[C:1]([O:5][C:6]([N:8]1[CH2:12][C@@H:11]([F:13])[CH2:10][C@H:9]1[C:14](O)=[O:15])=[O:7])([CH3:4])([CH3:3])[CH3:2].B.O1CCCC1.C(=O)(O)[O-].[Na+]>O1CCCC1>[F:13][C@@H:11]1[CH2:12][N:8]([C:6]([O:5][C:1]([CH3:2])([CH3:3])[CH3:4])=[O:7])[C@H:9]([CH2:14][OH:15])[CH2:10]1To a solution of (2S,4S)-1-tert-butoxycarbonyl-4-fluoropyrrolidine-2-carboxylic acid (4.7 g) in tetrahydrofuran (40 ml), a borane-tetrahydrofuran complex (0.95 M solution in tetrahydrofuran, 31.6 ml) was added under ice cooling, and the mixture was stirred at room temperature for 1 hour. Ice water and a saturated aqueous solution of sodium bicarbonate were added to the reaction solution, followed by extraction with ethyl acetate. The extract was washed with saturated saline and then dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure. The obtained residue was purified by silica gel column chromatography (n-hexane-ethyl acetate) to obtain the title compound (4.2 g).
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