The general procedure for the synthesis of 5-chloro-1H-pyrazol-3-amine from 3-chloro-5-nitro-1H-pyrazole was as follows: tin(II) chloride (12.8 g, 68 mmol) was added batchwise to a methanol (200 mL) solution of 3-chloro-5-nitro-1H-pyrazole (2.0 g, 13.6 mmol). Concentrated hydrochloric acid (10 mL) was added slowly at 0°C. The reaction mixture was stirred at room temperature for 6 h. The organic solvent was subsequently removed by distillation under reduced pressure. The residue was diluted with distilled water (20 mL) and neutralized with sodium carbonate (Na2CO3) to pH 7. Subsequently, extraction was carried out with ethyl acetate (EtOAc, 3 × 50 mL). The organic phases were combined, washed with saturated brine, dried over anhydrous sodium sulfate, filtered and concentrated to afford 5-chloro-1H-pyrazol-3-amine (1.4 g, 87% yield), which was used for subsequent reactions without further purification. The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 11.55 (broad single peak, 1H), 5.26 (single peak, 2H), 5.21 (single peak, 1H).
