In a 1 L round bottom flask, 1-bromo-2,5-dimethoxybenzene (50 g, 230 mmol) was dissolved in tetrahydrofuran (400 ml). After cooling the reaction mixture to -78°C, n-butyllithium (167 ml, 280 mmol) was added slowly and dropwise. The reaction temperature was maintained at -78°C with continuous stirring for 2 hours. Subsequently, trimethyl borate (36 ml, 320 mmol) was added. The reaction mixture was gradually warmed to room temperature and stirred overnight. Upon completion of the reaction, acidification was carried out by slow dropwise addition of 2N HCl solution. Extraction was carried out with deionized water and ethyl acetate and the organic layer was separated and dried over anhydrous magnesium sulfate. The dried organic phase was concentrated in vacuum to give the crude product. Finally, the purified 2,5-dimethoxyphenylboronic acid (20.8 g, 50% yield) was obtained by recrystallization from a solvent mixture of heptane and toluene.
