Elimination and addition reactions. Part XXVI. Asymmetric induction in additions of nucleophiles and electrophiles to αβ-unsaturated sulphoxides

Abstract

Optically pure αβ-unsaturated sulphoxides have been synthesised.

Addition of piperidine to (–)-(R)-(Z)-propenyl p-tolyl sulphoxide gives a quantitative yield of adduct with an optical yield of 70%. The absolute configuration of the asymmetric carbon centre (β-induction) of the major diastereoisomer is assigned by comparison of the rotation of the derived sulphide with that of a specimen synthesised from (+)-alanine. A lower optical yield is obtained in addition of piperidine to (+)-α-methylvinyl p-tolyl sulphoxide (α-induction). No discernible α-induction is found in additions of PhSD to p-tolyl vinyl sulphoxide.

Addition of bromine to (+)-p-tolyl vinyl sulphoxide gives the dibromide with an optical yield (α-induction) of 32%. The absolute configuration of the new asymmetric centre at carbon is assigned by using Brewster's rules. (+)-α-Methylvinyl p-tolyl sulphoxide gives a higher degree of asymmetric induction but yields of dibromide are low.

The relationship of the optical yields and absolute configurations of the adducts obtained in these nucleophilic and electrophilic additions is discussed with respect to the mechanisms and steric courses of the reactions.