Electrooxidative CH/PH functionalization as a novel way to synthesize benzo[b]phosphole oxides mediated by catalytic amounts of silver acetate

Abstract

Electrochemical joint oxidation of diphenylphosphine oxide with acetylenes in the presence of silver acetate (10%) as a catalyst yields benzo[b]phosphole oxide derivatives under mild conditions at room temperature without additional oxidants or initiators and with yields up to 100%. The redox properties of the key intermediate of the catalytic cycle have been investigated by cyclic voltammetry and EPR spectroscopy. The Ph₂P(O)Ag intermediate oxidizes easier (+0.05 V vs. Fc⁺/Fc) than all reaction precursors to form the phosphinyl radical Ph₂P(O)˙, fixed as a spin-adduct by ESR. Thus, a radical mechanism type through the Ag⁺/Ag⁰ couple was developed for electrocatalytic conditions.