Reaction-Phase-Selective Inter- and Intramolecular Photochemical Reaction of 2-Pyridone Derivatives

Phase-selective photochemical reaction of 2-pyridone derivatives was examined. Irradiation of 1 in benzene mainly gave rearrangement products 2. However, intermolecular [4 + 4] photocycloaddition proceeded quantitatively in the solid state, affording photodimers 3. An effective π−π stacking and dipole−dipole interaction between two pyridone moieties might play important roles in an effective arrangement of 1 for photodimerization in their crystal structures.