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.
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.
Protophilic versus silicophilic reactions in β-substituted silanes
作者:Steven L. Jones、Charles J. M. Stirling
DOI:10.1039/c39880001153
日期:——
in β-eliminations mediated by nucleophilic attack at silicon has been measured as a function of nucleophile, leaving group, and α-substituent; in some instances competition between protophilic and silicophilicreactions is observed.
A new elimination–rearrangement involving silicon migration
作者:Stefano Menichetti、Gwerydd Griffiths、Charles J. M. Stirling
DOI:10.1039/c39920000054
日期:——
Lithium diisopropylamide (LDA), a strongly basic, poorly silicophilic nucleophile reacts with α-phenylsitanes bearing β-leaving groups to cause 1,2-silyl migration and loss of the leaving group.
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.