To a solution of DABCO (8.8 g, 78.2 mmol) in anhydrous ether (250 mL) was slowly added n-BuLi (1.6 M hexane solution, 49 mL, 78.2 mmol) at -25 °C. The reaction mixture was stirred between -25 and -10°C for 45 minutes and subsequently cooled to -70°C. At -70 °C, 3-fluoropyridine (5.9 mL, 71 mmol) was added dropwise to the above reaction solution. The reaction temperature was maintained between -70 and -60 °C and stirring was continued for 1.5 hours. After that, DMF (11.0 mL, 2.0 eq.) was added to the reaction system. After stirring at -70 °C for 1.0 h, the reaction was quenched by slow addition of water (150 mL) and gradually warmed to room temperature. Upon completion of the reaction, the organic and aqueous layers were separated and the aqueous layer was extracted with dichloromethane (5 x 100 mL). All organic layers were combined, washed with saturated saline and dried with anhydrous sodium sulfate. After the solvent was removed by concentration under reduced pressure, the crude product was purified by silica gel column chromatography using ethyl acetate/hexane gradient elution to afford 3-fluoropyridine-2-aldehyde (5.4 g, 55-60% yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 7.54-7.57 (m, 2H), 8.61 (d, J = 2.20 Hz, 1H), 10.20 (s, 1H).
