Selenium-Radical Catalyzed Formal C( sp 2 ) Homologation via Self-Photosensitized N -Heterocyclic Selone

In this report, we disclose a pyrene-fused N -heterocyclic selone (NHS) catalyst that enables a self-photosensitized selenium radical-catalyzed sp 2 -carbon homologation, providing direct access to ring-expanded cyclobutanone derivatives. This practical one-pot, two-step method facilitates the skeletal reorganization of unpurified epoxides under violet LED irradiation, achieving high yields (up to 83%) and good functional group tolerance with a low catalyst loading. Mechanistic studies reveal the generation of a π-stabilized selenium radical via intersystem crossing and oxygen-mediated oxidation, modulated by a self-assembled three-electron σ-bonded complex “radical buffer” that sequesters excess radical species while slowly releasing the active catalyst. The late-stage functionalization of complex natural products and pharmaceuticals demonstrates the synthetic versatility of our integrated catalytic platform.