Identifying key intermediates generated in situ from Cu(II) salt-catalyzed C-H functionalization of aromatic amines...

Copper compounds involved in photocatalysis have recently spurred considerable interest for their novel transformations. However, mechanistic investigations are still in infancy. We find a new type of reaction, that is, Cu(II) salt-catalyzed C-H functionalization of aromatic amines triggered by visible light irradiation. An array of mechanistic observations, including high-resolution mass spectrometry, ultraviolet-visible absorption spectrum, electron spin resonance, x-ray absorption near-edge structure, and density functional theory calculation, have identified the key intermediates generated in situ in the transformation. Integration of single-electron transfer, singlet oxygen (¹O₂), and new absorption species, intermediate I and intermediate II formed in situ from Cu(II) salts and substrate amines or imines, respectively, is responsible for the N-H and C-H bond activation of secondary amines to couple with nucleophiles in air, thereby leading to the formation of quinoline, indolo[3,2-c]quinoline, β-amino acid, and 1,4-dihydropyridine derivatives in moderate to good yields under visible light irradiation at room temperature.