Synthesis of diphenylphosphine oxide derivatives from phosphines and methyl acetylenic carboxylate

Protonation of the highly reactive 1:1 intermediates (3), produced in the reaction between triphenylphosphine (1) and alkyl acetylenecarboxylates (2) by water leads to vinyltriphenylphophonium salts (3), which undergo coupling reaction with conjugate base to produce corresponding pentavalent phosphorus intermediates (5). The pentavalent phosphorus intermediates (5) are unstable and rearange to stable diphenylphosphine oxide derivatives (6) under reaction conditions