To a solution of 8-bromoisoquinoline (2.0 g, 9.6 mmol) in tetrahydrofuran (THF, 40 mL) was slowly added n-butyllithium (n-BuLi, 2.5 M, 4.2 mL, 10.6 mmol) dropwise at -78 °C and under nitrogen protection. After 1 hour of reaction, trimethyl borate (B(OMe)3, 2.0 g, 19.2 mmol) was added, followed by slow warming of the reaction mixture to 0 °C and kept for 1 hour. Upon completion of the reaction, the reaction was quenched with saturated aqueous sodium bicarbonate (NaHCO3) followed by three extractions with ethyl acetate (EtOAc). The organic layers were combined, washed with saturated saline, dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure. The residue was purified by silica gel column chromatography to afford the target product 8-isoquinolineboronic acid (680 mg, 41% yield) as a light yellow solid. Liquid chromatography-mass spectrometry (LCMS) analysis showed [M+H]+ m/z 174.1.
