Proflavine-catalysed trifluoromethylation of α,β-unsaturated carbonyls

Abstract

Radical trifluoromethylation of α,β-unsaturated carbonyl compounds has been achieved using proflavine hemisulfate as a metal-free photoredox catalyst under visible light irradiation. With sodium triflinate (CF3SO2Na) and trifluoroacetic acid as the CF3 and H-atom sources in oxygen-free acetonitrile, hydrotrifluoromethylation addition takes place across the double bond of substrates such as maleimide, enone and acrylamide. In contrast, CF3-substitution at the double bond is preferred for coumarin, uracil and (hetero)arenes while both addition and substitution are observed for thymine. A mechanism has been proposed where the excited-state proflavine hemisulfate performs a dual role as an electron acceptor to generate the CF3 radical and as a H-atom abstraction agent for the CF3-substitution reaction. A proflavine-H radical species is suggested to be the H-atom donor for hydrotrifluoromethylation.