N#N.[N:3]([C@H:6]1[C@H:10](O)[CH2:9][N:8]([C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[CH2:7]1)=[N+:4]=[N-:5].CCN(S(F)(F)[F:25])CC.C([O-])([O-])=O.[Na+].[Na+]>C(Cl)Cl>[N:3]([C@H:6]1[C@H:10]([F:25])[CH2:9][N:8]([C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[CH2:7]1)=[N+:4]=[N-:5]In a flame dried round-bottomed flask equipped with a magnetic stir bar and under inert atmosphere (N2), to a solution of trans-tert-butyl 3-azido-4-hydroxypyrrolidine-1-carboxylate (J. Med. Chem. 2010, 53, 6730-6746) (288 mg, 1.26 mmol) in CH2Cl2 (1.1 mL) was added dropwise a solution of DAST (0.345 mL, 2.61 mmol) in CH2Cl2 (1.1 mL) at −78° C. After being stirred for 2 h at −60° C., the reaction mixture was warmed to 0° C., poured into aq. 10% Na2CO3, and extracted with CH2Cl2. The organic layer was separated, washed with water, dried over MgSO4, and concentrated under reduced pressure. The residue was purified with FC (Hept/EA, 9.5:0.5→7:3) to afford trans-tert-butyl 3-azido-4-fluoropyrrolidine-1-carboxylate as a yellow oil. TLC: rf (Hept/EA, 7:3)=0.53.
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