Benzylic C-H Trifluoromethylation via Photoenol.

Photoenols generated in situ from ortho-methyl-substituted phenylketones such as benzophenones and acetophenones were trifluoromethylated with Togni reagent without any additive or catalyst. This trifluoromethylation reaction proceeded smoothly under photoirradiation conditions (365 nm). Various functional groups were tolerant of the reaction conditions. Interestingly, the trifluoromethyl group was exclusively introduced at the ortho-benzylic position. Mechanistic studies suggested that this reaction proceeds via formation of a photoenol, not via a radical pathway.