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General procedure for the synthesis of 4-tert-butoxycarbonylamino-2-bromopyridine from 4-amino-2-bromopyridine and di-tert-butyl dicarbonate: 2-bromopyridin-4-amine (100.0 g), triethylamine (Et3N, 64.8 g), and dichloromethane (DCM, 1.0 L) were added to the reaction vial and the reaction mixture was stirred for 15-30 min at 20-30 °C. Subsequently, 4-dimethylaminopyridine (DMAP, 3.5 g) was added to the reaction vial and di-tert-butyl dicarbonate ((Boc)2O, 416.3 g) was added slowly and dropwise. The reaction mixture was stirred continuously at 20-30 °C for 16 h, during which the progress of the reaction was monitored by HPLC. After completion of the reaction, the reaction mixture was washed with deionized water (2 L). The organic phase was separated and concentrated under reduced pressure to give the crude product as a yellow solid. The solid was stirred with methanol (MeOH, 300.0 mL) at 20-30 °C for 30 min and then filtered to give 4-tert-butoxycarbonylamino-2-bromopyridine (171.2 g) as an off-white solid.

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