5-Bromo-1,3-dihydrobenzimidazol-2-one (20.0 g, 93.9 mmol) was dissolved in anhydrous N,N-dimethylformamide (DMF, 150 mL) purged with argon. To this solution was sequentially added bis(pinacolato)diboron (28.6 g, 113 mmol), potassium acetate (KOAc, 27.6 g, 282 mmol), and a 1:1 complex of dichlorobis(triphenylphosphine)palladium(II) (PdCl2(DPPF), 7.67 g, 9.40 mmol) with dichloromethane (CH2Cl2). The reaction mixture was heated to 95 °C and kept overnight under mechanical stirring. After completion of the reaction, it was cooled to room temperature and diluted with brine (500 mL) and ethyl acetate (EtOAc, 750 mL). The mixture was filtered to remove the dark brown solid and the solid portion was washed well with ethyl acetate. The organic layer was separated, washed with water (3 x 500 mL), subsequently dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated under reduced pressure. The crude product was washed with dichloromethane/hexane (1:1) to afford the target product 2-oxo-2,3-dihydro-1H-benzimidazole-5-boronic acid pinacol ester (10.9 g, 44% yield). Thin layer chromatography (TLC) Rf = 0.52 (silica gel plate, unfolding reagent: dichloromethane/methanol = 85:15); melting point 313-315 °C (decomposition); 1H NMR (300 MHz, DMSO-d6) δ 1.27 (s, 12H), 6.92 (d, J = 7.7 Hz, 1H), 7.17 (s, 1H), 7.28 (d, J = 7.7 Hz, 1H), 10.62 (s, 1H), 10.74 (s, 1H); APCI MS m/z 261 [C13H17BN2O3 + H]+; HPLC purity 98.3%, retention time (tR) = 18.3 min; Calculated values for elemental analysis (C13H17BN2O3): C, 57.07; H, 6.82; N. Measured values: C, 56.69; H, 6.44; N, 10.21. HPLC conditions: Waters Symmetry C18 column (4.6 mm × 250 mm); mobile phase: water/acetonitrile (95:5 to 0:100 gradient elution); flow rate 1.0 mL/min (25 min); detection wavelength 254 nm.
