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

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.