC0430\ 58JMC601Ł or O!phosphorylisouronium salts "1^ X Cl1PO1# ð76CJC515Ł\ but the preferred method\ via the reactive chloroformamidinium "Vilsme! ier# salts "1^ X Cl#\ permits the preparation of sterically hindered pentaalkylguanidines "4a^ R0Ð R4 alkyl# ð73LA097\ 74LA1067\ 89T0728Ł and highly hindered analogues "e[g[\ 4a^ R0 But\ R1Ð R4 Pri# ð71JCS"P0#1974Ł[ The direct reaction of thioureas "0# with alkylamines in hot ethanol produces good yields of guanidines "4a^ e[g[\ R0 methyl\ R1ÐR4 H# in the presence of lead oxide ð58JMC447Ł[
"ii# N!Alkyliminocarbonyl derivatives from carbonimidic dihalides Tri!\ tetra! and pentaalkylguanidines are obtained from the reaction of carbonimidic dichloride "5# with two molar equivs of the same amine or one each of two di}erent amines ð58AG"E#19Ł "Scheme 0\ ii#[ An example of the reaction of a carbonimidic di~uoride is provided by per~uoro!1! azapropene "CF2N1CF1#\ which reacts with various dialkylamines such as dimethylamine ð67MI 501!90Ł and TMS diethylamide ð81IC377Ł to give 1!tri~uoromethylguanidines "4a^ R0 CF2\ R1Ð R4 Me\ Et#[
"iii# N!Alkyliminocarbonyl derivatives from carbodiimides The reactions of N\N?!dialkylcarbodiimides "7^ R0\ R1 alkyl# with ammonium or mono! and dialkylammonium salts at room temperature give high yields of di!\ tri! or tetraalkylguanidines "4a^ R0 R1 alkyl\ R2 H\ R3\ R4 H\ alkyl# "Scheme 0\ iii# ð51JA2562Ł[ Carbodiimides of type ButN1C1NCHR01 "8^ R0 But\ NMe1# react with NBS to a}ord unstable alkylidenecyanamidinium bromides "09^ R0 But\ NMe1\ X Br# which undergo von Braun elim! ination of ButBr to give alkylidenecyanamides "01^ R0 But\ NMe1# "Scheme 4#[ Treating the alkylidenecyanamide "01^ R0 But\ NMe1# with t!butyl chloride and antimony pentachloride pro! duces the stable hexachloroantimonate "09^ R0 But\ NMe1\ X SbCl5# in quantitative yield and this reacts with amines to give alkylideneuronium salts "00^ R0 But\ NMe1# ð73CB491Ł[ R1 But ButNH2, CH2Cl2 –50 °C, X = SbCl6 70%
R1
But N
•
NBS, CCl4, refux
N
N
R1
But
R1
+
N
H
H (11)
X–
R1
R1 N But
N
–ButX, X = Br, 70%
N
(9)
(10)
R1
ButCl, SbCl5, CH2Cl2 –30 °C, 100%
N R1
NC (12)
Scheme 5
"iv# N!Alkyliminocarbonyl derivatives from cyanamides Reactions of amines or amine salts with alkylcyanamides at room temperature give high yields of guanidines "Scheme 0\ iv# ð72HOU"E3#597Ł[ A particularly mild method performed at very low temperatures involves the reaction of cyanamidinium hexachloroantimonates with ammonia or mono! or dialkylamines "Scheme 5^ R1 R2 alkyl\ R3\ R4 H\ alkyl# ð73CB0050Ł[
R2
i, SbCl5, CH2Cl2, –78 °C ii, ButCl, CH2Cl2, –15 °C
NC N R3
>90%
But
R2
+
N
SbCl6–
N R3
R4R5NH, CH2Cl2, –78 °C
R2 N R3
But
+ HSbCl6
N
>90%
N R4 R5
Scheme 6
533
Iminocarbonyl and Any Other Elements
"v# N!Alkyliminocarbonyl derivatives by miscellaneous methods Complexes of mercury"II# chloride and t!butyl isocyanide react with an excess of mono! and dialkylamines to give guanidine derivatives and mercury through a redox decomposition reaction "Equation "3#^ R1 Bu\ R2 H or R1 R2 Et#[ The reaction with weak nucleophiles "e[g[\ aniline# is enhanced by the addition of strong bases "e[g[\ triethylamine# and a mechanism for the reaction has been proposed ð64JOM"83#222Ł[
But
3R2R3NH, THF, reflux
N C•HgCl2
R2 N R3
But N
(4)
•HCl
[–Hg, –R2R3NH2+ Cl–] >39–70%
N R3 R2
Lithium aluminum hydride reduction of various alkyl!substituted acylguanidines "4a^ R0 acyl\ R ÐR4 H\ alkyl# gives alkylguanidines in yields ranging from 40) to 51)[ The rate of the reaction depends on the number of NH atoms\ and yields are improved by using excess reducing agent in THF at room temperature ð66JOC2597Ł[ 1
5[10[0[0[2 N!Alkenyliminocarbonyl derivatives "i# N!Alkenyliminocarbonyl derivatives from amidinium salts Ketone imines react with Vilsmeier salts to give amino!substituted enimines "Equation "4#^ R H\ Me# ð64C403Ł[ R
Ph NH
R
Ph
(Me2N)2C+Cl Cl–, 2NEt3, CH2Cl2, reflux
NMe2
(5)
N
R = Me, 52%; R = H, 55%
NMe2
"ii# N!Alkenyliminocarbonyl derivatives from `uanidines 0\0\2\2!Tetramethylguanidine reacts with isobutyraldehyde or with dimethyl acetylenedi! carboxylate to give amino!substituted enimines "Scheme 6#[ The former reaction fails with aldehydes bearing one or no a!substituent\ and yields in the latter reaction are often poor owing to the base! sensitive nature of the acetylene ð64C403Ł[ NMe2 N
Me2CHCHO TsOH (cat.)
MeO2C CO2Me Et2O, –10 °C
NMe2
20%
HN 62%
NMe2
NMe2
MeO2C
CO2Me NMe2 N NMe2
Scheme 7
5[10[0[0[3 N!Aryliminocarbonyl derivatives The methods of synthesis of N!aryliminocarbonyl derivatives "i[e[\ 1!arylguanidines# are essen! tially the same as those used for 1!alkylguanidines[
"i# N!Aryliminocarbonyl derivatives from amidinium salts and urea derivatives Although anilines are less nucleophilic than alkylamines they will react with S!alkyl! isothiouronium salts "Scheme 0\ i# to give 1!arylguanidines "4a^ R0 aryl# ð55BSF62Ł\ and high yields of 1!phenyl!0\0\2\2!tetrabutylguanidine "4a^ R0 Ph\ R1ÐR4 Me# have been obtained from the
534
At Least One Nitro`en
reaction of aniline with chloroformamidinium "1^ X Cl\ R1ÐR4 Me\ yield 73)# ð89T0728Ł and O!phosphorylisouronium salts "1^ X Cl1PO1\ R1ÐR4 Me\ yield 35)# ð50CB1167Ł[ 1! "Arylimino#tetrahydroimidazoles such as clonidine "4a^ R0 1\5!Cl1C5H2\ R1 R3 H\ R2R4 "CH1#1# are prepared by the reaction of "a# S!methylisothiouronium salts "1^ X SMe\ R1 aryl\ R2ÐR4 H# with ethylenediamine ð67RTC40Ł^ "b# sulfonic acid derivatives "1^ X SO2−\ R1 R3 H\ R2R4 "CH1#1# with anilines ð75JOC0771Ł^ and "c# the complex formed from 0!acetyl! imidazolidinone and phosphorus oxychloride "1^ X Cl1PO1\ R1 H\ R3 MeCO\ R2R4 "CH1#1# with anilines followed by deacylation ð79AF0622Ł[ The transimination reaction of N!arylphosphimides with thioureas gives 1!arylguanidines in high yield "Equation "5## ð80MIP43525Ł[ BuS
BuS
H
+ N PPh3
O2N
PhH, reflux
N S
SO3H NHCO2Me
H
(6)
N
91%
O2N
N
SO3H NHCO2Me
"ii# N!Aryliminocarbonyl derivatives from carbonimidic dichlorides The stepwise replacement of the two chlorine atoms of the N!arylcarbonimidic dichloride "5^ R0 3!NCC5H3# by two di}erent monoalkylamines gives 0\2!dialkyl!1!arylguanidines "4a^ R0 3! NCC5H3\ R1 R3 alkyl\ R2 R4 H# in high yields "Scheme 0\ ii# ð81SC0080Ł[ The reaction of N!phenylcarbonimidic dichloride with TMS!dialkylamides gives high yields of intermediate chloro! formamidines which react further\ only in the case of sterically unhindered chloroformamidines "Scheme 7^ R0 Me# and TMS!dimethylamide\ to give 0\0\2\2!tetramethyl!1!phenylguanidine "R0 R1 Me# ð58TL0310Ł[ Organothallium amides "Me1TlNMe1# undergo related reactions ð62ZC081Ł[ The reaction of N!"1\3!dichlorophenyl#carbonimidic dichloride "5^ R0 1\3!Cl1C5H2# with ethylenediamine gives clonidine "4a^ R0 1\5!Cl1C5H2\ R1 R3 H\ R2R4 "CH1#1# ð67RTC40Ł[ Cl PhN Cl
TMS-NR12, 85 °C, 24 h R1
–TMS-Cl = Me, Et, Pr 54–84%
NR12 PhN Cl
TMS-NR22, 85 °C, 24 h –TMS-Cl = R2 = Me 98.5%
R1
NR12 PhN NR22
Scheme 8
"iii# N!Aryliminocarbonyl derivatives from carbodiimides 1!Aryl!0\2!disubstituted guanidines are prepared in good yields from N\N?!disubstituted car! bodiimides and anilines in the absence of solvent with or without heating^ in re~uxing toluene^ or in DMF at room temperature in the presence of sodium hydride "Scheme 0\ iii# ð79JMC02Ł[
"iv# N!Aryliminocarbonyl derivatives from cyanamides Arylcyanamides "6^ R1 H\ R2 aryl# react with ammonia and primary amines "Scheme 0\ iv# in methanol at 099>C in a steel bomb to give 1!arylguanidines "4b^ R0 R3 H\ R2 aryl\ R4 H\ alkyl# in reasonable yields "31Ð74)# ð64JMC89Ł[
535
Iminocarbonyl and Any Other Elements
"v# N!Aryliminocarbonyl derivatives by miscellaneous methods Triarylguanidines are obtained in good yield by the reaction of anilines with 1\1!dichloro!0\2! benzodioxole "Equation "6## ð53LA"564#031Ł[
NHPh
5 PhNH2, THF, reflux
O
O
Cl
Cl
(7)
PhN
97%
NHPh
5[10[0[0[4 N!Alkynyliminocarbonyl derivatives 1!"Phenylethynyl#!0\0\2\2!tetramethylguanidine is formed as a transient intermediate in the ~ash photolysis of phenylguanidinocyclopropenones "Scheme 8#[ An acylguanidine is the _nal product in aqueous solution ð80AG"E#0245Ł[ O –CO
Ph
N
NMe2
O
Me2N
hν, H2O
NMe2
NMe2 Ph
H2O
NMe2 Ph
N
N NMe2
Scheme 9
5[10[0[0[5 N!Acyliminocarbonyl derivatives The tautomerism of monoacylguanidines has been studied ð50CJC0906Ł[
"i# N!Acyliminocarbonyl derivatives from S!methylisothiourea Acylation of the free base of S!methylisothiouronium salts "1^ X SMe\ R1 alkyl\ R2ÐR4 H# with acid chlorides followed by treatment of the resulting S!methyl!N!acylthioureas with appropriate monoalkylamines gives 0!acyl!1\2!dialkylguanidines "4a^ R0 R1 alkyl\ R2 R3 H\ R4 acyl# ð64AF0366Ł[
"ii# N!Acyliminocarbonyl derivatives from cyanamides The reaction of N\N!dialkylcyanamides with acid chlorides gives acylated chloroformamidinium salts which on reaction with secondary amines produce acylated guanidines "Scheme 09^ R Me\ Et\ allyl# ð70MI 510!90Ł[ O
O C4F9COCl
NC NR2
72–94%
C4F9
NR2 N
R2NH 51–57%
Cl
NR2
C4F9 N
NR2
Scheme 10
"iii# N!Acyliminocarbonyl derivatives from `uanidines Unsubstituted and monosubstituted guanidines are acylated by condensation of the requisite guanidine free base with the appropriate acid ester ð50CJC0906\ 64AF0366Ł[ The preparation of di! and trisubstituted guanidines takes longer and in these cases acylation of guanidines with acid chlorides or anhydrides is the normal practice ð57JOC441Ł\ although mixtures of products invariably
536
At Least One Nitro`en
result ð64AF0366Ł[ Di! and triacylated guanidines have been deacylated selectively to give monoacyl! guanidines with either ethanol or a quaternary ammonium hydroxide ion!exchange resin ð66JOC2597Ł[ 1!Phenyl!0\0\2\2!tetramethylguanidine undergoes exchange reactions with benzoyl and thio! benzoyl isocyanates to give high yields of acylated or thioacylated guanidines "Equation "7## ð67LA0432Ł[ X
X
Ph
NMe2
NCO
PhN
Ph
NMe2 N
X = O, S 76–93%
NMe2
(8)
NMe2
1!"Thiocarbamoyl#guanidines are produced by the reaction of 0\0\2\2!tetramethylguanidine with N\N!dimethylthiocarbamoyl chloride ð61IJS"A#094Ł or isothiocyanates "Equation "8## ð71PIA330Ł[ R1
S N
NMe2
Cl R2 MeCN, reflux R1, R2 = Me, 46% or
HN NMe2
R1NCS, PriOH, 22 °C R1 = Me, Ph; R2 = H 70–90%
R1 N
S
R2
N
NMe2
(9)
NMe2
1!Amidinoureas "4a^ R0 ArNHCO# are obtained from the reaction of guanidines with aryl isocyanates "ArNCO# and:or carbamoyl chlorides "ArNRCOCl# ð67AF0324Ł[
"iv# N!Acyliminocarbonyl derivatives by miscellaneous methods Carbonic acid ortho!amides react with acid amides to give acylguanidines "Equation "09#^ R H\ Et\ Ph# ð68LA1985Ł[ O
+ PriO
R NH2
NMe2 NMe2 NMe2
O R
NMe2 N
(10)
NMe2
5[10[0[0[6 N!Cyanoiminocarbonyl derivatives "i# N!Cyanoiminocarbonyl derivatives from thioureas and their derivatives Cimetidine "05^ R 1!""4!methylimidazol!3!yl#methylthio#ethyl# "Scheme 00# is an example of an N!cyanoiminocarbonyl derivative which has been prepared by several methods[ These methods include the reaction of amine "02# with methyl isothiocyanate to give the thiourea "03#\ which is treated with lead cyanamide "i#^ the reaction of amine "02# with N!cyano!N?\S!dimethylisothiourea "ii#^ and the reaction of amine "02# with dimethylcyanodithioimidocarbonate followed by treatment of the intermediate S!methylisothiourea "04# with methylamine "iii# ð66JMC890Ł[ The Rathke reaction is acid catalysed and so the use of the weak base N!cyano!N?\S!dimethylisothiourea in "ii# leads to a low yield of product[ This limitation has been circumvented by the room temperature reaction of N!aryl! or N!alkyl!N?!cyanothioureas "0^ R1 R3 H\ R2 CN\ R4 aryl\ alkyl# with monoalkyl! amines in DMF in the presence of a water!soluble carbodiimide\ which gives 1!cyanoguanidines "4b^ R0 alkyl\ R2 CN\ R3 H\ R4 aryl\ alkyl# in a single step in high yields "×54)# ð78TL6202Ł[ The reaction works well with sterically hindered t!alkylamines and N\N!dialkylamines and is an improvement over the earlier procedure using dicyclohexylcarbodiimide"dcc# ð73SC0164Ł[ The room temperature reaction of cyanamide "R0NH1\ R0 CN# with a range of N!"3!pyridyl#thioureas "0^
537
Iminocarbonyl and Any Other Elements
R1 R4 H\ R2 3!pyridyl\ R3 Ph\ neopentyl\ etc[# in the presence of dcc also gives 1!cyano!0! "3!pyridyl#guanidines "4b^ R0 CN\ R2 3!pyridyl\ R3 Ph\ neopentyl\ etc[\ R4 H# in good yields "×39)# ð67JMC662Ł[ NHR S MeNCS, EtOH >80% i
NHMe (14) NC
PbNCN, DMF, reflux 43%
NHMe N
NC
SMe MeCN, 20%
R NH2 (13)
ii
NC
SMe
NHMe (16)
iii
N
NC
SMe EtOH, 73%
NHR N
MeNH2, EtOH 90%
NHR N SMe (15)
N
S
R= N H Scheme 11
"ii# N!Cyanoiminocarbonyl derivatives from carbodiimides The reaction of cyanamide "H1NCN# with carbodiimides gives 1!cyanoguanidines in high yields "Scheme 0\ iii#[ The reaction with hindered carbodiimides "7^ R0 aryl\ R1 t!alkyl# in the absence of solvent occurs smoothly in the presence of catalytic diisopropylethylamine\ whilst reaction with less!hindered carbodiimides is exothermic ð67JMC662Ł[
"iii# N!Cyanoiminocarbonyl derivatives from cyanamides The synthesis of monosubstituted 1!cyanoguanidines "4b^ R0 R4 H\ R2 CN\ R3 alkyl# is accomplished in reasonable yields by the condensation of sodium "or lithium# dicyanamide "6^ R1 Na\ R2 CN# with monoalkylammonium salts in either re~uxing t!butanol or water "Scheme 0\ iv# ð57JMC700Ł[ A cyanoguanidine is formed from the reaction of N!methyl!N!phenylcyanamide with sodium "Equation "00##[ The reaction is highly dependent on the nature of the nitrogen substituents and proceeds via an electron transfer mechanism involving the formation of a catalytic quantity of PhMeN− ð80CJC750Ł[ The same product is formed in a multistep sequence from the reaction of N! methyl!N!phenylcyanamide with phenyllithium in 47) yield ð60CJC1204Ł[ Na, PhMe
NC N(Me)Ph
NC
N(Me)Ph (11)
N 61%
N(Me)Ph
5[10[0[0[7 N!Haloiminocarbonyl derivatives The most common method of preparation of N!haloiminocarbonyl derivatives "N!halo! guanidines# is the elemental halogenation of appropriately substituted guanidines[ It should be
538
At Least One Nitro`en
noted that many N!haloguanidines are unstable and:or explosive and consequently most halo! genations in the laboratory are carried out on a small scale and with appropriate shielding and protective equipment[ The issue of tautomerism and double bond isomerism in unsymmetrical compounds has been studied ð56TL2740Ł[ Per~uoroguanidine is produced by the reaction of guanidine salts with elemental ~uorine either in aqueous solution ð64USP2857047Ł or in the absence of solvent but in the presence of alkali metal ~uorides as diluents ð56JOC0551\ 56JOC2748Ł "Equation "01##[ The latter technique has been extended to the direct ~uorination of cyanoguanidine in the presence of a large amount of sodium ~uoride "Equation "02## ð57JOC1411Ł[ In a similar way\ guanidine nitrate has been chlorinated to give a 26) yield of perchloroguanidine using a two!phase system consisting of water and chloroform in the presence of _nely divided marble and NaCl at −09>C "Equation "03## ð70MI 510!91Ł[ Fluorination of monoalkoxycarbonylguanidines gives tetra~uoro derivatives "Equation "04##\ whilst ~uorination of 0\2!bis"alkoxycarbonyl#guanidines gives not only the expected ~uorinated product\ but also produces some ~uorinolysis of the alkoxycarbonyl groups so that bis"alkoxycarbonyl#~uoro! guanidines and alkoxycarbonyltetra~uoroguanidines are both formed "Equation "05## ð58JOC1739Ł[ 1!Chloro! and 1!bromotetramethylguanidines are prepared by the direct halogenation of 0\0\2\2! tetramethylguanidine "Equation "06#^ Hal Cl\ Br# ð55JOC0315Ł[ NH2
NF2
excess F2
HN
FN
(12)
NH2
NF2
H
F excess F2, NaF
N CN
N CF2NF2
HN NH2
NF2 NH2
HN NH2
H
NCl2
excess Cl2 marble, NaCl
NCl2
F
OR
(15)
OR
FN
NH2
NF2
O
F
N HN
O N
excess F2
HN
(14)
ClN
O N
H
(13)
FN
O F
N excess F2
OR
FN
N H
OR N F
RO
+
(16) OR
FN NF2
RO O
O N
O NMe2 HN
Hal2
NMe2 (17)
HalN
NMe2
NMe2
1!Chloro!0\0!dialkylguanidines may be prepared by an oxidation route in which the appropriate unchlorinated guanidine salt is reacted with sodium hypochlorite in a two!phase solvent system at low temperature "Equation "07#^ X Cl\ NO2\ SO3#[ 0!Aryl!1!chloroguanidines "Equation "07#^ R0 Ph\ R1 H# are obtained in low yields "³09)# by this route owing to oxidative side reactions^ however\ if the possibility of the interfering aromatic quinone!type intermediates is eliminated "because\ e[g[\ R0 Ph\ R1 Me#\ then 1!chloro derivatives are obtained in high yields ð54ZN"B#0054Ł[ NR1R2 •HX
HN NH2
NaOCl, –5 °C, H2O–Et2O
NR1R2 (18)
ClN NH2
549
Iminocarbonyl and Any Other Elements
An example where a 1!haloguanidine is not prepared by the formation of a nitrogen0halogen bond is the reaction of an amine with an N!~uoroimine] the reaction of electron!de_cient penta~uoroguanidine with alkyl! or arylamines at low temperatures gives an adduct which on warming loses di~uoroamine to yield a tri~uorinated product "Scheme 01#[ The rate of reaction and the type of product formed depends upon the nucleophilicity of the amino component ð62JOC0964Ł[ NF2
R1R2NH, –110 °C
FN
NF2 NR1R2 NF2
FHN
NF2
NF2
–HNF2, 25 °C
FN NR1R2
Scheme 12
5[10[0[0[8 N!Chalcogenoiminocarbonyl derivatives "i# Oxy`en derivatives The most common methods of synthesis of hydroxyguanidines involve the reactions of N! substituted or unsubstituted hydroxylamines with S!alkylisothioureas ð56ZN"B#719\ 63JOC0055Ł or chloroformamidines ð57JA5735Ł\ carbodiimides ð61CB0698\ 62ZC47Ł\ and cyanamides "Scheme 02\ "i#Ð "iii#\ respectively# ð55JCS"C#1920\ 69CC795Ł[ R1 N
NR2R3
R4NHOH
R1 N
NR2R3 N R4
i
X
R1 N
R4NHOH R3
HO
•
ii =H
N R2
X = SR, Cl H2NOH R 1 = R4 = H
iii
R2 NC N R3 i, S-alkylisothioureas or chloroformamidines; ii, carbodiimides; iii, cyanamides Scheme 13
Tetrasubstituted hydroxyguanidines are best prepared from chloroformamidinium chlorides via reaction with O!"THP#hydroxylamine followed by removal of the protecting group with acid "Equation "08##[ Cyclic tri! and tetrasubstituted hydroxyguanidines are prepared by the reaction of phosgene!O!"THP#oxime with a diamine\ followed by removal of the protecting group "Equation "19## ð65JOC2142Ł[ Other methods for the formation of hydroxyguanidine!like compounds employ the reduction of nitro precursors[ Dinitroformaldehyde oxime is formed by the reduction of tri! nitromethane in an acid medium on a mercury cathode "Equation "10## ð64MI 510!90\ 65MI 510!90Ł\ and 0\0?!"hydroxyimidoyl#bis"1!aryl#diazenes are produced when 2!nitroformazans are reduced by H1S in aqueous alcoholic ammonia solution at 9>C "Equation "11## ð79MI 510!90Ł[ NR1R2 Cl
+
NR3R4
THP-O
Cl
i, THP-ONH2, NEt3 ii, H3O+
NR1R2
HO N
31–65%
i, R1NH(CH2)nNHR2, NEt3 ii, 3 mol l–1 HCl
N
(19) NR3R4
R1 N
HO
(CH2)n
N Cl
n = 2, 3 31–58%
N R2
(20)
540
At Least One Nitro`en NO2
+2e–, + 2H+
O2N
HO
NO2 (21)
N –H2O
NO2
NO2
Ar
Ar N N
N N
HO
H2S
(22)
N
O2N
N N
N NHAr
Ar
Alkoxyguanidines are prepared by methods analogous to those used for the hydroxy derivatives above but with O!alkylhydroxylamines in place of hydroxylamines[ They are also obtained by alkylation of hydroxyguanidines with alkyl bromides or iodides "Scheme 03# ð63JPR323Ł[ Acetoxy! and benzoyloxyguanidines are prepared by acylation of hydroxyguanidines "Scheme 03# ð69BAP458\ 63JPR323Ł[ O NR1R2
O R
NR1R2
HO
RCOCl
N
N
R5Hal
R5O
NR1R2 N
NR3R4
NR3R4
NR3R4
Scheme 14
"ii# Sulfur derivatives Penta~uorosulfenylguanidines are obtained from the reaction of SF4N1CCl1 either with dial! kylamines ð71JFC"08#300Ł or with more nucleophilic dialkylaminosilanes "Equation "12#^ R alkyl^ X H\ TMS# ð81IC377Ł[ They are also formed by the reaction of guanidine N0H bonds with sulfenyl chlorides ð48CB1452Ł[ F5S
Cl
R2NX
N Cl
NR2
F5S
R = alkyl; X = H, TMS
(23)
N NR2
Several methods for the synthesis of sulfonylguanidines are known[ The simplest method employs the condensation of an arylsulfonyl chloride with guanidine "Equation "13## ð39USP1107389Ł[ NH2•HNO3 ArSO2Cl +
HN NH2
H2O–Me2CO, NaOH
NH2
ArO2S
(24)
N NH2
The Rathke guanidine synthesis using S!methylisothiouronium salts tends to give low yields of sulfonylguanidines "Equation "14#^ X SMe# ð62JOC0480Ł\ and so the more reactive amidinium chlorides are usually employed "Equation "14#^ X Cl\ R0 Ar\ R1ÐR4 alkyl ð62JOC0480\ 68ZC149Ł^ X Cl\ R0 Me\ R1 Bui\ R2 H\ R3 R4 alkyl ð56AP"299#456Ł^ and X Cl R0 R1 Ph\ R2Ð R4 H ð63ZOR31Ł#[ Amidinium chlorides will react with a range of nitrogen nucleophiles other than amines\ such as sodium azide and hydrazine\ to give sulfonylcarbamimidic azides and N!""dialkylamino#hydrazinomethylene#sulfonamides "Scheme 04^ R1\ R2 Me\ Ph#[ Sulfonyl! carbamimidic azides react with triphenylphosphane to give iminophosphoranes ð71LA1094Ł[ The leaving!group ability of cyanide has been exploited in a sequence involving the room temperature reaction of 3!chloro!4!Ts!0\1\2!dithiazole with secondary amines to give N\N!dialkylcyano! formamidines which on heating with excess secondary amine give 1!Ts!tetraalkylguanidines "Scheme 05# ð81TL3852Ł[ The aryl! or alkylsulfonyl group can be attached to the nucleophile instead of the electrophile as in the reaction of arylsulfonamides with S!alkylisothioureas "Equation "15## ð56AG"E#751Ł[ "Alkylaminosulfonyl#guanidines have been prepared by the reaction of N\N!dialkyl! N?!chlorosulfonylchloroformamidines with primary or secondary amines "Equation "16## ð77JPR899Ł[ N!Sulfonylguanidines are also prepared by the reaction of amines with either S\S! dimethyl!N!arylsulfonyliminodithiocarbonimidate ð55CB1774Ł or N!Ts!carbonimidic dichloride "Equation "17#^ X MeS\ Cl# ð62JOC0480\ 66AP719\ 68JOC3425Ł[
541
Iminocarbonyl and Any Other Elements R1O2S
NR2R3
R1O2S
R4R5NH
N
NR2R3 (25)
N NR4R5
X
NR2R3
ArO2S
NR2R3
ArO2S
H2NNH2
N
N 72–86%
Cl NaN3 46–86%
NHNH2
AmiONO
NR2R3
ArO2S
NR2R3
ArO2S
PPh3
N
N
N PPh3
20–86%
N3
Scheme 15
TsN
Cl
NR12
R12NH, 22 °C
NR12
R22NH, CH2Cl2, reflux
TsN S
N
53–79%
TsN 40–99%
CN
S
NR22
Scheme 16
CO2Me
H
CO2Me
H
N
N
TsNH2
MeS
TsN
(26)
41%
N
N H
Ph
NR1R2
ClO2S N
Ph
R3R4NO2S
4 R3R4NH
NR1R2
RO2S
(27)
N NR3R4
Cl
X N
NR1R2
RO2S
2 R1R2NH
(28)
N NR1R2
X
A further method for the preparation of sulfonylguanidines involves the reaction of either N! sulfonyl!N?!alkylcarbodiimides with alkylamines "Scheme 06\ path "a#^ R0 Ph\ R1 But\ R2R3 "CH1#3# ð56AP"299#456Ł or N\N?!dialkylcarbodiimides with sulfonamides "Scheme 06\ path "b## ð69JCS"C#0318Ł[ R1O2S
R3R4NH
N
•
N
R1O2S
NHR2
R1SO2NH2
NR3R4
path b
N R2
path a
R3 N
•
N R2
Scheme 17
Finally\ sulfonylguanidines may by prepared by ð1¦1Ł cycloaddition reactions "Scheme 07# involving sulfonyl isocyanates and guanidines "Ar 3!MeC5H3\ X C\ Y O\ Z NPh# ð57AG"E#180Ł^ sulfonyl isocyanates and thioureas "Ar 3!MeC5H3\ X C\ Y O\ Z S# ð80CPB0828\ 81MI 510!91Ł^ and N!sul_nylsulfonamides and thioureas "Ar Me\ X S\ Y O\ Z S# ð56ACS0182Ł[ In a related reaction\ the crystalline bis"imino#thiazetidine\ formed from the reaction of methyl!t! butylcarbodiimide with tosyl isothiocyanate\ undergoes a reaction with excess dimethylamine at 9>C to give a tosylguanidine "Scheme 08# ð70BSB52Ł[ The anion of trinitromethane reacts with soft electrophiles like phenylsulfenyl chloride at the carbon atom to give C!substituted trinitromethane derivatives "Scheme 19^ M K\ Ag\ piperi!
542
At Least One Nitro`en Y
NR2
ArO2S N X Y
+
ArO2S
X Z
Z
NR2
N
NR2
ArO2S
NR2 N NR2
NR2
Scheme 18
TsN Ts N C
S
+ ButN C NMe
Me2NH, 0 °C
S
95%
NHBut
Me NMe
22 °C
N TsN
51%
NBut
S NMe2
Scheme 19
dinium# ð63MI 510!91Ł and with hard electrophiles like phenylsulfenyl tetra~uoroborate ð64IZV0558Ł\ acetyl chloride ð62IZV708Ł\ or TMS!Cl ð62ZOR785Ł at the oxygen atom to give aci!nitro derivatives "R PhS\ Ac\ TMS\ respectively#[
PhS
NO2 NO2 NO2
PhSCl
M+
–
NO2 NO2 NO2
RX
–O
+
NO2
N RO
NO2
Scheme 20
5[10[0[0[09 N!Aminoiminocarbonyl derivatives "i# Alkyl and aryl derivatives The methods of synthesis of N!aminoiminocarbonyl derivatives "N!aminoguanidines# are anal! ogous to those used for guanidines and will not be discussed in detail[ Scheme 10 shows the general methods of preparation from amidinium salts and hydrazines "i# ð89T2786Ł^ from thioureas and hydrazines "ii# ð99CB0947Ł^ from S!alkylisothiosemicarbazide "salts# and amines "iii# ð69JHC578Ł^ from cyanamides and hydrazines "iv# ð69CC795Ł^ from carbodiimides and hydrazines "v# ð55AP698Ł^ from S!alkylthiourea "salts# and hydrazines "vi# ð51LA"540#78Ł^ and from N!aminocarbonimidic dichlorides and amines ð61JOC1994Ł or the more reactive silylated amines\ e[g[\ TMS!NMe1 ð81IC377Ł "vii#[ These methods will not be discussed further[ All the theoretically possible methylated amino! guanidines "H1NNRC"1NR1#NR1\ where R Me or H# have been prepared ð52JMC172Ł[
"ii# Imino\ nitro\ nitroso and azido derivatives A wide range of imino and nitro derivatives of guanidines have been prepared by the reaction of aryl diazonium salts with nitroalkyl derivatives "the Bamberger reaction\ ð15LA"335#159Ł[ 0\4!Diaryl! 2!nitroformazans "07# are readily obtained by this procedure "Scheme 11#\ and any tendency to tar formation is minimised by keeping the temperature below 9>C\ waiting long enough for the nitrogen oxides to escape after diazotization\ and employing pure nitromethane and freshly distilled aryl! amines ð25JCS0582\ 32JA1289\ 46ZOB1023\ 76POL02Ł[ The reaction of nitromalonyl aldehyde anion "08# with aryl diazonium salts gives analogous products "Scheme 11^ X Cl\ BF3# ð54ZOR624\ 61ZOR221Ł[ Dinitroformaldehyde hydrazones have also been prepared from nitroalkyl derivatives by the con! densation of hydrazines with tetranitromethane at low temperatures "Scheme 12^ R0 R1 Me\ Et\ Ph# ð68IZV702\ 80CL458Ł and by the diazo coupling reaction of arylhydrazines with dinitromethane "Scheme 12^ R0 H\ R1 1!3!dinitrophenyl "dnp# ð66ACS"B#478Ł[ The reaction of aromatic diazo compounds with malonic acid instead of a nitroalkyl derivative "Equation "18## gives 0\4!diaryl!2! arylazoformazans ð63MI 510!90Ł via a 0\4!diarylformazan intermediate ð51MI 510!90\ 53ZOB1744Ł[
543
Iminocarbonyl and Any Other Elements N+R3R4
R5
Cl
NC N NR5R6
R6
R1R2NNH2 i
NR3R4
R1R2N
R1R2NNH2
iv
NR3R4
R1R2N
R3 = H
ii
NR5R6
NR4
R1R2NNH2
N
N
S
R1R2NNH2
NR5R6 R5R6NH
N R5
R1R2NNH2 i, R3R4NH ii, R5R6NH
iii
R1R2N
•
v
NR5R6
H
R4 N
NR3R4 N
vi
vii
NR4 RS
R1R2N
SR
Cl
NR5R6
N Cl i, amidinium salts; ii, thioureas; iii, S-alkylisothiosemicarbazides; iv, cyanamides and hydrazines; v, carbodiimides; vi, S-alkylthioureas; vii, dichlorocarbiimides Scheme 21
Ar MeNO2
2 ArN2+ 13–68%
CHO
ArN2+ X–, H2O
N N ArNHN
ArNHN
>60%
CHO O2N
21–70%
NO2
NO2 (18)
(17)
ArN2+ X–, DMF
–
Na+ CHO
(20)
(19)
Scheme 22
NO2
R1R2N
NO2
C(NO2)4
NH2
R1R2NN
40–90%
NO2 NO2
O2N
NO2
N2+
Scheme 23
O OH
N NAr
ArN2+, pH 5–6
(29)
ArNHN 18–40%
OH
N NAr
O
0\4!Diaryl!2!aminoformazans are prepared by nucleophilic displacement reactions of amines with 2!chloro! ð52ZOB002Ł or 2!nitro!0\4!diarylformazans "Equation "29#^ X Cl\ NO1\ R0\ R1 H\ alkyl# ð74JHC702Ł[ In a similar fashion\ N!aryl!0!nitromethanehydrazonyl azides are prepared by the reaction of sodium azide with bromo derivatives in aqueous alcoholic media "Equation "20## ð61ZOR28Ł\ and a wide range of "heteroarylmethyl#nitroguanidines have been prepared in the patent literature using the reaction of S!methyl!N!nitroisothioureas with amines "e[g[\ Equation "21## ð80EUP314867Ł[ N NAr
N NAr
HNR1R2
ArNHN
(30)
ArNHN >50%
X Br
NR1R2 N3
NaN3
ArNHN
(31)
ArNHN NO2
47–78%
NO2
544
At Least One Nitro`en Me
NH2
+
O2NN
NH2 N
EtOH, reflux
N S
H
O2NN
N
40%
SMe
N
(32)
S
Me
Cl
Cl
A kinetic study indicates that the nitration of syn!tetraethylguanidine with nitric acid is 699 times slower than the nitration of guanidine and occurs in sulfuric acid but not in acetic acid "Equation "22## ð46CJC416Ł[ NEt2
NEt2
HNO3–H2SO4
HN
(33)
O2NN 60%
NEt2
NEt2
Most 1!nitrosoguanidines are unstable and decompose to give the corresponding ureas and nitrogen^ however\ the 0\0\2\2!tetraphenyl derivative obtained by nitrosylation of 0\0\2\2!tetra! phenylguanidine is a stable solid at 19>C "Scheme 13# ð63BCJ824Ł[ 2!Nitrosoformazans are obtained by the reduction of 0\4!diaryl!2!nitroformazans with H1S "Equation "23## ð79MI 510!90Ł[ NR2
NR2
NOCl, CCl4, –20 °C
HN
ONN
R = Ph, 92%
NR2
NR2
NR2
–N2
O
R ≠ Ph
NR2
Scheme 24
N NAr
H2S, EtOH–NH3
ArNHN
N NAr ArNHN
NO2
(34) NO
5[10[0[0[00 N!P\ N!As\ N!Sb and N!Bi iminocarbonyl derivatives "i# Phosphorus"III# derivatives The few examples of this class of compounds are iminophosphinoguanidines which have been made by reaction of iminochlorophosphines with silylated guanidines "Equation "24## ð80ZOB390Ł[ Tris"trichlorophosphoranediylamino#carbenium salts are prepared by the photolysis of tri! azidocarbenium hexachloroantimonate in PCl2 "Equation "25## ð68AG"E#582Ł via a mechanism which is analogous to the Staudinger reaction of organic azides with phosphanes[ But
But
NMe2
+
TMS-N
But
N PCl
NMe2
>91%
But
N3 +
SbCl6– N3
3 PCl3, hν –3 N2
(35)
N
But
N3
NMe2
N P But
N PCl3
+
SbCl6–
Cl3P–N
NMe2
(36)
N PCl3
"ii# Phosphorus"V# derivatives Two major synthetic methods exist for this class of compound[ The _rst route entails formation of the amide bond by the reaction of phosphoryl chlorides with guanidines to give\ e[g[\ guanidinylphosphoric diamides "Equation "26## ð56JMC007\ 56JMC162Ł[ The second route involves the formation of two guanidinyl C0N bonds by the reaction of dichloromethylenephosphoramidic derivatives with dialkylamines "Equation "27##] thus\ reactions with excess dialkylamines produce
545
Iminocarbonyl and Any Other Elements
bis"dialkylamino#methylenephosphoramidic esters "X O\ R0 R1 Me\ Et\ allyl# ð58IZV008Ł and phosphoramidothioic acid derivatives "X S\ R0 R1 Me\ Et# ð63OMR"5#383\ 63ZOB427Ł\ whilst reactions with two di}erent amines produce mixed amide products "X O\ R0 Ph\ R1 Et# ð55ZOB350Ł[ A combination of both methods is provided by the reaction of dialkylcyanamides with phosphoryl chloride followed by treatment with dialkylamines "Scheme 14^ R0\ R1 various alkyl groups# ð63ZOB0153Ł[
+
P Me2N
P EtO
i, R12NH, NEt3 ii, R22NH, 2 NEt3
Cl
N
Me2N
R = H, 11% R = Me, 31%
NR2
X
EtO
P
HN
Cl
O
Me2N
NR2
O
Me2N
X
NR12
P EtO
Cl POCl3
Cl 45–75%
P
O
NR12
N
(38)
N NR22
Cl
R12NCN
(37)
NR2 EtO
>50%
NR2
N
R22N
R22NH
R22N
>50%
O
P
NR12
N
Cl
NR22
Scheme 25
"iii# As\ Sb and Bi derivatives The single report of guanidines attached to group 04 elements other than N or P refers to dative! bonded complexes of guanidines and bismuth or antimony trihalides ð77EUP162347Ł[
5[10[0[0[01 N!Si\ N!Ge and N!B iminocarbonyl derivatives N!Silylated guanidines are prepared by treating the corresponding guanidine with a chlorosilane in the presence of a base "Equation "28## ð64ZOR651Ł[ In the absence of added base\ a stable guanidinium salt ""Me1N#1CNHTMS#¦ Hal− is formed ð77JOM"228#130Ł[ NMe2 HN
TMS-Cl, NEt3
NMe2 (39)
TMS-N
NMe2
NMe2
The only example of N!germylated or N!borated guanidine derivatives are triarylboron complexes "Equation "39#^ R H\ Ph# ð67ZOB700\ 70ZOB779Ł[ NHR HN NHR
BAr3 18–99%
H
+
NHR (40)
N Ar3B –
NHR
5[10[0[1 Iminocarbonyl Derivatives with One Nitrogen and One P\ As\ Sb or Bi Function The majority of compounds in this class contain a phosphorus function[ Very few compounds contain arsenic functions\ and none contain antimony or bismuth functions[ The compounds will be discussed in the order of the substituent on the imino nitrogen atom[
546
At Least One Nitro`en 5[10[0[1[0 N!Alkylimino derivatives with one P or As function
The starting materials for N!alkyl! and N!arylimino derivatives are either chloroimine analogues or carbodiimides[ The few examples of N!alkylimino derivatives include compound "11^ R Bu#\ prepared by a MichaelisÐArbuzov reaction of the carbamimidic chloride "10# with trimethyl phos! phite "Equation "30## ð51BEP501114Ł\ and the amidinoarsine "13^ R0 C5H00\ Ph\ R1 C5H00\ R2 H\ Et#\ formed from the attack of alkali metal organoarsides on N\N?!dialkylcarbodiimides "12^ R0 C5H00\ Ph# "Equation "31## followed by hydrolysis or alkylation of the intermediate "lithio! amidino#arsines ð57JOM"02#252Ł[ Bun
Bun P(OMe)3
N CO2Et RN Cl
MeO
(21)
R1 N
•
N CO2Et RN
i, LiAsR22 ii, H2O or EtBr
N
P
(41)
O
OMe (22)
NR1R3 R1N
(42) AsR22 (24)
R1 (23)
5[10[0[1[1 N!Arylimino derivatives with one P function "i# Amidinophosphonates Amidinophosphonates "16# have been obtained by three di}erent methods "Scheme 15#[ The _rst method involves the reversible reaction of N\N?!diphenylcarbodiimide "14# with the phosphite triester "15# to give the amidinophosphonates "16^ Ar Ph\ R0 Me\ Et\ Bu\ Pri\ R1 Ph\ R2 TMS# ð89ZOB667Ł[ The second method is the direct aminolysis of imino chlorides "17#\ which has been used to give a wide range of amidinophosphonates "16^ Ar Ph\ 3!ClC5H3\ 2!MeC5H3\ 3\1!Cl"Me#C5H2\ R0 Me\ Et\ Pri\ R1 H\ R2 Me\ Et\ Pr\ Pri\ Bu\ But\ C5H02\ C5H00 or R1 R2 Me\ Et\ Pr\ Pri# ð66GEP1436401Ł[ The third method yields the amidinophosphonates "16^ Ar Ph\ R0 Me\ R1 Ph\ R2 COP"O#"OMe#1# via an exothermic MichaelisÐArbuzov reaction of trialkyl phosphites and the amidino chlorides "18# ð51BEP501114Ł[ Ar N
•
N Ar
TMS-OP(OR1)2 (26)
Ph
NR2R3 (MeO)3P, 100 °C
ArN P(OR1)2 O (27)
(25)
98%
O N
PhN
Cl Cl (29)
HNR2R3 10–96%
Cl ArN P(OR1)2 O (28) Scheme 26
"ii# Alkylideneamidophosphonates In a variant of the trialkyl phosphite and carbodiimide reaction\ treatment of triethyl phosphite with the chloroalkylcarbodiimide "29# gives the alkylideneamidophosphonate "20# "Equation "32## ð67ZOB0314Ł[
547
Iminocarbonyl and Any Other Elements Ph Ph
N N
•
P(OEt)3
N F3C
PhN
Ph Cl
CF3 P(OEt)2
(43)
O (31)
(30)
"iii# Amidinophosphines Phosphines which contain P0H or P0Si bonds will add across the C1N bond of carbodiimides with transfer of hydrogen or silicon from phosphorus to nitrogen "Scheme 16#^ thus\ the reaction of N\N?!diphenylcarbodiimide "21# with monophenylphosphine gives the bis"amidino#phosphine "22#^ with diphenylphosphine "23^ R0 R1 Ph\ R2 H# the product is the mono"amidino#phosphine "24^ R0 R1 Ph\ R2 H#^ and with tris"TMS#phosphine "23^ R0 R1 R2 TMS# it is the trisilylated amidinophosphine "24^ R0 R1 R2 TMS# ð71IZV0315Ł[ Treatment of compound "24^ R0 H\ TMS\ R1 R2 TMS# with methanol gives the desilylated product "26#[ Reaction of compound "24^ R0 R1 R2 TMS# with N\N?!diphenylcarbodiimide or reaction of excess compound "21# with tris"TMS#phosphine gives the product "25# ð70SRI168Ł[ Silicon appears to be transferred in preference to hydrogen because the reaction of bis"TMS#phosphine "23^ R0 H\ R1 R2 TMS# gives the product "24^ R0 H\ R1 R2 TMS#[ R2 R1 P
N(Ph)R3 PhN
PhHN
R3
Ph
(34)
N
•
N
PR1R2
NPh
PhPH2
PhP NPh
Ph
(35)
PhHN (33)
(32)
Ph N • N
R1 = R2 = R3 = TMS Ph MeOH R1 = H, TMS R2 = R3 = TMS
N(Ph)TMS N(Ph)TMS P N(Ph)TMS (36)
PhN
NHPh PhN PH2 (37) Scheme 27
5[10[0[1[2 N!Acylimino derivatives with one P function N!Acylimino derivatives are obtained from dichloromethyl isocyanate precursors[ The reaction of "dichlorophosphinyl#dichloromethyl isocyanate "27# with an alcohol ROH "R Me\ Et# in the cold gives the chloroimine "28^ R Me\ Et# which on treatment with diethylamine gives the N! acylimino compound "39^ R Me\ Et# "Scheme 17# ð60ZOB1044Ł[ Similarly\ the N!phos! phinylcarbonylimino derivative "31\ R Me\ Et# is obtained by treating the isocyanate "30^ R Me\ Et# with triethylphosphite "Equation "33## ð62ZOR0704Ł[ OCN Cl Cl
O P (38)
Cl Cl
O
O
Cl
ROH, NEt3
RO
N
P O
(39) Scheme 28
OR OR
NEt
Et2NH
RO
N
P O
(40)
OR OR
548
At Least One Nitro`en O
NR2 Cl Cl
OCN
P(OEt)3 50%
EtO EtO
P
NR2 N
P
O
O
(41)
OEt
(44)
OEt
(42)
5[10[0[1[3 Hydrazono derivatives with one P function Hydrazono derivatives are obtained by several di}erent reactions] the reaction of chloro! hydrazones with nitrogen nucleophiles^ the 0\2!addition reaction of amines and nitrile amines^ the treatment of diazonium salts with a!phosphineacetyl derivatives^ alkylation reactions^ and oxidation reactions[ N?!Aryl!C!"dialkoxyphosphoryl#formamidrazones "33^ X NR11\ Ar 3!NO1C5H3\ 3!HalC5H3\ 3!MeC5H3\ Hal F\ Cl\ Br\ I\ R0 OMe\ OEt\ OPri\ R1 Me\ Ph# are prepared in a yield of 18Ð 88) by the treatment of chlorohydrazono derivatives "32# with aqueous solutions of amines "Equation "34## ð89ZOB0182\ 89ZOB1583Ł[ Phosphonic acid diamides "33^ X NMe1\ Ar 3!NO1C5H3\ R0 NEt1# are prepared in a similar fashion ð89ZOB0875Ł\ whilst treating compound "32^ Ar 3! NO1C5H3\ R0 OPri# with sodium azide or sodium nitrite gives the azido! and nitrohydrazones "33^ X N2\ NO1\ Ar 3!NO1C5H3\ R0 OPri# ð89ZOB0879Ł[ Cl ArHN
N
P O
R1 R1
X
R22NH or NaN3 or
ArHN
NaNO2 or R3NHNH2
N
R1
P O
(43)
(45)
R1
(44)
N?!Phosphineformamidrazone "35# is obtained by the 0\2!addition of diisopropylamine to the nitrile imine "34# "Equation "35## ð80CB0628Ł[ Related 0\2!additions of monoalkylamines to nitrile imines have been reported ð81CC0163Ł[ F3C
F3C CF3
F3C
CF3 H P N N
Pri
2NH
P N– + N
F3C
54%
P
S
NPri2
NPri2
S
P
(46)
NPri
2
NPri2
NPri2
(45)
(46)
An interesting solvent e}ect is observed in the preparation of "arylhydrazono#"arylazomethyl# phosphonates "49^ Ar Ph\ 3!MeOC5H3\ 3!NO1C5H3\ 3!ClC5H3\ 3!BrC5H3\ 3!IC5H3\ R Me\ Et\ Pri#[ The reaction of the phosphinylaldehyde "36# with diazonium salts "37^ X Cl\ BF3# gives the phosphonate "49# as the major product in pyridine\ and compound "38# as the major product in water "Equation "36## ð75ZOB0316\ 76ZOB1356Ł[ Phosphonate "49^ Ar 3!NO1C5H3\ R Pri# has also been prepared by the reaction of compound "32^ Ar 3!NO1C5H3\ R0 Pri# with 3!nitrophenyl! hydrazine "Equation "34#^ R2 3!NO1C5H3# ð89ZOB0177Ł[ The coupling reaction of the phos! phineacetic acid salt "40# with 1 molar equivalents of diazonium salt "41# gives the bis"arylazo#methylenephosphine "42#\ which is isolated as the tetra~uoroborate salt "43^ Ar Ph\ 3!NO1C5H3\ 3!Me1NC5H3\ 1!MeOC5H3# "Scheme 18# ð51ZN"B#671Ł[ CHO
O
OHC
P OR OR (47)
+
+ ArN2
X–
ArHNN RO
(48)
(49)
P
O OR
N NAr
+
ArHNN RO
P
(50)
O OR
(47)
559
Iminocarbonyl and Any Other Elements +
HO2C
PPh3
Cl–
ArN N
–CO2
+
+ ArN2
N NAr
71–90%
(51)
N NAr
ArHN
HBF4
N
(52)
+
PPh3 BF4– (54)
PPh3 (53) Scheme 29
Other preparations of compounds in this class include the isolation of the inner salt "45# from the alkylation of the formamidrazone "44# with methyl iodide "Equation "37## ð80ZOB665Ł\ and oxidation of the amidrazone "46^ R But# with silver"I# oxide to give the N!"arylazo#"dialkoxyphos! phoryl#methylene!t!butylamine "47^ R But# "Equation "38## ð82S48Ł[ The "arylazo#imines "47# cannot be made with an N2!methylene group "e[g[\ R Me\ PhCH1# because the products of such reactions tautomerise to give N!alkylideneamide arylhydrazones which then cyclise to form dihydro! 0\1\3!triazoles[ H
H N
NMe2 N P
PriO
O
+
N
MeI
NMe2 N
60%
Me PriO
OPri
(55)
O
P
(48)
O–
(56)
NO2
NO2
Ag2O
N N H RHN O P PriO OPri (57)
(49)
N N
70%
RN P
PriO
O OPri (58)
5[10[0[1[4 Diazonium derivatives with one P function The diazonitromethyl derivatives "59^ R0 Ph\ R1 OMe^ R0 R1 Ph\ OMe\ OEt# and the nitrate side products "50# are obtained by treating the diazomethylphosphonates "48# with dinitrogen pentoxide "Equation "49## ð68LA0991Ł[ NO2
N2 O
P
(59)
R1 R2
N2O5, –20 °C
N2 O
P
R1 R2
(60)
ONO2
+ O
P
R1
(50)
R2 (61)
5[10[0[1[5 N\N!Dialkyliminium derivatives with one P function 1!Phosphaallylic salts and phosphorylated amidinium salts may be prepared from chloro! amidinium salts or phosphaalkenes[ 1!Phosphaallylic salt "57^ R1 Me\ X Cl# is formed in high yield by the reaction of tris"TMS#phosphane with two molar equivalents of the imidoyl chloride "55^ R1 Me# "Scheme 29# ð72AG"E#434\ 73AG"E#892Ł[ The analogous compound "57^ R1 Et\ X CF2SO2#\ along with other unidenti_ed products\ is formed by rearrangement of the 0\2!tetraalkylformamidinium!substituted cyclotetraphosphane "56# produced by cyclisation of the cationic diphosphene "53^ R01N Pri1N\ 1\1\5\5!tetramethylpiperidinyl^ R1 Et^ X CF2SO2#[ Diphosphene cation "53# is obtained by the reaction of the chlorophosphine "52# with TMS trifylate or by the condensation of phosphaalkene "51# with chlorophosphenium cation\ followed by valence isomerism of the _rst!formed phos! phaalkeneÐphosphenium cation "54# ð80TL1664Ł[ The 1!phosphaallylic salt "57^ R1 Me\ Et\ X Cl#
550
At Least One Nitro`en
is also prepared by leaving benzene solutions of the phosphaalkene "52# standing at room tem! perature for several hours[ NR22
NR22
R2
2N
R22N P
TMS
(63)
CF3SO3-TMS
ClP+NR12 CF3SO3–
NR22
NR22
R22N P
P NR12
(62)
+
Cl P
R22N
X–
P
P
P
NR12
+
X–
2
R2
NR22
+
Cl–
2N
Cl
NR12 (65)
(64)
(66) P(TMS)3 MeCN 80–96%
22 °C
NR22 +
R22N
NR12 P
P
P
P
R12N
2 X–
PhMe, 22 °C
+
NR22
R22N
NR22 P
+
NR22
X–
NR22
R22N (67)
(68) Scheme 30
The synthesis of phosphorylated amidinium salts is shown in Scheme 20[ Reaction of the cation "60^ R1 Me# with triethyl phosphite gives the phosphonic anhydride inner salt "62^ R1 Me# ð61JOC1629Ł via the monophosphorylated amidinium salt intermediate "58^ R1 Me# which can also\ depending upon reaction conditions\ give the betaine "69^ R1 Me# as the major product ð61JCS"D#1156\ 67JPR278Ł[ The reaction of the cation "60^ R1 Me# with an excess of diethyl phenyl! phosphonite gives the salt "65^ R1 Me#\ which is converted to the stable inner salt "61^ R1 Me# by gentle warming ð61JOC1629Ł[ In contrast\ ethyl and isopropyl diphenylphosphinite "63^ R2 Et\ Pri# have only one displaceable alkyl group and undergo a standard MichaelisÐArbuzov reaction with cation "60# to give the salt "64^ R1 Me# ð61JOC1629\ 67JPR278Ł[ The inner salt "61^ R1 Me# is also prepared by oxidation of the electron!rich phosphaalkene "66^ R1 Me# with ozone ð75AG"E#346Ł[
5[10[0[2 Iminocarbonyl Derivatives with One Nitrogen and One Metalloid Function This class of compounds consists largely of boron!containing compounds[ There appear to be no germanium!containing compounds and only one example of a silanecarboximidamide[
5[10[0[2[0 Silicon derivatives Silanecarboximidamide "68# is prepared from the reaction of N\N?!diphenylcarbodiimide "21# and bis"TMS#mercury "67# "Equation "40## ð61JOM"31#182Ł[
551
Iminocarbonyl and Any Other Elements NR22
+
R2
2N
O
2N
–EtCl
OEt
P
NR22
+
R2
P
O
OEt
O– OEt
(70)
(69) (70) P(OEt)3
NR22
+
R22N
+
R22N
Cl– Cl
PhP(OEt)2
O
P
–O
Ph
+
P O
NR22
O –O P O (73)
NR22
2 O3
–EtCl
–2 O2
NR22
+
2N
(72)
Ph2POR3 (74)
NR22
+
R2
O–
P
O
(71)
R22N
NR22
NR22
+
R22N
Ph
O
Ph
(75)
P
OEt
NR22 Cl–
R22N P
Ph (76)
Ph
(77)
Scheme 31
Ph N
•
N(Ph)TMS
Hg(TMS)2 (78)
N
PhN
Ph
(51) TMS (79)
(32)
5[10[0[2[1 Boron derivatives Borane carboximidamides "71# are crystalline compounds which are stabilised by internal donorÐ acceptor bonding ð71IZV1269Ł[ Compounds "71^ R0 Ph\ R1 R2 Me\ Pri\ R3 Bu\ Pri^ R0 Me\ R1 R2 Ph\ R3 Bu# ð68DOK"134#010Ł and "71^ R0 Ph\ R1 R3 Pri\ R2 H# ð71IZV1269Ł are prepared by the exothermic reaction of phenyl isocyanide with either a dialkylboryl derivative "70# or a boraneamidine "72^ R1 Pri#\ respectively "Scheme 21#[ The mechanism of the latter reaction may involve the intermediate "73#\ which undergoes an electrocyclic reaction[ The sterically hindered boraneamidine "72^ R1 But# gives the related product "71^ R0 Ph\ R1 H\ R2 But\ R3 Pri# via the insertion of phenylisonitrile into the nitrogenÐboron bond of the compound "72# instead of an electrocyclic reaction ð71IZV1269Ł[ The reaction of the 1!"dialkylboryl#aminopyridine "74# with phenyl isocyanide gives the product "75# by the electrocyclic and not the insertion mechanism "Equation "41## ð76IZV0028Ł[
PhNC
N
N H (85)
BBu2
87%
N PhN
(52)
+ B N H Bu Bu (86) –
The only examples of N?!alkylboranecarboximidamides reported in the literature are car! boximidamides "76^ R0 But\ R1 NMe1^ R0 Pri\ R1 Me# formed in very low yields as side products of other reactions ð79ZAAC"375#88\ 71JOM"120#080Ł[
552
At Least One Nitro`en R1
R1
R43B or
R2N NHR3
R2
R42BSalk
(80)
+
N R3 B– R4 R4 (81) N
PhNC
R2 N
77–89%
+
–
PhN R2 N
Ph R2HN
i, PhNC
PhN
N Pri2B
ii, [1,3]-H shift
–
B
N R3
R4 R4 (82)
Ph
+
R1
NH
B Pri
Pri (84)
(83)
Scheme 32
NMe2 R 1N BR22 (87)
5[10[0[3 Iminocarbonyl Derivatives with One Nitrogen and One Metal Function Most of the compounds in this section are carbene complexes of Group 07 transition metals that are formed by nucleophilic reactions of amines with isocyanide ligands of transition!metal complexes[
5[10[0[3[0 Group 07 transition!metal derivatives Azetidine reacts with the coordinated isocyanide ligand of the neutral complex "cis!77^ M Pd\ Pt\ R But\ 3!MeOC5H3# and the cationic complex "trans!89^ M Pd\ Pt# in THF to form the corresponding diaminocarbene derivatives "78 and 80# "Equations "42# and "43## ð89JCS"D#0086Ł[ Azetidine also reacts with the bis"isocyanide# complexes "cis!81^ R But\ 3!MeOC5H3#\ converting one or two ligands into acyclic carbenes "82^ R But and 83^ R 3!MeOC5H3# "Equation "44##[ The isocyanide complexes "cis!84^ M Pd\ Pt# react in THF with two equivs of azetidine to a}ord the cationic acyclic diaminocarbene complexes "85# containing a metal!coordinated azetidine ligand "Equation "45## ð89JCS"D#0086Ł[ Hydrido alkyl carbene complexes "87^ R CH1CN\ CH1CF2# are prepared by reaction of azetidine with hydrido alkyl isocyanide complexes "86# "Scheme 22#[ These latter complexes react with triphenylphosphine with elimination of HR to give the complex "trans! 88# by a nonreductive elimination pathway ð89OM0338Ł[ H N
NHR cis-
cis R N C M(PPh3)Cl2
N
(53) M(PPh3)Cl2 (89)
(88)
H
trans- MeO
–
N C M(PPh3)Cl BF4
(90)
H
N
+
trans-
+
N N M(PPh3)2Cl (91)
OMe
BF4–
(54)
553
Iminocarbonyl and Any Other Elements NHR
R = But
cis-
N Pd(NCR)Cl2
H N
(93)
cis-(RCN)2PdCl2
(55)
(92) R = 4-MeOC6H4
trans-
N
PdCl2
RHN
2
(94) H 2
Cl
N
N
cis-R N C M(PPhMe2)Cl2
M
PPhMe2 H N
+
Cl–
(56)
RHN (95)
(96)
Ph3P H N Pt R NH
H N
PPh3 N C Pt H R
MeO
PPh3 –HR
MeO
MeO (97)
Ph3P H N Pt PPh3 N
(99)
(98) Scheme 33
Dimethylamine and diethylamine have been used in place of azetidine in reactions with the tetrakis"t!butyl isocyanide#rhodium"I# salt "099# to give crystalline 0 ] 0 adducts "090^ R Me\ Et# containing a s!bonded amidinium cation "Equation "46## ð61JCS"D#0292Ł[ [(ButN≡C)4Rh]+ BF4–
R2NH
R2N
Rh(C≡NBut)3 BF4–
(57)
ButHN + (100)
(101)
5[10[0[3[1 Other metal derivatives The few examples of non group 07 transition metal derivatives include the trialkylstannyl! and trialkylplumbylformamidines "093^ M Sn\ Ar 3!MeC5H3\ R0 R1 Me^ M Pb\ Ar Ph\ R0 Bu\ R1 Et# obtained by the 0\0!addition of a metal amide "091# to an aryl isocyanide "092# "Equation "47## ð55TL2312\ 57JOM"03#216Ł and the bis"diazonitromethyl#mercury "095# prepared by the reaction of nitrodiazomethane "094# with mercury"II# oxide "Equation "48## ð60LA"642#032Ł[ NR22 R13MNR22 + ArNC (102)
ArN
(58)
MR13 (104)
(103)
NO2 NO2 N2
N2
+ HgO
Hg N2
(105)
NO2 (106)
(59)
554
At Least One P\ As\ Sb or Bi
5[10[1 IMINOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE P\ As\ Sb OR Bi FUNCTION "AND NO HALOGEN\ CHALCOGEN OR NITROGEN FUNCTIONS# 5[10[1[0 Iminocarbonyl Derivatives with One P\ As\ Sb or Bi Function and One P\ As\ Sb or Bi Function Although a number of iminocarbonyl derivatives containing two phosphorus functions exist\ there are no examples where the _rst function is phosphorus and the second function is arsenic\ antimony or bismuth[ Iminocarbonyl derivatives in which the _rst function is arsenic\ antimony or bismuth are known only for organometallic diazomethanes[
5[10[1[0[0 Iminocarbonyl derivatives with one P function and one P\ As\ Sb or Bi function "i# Bis"phosphino#iminocarbonyl derivatives Low!coordination phosphorus compounds such as the methylenephosphines "R \S !096# and "R \R !097# in which the carbon atom of the iminocarbonyl group is connected to two 2!valent phosphorus atoms\ are relatively unstable and have been studied very little ð71AG"E#337Ł[ However\ "diazomethylene#bis"phosphonous diamides# "000^ R Pri# are more stable and are formed in good yield by the addition of the chlorophosphane "009^ R Pri# to the lithium salt of the "bisphos! phanyl#diazomethane "098^ R Pri# "Equation "59## ð75JA6757\ 77JA1552\ 78JOM"261#190\ 89JA5166Ł[ Minor modi_cation to one of the reagents dramatically alters the course of the reaction\ and treatment of compound "098^ R C5H00# with compound "009^ R C5H00# gives a mixture of the diazo derivative "000^ R C5H00# and the nitrile imine "001^ R C5H00# in a 3 ] 10 ratio ð81JA5948Ł[ Ph
Ph P
Cl
TMS
N
Cl P
Ph
TMS
+ ClP(NR2)2
N2 Li (109)
TMS
P
Ph
TMS
(107) P(NR2)2
P N
(108)
–78 °C
P(NR2)2
+
N2 P(NR2)2 (111)
(110)
–
+
N N
P(NR2)2 (60)
(R2N)2P (112)
"ii# Bis"phosphinyl#iminocarbonyl derivatives The long list of compounds containing 4!valent phosphorus atoms includes diphenyl!\ dialkoxy!\ diamino!\ alkoxyamino! and alkoxy~uorophosphinyl derivatives\ and phosphinothioyl derivatives[ The methods of synthesis of all these compounds are essentially the same[ "a# Bis"phosphinyl#iminocarbonyl derivatives from carbonimidic dichlorides and or`anophosphorus rea`ents[ The reaction of carbonimidic dichlorides and organophosphorus compounds is the most popular method of synthesis of bis"phosphinyl#iminocarbonyl derivatives[ Gross et al[ have prepared a large number of "arylcarbonimidoyl#bisphosphonic acid esters by the reaction of a carbonimidic dichloride with "EtO#1P"O#R "Equation "50#^ R OEt ð61EGP82655Ł^ R Me or Et ð61JPR76Ł[ N! "Bis"diphenylphosphinyl#methylene#arylamines are produced in a similar fashion with Ph1P"O#"OR# "Equation "51#^ R Me\ Et# ð61EGP82655\ 61JPR76Ł[ P(O)(OEt)2
Cl
+ (EtO)2P(O)R
ArN Cl
ArN
(61) P(O)(OEt)2
555
Iminocarbonyl and Any Other Elements Cl
P(O)Ph2
+ 2 Ph2P(O)OMe
ArN
ArN
75–84%
Cl
(62) P(O)Ph2
The MichaelisÐArbuzov reaction of trichloromethyl isocyanate "002# with alkyldihalo!\ dial! kylhalo! and trialkyl phosphites has been studied extensively by Shokol et al[ "Scheme 23#[ Treatment of trichloromethyl isocyanate with two molar equivs of ClP"OEt#1 in the presence of FeCl2 as catalyst gives an intermediate "003# which can be reacted with a variety of nucleophiles^ for example\ ethanol gives the carbamate "005^ R OEt# ð64ZOB0854Ł[ In a similar fashion\ reaction of trichloro! methyl isocyanate with two molar equivs of "EtO#2P gives a related intermediate "004# which can be converted to either the ester "005^ R EtO# or urea "005^ R PhNH# by reaction with ethanol or aniline\ respectively ð62ZOB433Ł[ Phenylsulfonylimino derivatives "008^ R Me\ Et# are also prepared by the MichaelisÐArbuzov reaction "Equation "52## ð55CB0141Ł[ 2 ClP(OEt)2, FeCl3 (cat.)
OCN CCl3
P(O)(OEt)Cl Cl P(O)(OEt)Cl (114)
OCN
(113) 2 P(OEt)3
P(O)(OEt)2 Cl P(O)(OEt)2
OCN
EtOH
O R
EtOH or PhNH2
P(O)(OEt)2 N P(O)(OEt)2 (116)
(115) Scheme 34
Cl
PhSO2N >90%
Cl (117)
P(O)(OR)2
60 °C
+ (RO)3P
PhSO2N
(118)
(63) P(O)(OR)2 (119)
"b# Bis"phosphinyl#iminocarbonyl derivatives from carbonimidic dichlorides by metalÐhalo`en exchan`e[ N!"Bis"diphenylphosphinyl#methylene#arylamines are produced from carbonimidic dichlorides by metalÐhalogen exchange with Me1TlP"O#Ph1 "Equation "53## ð62ZC081Ł[ Cl
P(O)Ph2
+ 2 Ph2P(O)TlMe2
ArN Cl
43–88%
ArN
(64) P(O)Ph2
"c# Bis"phosphinyl#iminocarbonyl derivatives from tosyl azides[ "Diazomethylene#bisphos! phonates are synthesised by reaction of tosyl azide with the corresponding C0H active methylene precursor in the presence of potassium t!butoxide "Equation "54#^ X O\ R OMe\ OEt# ð57CB2623\ 57TL2060\ 81JOC067Ł[ The yield in the reaction is improved by using 1!naphthalene! sulfonyl azide in place of tosyl azide and by separating the silica!sensitive product from the insoluble sulfonamide by!product by _ltration rather than chromatography ð80S394Ł[ Bis"diphenyl! phosphinothioyl#imino derivatives are made by an analogous reaction "Equation "54#^ X S\ R Ph# ð64MI 510!91\ 64OMS"09#0910\ 68T070Ł[ Mixed diesters of "diazomethylene#bisphosphonates "010# are obtained in excellent yield by treating the potassium salt of the methylenebisphosphonate "019# with tosyl azide in THF "Scheme 24# ð61S240\ 66JA0156\ 71JOC0173Ł[ The methyl ester group of "010# is hydrolysed with careful temperature control to the phosphonate salt "011# via a trans! esteri_cation reaction with TMS!Br ð71JOC0173Ł[ The a!diazophosphonate intermediate "012# may be isolated by extraction from CCl3 solution into aqueous base or bu}er followed by evaporation[ A study of the stability and photochemical behaviour of a!diazophosphonates has been carried out by Bartlett et al[ ð71CC425\ 71JOC0173Ł[
556
At Least One P\ As\ Sb or Bi P(X)R2
P(X)R2
base
TsN3 + P(X)R2
P(O)(OPri)2
(65)
N2 P(X)R2
P(O)(OPri)2
KH, TsN3
N2
78%
P(O)(OMe)2
P(O)(OMe)2
(120)
(121) TMS-Br
P(O)(OPri)2
P(O)(OPri)2
i, K3PO4
N2
N2
ii, NaOH
P(O)(ONa)2
P(O)(O-TMS)2
(122)
(123) Scheme 35
"d# Bis"phosphinyl#iminocarbonyl derivatives from diazometallic salts[ a!Diazophosphonothioic diamides are made from diazolithium salts "Scheme 25#[ Addition of chlorophosphane derivatives "014^ R0 Ph\ NMe1# to the lithium salt of the thioxophosphoranyldiazomethane "013^ R1 NPri1# leads to the diazo compounds "015^ R0 Ph\ NMe1\ R1 NPri1#[ In contrast\ the chlorophosphanes "014^ R0 But\ NPri1# react with compound "013^ R1 NPri1# to give the stable nitrile imines "016^ R0 But\ NPri1\ R1 NPri1#[ In the same way\ chlorophosphane "014^ R0 NPri1# also reacts with compound "013^ R1 But# to give the nitrile imine "016^ R0 NPri1\ R1 But#[ Nitrile imine "016^ R0 R1 NPri1# rearranges on heating into the isomeric diazo derivatives "015^ R0 R1 NPri1#[ Reaction of the diazo compounds "015^ R0 Ph\ NMe1\ R1 NPri1# with elemental sulfur gives the bis"thioxophosphoranyl#diazo derivatives "017^ R0 Ph\ NMe1\ R1 NPri1# ð89JA5166Ł[ The chemistry of phosphinothioyl derivatives "015^ R0 R1 NPri1^ R0 NPri1\ R1 But^ and R0 Ph\ NMe1\ R1 NPri1# has been described by Bertrand and co!workers ð77AG"E#0249\ 77JA1552\ 89JA5166\ 80CB0628Ł[ P(S)R22
R12PCl (125), –78 °C
N2
P(S)R22 N2 PR12 (126)
Li (124) R12PCl (125) –78 °C 85% +
–
55 °C S8
PR12
P(S)R22
N N
N2
R22(S)P
P(S)R12 (128)
(127) Scheme 36
The diazosilver derivative "018# reacts with the chlorophosphine "029# to give the unstable "bis"TMS#methylene#phosphino#diazomethylphosphine oxide "020#\ which undergoes an immedi! ate 0\4!cyclisation and a TMS shift at low temperature to give the phosphadiazole "021# "Scheme 26# ð78S400Ł[ P(O)Ph2
TMS
+
N2 Ag (129)
ClP
–78 °C
N2
TMS (130)
P(O)Ph2 TMS P TMS (131)
Scheme 37
TMS P N N TMS (132)
P(O)Ph2
557
Iminocarbonyl and Any Other Elements
"e# Bis"phosphinyl#iminocarbonyl derivatives from arylisocyanates[ The only known example of a P\P?!"carbonimidoyl#bis"phosphonic diamide# is prepared from the reaction of a phosphorus"III# acid anhydride with an aryl isocyanate "Equation "55## ð71ZOB1076Ł[ P(O)(NEt2)2 (Et2N)2P
O
P(NEt2)2
+ PhNCO
PhN
(66) P(O)(NEt2)2
5[10[1[0[1 Iminocarbonyl derivatives with one As\ Sb or Bi function and another As\ Sb or Bi function The only representatives of this class of compound are the bis"2!valent# organometallic diazomethanes "024^ M As\ Sb\ Bi# prepared by treating arsino!\ stibino! and bismuthino dimethyl! amides "023^ M As\ Sb\ Bi# with diazomethane "022# "Equation "56## ð64JOM"82#228Ł[ Mixed organometallic derivatives arise from two step reactions ð66JOM"021#248Ł[ H
MMe2
+ Me2MNMe2
N2
MMe2 (135)
H (133)
(67)
N2
(134)
5[10[1[1 Iminocarbonyl Derivatives with One P\ As\ Sb or Bi Function and One Si\ Ge\ or B Function 5[10[1[1[0 Iminocarbonyl derivatives with one P function and one Si\ Ge or B function "i# Silicon derivatives All of the compounds in this class are phosphorus!containing silyldiazomethane derivatives[ They are often prepared by the reaction of the lithium salt of a diazomethane derivative with a stoichiometric amount of the requisite chlorophosphane or chlorosilane "Scheme 27#[ Thus\ dialkylphosphanylsilyldiazomethanes "026^ X lone pair\ R0R1R2Si TMS\ R3 R4 But# ð89JA5166Ł and dialkylaminophosphanylsilyldiazomethanes "026^ X lone pair\ R0R1R2Si TMS\ R3 R4 dialkylamino# ð81BSF256Ł are prepared readily from chlorophosphanes "025# at low temperature^ however\ the phosphavinyldiazoalkanes "026^ X lone pair\ R0R1R2Si TMS\ R3R4 ]C"TMS#1\ ]C"TMS#Ph# are only stable at −67>C and on warming undergo rearrangement reactions to give phosphadiazoles ð78S400Ł[ Silylated a!diazo phosphonates "026^ X O\ R0R1R2Si TMS\ TBDMS\ SiPri2\ R3 R4 OMe\ OEt# ð68LA0991\ 74JOM"189#22Ł and phos! phonothioic diamides "026^ X S\ R0R1R2Si TMS\ SiPh2\ R3 R4 NPri1# ð77JA1552\ 80JOC0790Ł are prepared from lithiated a!diazo phosphonates "027# by reaction with silyl electrophiles "Z Cl\ CF2SO2#[ The phosphonothioic diamides are formed via nitrile imine intermediates "R0R1R2SiN1N¦1C−P"S#NPri1#\ which are the only products isolated in reactions with bulky electrophiles\ "e[g[\ Pri2 SiCl#[ Li
P(X)R4R5
ClP(X)R4R5, –78 °C
N2
N2 SiR1R2R3 (136)
X = lone pair
SiR1R2R3 (137)
R1R2R3SiZ
P(X)R4R5 N2 Li (138)
Scheme 38
Dialkylaminophosphanylsilyldiazomethanes "026^ X lone pair\ R0R1R2Si TMS\ R3 R4 dialkylamino# are precursors of donor!substituted {stabilised| carbenes ð80AG"E#563\ 80NJC282\ 81BSF256Ł[ The diisopropylamino analogue "028# on ~ash thermolysis gives the stable phos! phanylcarbene "039# "Scheme 28#\ which undergoes a ð1¦2Ł cycloaddition followed by a ring! opening reaction with either N1O to give the diazo phosphonic diamide "031^ X O# in a yield of
558
At Least One P\ As\ Sb or Bi
59) ð80NJC282Ł or TMS!N2 at −67>C to 3>C to form the diazo compound "031^ X TMS!N# ð80AG"E#563Ł[ The reaction with N1O may be considered a formal oxidation of compound "028#[ P(NPri2)2
heat
Pri2N
(Pri2N)2P
N2O or TMS-N3
:
N2 80%
TMS
TMS
Pri
2N
P(X)(NPri2)2
N
N2
N
TMS
TMS
(140)
(139)
Z P
(141)
(142)
Scheme 39
a!Diazo phosphine sul_des "e[g[\ 033^ R But# ð89JA5166Ł and a!diazo phosphonothioic diamides "e[g[\ 033^ R NPri1# ð78JOC3315Ł may be prepared by direct sulfuration of the phosphanyl pre! cursors "032# "Equation "57##[ PR2
P(S)R2
S8, 22 °C
N2
N2 TMS
65–85%
(68) TMS
(143)
(144)
"ii# Germanium derivatives There are few reports of germanium derivatives\ but preparations involving the use of tri! alkylgermanium chloride are known[ Thus\ the a!diazo phosphonothioic diamide triethylgermanium derivative "034# is prepared by the same method as the silicon analogue "031# ð77JA1552Ł[ A reaction which exploits the weakness of the Ge0P bond of germylphosphines involves an insertion reaction of phenyl isocyanide "Equation "58## ð61JOM"23#72Ł[ P(S)(NPri2)2 N2 GeEt3 (145)
Ph
Et3GePEt2
NC
PEt2 PhN
(69) GeEt3
"iii# Boron derivatives The only examples of this class are the internal salts "037^ R H\ F#[ These are synthesised by oxidative ylidation of the a!diazophosphane "035# with CCl3 followed by reaction with boron! containing Lewis acids "Scheme 39# ð80AG"E#0043\ 81BSF256Ł[ Cl P(NPri2)2 N2
CCl4
Cl N2
•
P(NPri2)2
>80%
TMS (146)
BR3
(147)
+
P(NPri2)2 N2
–
BR3 (148)
Scheme 40
5[10[1[1[1 Iminocarbonyl derivatives with one As\ Sb or Bi function and one Si\ Ge or B function "a!Diazo"TMS#methyl#dimethyl arsines\ stibines and bismuthines "049^ M0 Si\ M1 As\ Sb\ Bi\ R Me\ n 2# are prepared by the reaction of "TMS#diazomethanes "038# with metal amides
569
Iminocarbonyl and Any Other Elements
"Equation "69##[ Trimethyltin chloride is used as a catalyst for the arsine derivative ð79JOM"080#260Ł[ The "diazotrimethylgermylmethyl#dimethylarsine "049^ M0 Ge\ M1 As\ R Me\ n 2# is pre! pared in a similar fashion ð66JOM"021#248Ł[ M1Me3 N2
Me2NM2Me2, <0 °C
M1Me3 N2
(70) M2Me3
(149)
(150)
5[10[1[2 Iminocarbonyl Derivatives with One P\ As\ Sb and Bi Function and One Metal Function The only examples of this class are diazomethane derivatives prepared as intermediates for the study of carbenes[ Most of the compounds are prepared by metallation or transmetallation of diazomethane precursors[
5[10[1[2[0 Iminocarbonyl derivatives with one P function and one metal function "i# Group 0 metals Diazolithium salts "041^ X lone pair\ R0 R1 NPri1^ X S\ R0 R1 NPri1\ But# are prepared at low temperature by treating the corresponding diazomethane precursors "042# with BuLi "Scheme 30# ð89JA5166\ 80OM2194Ł[ P(S)(NPri2)2
Me3SnCl, –78 °C
N2
95%
SnMe3
P(X)R1R2 N2 Li (152)
(151)
BuLi, –78 °C X = O or lone pair
P(X)R1R2 HgO or Hg(acac)2 X=O
N2 (153)
Ag2O or Ag(acac) X=O
P(O)R1R2
P(O)R1R2
N2
N2 Hg
Ag
N2
(155) P(O)R1R2 (154) Scheme 41
"ii# Transition metals The phosphorus!containing diazomethylsilver "044^ R0 R1 OMe\ OEt^ R0 OMe\ R1 Ph# ð60LA"637#196\ 78MI 510!90Ł and the bis"diazomethyl#mercury "043^ R0 R1 OMe\ OEt\ Ph# ð60JOC0268\ 60LA"637#196Ł are prepared by metallation reactions with metal oxides or metal acetyl! acetonates "Scheme 30#[ The stannyldiazomethane "040# is prepared by transmetallation of compound "041^ X S\ R0 R1 NPri1# with trimethylstannyl chloride ð81JA5948Ł[ The crystalline bis"diazomethylene#mercury"II# salt "046# is produced by the catalytic decomposition of the
560
At Least One Metalloid
diazomethylenephosphorane "045# with mercury"II# chloride followed by anion exchange with potassium hexa~uorophosphate "Equation "60## ð81BSF256Ł[
N2
•
PCl(NPri2)2
P+Cl(NPri2)2
i, HgCl2 ii, KPF6
N2 2 PF6–
Hg
90%
(71)
N2 P+Cl(NPri2)2
(156)
(157)
5[10[1[2[1 Iminocarbonyl derivatives with one As\ Sb and Bi function and one metal function Diazomethylarsine derivatives with trimethylstannyl and trimethylplumbyl substituents "047^ M Sn\ Pb# are prepared by metallation of diazomethylarsines "048# with metal amides "Scheme 31#[ Explosive bis"diazo"dimethylarsino#methyl#mercury "059# is produced using Hg"N"TMS#1#1 as metallating agent ð66JOM"021#248Ł[ AsMe2 AsMe2
Me3SnNMe2 or
N2 MMe3
Me3PbN(TMS)2
(158)
AsMe2
Hg[N(TMS)2]2
N2
N2 Hg N2 AsMe2 (160)
(159) Scheme 42
5[10[2 IMINOCARBONYL DERIVATIVES CONTAINING AT LEAST ONE METALLOID FUNCTION "AND NO HALOGEN\ CHALCOGEN\ OR GROUP 4 ELEMENT FUNCTIONS# 5[10[2[0 Iminocarbonyl Derivatives with Two Metalloid Functions 5[10[2[0[0 N!Unsubstituted iminocarbonyl derivatives The electronic structure of HN1C"TMS#1 has been calculated but its synthesis is not reported ð81MI 510!90Ł[
5[10[2[0[1 N!Alkyl! and N!aryliminocarbonyl derivatives These compounds are prepared by the insertion of alkyl! or aryl isocyanides into metalÐmetal bonds or by transmetallation reactions[ N!Alkylbis"silyl#imines are less stable than their N!aryl analogues and only one N!alkyl!sub! stituted compound has been reported[ The N!cyclohexyl derivative "050^ R C5H00# is prepared by the insertion reaction of N!cyclohexyl isocyanide into the Si0Si bond of a disilane with catalysis by Pd"9# ð76TL0182Ł or Pt"9# ð89JAP1198768Ł "Equation "61#\ M Pd\ Pt#[ Sterically!hindered t!alkyl isocyanides fail to undergo the reaction[ A wide range of N!aryl analogues has been prepared by the Pd"9#!catalysed method ð76TL0182Ł[ The reaction is exothermic with disilanes containing electron! withdrawing substituents[ A study of the insertion of aryl isocyanides into the Si0Si linkage of polysilanes indicates that palladium"II# acetate is a better catalyst for the preparation of poly"sila"N! substituted#imines# ð77JA2581\ 80JA7788Ł[ RNC + (R1R2R3Si)2
M(PPh3) (cat.)
NR (72) SiR1R2R3 R1R2R3Si (161)
561
Iminocarbonyl and Any Other Elements
"1\5!Xylylimino#bissilanes "054^ SiR0R1R2 TMS\ t!butyldimethylsilyl"TBDMS## are made from "1\5!xylylimino#"TMS#methyllithium "052# by treatment with the requisite chlorosilane "Scheme 32# ð76JA6777Ł[ ""1\5!Xylylimino#trialkylsilyl#metal derivatives are of interest as acyl anion synthetic equivalents^ the 1\5!xylylimino copper!containing compound "053# is more stable than its 1!toly! limino counterpart[
N SiR3 'Cu'X, THF, –78 °C BuLi, –78 °C
N
'Cu' (164)
N
SiR1R2R3
SiR1R2R3
SnMe3 (162)
Li (163)
TMS-Cl, >70%
N SiR1R2R3 TMS (165)
Scheme 43
5[10[2[0[2 N!Haloiminocarbonyl derivatives The electronic structures of the imines HalN1C"TMS#1 have been calculated but their syntheses are not reported ð81MI 510!90Ł[
5[10[2[0[3 N!Aminoiminocarbonyl "diazomethane# derivatives The major methods of preparation of this class of compounds are transmetallation\ diazo group transfer and cycloaddition reactions[ Examples of metallation reactions include the treatment of silylated ð76OM0746Ł and germylated ð69JCS"A#1843Ł lithiodiazomethanes "055^ R0 TMS\ GeMe2# with chlorosilanes and chlorogermanes to give bis"silyl#diazomethanes "056^ R0 TMS\ R1 TMS\ "TMS#SiMe1\ "TMS#2Si# and bis"ger! myl#diazomethanes "056^ R0 R1 GeMe2#\ respectively "Scheme 33#[ Bis"germyl#diazomethane "056^ R0 R1 GeMe2# is much less stable than its silyl counterpart and has also been prepared by a dimethylamine elimination reaction with diazomethane "057# ð69JCS"A#1843Ł[ This method fails for the less reactive amides of silicon "i[e[\ TMSNMe1# and boron "i[e[\ Ph1BNMe1# owing to their less ionic character[ A further method of preparation of this class of compound involves the transfer of the diazo group from tosyl azide to the carbanion "058^ R0 R1 TMS\ GeMe2# derived from bis"TMS#! or bis"germyl#methanes ð79JA0473Ł[ Me3GeNMe2
R1 N2 Li (166)
R2Cl
R1
R1, R2 = Me3Ge 58%
CH2N2 (168)
N2
R1, R2 = TMS, Me3Ge
R2 (167)
TsN3 R1 = R2 = TMS, Me3Ge
R1 Li R2 (169)
Scheme 44
A more complex route to bismetallated diazomethanes involves cycloaddition reactions of met! alloethenes "Scheme 34#[ Bis"TMS#diazomethane "062^ R0 R1 TMS# is formed by decomposition of the unstable ð1¦2Ł cycloadduct "060# derived from silaethene "069^ R0 R1 TMS# and N1O
562
At Least One Metalloid
ð77CB0396Ł[ A similar reaction involving the ð1¦2Ł cycloaddition of silaethene "069^ R0 TMS\ R1 TMS\ TBDMS# with a silyl azide R2N2 "R2 silyl group# forms siladihydrotriazole "063#\ which undergoes a ð1¦2Ł cycloreversion to give the product "062^ R0 TMS\ R1 TMS\ TBDMS# ð75CB0356\ 75CC480\ 76CB0192Ł[ Siladihydrotriazoles also rearrange by an alternative mechanism to give bis"silyl!substituted#diazomethanes and this reaction has been used to prepare a wide range of silyl compounds "064^ R0ÐR2 silyl group# ð75CB0356\ 76CB0192\ 76CB0102Ł[ Similar reactions are observed with the silaoxadiazole "060^ R0 R1 TMS#\ which rearranges to give the bis"silyl! substituted#diazomethane "061^ R0 R1 TMS# ð77CB0396Ł[ R1O SiMe2 N2 R2 (172)
Me2 1 R Si O N2O
N N
–1/n (Me2SiO)n
R2
R1
(171)
R1
– Me Si 2
Me2Si R2 (170)
N2
N
R2
R3 R3N3, –78 °C
R3 N
N N
(173)
>22 °C
Me2 1 R Si R2
R1R3N SiMe2 N2
(174)
R2 (175) Scheme 45
The use of the germaethene "066# and the alkylidenaminoborane "068# in reactions analogous to those shown for silaethene in Scheme 34 produces the respective germylsilyldiazomethanes "065 and 067# "Scheme 35# ð75CB1879\ 76CB0192Ł and the boranylsilyldiazomethane "079# "Equation "62## ð78CB484Ł[ TMS(But)N
TMS-O
TMS
ButN3
GeMe2
N2O
Me2Ge
N2
TMS
TMS (176)
GeMe2 N2 TMS (178)
(177) Scheme 46
TMS Pri
2NB
TMS (179)
(TMS)2N TMS-N3
BNPri2 N2
(73)
TMS (180)
Finally\ diazoalkanes are useful precursors to carbenoid species[ The transformation is catalysed by transition metals\ and an investigation of the reaction of the anion of "TMS#diazomethane with M"CO#4PPh2 "M Cr\ W# "Scheme 36# resulted in the isolation of two stable crystalline N!bonded diazoalkaneÐmetal complex intermediates "070^ M Cr\ W# ð77CC0487Ł[
5[10[2[0[4 N!Silyliminocarbonyl derivatives N!Silylated bis"TMS#imines "072^ R TMS\ "TMS#1NSiMe1# are formed as side products in the reaction of silaethene "071# with silyl azides "RN2# "Scheme 37# ð70CB2407\ 76CB0192Ł[
563
Iminocarbonyl and Any Other Elements Li TMS
TMS N
M(CO)5PPh3
N2
–CO
Li
TMS
OC OC
TMS N
TMS-Cl
N
–LiCl
PPh3
M CO
N
OC
CO
PPh3
M
OC
CO
CO
(181) Scheme 47
TMS
Me2 Si TMS
RN3
Me2Si
N
TMS
N N
TMS
TMS RN
–Me2SiN2
TMS
R (182)
(183) Scheme 48
5[10[2[1 Iminocarbonyl Derivatives with One Metalloid Function and One Metal Function The only examples of this class of compound have silicon as the metalloid[ 5[10[2[1[0 N!Alkyl! and N!aryliminocarbonyl derivatives These compounds are similar to iminocarbonyl derivatives with two metalloid functions "Section 5[10[2[0[1# and are prepared in a similar fashion by the insertion of alkyl! or aryl isocyanides into metalÐmetal bonds and by transmetallation reactions[ Organosilyl"N!alkylimino#stannanes "075^ R0 R1 Me\ R2 Pri\ C5H00\ C5H02\ 1!MeC5H3^ R0 Bu\ R1 Me\ R2 Pri^ R0 Me\ R1 But\ R2 Pri# are produced by the Pd"9#!catalysed insertion of isonitriles into the Si0Sn bond of organosilylstannanes "Equation "63## ð75CC879Ł[ The reaction proceeds in competition with the disproportionation of compound "073# to give the distannane "076# and disilane "077#[ The Pd"9#!catalysed reaction of "TMS#dimethylstannane with the sterically bulky ButNC gives only disproportionation products[ R1
2 3SnSiMe2R
+
SnR13
Pd(PPh3)4, PhMe
R3NC
R3N
28–71%
(184)
+ (R13Sn)2 + (R2Me2Si)2 SiMe2R2 (186)
(185)
(187)
(74)
(188)
The lithium derivative "052^ SiR2 TMS\ TBDMS#\ generated in situ at −67>C by trans! metallation of the trialkylstannane "051^ SiR2 TMS\ TBDMS# with BuLi\ has been converted into various copper reagents "054^ SiR2 TMS# by reaction with CuBr = SMe1 or Cu acetylide "Scheme 32# ð76JA6777\ 77TL244Ł[ The trialkylstannane "051^ SiR2 TMS\ TBDMS# is prepared by the isonitrile insertion reaction "Equation "63#^ R0 Me\ R1 Me\ But\ R2 1\5!Me1C5H2# ð76JA6777\ 77JA2581Ł[ An additional method of synthesis involves the deprotonation of carbene complexes of group 05 metals "078^ M Cr\ Mo\ W\ SiR2 Ph2Si\ Ph1MeSi# with strong bases to give carbene complexes "089# containing formal imino bonds "Equation "64## ð89JOM"274#110Ł[ EtHN
SiR3
OC
CO
OC
M
CO (189)
CO
base
Li+
EtN
SiR3
OC
CO
OC
M CO (190)
–
(75)
CO
5[10[2[1[1 N!Aminoiminocarbonyl "diazomethane# derivatives These compounds are obtained by metallation reactions[ Lithium silyldiazomethides "080^ SiR2 TMS\ tips\ TMS!SiMe1# are obtained by treatment of silyldiazomethanes "081# with BuLi or
564
Two Metal Functions
LDA "Scheme 38#[ The reaction is usually carried out at low temperature "−67>C# in THF as solvent ð74H"12#1260\ 80OM2194Ł[ The plumbyl! and stannyl"TMS#diazomethanes "082^ SiR2 TMS\ M Pb\ Sn# are obtained by reaction of "TMS#diazomethane "081# with metal amides ð79JOM"080#260Ł[ The stannyl"triisopropylsilyl#diazomethane "085# is obtained from the reaction of bis"trimethylstannyl#diazomethane "084# with Pri2 SiCl in a variety of solvents "THF\ CH1Cl1 or toluene#\ but the same reaction performed in the absence of solvent gives the bis"tri! isopropylsilyl#nitrile imine "083# "Scheme "49##[ A discussion of the scope and mechanism of these reactions has been provided by Bertrand and co!workers ð81JA5948Ł[ SiR3
SiR3
BuLi or LDA
N2
N2
Li (191)
SiR3
Me3MN(TMS)2
N2
>81%
MMe3 (193)
(192) Scheme 49
–
SiPri3
+
2 Pri3SiCl
N N
SnMe3
N2
neat
Pri3Si
SnMe3
2 Pri3SiCl
N2 SnMe3
solvent
SiPri3
(195)
(194)
(196)
Scheme 50
Organic diazoalkanes are useful as precursors to carbenoid species or as 0\2!dipolar cycloaddition reagents in heterocyclic synthesis\ and consequently a number of N!coordinated diazoalkane transition!metal complexes are known "see\ e[g[\ Scheme 36#[ C!Bonded metal diazoalkane complexes are fewer in number but examples include the crystalline "diazomethyl# trimethylsilanenickel"II# complex "088# which decomposes above −14>C[ It is formed by treatment of lithium "TMS#diazomethide "086# with the nickel reagent "087# in a high!yielding reaction "Scheme 40# ð89JA4240Ł[ The unstable "diazomethyl#trimethylsilanerhodium"I# complex "190# is prepared from the reagent "199#\ also in high yield\ and on reaction with iodomethane produces the more stable rhodium"III# diazo complex "191# ð76OM0711Ł[ TMS
N2
TMS
Cl2Ni(PMe3)2 (198)
N2 100%
Li
Me3P Ni PMe3 Cl (199)
(197) Rh(PMe3)4Cl (200)
N2 Me3P Me3P
TMS Rh
2 MeI
PMe3
N2 I
PMe3 –Me4PI
(201)
Me3P
TMS Rh
PMe3
Me PMe3 (202)
Scheme 51
5[10[3 IMINOCARBONYL DERIVATIVES CONTAINING TWO METAL FUNCTIONS There are no examples of this class of compound\ if organometallic complexes with bridging isocyanide ligands ð71COMC!I"3#412Ł are excluded[
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.22 Functions Containing Doubly Bonded P, As, Sb, Bi, Si, Ge, B or a Metal VADIM D. ROMANENKO Institute of Organic Chemistry, Kiev, Ukraine and MICHEL SANCHEZ and LYDIA LAMANDE´ Universite´ Paul Sabatier, Toulouse, France 5[11[0 FUNCTIONS CONTAINING DOUBLY BONDED P\ As\ Sb or Bi 5[11[0[0 General Remarks 5[11[0[1 Dicoordinate Phosphorus and Arsenic Derivatives 5[11[0[1[0 Dihalomethylenephosphines\ Hal1C1PY 5[11[0[1[1 Oxy`en! and sulfur!substituted methylenephosphines\ RO"X#C1PY and RS"X#C1PY 5[11[0[1[2 Nitro`en! and phosphorus!substituted methylenephosphines\ R1N"X#C1PY and R1P"X#C1PY 5[11[0[1[3 Silicon! and `ermanium!substituted methylenephosphines\ R2Si"X#C1PY and R2Ge"X#C1PY 5[11[0[1[4 Metallated methylenephosphines\ LnM"X#C1PY 5[11[0[1[5 C\C!diheterosubstituted methylenearsines\ X1C1AsY 5[11[0[2 Tricoordinate Phosphorus Derivatives 5[11[0[2[0 Stabilized ðX1C1PY1Ł ¦ species 5[11[0[2[1 Functions with a phosphorus!metal s!donor bond\ X1C1P"MLn#Y 5[11[0[2[2 s2l4!Methylenephosphoranes\ X1C1P"1Z#Y 5[11[0[3 Tetracoordinate Phosphorus Derivatives 5[11[0[3[0 Dihalosubstituted ylides\ Hal1C1PY2 5[11[0[3[1 Oxy`en!\ sulfur!\ and selenium!substituted ylides\ RE"X#C1PY2 "E O\ S\ or Se# 5[11[0[3[2 Nitro`en!\ phosphorus!\ arsenic! and antimony!substituted ylides\ R1E"X#C1PY2 "E N\ P\ As or Sb# 5[11[0[3[3 Silicon!\ `ermanium! and boron!substituted ylides\ R2E"X#C1PY2 "E Si or Ge# and R1B"X#C1PY2 5[11[0[3[4 Metal substituted ylides\ LnM"X#C1PY2 5[11[0[4 Tetracoordinate Arsenic\ Antimony and Bismuth Derivatives 5[11[0[4[0 C\C!Diheterosubstituted arsonium ylides\ X1C1AsY2 5[11[0[4[1 Stibonium and bismuthonium ylides bearin` heterosubstituents\ X1C1EY2 "E Sb or Bi# 5[11[1 FUNCTIONS CONTAINING A DOUBLY BONDED METALLOID 5[11[1[0 Tricoordinate Silicon and Germanium Derivatives 5[11[1[0[0 Disilylsubstituted silaethenes\ "R2Si#1C1SiY1 5[11[1[0[1 C\C!Diheterosubstituted `ermaethenes\ X1C1GeY1 5[11[1[1 Functions Incorporatin` a Doubly Bonded Boron 5[11[1[1[0 Methyleneboranes\ X1C1B0Y 5[11[1[1[1 1!Borataallenes\ ðX1C1B1CY1Ł−
566
567 567 567 567 572 573 577 589 580 580 580 581 581 583 583 586 699 691 694 696 696 697 698 698 698 609 601 601 604
567
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
5[11[2 FUNCTIONS INCORPORATING A DOUBLY BONDED METAL 5[11[2[0 Transition Metal Carbene Complexes 5[11[2[0[0 Dihalocarbene complexes\ Hal1C1MLn 5[11[2[0[1 Oxy`en!\ sulfur! and nitro`en!substituted carbene complexes\ RE"X#C1MLn "E O or S# and R1N"X#CMLn 5[11[2[0[2 Silicon!substituted carbene complexes\ R2Si"X#C1MLn 5[11[2[1 Functions With a Formal TinÐCarbon Double Bond
605 605 606 608 612 613
5[11[0 FUNCTIONS CONTAINING DOUBLY BONDED P\ As\ Sb or Bi 5[11[0[0 General Remarks The chemistry of functions X0X1C1E "X0\ X1 heteroatom substituents\ E P\ As\ Sb\ or Bi# featuring a double bond between carbon and the heavier Group 04 elements is centered largely around phosphorus[ The latter forms four types of isolable compounds "0Ð3# containing a formal C1P bond[ X1
X1 P Y
X2
+
X1
Y
X2
P
X2 (1)
Y
Z
X1
Y
X2
P Y
P
(2)
(3)
Y Y (4)
In contrast to the phosphorus species the chemistry of their arsenic analogues is in its infancy[ Although several structural types of the coordinatively unsaturated arsenic derivatives are known\ information about C\C!diheterosubstituted species X0X1C1As"Z#n"Y#m is very sparse[ There is no experimental evidence for double bonding between a X0X1C unit and trivalent or tetravalent antimony or bismuth[
5[11[0[1 Dicoordinate Phosphorus and Arsenic Derivatives The compounds X0X1C1EY "E P\ As# are currently named in Chemical Abstracts as methyl! enephosphines or methylenearsines[ They possess a genuine "pÐp#p double bond and can be regarded as the heavier congeners of alkenes[ The chemistry of phosphaalkenes is documented by two monographs ðB!77MI 511!90\ B!89MI 511!90Ł and by several comprehensive reviews ð70AG"E#620\ 75ZOB142\ 78T5908Ł that appeared in the last decade[ Individual aspects of phosphaalkene chemistry have been covered in numerous review articles[ The most important of these are by Becker\ Becker and Mundt ð72PS"03#156Ł\ Kroto ð71CSR324Ł\ Lutsenko ð73ZC234Ł\ and Grobe and co!workers ð75PS"17#128Ł[ The methods of preparation of the low coordinate arsenic compounds have been reviewed by Dianova and Zabotina ð80RCR051Ł[ This section concerns functions with two het! eroatomÐcarbon bonds\ whatever the nature of substituent on the phosphorus or arsenic[ Functions of the type R"X#C1EY "E P\ As^ R Alk\ Ar# are discussed in Chapter 4[12[ Simple heterosubstituted phosphaalkenes and arsaalkenes like F1C1PH\ "MeO#1C1PPh or Cl1C1AsPh are very unstable[ They polymerize rapidly\ forming\ dependent on the conditions\ dimeric or oligomeric compounds "X0X1CEY#n with C0E s!bonds[ Special kinetic or ther! modynamic factors are required to increase the stability of X0X1C1EY species ð70AG"E#620\ 89MI 511!90Ł[ Three general synthetic methods are applied to prepare the X0X1C1PY functions] "i# the 0\1!elimination reactions of suitable organophosphines\ "ii# condensation reactions\ and "iii# 0\2! trimethylsilyl migration "Scheme 0#[ All other methods are of relatively minor importance and are used only in special cases[ Table 0 surveys the diversity of the known C\C!diheterosubstituted phosphaalkenes reported to date with an example from each major class[ The list indicates the section in which speci_c phosphaalkene is covered and also the routes used for its synthesis[
5[11[0[1[0 Dihalomethylenephosphines\ Hal1C1PY The synthesis of compounds having this structure has been the subject of extensive investigations\ largely because of the ease of making stable molecules of this kind and because of the interesting
568
P\ As\ Sb Or Bi X2
Z
X1
1,2-elimination
P
–RZ
R Y RZ = HHal, TMS-Hal, (TMS)2O, Cl2 X1 R
Z
condensation
+ P Y –2 RZ Z X2 R RZ = HHal, MHal, MeOH, TMS-F Z
SiR3
X1 P X2
Y
1,3-silatropy
P X1 Y Z = O, S, NR Scheme 1
properties which they possess[ These phosphaalkenes allow derivatization at the sp1!hybridized carbon and they are therefore valuable synthons for the preparation of a large variety of novel functions\ such as Hal"X#C1PY\ X0X1C1PY and XC2P[ Practically all synthetic routes to the dihalomethylenephosphines are based on 0\1!elimination reactions[ As already noted\ F1C1PH is extremely unstable[ It has been identi_ed by microwave spec! troscopy as a product in the pyrolysis of CF2PH1 ð65CC402Ł or in the room temperature reactions between CF2PH1 and solid KOH or NaOEt ð67JA335\ 68CC542Ł[ Unlike F1C1PH\ per~uoro!1! phosphapropene "4# containing a bulky CF2 group on phosphorus is stable enough to be isolated in a pure state[ This compound was generated for the _rst time from the reaction of CF2PH1 with NaOMe ð54JCS5764Ł or ZnMe1 ð70IC2623\ 72IC1462Ł[ The product obtained by these methods is usually contaminated with other volatile substances and the starting phosphine[ In 0873 Grobe and Le Van developed a simple thermolysis procedure according to Equation "0# to produce "4# in almost quantitative yield ð73AG"E#609\ 76PS"29#390Ł[ The phosphaalkene formed at 09−2 torr is quenched from the gas phase at −085>C[ Unreacted starting phosphine is repeatedly fed through the hot zone until the conversion into "4# is complete[ The kinetic stability observed for the phosphaalkene "4# is rather high^ thus\ in ca[ 09) toluene or pentane solutions the dimer is _rst detectable after about 09 h at 14>C[ Therefore\ handling in vacuum lines and reactivity studies in organic solvents are possible under ordinary conditions[ SnMe3 F3 C
300–340 °C
F
10-3 torr
F
P
P CF3
CF3
+ Me3SnF
(1)
(5)
In analogy to "4#\ 1!phospha!0!per~uorobutene "5# is obtained from stannylphosphine[ The reaction leads to the isomeric phosphaalkenes "5# and "6# in a molar ratio of 2 ] 0 respectively "Equation "1## ð89ZN"B#037Ł[ SnMe3 F3C
330 °C
F
P
F3C P
CF2CF3
10-2 torr
CF2CF3
F
+
P
CF3
(2)
F (6)
(7)
Attempts to synthesize perchlorophosphaalkene "7# by means of dehydrohalogenation of dichloromethyldichlorophosphine with triethylamine yielded four!membered 0\2!diphosphetane "8# ð70ZOB1529Ł[ Evidence for the transient formation of phosphaalkene "7# comes from its trapping with the conjugated dienes to give 1!chlorophosphinines "Scheme 1# ð78TL706Ł[ Dichloromethylenephosphines having bulky substituents on phosphorus such as bis"trimethyl! silyl#amino!\ N!trimethylsilyl!t!butylamino! or 1\1\5\5!tetramethylpiperidino groups\ enjoy high thermal stability[ These may be prepared by the reaction of Cl1CHPCl1 with the corresponding lithium or sodium amides "Scheme 2#[ For example\ sodium bis"trimethylsilyl#amide reacts with Cl1CHPCl1 as a nucleophile and as a dehydrohalogenating agent to give the phosphaalkene "09# in good yield ð70DOK"145#0390\ 70ZOB1529Ł[ The reaction of But"TMS#NLi with Cl1CHPCl1 gives rise
579
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal Table 0 Known types of C\C!diheterosubstituted methylenephosphines[ X1 P Y X2
X1
X2
Method
Section number
F
F
a
6.22.1.2.1
F2C=PCF3
84AG(E)710
Cl
Cl
a
6.22.1.2.1
Cl2C=PN(TMS)2
84ZOB1520
Br
Cl
a
6.22.1.2.1
Br(Cl)C=PAr*
87ZAAC(553)7
Br
Br
a
6.22.1.2.1
Br2C=PAr*
89ZOB1902
I
I
a
6.22.1.2.1
I2C=PAr*
89ZOB1902
RO
F
a, b
6.22.1.2.2
MeO(F)C=PCF3
86ZN(B)149
RO
RO
a, b
6.22.1.2.2
(TMS-O)2C=PPh
84TL4447
RS
RS
a, b
6.22.1.2.2
(BuiS)2C=PBut
85ZOB264
R2N
F
a
6.22.1.2.3
R2N(F)C=PCF3
86ZN(B)149
R2N
RO
a
6.22.1.2.3
Me2N(MeO)C=PCF3
91HC385
R2N
RS
b
6.22.1.2.3
Me2N(TMS-S)C=PBut
84ZAAC(518)21
R2N
R2N
d
6.22.1.2.3
(Me2N)2C=PH
85ZOB1188
R2P
F
a
6.22.1.2.3
Me2P(F)C=PCF3
86ZN(B)149
R2P
Cl
e
6.22.1.2.3
[Cl(Ar*)P]ClC=PAr*
89TL177
R2P
Br
e
6.22.1.2.3
[Br(Ar*)P]BrC=PAr*
89TL177
R2P
RO
b
6.22.1.2.3
Ar*PH(TMS-O)C=PAr*
84AG(E)619
R2P
RS
e
6.22.1.2.3
Ar*PH(HS)C=PAr*
84AG(E)970
R2P
R2N
e
6.22.1.2.3
(R2N)2P(R2N)C=PNR2 (R = Pri)
86JA7868
Example
Ref.
But R—P—P—R
d
P
6.22.1.2.3
88CB281
P Ar
P But
Ar = 2,4-But2-4-MeC6H2 R3Si
Br
d
6.22.1.2.3
TMS(Br)C=PAr*
84TL4109
R3Si
R3Si
a
6.22.1.2.4
(TMS)2C=PCl
81ZC357
R3Ge
R3Si
e
6.22.1.2.4
P Y TMS X = (TMS)2N Y = 2,2,6,6-tetramethyl-piperidino
92IC3493
Li
Cl
d
6.22.1.2.5
Li(Cl)C=PAr*
88CL1733
X2(Me2N)Ge
TMS-O LnRe
RO
P
6.22.1.2.5
But
85AG(E)53
Cp(NO)(CO)Re Cl(Et3P)2Pt LnPt
Cl
d
6.22.1.2.5
P Ar* Cl
91JA9379
570
P\ As\ Sb Or Bi Table 0 "continued# X1
X2
Method
Section number
LnPt
LnPt
d
6.22.1.2.5
Example
Ref.
Cl(Et3P)2Pt P Ar*
91JA9379
Cl(Et3P)Pt R3Sn
Cl
d
6.22.1.2.5
Me3Sn(Cl)C=PAr*
85TL3551
R3Sn
Br
d
6.22.1.2.5
Me3Sn(Br)C=PAr*
85TL3551
X2(Me2N)Sn R3Sn
R3Si
d
6.22.1.2.5
P Y TMS X = (TMS)2N Y = 2,2,6,6-tetramethyl-piperidino
92IC3493
Ar* = 2,4,6-tri-t-butylphenyl. a 1,2-Elimination. b 1,3-Trimethylsilyl migration. c Condensation reactions. d Reactions at peripheral substituents. e Miscellaneous.
Cl 20 °C
PCl2 Cl
P
Cl
Cl
P
Cl
1/2
73%
Cl
Cl
Cl (9)
Cl
Et3N
P
–HCl
Cl
R
Cl
R
R
R
(8)
Et3N, benzene
R
R –2 HCl
5h, 80 °C
P
Cl Cl
P Cl
Cl
R = H 33% R = Me 35% Scheme 2
to the phosphaalkene "01# ð73ZOB0419Ł[ The dibromo!substituted methylenephosphines are also available by this method "00#\ however\ the di.culties of synthesizing starting dibromophosphine Br1CHPBr1 essentially limit this synthetic methodology[ R2NNa
X
NR2 P
X
X
P NR2 X (10) X = Cl 76% (11) X = Br 70%
X
2 But(R)NLi
But
Cl P N
PCl2 X
X
R2NNa
58%
R
Cl (12)
R = TMS; X = Cl, Br Scheme 3
A simpler synthesis of dichloromethylenephosphines involves dechlorination of the compounds "02# with tris"diethylamido#phosphite as shown in Scheme 3 ð77ZOB0812Ł[ Trichloromethyl! phosphines "02# are accessible through a one!pot synthesis starting from R1NPCl1 and the two! component system CCl3:"Et1N#2P ð77ZOB371Ł[ Treatment of the bulky phosphites R1NPCl1 with CCl3 and But2P in a molar ratio of 0 ] 0 ] 1 allows the preparation of the phosphaalkenes without isolation of the intermediate trichloromethylphosphines ð77ZOB0812Ł[ Phosphaalkenes Hal1C1PPh are not stable enough to permit isolation[ Methyl\ isopropyl or t!butyl substituents in the 1!\ 3!\ and 5!positions of the phenyl ring greatly increase the kinetic stability[ Thus\ the compound "03# is air! and moisture!sensitive but very thermally stable "until
571
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal CCl3
–60 °C, ether
CCl4 +
R2NPCl2 +
Cl
(Et2N)3P 60–78%
(13)
NR2 (13)
Cl
(Et2N)3P
2 But3P
P
0 °C, ether, >95%
CCl4 +
R2NPCl2
0 °C, ether
NR2
Cl
+ (Et2N)3P+Cl Cl–
P
R2N = Pri2N, But2N,
N
Scheme 4
049>C#^ it can be stored without change for months in an inert atmosphere[ The best route to "03# is the reaction of dichloromesitylphosphine with the system CCl3:"Et1N#2P ð81ZOB837Ł[ Dihalomethylenephosphines "04# ð77CB170Ł and "05#Ð"08# which are sterically protected by the 1\3! di!t!butyl!3!methylphenyl or 1\3\5!tri!t!butylphenyl groups are not sensitive towards air[ Di~uoro! and dichloromethylenephosphines "05# ð76ZAAC"442#6Ł and "06# ð80CB1566Ł have been isolated in good yield "53) and 62)# from the reaction of chloro"trihalomethyl#phosphines with n!butyl! lithium "Scheme 4# and dichloromethylenephosphines "04# and "06# ð74TL2440Ł were isolated in moderate yields from the reactions of trichloromethylphosphines with 0\4!diazabicycloð4[3[9Łundec! 4!ene "dbu# "Schemes 5 and 6#[ Although the latter methods are also applied to the synthesis of dibromo! and diiodomethylenephosphines\ the more practical route to the compounds "06#Ð"08# starts from dichloro"1\3\5!tri!t!butylphenyl#phosphine[ This compound reacts with the two!com! ponent system CHal3:"Et1N#2P "Hal Cl\ Br# in ether to give phosphaalkenes "06# and "07# "Scheme 7# ð78ZOB0891Ł[ Extension of this procedure to the preparation of diiodomethylenephosphines "08# was unsuccessful[ However\ in the presence of tris"t!butyl#phosphine\ Ar PCl1 "Ar 1\3\5!tri!t! butylphenyl# reacted smoothly with CHI2 to give the compound "08# in good yield "Scheme 8#[ Cl
Cl
P
P Cl But
Cl
But (14) 70%
(15) 41%
X But
P X But
But 64% 〈87ZAAC(553)7〉 62% 〈89ZOB1902〉; 〈85TL3551〉; 73% 〈91CB2677〉 63% 〈89ZOB1902〉; 〈85TL3551〉; 55% 〈91CB2677〉 34% 〈89ZOB1902〉; 93% 〈91CB2677〉
(16) X = F (17) X = Cl (18) X = Br (19) X = I
X3C
PCl2
ArLi
Cl X3C
P
BunLi
Ar X = F 〈87ZAAC(553)7〉, Cl 〈91CB2677〉 Scheme 5
(16)
572
P\ As\ Sb Or Bi H Ar
H
CCl4
P
Cl3C
dbu
P
Li
(15)
Ar Scheme 6 Cl
Cl P
Cl
dbu
(17)
Ar Scheme 7
ArPCl2 + CHal4 + 2 Et3P
(17) or (18)
+ 2 Et3PHalCl
Scheme 8 ArPCl2 + 2CHI3 + 2 But3P Scheme 9
(19) + 2 But3P(Cl)I
The only known mixed chlorobromomethylenephosphine Cl"Br#C1PAr has been obtained by addition of bromine to the phosphaalkene H"Cl#C1PAr "in turn obtained by base!catalyzed condensation of Ar PH1 with trichloromethane ð73AG"E#784Ł followed by dehydrohalogenation of the intermediate phosphine ClBr1CHP"Ar #Br ð76ZAAC"442#6Ł#[
5[11[0[1[1 Oxygen! and sulfur!substituted methylenephosphines\ RO"X#C1PY and RS"X#C1PY "i# Synthesis by dehydrochlorination reactions Per~uoro!1!phosphapropene "4# reacts with alcohols to yield phosphines "19# which can be readily dehydrohalogenated to ~uoro"alkoxy#methylenephosphines "10#[ Sulfur!substituted methylene! phosphines could not be obtained by such a reaction because addition of thiols to "4# leads to compounds having the structure "11# "Scheme 09# ð75ZN"B#038Ł[ In the presence of Pri1NH the phosphines "19# react with AlkOH to give the phosphaalkenes AlkO"RO#C1PCF2[ With Et1NH\ the compound F2CP"H#CO1Me undergoes an additionÐelimination process yielding the pushÐpull system Et1N"F#C1PCO1Me[ Phosphaalkenes "10# react with primary amines AlkNH1 "Alk But\ Me# with stereoselective formation of the fairly labile phosphaalkenes AlkNH"RO#C1PCF2 ð82ZN"B#47Ł[ F
SMe P
F
CF3 (22)
MeSH
F
F
ROH
80%
CF3
F
H
RO
P 87–100%
F
(5)
Et3N
P
CHCl3, 20 °C >95%
CF3 (20)
F P CF3
RO (21)
R = Me, Et, Pri, PhCH2 Scheme 10
Base!induced dehydrohalogenation is the best method for producing bis"alkylthio#methyl! enephosphines from readily available chlorophosphines "12# or "14# ð76PS"29#322Ł[ For instance\ the compound "12# underwent dehydrochlorination when treated with an equimolar amount of triethylamine "Equation "2## ð74ZOB153\ 74ZOB1686Ł[ Similarly\ compounds "15# may be prepared by treatment of the chlorophosphines "14# with "TMS#1NLi "Equation "3## ð72ZOB362\ 74ZOB153Ł[ Phosphaalkenes "13# are at the borderline of kinetic stability[ They are stable in solution up to 9>C but dimerize to 0\2!diphosphetanes within a few hours at ambient temperatures[ The displacement of a chloride from "13# by various kinds of nucleophiles such as primary or secondary amines and phosphines has been used for the preparation of novel P!functionalized phosphaalkenes ð74ZOB153Ł[ RS PCl2 RS
Et3N
RS
–10 °C, ether 90–95%
RS
(23)
Cl (24)
R = Me, Bui
(3)
P
573
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal RS
Cl
RS
RS
(TMS)2NLi
P
(4)
P –30 °C, THF 50–90%
Y (25)
Y
RS (26)
Y = But, (TMS)2N
"ii# Synthesis by reactions includin` ð0\2Ł!silyl mi`ration ð0\2Ł!Silyl migration is one of the most useful routes to numerous functions of the type TMSO"X#C1PY or TMSS"X#C1PY[ The method is based on the ð0\2Ł migration of a P!silyl group to doubly bonded oxygen or sulfur and is usually used in combination with the preceding addition or condensation reactions[ Scheme 00 illustrates the formation of oxygen! and sulfur!substituted functions X1C1PY via insertion of carbon dioxide ð73TL3336Ł or carbon disul_de ð79ZAAC"352#033\ 73ZAAC"406#64\ 73ZAAC"406#78Ł between the P0Si bond followed by silyl migration[ Another possibility to generate thiol!substituted phosphaalkenes starts from lithium silylphosphide Ar P"Li#TMS "Ar 1\3\5! tri!t!butylphenyl# which readily reacts with CS1 forming the lithium sul_domethylene!phosphine TMS"LiS#C1PAr ð77MI 511!91Ł[ O
TMS-O
CO2 HMPA, 20 °C
TMS-O
P
TMS
P R TMS-O R = Me, But, Ph
R RP(TMS)2 S
CS2 –S
DME, 20 °C 82%
TMS-S P R TMS-S R = Me, But, Ph, Mes
+
P(TMS)2R
HMPA = hexamethylphosphoramide Scheme 11
Although the method is successful for some other types of heterocumulenes "vide infra#\ it is not general[ Depending upon the nature of the heterocumulene\ interaction of the reagents may lead to the phosphaalkene or the reaction may be terminated by the formation of addition product[ Aryl isocyanates ð68ZAAC"348#76\ 58JCS"C#1991Ł\ aryl isothiocyanates ð74ZAAC"419#019\ 74ZAAC"419#028Ł\ and diphenylketene ð70ZOB1078Ł react with silylphosphines to give only addition products[ As it will be seen below some trimethylsilyloxy!substituted phosphaalkenes may be obtained from silylphosphines "TMS#1PR or "TMS#2P and carbonic acid halides[ However\ this method does not work in the case of chlorides of the type ROC"O#Cl ð79ZOB122Ł or R1NC"S#Cl ð73ZAAC"407#10Ł[ A variant of the ð0\2Ł silatropic methodology is provided by the reaction of phosphenimidous amides "16# with 1!lithium!1!trimethylsilyl!0\2!dithiane[ The reaction proceeds via nucleophilic displacement at the dicoordinated phosphorus atom with subsequent silyl migration from carbon to nitrogen "Scheme 01# ð73ZOB854Ł[ S
Li
S
TMS
S
–78 °C, THF
+
(TMS)2N (27)
P NR
~[TMS]
S
P NR
R P N
–(TMS)2NLi
R=
S But,
TMS
59–68%
S
TMS
TMS
Scheme 12
5[11[0[1[2 Nitrogen! and phosphorus!substituted methylenephosphines\ R1N"X#C1PY and R1P"X#C1PY "i# From C\C!dihalomethylenephosphines There are several useful examples of the formation of amino!substituted phosphaalkenes starting from tri~uoromethylphosphines ð82PS"65#154Ł[ Thus ~uoro"amino#methylenephosphines "17# and
574
P\ As\ Sb Or Bi
"18# have been prepared in high yields by reacting CF2PH1 or "CF2#1PH with Me1NH or Et1NH "Equations "4# and "5## ð77CB544\ 89CB1206Ł[ The reaction of di~uoromethylenephosphine F1C1PCF2 "4# with two equivalents of R1NH also gives phosphaalkenes "18# via a series of HF elimination and R1NH addition steps ð77CB544Ł[ A similar process has been employed for the synthesis of the compound "29# "Scheme 02#[ The transformation can be carried out as a one!pot reaction without isolating the known phosphaalkene "10# ð80HAC274Ł[ An alternative route to compounds of type "29# could be the base!catalysed addition of alcohols to "18# followed by HF elimination[ In practice this route has failed because the aminomethylenephosphines do not react with alcohols[ F
3 R2NH
F3CPH2
PH
40–60%
(5)
R2N (28)
R = Me, Et, Prn
F
3 R2NH
(F3C)2PH
CF3
P R2N
(6)
(29)
R = Me, Et, Prn
(5)
ROH
F RO
CF3
F
RO
R2NH
P
CF3 P
H
R2NH
F
R2N RO F
CF3 P
R2NH 58%
H
(21)
RO
CF3 P
R2N (30)
R = Me, Et Scheme 13
Bis"amino#methylenephosphines have been suggested as intermediates in the reactions of Cl1C1PN"TMS#1 with "TMS#1NLi and But"TMS#NLi\ but they have not been detected directly ð78TL3702Ł[ However\ phosphino!substituted phosphaalkene "20# has been isolated and character! ized from the reaction of dichloromethylenephosphine "04# with 0\1!dipotassium diorganylphos! phides "Equation "6## ð77CB170Ł[ But
Cl
K(But)P–P(But)K
P
n-pentane, –80 °C
P
P Cl
Ar*
Ar*
But
(15)
(7)
P (31)
Ar* = 2,4-But2-4-MeC6H2
"ii# Synthesis by condensation reactions The simplest route for the synthesis of bis"amino#methylenephosphines is the condensation of silylphosphines with functionally substituted dihaloalkanes containing mobile halogen atoms[ The formation of phosphaalkene "21# from bis"dialkylamino#di~uoromethanes and silylphosphines is illustrated in Equation "7#[ Due to the high a.nity of silicon for ~uorine\ the reaction proceeds under mild conditions[ Yields are good to excellent in most examples ð71ZOB0814\ 89ZOB1127Ł[ The use of P"TMS#2 in the reaction makes it possible to obtain P!trimethylsilyl!substituted phos! phaalkenes "22# which are key compounds for the preparation of a broad spectrum P!functionalized bis"amino#methylenephosphines "Equation "8## ð72ZOB0561\ 74ZOB110\ 74ZOB0326\ 76ZOB890\ 89ZOB1127\ 80ZOB390Ł[
575
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal Me2N
F
(8)
P 65–95%
F
Me2N
Me2N
20 °C
+ (TMS)2PR
Me2N (32)
R
R = But, Ph, 2, 4, 6-But3C6H2
R2N R2N
–TMS-Cl
+ YCl
P
R2N P R2N
TMS
(9) Y
(33) Y = Ph3Ge, 20 °C, benzene, 75% 〈85ZOB221〉; Ph3Sn, 20 °C, benzene, 95%, 〈85ZOB221〉; But2P, 0 °C, ether, 80% 〈90ZOB2238〉; (TMS)2C=P, 0 °C, ether, >90% 〈87ZOB901〉; Ar*N=P, 0 °C, ether, 91% 〈91ZOB401〉
Unlike the covalent ~uorinated analogues\ the ionic imidoyl chlorides "23# react with tris"trimethylsilyl#phosphine in a 1 ] 0 ratio\ forming the mesomerically stabilized phosphaalkene "24# "Equation "09## ð72AG"E#434\ 73AG"E#892\ 76PS"29#384Ł[
2[(Me2N)2CCl]+Cl–
+
MeCN, 20 °C
Me2N
32%
Me2N
P(TMS)3
NMe2
Cl–
P
(34)
+
(10)
NMe2 (35)
The successful alternative method for bis"amino#methylenephosphine synthesis involves reactions of phosphines and metal phosphides with highly reactive masked carbonyl compounds[ For example\ amide acetals condense with arylphosphines forming dialkylamino!substituted phosphaalkenes ð79TL0030\ 72TL4774Ł[ Alkylphosphines are inert with respect to amide acetals[ However\ sodium phosphides readily react with carbenium tetra~uoroborates giving phosphaalkenes "21# "Equation "00## ð70ZC396\ 70TL3364Ł[ The method is suitable for obtaining the P!hydrogen substituted derivative "21^ R H# ð72ZC88Ł[ [(Me2N)2(EtO)C]+BF4–
+
RPHNa
20 °C, THF
Me2N P Me2N (32)
(11) R
"iii# Reactions involvin` trimethylsilyl mi`rations There are some useful speci_c syntheses of the amino! and phosphino!substituted methyl! enephosphines based on the reactions of silylphosphines such as RP"TMS#1 and P"TMS#2 with carbonic acid halides[ Phosgene ð68AG"E#358\ 72CB098Ł and isocyanide dichlorides ð68AG"E#762\ 71AG"E#337\ 71CB0506\ 72CB0762Ł were shown to undergo double substitution giving the phosphaalkenes "25# and "26# "Scheme 03#[ R1
R1N
TMS N PR TMS
R Cl2C=NR1
P TMS
P
P
TMS
Cl2CO
TMS-O P TMS
R
R
2 RP(TMS)2
P
R
R (36)
(37) Scheme 14
In the reaction of COCl1 with ButP"TMS#1\ t!butylphosphaketene\ ButP1C1O\ has been detected as an intermediate by 20P!NMR[ When the temperature exceeds −59>C it dimerizes yielding the corresponding 0\2!diphosphetane[ The presence of silylphosphine in excess leads to the phos! phaalkene "25# ð72TL1528Ł[ Interaction of benzoylisocyanide dichloride with PhP"TMS#1 yields by halosilane condensation the phosphaalkene "27#\ which then undergoes cyclization and phosphorus
576
P\ As\ Sb Or Bi
to oxygen migration of the silyl group yielding the isomeric 0\2!azaphosphetidine "28# with an exocyclic P1C bond "Scheme 04# ð71CB1260Ł[ O
O Cl
Ph
TMS
TMS N
2 PhP(TMS)2
Ph TMS
N Cl
TMS-O
MeCN, 20 °C
P
P
Ph
Ph
32%
P
Ph
N P Ph
Ph (38)
(39)
Scheme 15
A number of amino! and phosphino!substituted methylenephosphines have been prepared by addition of silylphosphines to heterocumulenes[ Examples of the successful application of this method are shown in Equations "01# ð79JOM"081#22\ 70SRI168Ł and "02# ð75TL0550\ 77ZAAC"445#6Ł[ The synthesis of "39# was achieved from 0\1!bisðbis"trimethylsilyl#phosphinoŁbenzene and diphenyl! carbodiimide ð74ZAAC"418#105Ł[ The treatment of silyldiphosphines TMS"R#PP"R#TMS by two moles of 1\3\5!tri!t!butylphenylphosphaketene\ Ar P1C1O\ leads to compounds "30# ð75CB1637Ł[ The addition of Ar P"H#TMS ð73AG"E#508Ł and But"RO#C1PR "R TMS# ð75TL0550Ł to the phosphaketene Ar P1C1O with the formation of the corresponding phosphaalkenes has been reported[ hexane, 20 °C
Ph(Y)N
71–95%
Ph(Y)N
+ RPY2
PhN C NPh
P
(12) R
R = Me, Cy, But, Ar; Y = TMS
XY hexane, 20 °C
2 Ar
P
+ RPY2
C X
Ar P
R
(13)
P
52–62%
P
X = O, PhN; Y = TMS
XY
Ar
TMS-O R [TMS(Ph)N]2C
P R
[TMS(Ph)N]2C
P
P
P
P
P
Ar Ar
TMS-O (41)
(40)
Silylphosphine "31# containing the very bulky 1\3\5!tri!t!butylphenyl group reacts with thiophos! gene at −67>C to yield phosphaalkene "32# instead of the expected phosphathioketene[ The latter can be regenerated from "32# by photolysis[ Its reaction with 1\3\5!tri!t!butylphenylphosphine provides a convenient route to functionalized phosphaalkene "33# "Scheme 05# ð73AG"E#869Ł[
Ar*P(TMS)2
Cl2C=S
HS
S Ar*
P
C
S
1/2 S
P P
(42)
Ar*PH2
Ar* (43)
Ar*
hν
P Ar* H P Ar* (44)
Ar* = 2, 4, 6-But3C6H2 Scheme 16
As noted previously\ alkyl! and aryl isocyanates react with silylphosphines to give the addition products which exist in the form of acylphosphides ð68ZAAC"348#76Ł[ In contrast to simple isocy! anates\ a reaction between a!methoxybenzyl isocyanate and ButP"TMS#1 led to the corresponding acylphosphide which underwent 0\1!elimination of TMS!OMe and ð0\2Ł trimethylsilyl shift from phosphorus to oxygen\ to a}ord the functionalized phosphaalkene ð73ZOB604Ł[
577
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
"iv# Intramolecular rearran`ements Diphosphiranes "34# formed in the reaction of diphosphenes with halocarbenes readily undergo a photoinduced rearrangement with migration of chlorine to the phosphorus atom ð76PS"29#384\ t 78CC482\ 89JOC4649Ł[ The halocarbenes were generated by the reaction of Bu OK or BuLi with an excess of the corresponding haloform or alternatively from tetrahalomethanes and BuLi at low temperatures "Scheme 06#[ The scope of this method is restricted to 0\2!diphosphapropenes "35# containing very bulky substituents on phosphorus[ R1 P
R1
[:CHal2]
P R2
pentane, 20 °C
P
Hal
P
R1
R2
hν 50–80%
Hal
Hal
P
P
R2
Hal (46)
(45) R1, R2 = 2, 4, 6-But3C6H2 Scheme 17
5[11[0[1[3 Silicon! and germanium!substituted methylenephosphines\ R2Si"X#C1PY and R2Ge"X#C1PY Starting in 0870 "with the synthesis of the _rst C!silylated phosphaalkene ð70ZAAC"362#74Ł\ approximately forty stable silicon! and germanium!substituted methylenephosphines have been synthesized so far\ the stability of which is due primarily to the presence of bulky silyl or germyl substituents on the carbon atom ð77MI 511!90\ 89MI 511!90Ł[ Two principal methods for the preparation of the compounds include 0\1!elimination reactions and derivatization of the other types of low! coordinated phosphorus derivatives[
"i# Synthesis by elimination reactions Several P!substituted bis"trimethylsilyl#methylenephosphines were obtained by dehydro! chlorination of the corresponding chlorophosphines "Scheme 07# ð70TL1048\ 70TL3846\ 74OM228Ł[ Base!induced hydrogen halide elimination requires both strong and bulky bases to prevent nucle! ophilic substitution at the phosphorus atom or addition of the base to the P1C bond[ The best reagents meeting these conditions are dbu and 0\3!diazabicycloð1[1[1Łoctane "dabco#^ triethylamine in most cases was not e}ective[
(TMS)2CHLi
YPCl2
TMS
Y
B
TMS
P TMS
Y P
Cl
–HCl
TMS
Y = Cl, Br 〈81TL2159〉, 2, 4, 6-Me3C6H2 〈85OM339〉; B = dabco, dbu Scheme 18
The synthesis of bis"trimethylsilyl#methylenephosphines is sometimes more simple where the key stage is the thermal elimination of chlorotrimethylsilane[ The reaction is promoted by the energy gained from Cl0Si bond formation and the reduction of steric hindrance at the phosphorus atom by cleavage of the bulky silyl group[ The latter circumstance is essential because sterically unhindered halophosphines\ containing the Hal0P0C0TMS skeleton\ are thermally quite stable[ For instance\ among the compounds TMSCH1PCl1\ "TMS#1CHPCl1 and "TMS#2CPCl1 only the last one splits o} chlorosilane under su.ciently gentle conditions "049>C\ 9[90 torr#\ giving phosphaalkene "36# ð70ZC246Ł[ The syntheses of compounds "37# and "38# are examples of the use of chlorosilane
578
P\ As\ Sb Or Bi
elimination methodology to obtain P!alkyl! and P!aryl!substituted phosphaalkenes "Scheme 08# ð70ZAAC"362#74Ł[
(TMS)3CLi
TMS TMS TMS
YPCl2 ether, 20 °C
Y
150–200 °C 0.01 torr
TMS
P
Y P
Cl
–TMS-Cl
TMS (47) (48) (49)
Y = Cl Y = But Y = Ph
74% 23% 69%
Scheme 19
By analogy with the 0\1!dihalogen elimination of vicinal dihaloalkanes with electropositive metals\ the dechlorination of P!chloro!a!chloroalkylphosphines with lithium provides an additional tool for phosphaalkene synthesis ð70TL3846Ł[ The generality of this approach is restricted\ however\ by di.culties in the preparation of the starting material[
"ii# Derivatization and rearran`ements Treatment of the highly hindered phosphaalkene "49# with bromine leads to the compound "40# "Equation "03## ð73TL3098Ł[ When N!bromosuccinimide was utilized as a halogenating reagent\ dibromomethylenephosphine was obtained ð74TL2440Ł[ TMS
Br2
P TMS
Ar*
(50) Ar* = 2, 4, 6-But3C6H2
Br P Ar*
(14)
TMS (51)
P!Chloro!bis"trimethylsilyl#methylenephosphine "36# has a reactivity which is comparable to that of the secondary chlorophosphines "R1PCl#[ It is therefore a key compound for the preparation of P!functionalized derivatives such as alkoxy!\ alkylthio!\ amino! and phosphino!substituted deriva! tives ð70AG"E#620\ 71AG"E#108\ 77IC673\ 78S400Ł[ P!Fluoro!C\C!bis"trimethylsilyl#methylenephosphine was obtained by exchange reactions with AgF ð73ZOB1799Ł\ and AgBF3 ð76ZAAC"434#6Ł[ Chlorine substitution at the two!coordinate phosphorus atom in "36# by bromine and iodine with TMS!Br and TMS!I proceeds as readily as with chlorophosphines ð73ZOB1799Ł[ The treatment of phos! phaalkene "36# with But1AsLi gives a P!arsino!substituted phosphaalkene ð74ZOB0751Ł[ The coupling reactions of "36# with "R1N#1C1PTMS ð76ZOB890Ł and Ph2P1CH1 ð78TL5758Ł lead to the cor! responding diphosphabutadienes[ Even the selective replacement of the halogen by alkyl and aryl groups with organolithium and Grignard reagents can be accomplished under mild conditions ð73TL3098\ 73JA6904\ 74ZOB1103Ł[ The reaction of "36# with pentamethylcyclopentadienyllithium "Cp Li# in hexane at room temperature a}ords moderate yields of the phosphaalkene "TMS#1C1PCp ð74C166Ł[ P!"Ethynyl#phosphaalkenes were obtained in good yield by reacting "36# with alkynyl Grignard reagents ð73CB1582Ł[ Treatment of "36# with alkali metallates of molybdenum and tungsten yields the bis"trimethylsilyl#methylenephosphines in which metalÐligand fragments are bonded to the phosphorus ð74CC0576\ 75OM482Ł[ Another synthetic approach to the compounds "TMS#1C1P0MLn was developed by Niecke and co!workers ð74C166\ 76CC09Ł[ It is based on cleavage of the P0C bond of the phosphaalkene "TMS#1C1P0Cp with complexes of the type ðM"CO#2"MeCN#2Ł "M Mo\ W#[ There are several useful methods for the synthesis of silyl! and germyl!substituted phosphaalkenes based on the reactions of other types of low!coordinate phosphorus compounds\ but none of the reactions is general ð76ZOB0322Ł[ For example\ the phosphaalkenes "42# have been synthesized from the aminoiminophosphines "41# by a reaction involving the nucleophilic displacement at the two! coordinate phosphorus atom with subsequent ð0\2Ł!silyl rearrangement "Scheme 19# ð73PS"08#078Ł[ The mixed C!germyl!C!silyl!substituted phosphaalkenes\ X0X11Ge"TMS#C1PY\ have been recently obtained by reacting a stable phosphinocarbene ðTMS"X0YP#C]Ł "X0 Me1N\ Y 1\1\5\5!tetra! methylpiperidino# and germanediyls ðGeX11Ł "X1 "TMS#1N or Ar NH# ð81IC2382Ł[
589
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal R
TMS TMS TMS
THF, –78 °C
+ LiC(TMS)3
P N
–(TMS)2NLi
(TMS)2N
TMS P
P NR
TMS
N TMS R (53)
R = But, TMS
(52)
Scheme 20
5[11[0[1[4 Metallated methylenephosphines\ LnM"X#C1PY HalogenÐlithium exchange reactions provide the most general method for the preparation of metallated methylenephosphines[ Thus\ the C0Cl bond in dichloromethylenephosphine "06# is selectively cleaved by n!butyllithium at −79>C in a mixture of ether and toluene ð74TL2440Ł[ The same lithio"chloro#methylenephosphine can be produced via the reaction of Br"Cl#C1PAr with "TMS#1PLi ð76ZAAC"434#6Ł[ Alternatively\ the lithiated phosphaalkene "43# has been generated in near quantitative yield from phosphaalkene H"Cl#C1PAr and t!butyllithium at −67>C in THF ð77CL0622Ł[ The successive treatment of "06# with butyllithium followed by an electrophile such as TMS!Cl\ Me2GeCl or Me2SnCl gives trimethylsilyl!\ trimethylgermyl! or trimethylstannyl!sub! stituted methylenephosphines "44# "Scheme 10# ð74TL2440\ 80CB1566Ł[ At room temperature lithiomethylenephosphine "43# is unstable and easily splits o} lithium chloride to yield the phos! phaalkyne Ar CP ð77CL0622Ł[ A similar transformation has been described for C\C!dichloro! methylene!P!"1\1\5\5!tetramethylpiperidino#phosphine ð78ZOB1022Ł[ Cl
Li
BunLi
Cl
Me3MCl
P Ar*
P ether/toluene, –80 °C
Ar*
Me3M P Ar* Cl
Cl
(17)
(54)
(55)
M = Si, Ge, Sn Scheme 21
The silatropic route to the P1C bond formation represents an alternative strategy for the synthesis of C!metallated methylenephosphines ð77CRV0216Ł[ For example\ treatment of the complex ðRe"CO#1"NO#"h4!C4Me4#ŁðBF3Ł with LiP"R#TMS yields the phosphaalkenyl complexes "45#[ The reaction involves formation of phosphino!carbonyl complexes via nucleophilic addition of phos! phide to a CO ligand prior to the ð0\2Ł!silyl migration from phosphorus to oxygen "Scheme 11# ð74AG"E#42Ł[ Cationic Fe and Ru complexes of the type ðM"h4!C4Me4#"CO#2Ł¦ react with lithium phosphide LiP"Ar #TMS analogously ð75CB0746Ł[ Cp* OC
LiP(R)TMS
Re
CO NO
ether, –80 °C
OC
Cp*
R
Re
P
ON
Cp* 20 °C
TMS
25–30%
OC
O
Re
P
R
ON
O-TMS (55)
R = But, TMS Scheme 22
Another approach to metallated methylenephosphines is based on the oxidative insertion of transition!metal complexes into the C0Hal bond of the C!halomethylenephosphine[ Angelici and co!workers used this method for preparing phosphaalkenylÐplatinum complexes "46# and "47# containing Pt0C s!bond "Scheme 12# ð80JA8268Ł[ Under similar conditions\ reaction of the phos! phaalkene "06# with Pd"PPh2#3 a}ords the phosphaalkyne\ Ar CP[ The transformation was inter! preted as a multi!step process including the generation of the unstable palladium!substituted methylenephosphine\ Cl"L2Pd#C1PAr "L PPh2#\ and its subsequent conversion into phos! phaisocyanide which isomerizes to phosphaalkyne ð81TL1870\ 82OM3154Ł[ Cl
Cl
PtL4
P Cl
L benzene, 20 °C 85%
Ar* (17)
Ar* =
Pt
Cl
L
PtL4
P Cl
Ar* (57)
2,4,6-But
3C6H2;
L = PEt3 Scheme 23
benzene, 20 °C 65%
Pt L Cl Pt
L P L (58)
Ar*
580
P\ As\ Sb Or Bi 5[11[0[1[5 C\C!diheterosubstituted methylenearsines\ X1C1AsY
Only sparse information is available concerning heterosubstituted arsaalkenes ð80RCR051Ł[ This neglect stems largely from the ease of their oligomerization and polymerization which not only makes them di.cult to isolate\ but hitherto has precluded their use in preparative chemistry[ Di~uoromethylenearsine\ F1C1AsCF2\ obtained by pyrolysis of a stannylarsine\ Me2SnAs"CF2#1\ has been described by Grobe and Duc Le Van ð73AG"E#609Ł[ Despite its high reactivity\ the arsaalkene could be unequivocally characterized by its 08F NMR spectrum at −009>C and _nally identi_ed by its dimerization products[ A dialkylamino group on sp1!hybridized carbon was found to stabilize methylenearsines R1N"R#C1AsAr ð81PS"55#146Ł[ However\ no attempts have so far been made to obtain C\C! bis"amino#!substituted arsaalkenes[ An unexpected reaction leading to the formation of the stable tricyclic macroheterocycle "59# containing Si"N#C1As fragment was observed when silaarsene "48# was treated with 0\5!diisocyanohexane "Equation "04## ð82CC0474Ł[ As
SiPri3
Ar Ar
N
Si
CN
Si As Ar SiPri3
NC
N
Ar
toluene, –80 °C
N
Si Ar
(59) Ar =
(15)
Ar
N
2,4,6-Pri
3C6H2
Pri3Si
As
(60)
5[11[0[2 Tricoordinate Phosphorus Derivatives 5[11[0[2[0 Stabilized ðX1C1PY1Ł¦ species Stabilized ðX1C1PY1Ł¦ species are the heavier congeners of iminium ions ðX1C1NR1Ł¦\ and are named as methylenephosphonium ions[ They have been investigated only brie~y\ due primarily to their low stability[ After several years of speculation about these species ð73JPC0870\ 75JA4284\ 76CC0288Ł Bertrand and co!workers were able to prepare\ isolate and characterize the _rst stable methylenephosphonium salt "51# starting from the electron rich diazo compound "50# according to Scheme 13 ð78JA5742Ł[ These same workers discovered that the diazo compound "50# reacts with triethylboron in toluene at −79>C to give the borane!carbene adduct which can be regarded as a methylenephosphonium type compound ð82CC0243Ł[ Grutzmacher et al[ suggested the more general route to the compounds ðX1C1PY1Ł¦A− based on chloride ion abstraction from P!chlorinated ylides as illustrated in Scheme 14 ð80AG"E#698\ 82CC562Ł[ The main side process is oxidation of the substrates by the system Al1Cl5ÐCH1Cl1 to radical cations ð"TMS#1CP"Cl#R1Ł=¦ and their subsequent transformation into chlorophosphonium salts ð"TMS#1CHP"Cl#R1Ł¦AlCl3− ð82PS"65#10Ł[ When P!chloro!P\P!bis"dialkylamino# substituted ylides react with Al1Cl5 in dichloromethane solution\ the side reaction now predominates and the only reaction product is the phosphonium salt ð82PS"65#10Ł[ P(NPri2)2
TMS
hν or ∆
N2
–
+
NPri2
NPri2 TMS
P
NPri2
NPri2
TMS
P
CF3SO3TMS Et2O, –78°C 70%
(61)
TMS
+
NPri2
P
TMS NPri2 CF3SO3– (62)
Scheme 24 TMS Li TMS
R2PCl
TMS
R
CCl4
TMS
P THF, –78 °C 100%
TMS
R P
R
hexane, –78 °C 100%
Scheme 25
TMS
0.5 Al2Cl3
Cl R
TMS
+
R
P
CH2Cl2, –78 °C
TMS R AlCl4–
581
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
5[11[0[2[1 Functions with a phosphorus!metal s!donor bond\ X1C1P"MLn#Y Phosphaalkene transition!metal complexes have been reviewed in 0874 by Scherer ð74AG"E#813Ł\ in 0870 and 0878 by Appel and Knoll ð70AG"E#620\ B!78MI 511!90Ł\ and in 0877 by Nixon ð77CRV0216Ł[ Generally\ three synthetic methods can be applied to prepare h0"P#!coordinated methyl! enephosphines] "i# complexation of a phosphaalkene which already possesses the P1C double bond\ "ii# the so!called {phospha!Wittig| synthesis ð89OM682\ 81ACR89Ł\ and "iii# an approach based on the reactions of terminal phosphinidene complexes ð76AG"E#164Ł "Scheme 15#[ However\ practically all known C\C!diheterosubstituted phosphaalkene complexes X1C1P"MLn#Y were obtained by start! ing with compounds in which a phosphorus!carbon double bond already exists[ Table 1 summarizes some typical examples[ The formulation of the complexes was based on mass spectral and NMR data and in many cases was con_rmed by single!crystal x!ray crystallographic studies[ X1
+ MLn
P X2
Y i
X1
–
O X2
+
Y P
OR P
OR LnM O
ii
MLn
X1 P X2
Y ∆
X1
Y
MLn P
X1 iii
M1Ln
Y P MLn
M1Ln
+
X2
X2
MLn, M1Ln = Cr(CO)5, W(CO)5 Scheme 26
Table 1 h0!Metal complexes derived from C\C!diheterosubstituted phosphaalkenes[ Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Phosphaalkene\ X0X1C1PY Rea`ent Complex Ref[ X1 Y X0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * F F F2C Cr"CO#4"CH1Cl1# F1C1PðCr"CO#4ŁCF2 77CB544 F Me1N F 2C Cr"CO#4"THF# F"Me1N#C1PðCr"CO#4ŁCF2 77CB544 F2C Cr"CO#4"THF# EtO"Me1N#C1PðCr"CO#4ŁCF2 80HC274 EtO Me1N TMS TMS "TMS#1N Fe"CO#4 "TMS#1C1PðFe"CO#3ŁN"TMS#1 73OM0021 "TMS#1C1PðFe"CO#3ŁAr 73TL3098 TMS TMS Ar Fe"CO#4 TMS TMS Cl ðPtCl1"PEt2#Ł1 "TMS#1C1Pð"PEt2#Cl1ŁCl 81ZOB363 "TMS#1C1PðRhCl"PPh2#1ŁCl 78JOM"257#C18 TMS TMS Cl RhCl"PPh2#1 TMS TMS Me4C4 AgSO2CF2 ð"TMS#1C1P"Ag#C4Me4Ł¦CF2SO2− 74C166 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * Ar 1\3\5!tri!t!butylphenyl
5[11[0[2[2 s2l4!Methylenephosphoranes\ X1C1P"1Z#Y Stable s2l4!methylenephosphoranes have been reported with Z R1C\ O\ S\ Se and RN[ The hetero substituents on the carbon atom "X# are almost completely restricted in the known examples to silyl groups[ General aspects of the chemistry of s2l4!phosphoranes were covered in a recent monography ð81MI 511!90Ł and several reviews ð70TCC60\ 71HOU"E0#472\ 75PS"15#216\ B!89MI 511!90Ł[ Tetrakis"trimethylsilyl#! substituted bis"methylene#phosphoranes\ ð"TMS#1C1Ł1PY\ can be obtained directly from organo! dichlorophosphines and lithium bis"trimethylsilyl#chloromethanide "vide infra#[ The synthesis of other types of s2l4!methylenephosphoranes is based on 0\0!oxidative addition reactions to di! coordinated phosphorus derivatives[ Both methylenephosphines and iminophosphines can be employed as substrates for the synthesis of methylene"imino#phosphoranes[ Since the stable oxo!\ thioxo!\ and selenoxo!phosphines ðYP1O"S\Se#Ł are unknown\ the methods for preparing corresponding phosphoranes consist of the reactions of methylenephosphines with elemental oxygen\ sulfur or selenium[
582
P\ As\ Sb Or Bi "i# From or`anodichlorophosphines
The bis"methylene#phosphoranes of type ðTMS#1C1Ł1PY can be obtained by reaction of the lithiated chlorobis"trimethylsilyl#methane with dichlorophosphines ð71AG"E#79\ 75CB424\ 77PS"25#036Ł[ The synthesis is a three!step process as shown in Scheme 16[ All P!substituted bis"methyl! ene#phosphoranes bearing four silyl groups are thermally stable\ soluble in nonpolar solvents\ and somewhat volatile[ Attempts to apply this approach to the synthesis of bis"methylene#!arsoranes were unsuccessful[ Unlike the analogous phosphoranes\ bis"methylene#!arsoranes are unstable and isomerize within a short period of time into the stable arsiranes ð74AG"E#308Ł[ Cl TMS TMS
Li
Y PCl2
Y P
ether/THF, –78 °C
Cl
Cl TMS TMS
Li
Cl TMS TMS
Y P
–LiCl –Cl2C(TMS)2
TMS
Li
TMS
Cl TMS TMS
ether/THF, –78 °C 55–80%
TMS
Y P
TMS
TMS TMS (63)
Y = Me2N, PhS, Ph2CH, C2H5CH(Me) Scheme 27
The reaction of PCl2 with three equivalents of "TMS#1CClLi leads to the stable bis"methyl! ene#chlorophosphorane "52^ Y Cl# which is a key substance for the synthesis of other P!func! tionalized derivatives ð71TL1906Ł[ Another procedure to obtain this compound involves the reaction of bis"methylene#methoxyphosphorane ð"TMS#1C1Ł1POMe with BCl2[ The bromo! and iodo!sub! stituted compounds are also available by this method ð73ZC273Ł[
"ii# From methylenephosphines and iminophosphines As shown in Scheme 17 the action of some carbenoids on phosphaalkenes a}ords monomeric bis"methylene#phosphoranes of the type "53# ð75CB0866Ł[ The same approach has been employed for the synthesis of some methylene"imino#phosphoranes[ For example\ when aminoiminophosphines\ R1N0P1NR\ ð72ZOB582Ł or P!organoiminophosphines\ RP1NR\ ð80ZOB68Ł reacted with "TMS#1CClLi in THF at −099>C\ the corresponding methylene"imino#phosphoranes were isolated in yields of 44Ð79)[ The mechanism postulated for the reactions includes addition of the organo! lithium derivative to the P1N bond followed by 0\1!elimination of lithium chloride[ X1
+
P X2
Entry 1 2 3 4 5 6
Y
Li
X1
X3 X4 Cl
Y (TMS)2N Et2N Pri2N But 2, 4, 6-Me3C6H2 2, 4, 6-Me3C6H2
ether/THF, –78 °C
Y P X4
X2 X3 (64) X1 Cl Cl TMS H Ph TMS
X2 Cl Cl TMS But Ph TMS
X3 TMS TMS H TMS TMS Ph
X4 TMS TMS H TMS TMS Ph
Scheme 28
As an alternative to the synthesis of methylene"imino#phosphoranes from iminophosphines the reverse process\ namely the transfer of an imino group to methylenephosphine\ may be employed for the preparation of these compounds[ Besides organic azides\ the synthetic application of which in low coordinated phosphorus chemistry is widely discussed in references ðB!89MI 511!90\ 81MI 511! 90Ł\ N!silylated chloroamines have been used as oxidants for methylenephosphines "Scheme 18#[ The reaction was found to proceed via oxidative addition of the chloroamine to give a P!halogenated
583
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
ylide\ which is further converted into the methylene"imino#phosphorane by elimination of chloro! trimethylsilane ð78ZOB1020Ł[
TMS P Y TMS
R N Cl TMS benzene, 0 °C
Cl
TMS
>20 °C
TMS
P Y TMS R
N
Y P
54–75%
TMS
NR
TMS
R = But, TMS; Y = Ph, R2N Scheme 29
The methylene"oxo!\ thioxo! or selenoxo#phosphoranes\ X1C1P"1Z#R "Z O\ S or Se#\ have been obtained by oxidation of the phosphaalkenes with ozone\ sulfur or selenium[ These tricoor! dinate pentavalent phosphorus species are stable only in the presence of sterically demanding groups at the P1C bond[ Thus\ among the compounds X0X1C1P"1O#Y "X0\X1 heteroatom substituents# the methylene"oxo#!phosphorane "TMS#1C1P"1O#Ar "Ar 1\3\5!tri!t!butyl! phenyl# is the only known stable compound ð73TL3098Ł[ The range of phosphoranes X0X1C1P"1S^Se#Y is somewhat larger than that of methylene"oxo#phosphoranes^ however\ the possibilities for the synthesis of stable examples of these compounds are relatively limited ð70CC61\ 73CC587\ 73TL3098Ł[
5[11[0[3 Tetracoordinate Phosphorus Derivatives Tetracoordinate phosphorus derivatives of the type X0X1CPY2 "methylenephosphoranes or phos! phonium ylides# have received considerable attention[ Their structure and chemical properties have been reviewed by several authors as part of a wider discussion of phosphonium ylide chemistry ð71RCR0\ 71HOU"E0#505\ 72RCR0985\ 80RCR280\ 80COS"5#060Ł[ This survey covers only the major devel! opments in the synthesis of C\C!diheterosubstituted ylide functions^ readers are referred to pub! lications cited in the text for a more thorough treatment of other aspects of methylenephosphorane chemistry[ Structurally s3l4!methylenephosphoranes may be represented as hybrids of covalent\ 0 1 X X C1PY2 "ylene#\ and dipolar\ X0X1C−0P¦Y2 "ylide#\ structures[ Hetero substituents at the ylide carbon atom in~uence the stability of the compounds markedly since s!donor and p!acceptor groups "e[g[\ electropositive elements# stabilize ylides\ whereas p!donors and s!acceptors "e[g[\ electronegative elements# destabilize them ð68JA6058Ł[ Lifetimes of nonstabilized ylides vary from several hours at ambient temperature to short periods at low temperatures[ Synthetic routes to the C\C!heterosubstituted phosphonium ylides are based on the following procedures] "i# the direct introduction of a methylene group "X0X1C# into tervalent phosphorus compounds "PY2#^ "ii# the synthesis from phosphonium salts^ "iii# the oxidative ylidation of tertiary phosphines containing a mobile hydrogen atom at the a!carbon atom and behaving as CH acids^ "iv# the rearrangement of a!haloalkylphosphines into P!halogenated ylides[ The other methods of synthesis are used only in individual instances\ but they sometimes have an advantage over standard methods[
5[11[0[3[0 Dihalosubstituted ylides\ Hal1C1PY2 C\C!Dihalomethylenephosphoranes are valuable synthons for the Wittig alkenation reactions ð51JA0634\ 78CRV752Ł[ Nevertheless\ the number of such compounds which have been isolated and characterized is rather limited[ Owing to their low stability and high reactivity dihalomethylene ylides are usually generated in situ and quenched with a carbonyl compound[ Barton and co!workers utilized such an in situ generationÐcapture methodology for the reactions of tertiary phosphines "especially triphenylphosphine# with sodium chlorodi~uoroacetate and car! bonyl compounds "Scheme 29# ð56JOC0200\ 57JOC0743\ 60JFC"0#236\ 61JA719Ł[ Di~uoromethyl!
584
P\ As\ Sb Or Bi
enetributylphosphorane\ F1C1PBun2\ has also been prepared in situ via the reaction of tributylphosphine with sodium chlorodi~uoroacetate in N!methylpyrrolidone ð54JOC0916Ł[ R1 Ph3P
CF2ClCO2Na
O
F
R2
PPh3
DIGLYME 140–150 °C
15–80%
F
F
R1
F
R2
Scheme 30
Triphenylphosphine assisted decomposition of mercurials\ PhHgCFCl1 ð65CAR"35#8Ł and PhHgCX1Br "X Cl\ Br# ð54JOM"2#226Ł\ provided a route to a series of methylenephosphoranes "55#[ Mechanistic studies suggested the intermediacy of an ylideÐmercuric halide complex "54# which dissociates to a}ord the reactive methylenephosphorane species "Scheme 20#[ R1
X1 X2
HgPh
X1
Ph3P
+
X2
Br
O
X1
PPh3
Br–
R2
PPh3 + PhHgBr X2
PhHg (65)
X1
R1
X2
R2
(66)
X1 = X2 = Cl, Br; X1 = H, X2 = Cl, Br Scheme 31
The well known in situ synthesis of dihalomethylenephosphoranes involves the reaction of halo! form with potassium t!butoxide in the presence of tertiary phosphines[ This method has proved especially successful for the formation of dihalomethylenetriphenylphosphoranes "Scheme 21# ð51JA743Ł[ Dichlorocarbene can also be generated from chloroform and 49) aq[ sodium hydroxide solution under phase transfer conditions ð73T0412Ł[ Another e.cient route to dihalomethylene ylides is based on the dehalogenation of phosphonium salts with Group 1B metals ð68JOM"058#012\ 66JFC"09#020\ 64JOC1685Ł or suitable tervalent phosphorus derivatives ð71HOU"E0#505Ł[ The most direct procedure consists of interaction of phosphines with tetrahalomethanes "Scheme 22#[ Evidence has been provided that the initial step of the reaction sequence is the formation of an ion pair formed via attack of phosphorus on a halogen[ Subsequent recombination of the ion pair "in the absence of a trapping agent# and dehalogenation of the resultant phosphonium salt results in the formation of the ylide and the dihalophosphorane[ The reaction is very simple to carry out in the laboratory and is a good general preparative method[ In particular\ using this approach Appel and Veltman were able for the _rst time to isolate dichloromethylene!triphenylphosphorane in a pure state ð66TL288Ł[ From tertiary phosphines and mixed tetrahalomethanes di~uoro! and dichloro! methylenephosphoranes are formed preferentially ð64TL2678\ 65JA445Ł[ The addition of zinc dust proved to be favorable in the synthesis of the di~uoro ð68CL872\ 70TL0310Ł\ dibromo ð61TL2658\ 72TL2276Ł\ and diiodomethylenephosphoranes ð74CC185Ł[ Subsequent improvements include the use of activated magnesium instead of zinc ð81TL572Ł[ The method was also successful for a generation in situ of highly reactive tris"dialkylamido#phosphonium ylides containing a dihalomethylene group ð66TL0128\ 79S443\ 73JOC695Ł[ R1 ButOK
X
heptane, 0 °C
X
O
CHX3 + PPh3
PPh3
R2 9–81%
X
R1
X
R2
X = Cl, Br Scheme 32
CX4
R3P
{ [X3C]– [R3PX]+
+
[X3CPR3] X–
}
R3P
X PR3
+ R3PX2
X X = Cl, Br; R = Alk, Ar, Alk2N Scheme 33
In contrast to tertiary phosphines\ dialkyl! and diarylchlorophosphines do not react with tetra! halomethanes due to the low nucleophilicity of the phosphorus atom[ However\ di!t!butyl~uoro! phosphine can be converted into the ylides "56# by the reaction with tetrachloro! and
585
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
tetrabromomethane ð77ZOB1053Ł[ The compounds "56# are remarkably stable and can be recrys! tallized from pentane "Equation "05##[ 35 °C, 72 h
X
92–95%
X
F
CX4 + 2R2PF X = Cl, Br; R = But
+ [R2P(F)X]+ X–
R
P
(16)
R (67)
Dichloromethylene"amino#di~uorophosphoranes "58# have been produced in good yields from the phosphorane "57# by the reaction with amines followed by dechlorination with hexa! ethyltriamidophosphite "Scheme 23# ð89ZOB1703Ł[ The best method for preparing dichloro! methylenebis"amino#~uorophosphoranes "69# is based on the reaction of tetraalkyl! diamido~uorophosphites with carbon tetrachloride[ These ylides may be distilled and kept in an inert atmosphere without signi_cant decomposition ð76ZOB1683Ł[ P!Chlorinated analogues of the ylide "69# can not be obtained by this route since they readily add tetraalkyldiamidochlorophosphites to give the phosphonium salts "60# ð76ZOB1030Ł[ However\ the dechlorination of phosphonium salt "61# with hexamethyltriamidophosphite proceeded quite smoothly and enabled the ylide "62# to be prepared in high yield "Scheme 24# ð78ZOB848Ł[ F Cl3C
P
F (68)
Cl
R2NY
Cl
ether –90 °C→ 0 °C
F Cl3C
P F
NR2 Cl
(Et2N)3P
Cl
F
ether, –30 °C 62–75%
Cl
F (69)
P NR2
R = Me, Et, Pri; Y = H, TMS Scheme 34
Cl
NR2 P
Cl
R2N
F
R2N
NR2
(70) R = Me, Et, Pri
Y2PI
(Et2N)3P/CCl4
Cl3C
PY2
+
Cl P
C
Cl
P Cl
NR2 NR2
Cl–
(71) R = Et, Pri
Cl2
Cl3C
P Cl
Y = Pri2N
Y Y
+
(Et2N)3P
Cl–
Cl
Cl
Cl
Y
P Y
CH2Cl2, 20 °C 90%
(72)
(73)
Scheme 35
A convenient method for the synthesis of P0Cl ylides containing a dihalomethylene group involves 0\1"C to P#!halotropic rearrangement[ Lutsenko and co!workers obtained bis"dimethyl! amino#trichloromethylphosphine "63#\ which is stable at room temperature\ by an exchange reaction of dichloro"trichloromethyl#phosphine with dimethylamine[ The product was puri_ed by distillation in vacuum and was then converted into the P!chloro ylide "64# by boiling in dichloromethane "Scheme 25# ð74ZOB0083Ł[ It was shown that the rearrangement is strongly catalyzed by the phos! phonium salt ð"Me1N#1P"Cl#CCl2Ł¦Cl− ð77ZOB0350Ł[ Similar chlorotropic rearrangement was observed for trichloromethylphosphine "65#[ The latter\ in the absence of solvent\ in 1 h at room temperature is converted in 69) yield into ylide "66# "Scheme 26# ð78ZOB0893Ł[ Cl3C
PCl2
Me2NH
NMe2 Cl3C
CH2Cl2
Cl
NMe2
Cl
NMe2
P
P NMe2
(74)
45 °C, 2 h
Cl
(75)
Scheme 36
Other methods for the synthesis of dihalo ylides are restricted to examples including substitution of a proton at the ylide carbon atom[ For example\ exchange of hydrogen atoms at the ylide carbon atom in the compounds R"H#C1P"F#"NEt1#1 "R H\ Alk# by chlorine occurs on reaction with carbon tetrachloride in ether at −09>C in yields of 69Ð74) ð78ZOB229Ł[ P!Halo ylides formed by
586
P\ As\ Sb Or Bi (Et2N)3P/CCl4
R2PCl
Cl3C
R = But
R
20 °C, 2 h
Cl
R
R
70%
Cl
R
P
P
(76)
Cl
(77)
Scheme 37
reaction of tervalent phosphorus compounds with carbon tetrahalides may also react with a second molecule of CCl3 or CBr3 exchanging a hydrogen atom at the a!carbon atom by an atom of halogen ð77ZOB380Ł[ The preparative applicability of this approach\ however\ seems to be limited[
5[11[0[3[1 Oxygen!\ sulfur!\ and selenium!substituted ylides\ RE"X#C1PY2 "E O\ S\ or Se# Phosphorus ylides carrying at least one oxygen at the a!carbon atom are very unstable at room temperature and can only be generated and detected in situ ð50CB0262\ 51CB1403\ 53TL2212Ł[ Ylides of the type "RO#1C1PY2 have not yet been characterized[ Ab initio calculations show that substituents like OH stabilize singlet carbenes but not the phosphonium ylides[ Therefore C0O substituted methylenephosphoranes have an enhanced tendency to dissociate\ in agreement with experimental observations ð75CB0220Ł[ The synthetic chemistry of C0S substituted phosphorus ylides is considerably richer than for their oxygen analogues[ Direct incorporation of "RS#1C units into tervalent phosphorus compounds may be achieved by the carbenoid method[ One of the earliest in situ syntheses involved the thermal decomposition of p!toluenesulfonylhydrazone salts "67# in THF containing a severalfold excess of triphenylphosphine "Scheme 27# ð53TL134Ł[ The reaction is not applicable to arylthiomethyl! enephosphoranes[ Subsequently\ Seebach and co!workers suggested an excellent one!pot synthesis of bis"phenylthio#methylene ylide "79# based on the reaction of tris"phenylthio#methyllithium "68# with phosphines "Scheme 28# ð61CB376Ł[ The reaction pathway was rationalized by assuming the existence of an equilibrium between a carbenoid and a carbene[ Tris"phenylseleno#methyllithium reacts with triphenylphosphine similarly to give the bis"phenylseleno#methylenephosphorane in 54) yield ð61CB400Ł[ Comparison with the analogous sulfur ylide shows that PhSe groups stabilize adjacent carbanionic centers nearly as well as PhS groups do[ RS NN(Na)Ts RS
PPh3 THF, ∆
RS PPh3
ArCHO 64%
RS
RS RS
Ar
(78) R = Me, Et; Ar = 4-O2NC6H4 Scheme 38
PhS
BuLi
SPh PhS
THF, –30 °C
R = Bun, Ph, MeO
PhS PhS PhS
R3P
PhS PR3
Li
(79)
24 h, 20 °C >77%
PhS (80)
Scheme 39
Methylenephosphoranes containing alkylthio or arylthio functionality may be readily synthesized by the transylidation reaction of sulfenyl halides with two equivalents of an alkylidenephosphorane ð71HOU"E0#505Ł[ In methylenetriphenylphosphorane\ H1CPPh2\ both a!protons may be substituted by sulfenyl groups[ The phenylthio and methylthio groups may also be introduced by N!methyl!N! phenylthioacetamide and dimethylsuccinimidosulfonium chloride[ These methods avoid the dis! advantage of requiring two moles of starting ylide as in the reaction with sulfenyl halides ð80COS"5#060Ł[ In a similar fashion\ seleno!substituted ylides can be synthesized using areneselenyl chlorides or bromides ð65JOM"003#170\ 68CB244Ł[ Mixed phenylseleno"phenylthio#methylenephosphorane "71# has
587
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
been prepared from chloromethyl phenyl sul_de via phenylthiomethylenephosphorane "70# "Scheme 39# ð72CB0844Ł[ PhS
Cl
PPh3
BuLi
+
PPh3 Cl–
PhS
toluene 14h, 110 °C
PhS
PhSeCl
PPh3
pentane/THF –50 °C
THF, –50 °C 49%
(81)
PhS PPh3 PhSe (82)
Scheme 40
Unlike bis"phenylthio#methylenetributylphosphorane "79^ R Bun# which is stable enough to be isolated in pure state\ ylides of the type "73# can only be generated in situ[ These species have received increased attention since they were shown to present great synthetic potential in the synthesis of derivatives and analogues of bis"ethylenedithio#tetrathiafulvalene ð75T0198\ 82PS"63#168Ł[ The most simple synthetic route to ylides "73# is shown in Scheme 30[ Deprotonation of phosphonium salts "72# yields an ylide which can be trapped in good yield with a carbonyl compound to a}ord a dithiafulvalene ð65TL2584\ 67JOC258\ 72TL2358\ 80S15Ł[ Taking into account the availability of starting materials and the usually high yields in all steps\ this is the method of choice for the synthesis of ylides "73# in cases where R0 and R1 equal H\ alkyl\ or a condensed p!donor ring[ However\ this sequence of reactions cannot be employed for the preparation of ylides in which R0 and R1 are electron!withdrawing groups[ The latter are available from the reaction of carbon disul_de!tri!n! butylphosphine adduct with activated carbonÐcarbon multiple bonds ð60JA3850\ 64CC859\ 68JOC829Ł[ For example\ when the CS1ÐBu2P adduct is treated with a mixture of dimethyl alkynedicarboxylate and ~uoroboric acid etherate at −54>C\ the initially produced phosphorane "74# is trapped by protonation\ and the resulting phosphonium salt "75# can be isolated in yields up to 61)[ Under aprotic conditions\ salt "75# can be used for the in situ generation of the unstable ylide "74# "Scheme 31# ð68JOC829Ł[ The same approach has proved successful for the preparation of selenium analogues of the ylide "74# ð73TL3116Ł[ R1
X
R1
R 3P
X
R2
MeCN, 20 °C >90%
X BF4–
X
R2
BuLi or Et3N
+
PR3 BF4–
+
THF
(83) R1
R1
O
X PR3
X
R1
R2
X
R2
75–95%
X
R2
R1
R2
(84) S
R1 ,
= H/H,
X = S, Se; R = Alkyl, Aryl;
,
R2
S
Scheme 41
+
S
Bun3P
Bun3P + CS2
MeO2C
CO2Me
S– MeO2C
S PBun3
MeO2C
S
HBF4 BuLi
(85)
MeO2C
S
+
PBun3
MeO2C
S (86)
Scheme 42
Among chalcogen!substituted phosphonium ylides\ those containing the bis"arenesulfonyl or alkanesulfonyl#methylene functionality are the most available[ Due to the e.cient stabilization of a negative charge on the ylidic carbon atom by hexavalent sulfur\ these species are very stable and can be synthesized directly from the dichlorophosphoranes and bis"arenesulfonyl#methanes in the presence of triethylamine ð47CB326\ 71HOU"E0#505Ł[ The reaction of polychlorophosphoranes with
588
P\ As\ Sb Or Bi
activated methylene compounds a}ords bis"arenesulfonyl#methylene ylides "76# with both one and two chlorine atoms at the phosphorus atom "Scheme 32# ð66ZOB1289\ 71ZOB0427Ł[ ArO2S
SO2Ar
+
ArO2S
Et3N
+ PhnPCl5–n
P(Cl4–n)Phn
THF, –30 °C
Cl–
Et3N >50%
ArO2S
ArO2S P(Cl3–n)Phn ArO2S (87) n = 1, 2; Ar = 4-XC6H4 (X = H, Cl, Me, MeO) Scheme 43
Bis"benzenesulfonyl#halomethanes\ being comparatively strong CH!acids\ react with chloro! diphenylphosphine in the presence of triethylamine with the formation of tertiary a!haloalkylphos! phines "77#[ The latter rearrange smoothly into P!halogenated ylides "78#\ which are isolated in good yield as stable crystalline compounds and are used as reagents in various chemical conversions "Scheme 33# ð66ZOR164Ł[ A successful alternative approach to the ylide species such as "78# utilizes reaction of bis"arenesulfonyl#methylenephosphines\ "ArSO1#1CHPY1\ with carbon tetrahalides ð68ZOB093Ł[ Electronegative arenesulfonyl groups at the a!carbon atom reduce the reactivity of the tervalent phosphorus atom towards the polyhaloalkanes[ However the reaction rate may in this case be increased by the addition to the reaction medium of tertiary amines[ PhO2S X
Et3N
+ ClPPh2
ether, 0 °C
PhO2S X = Cl, Br
Ph PhO2S X P Ph PhO2S (88)
~ [X]
PhO2S PhO2S (89)
Ph P X Ph
Scheme 44
Sulfonyl stabilized methylenephosphoranes are also available from simple ylides\ R"H#CPPh2 "R H\ alkyl\ aryl# and sulfonic acid halides in a transylidation reaction[ However\ this method is far from straightforward[ Aromatic and aliphatic sulfonyl ~uorides are most suitable for the introduction of a sulfonyl group into the a!position of methylenephosphoranes[ Aliphatic sulfonyl chlorides give only poor yields of alkanesulfonyl substituted ylides[ With aromatic sulfonyl chlorides halogenation and sulfenation may occur instead of sulfonation ð61RTC26\ 63JOC1617Ł[ Hadjiarapoglou and Varvoglis have reported a more direct and general approach to bis"arene! sulfonyl or alkanesulfonyl#methylenephosphoranes based on transylidation with phenylio! donium ylides "Equation "06## ð77S802Ł[ The reaction is catalyzed by cupric acetonylacetonate and most likely involves the initial complexing of the reactants with the Cu atom\ followed by transylidation[ Among ylides obtained by this method tris"ethoxy#phosphonium ylide "89\ X0 X1 PhSO1\ Y EtO# is of special interest because it is one of the few known stable trialkoxyphosphonium ylides ð77S802Ł[ As a further development of this work the synthesis of ylides containing bis"per~uoroalkanesulfonyl#methylene functionality has been achieved by reaction of phenyliodonium bis"per~uoroalkanesulfonyl#methide with phosphines ð82JFC"59#064Ł[ X1 IPh X2
+ PY3
Cu(acac)2/CHCl3 48–92%
X1 PY3 X2 (90)
(17)
X1, X2 = PhSO2, 4-MeC6H4SO2, MeSO2, –SO2(CH2)3SO2–; Y = Ph, OEt
Certain P!functionalized phosphonium ylides may be synthesized starting from bis"arene! sulfonyl#methylphosphine oxides\ "ArSO1#1CHP"O#R1\ which exist in solution in equilibrium with the corresponding methylenephosphoranes ð72RCR0985Ł[ For example\ the reactions of the title phosphine oxides with phosphorus pentachloride and diazomethane lead to the formation of the corresponding P!chloro and P!methoxy phosphonium ylides ð71ZOB0427Ł[ It should be noted that P!alkoxy substituted phosphonium ylides readily rearrange into phosphonates with migration of the alkyl group to the ylide carbon atom "the ylide version of the Pishchimuka reaction ð64CB1354Ł#[ However\ since the electron!withdrawing arenesulfonyl substituents reduce the nucleophilicity of
699
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
the ylide carbon\ the compounds "ArSO1#1C1P"OR#R1 are considerably more stable than their C!alkylated or arylated analogues[ The ylide "PhSO1#1C1P"OMe#Ph1 was reported to be stable on heating to 199>C ð68ZOB093Ł[
5[11[0[3[2 Nitrogen!\ phosphorus!\ arsenic! and antimony!substituted ylides\ R1E"X#C1PY2 "E N\ P\ As or Sb# Ab initio calculations predict thermal instability for the aminomethylenephosphorane H1N"H#C1PH2 with respect to dissociation to phosphine PH2 and singlet carbene ðH1N"H#C]Ł ð75CB0220Ł[ In accordance with the theoretical data simple C!amino!substituted phosphonium ylides are extremely labile compounds[ Few examples of this class have been isolated and fully characterized[ The _rst stable methylenephosphoranes with a dialkylamino group at the ylide carbon atom were prepared by Grobe and co!workers in 0878 ð78NJC252Ł[ It was reported that ~uorophosphaalkenes "18# reacted with tertiary phosphines according to Equation "07# to give the phosphorus ylide "80#[ The rate of reaction under discussion strongly depends on both substituents R0 and R1 and is mainly in~uenced by steric e}ects[ This is demonstrated by the fact that phosphaalkenes "18# do not react with tri!t!butylphosphine and triphenylphosphine[ The ylides "80# show a surprising thermal stability] slow decomposition occurs only at temperatures above 49>C[ A 29) solution of the compound "80^ R0 Me\ X Me1N# in toluene does not change even on heating to 79>C for several hours[ The unusual stability of the ylides "80# has been explained by electron delocalization in the planar PIIICNPV skeleton aided by the electron withdrawing substituents CF2 and F on the tervalent phosphorus atom[ As a further development of this work the synthesis of ylides "81# and "82# with other p!donor substituents has been achieved by reaction of di~uoro! and ~uoro! "alkoxy#methylenephosphines with trialkylphosphines ð81CB456Ł[ Compounds "81# and "82# are stable up to about 09>C\ but decompose at higher temperatures yielding in the case of the C0F substituted ylide di~uorotrimethylphosphorane as the main product[ Similar to the ylide "80# the ~uorine and oxygen substituted ylides owe their existence to the electron withdrawing e}ect of the F2C"F#P unit which overrides the destabilizing in~uence of the ~uorine or alkoxy substituents on the ylide carbon atom[ X
X
toluene
+
P F
CF3
PR13
PR1
3
F3C
–196 to 20 °C 30–100%
(18)
P
F (91)–(93)
(1); (21) and (29)
X = R2N (29, 91), F (5, 92), R2O (21, 93); R1, R2 = Me, Et
At least in a very formal sense\ one can consider the compound "84# produced by reaction of trimethylphosphine with cationic carbyne complex "83# as a C!dialkylamino!substituted phos! phonium salt\ although it is obvious that the real bonding pattern of this cationic half ylide is much closer to the mesomerically stabilized zwitterionic structure "Scheme 34# ð67CB1340Ł[
[(CO)5Cr=CNEt2]+ [BF4]– (94)
2 Me3P CH2Cl2, –40 °C
(CO)5Cr
PMe3 NEt2 PMe3
+
Et2N BF4–
89%
Me3P
+
PMe3
BF4–
(95) Scheme 45
Unlike nitrogen\ the heavier Group 04 elements\ especially phosphorus\ exert a stabilizing e}ect on the ylide functions and consequently numerous phosphino substituted phosphonium ylides have been synthesized and thoroughly investigated[ These will\ however\ despite their abundance\ be treated brie~y here because of the availability of a series of review articles that provide quick access to the original papers published up to 0878 ð72RCR0985\ 80COS"5#060\ 80RCR280Ł[ The most general synthesis of phosphino substituted phosphonium ylides is based on trans! ylidation methodology\ investigated by Schmidbaur and co!workers in the early 0869s ð69AG"E#66\ 60CB049Ł[ This route in generalized form is outlined in Scheme 35[ Ylides carrying at least one hydrogen atom at the a!carbon atom react with chlorodialkyl! or chlorodiarylphosphines with
690
P\ As\ Sb Or Bi
the formation of a!substituted phosphonium salts\ from which phosphino!substituted ylides are generated by deprotonation[ If the reaction provides a salt whose acidity is greater than that of the starting ylide precursor\ a second mole of the starting ylide reacts with the zwitterionic intermediate in a transylidation reaction ð80COS"5#060Ł[ A large variety of phosphino substituted ylides have been made by this method ðB!61MI 511!90\ 80RCR280Ł[ The synthesis of arsenic! and antimony!substituted ylides may be carried out analogously[ From methylenetriphenylphosphorane and phosphorus\ arsenic\ and antimony halogen compounds the corresponding disubstituted ylides such as "85#Ð"87# are available via double transylidation ð55LA"588#39\ 69JPR345\ 73OM27\ 73ZN"B#0345Ł[ X
X
R2PCl
PY3
X
B
+
PY3 Cl–
PY3
HCl•B
R2P
R2P
Scheme 46
Ph2E PPh3 Ph2E (96) E = P 〈66LA(699)40, 70JPR(312)456〉 (97) E = As 〈84ZN(B)1456) (98) E = Sb 〈84OM38〉
Reactions of ylide anions with electrophiles lead directly to functionalized ylides ð76AG"E#68\ For instance\ the ylide "88# can be metallated at the methyl group by LiMe\ NaNH1 or KH to give partially solvated products "099#[ The reaction of the latter with chloro! diphenylphosphine leads to the new ylides "090# and "091# "Scheme 36# ð72CB0275Ł[ Pure "090# is obtained from "099^ M Li# and chlorodiphenylphosphine in the presence of TMEDA[ 76TL1000Ł[
P Ph2P
Ph Ph Me
Ph Ph – CH 2 (100)
MeLi, NaNH2 or KH
P
Ph2P
(99) Ph
Ph
Ph
P PPh2 PPh2 (101)
THF, –40 °C
Ph P
+
Ph2PCl
M+
PPh2
PPh2 PPh2 (102)
Scheme 47
The convenient procedure for the synthesis of methylenephosphoranes bearing phosphorus\ arsenic or antimony at the ylidic carbon atom is condensation of trimethylsilyl!substituted ylides with chlorophosphines\ chloroarsines and chlorostibines[ The reactions proceed in a 0 ] 0 ratio of starting reagents and are followed by elimination of chlorotrimethylsilane[ This method permits access to compounds which are often di.cult to obtain by other routes and produces salt!free functionalized ylides in good yield[ The silylated precursors\ representing the starting materials for the syntheses are readily available with a large variety of substituents "cf[ Section 5[11[0[3[3#[ The reactions in both Equation "08# and Scheme 37 constitute examples from the literature which illustrate the synthetic potential of the method[ Cl3Si Cl3Si
2 PCl3 benzene, 0 °C 78%
Cl2P Cl2P
Cl P Me Me
Me
TMS
2 Me2PCl
PMe3 TMS
Cl P Me Me
ether, 0 °C 94%
+ P Me Cl– PMe3 TMS
Me2P
Scheme 48
(19)
MeLi
Me2P
ether/THF, –30 °C 54%
TMS
PMe3
691
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
Ylides bearing s2l4 and s1l2 phosphorus at the anionic centre are stable enough to be isolated[ A methylenephosphorane bearing two!coordinate phosphorus at the ylidic carbon atom was obtained by reaction of phosphonium salt "092# with three equivalents of sodium bis"trimethylsilyl#amide in THF at −67>C[ Compound "093# is probably formed via ð0\2Ł!silyl migration[ According to an x! ray analysis\ this ylide can be described as a hetero allyl anion with a three!center!four!electron bond C00P00N0[ Oxidative addition of sulfur or selenium results in the formation of the imino"thioxo#phosphorane "094# or imino"selenoxo#phosphorane "095# "Scheme 38# ð80CB218Ł[ TMS
3 NaN(TMS)2
+
P(NMe2)3 BF4–
Cl2P
N P
THF, –78 °C
(103) TMS
P(NMe2)3
C
P(NMe2)3
TMS TMS
1/n Zn
P(NMe2)3
TMS N P (104)
TMS N P Z (105) Z = S (106) Z = Se Scheme 49
5[11[0[3[3 Silicon!\ germanium! and boron!substituted ylides\ R2E"X#C1PY2 "E Si or Ge# and R1B"X#C1PY2 Trialkylsilyl groups exhibit a pronounced stabilizing e}ect on ylidic carbanions^ therefore\ numerous silicon substituted phosphonium ylides are available and widely used in preparative chemistry[ A few review articles serve very well as introductions to this _eld ð64ACR51\ 80RCR280\ 80COS"5#060Ł[ Germanium! and boron!substituted phosphonium ylides are considerably less studied[ A wide variety of a!silylated methylenephosphoranes have been synthesized from simple methyl! enephosphoranes and chloroalkyl"aryl#silanes "especially TMS!Cl# by transylidation ð71AG"E#434\ 74AG"E#0957\ 81S676Ł[ From methylenetrialkyl"aryl#phosphoranes both mono! or bis!silylated prod! ucts may result "Scheme 49# ð56CB0921\ 81CB0942Ł[ Apart from the above mentioned silicon halogen compounds\ siletanes\ 0\2!disiletanes and the highly strained hexamethylsiliranes have been reacted with methylenephosphoranes to give the corresponding silicon substituted ylides ð80COS"5#060Ł[ The introduction of germanium substituents may be carried out analogously or starting from ylide anions "Scheme 40# ð56CB0921\ 66CB566Ł[ Mixed silicon:germanium or silicon:tin substituted ylides were synthesized by reacting the monosilylmethylenephosphorane "096# with germyl or stannyl chlorides "Equation "19## ð56CB0921Ł[ TMS-Cl
3 H2C
2
PR3
TMS PR3
–[MePR3]+ Cl–
TMS-Cl
TMS
–[TMS-CH2PR3]+ Cl–
TMS
PR3
R = Me, Ph Scheme 50
3 H2C
Me3Ge
2 Me3GeCl
PPh3
PR3
Et2O, 20 °C 51%
Me3Ge
i, 2 LiR ii, Me3GeCl THF, –10 °C 60%
H2C
PMe3
Scheme 51
2
Me3MCl
TMS PMe3
(107) M = Ge, Sn
ether, 20 °C 52–62%
TMS PMe3
(20)
Me3M
The reaction of methylenetrimethylphosphorane with dichlorodimethylsilane leads via a twofold transylidation to the formation of Si!bridged bisphosphorane "097# "Scheme 41# ð69CB86Ł[ At elevated temperatures and in the presence of excess ylide as a catalyst\ the four!membered ring
692
P\ As\ Sb Or Bi
undergoes an isomerization through ring expansion "097#Ð"098# ð63AG"E#439Ł[ Methylenetriphenyl! phosphorane reacts with 0\1!dichlorotetramethyldisilane to give a methylenephosphorane "009# with two exocyclic ylide functions "Equation "10## ð69AG"E#626Ł[ Me
Me Si
2 Me2SiCl2
6 H2C
PMe3
Me3P ether, 35 °C 55%
∆
PMe3 Si Me
Me
Me Me Si Me Me3P P Me Me Si Me (109)
(108) Scheme 52
6 H2C
PMe3
Me Me 2 Me Si Si Me Cl Cl
+
Me2 Me2 Si Si
Et2O, 20 °C
Me3P
17%
PMe3
(21)
Si Si Me2 Me2 (110)
A moderately important process for the preparation of silyl ylides is transsilylation[ This method provides a means of introducing more complicated substituents\ starting from simple trimethylsilyl ylides[ Equation "11# gives some selected examples[ As a rule these reactions proceed su.ciently rapidly even at room temperature to give pure products in high yields^ the only by!product formed in the reactions is the readily separable chlorotrialkylsilane ð60CB049\ 69AG"E#66Ł[ TMS
Rn(Hal3–n)Si
+ 2 RnSiHal4–n
PMe3
PMe3
62–69%
TMS
(22)
Rn(Hal3–n)Si
RnSiHal4–n = Me2SiCl2, MeSiCl3, SiCl4, Me2SiBr2, SiBr4, Me(ClCH2)SiCl2, ClCH2SiCl3, MeSiHCl2, HSiCl3, Me2SiFCl
The silicon substituted P!chloro ylides are available by 0\1"C to P# halotropic rearrangements of trimethylsilyl substituted a!haloalkylphosphines[ The latter may in turn be prepared by reacting silylalkylphosphines with tetrahalomethanes or condensation of perchlorinated carbosilanes with lithio! and silylphosphines[ The interaction of compounds of the type "000# with carbon tetrahalides "CCl3\ CBrCl2\ CBr3# is usually carried out in dichloromethane at room temperature or below 9>C[ Yields of ylides obtained in this way are usually very high "Equation "12## ð68CB0957Ł[ However\ in certain cases tervalent phosphorus compounds containing trimethylsilyl groups on the a!carbon atom react with carbon tetrahalides with elimination of trihalotrimethylsilylmethane instead of haloform[ It should be noted that ylide "001# containing a trimethylsilyl group at the sp1!hybridized carbon atom is readily desilylated by excess of carbon tetrachloride to give carbodiphosphorane "002# "Scheme 42# ð68CB537Ł[ X
Y
X
CHal4
P TMS (111)
Y
CH2Cl2, <20 °C
TMS
Y P Y Hal
(23)
Hal = Cl, Br; X = TMS, Ph, H; Y = Ph, R2N, RO PPh2 TMS PPh2
CCl4
Ph2P
CH2Cl2, ∆
TMS
P
Ph Ph Cl
(112)
CCl4 87%
Ph Ph P Cl
C
P
Ph Ph Cl
(113)
Scheme 53
The a\a!disilyl substituted P!chloro ylides have been prepared in good yields via the reaction of chlorocarbosilanes with lithio! or silylphosphines "Schemes 43 and 44#[ If C\C!dihalo!0\2\4! trisilacyclohexanes are used the major products are methylenephosphoranes "003# with exocyclic
693
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
ylide functions "Equation "13##[ These are stable crystalline substances or liquids distillable in vacuum ð70ZAAC"361#34\ 73ZAAC"400#84Ł[ Me2PLi
Cl4–nC(SiCl3)n
Me P Me Cl
Cl2–n(Cl3Si)nC
Cl3–n(SiCl3)nCPMe2
DME, –30 °C
n = 1, 2
Scheme 54
Me TMS
Cl
Me2P-TMS
TMS
Cl
DME, ∆
TMS
P Me
TMS
TMS
Cl
TMS
Me P Me Cl
Scheme 55
R2 Si Hal
R2 Si
Me2P-TMS
R2Si
R2Si
DME, –20 °C Si Hal 29–78% R2 Hal = Cl, Br; R = F, Cl, Me
Si R2 (114)
Me P Me Cl
(24)
P!Chloro ylides "004# containing trichlorosilyl groups on the a!carbon selectively exchange the chlorine atom on phosphorus for a dimethylphosphine group on interaction with lithium dimethyl! phosphide^ the trichlorosilyl groups are una}ected by this[ In addition\ during the reaction of ylide "004# with Me"TMS#PLi\ the P0P ylide "005# is formed which reacts with a second molecule of the P0Cl ylide and is converted into a double ylide with a P0P bond "006# "Scheme 45# ð73ZAAC"407#03Ł[ Cl3Si
Me P Me Cl Cl3Si (115) R = Me, TMS
R(Me)PLi
Me
Cl3Si
P Cl3Si
R
Cl3Si
(115)
P
P Me
Me (116)
Me Me
R = TMS
Cl3Si
SiCl3
+ ClP(Me)R
P
Me Me (117)
SiCl3
Scheme 56
It has been reported that photolysis of phosphinodiazomethane "007# in benzene at room tem! perature in the presence of an excess of chlorotrimethylsilane gives the ylide "008# in almost quantitative yield ð77JA5352Ł "Scheme 46#[ The generality of this approach is restricted by possible di.culties in the preparation of the requisite phosphinocarbenes[ Dialkylborylalkylidenetriphenylphosphoranes have been studied rarely[ They are available via transylidation starting from simple alkylidenephosphoranes and chlorodialkyl! or dichloro! alkylboranes ð73AG"E#270\ 75AG"E#448Ł[ The synthesis of the mixed siliconÐboron substituted ylide "019# follows the reaction pathway analogous to the approach to disilylated methylenephosphorane "008# "Scheme 47# ð82CC0243Ł[ The _rst C!gallyl!substituted phosphorus ylide\ "R1N#1P"Me#1C"TMS#GaMe1\ was recently pre! pared by the reaction of a stable phosphinocarbene with GaMe2 ð83AG"E#467Ł[ TMS
P(NR2)2 N2
.. .. NR2 TMS C P NR2
hν, 300 nm C6H6, 20 °C
–
TMS C
+
NR2
P NR2
(118) TMS
R = Pri
NR2 P NR2 TMS Cl (119) Scheme 57
NR2
TMS-Cl
TMS C C6H6, 20 °C
P NR2
694
P\ As\ Sb Or Bi .. .. NR2 TMS C P NR2 R = Pri
TMS
B(OMe)3
NR2
TMS MeO (MeO)2B
P NR2
(MeO)3B
NR2
TMS
NR2 P NR2 (MeO)2B OMe (120)
P NR2
Scheme 58
5[11[0[3[4 Metal substituted ylides\ LnM"X#C1PY2 Whereas the chemistry of the metal complexes of phosphorus ylides "010# has been the subject of intensive investigation and has developed into a rapidly growing _eld of research with important applications ðB!71MI 511!90\ 72AG"E#896\ 72CCR0Ł\ the chemistry of metal substituted ylides "011# has been investigated relatively little[ Moreover\ most of the examples that have been studied in detail are derived from the simple methylenephosphoranes\ H1CPY2[ –M
M
M
+
PY3
+
PY3
PY3
–
(121)
X
(122)
Under this heading\ only the synthesis of functions of the type "011# which formally arise from substitution of a hydrogen atom at the ylidic carbon by a metal atom will be considered[ Metal complexes of phosphonium ylides will not be discussed[ "i# Ylides with a Li0C bond The synthesis of lithiated ylides by direct substitution of a proton at the a!carbon atom seems to be restricted to alkylidenephosphoranes[ In 0871 Corey and co!workers reported that a!lithiomethylenetriphenylphosphorane "015# is available by reaction of the corresponding ylide with t!butyllithium in THF solution at low tem! perature ð71JA3613Ł[ The same lithium substituted ylide can be generated by reaction of methyl! triphenylphosphonium bromide with 1 equivalents of s!butyllithium in ether[ However\ examination of the reactions by means of low temperature NMR spectroscopy showed that the interaction of the methylenetriphenylphosphorane with lithium alkyls includes replacement of a phenyl group at the phosphorus atom by an alkyl group with formation of the ylide "012# "route a# and metallation of a benzene ring with formation of the ylide "013# "route b#[ Spectral characteristics of the lithiated ylide obtained by the exchange reaction of bromomethylenephosphorane "014# with t!butyllithium in hexane at −64>C di}ered from those for the lithiated ylide prepared by direct metallation ð72C09\ 73TL3986\ 74TL0512Ł[ To explain these results it was proposed that lithium methylide "015# exists in a metallotropic tautomeric equilibrium with the ylide "013# lithiated in the benzene ring "Scheme 48# ð74TL444Ł[ H2C
PPh3 RLi b
a –PhLi
Ph Ph R
H2C
H2C
–RH
Ph Ph Li
(123) (124)
ButLi
Br PPh3 (125)
Li PPh3
hexane, –75 °C
(126) Scheme 59
Li
PPh2
695
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
The reaction of methylenetrialkylphosphoranes with equimolar amounts of methyl! or butyl! lithium proceeds with lithiation of one of alkyl groups[ The use of excess of organolithium com! pounds leads to the formation of twofold lithiated ylides "016# "Scheme 59# ð70JOM"198#C09Ł[ Metallation of silylated methylenetrialkylphosphoranes "e[g[\ TMS"H#C1PMe2# again occurs in the alkyl groups and a}ords products with two carbanionic centers[
H2C
R P Me Me
–
BuLi
H2C
+
R Li+
P –
BuLi
Me
H2C
–
–H C 2 + H2C P –H C 2
R
2 Li+
(127) Scheme 60
The monomeric phosphonium ylides a!substituted by Group I metals other than lithium or by alkaline earth metals have not been described[
"ii# Ylides with a transition metalÐcarbon bond The _rst attempts to obtain phosphonium ylides with a transition metal atom in place of the ylide hydrogen atom met with little success since the simplest reactions "e[g[\ of metal halides with H1CPR2# yield only insoluble products which are di.cult to characterize ð66ZN"B#747Ł[ Kaska and co!workers have successfully exploited the stabilizing in~uence of the h4!cyclopentadienyl group to e}ect substitution of a proton at the ylide carbon atom by a "h4!C4H4#1ZrCl group[ Bis"h4! cyclopentadienyl#chlorozirconylmethylenetriphenylphosphorane "017# was isolated as yellow! orange needles in 64) yield[ In a similar fashion "h4!C4H4#1HfCl1 reacts with two equivalents of methylenetriphenylphosphorane in THF for 03 days at room temperature to give hafnium!sub! stituted ylide "018# "Equation "14## ð79ZN"B#0178Ł[
(η5-C5H5)2MCl2 + 2 H2C
THF, 20 °C
PPh3
Cl (η5-C5H5)2M
–[MePPh3]+ Cl–
(25) PPh3
(128) M = Zr (129) M = Hf
Subsequently the series of complexes of Group 3 metals with bridging ylide ligands has been described[ Thus\ when the methylenephosphorane "029# containing bulky diethylamino groups on the phosphorus atom was allowed to react with TiCl3\ the bis"phosphoranylidene# dititanacyclobutane "020# has been isolated in over 69) yield "Equation "15## ð75AG"E#463Ł[ Anal! ogously\ reaction of the ylide H1CPMe2 with TiCl1"NMe1#1 a}ords the 0\2!bis"dimethyl! amino#dititanacyclobutane ð66ZN"B#747Ł[ In both reactions the ylides are deprotonating in the manner of a transylidation\ giving rise to the formation of a phosphonium salt as a by!product[ When an excess of methylenetris"dimethylamino#phosphorane was treated with TiCl1"NMe1#1 according to the same procedure "by employing the phosphorus methylide as base as well as nucleophile#\ compound "021# having di}erent terminal ligands on titanium was obtained in 2) yield[ The addition of 1\3\5!trimethylpyridine to an equimolar mixture of ylide and TiCl1"NMe1#1 provided the metallacycle "022# in 06) yield "Scheme 50# ð82AG"E#443Ł[ Use of TiCl2"NMe1# in place of TiCl1"NMe1#1 a}orded "022# in the same isolated yield[ Compound "022# underwent ligand exchange reactions at titanium without disruption of the metallacycle core[ Thus\ the addition of 1[4 equi! valents of Ti"NMe1#3 to "022# at ambient temperature a}orded "021# in quantitative yield[ It should be noted that because of their two oxophilic centers\ the metal!substituted ylides of type "022# may be regarded as a synthetic equivalent for a carbon atom for the selective production of allenes from unhindered aromatic aldehydes[ For example\ metallacycle "022# reacted immediately with an excess of 3!methylbenzaldehyde or 3!methoxybenzaldehyde in THF solution to give the corresponding 0\2!diarylallenes in 32) and 39) isolated yield\ respectively\ based on an expected two equivalents of allene per metallacycle "Equation "16##[ The compound "022# underwent the same reaction with 3!methylbenzaldehyde in 19) yield ð82AG"E#443Ł[
696
P\ As\ Sb Or Bi Cl 4 TiCl4 +
6 H2C
P(NEt2)3
Cl Ti
Et2O/toluene, 20 °C
(Et2N)3P
P(NEt2)3
–2 [(Et2N)3PMe]2TiCl6
Cl Cl (131)
(130)
Cl 2 TiCl2(NMe2)2 +
3 H2C
(26)
Ti
P(NMe2)3
NMe2 Ti
Et2O/toluene, 20 °C
(Me2N)3P
P(NMe2)3 Ti Cl NMe2 (132) 2 Ti(NMe2)3Cl
2 Ti(NMe2)4 Cl
Cl TiCl2(NMe2)2 +
H2C
P(NMe2)3
Ti
N
(Me2N)3P
toluene, 20 °C
P(NMe2)3 Ti Cl Cl (133)
Scheme 61
Ar (133) + ArCHO
THF, 25 °C, <5 min
•
(27)
Ar
Ar = p-MeC6H4, p-MeOC6H4
0\2!Dizirconiacyclobutane containing exocyclic ylide functions has been synthesized from ðMe2CCH1Ł3Zr and excess H1CPMe2 ð72OM043Ł[ Tin! and lead!substituted ylides are available from methylenephosphoranes and stannyl or plum! byl chlorides via transylidation reactions "cf[ Section 5[11[0[3[3# ð66CB566Ł[
5[11[0[4 Tetracoordinate Arsenic\ Antimony and Bismuth Derivatives In comparison with the phosphonium ylides "X0X1CPY2# relatively little information is available regarding the synthesis of C\C!diheterosubstituted arsonium\ stibonium and bismuthonium ylides "X0X1CEY2# ðB!69MI 511!90\ 71AOC"19#004\ 71COMC!I"1#570\ 76CSR34Ł[ The size di}erence between car! bon and arsenic\ antimony and bismuth atoms leads to relatively ine.cient ppÐdp overlap between the C!sp1 orbitals and the large and more di}use d!orbitals of the heteroatom "E#\ and to decreased electrostatic interaction across the ylide P¦0E− bond[ Consequently\ arsonium\ and especially stibonium and bismuthonium ylides\ are in general more dipolar than their phosphorus analogs and have a tendency to decompose both in solution and in the solid state unless there is electronic stabilization[ A signi_cant increase in stability of the ylides X0X1CEY2 is observed\ however\ if electron withdrawing groups "X0\ X1# are conjugated with the ylidic carbon atom[ For example\ bis"arenesulfonyl#!substituted arsonium ylides are thermodynamically stable at ambient temperature and may be kept in air without signi_cant decomposition[ Stibonium ylides need anhydrous con! ditions and are frequently not isolated but used in situ[ Bismuthonium ylides are the most unstable of all Group 4B ylides[ The methods available for the synthesis of arsonium\ stibonium and bismuthonium ylides are nearly all analogous to methods used for the corresponding phosphonium ylides[
5[11[0[4[0 C\C!Diheterosubstituted arsonium ylides\ X1C1AsY2 Among the above ylides the only well characterized and studied compounds are bis"arenesulfonyl#methylenetriarylarsoranes[ The most simple synthesis of these compounds is based
697
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
on the reaction of dichloroarsoranes with compounds having acidic methylene groups\ _rst inves! tigated by Horner and Oediger in the late 0849s ð47CB326\ 48LA"516#031Ł[ For example\ "PhSO1#1 CAsPh2 is prepared in 38) yield by heating bis"benzenesulfonyl#methane with Ph2AsCl1 in benzene in the presence of triethylamine[ The strong stabilizing in~uence of the PhSO1 groups upon the C1As bond is clearly indicated by the remarkable stability of the triphenylarsonium bis"benzenesulfonyl#methylide towards oxygen and water over a period of days[ The structure of this ylide was con_rmed by x!ray crystallography ð77JCS"P1#0718Ł[ Variants of the above method include reaction of "ArSO1#1CH1 with triphenylarsine oxide in re~uxing acetic anhydride ð62T0586Ł[ The reaction presumably proceeds with initial formation of an acetoxyarsonium cation ðPh2AsOAcŁ¦[ This then reacts with a carbanion ð"ArSO1#1CHŁ− to form an arsonium salt which is readily converted into an ylide by loss of a proton[ The method is limited to the preparation of highly stabilized arsonium ylides since it is necessary that the methylene reactant should be a fairly strong carbon acid[ Almost all examples of this approach have utilized triphenyl substituted arsenic derivatives[ Silyl substituted arsonium ylides can be prepared by the salt method based on the reaction of an arsonium salt\ usually obtained from a functionalized alkyl halide and an arsine\ with a suitable base[ Thus triphenylarsonium trimethylsilylmethylide\ TMSCHAsPh2\ has been prepared in good yield by treatment of the corresponding a!trimethylsilyl substituted onium salt with butyllithium in ethyl ether ð54IC0347Ł[ The compound is also available from the reaction of the simple ylide H1CAsPPh2 with chlorotrimethylsilane followed by dehydrochlorination of the so formed arsonium salt with phenyllithium ð73TL3314Ł[ The ylide TMSCHAsPh2 readily undergoes desilylation by trimethylsilanol ð57IC057Ł[ Similar reaction of the ylide with TMSOGeMe2 leads to a monogermyl substituted arsonium ylide which disproportionates in solution to give "Me2Ge#1CAsPh2 "61)# ð66CB566Ł[ The interaction of quaternary arsonium salt "023# with NaNH1 in liquid ammonia occurs as outlined in Scheme 51 to give ylide "024#[ Treatment of the latter with Ph1AsCl a}ords diarsenylmethylenearsorane "025# as the product of a transylidation reaction ð74OM233\ 76CB0170Ł[ +
Ph2As
AsMePh2 I–
NaNH2
Ph2As
(134)
AsMePh2 (135)
Ph2AsCl benzene, 75 °C 94%
Ph2As AsMePh2 Ph2As (136)
Scheme 62
Another method for the synthesis of bis"arenesulfonyl#methylenearsoranes consists of thermal decomposition of diazo compounds in the presence of an arsine "Equation "17##[ The initial meth! odology consisted of heating a mixture of the diazo compound with an excess of the trapping agent\ without solvent\ above the decomposition point of the diazo compound[ Subsequent improvement includes the use of bis"hexa~uoroacetylacetonato#copper\ Cu"hfacac#1\ as a homogeneous catalyst ð71T2244\ 77S208Ł[ (ArSO2)2CN2 + Ph3As Ar = Ph, 4-MeC6H4
Cu(hfa)2 benzene, reflux 58–69%
ArO2S AsPPh3
(28)
ArO2S
Related to the conversion of diazo compounds into arsonium ylides is the formation of arsonium ylides by thermal or photolytical decomposition of iodonium ylides[ For example\ by analogy with the synthesis of phosphonium ylides shown in Equation "06#\ arsonium ylides can be obtained from phenyliodonium bis"arenesulfonyl#methylides and triphenylarsine in yields of 48Ð61) ð77S802Ł[
5[11[0[4[1 Stibonium and bismuthonium ylides bearing heterosubstituents\ X1C1EY2 "E Sb or Bi# Isolable examples of the above compounds\ with the exception of bis"arenesulfonyl#!substituted ylides\ are virtually unknown[ The likely reason is their low stability[ Use of copper hexa! ~uoroacetylacetonate as a catalyst has enabled the ylides "ArSO1#1CSbPh2\ Ar Ph "67)# and 3!MeC5H3 "66)# to be obtained from triphenyl!antimony and the diazo compounds "ArSO1#1CN1 in boiling benzene ð75T2776Ł[ These stibonium ylides are stable for long periods if kept in a dry atmosphere but in solution they are readily hydrolysed if any moisture is present[ Being dipolar
698
Metalloid
molecules the ylides are insoluble in alkanes and ether[ Attempts to prepare stibonium ylides from dichlorotriphenylantimony always led to ylides contaminated with "Ph2SbCl#1O ð77JCS"P1#0718Ł[ The bismuthonium ylide "PhSO1#1CBiPh2 has been made by the same method ð77S208Ł[ Although reasonably stable as a solid it decomposed rapidly in solution and hence could not be puri_ed ð77S208Ł[ It was also reported that this ylide can be generated by interaction of "PhSO1#1CHNa with Ph2BiCl1 or Ph2BiO "89BCJ849#[ It should be noted here that stibonium and bismuthonium ylides have speci_c chemical properties which little resemble those of phosphonium ylides[ Thus they do not take part in Wittig reactions\ even with very reactive aldehydes ð75T2776\ 77JCS"P1#0718Ł[ 5[11[1 FUNCTIONS CONTAINING A DOUBLY BONDED METALLOID 5[11[1[0 Tricoordinate Silicon and Germanium Derivatives Despite the intense activity on multiply bonded silicon and germanium species ð74CRV308\ there is little information on C\C!dihetero! substituted functions X0X1C1EY1 "E Si or Ge#[ Among the latter only disilicon!substituted "X0\ X1 R2Si# silaethenes have been studied in considerable detail by Wiberg and co!workers ð73JOM"162#030Ł over the past two decades[ The most successful method for the generation of these compounds involves 0\1!elimination from a!lithiated silanes carrying a good leaving group on the silicon atom[ B!78MI 511!91\ 89CRV172\ 89JOM"399#010\ 83CCR316Ł
5[11[1[0[0 Disilylsubstituted silaethenes\ "R2Si#1C1SiY1 A synthetic approach to disilylsubstituted silaethenes is shown in Scheme 52[ Generally\ the 0\1! elimination of LiY from the silanes "026# is reversible[ With poor leaving groups\ such as Y MeO or PhO\ the equilibrium disfavors the silaethene[ In the case of good leaving groups\ such as Hal\ ArSO1 or "PhO#1PO1\ the equilibrium lies to the right ð73JOM"162#030\ 78CB398Ł[ The rate of elim! ination of LiY from "026# in ether obeys _rst!order kinetics and increases for substituent Y in the sequence Ph1PO1 ³F³SPh³Ph1PO3 ³I³Br³Cl³p!MeC5H3SO2 ð70CB2494Ł[ The solvent also has an important in~uence on the results of these reactions[ In general\ the silaethenes tend to be formed as intermediates in ether solutions\ while in tetrahydrofuran they are not[ In a less basic solvent such as pentane\ silaethene formation would be favored even more\ but the lithiation step then proceeds too slowly[ Thus\ a solvent of intermediate basicity like diethyl ether is the best compromise medium for the formation of silaethenes[ TMS TMS Br
R Si R Y
R = Me, But, Ph
RLi
TMS R TMS Si R Li Y (137)
–LiY +LiY
TMS
R Si
TMS (138)
R
Scheme 63
Thermal elimination of ~uorotrimethylsilane represents an alternative to the elimination reactions in solution[ For example\ the silaethene "TMS#1C1SiPh1 can also be generated by the vapor phase pyrolysis of "TMS#2CSiFPh1 ð79JOM"075#298Ł[ Silaethenes "027# are unstable even at −67>C and their existence was demonstrated by charac! teristic trapping experiments ð76CB0594Ł as well as by the formation of remarkably stable adducts with Lewis bases such as trimethylamine ð75JOM"204#8Ł\ N!"trimethylsilyl#benzophenone imine ð76ZN"B#0944\ 76ZN"B#0951Ł and benzophenone ð77ZN"B#0357Ł "Table 2#[ In the absence of trapping reagents\ the formation of dimers or rearrangement products was observed ð70CB1976\ 70CB2494\ 70CB2407Ł[ Note that some of the derivatives of "027# obtained by cycloaddition of unsaturated compounds\ for example\ N!"trimethylsilyl#benzophenone imine\ can be used as a {store| for sila! ethenes "027# since they decompose easily to the starting materials by thermal cycloreversion ð80CB0870Ł[ An increase in the bulkiness of one of the substituents through the use of a TBDMS group led to an isolable silaethene "039# ð72AG"E#0994Ł[ Transformation of ð"TMS#1CLi0SiFBut1 = 3THFŁ "028# into "039# proceeds in diethyl ether in the presence of chlorotrimethylsilane at room temperature and leads to a monotetrahydrofuran adduct of "039# "34)# ð72AG"E#0994Ł[ Pure crystalline silaethene is obtained from the adduct by removing THF by azeotropic distillation with benzene[ It is kinetically
609
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal Table 2 Generation and trapping of transient silaethenes R0"TMS#C1SiR11 "027#[
Ð*ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ Silaethene Precursor Trappin` rea`ent or detected product Ref[ R1 R0 ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ * 1\2!dimethylbutadiene\ TMSN1 66AG"E#217 TMS Me "TMS#1"Me1YSi#CLi Y Ph1PO1\ Ph1PO2\ Ph1PO3\ p!MeC5H3SO2 NTMS and TMSN2^ dimer MeOH:MeONa 67JOM"046#C49\ TMS Me "TMS#2CSiMe1Y Y Cl\ Br\ I 79JOM"080#244 TMS Ph "TMS#2CSiPh1Y Y Cl\ Br\ I MeOH:MeONa 79JOM"080#244 TMS Me "TMS#1"Me1YSi#CLi Y F\ Cl\ 1\2!dimethylbutadiene^ dimer 70CB1976\ 70CB2494 Br\ I\ PhS\ p!MeC5H3SO2\ MeSO2\ Ph1PO1\ Ph1PO2\ Ph1PO3 TMS Me "TMS#1"Me1YSi#CLi Y "PhO#1PO1 TMS!OMe\ TMS!Cl\ TMSN1 70CB2407 NTMS\ RN2\ N1O\ Ph1CO\ PhCN\ Ph1C NTMS\ butadiene\ isoprene\ 1\2!dimethyl!butadiene and isobutene TMS Ph "TMS#2CSiPh1F rearrangement products 79JOM"075#298 "MeBut1Si#"TMS#"Me1FSi#CLi 0\2!butadiene 75CB0344 MeBut1Si Me t TMS Me Adduct of silaethene with Me2N Bu N2\ Ph1CNTMS\ acetone\ 75JOM"204#8 isobutene benzophenone 77ZN"B#0357 TMS Me "TMS#1"Me1YSi#CLi Y F\ Br\ Ph1PO3 TMS Me "TMS#1"Me1YSi#CLi Y F\ Br Ph1C1NTMS 76ZN"B#0944\ 76ZN"B#0951 TMS Me adduct of silaethene with organic dienes and trans!piperylene 75CB2387\ 75CB0594\ 80CB0870 Ph1CNTMS TMS Ph "TMS#1"Ph1YSi#CLi Y H\ Hal\ RLi\ Ph1CNTMS\ 1\2! 78CB398 OMe\ OPh\ Bu\ Ph dimethylbutadiene ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ *
stable at ambient temperature and decomposes slowly at 59>C[ The 0H and 02C NMR spectra of the silaethene "039# indicate a rapid intramolecular methyl exchange "Scheme 53# ð74AG"E#118\ 75CB0356Ł[ X!ray!structure determinations are now available for free silaethene "039# ð74AG"E#118\ ¦ 76OM21Ł\ its donor adducts with THF ð73JOM"160#270Ł\ and ~uoride anion "as its Li"01!crown!3#1Ł salt# ð76OM24Ł[
TMS But TMS Si But F Li (139)
Li ether, RT
But
TMS
TMS-Cl
F
Si
–LiCl, –TMS-F
TMS
Cl TMS
TMS MeBut2Si
But
Me Si Me
(140) Me
TMS
Me
Me
TMS
Si SiBut2Me (140b)
MeBut2Si
TMS TMS
Si Me
(140)
SiBut2 (140a)
Scheme 64
5[11[1[0[1 C\C!Diheterosubstituted germaethenes\ X1C1GeY1 The formation of transient germaethene "030# was postulated in the reaction of chloro! diphenylðtris"trimethylsilyl#methylŁgermane with cesium ~uoride ð72IZV848Ł[ It can be speculated
600
Metalloid
that the precursor of "031# is the germaethene "030#\ which loses a TMS group to give a second unstable germaethene followed by cyclodimerization to give "031# "Scheme 54#[ TMS TMS TMS
Ph Ge Ph Cl
TMS
TMS
CsF
TMS
GePh2 –TMS-Cl
GePh2 GePh2
TMS
Ph2Ge TMS (142)
(141) Scheme 65
A more established process for the generation of germaethenes is based on the formation of the C1Ge double bond by the salt elimination method "Scheme 55# ð75CB1855Ł[ For example\ thermal decomposition of germyldisilylmethanes "032# in diethyl ether at −009>C to 099>C "depending on X# leads to transient germaethene "033#[ The latter has been identi_ed by its chemical reactivity] both by insertion into the O0H bond of alcohols ð75CB1879Ł and by ene reactions ð75CB1855\ 76CB0192Ł[ Various cycloaddition reactions have also been observed] ð1¦1Ł cycloadditions are obtained with the C1C bond of CH11CHOMe and the C1O bond of ketones ð75CB1879Ł\ ð1¦2Ł cycloadducts are obtained with azides and N1O4 ð76CB0192Ł\ and ð1¦3Ł cycloadducts with dienes ð75CB1879\ 76CB0192Ł[ The unwanted side reactions can be reduced by adding a su.cient excess of trapping agent\ by the slow generation of the germaethene\ and by increasing the reaction tempera! ture[ If no trapping agents are added during the elimination of LiX from "032# the formation of {head to tail dimer| is observed[ Under special conditions "high temperatures or reactive substituents# germaethenes also stabilize themselves by rearrangement ð73JOM"162#030Ł[ By comparison with the silaethene "TMS#1C1SiMe1 the Lewis acidity of germaethene "033# is weaker and its double bond is less polar ð75CB1879Ł[ TMS TMS 2 TMS Br
Me Ge Me X
TMS 2 TMS Li
RLi RBr
TMS
Me Ge Me X
TMS
GeMe2
2 TMS
(143) X = F, Br, OMe, OPh, OC6F5, SPh, Ph2PO4, Ph2PO2 Scheme 66
GeMe2
Me2Ge
TMS
TMS
(144)
So far\ evidence for a stable C\C!diheterosubstituted germaethene is scarce[ The only isolated compounds with three heteroatoms attached to sp1!hybridized carbon are germaethenes "037# and "038# obtained by the reaction between the electrophilic cryptocarbene "034# and the stable ger! mylenes "035# and "036# "Scheme 56# ð76AG"E#687\ 76PAC0900Ł[ But :Ge[N(TMS)2]2 (146)
But TMS
B
TMS
B
TMS
B
TMS
B
But (148)
But
: But
N :Ge
N(TMS)2 Ge N(TMS)2
SiMe2 N But (147)
But
But
N
B
TMS
SiMe2
Ge
(145) TMS
B
N
But (149)
But
But TMS
B
TMS
B
(148) + HCl
N(TMS)2 Ge Cl N(TMS)2
But (150) Scheme 67
601
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
The yellow crystals "037# and "038# very slowly decolorize on exposure to air and melt without decomposition[ The presence of the C1Ge double bond in "037# has been con_rmed by x!ray di}raction[ Germaethene "037# adds HCl with quantitative formation of the 0\2!diboretane "049#[
5[11[1[1 Functions Incorporating a Doubly Bonded Boron Like the silaethenes and the germaethenes\ compounds with a C1B double bond are stable only when they are sterically shielded by large substituents[ In addition\ electronic stabilization of the electron!de_cient boron center is necessary either through pÐp delocalization "classical methylene! boranes "040#\ or borataallenes "041# or through sÐp interaction of the neighboring C0X bonds with the dicoordinate boron atom "nonclassical methyleneboranes with the three!center\ two! electron 2c!1e bonds\ "042## "Scheme 57# ð74MI 511!90\ 76MI 511!90\ 82AG"E#874Ł[ X X
X
.. B NR2
+
X
(151)
X
R R
X
R B
–
B N
R
–
–
B
X
X
R
R
(152) X
X B R1
R2
B R R1
(153) Scheme 68
A few standard and many unique reactions have been used to prepare compounds with a C1B bond[ For reason of space\ emphasis will be placed on the preparatively important methods for the synthesis of C\C!diheterosubstituted methyleneboranes[ Some C!monoheterosubstituted derivatives are described because their reactions are useful for the preparation of functionalized methylene! boranes[ There are also a number of specialized methods for the formation of a C1B bond which\ however\ do not seem to have general applicability[ For further details a comprehensive review on this subject should be consulted ð82AG"E#874Ł[ It should also be noted that the reactivity of methyleneboranes resembles that of vinyl cations and also that of silaethenes[ The tricoordinate silicon atom is related to the dicoordinate boron atom through the diagonal relationship in the periodic system of elements ð89AG"E#390\ 89CB636Ł[
5[11[1[1[0 Methyleneboranes\ X1C1B0Y "i# 0\1!Elimination reactions C\C!Disilyl!substituted methyleneboranes can be synthesized by the elimination of ~uoro! trimethylsilane or methoxytrimethylsilane from tris"trimethylsilyl#methylboranes at temperature between 369>C and 459>C "Equation "18##[ This method has proved successful for the preparation not only of the amino"methylene#boranes "045# ð76CB0958Ł and "046# ð78CB484Ł but also the methyl! eneboranes "043# and "044# with methyl and t!butyl groups on the boron atoms ð78CB0946Ł[ Com! pounds "044#Ð"046# are remarkably stable\ whereas methyleneborane "043# rapidly dimerizes to the corresponding 0\2!diboretane[ X!ray structural data is available for the compounds "044# ð78CB0946Ł and "045# ð76CB0958Ł[ TMS TMS TMS
R
450–560 °C
TMS
Y
–TMS-Y
TMS
B R
B
Y = F, MeO
(154) (155) (156) (157)
R = Me, 73% R = But, 54% R = Pri2N, 67% R = 2,2,6,6-tetramethylpiperidino
(29)
602
Metalloid
Attempts to prepare the halo"methylene#boranes "047# via elimination of TMSOMe from "TMS#2CB"OMe#Hal resulted in the rearrangement products "059# "Scheme 58# ð89CB636Ł[ The authors supposed that the anticipated compounds "047# underwent a double ð0\2Ł shift of the Me and Hal groups\ via the intermediates "048#[ The boranes "059a\b# cyclodimerize at the B1C bond at 14>C and 58>C\ respectively[ Benzophenone reacts easily with "059# to produce the cyclic 0\1! oxaboretanes ð89CB636Ł[ TMS TMS TMS
OMe B
TMS
540 °C
TMS B Hal
B Me
B
TMS
Hal
TMS
Me
Me2Si (158)
Me2Si
Hal
Hal
(159)
(160a) (160b)
Hal = Cl Hal = Br
Scheme 69
"ii# Cycloreversion reactions The thermal cycloreversion of 0!bora!1\3!cyclohexadienes ð74AG"E#0954Ł\ 0\2!diboretanes ð78AG"E#673Ł and 0\1!dihydroboretes ð89AG"E#390Ł is of considerable potential for the generation of methyleneboranes[ For example\ upon melting "037>C and 066>C\ respectively# 0\2!diboretanes "050a\b# furnish the readily volatile methyleneboranes "051a\b#\ which can be separated by con! densation "yield ca[ 24)# from mixtures of predominantly higher boiling products "Equation "29## ð78AG"E#673Ł[ The bis"stannyl#methyleneborane "052b# has been detected by multinuclear NMR spectroscopy ð89AG"E#390Ł[ Ar TMS TMS
B B
∆
TMS
35–42%
TMS
SnMe3 SnMe3
Me3Sn B Ar
Ar (161a) Ar = 2, 4, 6-Me3C6H2 (161b) Ar = 2, 3, 5, 6-Me4C6H
+
(30)
B Ar Me3Sn
(162a, b)
(163a, b)
The thermal cycloreversion of 0\1!dihydroborete "053# takes place at 019>C "reverse reaction to the formation of "053##[ Distillation into CD1Cl1 cooled to −79>C a}orded a solution of "054#\ which was investigated spectroscopically and trapped in a subsequent reaction step by 3!t!butyl! pyridine "Scheme 69# ð89AG"E#390Ł[ But
Me3Sn Me3Sn Me3Sn
Ar TMS
TMS (164)
Me3Sn
∆
B TMS
TMS
Ar B
B Ar Me3Sn (165)
N
Me3Sn
N
100% (NMR)
But
Ar = 2,3,5,6-Me4C6H Scheme 70
"iii# Miscellaneous reactions Berndt and co!workers obtained the methyleneboranes "057# from an attempt to trap an inter! mediate in the reductive dimerization of diboranes "055# by addition of bis"trimethylsilyl#acetylene ð71JOM"123#C06\ 73ZN"B#0931\ 89AG"E#287Ł[ They found that the diboranes "055# themselves reacted with the alkyne\ and 0\0!diborylalkenes "056# could be reduced by a sodium:potassium alloy
603
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
ð77AG"E#850Ł\ magnesium under ultrasonication ð77ZN"B#790Ł or Bogdanovic|!magnesium in diethyl ether ð89AG"E#287Ł to yield boriranylideneboranes "057# "Scheme 60#[ R R
R
TMS
B B Cl
TMS
Cl
R
TMS
B Cl
+2 e–
TMS
B Cl
–2 Cl–
TMS
B R
TMS
TMS
TMS
R (167)
(166)
R B
B B R
(168a–c)
R = 2,3,5,6-Me4C6H (a), 2,4,6-Me3C6H2 (b), But (c) Scheme 71
Reaction of "057a# with mesityl"trimethylsilyl#acetylene results in the formation of ðboryl "silyl#methyleneŁborane "058#[ Similarly\ treatment of "057a# with bis"trimethylstannyl#acetylene a}ords ðboryl"stannyl#methyleneŁborane "069# "Scheme 61# ð82AG"E#874Ł[ TMS TMS
B R
Mes
R B
TMS •
R TMS TMS
TMS
Mes
B
(169) B R
(168a)
Me3Sn Me3Sn
B R
SnMe3
TMS
R B •
TMS
Me3Sn (170) Scheme 72
The C0C bond of the three!membered ring in the compounds "057# is reductively cleaved by lithium in ether to give the borataalkynes "060# ð77AG"E#850Ł[ These compounds can also be obtained by reaction of the 0\0!diborylalkenes "056# with an excess of lithium in diethyl ether "Scheme 62# ð78AG"E#670Ł[ The interaction of the borylborataalkynes with electrophiles has provided a route to several new methyleneboranes[ Thus\ the reaction of "060# with Me2SnCl gave the ðboryl"stannyl#methyleneŁborane "061# ð89ZN"B#189Ł[ The action of aryldi~uoroboranes\ RBF1\ on "060# resulted in formation of the stable "diborylmethylene#boranes "062# ð78AG"E#670Ł[ In the same fashion the borataalkynes "060# react with 0\0!diaryl!1\1!di~uorodiborane\ Dur1BBF1\ to form the orange!red B!boryl"0\2!diboretane!1!ylidene#boranes "063# ð80AG"E#483Ł[
R TMS
–
2 Li
B
TMS
R
R
B R
100% (NMR)
–
B
B R
TMS
2Li+
4 Li
TMS
(168)
TMS
R
B
TMS
B
TMS
B
B BDur2
B R TMS
B Cl R (167)
(171)
Me3Sn B R TMS B TMS R
B Cl
TMS
R
(172) R = Mes
TMS
B R (173)
R = 2,4,6-Me3C6H2 (Mes), 2,3,5,6-Me4C6H (Dur) Scheme 73
R (174)
604
Metalloid 5[11[1[1[1 1!Borataallenes\ ðX1C1B1CY1Ł−
Among the methods which can be used to prepare 1!borataallenes the most important one involves the thermal isomerization of C!borylboriranides ð81AG"E#0127Ł[ 1!Borataallene "066# is formed together with the 0\2!diboretanide "065# by heating "009>C\ 2 h# a toluene solution of the boriranide "064#[ In this reaction\ the C0C bond of the three!membered ring is cleaved\ and for each product a di}erent duryl group migrates from a boron atom to the carbon atom located between the two boron atoms "Scheme 63# ð82AG"E#874Ł[ TMS
Dur TMS TMS
TMS
R
+RLi
B
B
–
Li+
B
Dur
B R
Dur (175)
(168)
∆
R B
TMS
Dur1
B
TMS
R
[1,2]-Dur1
B
TMS
..
Dur1
[1,2]-Dur2
R –
B B
TMS
Dur2
Dur2
Li+ Dur
– B
R = Ph
Dur1
TMS
Ph
B
–
TMS Li+
B
TMS Dur2
Dur (176)
TMS (177)
Dur = 2,3,5,6-Me4C6H Scheme 74
The 1!borataallenes "079# are accessible through thermal isomerization of 1!boryl!0\2!dibor! etanides "067# "Scheme 64#[ Presumably\ this reaction initially involves a ring!opening to give "068#\ a process typical of 0\2!diboretanes[ Then\ one aryl group undergoes a ð0\2Ł migration from a tri! to the dicoordinate boron atom[ Compound "067# is accessible from the methyleneborane "062# and t!butyllithium "19)# ð89AG"E#0929Ł[ The high reactivity of the boronÐcarbon double bond in the methyleneboranes "051# has also R B
TMS
R B B
TMS
ButLi
B B
TMS TMS
R (178)
R –
70%
TMS Li+ TMS
R B R (180)
TMS B
B R
–
B
B
Li+ But
220 °C
R B
–
But
R (173)
But
R
Li+
R
TMS B R (179)
R = 2,3,5,6-tetramethylphenyl Scheme 75
605
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
been exploited in the synthesis of 1!borataallenes and 1\2!diboratabutadienes "Scheme 65#[ The methyleneborane "051a# reacts with lithium in toluene at 14>C to give the 1\2!diboratabutadiene "071a#\ the symmetrical dimer of its radical anion "070a#[ Under the same conditions\ "051b# yields the 1!borataallene "072b# "the unsymmetrical dimer of the radical anion "070b## as major product "45)# together with "071b# as minor product "05)# ð89AG"E#0929Ł[ TMS B Ar TMS (162a, b) Li
R1 TMS B Ar
TMS
Li+
–
.
B
TMS
R2
TMS R1 (181a) (181b)
R1 = H, R2 = Me R1 = R2 = Me
TMS TMS TMS
TMS –
B
B–
Ar
TMS 2Li+
B
–
–
TMS
Ar
Ar
TMS
B 2Li+
TMS (182a, b)
(183b)
Ar = 2, 4, 6-Me3C6H2 (a); 2, 3, 5, 6-Me4C6H (b) Scheme 76
The reactions of 1!borataallenes with electrophiles have been used as a method for preparation of a few types of heterosubstituted methyleneboranes\ including C\C!diboryl derivatives[ For exam! ple\ 0\0!diboryl!1!borataallenes "079# can be protonated with cyclopentadiene to give the "diborylmethylene#boranes[ In all cases the electrophiles attack the carbon atom bonded to the two trimethylsilyl groups regioselectively\ with the result that only "diborylmethylene#boranes and not the isomeric "disilylmethylene#boranes result ð82AG"E#874Ł[
5[11[2 FUNCTIONS INCORPORATING A DOUBLY BONDED METAL 5[11[2[0 Transition Metal Carbene Complexes For the purpose of this survey\ transition metal C\C!diheterosubstituted carbene complexes will be de_ned as the species of the formula X0X1C1MLn which formally contain a double bond between carbon and the transition metal[ Systematic "IUPAC# nomenclature for these compounds uses the su.x {ylidene|\ the ligand being regarded as neutral with respect to the metal oxidation state^ thus the complex ð"OC#4Cr1C"OMe#ClŁ is called pentacarbonylðchloro"methoxy#methylideneŁ chromium"9#\ but trivially is chloro"methoxy#carbenepentacarbonylchromium"9#[ Complexes containing heterosubstituted carbene ligand were _rst prepared by Fischer in the 0859s ð53AG"E#479\ 65AOC"03#0Ł[ Since then this _eld has experienced explosive growth and continues to expand at a rapid rate ð61CRV434\ 62CSR88\ 79MI 511!90\ 78CRV0692Ł[ A large number of methods have been developed\ providing access to a great variety of carbene complexes involving nearly all the transition metals[ Various aspects of this chemistry have been reviewed extensively in recent years ð75AOC"14#010\ 77CRV0182\ 80SL270\ 80CSR492Ł[ Therefore\ only most important synthetic examples will be selected here from the abundance of material available ðB!73MI 511!90\ 78MI 511!92Ł[
606
Metal 5[11[2[0[0 Dihalocarbene complexes\ Hal1C1MLn
The _rst transition metal dihalocarbene complex of the type Hal1C1MLn was prepared in 0866 by reaction of tetraphenylporphyrinoiron"II#\ ð"TPP#FeIIŁ\ with CCl3 in the presence of excess iron powder ð66CC537\ 77CSR0010Ł[ In 0867 the di~uorocarbene complex of molybdenum\ ð"h4!C4H4# "CO#2Mo1CF1Ł¦\ was detected in solution by 08F and 02C NMR spectroscopy ð67JOM"042#56Ł[ In 0879 a stable dichlorocarbene complex of osmium"I# was described ð79JA0195Ł and since then a large number of dihalocarbene complexes has been prepared and thoroughly characterized ð72MI 511!90Ł[ The review by Brothers and Roper ð77CRV0182Ł provides a valuable survey of the literature up to 0876[ Several synthetic routes to Hal1C1MLn species have been developed\ but each one is appropriate for only a limited number of transition metal substrates[ The most general method for the prep! aration of the dihalocarbene complexes starts from metal trihalomethyl derivatives\ Hal2C0MLn[ "i# Synthesis from trihalomethyl complexes The chemistry of tri~uoromethyl derivatives of the transition metals has been the focus of much attention ð82AOC"24#100Ł[ As a result\ many transition metal tri~uoromethyl species are known\ and these o}er the possibility of modi_cation of the CF2 ligand to form Hal1C1MLn carbene complexes[ In principle an electrophilic attack on coordinated CF2 ligand using H¦\ TMS¦\ BF2 or SbF4 as ~uoride anion abstracting agents lead to di~uorocarbene complexes "Scheme 66#[ Thus\ the ruthenium"II# complex "073#\ when treated with anhydrous HCl or TMS!Cl as ~uoride abstracting reagents forms the di~uorocarbene product "074# "Scheme 67# ð71JOM"123#C8Ł[ The attack of SbF4 on the CF2 group in CpMo"CF2#"CO#2 generates the cationic di~uorocarbene complex ðF1C1Mo"Cp#"CO#2ŁSbF5 ð67JOM"042#56Ł[ Likewise\ ðF1C1Mn"CO#4ŁBF3 is obtained from Mn"CO#4"CF2# and BF2 ð74OM0729Ł[ F3C MLn
+
F
–F–
F
–L
MLn
MLn-1
F
F
Scheme 77
MeCN Cl
L Ru
L (184) L = PPh3
+
L Cl
MeCN
HCl or TMS-Cl
CF3
OC
benzene, RT
Cl Ru L
CF2
Cl
Cl–
OC
L Ru L (185)
Cl CF2
Scheme 78
Reaction of tri~uoromethyl complexes with BHal2 "Hal Cl\ Br\ I# converts F2CMLn to Hal2CMLn[ The use of excess BHal2 resulted in both halide exchange and stabilization of the cationic dihalocarbene complexes[ For example\ treatment of "075# with excess BCl2 produced the stable dichlorocarbene complex "076# which was fully characterized\ including an x!ray crystal structure study[ An analogous reaction was successfully used in the preparation of dibromocarbene complex "077# "Equation "20## ð73OM203\ 74OM0729\ 77CRV0182Ł[ Tri~uoromethyl species ðF2C"Cp#Fe"CO# "PPh2#Ł ð74OM0729Ł and ðF2C"Cl#Ru"CO#1"PPh2#1Ł ð75AOC"14#010Ł also react with BCl2 to give dichlorocarbene complexes[
CpFe(CF3)(CO)2
2BHal3 benzene, RT
(186)
+
Hal Fe(Cp)(CO)2
BHal4–
(31)
Hal (187) Hal = Cl (188) Hal = Br
"ii# From reactions with Cd"CF2#1 and H`"CCl2#1 Roper and co!workers found that the highly reactive complex ðCd"CF2#1 = GLYMEŁ ð75IS41Ł can be used for CF1 transfer to a suitable metal substrate ð75AOC"14#010Ł[ A good example of
607
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
this method is the synthesis of di~uorocarbene ruthenium and osmium complexes "078# "Equa! tion "21## ð75JOM"299#056\ 72CC608Ł[ The oxidative addition product F2CRu"CdCF2#"CO#1"PPh2#1 is a likely intermediate in this reaction[ Other zerovalent ruthenium and osmium complexes\ RuCl"NO#"PPh2#1\ OsCl"NO#"PPh2#2 and Os"CO#"CS#"PPh2#2\ react similarly\ giving F1C1MCl"NO# "PPh2#1 "M Ru\ Os# and F1C1Os"CO#"CS#"PPh2#1\ respectively ð77CRV0182Ł[ F
Cd(CF3)2•GLYME
M(CO)2(PPh3)3
(32)
M(CO)2(PPh3)2 F (189) M = Ru, Os
The cadmium reagent was also successfully used for CF1 transfer to a d 7 iridium center[ An example is the preparation of the di~uorocarbene complex F1C1Ir"I#"CO#"PPh2#1 from IrI"CO# "PPh2#1[ At higher temperatures\ reaction of ðCd"CF2#1 = glymeŁ with Vaska|s complex or with F2CIr"CO#"PPh2#1 results in transfer of a CF1 group and also\ for the former substrate\ replacement of chloride with CF2 "Equation "22## ð77CRV0182Ł[ F
Cd(CF3)2•GLYME
IrCl(CO)(PPh3)3
(33)
Ir(CF3)(CO)(PPh3)2 F
The mercury compound Hg"CF2#1 oxidatively adds across one Hg0C bond to Ru"CO#1"PPh2#1 producing the stable complex F2CRu"HgCF2#"CO#1"PPh2#1\ containing both F2C and F2CHg ligands ð71JOM"123#C8Ł[ However\ ruthenium ð71JOM"122#C48Ł\ osmium ð79JA0195Ł and iridium ð71JOM"125#C6Ł d 5 complexes react with Hg"CCl2#1 to give the dichlorocarbene species "Equations "23# and "24##^ the probable explanation is that Cl2C0M derivatives are formed as intermediates but then lose a phosphine ligand\ HCCl2 and mercury[ The osmium and iridium complexes have been structurally characterized ð71JOM"125#C6Ł[ Cl
Hg(CCl3)2
MHCl(CO)(PPh3)3 toluene (reflux) 80%
M = Ru, Os
MCl2(CO)(PPh3)2
(34)
IrCl3(PPh3)2
(35)
Cl
Cl
Hg(CCl3)2
IrHCl2(PPh3)3 toluene (reflux) 80%
Cl
"iii# Modi_cation of dichlorocarbene complexes The displacement of chloride from a Cl1C ligand by other nucleophiles can\ in some cases\ be used for the preparation of new dihalocarbene complexes[ Thus\ by analogy with the conversion of RCOBr to RCOF upon reaction with ðCd"CF2#1 = glymeŁ the reaction of the osmium complex "089# with the cadmium reagent includes exchange of a chloro for a ~uoro substituent in a metal coordination sphere "Equation "25## ð73JOM"158#C44Ł[ The use of AgClO3ÐMeCN to abstract a labile chloride from a carbene complex\ with concomitant coordination of acetonitrile or CO\ is a useful route to several ruthenium and osmium cationic complexes "Structures "080#Ð"082#^ Equation "26## ð73JOM"158#C44\ 77CRV0182Ł[ Cl Os(CO)(PPh3)2
F
Cd(CF3)2•GLYME
(36)
Os(CO)(PPh3)2
MeCN, RT
Cl
Cl
(190) Cl MCl2(CE)(PPh3)2 Cl
AgClO4/MeCN
+
F MCl(MeCN)(CE)(PPh3)2 Cl (191) (192) (193)
M = Ru, E = O M = Os, E = O M = Os, E = S
ClO4–
(37)
608
Metal
5[11[2[0[1 Oxygen!\ sulfur! and nitrogen!substituted carbene complexes\ RE"X#C1MLn "E O or S# and R1N"X#CMLn Since very authoritative reviews of the O!\ S! and N!substituted transition metal carbene com! plexes exist ð79MI 511!90\ B!73MI 511!90\ 80SL270Ł only a brief survey of some of the more general synthetic approaches will be provided here[ Basically\ three strategies are used for the preparation of the title compounds] "i# modi_cation of a coordinated "noncarbene# carbon ligand\ "ii# modi! _cation of a carbene or carbyne ligand coordinated to a metal\ "iii# reactions of transition metal complexes with organic carbene precursors[ The various types of synthesis have di}ered widely and it will be convenient to deal with each separately[
"i# From lithium acyl metallates The route from lithium acyl metallates is the most useful and general approach to the preparation of oxygen!substituted carbene complexes from noncarbene precursors[ In this method a carbonyl ligand is converted into an alkoxy! or aryloxycarbene ligand by successive addition of a nucleophile "083# and an electrophile "Scheme 68# ð65AOC"03#0\ B!73MI 511!90Ł[ Various metal carbonyls have been used as precursors to carbene complexes\ including W"CO#5\ Cr"CO#5\ Mo"CO#5\ Mn1"CO#09\ Tc1"CO#09\ Re1"CO#09\ Fe"CO#4 and Ni"CO#3[ These compounds are arranged in order of decreasing stability of the carbene product ð79MI 511!90Ł[
(OC)mMLn
Nu–
Nu
R+
M(CO)m–1Ln –O
Nu M(CO)m–1Ln RO
(194) Scheme 79
Alkoxycarbene complexes are normally synthesized by the original Fischer procedure\ involving the reaction of an organolithium reagent with a metal carbonyl\ followed by alkylation of the resulting {ate| complex[ Alkylation can be performed with oxonium salts ð58CB0384Ł\ methyl ~uoro! sulfonate ð62SRI138Ł or methyl tri~ate ð89TL1418Ł[ More recently it was shown that the use of phase transfer conditions su.ciently activate the acyl metallate to allow alkylation by readily accessible alkyl halides[ The procedure is preparatively useful for accessing chromium containing carbenes\ but yields of the analogous molybdenum and tungsten containing species are only ³09) ð82OM1795Ł[ Chlorosilanes have been used to generate silyloxycarbene complexes ð66CB1463\ 57JOM"01#P0Ł[ A wide range of other heterosubstituted carbene complexes has been synthesized via the metal carbonyl route ðB!73MI 511!90\ 78MI 511!92Ł[ Selected examples are presented in Table 3[
"ii# Electrophilic addition to coordinated acyl\ thioacyl and imidoyl li`ands Alkylation of anionic acyl metallate is the second step in the classic Fischer synthesis of carbene complexes[ A related synthetic technique involves electrophilic addition to certain neutral acyl complexes ð63JOM"79#C24\ 63JOM"70#C6\ 64BCJ2580\ 65JOM"001#116\ 67JOM"048#62Ł[ Selected reactions are presented here to illustrate the scope of this type of transformation[ The adducts of alkoxy"dialkylamino#carbenes with Hg1¦ are synthesized by methylation of bis"carbamoyl#mercury compounds with trimethyl! or triethyloxonium ~uoroborate "Equation "27## ð56AG"E#459Ł[ Thioacyl platinum complex reacts in a similar fashion "Equation "28## ð64IC0402Ł[ The conversion of several acyl complexes into C\C!dioxygen!substituted cyclic carbene ligands has been achieved by intramolecular alkylation reactions "Equations "39# and "30## ð63JCS"D#240\ 63JCS"D#0078\ 65JOM"002#C34Ł[ Hg(CONR2)2
Me3O+ BF4– CH2Cl2, RT
{[MeO(R2N)C]2Hg}2+ 2BF4–
(38)
619
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
Table 3 Selected examples illustrating the synthesis of diheterosubstituted metal carbene complexes via acylmetallates[ Reaction
Cr(CO)6
Ref.
20
76JOM(118)C33 70AG(E)309
40
74JCS(D)1494
50
77JCS(D)1272
1.5
72CB2558
15.4
77CB3467 76JOM(113)C31
75
88JOM(355)437
70
93JOM(459)55
EtO
i, Et2NLi
Cr(CO)5
ii, Et3O+BF4–
Et2N EtO
i, Ph2C=NLi
Cr(CO)6
Yield (%)
Ph
Cr(CO)5
ii, Et3O+BF4–
N Ph
Me N (OC)5Mo
W(CO)6
cis-(OC)4Mo
ii, MeOSO2F
N Me
W(CO)6
Me N
i, MeLi
MeO EtO
i, Me2PLi
W(CO)4-cis
ii, Et3O+BF4–
Me2P
2
EtO
i, Ph3SiLi
W(CO)5
ii, Et3O+BF4–
Ph3SnCo(CO)4
Ph3Si EtO
i, Cy2NLi
Co(CO)3SnPh3
ii, Et3O+BF4–
Cy2N EtO
i, Mes2Si(H)Li
Cr(CO)6
N Me
ii, Et3O+BF4–
Cr(CO)5 Mes2(H)Si
S
MeSO3F
NMe2
trans-Cl(Ph3P)2Pt
+
MeS
CH2Cl2, RT 80%
O O
+
AgBF4
Mn(CO)5
Mn(CO)5
BF4–
(40)
60%
H
HOCH2CH2Cl/Et3N
[OsCl(CO)2(CNR)(PPh3)2]+
(39)
MeS
H
Cl
FSO3–
Pt(PPh3)2Cl
trans-
+
O OsCl(CO)(CNR)(PPh3)2
Cl–
(41)
O
R = p-tolyl
Some dithiocarbene complexes can be obtained via h1!CS1 adducts of transition metals[ An example is alkylation of the osmium complex "084# with MeI "Equation "31## ð64JOM"89#C23Ł[ Cyclic dithio! and disilenocarbene ligands are formed when dihaloalkanes are used as the electrophilic reagents in these reactions "Equation "32## ð65JOM"096#C26Ł[
(OC)2(PPh3)2Os
S S
+
I–
I(CO)2(PPh3)2Os benzene, RT
(195)
SMe
MeI
SMe
(42)
610
Metal (OC)2(PPh3)2Ru
E
Se
BrCH2CH2Br
RuBr2(CO)(PPh3)2
(43)
Se
E E = S or Se
"iii# Nucleophilic addition to coordinated isocyanides Coordinated isocyanides react with nucleophiles to yield carbene complexes[ Platinum"II# and palladium"II# species have been most extensively investigated\ and the range of nucleophilic reagents employed in these reactions has included alcohols\ amines and thiols[ The typical examples are shown in Equations "33# and "34# ð58CC0211\ 60JCS"A#10\ 63JOM"70#C6Ł[ The method has been extended to gold"I# ð62G262Ł\ mercury"II# ð58JOM"05#164\ 69JOM"14#144Ł\ iron"II# ð58CC312\ 69JOM"13#194\ 61JA306Ł\ nickel"II# ð63JCS"D#246Ł\ ruthenium"II# ð62JA3658\ 63IC810Ł and osmium"II# ð64JOM"80#C50Ł compounds[ Examples from more recent literature include preparation of chromium carbene com! plexes by reaction of coordinated trichloromethylisocyanide ð77AG"E#0233\ 78CB0896Ł and tri~uoro! methylisocyanide ð89CB640Ł with secondary amines and synthesis of neutral _ve!membered cyclic diamino!\ aminothio!\ and aminooxycarbene derivatives of palladium"II# and platinum"II# starting from the isocyanide complexes cis!Cl1"PPh2#M"CNR# ð77IC1798Ł[ RX
RXH
PtBr2(PEt3)
(Et3P)Br2Pt(CNMe) 40–90%
(44)
MeHN
RXH = MeOH, PrnOH, PhNH2, BusNH2
+
[(MeNC)4Pt]2
EtSH
(PF6–)2
2+
EtS
2PF6–
Pt(CNMe) MeHN
(45)
2
"iv# From or`anic carbene precursors A wide range of C\C!dinitrogen substituted carbene complexes has been synthesized via scission of electron!rich alkenes ð79MI 511!90Ł[ The early works dealt with platinum complexes where the carbene could be introduced via halogen!bridge cleavage or ligand displacement ð61CRV434\ 64JOM"099#028Ł[ The _rst carbene complex "085# prepared in this way is shown in Equation "35# ð60CC399Ł[ This reaction\ which is normally carried out in re~uxing xylene\ was generalized[ Other carbene complexes have been obtained by this procedure including the complexes of chromium"9# ð66JCS"D#1059Ł\ molybdenum"9# ð66JCS"D#0161Ł\ tungsten"9# ð66JCS"D#0172Ł\ ruthenium"I# ð61CC816\ 66MI 511!90Ł\ iridium"I# ð63JCS"D#0716Ł\ osmium"II# ð67JCS"D#715\ 67JCS"D#726Ł\ and ruthenium"II# ð65CC533\ 66JCS"D#1061\ 67JCS"D#726\ 68JCS"D#0818Ł[ Ph Ph Et3P Pt Cl
Cl
Cl
N
N
N
+
Pt Cl
N
PEt3
Ph N
xylene (reflux)
Pt PEt3
2 Ph Ph
Cl (46)
N
Cl Ph (196)
A related synthetic technique involves reactions of transition metal complexes with electron rich `em!dichlorides in which the C0Cl bonds have appreciable ionic character ð79MI 511!90Ł[ Two examples are shown in Equations "36# ð61CC740Ł and "37# ð64CC818Ł[ The procedure is signi_cant in that it allows the preparation of carbene complexes in unusually high oxidation states ð63JCS"D#0480\ 67JCS"D#237Ł[ Imidazolium\ oxazolium and thiazolium salts have been used to obtain certain carbene complexes ð64JCS"D#828\ 75AOC"14#010Ł[ Although the products of these reactions are often di.cult to prepare by other methods\ this technique is of limited applicability[
611
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal PhHN
CHCl3, 20 °C
(Ph3P)3RhCl + [(PhNH)2CCl]+ Cl–
Rh(PPh3)2Cl3
(47)
PhHN Me2N
LiClO4
(OC)5MnNa + (Me2NCCl2)+ Cl–
+
Mn(CO)5
THF, 20 °C 24%
ClO4–
(48)
Cl
The homoleptic bis"carbene# adducts of silver"I# and copper"I# are available directly from the reaction of the stable nucleophilic carbene 0\2!dimesitylimidazol!1!ylidene and the corresponding metal tri~ate ð82OM2394Ł[
"v# Syntheses involvin` functionalization of the carbene li`and The nucleophilic substitution reactions at the carbene carbon have found wide application in the modi_cation of carbene ligands ð79MI 511!90\ B!73MI 511!90Ł[ The alkoxycarbene complexes\ which are obtainable directly from the carbonylmetal compounds\ can be used as organometallic ester equivalents ð80SL270Ł[ Thiols\ primary and secondary amines\ and organolithium compounds react by substituting for the alkoxy group\ leading to heteroatom!stabilized carbene complexes[ Reactions normally a}ord excellent yields\ and products are easily separated[ An example is the preparation of the carbene complex "086# by aminolysis of an alkoxycarbene substrate "Equation "38## ð65JOM"002#C20\ 66CB2356Ł[ EtO Cr(CO)5 Ph3Si
Me2N
Me2NH
Cr(CO)5
ether, –78 °C 89%
(49)
Ph3Si (197)
Halide displacement from the dihalocarbene ligands by nitrogen\ oxygen and sulfur based nucleo! philes frequently leads to the formation of new heteroatom!substituted carbene complexes ð79MI 511!90\ 77CRV0182Ł[Equations "49#Ð"41# illustrate the scope of this method[ Primary alkyl! and aryl! amines react with dihalocarbene complexes to give products containing isocyanide ligands ð71JOM"122#C48\ 71JOM"123#C8\ 73OM203\ 77JOM"227#282Ł[ The mechanism of isocyanide formation may involve successive HCl loss from a Cl"RNH#C1MLn intermediate[ The reaction of the ruthenium complex ðCl1C1RuCl1"CO#"PPh2#1Ł with ethanolamine includes the formation of the isocyanide complex and its subsequent cyclization into an aminoalkoxycarbene complex ð71JOM"122#C48Ł[ Cl RuCl2(CO)(PPh3)2
Cl
Me2NH
Cl
RuCl2(CO)(PPh3)2
(50)
Me2N
F
F RSH
OsCl2(CO)(PPh3)2 Cl
OsCl2(CO)(PPh3)2
(51)
RS
Cl IrCl3(PPh3)2
HSCH2CH2SH
Cl
S IrCl3(PPh3)2
(52)
S
"vi# Nucleophilic addition to carbyne complexes Carbyne complexes can be converted into carbene complexes by the nucleophilic addition reac! tions ð66JOM"018#086Ł[ In some cases this route leads to transition metal carbenes that are inaccessible by any of the other synthetic methods[ Two examples\ one resulting from nucleophilic addition to
612
Metal
the carbyne complexes "087# ~uoride anion ð65AG"E#505Ł and the other resulting from addition of lithium thiocyanate ð66JOM"017#C38\ 67CB2431Ł\ are shown in Scheme 79[ Many related reactions have been described ð80AOC"21#116Ł[ Bun4N+F– CH2Cl2/THF, –78 °C 61%
[(OC)5Cr
Cr(CO)5 F
NR2]+ BF4– (198)
R = Me, Et
Et2N
LiSCN
SCN Cr(CO)5
CH2Cl2, 0 °C 83%
Et2N
Scheme 80
"vii# Miscellaneous Open chain Fischer type carbene complexes "CO#4Cr1C"OMe#CH1R0 react easily with N\N! dimethylformamideÐdialkyl acetal "dmfÐdaa#[ When R0 H\ the carbene complex "CO#4Cr1 C"OMe#CH1CHNMe1 is formed in high yield^ however\ when R0 alkyl\ the reaction products are dialkoxy complexes "CO#4Cr1C"OMe#OR1\ in which the OR1 group comes from the dmfÐdaa ð82OM1883Ł[ The latter reaction represents a new and general method for the synthesis of chromium dialkoxycarbene complexes[ Various neutral and cationic gold"I# amino"thio#carbene complexes were obtained in satisfactory yields on addition of lithiated 3!methylthiazole to gold"I# chloride compounds and subsequent protonation or alkylation of the products formed ð89CC0611Ł[ Similarly\ the _rst monocarbene complex of copper"I# has recently been synthesized by alkylation of a thiazolyl cuprate"I#\ ðLin CuCl"dmt#mŁ "dmt 3\4!dimethylthiazolyl#\ with CF2SO2Me ð83AG"E#561Ł[
5[11[2[0[2 Silicon!substituted carbene complexes\ R2Si"X#C1MLn The chemistry of silyl!substituted Fischer!type carbene complexes was reviewed by Schubert ð77JOM"247#104Ł[ Compared with the rich chemistry of transition metal carbene complexes having electron!donating substituents at the carbene carbon center\ compounds R2Si"X#C1MLn have been investigated only brie~y[ The alkoxy"silyl#carbene complexes R2Si"EtO#C1MLn "M Cr\ Mo or W# can be prepared by standard methods from metal carbonyls and alkali!metal silyls\ followed by alkylation with EtO2¦BF3− ð66CB2356\ 82JOM"348#44Ł[ Several alkylthio"silyl#carbene complexes were obtained via the nucleophilic displacement of an alkoxy group from a complexed silyl!substituted carbene ligand ð75CB1899Ł[ For example\ Ph2Si"EtO#CW"CO#4 reacts with EtSH in the presence of disul_de "Et1S1# to give Ph2Si"EtS#CW"CO#4 in almost quantitative yield[ Reaction of alkoxy"silyl#carbene complexes with ammonia\ primary and secondary amines yields amino"silyl#carbene complexes if the amine is not too bulky ð75OM062\ 82JOM"348#44Ł[ With bulky amines "e[g[\ HNPri1\ HNCy1# no aminolysis takes place[ When the sterically demanding amines HNEt1\ HNBunMe or HN"CH1Ph#Me are used\ monoalkylamino!substituted carbene complexes R2Si"AlkNH#CM"CO#4 are formed instead\ owing to cleavage of one of the N!alkyl substituents ð89JOM"274#110Ł[ Depending on the group X thermolysis of silyl!substituted carbene complexes R2Si"X#CM"CO#4 results in fragmentation of the carbene ligand "X OAlk or NHAlk#\ formation of stable 05! electron carbene complexes R2Si"Alk1N#CMLn\ or formation of ketenes Ph2Si"X#C1C1O "X RO\ RS# ð77JOM"244#132\ 78JOM"262#192\ 89JOM"274#110Ł[ The stabilities of the carbene complexes R2Si"Alk1N#CM"CO#3 decrease in the order W×Mo½Cr for a given R2Si group\ and in order Ph2Si×MePh1Si×Me1PhSi for a given metal ð77JOM"247#104Ł[
613
Doubly Bonded P\ As\ Sb\ Bi\ Si\ Ge\ B or a Metal
5[11[2[1 Functions With a Formal TinÐCarbon Double Bond Isolable compounds of doubly bonded tin are very rare ð89CRV172\ 81OM1637Ł[ Up to 0884 only two examples of the stable heterosubstituted stannaalkenes have been described[ The Berndt compounds "088# were synthesized by the reaction between stannylenes and the cryptocarbene "034# "Equation "42## ð76AG"E#435Ł[ The structure of "088a# has been con_rmed by x!ray crystallography[ But B R2Sn +
But TMS
:
B
TMS
B
TMS
R2Sn B
(53)
TMS
But
But
(145)
(199a, b) But N
Me R2Sn = [(TMS)2CH]2Sn (a) or
Sn (b)
Si Me
N But
The chemistry of stannaalkenes is not well developed\ and only the addition of HCl across the tinÐcarbon double bond has been performed[
Copyright
#
1995, Elsevier Ltd. All R ights Reserved
Comprehensive Organic Functional Group Transformations
6.23 Tricoordinated Stabilized Cations and Radicals, +CXYZ and ·CXYZ THOMAS L. GILCHRIST University of Liverpool, UK 5[12[0 CARBOCATIONS BEARING THREE HETEROATOM FUNCTIONS 5[12[0[0 Introduction 5[12[0[1 Cations Bearin` Three Halo`ens 5[12[0[2 Cations Bearin` Halo`en and Chalco`en Functions 5[12[0[3 Cations Bearin` Halo`en\ Other Elements and "Possibly# Chalco`en Functions 5[12[0[3[0 Cations bearin` two halo`ens and one nitro`en function 5[12[0[3[1 Cations bearin` two halo`ens and one other heteroatom function 5[12[0[3[2 Cations bearin` one halo`en\ one chalco`en and one nitro`en function 5[12[0[3[3 Cations bearin` one halo`en and two nitro`en functions 5[12[0[4 Cations Bearin` Three Chalco`en Functions 5[12[0[4[0 Three oxy`en functions 5[12[0[4[1 Three sulfur functions 5[12[0[4[2 Three selenium functions 5[12[0[5 Cations Bearin` Chalco`en and Nitro`en Functions 5[12[0[5[0 Two oxy`en and one nitro`en function 5[12[0[5[1 Two sulfur and one nitro`en function 5[12[0[5[2 Two selenium and one nitro`en function 5[12[0[5[3 Two different chalco`en and one nitro`en function 5[12[0[5[4 One oxy`en and two nitro`en functions 5[12[0[5[5 One sulfur and two nitro`en functions 5[12[0[5[6 One selenium and two nitro`en functions 5[12[0[6 Cations Bearin` Chalco`en\ Metal and "Possibly# Nitro`en Functions 5[12[0[7 Cations Bearin` Three Nitro`en Functions 5[12[0[8 Cations Bearin` Nitro`en and Other Element Functions 5[12[0[09 Cations Bearin` Phosphorus and Silicon Functions 5[12[1 CARBON!CENTERED RADICALS BEARING THREE HETEROATOM FUNCTIONS
614 615 615 615 616 616 616 616 617 618 618 618 618 618 618 629 629 629 620 620 621 621 621 622 622 623
5[12[0 CARBOCATIONS BEARING THREE HETEROATOM FUNCTIONS The aim of this chapter is to draw together the literature on the methods of preparation of salts in which the positively charged component is\ at least formally\ a carbocation with three attached heteroatom functions[ Many salts of this type are isolable and several methods of preparation have been discussed in earlier chapters of this volume[ The carbocations have been classi_ed according to the types of heteroatom attached to carbon[ This review also contains a brief discussion of 614
615
Tricoordinated Stabilized Cations and Radicals
carbon!centered radicals with three heteroatom functions[ None of these species is isolable but a few such radicals can be classi_ed as {persistent| ð65ACR02Ł[
5[12[0[0 Introduction Tricoordinate carbocations are well established as reaction intermediates but special stabilizing factors are necessary to permit salts containing such cations to be isolated[ Heteroatom substituents can provide the necessary stabilization by electron donation from a lone pair into the vacant p! orbital on carbon[ Nitrogen is the most e}ective of the common heteroatoms at this type of electron pair donation\ to the extent that the presence of just one nitrogen substituent can enable salts of the formal carbocation to be isolated[ The structure of such a cation can be represented as a resonance hybrid of carbenium ion "0a# and iminium ion "0b# forms[ On the basis of x!ray crystal structure data and spectroscopic evidence it is clear that the structures are much more accurately represented as the iminium ions "0b# containing a formal double bond\ and with the positive charge largely centered on nitrogen[ When the formal carbocation bears more than one heteroatom substituent there are further possibilities for charge delocalisation[ X
X +
+
NR2
NR2
Y (1a) carbenium ion
Y (1b) iminium ion
This chapter includes examples of methods of preparation of salts in which the cations contain a tricoordinate carbon atom with three attached heteroatoms[ The positive charge is delocalised\ to a greater or lesser extent\ over the heteroatom substituents and the bonds to the central carbon have considerable p!bonding character[ The types of structure discussed include some species which are not normally regarded as stabilized carbocations\ such as dichloroiminium cations and cationic metal carbene complexes^ examples of these types are included to illustrate the range of possible substituents[
5[12[0[1 Cations Bearing Three Halogens The salts ¦CX2SbF4X− "X Cl\ Br and I# have been generated at −67>C by reaction of the appropriate tetrahalides CX3 with antimony penta~uoride in SO1ClF ð78JA7919Ł[ The salts are stable in solution below −49>C and spectroscopic data were obtained[ The corresponding tri~uoromethyl cation could not be generated in this way[ It has been suggested that the p!electron donor ability of ~uorine is more than o}set by its electron!withdrawing inductive e}ect] calculations predict that the tri~uoromethyl cation should be less stable than the other trihalomethyl cations ð80CC864Ł[
5[12[0[2 Cations Bearing Halogen and Chalcogen Functions There are few examples of isolable salts of this type[ The salt "1# bearing one ~uorine and two sulfur functions\ and analogues with one chlorine or one bromine substituent\ have been prepared from tetra~uoro!0\2!dithietane as shown in Scheme 0 ð74CB3886\ 89CB0524Ł[ X!ray data has been obtained for "1# ð74CB4996Ł and a series of related salts has been studied spectroscopically ð76CB318Ł[
F
S
F
S
F
AsF5
F
S
F
75%
F
S (2)
AsF6– +
X–
F
S
X = Cl, Br
F
S
F
Scheme 1
X F
AsF5
F
S
F
S
AsF6– +
X
616
Carbocations 5[12[0[3 Cations Bearing Halogen\ Other Elements and "Possibly# Chalcogen Functions 5[12[0[3[0 Cations bearing two halogens and one nitrogen function
Dichloroiminium salts\ and in particular N\N!dimethyldichloroiminium chloride "2#\ are impor! tant reagents with a wide range of synthetic applications[ Dihaloiminium salts with bromine or iodine substituents are known but have been little studied[ Stable di~uoroiminium salts have not been described[ The chemistry of dihaloiminium salts has been reviewed by Janousek and Viehe ðB! 65MI 512!90Ł and by Marhold ð72HOU"E3#544Ł[ The salt Cl1C1NH1¦SbCl5− has been prepared from cyanogen chloride\ HCl and antimony pentachloride^ compounds BrClC1NH1¦SbCl5− and ClIC1NH1¦SbCl5− are prepared anal! ogously from cyanogen bromide and cyanogen iodide ð53CB0175Ł[ Salts of this type can also be prepared by protonation or alkylation of carbonimidic dichlorides "isocyanide dichlorides# ð61CB2949\ 72HOU"E3#544\ 81ZAAC"506#025Ł^ an example is the protonation of Cl1C1NCl in a superacid medium "HF and SbF5# ð81ZAAC"506#025Ł[ The method of choice for preparing N\N!dialkyl! dichloroiminium salts is\ however\ usually based on the chlorination of thiocarbonyl chlorides or thiocarbamates ð62ZOR28\ 72HOU"E3#544Ł[ The preparation can be carried out in one pot starting from a secondary amine\ carbon disul_de and a chlorinating agent such as chlorine or phosphorus pentachloride^ thus\ the salt "3# was prepared "80)# from pyrrolidine ð78SC1714Ł[ The dibromo compound "4# was obtained in a similar way\ by reaction of the disul_de "5# with bromine "Equation "0## ð63ZOR338Ł[ The corresponding diiodo compound "6# was prepared from the salt "2# in good yield by heating with three equivalents of iodomethane ð68ZOR104Ł[ Cl
Cl
+
I
+
NMe2 Cl– Cl
Cl (3)
I (4)
(7)
S Me2N
S
Br2
S
S (6)
+
NMe2 I–
Cl–
N
NMe2
Br
+
NMe2 Br–
(1)
Br (5)
5[12[0[3[1 Cations bearing two halogens and one other heteroatom function Several transition metal complexes exist in which a dihalocarbene acts as a ligand ð77CRV0182Ł[ In some of these the metal complex bears an overall positive charge and the species can formally be regarded as a stabilized carbocation bearing three heteroatoms[ Structural studies have shown that there is considerable back donation of electrons from the metal to the dihalocarbene ligand in these complexes\ so the metal to carbon bond is best regarded as a double bond[ Cationic complexes containing the CF1 ligand can be formed from tri~uoromethyl complexes by abstraction of ~uoride using antimony penta~uoride or boron tri~uoride[ The complex ðCpMo"CF1#"CO#2Ł¦SbF5− was detected in solution at low temperature from the reaction of antimony penta~uoride with CpMoCF2"CO#2 ð67JOM"042#56Ł[ The iron complex ðCpFe"CF1# "CO#PPh2Ł¦BF3−\ prepared in a similar manner\ was fully characterised ð74OM0729Ł[ The cor! responding dichlorocarbene complex ðCpFe"CCl1#"CO#PPh2Ł¦BF3− was prepared by halide exchange\ with BCl2 as the Lewis acid ð74OM0729Ł[ Ruthenium"II# and osmium"II# complexes of the type ðM"CClX#"MeCN#"CO#"PPh2#1Ł¦Y− "X Cl or F# are formed by abstraction of a chloride ligand from neutral carbene complexes by silver"I# salts in acetonitrile ð73JOM"158#C44\ 77CRV0182Ł[
5[12[0[3[2 Cations bearing one halogen\ one chalcogen and one nitrogen function The reaction of N\N!dimethyldichloroiminium chloride "2# with phenol or with thiophenol results in the formation of cations of this type "Scheme 1# ðB!65MI 512!90Ł[ Cations "7# with sulfur substituents
617
Tricoordinated Stabilized Cations and Radicals
can also be prepared by chlorination of dithiocarbamate esters ðB!68MI 512!91Ł[ Thiocyanates RSCN "R Me\ Ph# react with HBr to form isolable salts ðRSC"Br#NH1Ł¦Br− ð53CB2051Ł and the reaction of aryl cyanates with phosphorus pentachloride leads to the formation of the salts "8# in high yield ð61JGU86Ł[ Cl
Cl
PhXH
+
NMe2 Cl–
X = O, S; R = Ph
Cl
+
NMe2 Cl– RX
(3)
PCl5 X=S
S NMe2 RS
(8) Scheme 2
+
Cl PCl6–
N PCl ArO
3
(9)
5[12[0[3[3 Cations bearing one halogen and two nitrogen functions Salts of this type are well represented in the literature^ many are stable\ isolable solids[ Those in which the two nitrogen functions are dialkylamino groups are the best known and the methods of preparation of chloroformamidinium salts has been reviewed ðB!68MI 512!90Ł[ The simplest salts of this class are derived from cyanamides by reaction with HCl or HBr[ Cyanamide reacts with HCl to give the salt H1NC"Cl#1NH1¦Cl− as a solid which is stable for a month at room temperature in anhydrous conditions ð89JMC323Ł[ Dialkylcyanamides react with HBr in a similar way ð77JCS"P0#788Ł[ Carbodiimides react with 1 mol HCl to give salts ð"RNH#1CClŁ¦Cl− ðB!68MI 512!90Ł and it is possible to form a crystalline ~uorine substituted salt "09# by reaction of "CF2#1NC"F#1NCF2 with HF:AsF4 below −29>C ð76JFC"26#148Ł[ Dimethylcyanamide has also been used as the starting material for more complex salts^ examples include the sulfur!containing species "00# formed by reaction with sulfur dichloride ð74IC1342Ł and the conjugated iminium salts "01# which were produced from N!arylbenzamides\ phosphorus oxychloride and perchloric acid ð76CC88Ł[ F
Cl
+
Cl
+
NHCF3 AsF6–•HF
N S
(CF3)2N
Me2N
Me2N
3
ClO4– NAr
Ph (11)
(10)
+
NH
Cl3–
(12)
The most general method for the preparation of chloroformamidinium salts is the chlorination of ureas or thioureas using phosgene or similar reagents ðB!68MI 512!90Ł[ An example of the reaction\ the chlorination of tetramethylurea\ is shown in Equation "1# ð68S228Ł[ Another potentially general method is the reaction of dichloroiminium salts such as "2# with nitrogen nucleophiles but this is not always successful since the reactions often proceed further\ particularly when basic amines are used as nucleophiles ðB!65MI 512!90Ł[ An example of a salt which has been prepared by this method is "02#\ which was prepared from "2# and azidotrimethylsilane ð64C198Ł[ O
COCl2
NMe2
89%
Me2N
Cl NMe2+ Cl– N3 (13)
Cl NMe2+ Cl– Me2N
(2)
618
Carbocations 5[12[0[4 Cations Bearing Three Chalcogen Functions 5[12[0[4[0 Three oxygen functions
Tris"alkoxy#methylium salts\ "RO#2C¦BF3−\ are isolable species[ A review of the early work on their preparation and properties is available ðB!60MI 512!90Ł and they are referred to in more recent reviews on carbenium ions ð76CSR64\ 82AG"E#656Ł[ The best method for their preparation is the reaction of the ortho!carbonate C"OR#3 with boron tri~uoride etherate and HBF3^ papers which provide good experimental details are available for the preparation of the triethoxy! ð76JOM"217#138Ł and the trimethoxy! ð78SC1296Ł substituted carbenium tetra~uoroborates[ Hexachloroantimonate salts can be made in an analogous manner[ The salt "EtO#2C¦BF3− has also been prepared by O! alkylation of diethyl carbonate ð70LA69Ł[ The parent cation ¦C"OH#2 has been generated in a superacid medium from di!t!butyl carbonate ð82AG"E#656Ł[
5[12[0[4[1 Three sulfur functions There are several examples of the preparation of stable salts of carbenium ions bearing three sulfur functions[ The methods for their preparation are analogous to those used for the tris! "alkoxy#carbenium ions but\ since it is much easier to alkylate sulfur than oxygen\ a wider range of alkylating agents can be used[ The most convenient method of preparation is usually S!alkylation of trithiocarbonate diesters "Equation "2## ð56TL1636\ 77S11Ł[ This method has been reviewed brie~y ð55AHC"6#28Ł and there are many more recent examples\ including the preparation of some species in which the substituents provide little stabilization to the cation[ Some examples "salts "03# ð67JOC567Ł\ "04# ð81JOC0585Ł and "05# ð89CB0524Ł# are shown[ Less commonly\ tetrathio!ortho!carbonates are used as starting materials ð56TL1636\ 83CB486Ł^ the stable salt "06# was prepared by this method ð83CB486Ł[ Tri! thiocarbonates have also been S!arylated using arenediazonium tetra~uoroborates ð71JPR558Ł[ NC
MeSe
S +
NC
SMe
S
S +
–OSO F 2
MeSe
SMe BF4–
S
(14)
F
S
F
S
+
(15)
SMe AsF6–
(16)
R 1S
R2X
S R 1S
(F3CS)3C+ AsF6– (17)
R1S +
SR2 X–
(3)
R1S
5[12[0[4[2 Three selenium functions The salt "07# was generated by Se!alkylation of the corresponding triselenocarbonate ð64TL0148Ł[ Salts containing mixed sulfur and selenium substituents were also generated[ Se +
SeMe I–
Se (18)
5[12[0[5 Cations Bearing Chalcogen and Nitrogen Functions 5[12[0[5[0 Two oxygen and one nitrogen function In principle\ salts of this type are readily available from dichloroiminium salts and alcohols[ This reaction is successful with the salt "2# and phenol\ catechol and pinacol ðB!65MI 512!90Ł^ thus\ "08# was prepared from "2# and pinacol[ With simple alcohols the chloride salts are unstable\ chloride acting as a nucleophile to displace one of the oxygen functions[ The problem is overcome with
629
Tricoordinated Stabilized Cations and Radicals
nonnucleophilic counterions^ for example\ the salt "EtO#1C1NH1¦SbCl5− can be isolated ð55ZAAC"233#002Ł[ O
+
NMe2 Cl– O (19)
Another method of preparation is O!alkylation of urethanes[ N\N!Dimethylurethane was ethylated with triethyloxonium tetra~uoroborate to give "19# ð50LA"530#0Ł and the same method was used to prepare the salt "10# from "MeO#1C1NCO1Et ð81CB1376Ł[ EtO
MeO
+
NMe2 BF4–
OEt
+
BF4–
N OEt
MeO
EtO (20)
(21)
5[12[0[5[1 Two sulfur and one nitrogen function These salts are most often prepared by S!alkylation of dithiocarbamates ð63BCJ287\ 74S780Ł^ for example\ the salt "11# was prepared "74)# by methylation of the cyclic dithiocarbamate with dimethyl sulfate and subsequent reaction with sodium perchlorate "Equation "3## ð63BCJ287Ł[ Double alkylation of dithiocarbamate salts is also possible] thus\ the salt "12# was derived from Me1NCS1−Na¦ and 0\1!bis"bromomethyl#benzene ð63BCJ287Ł[ An alternative method of prep! aration is N!alkylation of iminodithiocarbonates "R0S#1C1NR1 ð57T5374Ł[ Me
Me
i, Me2SO4 ii, NaClO4
N
N +
S
85%
S
SMe ClO4–
(4)
S (22)
S NMe2+ ClO4– S (23)
5[12[0[5[2 Two selenium and one nitrogen function Two examples of salts in which the cations bear these functional groups are "13# and "14#[ Both were prepared from salts containing the anion Me1NCSe1−\ by alkylation with 0\2!dibromopropane and 2!bromobutan!1!one\ respectively ð61BCJ378\ 79CC755Ł[ Se
Se
+
Me2SnBr42–
NMe2
NMe2+
–OCOCF 3
Se
Se 2
(24)
(25)
5[12[0[5[3 Two different chalcogen and one nitrogen function Iminothiocarbonate salts unsubstituted on nitrogen can be prepared either by S!alkylation of thiourethanes or by the addition of alcohols and HCl to thiocyanates "Scheme 2# ð72HOU"E3#566Ł[
620
Carbocations
The dithiocarbamidic ester "15# can be cyclised by S!methylation and the salt "16# can be isolated in good yield after the addition of sodium perchlorate ð68S071Ł[ R1O
R1O
R2I X=I
S
R2S
S
Ph
N
X = Cl
R2S Scheme 3
S Ph
R1OH, HCl
+
NH2 X–
NH2
O NMe2+ ClO4–
NMe2 S
O
(27)
(26)
Several salts of cations bearing sulfur\ selenium and nitrogen functions have been isolated[ An example is the salt "17#^ this was obtained "in a 42) yield# by ring contraction of the six!membered heterocycle "18# which was brought about by reaction with HI ð73S556Ł[ Ph
Ph
S +
NH2
S
I–
Se (28)
Se (29)
SEt N
5[12[0[5[4 One oxygen and two nitrogen functions Tetraalkylureas are alkylated on oxygen by trialkyloxonium tetra~uoroborates^ for example\ the salt ð"Me1N#1COEtŁ¦BF3− was prepared in high yield from tetramethylurea and triethyloxonium tetra~uoroborate ð50LA"530#0Ł^ trimethyloxonium tetra~uoroborate has also been used ð60LA"632#0Ł[ With some tetraalkyureas\ N!alkylation can compete[ An alternative procedure for the preparation of salts is the displacement of chloride from chloroformamidinium cations by alcohols or alkoxides[ The salt "29# was prepared in this way "in a 46) yield# from ð"Me1N#1CClŁ¦Cl− ð60LA"632#0Ł[ An interesting example of this reaction is the preparation of the salt "20# "Equation "4## ð56CB2208Ł[ Salts unsubstituted on nitrogen are obtained by the addition of alcohols to cyanamide^ thus\ ðBnOC"NH1#1Ł¦ −OTs was prepared "in an 70) yield# from benzyl alcohol\ cyanamide and p! toluenesulfonic acid in dry chloroform ð76TL0858Ł[ PhO
+
NMe2 Cl– Me2N (30) Cl
+
NH2 SbCl6– N3
MeOH 74%
MeO
+
NH2 SbCl6–
(5)
N3 (31)
5[12[0[5[5 One sulfur and two nitrogen functions Thioureas are readily alkylated on sulfur by a wide range of electrophiles to give stable iso! thiouronium salts "21# "Equation "5## ð72HOU"E3#589Ł[ This is by far the most important method of preparation of these salts[ Thioureas can also be S!arylated by means of arenediazonium salts[ By
621
Tricoordinated Stabilized Cations and Radicals
analogy with the preparation of the salt "29#\ S!arylisothiouronium salts can also be prepared by the reaction of chloroformamidinium salts with thiophenols ð58LA"616#117Ł[ S
R2S
R2X
NR12
+
(6)
NR12X–
R1
2N
R12N (32)
5[12[0[5[6 One selenium and two nitrogen functions The reaction of selenoureas with alkylating agents is analogous to that of thioureas and stable salts "22# can be isolated ð51JOC1788\ 75NJC40Ł[ R2Se
+
NR12X– R12N (33)
5[12[0[6 Cations Bearing Chalcogen\ Metal and "Possibly# Nitrogen Functions There are two general methods for the preparation of cationic carbene complexes of this class] "i# alkylation of a ligand on sulfur or oxygen and "ii# nucleophilic addition to an isocyanide ligand[ An example of a preparation of the _rst type is the formation of the mercury complex shown in Equation "6# ð56AG"E#459Ł[ The platinum complex "23# was similarly prepared by S!methylation of a thioamide function ð64IC0402Ł[ The complex "24# was formed by alkylation of both sulfur atoms of a CS1 ligand by 0\1!dibromoethane ð65JOM"096#C26Ł[ Several related preparations have been reported ð63JCS"D#240\ 64JCS"D#828\ 64JOM"89#C23Ł[ The second approach is illustrated by the prep! aration of the platinum complex "25# by addition of ethanethiol to isocyanide ligands of "26# ð61IC1958Ł[ Attempts to add alcohols to coordinated isocyanides are generally unsuccessful\ although an intramolecular addition has been reported ð63AG"E#488Ł[ 2+
Et2N
Hg O
NEt2
Et2N
Me3O+ BF4–
Hg
NEt2
2BF4–
(7)
MeO MeO
O
2+
PPh3 SMe Cl
PPh3 NMe2 (34)
SEt
S FSO3–
Pt
MeHN
+
+
Os(Br)(CO)(PPh3)2
ClO4–
MeN
NMe
Pt
2PF6–
S MeHN (35)
SEt (36)
[Pt(CNMe)4]2+ 2PF6– (37)
5[12[0[7 Cations Bearing Three Nitrogen Functions Methods for the preparation of guanidines have been described in Chapter 5[10[ Guanidines are strong bases and excellent nucleophiles\ so that a great many guanidinium salts have been prepared by protonation or alkylation of guanidines[ Even guanidines bearing electron!withdrawing sub! stituents can be alkylated] an example is the preparation of the guanidinium salt "27# "in a 57)
622
Carbocations
yield# by alkylation of N!cyano!N?\N?\N?\N?!tetramethylguanidine with triethyloxonium tetra! ~uoroborate ð73CB491Ł[ +
Me2N NCNEt
BF4–
Me2N (38)
Salts "28# and "39# with cations bearing one and two azido functions have been prepared by displacement of chloride from the corresponding chloro!substituted cations ð56CB2164Ł[ Tris "azido#carbenium hexachloroantimonate "30# is isolated in high yield from the reaction of tetra! chloroantimony"V# azide\ "SbCl3N2#1\ with carbon tetrachloride ð55AG"E#730\ 56CB2614Ł[ This salt reacts with PCl2 ð68AG"E#582Ł and with PBr2 ð79ZAAC"357#054Ł to give the new salts "31^ X Cl or Br#[ +
+
N3 NH2
Cl–
N3
SbCl6–
NH2
H2N
+
+
N3
N3
N3 (40)
N
X3P
N
SbX6–
N
SbCl6–
N3
(39)
X3P
(41)
PX3 (42)
5[12[0[8 Cations Bearing Nitrogen and Other Element Functions A few salts have been described in which the cation bears two nitrogen and one phosphorus function ð61JOC1629\ 67JPR278Ł[ The most stable of these is the crystalline salt "32# which was prepared as shown in Equation "7# ð67JPR278Ł[ The salt "33#\ described by the authors as a {cationic half ylide|\ has also been prepared ð67CB1340Ł[ There are a number of cationic carbene complexes of this class known\ of which "34# is an example ð82OM2394Ł^ this was prepared from the stable carbene and silver tri~ate[ +
+
Me2N Cl–
Cl
Me2N
Ph2POPri
P(O)Ph2
81%
Me2N
Cl–
(8)
Me2N (43)
+
Me3P NEt2
Ar N
Ar N
N Ar
N Ar
Me3P
Tf–
Ag
BF4–
(44)
+
(45)
5[12[0[09 Cations Bearing Phosphorus and Silicon Functions The salt "35# has been prepared as shown in Equation "8#^ it is a colourless solid which is unstable above −29>C ð80AG"E#698\ 82PS"65#10Ł[ Crystal structure determinations carried out on closely related salts show that both phosphorus and carbon are trigonal planar] the salt can be regarded as the phosphorus analogue of an iminium salt\ with stabilization of the carbenium ion by the lone pair
623
Tricoordinated Stabilized Cations and Radicals
on phosphorus[ The salt "36# has also been isolated but in this case the nitrogen substituents on phosphorus bear much of the positive charge ð78JA5742Ł[ +
TMS
TMS
AlCl3
P(Cl)But2
PBut2
AlCl4–
(9)
TMS
TMS
(46) +
TMS P(NPri2)2
Tf–
TMS (47)
5[12[1 CARBON!CENTERED RADICALS BEARING THREE HETEROATOM FUNCTIONS No carbon!centered radicals bearing three heteroatom functions can be regarded as {stable| in that they cannot be isolated and handled\ but a few such radicals have signi_cant lifetimes "ranging from a few seconds to a few hours# in solution[ Such radicals have been described as {persistent| ð65ACR02Ł[ These radicals bear silicon\ phosphorus or sulfur substituents and their increased lifetime can be ascribed to steric factors rather than to electron delocalization[ The tris"trimethylsilyl#methyl radical =C"TMS#2 can be generated by decomposition of ð"TMS#2CŁ1Hg ð69CC448Ł or by reduction of "TMS#2CI ð80CC0597Ł[ This radical is long!lived in solution[ A number of carbon radicals bearing three sulfur functions can also be described as persistent\ among them =C"SCF2#2\ which is generated reversibly from its dimer at room temperature ð68JA5171Ł\ and =C"SCF2#1SC5F4\ which is produced from its dimer at 039Ð089>C ð73T3852Ł[ A number of other radicals bearing three sulfur functions or two sulfur and one silicon function can be produced by thermal dissociation of their dimers ð66CB1779Ł[ A series of persistent radicals "37# has been produced by the reaction of the dithioesters "38^ X O or S# with a wide range of radicals R=\ including MeS=\ Me= and Ph2Pb= ð82JA7333Ł[ RS
X • P(OEt) 2 (48)
#
X P(OEt)2
MeS
MeS
Copyright
S
1995, Elsevier Ltd. All R ights Reserved
(49)
Comprehensive Organic Functional Group Transformations
References to Volume 6 EXPLANATION OF THE REFERENCE SYSTEM Throughout this work, references are designated by a number-lettering coding of which the first two numbers denote tens and units of the year of publication, the next one to three letters denote the journal, and the final numbers denote the page. This code appears in the text each time a reference is quoted; the advantages of this system are outlined in the Introduction. The system has been used previously in "Comprehensive Heterocyclic Chemistry," eds A. R. Katritzky and C. W. Rees, Pergamon, Oxford, 1984 and is based on that used in the following two monographs: (a) A. R. Katritzky and J. M. Lagowski, "Chemistry of the Heterocyclic N-Oxides," Academic Press, New York, 1971; (b) J. Elguero, C. Marzin, A. R. Katritzky and P. Linda, "The Tautomerism of Heterocycles," in "Advances in Heterocyclic Chemistry," Supplement 1, Academic Press, New York, 1976. The following additional notes apply: 1. A list of journal codes in alphabetical order, together with the journals to which they refer, is given immediately following these notes. Journal names are abbreviated throughout using the CASSI (Chemical Abstracts Service Source Index) system. 2. Each volume contains all the references cited in that volume; no separate lists are given for individual chapters. 3. The list of references is arranged in order of (a) year, (b) journal in alphabetical order of journal code, (c) part letter or number if relevant, (d) volume number if relevant, (e) page number. 4. In the reference list the code is followed by (a) the complete literature citation in the conventional manner and (b) the number(s) of the page(s) on which the reference appears, whether in the text or in tables, schemes, etc. 5. For nontwentieth-century references the year is given in full in the code. 6. For journals which are published in separate parts, the part letter or number is given (when necessary) in parentheses immediately after the journal code letters. 7. Journal volume numbers are not included in the code numbers unless more than one volume was published in the year in question, in which case the volume number is included in parentheses immediately after the journal code letters. 8. Patents are assigned appropriate three-letter codes. 9. Frequently cited books are assigned codes. 10. Less common journals and books are given the code "MI" for miscellaneous with the whole code for books prefixed by the letter "B-". 11. Where journals have changed names, the same code is used throughout, e.g. CB refers to both Chem. Ber. and to Bar. Dtsch. Chem. Ges. Journal Codes AAC ABC AC AC(P) AC(R) ACH
Antimicrob. Agents Chemother. Agric. Biol. Chem. Appl. Catal. Ann. Chim. (Paris) Ann. Chim. (Rome) Acta Chim. Acad. Sci. Hung. 735
736 ACR ACS ACS(A) ACS(B) AF AFC AG AG(E) AHC AHCS AI AJC AK AKZ AM AMLS AMS ANC ANL ANY AOC AP APO AQ AR AR(A) AR(B) ARP ASI ASIN AX AX(A) AX(B) B BAP BAU BBA BBR BCJ BEP BJ BJP BMC BP BPJ BRP BSB BSF BSF(2) C CA CAN CAR CAT CB
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56ACS1006
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55JA5033 55JA5601 55JA6644 55JCS1881 55JCS2532 55JCS3871 55JOC1573 55MI 618-01 55OSC(3)773 55OSC(3)803 55USP2704776 55USP2709184 55USP2709186 55USP2709187 55USP2709188 55USP2709190
78,79
748 56AG754 56BRP749408 56BSF1441 56CB314 56CB343 56CB1160 56CB2060 56CB2562 56CB2578 56CI(M)371 56JA97 56JA479 56JA4450 56JA4458 56JA5292 56JA5637 56JA6070 56JAP10924 56JCS508 56JCS3416 56JOC1319 56M323 B-56MI 614-01 56USP2729687 56USP2739989 56USP2744147 56USP2744148 56USP2745886 56USP2748177 56USP2755314 56USP2757214
57BRP757893 57BRP767779 57CB2460 57CJC527 57GEP1002355 57GEP1018054 57HCA604 57IZV48 57IZV199 57JA20 57JA69 57JA366 57JA3351 57JA3611 57JA4159 57JA4708 57JA5493 57JA5628 57JA5654 57JA5710 57JA5717 57JA5801 57JA6180 57JCS30 57JCS1741 57JCS2735
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72ACS1874 72AG993 72AG(E)473 72AG(E)949 72AG(E)964 72ANY(192)101 72BCJ489 72BCJ960 72BCJ1797 72BCJ2937 72CA(77) 125952 72CB487 72CB511 72CB820 72CB1340 72CB1709 72CB2558 72CB2815 72CB2854 72CB3050 72CB3280
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72MI 610-01 72MI 612-01 B-72MI 614-01 B-72MI 622-01 72RTC37 72RTC331 72RTC349 72RTC1117 72S32 72S39 72S81 72S351 72S418 72S599 72T1965 72TL2939 72TL3769 72TL3827 72TL3957
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80AF1733 80AG411 80AG1055 80AG(E)201 80AG(E)203 80AG(E)942 80AHC(27)151 80AJC287 80AOC(18)1 80AP(313)995 80AQ183 80BCJ3687
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814 86ZOR2618
87AF1O03 87AF1008 87AG681 87AG(E)79 87AG(E)134 87AG(E)275 87AG(E)314 87AG(E)359 87AG(E)546 87AG(E)584 87AG(E)681 87AG(E)798 87AG(E)894 87AG(E)908 87AG(E)1 111 87AJC795 87AOC(27)169 87BCJ435 87BCJ1204 87BCJ1807 87BCJ1853 87BCJ3687 87CB339 87CB421 87CB429 87CB653 87CB987 87CB1069 87CB1203 87CB1213 87CB1271 87CB1281 87CB1357 87CB1421 87CB1499 87CB1581 87CB1605 87CB1707 87CC10 87CC99 87CC147 87CC410 87CC472 87CC1092 87CC1183 87CC1228 87CC1399 87CC1461 87CC1701 87CCC1764 87CJC626 87CL2177 87CPB156 87CPB1734
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822 88ZN(B)75 88ZN(B)801 88ZN(B)1038 88ZN(B)1416 88ZN(B)1468 88ZOB26 88ZOB393 88ZOB482 88ZOB491 88ZOB1066 88ZOB1447 88ZOB1461 88ZOB1468 88ZOB1489 88ZOB1516 88ZOB1525 88ZOB1923 88ZOB1927 88ZOB2164 88ZOB2167 88ZOB2168 88ZOR117 88ZOR644 88ZOR1327 88ZOR1513 88ZOR2019
89ACR15 89AF539 89AG617 89AG929 89AG(E)53 89AG(E)55 89AG(E)221 89AG(E)452 89AG(E)781 89AG(E)784 89AG(E)1013 89AJC1235 89BAU1570 89BCJ967
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Comprehensive Organic Functional Group Transformations
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