Electrochemical Synthesis of Benzo[b]Phosphole Oxides via Dehydrogenative Annulation Using 1,4-Diazabicyclo [2.2.2]Octane as a Mediator

The electrochemical intermolecular annulation of diarylphosphine oxides with alkynes for the synthesis of benzo[b]phosphole oxides has been reported. The reaction proceeded under transition-metal- and oxidant-free conditions via indirect electrolysis, using 1,4-diazabicyclo[2.2.2]octane as a mediator. High-surface-area carbon electrodes, such as carbon felt and reticulated vitreous carbon, are essential for this reaction. Several diarylphosphine oxides and alkynes were applied to electrochemical annulation, and the corresponding benzo[b]phosphole oxides were obtained. Mechanistic studies suggested that the reaction proceeds via radical intermediates generated through multiple pathways.