Organic sulfur mechanisms. 19. Sulfene–tertiary amine zwitterions and base size effects in sulfene condensations

Abstract

The effect of changing the size of the tertiary alkylamine has been investigated in two systems: (a) the reaction of phenylmethanesulfonyl chloride with a tertiary amine, and (b) the formation of the β-sultone from the reaction of chloral, ethanesulfonyl chloride, and a tertiary amine. In the first reaction the yield of stilbene (3) or stilbene episulfone (4) increases and that of the thiobenzoyl chloride S-oxides (5) decreases as the size of the base decreases, as expected for a mechanism involving a tertiary amine – sulfene zwitterion in the formation of the stilbene products. In the second reaction the yield of the β-sultone is much enhanced by the use of a small amine; the latter observation precludes a simple sulfene–chloral cycloaddition mechanism and points to a zwitterionic intermediate derived from the amine and either the sulfene or chloral.