[C:1]([O:5][C:6]([NH:8][C@H:9]([CH2:13][O:14][CH:15]([F:17])[F:16])[C:10]([OH:12])=O)=[O:7])([CH3:4])([CH3:3])[CH3:2].C(N(CC)CC)C.ClC(OCC(C)C)=O.[CH2:33]([NH2:40])[C:34]1[CH:39]=[CH:38][CH:37]=[CH:36][CH:35]=1>C1COCC1.C(OCC)(=O)C>[CH2:33]([NH:40][C:10](=[O:12])[C@H:9]([NH:8][C:6](=[O:7])[O:5][C:1]([CH3:2])([CH3:3])[CH3:4])[CH2:13][O:14][CH:15]([F:17])[F:16])[C:34]1[CH:39]=[CH:38][CH:37]=[CH:36][CH:35]=1
To a solution of (2R)-2-[(tert-butoxycarbonyl)amino]-3-(difluoromethoxy)propanoic acid (510 mg, 2.0 mmol) and triethylamine (607.1 mg, 6 mmol) in THF (10 mL) at −78° C., isobutyl chloroformate (348 mg, 2.55 mmol) was added dropwise. After 30 minutes, benzylamine (321.5 mg, 3.0 mmol) was added and the reaction mixture allowed to warm up to room temperature. The mixture then was diluted with ethyl acetate and washed with water, 0.5N HCl and Brine. The organic layer was dried over magnesium sulphate, concentrated, and triturated with ether-hexanes (1:3) to give tert-butyl {(1R)-2-(benzylamino)-1-[(difluoromethoxy)methyl]-2-oxoethyl}carbamate (345 mg, 50%) as a white solid. 1H NMR (300 MHz, CDCl3): δ(ppm) 7.40-7.80 (m, 5H), 6.60 (t, 1H), 6.22 (wt, 1H), 5.25 (w, 1H), 4.32-4.55 (m, 4H), 4.05 (dd, 1H) and 1.48 (s, 9H).
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