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 (λ = 450 nm), catalytic amounts of an iridium­(III) photosensitizer and cobaloxime catalyst transform various <i>N</i>-aryl enamines exclusively into indoles. Our methodology affords indoles in good to excellent yields under mild reaction conditions and produces H₂ as the only byproduct. Spectroscopic and electrochemical studies verify that the designed system proceeds via visible-light-catalyzed oxidation of <i>N</i>-aryl enamines, followed by intramolecular radical addition to yield the indoles smoothly under ambient conditions