A Catalyst-Free Three-Component Approach to Sulfonated Indole-Fused Diazepinones via SO ₂ Insertion

A green, efficient, and environmentally benign synthetic strategy has been established for the preparation of diverse sulfonated indole-fused 1,4-diazepinones via catalyst-free multicomponent radical annulation. Notably, this radical cyclization also provides direct access to sulfonated indole-fused seven-membered diazepinones. The protocol features mild conditions, broad substrate scope, high yields (up to >99%), and excellent diastereoselectivity (up to >20:1 dr).