To a solution of (2R, 4S)-4-(4-benzyloxyphenyl)-5-oxo-pyrrolidine-2-carboxylic acid (330 mg, 1.06 mmol), N-methyl morpholine (0.25 mL, 2.3 mmol) and O-(2-trimethylsilylethyl) hydroxylamine hydrochloride (220 mg, 1.30 mmol) in CH2Cl2 (20 mL) was added (benztriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluoroborate (560 mg, 1.27 mmol). The reaction was stirred at room temperature for 6 hours. After dilution with CH2Cl2, the mixture was washed sequentially with aqueous 0.5M HCl solution, water, aqueous saturated NaHCO3 solution, and brine. The solution was dried over MgSO4 and concentrated to a white solid that was triturated with ethyl acetate and set aside. The trituration filtrate was concentrated and chromatographed on silica gel eluting with 5% methanol in chloroform. Fractions containing the title compound were combined and concentrated to afford a white solid that was combined with the solid obtained directly from the crude product mixture. The sample was stirred in water overnight. The title compound was collected by filtration and dried. The yield was 194 mg (43%).
