A brown suspension was formed from 3,5-difluoro-2-hydrazinylpyridine (Intermediate 18, 16.0 g, 110.26 mmol), which was dissolved in a 500 mL round-bottomed flask with CHCl3 (158 mL). The reaction system was heated to 40 °C, followed by slow dropwise addition of bromine (14.20 mL, 275.65 mmol) over 15 min. After the dropwise addition was completed, the reaction mixture was warmed to 60 °C and refluxed for 1 hour. Upon completion of the reaction, it was cooled to room temperature and the flask was placed in an ice bath to stand. NaHCO3 solution was added slowly to quench the reaction. The reaction mixture was partitioned and extracted with DCM (2 x 80 mL), and the organic phase was dried and concentrated with Na2SO4 to give the crude product. The crude product was purified by silica gel column chromatography using EtOAc/hexane (0-20%) gradient elution. The target fraction was collected and concentrated to afford 2-bromo-3,5-difluoropyridine (12.0 g, 56% yield). The product was confirmed by 1H NMR (δ 8.18 (td, 1H), 8.46 (d, 1H)).
