The general procedure for the synthesis of 2-bromo-1-fluoro-4-iodobenzene from 3-bromo-4-fluoroaniline is as follows: in a 1L four-necked round-bottomed flask equipped with a stirrer, a Liebig condenser, a 100mL dropping funnel, and a thermometer, 630mL of water, 84mL (0.926mol) of concentrated hydrochloric acid, and 54.7g (0.241 mol) of 3-bromo-4-fluoroaniline were added at room temperature and stirred for 24 hours. Subsequently, the reaction mixture was cooled to -10 °C with an ice-water bath and 19.0 g (0.270 mol) of sodium nitrite in 63 mL of aqueous solution was slowly added dropwise, controlling the temperature not to exceed 5 °C during the dropwise addition. After the dropwise addition was completed, stirring was continued at 5 °C or lower for 30 min, and the reaction solution was filtered through a filter aid to obtain an aqueous solution of the diazonium salt.
In another 2L four-necked round-bottomed flask equipped with a stirrer, an Erlenmeyer condenser, a 1L dropping funnel, and a thermometer, 42.0 g (0.251 mol) of potassium iodide and 125 mL of water were added, and the mixture was cooled to 10°C and stirred. Subsequently, the aqueous diazonium salt solution prepared above was slowly added dropwise. Upon completion of the dropwise addition, the ice water bath was removed and the reaction mixture was allowed to warm naturally to room temperature, then heated to 40 °C and stirred at that temperature for 4 hours. Upon completion of the reaction, the reaction solution was cooled to room temperature, 270 mL of dichloromethane (DCM) was added, and transferred to a 2L dispensing funnel to separate the aqueous layer. The aqueous layer was extracted with 220 mL of DCM, and the organic layer was combined and washed three times with 220 mL of 20% aqueous sodium thiosulfate, 220 mL of saturated saline, and 220 mL of water, in that order. The organic layer was dried over anhydrous magnesium sulfate, filtered to remove the desiccant, and distilled under reduced pressure to remove the solvent to obtain the crude product.
The crude product was purified by silica gel column chromatography with n-heptane as the unfolding agent, and 62.5 g (86.0% yield) of 2-bromo-1-fluoro-4-iodobenzene was finally obtained.
