O-Difluoromethylation of 1,3-Diones with S-Difluoromethyl Sulfonium Salt.

The O-difluoromethylation of 1,3-diones with S-difluoromethyl sulfonium salt is described. The sulfonium salt was previously believed to be a direct difluoromethylation reagent, but our mechanistic investigation reveals that the O-difluoromethylation reaction proceeds not only via the direct transfer of the CF2H group, but also via a difluorocarbene process. This work represents the first protocol for mild O-difluoromethylation of acyclic 1,3-diones.