C,C-Coupling with sulfur-stabilized carbanions - 7. Diastereoselectivity in the addition of electrophiles to the carbanions of 2-(alkylthio)thiolane 1-oxides

Article abstract of DOI:10.1016/S0040-4020(96)01184-2

Pure diastereoisomers of the 2-(alkylthio)thiolane 1-oxides 2 were prepared in a three-step synthesis. The carbanions of 2 were generated with different bases and treated with iodomethane and carbonyl compounds to form the methyl derivatives 6 and the carbinols 7, respectively. The conformational stability (α-diastereoselectivity) of the carbanions as well as the asymmetric induction during the reaction with prochiral electrophiles (β-diastereoselectivity) was studied. A mechanism for the reaction with carbonyl compounds is proposed, which involves a six-membered cyclic transition state formed from the sulfoxide moiety and the metal cation. - Steric effects of the substrate and the electrophile are discussed.