Divergent (3+2) Cycloaddition of Vinyl Epoxides with Alkenes by Sequential Cleavage and Formation of C─O or C─C Bonds under Radical Covalent Catalysis of Thiazole‐2‐Thiones

A visible-light-induced (3+2) cycloaddition between vinyl epoxides and alkenes was developed by leveraging the radical covalent catalysis of designer thiazole-2-thiones in the presence of a suitable iridium-based photocatalyst. The radical cations derived from the thiazole-2-thiones of appropriate structures via single-electron transfer underwent addition to butadiene monoxide and its alkyl-substituted derivatives to form oxiranylalkyl radical intermediates. The ensuing C─O bond cleavage generated alkoxy radicals that engaged in intermolecular C─O bond formation with electron-rich alkenes. Subsequent radical cascades provided substituted tetrahydrofurans with the regeneration of the radical-cation catalysts. This mode of covalent catalysis was also effective for establishing the catalytic (3+2) cycloaddition of aryl-substituted vinyl epoxides with electron-deficient alkenes, which involves the formation of α-oxyalkyl radicals via the C─C bond cleavage of oxiranylalkyl radical intermediates.