Visible Light Photoredox Catalysis: Generation and Addition of N-Aryltetrahydroisoquinoline-Derived α-Amino Radicals to Michael Acceptors

The photoredox-catalyzed coupling of N-aryltetrahydroisoquinoline and Michael acceptors was achieved using Ru(bpy)3Cl2 or [Ir(ppy)2(dtb-bpy)]PF6 in combination with irradiation at 455 nm generated by a blue LED, demonstrating the trapping of visible light generated α-amino radicals. While intermolecular reactions lead to products formed by a conjugate addition, in intramolecular variants further dehydrogenation occurs, leading directly to 5,6-dihydroindolo[2,1-a]tetrahydroisoquinolines, which are relevant as potential immunosuppressive agents.