The diastereoselectivity of electrophilic attack on trigonal carbon adjacent to a stereogenic centre: diastereoselective protonation, epoxidation and acylation of allylsilanes

The four allylsilanes 6 and 8, which have a stereogenic centre carrying a phenyl group, a methyl group and a hydrogen atom adjacent to the nucleophilic end of the double bond, react with protic (or deuteronic) acid, m-chloroperbenzoic acid and chlorosulfonyl isocyanate to give electrophilic substitution of the allylsilane, with diastereoselectivity in the sense 2, in conformity to a general rule for electrophilic attack on a double bond adjacent to a stereogenic centre. The most reliably stereoselective reactions took place with the allylsilane 6b, in which the stereogenic centre is cis to a group larger than a hydrogen atom in both the E- and Z-isomer. In general, chlorosulfonyl isocyanate induces higher stereoselectivity than the peracid, and the peracid higher stereoselectivity than the proton (or deuteron).