[NH2:1][C:2]1[O:6][N:5]=[C:4]([CH:7]([CH2:9][CH3:10])[CH3:8])[CH:3]=1.N1C=CC=CC=1.Cl[C:18]([O:20][CH2:21][C:22]([Cl:25])([Cl:24])[Cl:23])=[O:19]>C(Cl)Cl>[Cl:23][C:22]([Cl:25])([Cl:24])[CH2:21][O:20][C:18](=[O:19])[NH:1][C:2]1[O:6][N:5]=[C:4]([CH:7]([CH2:9][CH3:10])[CH3:8])[CH:3]=1To a solution of 5-amino-3-sec-butylisoxazole (500 mg; 3.57 mmol; 1 equiv.) and pyridine (0.58 mL; 7.13 mmol; 2 equiv.) in DCM (30 mL) was added 0.74 mL (5.35 mmol; 1.5 equiv.) of 2,2,2-trichloroethyl chloroformate dropwise. The reaction mixture was stirred overnight at room temperature, then diluted with DCM, and washed sequentially with water, 1N HCL aqueous solution, saturated aqueous NaHCO3 solution and brine. The organic layer was dried over Na2SO4, filtered, and the filtrate was concentrated under reduced pressure. The residue, 1.58 g of (3-sec-Butyl-isoxazol-5-yl)-carbamic acid 2,2,2-trichloro-ethyl ester was isolated as a pale yellow oil, and used as is in the next step.
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