General procedure for the synthesis of ethyl 5-amino-pyrazole-3-carboxylate from ethyl 5-nitro-1H-pyrazole-3-carboxylate: ethyl 5-nitro-1H-pyrazole-3-carboxylate (0.925 g, 0.500 mmol) was dissolved in anhydrous ethanol (10 mL) and 10% Pd/C catalyst (0.100 g) was added. The reaction mixture was stirred at room temperature for 18 h under hydrogen atmosphere. Upon completion of the reaction, the catalyst was removed by diatomaceous earth filtration and the filtrate was concentrated under reduced pressure to afford the green solid product ethyl 5-amino-pyrazole-3-carboxylate (0.70 g, 90% yield). The product was confirmed by NMR hydrogen spectrum (1H NMR, CD3OD): δ 6.0 (s, 1H), 4.3 (q, 2H, J = 7.1 Hz, CO2CH2CH3), 1.4 (t, 3H, J = 7.1 Hz, CO2CH2CH3). Mass spectrum (ESI+): m/z 156 [M + H]+.
