General procedure for the preparation of 5-iodo-2-methyl-2H-indazole: To a solution of 5-iodo-1H-indazole (500 g, 2.05 mol) in ethyl acetate (EtOAc, 4 L) was added trimethoxonium tetrafluoroborate (450 g, 3.04 mol). The resulting white suspension was stirred at room temperature for 2 h and subsequently concentrated under reduced pressure. Water (1 L) was added to the concentrated residue and the pH was adjusted with 10% aqueous sodium hydroxide (NaOH) to 12. The solid was collected by filtration and redissolved in dichloromethane (DCM, 5 L). After filtration to remove insoluble matter, the filtrate was washed with 10% aqueous NaOH (2 × 100 mL). The organic layer was dried with anhydrous sodium sulfate (Na2SO4), filtered through a short silica gel column and concentrated again. Methyl tert-butyl ether was added to the residue to form a slurry and the product was collected by filtration to give the final title compound 5-iodo-2-methyl-2H-indazole (360 g, 68.0% yield). Mass spectrometry (MS) data: m/z 259.0 ([M+H]+).
