Asymmetric Electrooxidation of Indoles: Mechanistic Insights from an Enantioselective Bromoradical Addition Pathway

Oxidative rearrangement of tetrahydro-β-carbolines (THβCs) represents a straightforward route to the synthesis of spirooxindoles. Herein, we disclose the first bromoradical (Br•)-initiated enantioselective electrooxidative rearrangement of THβCs, leading to highly enantioenriched spirooxindoles. Mechanistically, asymmetric Br• addition to THβCs initiates the reaction, distinguishing this process from established pathways induced by either halogen cations (X⁺) or single-electron transfer (SET). Successful trapping of the key radical intermediate provides explicit evidence of this unprecedented Br•-mediated mechanism.