Trapping of reactive intermediates from phosphites and dimethyl acetylenedicarboxylate. Diversion of reaction pathway towards stable phosphole derivatives

Abstract

Trialkyl phosphites and dimethyl acetylene-dicarboxylate react at –50 °C to give the cyclopropenyl-methylene trialkoxyphosphonium ylid (1), which at –10 °C cyclises to the novel five-co-ordinate phosphorane (2); at 20 °C the phosphorane (2) rearranges to the cyclic ylide (3), whilst hydrogen bromide gas at –10 °C converts the phosphorane (2) into a stable phosphole derivative (4).