Harnessing visible light for metal-free trifluoromethylation/cyclization of unactivated alkenes†

Abstract

Visible light-driven radical trifluoromethylation/cyclization of unactivated alkenes offers a sustainable alternative to conventional methods for constructing chroman-4-one and related heterocyclic scaffolds. Herein, we report a metal-free photocatalytic system utilizing rhodamine B as an organic photocatalyst and Togni II reagent as a trifluoromethyl source. This mild protocol enables efficient intramolecular tandem cyclization, affording diverse chroman-4-ones, dihydroquinolin-4-ones, and 1-indanones (24–69% yields) with broad functional group tolerance. The operational simplicity and avoidance of transition metals highlight the synthetic utility of this approach.