Vinylogous nucleophilic catalysis. The tertiary amine promoted reaction of ethenesulfonyl chloride with alcohols

Abstract

Ethenesulfonyl chloride (1) reacts with alcohols in the presence of tertiary amines to give a mixture of the alkyl ethenesulfonate (5) and the alkyl betylate (R3′N+CH2CH2SO2OR Cl−). With pyridine and neopentyl alcohol the product composition from the reaction of 1 is identical to that from the pyridinio-sulfonyl chloride (9). These results, when taken with experiments with deuterium labelled reagents, lead to the conclusion that the major (~80%) reaction pathway involves conversion of 1 or 9 to the sulfene 8, which reacts with the alcohol to form 5 or the betylate, and hence vinylogous nucleophilic catalysis is the major process leading to 5. The labelling experiments disclosed a minor pathway, evidently involving interconversion of 1 and 9. Examination of possible mechanisms leads to the suggestion that the sulfene is formed from 1 or 9 by way of the carbanion (14), i.e., that 9 reacts by an E1cB process, and that the minor pathway is simply the result of side reactions of the carbanion (14). Keywords: sulfenes, sulfonyl transfer mechanisms, vinylogous nucleophilic catalysis.