Intramolecular Photocyclization of Enamide Linked 1,5-Dienes Enables Divergent Synthesis of Pyridin-2-one Derivatives

An energy transfer (EnT) catalyzed photocyclization process for the divergent synthesis of substituted 3,4-dihydropyridin-2(1<i>H</i>)-ones and pyridine-2-ones in sustainable solvents is realized by tuning the reaction conditions. The present metal-free system exhibits a high reaction efficiency and good functional group tolerance. Notably, the TEMPO-trap experiment, control experiments, and DFT calculations have offered evidence supporting the proposed catalytic cycle.