Sodium borohydride: repurposing from a reducing agent to a reductive cyclization reagent for N-(2-iodoaryl)acrylamides.

Herein, we report that NaBH4 facilitates an unusual reductive cyclization of N-(2-iodoaryl)acrylamide derivatives to afford oxindoles without the need for external initiators. While other hydride donors failed to achieve this transformation, NaBH4 enabled it with a broad scope. Control experiments and DFT studies support a unimolecular radical-nucleophilic substitution (SRN1) pathway.