Methyl 1H-pyrazole-3-carboxylate (0.5 g, 4.3 mmol, 1.1 eq.) and N-iodosuccinimide (NIS) (0.97 g, 3.9 mmol, 1 eq.) were dissolved in acetonitrile (15 mL), and trifluoroacetic acid (0.1 mL) was added as a catalyst. The reaction mixture was stirred at room temperature for 3 hours. Upon completion of the reaction, the mixture was concentrated to remove the solvent. The concentrated residue was partitioned between ethyl acetate (EtOAc) and 5% aqueous sodium bicarbonate (NaHCO3). The organic layer was separated, dried with anhydrous sodium sulfate (Na2SO4), filtered and concentrated. Finally, the residue was purified by silica gel column chromatography to afford the target product methyl 4-iodo-1H-pyrazole-3-carboxylate (0.61 g, 61% yield).
