[Synthesis]
The general procedure for the synthesis of 5-bromo-2-iodophenol from 2-amino-5-bromophenol was as follows: 2-amino-5-bromophenol (2.50 g, 13.30 mmol) was dissolved in anhydrous THF (12 mL) at -30 to -40 °C and cooled in a dry ice-MeCN bath. Boron trifluoride diethyl ether compound (BF3-Et2O, 4.92 mL, 39.90 mmol) was added slowly and dropwise under nitrogen protection. After the reaction mixture was stirred at -30 °C for 10 min, tert-butyl nitrite (tBuONO, 2.39 mL, 19.94 mmol) was added dropwise. Subsequently, the reaction mixture was slowly warmed to room temperature and stirring was continued for 1.5 hours to form a suspension. Petroleum ether (50 mL) was added to promote precipitation, the supernatant was removed by decantation, and the remaining solid was washed with petroleum ether to give a white solid. The solid was dissolved in dry MeCN (20 mL) and cooled in an ice bath. Potassium iodide (KI, 11.00 g, 66.26 mmol) and iodine (I2, 6.00 g, 23.64 mmol) were added sequentially. The reaction mixture was stirred at room temperature for 4 hours before saturated sodium thiosulfate solution (50 mL) was added to terminate the reaction. The mixture was extracted three times with ethyl acetate, the organic phases were combined, washed sequentially with water and brine, dried over anhydrous sodium sulfate and filtered through a diatomaceous earth pad. The solvent was removed by concentration under reduced pressure and the resulting crude product was purified by silica gel column chromatography using a mixture of ethyl acetate and petroleum ether (v/v 1:9) as eluent to give 5-bromo-2-iodophenol as a light-colored solid in the end (2.83 g, 71% yield).1H NMR (CDCl3) δ 7.50 (d, J=8.5 Hz, 1H), 7.16 (d, J= 2.2Hz, 1H), 6.84 (dd, J=2.2,8.5Hz, 1H), 5.39 (s, 1H) ppm. |