Electrochemical Synthesis of Benzo[ <i>b</i> ]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.