General procedure for the synthesis of 5-bromo-3-methoxy-2-nitropyridine from 3-bromo-5-methoxypyridine: 3-bromo-5-methoxypyridine (20.91 g, 0.11 mol) was dissolved in concentrated sulphuric acid (63 ml), and nitric acid (5.2 ml, 0.12 mol) was slowly added dropwise in an ice-bath under cooled conditions, and the reaction mixture was stirred for 20 h at room temperature. After completion of the reaction, the mixture was carefully poured into ice water with continuous stirring. The precipitated solid was collected by filtration and washed with cold water. The resulting solid was dissolved in ethyl acetate and the organic layer was washed sequentially with saturated aqueous sodium bicarbonate and saturated brine, followed by drying with anhydrous magnesium sulfate. After filtration to remove the drying agent, the filtrate was concentrated under reduced pressure to afford the target product 5-bromo-3-methoxy-2-nitropyridine (21.97 g, 85% yield) in the form of a light yellow solid. The structure of the product was confirmed by 1H NMR (CDCl3, 400 MHz): δ 4.01 (3H, s), 7.68 (1H, d, J = 1.6 Hz), 8.16 (1H, d, J = 1.9 Hz).
