Synthesis
General procedure for the synthesis of 2-hydroxy-5-chloro-3-bromopyridine from 5-chloropyridin-2-one: 5-chloro-2-hydroxypyridine (20.1 g, 155.4 mmol) and bromine (11.9 mL) were dissolved in acetic acid (250 mL), and the reaction was stirred for 2 hours at room temperature. Upon completion of the reaction, the solvent was removed by vacuum evaporation. The residue was extracted by adding ethyl acetate (600 mL) and saturated sodium bicarbonate solution (300 mL). The organic layer was washed sequentially with saturated sodium bicarbonate solution (2 x 200 mL) and brine, followed by drying and concentration with anhydrous sodium sulfate to give the crude product. The crude product was recrystallized by hexane/ether mixed solvent to afford purified 3-bromo-5-chloro-2-hydroxypyridine (21.3 g, 66% yield), which could be used directly in the subsequent reaction.
References
[1] Patent: WO2004/72037, 2004, A1. Location in patent: Page 11
[2] Bioorganic and Medicinal Chemistry Letters, 1998, vol. 8, # 19, p. 2777 - 2782
[3] Patent: US5861419, 1999, A
[4] Patent: US6245797, 2001, B1
[5] Patent: WO2014/141110, 2014, A2. Location in patent: Page/Page column 83; 84
