The general procedure for the synthesis of 5-bromo-2-methoxy-4-methyl-3-nitropyridine using 2-methoxy-3-nitro-4-methylpyridine as starting material was as follows: sodium acetate (365 g, 5.37 mol) was slowly added to a stirring solution of 2-methoxy-4-methyl-3-nitropyridine (250 g, 1.49 mol) in acetic acid (1.5 L) at room temperature. Subsequently, bromine (Br2, 639 g, 4.00 mol) was added dropwise and the dropwise addition time was controlled to be less than 30 minutes. After addition, the reaction mixture was warmed up to 80 °C for 12 h, during which the progress of the reaction was monitored by thin-layer chromatography (TLC) to confirm that the reaction was complete. Upon completion of the reaction, the mixture was cooled to 0 °C and 10% aqueous solution (1.5 L) and saturated aqueous sodium sulfate solution (1.5 L) were added sequentially to quench the reaction. The resulting solid product was collected by filtration, washed with water, and then dried under reduced pressure to finally obtain 5-bromo-2-methoxy-4-methyl-3-nitropyridine (302 g, 82.2% yield) as a light yellow solid. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 8.25 (s, 1H), 3.94 (s, 3H), 2.29 (s, 3H).
