General procedure for the synthesis of 4-chloro-3-iodo-1H-indazole from 4-chloro-1H-indazole: To a solution of 4-chloro-1H-indazole (1.7 g, 11.2 mmol, 1.0 equiv) in N,N-dimethylformamide (DMF, 20 mL) was added potassium hydroxide (KOH, 1.25 g, 22.4 mmol, 2.0 equiv). The reaction mixture was stirred at room temperature for 30 minutes. Subsequently, iodine (I2, 5.64 g, 22.4 mmol, 2.0 eq.) was added to the reaction system in batches at 0 °C and the mixture was stirred at room temperature overnight. The completion of the reaction was confirmed by liquid chromatography-mass spectrometry (LC-MS) analysis. The reaction mixture was poured into ice water and extracted with ethyl acetate (EtOAc, 50 mL x 2). The combined organic phases were washed sequentially with saturated sodium sulfite (Na2SO3, 20 mL × 2) aqueous solution and brine (20 mL × 2), and concentrated after drying with anhydrous sodium sulfate (Na2SO4) to obtain the target product 4-chloro-3-iodo-1H-indazole (2.7 g, 9.7 mmol, yield: 87%).LC/MS analysis showed that the molecular ion peak (M+) had a m/z was 279.
