A NEW SILICON-MEDIATED ELIMINATION-REARRANGEMENT

Treatment of trimethylsilylethanes bearing alpha a-phenyl groups and b eta-phenylthio, phenylsulfonyl or cyano groups with LDA causes elimina tion-rearrangement mediated by the beta-carbanionic species. Mechanist ic conclusions are based on isotopic labelling experiments, the effect s of substituents and approximate kinetics. These suggest that trimeth ylsilyl is the migrating group, that cleavage of the bond to the leavi ng group is little advanced in the transition structure and that placi ng of a substituent to encourage Si-C bond cleavage is mandatory.