Controllable synthesis of benzoxazinones and 2-hydroxy-3-indolinones by visible-light-promoted 5-endo-dig N-radical cyclization cascade

In recent years, significant advances have been made on photoredox-catalyzed N-radical addition to C-C unsaturated bond via N-H bond cleavage. However, these N-centered radical additions have so far been mostly limited to the alkenes, and to our knowledge, N-radical 5-endo-dig cyclizations of alkynes have been less exploited. Herein, we disclose an 5-endo-dig N-radical cascade cyclization of o-ethynylacetamides by photoredox catalysis involving rare radical cleavage of C-C triple bond, allowing the practical and controllable synthesis of a diverse array of valuable benzoxazinones and 2-hydroxy-3-indolinones in moderate to good yields under mild conditions. Furthermore, a mechanistic rationale for this radical cyclization cascade is supported by various control experiments and theoretical calculations.