Elimination–rearrangement in β-functionalised silanes—the direction of the rearrangement and its scope
摘要:
A new eliminative rearrangement of beta-silyl carbanions requires phenyl on carbon alpha- to silicon when the conjugate acid has a pK(a) (DMSO) in the range 12-30; rearrangement involves silicon and not phenyl migration.
Treatment of trimethylsilylethanes bearing alpha a-phenyl groups and beta-phenylthio, phenylsulfonyl or cyano groups with LDA causes elimination-rearrangement mediated by the beta-carbanionic species. Mechanistic conclusions are based on isotopic labelling experiments, the effects of substituents and approximate kinetics. These suggest that trimethylsilyl is the migrating group, that cleavage of the bond to the leaving group is little advanced in the transition structure and that placing of a substituent to encourage Si-C bond cleavage is mandatory.