Photoinduced Cyclization of 2-Alkynylanilines to Access 3-Bromoindole Scaffolds

Herein, we report a visible-light-driven, photocatalyst-free protocol for synthesizing 3-bromoindoles via tandem cyclization–bromination from readily available 2-alkynyl anilines and ethyl 2,2-dibromo-3-oxobutanoate as the bromine source. This operationally simple method enables simultaneous indole formation and C3-bromination in one step, featuring broad substrate scope, excellent functional group tolerance, and good scalability. Mechanistic studies support a radical pathway initiated by visible-light-induced homolytic cleavage. Synthetic utility is demonstrated by gram-scale synthesis and diverse late-stage derivatizations.