84476-99-3

1017793-20-2

Preparative Example 2: Synthesis of 2,5-difluoro-4-iodopyridine Diisopropylamine (17 mL, 122 mmol) was added to tetrahydrofuran (220 mL) under nitrogen protection, and the mixture was cooled to -20 °C. Slowly n-butyllithium (49 mL, 122.5 mmol) was added dropwise, and after the drop was completed, the reaction mixture was stirred at -20 °C for 0.5 h and subsequently cooled to -78 °C. At this temperature, a tetrahydrofuran (30 mL) solution of 2,5-difluoropyridine (13.3 g, 115 mmol) was slowly added and the reaction temperature was maintained at -78 °C with stirring for 4 hours. Iodine (32 g, 126 mmol) was dissolved in tetrahydrofuran (100 mL) and slowly added to the above reaction solution and continued to stir at -78 °C for 1 hour. After the reaction was completed, water (10 mL) and tetrahydrofuran (30 mL) were added and slowly warmed to room temperature. The reaction was quenched by the addition of saturated sodium thiosulfate solution. The organic phase was separated and the aqueous phase was extracted with ethyl acetate (3 x 100 mL). The organic phases were combined, dried with anhydrous sodium sulfate, filtered and the filtrate was concentrated. Purification by silica gel column chromatography (eluent: petroleum ether/ethyl acetate=50:1) afforded the target product 2,5-difluoro-4-iodopyridine (13.5 g, 48% yield).