The general procedure for the synthesis of 2,6-dibromo-3-nitropyridine from 2,6-dichloro-3-nitropyridine was as follows (Intermediate 6: 2,6-dibromo-3-nitropyridine, Scheme 12): Commercially available 2,6-dichloro-3-nitropyridine (10.0 g, 51.8 mmol) was mixed with a 33% HBr/AcOH solution (120 mL) and heated at 80°C. The reaction was carried out for 3 hours. The reaction was heated at 80°C for 3 hours. After completion of the reaction, the reaction solution was concentrated in vacuum. The resulting residue was dissolved in EtOAc and washed with saturated aqueous sodium bicarbonate. The organic phase was dried over anhydrous sodium sulfate and concentrated again under vacuum. The final product 2,6-dibromo-3-nitropyridine 14.4 g (99% yield) was obtained, which can be used as intermediate 6 without further purification. The product was analyzed by GC/MS showing a purity of 94% with a retention time (tR) of 7.56 min (tR of raw material was 6.93 min), and the characteristic peaks of the mass spectra (m/z) were 280/282/284 (M, 38%), 222/224/226 (35%), and 76 (100%), and the detection instrument was Finnegan LCQ.
