Metallaphotoredox-Catalyzed C−H Activation: Regio-Selective Annulation of Allenes with Benzamide

We have developed an efficient annulation of benzamides with allenes using cobalt and photoredox dual catalysis under an oxygen atmosphere. This reaction provides a mild and environmentally friendly method for the construction of isoquinolinon scaffolds in good to excellent yields, which demonstrates broad substrate scopes, high regioselectivity, and good functional group compatibility. Notably, this transformation feathers an alternative strategy for the regeneration of cobalt catalyst with the aid of Eosin Y. Preliminary mechanism studies reveal that a radical-mediated cascade annulation is involved in this reaction.