Trifluoromethanesulfonic anhydride → 3-Oxo-5-(trifluoromethyl)cyclohex-1-enyl trifluoromethanesulfonate

To a suspension of 5-(trifluoromethyl)cyclohexane-1,3-dione (1.0 eq) in DCM (0.23 M) was added TEA (1.2 eq) to give a clear solution. The mixture was cooled to 0° C. And then Tf2O (1.05 eq) in DCM was added dropwise. The reaction mixture was stirred at that temperature for 2 hours. The reaction mixture was diluted with DCM, and washed with water, aq. NaHCO3, brine, and was dried over MgSO4, filtered and concentrated to give 3-oxo-5-(trifluoromethyl)cyclohex-1-enyl trifluoromethanesulfonate, which was used to next step directly. LC/MS (m/z): MH+=313.0, Rt=1.02 min.