Vinylsilanes, Grignard reaction

The main synthetic pathways to vinylsilanes are (a) direct processes in the gas phase, (b) Grignard reactions, (c) metallation reactions (e.g. with lithiated reagents), (d) hydrosilylation of alkynes and related addition reactions, (e) hydrogenation of alky-nylsilanes, and (f) elimination reactions of alkylsilanes. Methods (a)-(e) are mostly used method (f), however, has become less common nowadays. 

Cleavage of Si—C bonds (12,243-245). This oxidation can be used to convert vinylsilanes in three steps to syn- or anti-1,2-diols. Thus Grignard reagents cleave epoxides of vinylsilanes selectively to (3-hydroxy silanes, which can be oxidized with retention of configuration to 1,2-diols. When applied to an (E)-vinylsilane, the sequence results in the syn-l,2-diol the an -l,2-diol is obtained from a (Z)-vinylsilane by the same reactions. 

One of the classical solutions to overcome the low reactivity is to render the carbomagnesiation intramolecular. For example, Utimoto and coworkers reported that the reaction of ( )-6-bromo-3-methyl-l-trimethylsilyl-l-hexene (85) with magnesium produces the corresponding Grignard reagent 86, which intramolecularly adds to the vinylsilane moiety from the less hindered side affording a single stereoisomer of cycUzed product 87 (Scheme 60) °°. 

Organolithium190-192 and Grignard reagents193 react with vinylsilanes to give a-silylcarbanions (equation 120). Such reactions are difficult with unsubstituted vinylsilanes. 

Reaction of H2C—CHSiMeCh (obtained from the catalyzed hydrosilylation of acetylene with MeSiCbH) with an ephedrine-derived lithium dialkylamide produces Ae chiral vinylsilane (1). Addition of BuU to this vinylsilane followed by treatment with MgBr2 gives the corresponding Grignard reagent... 

Table 3 Generation and Reactions of a-Aryl- or a-Silylalkyl Grignard Reagents from Styrenes or a Vinylsilane by Hydromagnesation...

Vinylsilanes have been prepared by an extensive range of methods utilising halogen,oxygen, and sulphur substituted precursors, acetylenes and CO (with Me SiCHjLi)while Me SiCH-CHCOjH behaves as an acetylene equivalent in Diels-Alder reactions, and trimethylsilylvinyl triflate as an alkylidene carbene source. Grignard reagents add to vinylsilanes to give silyl hydrocarbons on... 

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