In a 250ml double-necked flask, add treated Mg strips (2.15g, 90mmol), 2 iodine grains, and under nitrogen protection, evacuate three times. Under heating conditions, slowly add anhydrous THF solution of compound p-methylbromobenzene (compound 1, 60mmol) using a syringe. After the reaction is initiated, reflux is maintained, and the remaining solution is added. After the addition is complete, the reaction is refluxed for 5 hours to obtain Grignard reagent for p-bromotoluene (compound 2). After cooling to room temperature, the reaction apparatus is transferred to a low-temperature reactor, and the temperature is adjusted to -20℃. After 5 minutes, anhydrous THF solution of trimethyl borate (9.36g, 90mmol) is added using a syringe. After the addition is complete, the reaction is carried out at room temperature for 3 hours. Then, 100ml of 2mol/L HCl solution is added to initiate the hydrolysis reaction, and the reaction is detected by TLC. After the reaction was complete, THF was removed by rotary evaporation under reduced pressure. The aqueous phase was extracted three times with ethyl acetate. The extracted organic phases were combined and washed with water and saturated brine until neutral. The mixture was then dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation under reduced pressure. Recrystallization from anhydrous ethanol yielded 4.66 g of 4-Tolylboronic acid (compound 3), with a yield of 57%.
