Synthesis
First, 5.07 g of magnesium shavings and 80 mL of anhydrous tetrahydrofuran were added to a 500 mL three-necked flask that had been displaced by argon. A small amount of iodine crystals was added to activate the magnesium. Subsequently, 100 mL of anhydrous tetrahydrofuran solution containing 45.7 g of 4-bromo-1-benzyloxybenzene (obtained from synthesis step 10-a) was slowly added dropwise to the above mixture under stirring conditions. After the dropwise addition was completed, the reaction mixture was heated and refluxed and stirred for 30 minutes and subsequently cooled to -40°C. At this temperature, 60 mL of anhydrous tetrahydrofuran solution containing 21.66 g of trimethylborate was slowly added dropwise. After the dropwise addition was completed, the reaction mixture was allowed to gradually warm up to room temperature and reflux stirring was continued for 30 minutes. After that, the reaction mixture was cooled to 0 °C again, 200 mL of 10% aqueous sulfuric acid solution was added and stirred for 1 hour. Upon completion of the reaction, toluene was added to the mixture to extract the organic layer. The organic layer was washed with saturated sodium chloride solution and dried with anhydrous sodium sulfate. The solvent was removed by distillation under reduced pressure and the crude product obtained was recrystallized from toluene to give 36.5 g (yield: 92.1%) of the title compound 4-benzyloxyphenylboronic acid.
References
[1] Patent: US6388146, 2002, B1. Location in patent: Page column 35
[2] Angewandte Chemie - International Edition, 2004, vol. 43, # 39, p. 5235 - 5238
[3] Organic and Biomolecular Chemistry, 2010, vol. 8, # 21, p. 4831 - 4833
[4] European Journal of Organic Chemistry, 2012, # 7, p. 1448 - 1454
[5] Journal of the American Chemical Society, 2011, vol. 133, # 39, p. 15674 - 15685
