Elimination and addition reactions. Part XXV. Addition–elimination reactions of phenoxyvinyl sulphones

Abstract

Reactions of cis- and trans-2-phenoxyvinyl p-tolyl sulphones with alcoholic alkoxides have been studied. Product analyses and kinetic studies show that in each case a two-stage addition–elimination pathway is followed. The elimination step is assigned the (E1cB)_R mechanism on the basis of measurements carried out in deuteriated solvents. The rate constants and activation parameters for both addition and elimination stages match closely the rate constants and activation parameters obtained for models which simulate the two stages individually. The results are discussed against the background of earlier work on elimination of poor leaving groups from activated saturated substrates, and of good leaving groups, particularly halide, from activated, unsaturated substrates. It is now shown that in an activated, unsaturated system with a poor leaving group, elimination with formation of acetylene does not compete effectively with an initial addition step.