Acridine Photocatalysis: Insights into the Mechanism and Development of a Dual-Catalytic Direct Decarboxylative Conjugate Addition

Conjugate addition is one of the most synthetically useful carbon-carbon bond-forming reactions; however, reactive carbon nucleophiles are typically required to effect the addition. Radical conjugate addition provides an avenue for replacing reactive nucleophiles with convenient radical precursors. Carboxylic acids can serve as simple and stable radical precursors by way of decarboxylation, but activation to reactive esters is typically necessary to facilitate the challenging decarboxylation. Here, we report a direct, dual-catalytic decarboxylative radical conjugate addition of a wide range of carboxylic acids that does not require acid preactivation and is enabled by the visible light-driven acridine photocatalysis interfaced with an efficient copper catalytic cycle. Mechanistic and computational studies provide insights into the roles of the ligands and metal species in the dual-catalytic process and the photocatalytic activity of substituted acridines.