A Visible Light Photocatalytic Cross-Dehydrogenative Coupling/Dehydrogenation/6-Cyclization/Oxidation Cascade: Synthesis of 12-Nitroindoloisoquinolines from 2-Aryltetrahydroisoquinolines

A visible light-induced photocatalytic dehydrogenation/6-cyclization/oxidation cascade converts 1-(nitromethyl)-2-aryl-1,2,3,4-tetrahydroisoquinolines into novel 12-nitro-substituted tetracyclic indolo[2,1-a]isoquinoline derivatives. Various photocatalysts promote the reaction in the presence of air and a base, the most efficient being 1-aminoanthraquinone in combination with K3PO4. Further, the 12-nitroindoloisoquinoline products can be accessed directly from C1-unfunctionalized 2-aryl-1,2,3,4-tetrahydroisoquinolines by extending the one-pot protocol with a foregoing photocatalytic cross-dehydrogenative coupling reaction, resulting in a quadruple cascade transformation.