Electrochemical Oxidation of Triphenylphosphine in the Presence of Allylsilanes : Voltammetric Studies and Regioselective Preparation of Allyltriphenylphosphonium Salts

Electrochemical oxidation of triphenylphosphine (1) in dichloromethane containing allylsilanes (2) in an undivided cell afforded allyltriphenylphosphonium salts (3). The addition of 1 to 2 took place exclusively at the γ-position of 2 and the reaction was extended to provide a convenient method for the synthesis of cyclic phosphonium salts (3) bearing β-exo-methylene. The yields of 3 depended on the cathode material : use of a lead cathode, which has a high hydrogen overpotential, gave favorable results. Based on the results of the voltammetric study, the process of formation of 3 is suggested to involve electrophilic attack of the triphenylphosphine radical cation on 2 as the key step.