Inter and Intramolecular Radical Additions of Aryl Halides Catalyzed by Diazaphospholenes

Diazaphospholenes have been widely used as hydride transfer catalysts, however their use in radical reactions and as photocatalysts is a recently emerging area. In this work, we show how stoichiometric radical cyclizations of aryl iodides mediated by diazaphospholene hydrides can be made catalytic by the combination of phenylsilane and alkali metal salts to regenerate the diazaphospholene hydride under the reaction conditions. The scope was expanded to include aryl bromides. These transformations required visible light irradiation, with twenty substrates undergoing cyclization, including a dearomative cyclization. Extension to six intermolecular radical hydroarylations with arenes, thiophenes, and a pyridine was also accomplished.