One-Pot Synthesis of Alkyl 3-(Diphenylphosphoryl)-3-(10H-phenothiazin-10-yl)propanoates from Alkyl Acetylenecarboxylates,Phenothiazine, and Triphenylphosphine

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates by phenothiazine, leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with conjugate bases to produce the corresponding phosphorus ylides. The phosphorus ylides react with water forming phenothiazine containing diphenylphosphine oxide derivatives in moderate yields.