Direct deoxygenative C–N coupling to construct indazole under visible light†

The green synthesis of medicines with an indazole skeleton has gained significant attention in recent years. Sustainable and environmentally friendly approaches for the synthesis of this important class of heterocyclic compounds from azobenzenes are attractive but rare. In this work, a series of neat, fast, and efficient reactions are well developed as a notable methodology for the photo-organic synthesis of indazoles. Metal and hydrogen source-free direct deoxygenative cyclization of o-carbonyl azobenzene under visible light is achieved through a new mechanism with huge potential in reduction cyclization reactions. Most examples are shown to give the corresponding 2H-indazole products in excellent yields, demonstrating that the present reaction has a wide substrate scope and good functional group tolerance.