Under nitrogen protection, 8.0 g (0.33 mol) of magnesium metal and a few iodine crystals were added to the reaction flask. In a dropping funnel, 56.9 g (0.36 mol) of 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, 48.3 g (0.3 mol) of 1-bromo-1-cyclohexene and 300 ml of anhydrous tetrahydrofuran were mixed well. The temperature of the reaction system was raised to 40-45 °C and the first 25 ml of the mixed solution was added slowly dropwise, observing the iodine-induced color change as a sign of the start of the reaction. The reaction temperature was maintained at 40-55 °C and the dropwise addition of the remaining mixed solution was completed. Subsequently, the reaction was gradually heated to reflux and continued for 2-3 h. The reaction was monitored by GC until the disappearance of the raw material. The reaction solution was cooled to 0-10 °C and the reaction was quenched by slow addition of saturated NH4Cl solution and pH was adjusted to 5-6. The organic layer was separated and the aqueous layer was extracted with 150 ml of methyl tertiary butyl ether (MTBE). The organic layers were combined, washed with saturated brine and concentrated under reduced pressure to remove the solvent. Finally, distilled under high vacuum, collected 80-83 ℃ fraction, obtained colorless transparent liquid cyclohexene-1-ylboronic acid 50.5 g, yield 81%.
