Synthesis
A solution was prepared by dissolving styrene (2.083 g, 20 mmol) and trimethylsilane (1.484 g, 20 mmol) in hexane (6 mL) at -80 °C. The solution was slowly added dropwise to a solution of BBr3 (5.010 g, 20 mmol) in hexane (6 mL). The reaction system was controlled to gradually warm up to room temperature over a period of 2 hours. Upon completion of the reaction, the solvent was removed by evaporation under vacuum. Water (4 mL) was added to the residue, at which point the release of gaseous HBr and an increase in the temperature of the system was observed. After cooling the system to room temperature, the solvent was again evaporated under vacuum. The resulting white precipitate was purified by recrystallization from a minimal amount of water to give 2.73 g (69% yield) of 2-phenylethylboronic acid. Methanol (0.81 mL, 20 mmol) was added to a suspension of 2-phenylethylboronic acid (1.5 g, 10 mmol) in pentane (6 mL) and the reaction was stirred for 20 min at room temperature. MgSO4 was then added and stirring was continued for 10 minutes before the organic phase was separated. Methanol (0.81 mL, 20 mmol) was added again to the aqueous phase and stirred at room temperature for 20 min before adding MgSO4 and stirring for 10 min to separate the organic phase. All organic phase extracts were combined, concentrated and the residue was purified by vacuum distillation to give 1.19 g (67% yield) of a colorless liquid dimethyl 2-phenylborate.
References
[1] Tetrahedron Letters, 2003, vol. 44, # 42, p. 7789 - 7792
[2] Tetrahedron Letters, 2011, vol. 52, # 41, p. 5259 - 5263
[3] Journal of Organic Chemistry, 2008, vol. 73, # 5, p. 1898 - 1905
[4] Patent: WO2008/103016, 2008, A1. Location in patent: Page/Page column 7
