[NH2:1][C:2](=O)[C@@H:3]([NH:8][C:9](=[O:15])[O:10][C:11]([CH3:14])([CH3:13])[CH3:12])[CH2:4][CH:5]1[CH2:7][CH2:6]1.C(N(CC)CC)C.FC(F)(F)C(OC(=O)C(F)(F)F)=O>C(Cl)Cl>[C:2]([C@@H:3]([NH:8][C:9](=[O:15])[O:10][C:11]([CH3:13])([CH3:12])[CH3:14])[CH2:4][CH:5]1[CH2:7][CH2:6]1)#[N:1]To a solution of (S)-tert-butyl 1-amino-3-cyclopropyl-1-oxopropan-2-ylcarbamate (3.7 g, 16 mmol) and triethylamine (6.55 g, 65 mmol) in methylene chloride (50 mL) was added trifluoroacetic acid anhydride (6.81 g, 32 mmol) dropwise at 0° C. The resulting mixture was allowed to warm to room temperature and stirred for 4 h. The mixture was washed with water (150 mL), citric acid (150 mL, 5 M) and brine (150 mL). The organic phase was dried over anhydrous sodium sulfate and concentrated to give product (3.31 g, 97%) as a yellow solid; MS (EI): m/e 233.1 [M+Na]+.
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