An Oxidant-Free Strategy for Indole Synthesis via Intramolecular C-C Bond Construction under Visible Light Irradiation: Cross-Coupling Hydrogen Evolution Reaction

We describe here an oxidant-free strategy to synthesize indoles, i.e., under visible-light irradiation (lambda = 450 nm), catalytic amounts of an iridium(III) photosensitizer and cobaloxime catalyst transform various N-aryl enamines exclusively into indoles. Our methodology affords indoles in good to excellent yields under mild reaction conditions and produces H-2 as the only byproduct. Spectroscopic and electrochemical studies verify that the designed system proceeds via visible-light-catalyzed oxidation of N-aryl enamines, followed by intramolecular radical addition to yield the indoles smoothly under ambient conditions.