L Trimethylsilyl vinyllithium

Vinyltrimethylsilane Metal. l-TrimethylsUylvinyl metal species are mostly used as acyl anion equivalents and as hindered vinyl anion substitutes. l-(trimethylsilyl)vinyllithium is easily accessible from (l-bromovinyl)trimethylsilane by treatment with n-butyllithium at —78°C in ether (eq 1). Other solvents and alkyllithiums can also be used for the metal-halogen exchange. The use of (l-chlorovinyl)trimethylsilane or the direct reaction of (l-bromovinyl)trimethylsilane with lithium metal are not proper methods for generating the lithium species. ... 

Preparative Methods prepared by the reaction of [E)-2-(trimethylsilyl)vinyllithium with methyl chloroformate or by carbonation of the corresponding Grignard reagent prepared from (l-bromovinyl)trimethylsilane, giving 2-trimethyl-silylacrylic acid. The methyl ester is prepared from the acid by direct esterification with absolute methanol in the presence of mineral acid, by reaction with diazomethane at low temperature, or by treatment with BF3-MeOH complex. For preparation of various trialkylsilylacrylic acid esters and f-butyl 2-trimethylsilylcrotonate, see the cited references. 

Preparative Methods attempts to produce synthetically useful quantities of ( )-2-(trimethylsilyl)vinyllithium (1) by reaction of lithium metal with (2-bromovinyl)trimethylsilane (2) failed because of concomitant metalation-elimination processes involving (1) and ) However, the transmetalation process between (2) and excess f-butyllithium has been effectively used to provide (1) (eq 1). An alternative route to (1) employs the transmetalation of a l-(trimethylsilyl)-2-stannylethylene with organolithium reagents (eqs 2 and 3). ... 

Triphenyl- [1] and trimethylvinylsilane [2] as well as l,l-bis(trimethylsilyl)ethylene [3] are known to react with lithium metal in THF yielding 1,4-dilithiobutane derivatives by a dimerizing Schlenk addition. Interestingly, by using hexane as the solvent trimethylvinylsilane 1 does not yield the dimer product 2 but a 1 1 -mixture of the corresponding vinyllithium compound 3 and the lithioalkyne 4... 

Starting with l,l-bis(trimethylsilyl)ethylene (5) in hexane or diethyl ether as the solvent we obtained another dimeric product, a monolithiumorganic compound 8 which was shown not to be formed by lithium hydride elimination from the 1,4-dilithiobutane derivative 6, the only product in THF as the solvent. Obviously the vinyllithium derivative 7, primarily formed in the same manner as vinyllithium from ethylene [4], in contrast to vinyllithium [4] does not add further lithium atoms but adds itself to the starting material 5 yielding 8 ... 

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