Thiophilic nucleophilic trifluoromethylation of α-substituted dithioesters. Access to S-trifluoromethyl ketene dithioacetals and their reactivity with electrophilic species

The nucleophilic trifluoromethylation of dithioesters bearing a nucleofugal group in α-position, using CF3TMS under fluoride activation, afforded unprecedented S-CF3 ketene dithioacetals via a domino process thiophilic trifluoromethylation–β-elimination. The best results were obtained with non-enolisable α-carbamoyloxydithioesters. The higher homologues S-C2F5 ketene dithioacetals were prepared by a similar way. These new dithioacetals react with methylating reagents quantitatively and chemoselectively at sulfur to give stable dimethylsulfonium type salts. They react more classically with triflic acid, protonation taking place at the β-carbon to give a dithiolium salt, characterized in solution but non-isolable.