Add sodium triacetoxyborohydride (156 mg, 0.73 mmol) to a mixture of 3-fluoro-4-oxopyrrolidine-1-carboxylic acid tert-butyl ester (100 mg, 0.5 mmol) and 2,4-dichlorobenzylamine (65 μL, 0.5 mmol) in 1,2-dichloroethane (1.5 mL), followed by 2 drops of glacial acetic acid and stir overnight at room temperature. Pour the crude mixture into 2 N sodium hydroxide and extract with ethyl acetate, wash with water, dry (magnesium sulfate), concentrate and chromatograph on silica gel to give 3-(2,4-dichlorobenzylamino)-4-fluoropyrrolidine-1-carboxylic acid tert-butyl ester (40 mg, 20%). 1H NMR (300 MHz, CDCl3) δ 7.36-7.44 (2H, m), 7.20-7.28 (1H, m), 5.03 (1H, d, J=54.07 Hz), 3.21-3.95 (6H, m), 2.99-3.15 (1H, m), 1.45 (9H, s), MS (ES): m/z=363 [M+].
