[CH3:1][CH:2]1[CH2:7][N:6]([C:8]2[N:12]([CH3:13])[N:11]=[CH:10][C:9]=2[N+:14]([O-])=O)[CH2:5][CH2:4][N:3]1[C:17]([O:19][C:20]([CH3:23])([CH3:22])[CH3:21])=[O:18].[NH4+].[Cl-]>CO.O.[Zn]>[NH2:14][C:9]1[CH:10]=[N:11][N:12]([CH3:13])[C:8]=1[N:6]1[CH2:5][CH2:4][N:3]([C:17]([O:19][C:20]([CH3:22])([CH3:21])[CH3:23])=[O:18])[CH:2]([CH3:1])[CH2:7]1
To a solution of tert-butyl (±)-2-methyl-4-(1-methyl-4-nitro-1H-pyrazol-5-yl)piperazine-1-carboxylate (500 mg, 1.54 mmol) in MeOH (20 mL) and H2O (5 mL) was added zinc (845 mg, 13 mmol) and NH4Cl (1.4 g, 26 mmol). The reaction mixture was stirred at ambient temperature for 2 hours and filtered through Celite. The filtrate was concentrated under reduced pressure to give a residue. The residue was purified by silica gel chromatography PE/EtOAc (10/1˜1/10) as eluting solvents to give tert-butyl (±)-4-(4-amino-1-methyl-1H-pyrazol-5-yl)-2-methylpiperazine-1-carboxylate (650 mg, ˜100%) as red solid. 1H NMR (500 MHz, CD3OD) δ (ppm): 7.22 (s, 1H), 4.35-4.33 (m, 1H), 4.12-4.11 (m, 1H), 3.94 (s, 3H), 3.43-3.46 (m, 1H), 3.25-3.30 (m, 2H), 3.01-3.00 (m, 1H), 2.89-2.87 (d, J=12 Hz, 1H), 1.49 (s, 9H), 1.34-1.36 (d, J=5.6 Hz, 3H); MS (ESI) m/z=296 (M+H+).
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