General procedure for the synthesis of 3-fluoro-4-iodophenol from 4-amino-3-fluorophenol: 4-amino-3-fluorophenol (5 g, 39.4 mmol) was suspended in 15 mL of water and H2SO4 (4.62 g), and the mixture was cooled to -5 °C in an ice-salt bath. A solution of sodium nitrite (2.71 g, 39.4 mmol) in 15 mL of water was added slowly and dropwise to the mixture, keeping the internal temperature below +2 °C. The resulting brown solution was continued to be stirred at -5°C for 15 min. Subsequently, a solution of potassium iodide (7.87 g, 47.2 mmol) in 30 mL of water was added slowly and dropwise. After addition, the reaction mixture was stirred at room temperature for 4 hours. After the reaction was completed, the reaction mixture was diluted with EtOAc. The organic layer was washed sequentially with water and brine, dried over anhydrous sodium sulfate, filtered and concentrated to afford the target product 3-fluoro-4-iodophenol (5 g, 53.3% yield).
