[F:1][C:2]1([F:22])[CH:6](OS(C(F)(F)F)(=O)=O)[CH2:5][N:4]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[CH2:3]1.[N-:23]=[N+:24]=[N-:25].C([N+](CCCC)(CCCC)CCCC)CCC>CN(C=O)C.CC(OC)(C)C>[N:23]([CH:6]1[CH2:5][N:4]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[CH2:3][C:2]1([F:22])[F:1])=[N+:24]=[N-:25]tert-Butyl 3,3-difluoro-4-{[(trifluoromethyl)sulfonyl]oxy}pyrrolidine-1-carboxylate (5.56 g, 15.2 mmol) was dissolved in DMF (20 mL) and cooled in an ice bath under nitrogen atmosphere. Tetrabutylammonium azide (TBA-N3, 4.8 g, 17 mmol, 1.1 mol eq) in DMF (15 mL) was added slowly over 15 min via an addition funnel. The reaction mixture was stirred in the cold bath and was allowed to warm to ambient temperature gradually. After 16 hr, the reaction was diluted with MTBE (300 mL), washed with sat. aq. NaHCO3 (2×30 mL), and brine (2×30 mL), dried over Na2SO4 and evaporated to give a residue. This crude material was purified on silica (40 g) with gradients from 100% heptane to 20% ethyl acetate-80% heptane to give the title product as a colorless oil (3.02 g, 80% yield, >95% purity). 1H NMR (400 MHz, chloroform-d) δ ppm 4.06 (dtd, J=8.86, 5.41, 5.41, 3.91 Hz, 1 H) 3.65-3.83 (m, 3 H) 3.36-3.57 (m, 1 H) 1.47 (s, 9 H). 19F NMR (376 MHz, chloroform-d) δ ppm −106.10-−102.44 (m, 1 F) −120.14-−116.68 (m, 1 F). m/z (ESI+) for C9H14F2N4O2 149 (small)/123 (M+H)+.
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