Reactions of phosphines with acetylenes. Part 18. The mechanism of formation of 1,2-alkylidenediphosphoranes

Abstract

The reactions of dimethyl acetylenedicarboxylate and dibenzoylacetylene with a variety of tertiary arylphosphines, in excess, have been studied. Evidence is presented to show that 1,2-alkylidenediphosphoranes are formed via zwitterionic intermediates which have the character of nucleophilic carbenes. 1,2-Bismethoxycarbonyl-2-thioxoethylidenetriphenylphosphorane and 1,2-dibenzoyl-2-thioxoethylidenetriphenylphosphorane have been isolated by trapping the intermediate with sulphur.