To a 250-mL round-bottomed flask, magnesium powder (0.72 g, 0.03 mol), 4-propylbromobenzene (2 g, 0.01 mol), tributyl borate
ester (4 g, 0.02 mol), 20 mL of tetrahydrofuran dried over molecular sieves and fitted with a reflux condenser tube. In an ultrasonic cleaner heating
to 40 C and then subjected to ultrasonic radiation, and the reaction was completed after 1 hour. Add 5 mL of 2 mol-L-1 hydrochloric acid and stir for a few moments to separate the organic
layer. The aqueous layer was extracted with ethyl acetate (10 mL x 2), several layers were combined and washed with water to neutral, dried and the solvent was removed to give
to the crude product. Recrystallization was carried out with ethanol:water = 2:1, and after drying under reduced pressure 1.11 g of solid powder was obtained in 68% yield.
