Synthesis
General procedure for the synthesis of 3-methoxy-2-formylphenylboronic acid from triisopropyl borate: tert-butyllithium solution (9.0 mL, 1.7 M in pentane) was added dropwise to a stirring solution of 2-(2-methoxyphenyl)-1,3-dimethylimidazolidinium (2.0 g, 9.8 mmol) in tetrahydrofuran (5 mL) under nitrogen protection, and the reaction temperature was maintained at -10 °C, followed by continued stirring at 0-5 °C for 2 hours. Upon completion of the reaction, the mixture was cooled to -50 °C and triisopropyl borate (3.5 mL, 15 mmol) was slowly added. The reaction solution was gradually warmed to 0 °C over 3 hours. 2N hydrochloric acid (120 mL) was added at 0 °C and stirred for 30 min. The reaction mixture was returned to room temperature and diluted with ethyl acetate. The organic phase was washed sequentially with 1N hydrochloric acid (2×) and saturated saline, dried over anhydrous sodium sulfate and concentrated to give a yellow crude product. The crude product was purified by reversed-phase high-performance liquid chromatography, and after removal of the solvent, 1.3 g of 3-methoxy-2-formylphenylboronic acid in the form of a light yellow solid was obtained in 75% yield.ESI-MS m/e 177 (MH+).
