The general procedure for the synthesis of 2,4,6-trimethylphenylboronic acid from 2-bromo-1,3,5-trimethylbenzene was as follows: magnesium chips (60.27 mmol) were added to a dry three-necked round-bottomed flask along with anhydrous tetrahydrofuran (30 mL), and the suspension was stirred to form a suspension. Bromoisopropene (13.07 mmol) was slowly added and heated to initiate the formation of Grignard's reagent. Subsequently, 2-bromo-1,3,5-trimethylbenzene (32.02 mmol) was dissolved in anhydrous tetrahydrofuran (30 mL) and slowly added dropwise to the reaction system through a constant pressure dropping funnel. The reaction mixture was heated to reflux for 4.5 hours. Upon completion, the reaction system was cooled to -78 °C. Triethyl borate (111.66 mmol) was added dropwise over 15 minutes. After the dropwise addition was completed, the reaction system was allowed to slowly warm up to room temperature and stirring was continued for 5 hours. Subsequently, the reaction mixture was cooled to 0 °C, the reaction was quenched with 1 M hydrochloric acid solution and stirred for 2 hours. The reaction mixture was extracted three times with ether and the organic phases were combined. The organic phase was washed with saturated brine and dried over anhydrous sodium sulfate. After drying, the desiccant was removed by filtration and the filtrate was concentrated under reduced pressure to give the crude product. The crude product was recrystallized in benzene to give pure 2,4,6-trimethylphenylboronic acid (26.10 mmol, 58% yield). The product was characterized by 1H-NMR (400 MHz, CDCl3) and 13C-NMR (100 MHz, CDCl3) with the following data: 1H-NMR δ= 6.82 (s, 2H), 4.73 (brs, 2H), 2.33 (s, 6H), 2.26 (s, 3H); 13C-NMR δ= 139.64, 138.66, 127.99, 127.26, 22.89, 22.03, 21.12.
