A solution was prepared by dissolving 4-bromo-3-fluorotoluene (10 g) in tetrahydrofuran (THF, 50 mL) under a dry nitrogen atmosphere and cooled to -72 °C. Subsequently, a hexane solution (35 mL) of 1.6 M n-butyllithium was slowly added at -72 °C, the reaction temperature was controlled not to exceed -65 °C and stirring was continued for 1 h at this temperature. A solution prepared by dissolving iodine (14.8 g) in THF (30 mL) was added to the above reaction mixture at -72 °C, ensuring that the internal temperature was not higher than -60 °C, after which it was slowly warmed to room temperature. Upon completion of the reaction, saturated aqueous ammonium chloride solution and hexane were added to the mixture to separate the organic layer. The organic layer was sequentially washed twice with 10% aqueous sodium sulfite, then with saturated brine and finally dried with anhydrous sodium sulfate. The desiccant was removed by filtration and the organic solvent was removed by distillation under reduced pressure. The residue was purified by silica gel column chromatography to give 13.0 g of 3-fluoro-4-iodotoluene as a yellow liquid.
