Synthesis
General procedure for the synthesis of 6-bromo-2-fluoro-3-pyridinol from 2-fluoro-3-hydroxypyridine: Bromine (1.56 g, 9.73 mmol) was slowly added to a stirred solution of 2-fluoro-3-hydroxypyridine (1.10 g, 9.73 mmol) and sodium acetate (0.80 g, 9.73 mmol) in acetic acid (10 mL) at 5 °C. The reaction mixture was gradually warmed to room temperature and stirred continuously for 4 hours at room temperature. Upon completion of the reaction, the mixture was poured into ice water and neutralized with 2N sodium hydroxide solution to a pH of about 7, followed by extraction with ethyl acetate. The organic phases were combined, washed sequentially with water and saturated saline, dried over anhydrous sodium sulfate, and the filtrate was concentrated by filtration to give a yellow oily crude product. The crude product was purified by rapid chromatography on a silica gel column with an eluent of 1:20 ethyl acetate/dichloromethane to give a colorless oil, which solidified to a white solid after standing. The solid was recrystallized with hexane to give 0.2 g (11% yield) of 6-bromo-2-fluoro-3-pyridinol. The solid obtained by concentrating the filtrate was recrystallized with 2:1 hexane/benzene to give another 0.57 g (31% yield) of 6-bromo-2-fluoro-3-pyridinol. The product was characterized by 1H NMR (400 MHz, DMSO-d6) and LRMS (ESI): 1H NMR δ 10.77 (s, 1H), 7.40-7.30 (m, 2H); LRMS m/z 192/194 (M + H).
References
[1] Patent: WO2005/35522, 2005, A1. Location in patent: Page/Page column 74
[2] Patent: WO2005/35523, 2005, A1. Location in patent: Page/Page column 42-43
[3] Patent: WO2017/91818, 2017, A1. Location in patent: Page/Page column 176
[4] Patent: US2010/29650, 2010, A1. Location in patent: Page/Page column 64
[5] Patent: WO2015/48507, 2015, A1. Location in patent: Paragraph 0175
