General procedure for the synthesis of 5-bromo-4-methyl-3-nitro-2(1H)-pyridinone from 2-amino-5-bromo-3-nitro-4-methylpyridine: to a solution of 5-bromo-4-methyl-3-nitro-pyridin-2-amine (28 g, 121 mmol) in water (900 ml) was slowly added concentrated sulfuric acid (28 ml) at 0 °C, followed by batchwise addition of sodium nitrite (20.91 g, 303 mmol). Water (100 ml) was added dropwise to control the reaction temperature. The reaction mixture was stirred at 0°C and then slowly warmed up to room temperature and kept for 2 hours. Subsequently, the reaction mixture was heated to 100 °C and maintained for 4 hours. Upon completion of the reaction, it was cooled to room temperature, the precipitated solid was collected by filtration, washed with water and dried to afford the target product 5-bromo-4-methyl-3-nitro-2(1H)-pyridinone as a light yellow solid (24.0 g, 85% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 12.97 (s, 1H), 8.01 (s, 1H), 2.21 (s, 3H); LC/MS analysis showed m/z 233 ([M+H]+).
