Photocatalytic Selective Synthesis of Hemiketals from Alkenes, α-Halo Acylarenes, and Water via <i>N</i> -Methylindole Catalysis

Herein, we report a visible-light-mediated <i>N</i>-methylindole-catalyzed difunctionalization of alkenes, enabling efficient and highly selective synthesis of five-membered hemiketals and polysubstituted tetrahydrofuran derivatives. In this transformation, readily available <i>N</i>-methylindole acts as both the catalyst and the electron donor of the EDA complex. Under photoirradiation and Lewis acid catalysis, single-electron transfer occurs between <i>N</i>-methylindole and α-halogenated acylarenes via EDA complexes, triggering subsequent radical addition and cyclization reactions. Notably, intramolecular cyclization between the benzylic carbocation and the carbonyl group is the key step in this reaction. Overall, this strategy features a novel synthetic approach, mild reaction conditions, and excellent chemoselectivity, offering a new pathway for synthesizing complex heterocyclic compounds.