(c) Synthesis of tert-butyl 4-amino-1H-pyrazole-1-carboxylate (A55): tert-butyl 4-nitro-1H-pyrazole-1-carboxylate (A54, 3.70 g, 17.4 mmol) and 10% Pd/C (0.300 g) were suspended in EtOH (150 mL) and moistened with ~5% water. The reaction mixture was stirred for 20 h at room temperature under hydrogen (1 atm) atmosphere. Upon completion of the reaction, the reaction mixture was filtered through diatomaceous earth and the filter cake was washed with EtOAc (about 100 mL). The filtrate was concentrated under reduced pressure to afford tert-butyl 4-amino-1H-pyrazole-1-carboxylate (3.09 g, 97% yield) as a light brown solid.1H NMR (400 MHz, CDCl3) δ 7.54 (d, J = 0.6 Hz, 1H), 7.40 (d, J = 0.8 Hz, 1H), 3.10 (s, 2H), 1.62 (s, 9H). LCMS analysis: retention time (rt) 3.75 min; no product ions detected.
