A new version of Umemoto's reagents: A three-step one-pot preparation of 2,3,7,8-tetrafluoro-S-(trifluoromethyl)dibenzothiophenium triflate

A new one-pot method was developed for the practical preparation of powerful electrophilic trifluoromethylating agent, 2,3,7,8-tetrafluoro-S-(trifluoromethyl)dibenzothiophenium triflate 2. This method comprised of three steps; (1) in situ generation of trifluoromethanesulfinyl trifluoroacetate 7, (2) treatment of 3,3',4,4'-tetrafluorobiphenyl with 7 in the presence of trifluoromethanesulfonic acid and trifluoroacetic anhydride, and (3) treatment of the resulting mixture with hydrogen peroxide. By means of this effective three-step one-pot method, 2 was prepared in a good isolated yield by simple water-washing method. It is thus expected that easy access to 2 may lead to its wider or new applications to many areas, because tetrafluoro reagent 2 is much more powerful than 2,8-difluoro-S-(trifluoromethyl)dibenzothiophenium triflate 1.