Step 1. 2,4-Dibromo-5-nitropyridine (3.67 g) was dissolved in tetrahydrofuran (THF, 150 mL) under the protection of nitrogen, followed by the addition of methanol solution of ammonia (2 M) and triethylamine (5 mL) sequentially. The reaction mixture was stirred at room temperature for 50 hours. Upon completion of the reaction, the reaction mixture was concentrated, the residue was dissolved in ethyl acetate (EtOAc), filtered through a silica gel pad, and the filtrate was concentrated under vacuum to afford 2-bromo-5-nitro-4-aminopyridine in 95% yield.
