synthesis of 2,5-Dibromo-3-nitropyridine: To a suspension 5-bromo-3-nitro-pyridin-2-ol (20 g, 91.32 mmol) in toluene (100 ml) was added DMF (0.7 ml, 9.13 mmol) and the mixture was heated to 90??C. (the reaction mixture was protected from light). A solution of POBr3 (31. 41 g, 109.51 mmol) in toluene (40 ml) was added dropwise at 90??C. and the reaction mixture was stirred at that temperature for 16 h. The mixture was allowed to cool to room temperature and toluene (50 ml) and water (50 ml) were added. The organic layer was separated, washed successively with aqueous 1N NaOH (60 ml), water (60 ml) and brine (30 ml), dried with Na2SO4 and evaporated obtain 2,5-Dibromo-3-nitropyridine. Yellow solid, yield 25.2 g, 97%.
