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.