Copper-Catalyzed Aerobic Selective Oxidation of Tetrahydrocarbolines

We report a safe and convenient open-flask copper-catalyzed selective oxidation/functionalization methodology for tetrahydrocarbolines and tetrahydro-β-carbolines that employs atmospheric O2 as the terminal oxidant. The system is applicable to oxidative rearrangement of tetrahydro-β-carbolines, tetrahydrocarboline oxidation to α-alkoxy carbazoles and spirooxindoles, and Witkop oxidation. Mechanistic experiments indicated that a single-electron oxidation process is responsible for the tunable selectivity control. This copper-catalysis protocol represents a significant advance in the field of indole oxidation.