The general procedure for the synthesis of trans-BETA-styrene boronic acid from (E)-(2-bromovinyl)benzene is as follows: in a 50 mL round-bottomed flask (equipped with a side arm, condenser, and stirring bar) triphenylphosphine (0.131 g, 0.5 mmol, 20 mol%), p-iodoanisole (0.585 g, 2.5 mmol), and triethylamine (1.78 mL. 12.5 mmol). The reaction system was degassed three times by alternating vacuum and argon filling. Palladium dichloride (0.023 g, 0.13 mmol, 5 mol%) was added under positive argon atmosphere. After stirring for 15 minutes at room temperature, diisopropylaminoborane (5 mL, 1 M THF solution, 5 mmol) was added and the reaction mixture was again degassed three times by alternating vacuum and argon filling. The reaction mixture was heated to reflux and kept at reflux for 12 hours. Upon completion of the reaction, the reaction solution was cooled to 0 °C, and 6 mL of methanol was slowly added (note: this process is an exothermic reaction accompanied by hydrogen release). Stirring was continued for 15 minutes and then concentrated under reduced pressure to remove all solvent to give a black solid. The solid was dissolved in 3M sodium hydroxide solution (8 mL) and subsequently washed with hexane (3 x 10 mL). The aqueous phase was cooled to 0°C (ice bath) and acidified with concentrated hydrochloric acid to pH ≤ 1, at which point the boric acid precipitated as a white solid. The aqueous phase was extracted with ether (3 x 10 mL), the organic phases were combined, dried with magnesium sulfate and filtered. Finally, the solvent was removed by concentration under reduced pressure to obtain the target product, trans-BETA-styrene boronic acid, as a white solid.
![[(Z)-2-bromoethenyl]benzene](/CAS/GIF/588-72-7.gif)
