To a solution of ethyl 1H-pyrazole-3-carboxylate (10.0 g, 71.4 mmol) in dichloromethane (DCM, 30 mL) was added N-iodosuccinimide (NIS, 22.5 g, 100 mmol) at room temperature. The reaction mixture was stirred at room temperature for 24 hours. Upon completion of the reaction, the reaction was quenched with distilled water (50 mL) and extracted with ethyl acetate (EtOAc, 60 mL x 3). The organic phases were combined, washed with saturated saline (50 mL × 3) and dried over anhydrous sodium sulfate (Na2SO4). After filtration, the filtrate was concentrated under reduced pressure. The residue was purified by column chromatography (eluent: petroleum ether/ethyl acetate, 1:5, v/v) to afford the target compound ethyl 4-iodo-1H-pyrazole-3-carboxylate (15.5 g, 82% yield). Mass spectrum (ESI+): m/z 267 [M+H]+.
