Photocatalyst-Free Singlet Oxygen-Induced Oxygenation: A Strategy for the Preparation of 5-Cyano-2-pyridones Driven by Blue-Light Irradiation.

A mild, catalyst- and metal-free photochemical protocol for the oxygenation of 3-cyano-1,4-dihydropyridines to 5-cyano-2-pyridones was developed. Utilizing molecular oxygen from the air as the oxidant and a cheap blue LED lamp as the light source, a variety of 3-cyano-1,4-dihydropyridines were converted into the corresponding 5-cyano-2-pyridones in moderate to excellent yields. Exploration of the substrate scope revealed that 3-cyano and 4-aryl groups play an important role in the formation of 2-pyridone.