Photochemistry of 6-Chloro-2-pyridones: The First Example for Electrocyclic Ring Opening of the Pyridone Ring System

Irradiation of 6-chloro-2-pyridone in methanol gave two geometrical isomers (@ and trans) of methyl 4-cyano-3butenoate and trans isomer of methyl 4-cyano-2-butenoate: this and the related reactions provide the first example for the photochemical electrocyclic ring opening of 2-pyridone ring.Photochemical behavior of 2-pyridones and 2-pyrones is guite similar in many respects.They gave photo-pyridones and -pyrones through intramolecular cycli-