tert-Butylhydrazine monohydrochloride → 1-Tert-butoxycarbonyl-4-(1-tert-butyl-3-methyl-5-pyrazolyl)piperazine

1-Acetoacetyl-4-tert-butoxycarbonylpiperazine [product of Example 222 (1), 3.92 g] was dissolved in ethanol (300 mL), and tert-butylhydrazine hydrochloride (1.81 g) and molecular sieves 3A (10 g) were added thereto at room temperature. The mixture was stirred for 15 hr. The reaction mixture was filtrated and the filtrate was concentrated under reduced pressure. The residue was dissolved in pyridine (200 mL), and phosphorus oxychloride (3.0 mL) was added thereto at room temperature. The mixture was stirred for 24 hr. The reaction mixture was concentrated under reduced pressure, the residue was acidified with dilute hydrochloric acid to pH 3. The mixture was extracted with ethyl acetate. The extract was washed successively with saturated aqueous sodium hydrogencarbonate solution and brine and dried. The solvent was evaporated under reduced pressure and the residue was purified by silica gel chromatography to give 1-tert-butoxycarbonyl-4-(1-tert-butyl-3-methyl-5-pyrazolyl)piperazine (886 mg) as an oil.