To a solution of diisopropylamine (174.4 g, 1.73 mol) in anhydrous THF (3 L) was added slowly and dropwise 2.5 M hexane solution of n-butyllithium (n-BuLi) (685 mL, 1.71 mol) at -10 °C. The reaction mixture was stirred at 0 °C for 35 min. Subsequently, the mixture was cooled to -70 °C and a solution of anhydrous THF (1 L) of 2-fluoro-3-iodopyridine (350 g, 1.57 mol) was added. The mixture was continued to be stirred at -70 °C for 2 hours. Ethyl formate (HCOOEt) (128 g, 1.73 mol) was slowly added dropwise while maintaining -70 °C. After the dropwise addition, the reaction mixture was gradually warmed up to room temperature and the reaction was quenched with ice water (4 L). The reaction mixture was diluted with ethyl acetate (EtOAc) (4 L) and the organic layer was washed with brine (500 mL). The organic layer was dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with the eluent being petroleum ether: ethyl acetate (10:1, v/v) to afford the target product 2-fluoro-4-iodopyridine-3-carbaldehyde (180 g, 46% yield) as a yellow solid.1H NMR (400 MHz, CDCl3) δ ppm: 10.08 (s, 1H), 7.91 (d, 1H), 7.81 (d, 1H). 1H).
