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To a solution of l-tert-butyl-4-nitro-lH-pyrazole (1.10 g, " 6.5 mmol) in methanol (20 mL) was added 10percent palladium carbon (containing 50percent water, 442 rug) , and the mixture was stirred under a hydrogen atmosphere at room temperature for 3 hr. The catalyst was filtered off and the filtrate was concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, hexane/ethyl acetate=70/30->0/100) to give the title compound (838 mg, 92percent) . 1H-NMR (CDCl3, 300 MHz) δ 1-53 (9H, s) , 2.86 (2H, br s) , 7.15(IH, s) , 7.19 (IH, s) .
Reference：
[1] Patent: WO2007/4749, 2007, A1, . Location in patent: Page/Page column 155
[2] Bioorganic and Medicinal Chemistry, 2010, vol. 18, # 20, p. 7150 - 7163
[3] Patent: WO2012/61337, 2012, A1, . Location in patent: Page/Page column 48
[4] Bioorganic and Medicinal Chemistry Letters, 2018, vol. 28, # 2, p. 145 - 151
With nitric acid; In sulfuric acid; at 0℃; for 0.5h;
HNO3 (11.7 g, 185 mmol)was added dropwise to a mixture of 1-tert-butyHH-pyrazole (23 g, 185 mmol) in cone. H2SO4 (30 mL) at O0C. The resulting mixture was stirred at O0C for 30 min and was poured onto crashed ice. The aqueous mixture was extracted with EtOAc. The combined organics were washed with brine, dried (MgSO4) and concentrated in vacuo to give 1- tert-butyI-4-nitro-lH-pyrazole (2Og, 64 % yield). 1H NMR (400 MHz, DMSO-rffi): <S8.85 (s, 1 H), 8.23 (s, I H), 1.52 (s, 9 H).
With potassium carbonate; In N,N-dimethyl-formamide; at 80.0℃; for 72.0h;
To a solution of 4-nitropyrazole (1.13 g, 10 mmol) and 2- bromo-2-methylpropane (17.81 g, 130 mmol) in N,N- dimethylformamide (50 mL) was added potassium carbonate (21.56 g, 156 mmol) and the mixture was stirred at 800C for 3 days.The reaction mixture was diluted with water (200 mL) , and extracted with ethyl acetate (100mLchi3) . The organic layer was washed with water (50 mL) and saturated brine (50 mL) , and concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, hexane/ethyl acetate=100/0?60/40) to give the title compound (1.13 g, 67%) as a white solid.1H-NMR (CDCl3, 300 MHz) delta 1-63 (9H, s) , 8.09 (IH, s) , 8.24 (IH, s) .
With hydrogen;palladium 10% on activated carbon; In methanol; at 20℃; for 3.0h;
To a solution of l-tert-butyl-4-nitro-lH-pyrazole (1.10 g, " 6.5 mmol) in methanol (20 mL) was added 10% palladium carbon (containing 50% water, 442 rug) , and the mixture was stirred under a hydrogen atmosphere at room temperature for 3 hr. The catalyst was filtered off and the filtrate was concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, hexane/ethyl acetate=70/30->0/100) to give the title compound (838 mg, 92%) . 1H-NMR (CDCl3, 300 MHz) delta 1-53 (9H, s) , 2.86 (2H, br s) , 7.15(IH, s) , 7.19 (IH, s) .
With hydrogen;palladium 10% on activated carbon; In methanol; for 1.0h;
To a solution of 4-nitro- IH-pyrazole which was prepared as described in J. Med Chem. 2005, 48, 5780 (0.5 g, 4.4 mmol) in dioxane (8 mL) was added tert-butylacetate (3 mL) and cone. Iota¾804 (0.26 mL) and the mixture was stirred for 18 h at room temperature. The reaction mixture was diluted with sat. NaHC03, volatiles were evaporated and mixture was extracted with ethyl acetate. The organic phase was dried (MgS04), filtered and evaporated to afford a crude residue which was purified bychromatography on silica gel (CH2CI2). Isolated l-tert-butyl-4-nitro-lH-pyrazole (250 mg): 1H NMR (400 MHz, DMSO-d6) delta 8.24 (s, 1H), 8.09 (s, 1H), 1.63 (s, 9H). To a solution 1- tert-butyl-4-nitro-lH-pyrazole (250 mg, 1.5 mmol) in methanol (10 mL) was added 10% Pd/C (80 mg) and the mixture was stirred under hydrogen for lh. The reaction was filtered and the filtrate was evaporated to afford l-tert-butyl-lH-pyrazol-4-amine which was used directly without any further purification.
To a solution of 4-nitro- IH-pyrazole which was prepared as described in J. Med Chem. 2005, 48, 5780 (0.5 g, 4.4 mmol) in dioxane (8 mL) was added tert-butylacetate (3 mL) and cone. Iota¾804 (0.26 mL) and the mixture was stirred for 18 h at room temperature. The reaction mixture was diluted with sat. NaHC03, volatiles were evaporated and mixture was extracted with ethyl acetate. The organic phase was dried (MgS04), filtered and evaporated to afford a crude residue which was purified bychromatography on silica gel (CH2CI2). Isolated l-tert-butyl-4-nitro-lH-pyrazole (250 mg): 1H NMR (400 MHz, DMSO-d6) delta 8.24 (s, 1H), 8.09 (s, 1H), 1.63 (s, 9H). To a solution 1- tert-butyl-4-nitro-lH-pyrazole (250 mg, 1.5 mmol) in methanol (10 mL) was added 10% Pd/C (80 mg) and the mixture was stirred under hydrogen for lh. The reaction was filtered and the filtrate was evaporated to afford l-tert-butyl-lH-pyrazol-4-amine which was used directly without any further purification.
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