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a) A suspension of 6-bromo-1H-indazole (82.74 mmol), 4-dimethylaminopyridine (DMAP, 16.55 mmol), and triethylamine (Et3N, 19.56 mL) in acetonitrile (CH3CN) was slowly added to an acetonitrile solution of di-tert-butyl dicarbonate (82.74 mmol) over a period of 15 min at 0°C, keeping the internal temperature no more than 5°C. The reaction mixture was gradually warmed to room temperature and stirred continuously for 18 hours. After completion of the reaction, the mixture was concentrated under reduced pressure and the residue was purified by fast column chromatography (eluent: 7% ethyl acetate/petroleum ether) to afford tert-butyl 6-bromo-1H-indazole-1-carboxylate (23.2 g, 94% yield) as a white solid.

[1] Patent: WO2012/37298, 2012, A1. Location in patent: Page/Page column 49
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