Under nitrogen protection, o-bromophenylboronic acid trimer (cas:1229227-01-3) was added to anhydrous tetrahydrofuran (600 mL). The mixture was transferred to a 2 L three-neck flask and N,N-dimethylformamide (87.7 g, 1.2 mol) was added. Subsequently, the reaction system was cooled to -70 °C to -80 °C and 2.5 M n-butyllithium hexane solution (520 mL, 1.3 mol) was slowly added dropwise with controlled titration rate to keep the reaction temperature from exceeding -70 °C. Stirring was continued at this temperature for 1-3 h. The reaction mixture was then allowed to warm up to room temperature naturally, and stirring was continued for another 3-5 h. The reaction was monitored by TLC. The progress of the reaction was monitored by TLC and after confirming the completion of the reaction, the system was cooled to 0°C, 15% aqueous hydrochloric acid was added to quench the reaction, and the pH was adjusted to 1-2. Stirring was continued at room temperature for 3-5 h to ensure complete hydrolysis of the trimer. Subsequently, the reaction solution was distilled to remove the organic solvent and filtered to obtain the solid product. Finally, purification by recrystallization from toluene gave 93.0 g of light gray solid 2-formylphenylboronic acid with 99.0% HPLC purity and 62% yield.
