Tetrahydrofuran → 5-Bromo-2-fluoro-3-pyridinecarboxaldehyde

To a stirred solution of DIPEA (44.1 mL, 312 mmol) in dry THF (500 mL) at −78° C. was added dropwise n-BuLi (2.5M in hexanes, 125 mL, 313 mmol). The temperature was warmed to rt and stirred for 10 minutes. The solution was cooled to −78° C. and a solution of 5-bromo-2-fluoro-pyridine (1) (50.0 g, 284 mmol) in THF (500 mL) added dropwise. The reaction mixture was stirred at −78° C. for 45 minutes then quenched with 10% citric acid in THF (250 mL) at −78° C. The solution was warmed to rt then diluted with H2O (250 mL). The solution was extracted with EtOAc (3×250 mL) and the combined organics washed with saturated brine solution (250 mL), dried (Na2SO4), filtered and the solvent evaporated in vacuo. The crude product was purified by column chromatography (100-200 mesh silica gel, 20% EtOAc-pet ether) to provide the title compound as a white solid (36.0 g, 62%); Rf: 0.7 (10% EtOAc-pet ether).