A Photochemical Intramolecular C-N Coupling Toward the Synthesis of Benzimidazole-Fused Phenanthridines

Herein, we report a direct photochemical dehydrogenative C-N coupling of unactivated C(sp(2))-H and N(sp(2))-H bonds. The catalysts or additive-free transformation of 2-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole to benzo[4,5]imidazo[1,2-f]phenanthiidine was achieved at, similar to 350 nm of irradiation via epsilon-hydrogen abstraction. DFT calculations helped to understand that the N-H center dot center dot center dot pi interaction was essential for the reaction to proceed at a lower energy than expected.