The general procedure for the synthesis of 3-cyanophenylboronic acid from triisopropyl borate and m-bromobenzonitrile was as follows: 20 g of 3-bromobenzonitrile was dissolved in 100 ml of anhydrous tetrahydrofuran (THF) and mixed with 37.6 ml of triisopropoxyborane under nitrogen protection. The reaction system was cooled to -78 °C, followed by the slow dropwise addition of 98.3 ml of 1.6 M n-butyllithium hexane solution under stirring for about 30 minutes. The reaction mixture was continued to be stirred at room temperature for 30 minutes, then cooled to 0°C and 220 ml of 4M sulfuric acid solution was added. The reaction solution was heated to reflux overnight, cooled again to 0°C, and 340 ml of 5M aqueous sodium hydroxide solution was added, followed by extraction with 200 ml of diethyl ether. The aqueous phase was separated and the pH was adjusted to 2 with 6 M hydrochloric acid and extracted twice with 300 ml ethyl acetate. The ethyl acetate layers were combined, dried with anhydrous magnesium sulfate (MgSO4) and the solvent was removed by distillation under reduced pressure. The resulting crude product was recrystallized by DMF-water system to give 11.6 g (72% yield) of 3-cyanophenylboronic acid as light yellow needle-like crystals. The product was characterized by 1H NMR (270 MHz, DMSO-d6): δ 8.5 (brs, 2H), 8.3-7.6 (m, 4H).
