Control of regioselectivity in reactions of dialkylstannylene acetals. Part I. A dramatic reversal of regioselectivity in mono-p-toluenesulfonation reactions

Abstract

The regioselectivities of 11-toluenesulfonation reactions of dialkylstannylene acetals obtained from a number of carbohydrate-derived terminal 1,2-diols in the absence of added nucleophiles have been explored as functions of the carbohydrate structure, the nature of the alkyl group on tin, the solvent, and the reaction temperature. Virtually all dibutylstannylene acetals react preferentially on the primary oxygen atom, sometimes with excellent regioselectivity. Increasing the steric bulk of the alkyl sub-stituents on tin increases the preference for reaction at the secondary oxygen atom, but at the expense of increased reaction times. Hexamethylenestannylene acetals react at about the same rate as dibutylstannylene acetals; in almost all cases, they react preferentially on the secondary oxygen atom, sometimes with excellent regioselectivity.