Synthesis
(b) Synthesis of 2,5-dibromo-3-aminopyridine: 2,5-dibromo-3-nitropyridine (2.5 g, 8.87 mmol) was dissolved in acetic acid (10 mL) and stirred until completely dissolved. Powdered iron (2.476 g, 44.3 mmol) was then added and the reaction mixture was heated to 80 °C under vigorous stirring and maintained for 15 min. Upon completion of the reaction, the mixture was filtered through a diatomaceous earth pad to remove solid impurities and the filter cake was washed with ether and ethyl acetate (EtOAc). The organic layers were combined and washed sequentially with water and saturated brine to remove water-soluble impurities. The organic layers were dried over anhydrous magnesium sulfate, filtered and concentrated to give the crude product. The crude product was purified by silica gel column chromatography using 0-30% ethyl acetate/hexane gradient elution to collect the target components, and concentrated under reduced pressure to give 2,5-dibromopyridin-3-amine (1.7 g, 6.75 mmol, 76% yield) as a white solid. The mass spectrum (electrospray positive ion mode) showed m/z 252 ([M+H]+).
References
[1] Bulletin des Societes Chimiques Belges, 1988, vol. 97, # 1, p. 51 - 54
[2] Patent: WO2008/128961, 2008, A1. Location in patent: Page/Page column 37; 73
[3] Journal of Medicinal Chemistry, 2010, vol. 53, # 10, p. 3927 - 3936
[4] Patent: WO2007/107758, 2007, A1. Location in patent: Page/Page column 125
[5] Journal of the Chemical Society, 1952, p. 2042,2044
