[CH3:1][O:2][C:3]1[CH:4]=[C:5]([C:9]2[O:10][CH2:11][C:12](=[O:14])[N:13]=2)[CH:6]=[CH:7][CH:8]=1.N1C(C)=CC=CC=1C.[O:23](S(C(F)(F)F)(=O)=O)[S:24]([C:27]([F:30])([F:29])[F:28])(=O)=[O:25]>C(Cl)Cl>[F:28][C:27]([F:30])([F:29])[S:24]([O:14][C:12]1[N:13]=[C:9]([C:5]2[CH:6]=[CH:7][CH:8]=[C:3]([O:2][CH3:1])[CH:4]=2)[O:10][CH:11]=1)(=[O:25])=[O:23]Compound 16 (516 mg, 1 eq) was dissolved in CH2Cl2. To the resulting solution, at 0° C., was added 501 μL (1.6 eq) of 2,6-lutidine, followed by the dropwise addition of Tf2O (681 ml, 1.5 eq). The resulting mixture was stirred for 4 h at RT, then an additional 501 μL (1.6 eq) of 2,6-lutidine and 681 ml (1.5 eq) of Tf2O were added. After 1 h, the mixture was evaporated and the residue purified by flash chromatography (SiO2, CH2Cl2/hexane, 9/1) giving 17 as a red oil in 75% yield.
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