Intermolecular 2+2 Imine-Olefin Photocycloadditions Enabled by Cu(I)-Alkene MLCT

2+2 Photocycloadditions are idealized, convergent approaches to the construction of 4-membered heterocyclic rings, including azetidines. However, methods of direct excitation are limited by the unfavorable photophysical properties of imines and electronically unbiased alkenes. Here, we report copper-catalyzed photocycloadditions of non-conjugated imines and alkenes to produce a variety of substituted azetidines. Ligand design allows this base metal-catalyzed method to achieve 2+2 imine-olefin photocycloaddition via selective alkene activation through a coordination-MLCT pathway.