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.

Graphical abstractα-Dimethylcarbamoyldithioesters react with CF3TMS under fluoride activation to lead to the title compounds. The latter are methylated at sulfur, and protonated at carbon. The corresponding salts are characterized.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Domino S-trifluoromethylation–β-elimination from α-substituted dithioates is described.► α-Substituted dithioesters react with CF3TMS to give S-CF3 ketene dithioacetals ► Reaction of S-CF3 ketene dithioacetals with electrophiles is described ► S-CF3 ketene dithioacetals are methylated at sulfur and protonated at carbon.