TFA-Promoted Intermolecular Friedel-Crafts Alkylation of Arenes with 2,2,2-Trifluoroethylaryl Sulfoxides.

The classical Pummerer rearrangement of 2,2,2-trifluoroethylaryl sulfoxide with trifluoracetic anhydride (TFAA) affords the S,O-acetal efficiently. In the presence of trifluoracetic acid (TFA) as the co-solvent, the S,O-acetal can regenerate reactive thionium intermediate of Pummerer rearrangement. When employing arenes as nucleophiles, this strategy produces corresponding 1-thiyl-2,2,2-trifluoroethyl arenes with excellent yields under metal-free conditions.