Unlocking C–H Functionalization at Room Temperature via a Light-Mediated Protodemetalation Reaction

Herein, we report on the photocatalytic ortho-alkylation reaction of 2-phenyl pyridines with N-protected maleimides using [Cp*RhCl2]2 as a catalyst and propionic acid as an additive at room temperature. Experimental and theoretical studies suggest a reaction mechanism that consists of a dark and a light reaction: while cyclometalation and migratory insertion can proceed at room temperature in the dark, the photochemical excitation of reaction intermediates is required to facilitate the decomplexation of the directing group and allow a ligand exchange with propionic acid. This photochemical ligand exchange enables a facile protodemetalation reaction to regenerate the catalyst and give the reaction product. We studied this reaction in a broad substrate scope, including different directing groups and N-substituted maleimides to yield succinimides in high yield (49 examples, up to 96% yield).