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Step 1: Synthesis of 2,3-dichloro-4-iodopyridine Under argon protection, 2,3-dichloropyridine (20 g, 135.1 mmol) was dissolved in anhydrous tetrahydrofuran (350 mL), and cooled to -78 °C. At -78 °C, n-butyllithium (2.4 M hexane solution, 59.12 mL, 141.9 mmol) was slowly added dropwise, and after completion of the dropwise addition, the reaction mixture was continued to be stirred at -78 °C for 90 min. Subsequently, anhydrous tetrahydrofuran (100 mL) solution of iodine (41 g, 161.5 mmol) was slowly added dropwise, and after completion of the dropwise addition, stirring was continued at -78°C for 60 minutes. After completion of the reaction, the reaction mixture was slowly warmed up to room temperature. The reaction was quenched with saturated ammonium chloride solution (100 mL), diluted with water (100 mL) and extracted with ethyl acetate (200 mL x 3). The organic phases were combined, washed with brine solution (200 mL x 2), dried over anhydrous sodium sulfate, filtered and concentrated. The residue was purified by column chromatography (silica gel, petroleum ether: ethyl acetate= 100:1) to afford the yellow solid product 2,3-dichloro-4-iodopyridine (31.5 g, yield: 85.1%). 1H NMR (300 MHz, DMSO-d6): δ 8.08 (d, J = 5.4 Hz, 1H), 8.65 (d, J = 5.4 Hz, 1H). MS (ESI+): m/z 273.9 [M + H]+.