General procedure for the synthesis of 4-iodo-1-methyl-1H-pyrazole-5-carboxylic acid from ethyl 4-iodo-1-methyl-1H-pyrazole-5-carboxylate: to a stirred solution of ethyl 4-iodo-1-methyl-1H-pyrazole-5-carboxylate (700 mg, 2.5 mmol) in a solvent mixture of 15 mL MeOH/H2O/THF (v/v/v = 1:1:1) Lithium hydroxide monohydrate (1.05 g, 25 mmol) was added. After addition, the reaction solution was stirred at 25°C for 2 hours. After the completion of the reaction, the mixture was concentrated under reduced pressure and the pH was adjusted to 4 with 1N HCl. The aqueous phase was extracted with EtOAc, and the organic layers were combined, washed with saturated brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure to obtain the crude 4-iodo-1-methyl-1H-pyrazole-5-carboxylic acid (623.0 mg, crude yield 98%), which was used directly in the next step without further purification. The crude product was directly used in the next step without further purification.
