Visible-Light-Induced Cycloaddition and Proton Transfer of 1,4-Dihydropyridines: An Integrated Experimental and DFT Study

The photoreaction of 1,4-dihydropyridines (1,4-DHPs) is a powerful strategy for constructing structurally complex molecules, yet controlling product distribution remains challenging. Here, we report a visible-light-induced transformation that enables access to 3,9-diazatetraasteranes (2) and 3,12-diazatetracyclododecane-dienes (3). The product distribution is governed by the photocatalyst, solvent environment, and irradiation wavelength. Formation of 2 depends primarily on the excitation wavelength, whereas the generation of 3 requires photocatalyst engagement and occurs selectively in protic solvents. Mechanistic studies indicate that 2 arises through sequential inter- and intramolecular [2 + 2] photocycloadditions of 1,4-DHPs. In contrast, 3 is formed through an initial photocatalyst-mediated oxidation followed by proton transfer, ultimately triggering an intermolecular [3 + 2] photocycloaddition. DFT calculations further elucidate the origin of the observed selective formation of products and support mechanistic pathways.