[C:1]([C:5]1[CH:9]=[C:8]([NH2:10])[N:7]([CH2:11][CH3:12])[N:6]=1)([CH3:4])([CH3:3])[CH3:2].[OH-].[Na+].Cl[C:16]([O:18][CH2:19][C:20]([Cl:23])([Cl:22])[Cl:21])=[O:17]>C(OCC)(=O)C.O>[Cl:21][C:20]([Cl:23])([Cl:22])[CH2:19][O:18][C:16](=[O:17])[NH:10][C:8]1[N:7]([CH2:11][CH3:12])[N:6]=[C:5]([C:1]([CH3:4])([CH3:2])[CH3:3])[CH:9]=1To a stirred mixture of 3-tert-butyl-1-ethyl-1H-pyrazole-5-amine (0.500 g, 2.99 mmol) in ethyl acetate (7.5 mL) and 1 M aqueous NaOH (7.5 mL, 7.5 mmol), cooled in an ice bath, was added 2,2,2-trichloroethyl chloroformate (0.453 mL, 3.29 mmol) and the mixture was stirred for 45 min. The mixture was diluted with water and extracted twice with ethyl acetate. The combined organic extracts were dried (MgSO4) and evaporated. The residue was crystallised from pentane-diethyl ether (1:1) to give the title compound (0.078 g) as a white solid. The mother liquors were evaporated and purified by column chromatography (0-40% EtOAc/cyclohexane) to give the title compound (0.817 g) as a colorless oil (Total yield 0.895 g, 87%). LCMS (Method 3): Rt 4.09 min, m/z 342/344/346 [MH+]. 1H NMR (300 MHz, CDCl3): 1.44 (12H, m), 4.78-4.83 (2H, m), 4.88 (2H, s), 6.53 (1H, s), 9.82 (1H, s).
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