Synthesis
To a stirred solution of 2-bromo-5-fluoropyridine-4-carboxylic acid (2.8 g, 12.78 mmol) in methanol (30 ml) was slowly added thionyl chloride (7.54 g, 63.9 mmol) at room temperature. The reaction mixture was stirred continuously for 16 hours at room temperature. After completion of the reaction, the solvent was removed by concentration under reduced pressure. The residue was dissolved in water (100 ml) and the pH was adjusted with saturated sodium bicarbonate solution to 8. Subsequently, extraction was carried out with ethyl acetate (2 x 100 ml). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give methyl 2-bromo-5-fluoroisonicotinate (2.2 g, 73% yield) as a light yellow solid. The results were analyzed by liquid chromatography-mass spectrometry (Method 8): retention time (Rt) = 2.41 min; mass-to-charge ratio (m/z) = 234.07 ([M+H]+).
References
[1] Patent: WO2006/45514, 2006, A1. Location in patent: Page/Page column 38
[2] Patent: WO2017/207813, 2017, A1. Location in patent: Page/Page column 150
