Synthesis
To a 200 mL round-bottomed flask equipped with a magnetic stirrer was sequentially added [1,1'-bis(diphenylphosphino)ferrocene]palladium(II) dichloride (0.799 g, 1.09 mmol), 4,4,4',4',5,5,5',5'-octamethyl-2,2'-bis(1,3,2-dioxaborolane) (bis(boronic acid pinacol ester), 6.65 g 26.2 mmol) and potassium acetate (4.28 g, 43.7 mmol). 1,4-dioxane (100 mL) was added to dissolve the above solid mixture. The flask was sealed, evacuated and displaced three times with nitrogen to exclude oxygen. Methyl 2-(4-bromophenyl)acetate (5.00 g, 21.8 mmol) was then added. The reaction mixture was heated to 70 °C and kept stirring for 6 hours. After completion of the reaction, it was cooled to room temperature and the reaction solution was poured into saturated brine to separate the organic and aqueous phases. The aqueous phase was extracted with ethyl acetate (3 x 125 mL), the organic phases were combined and dried with anhydrous magnesium sulfate. The desiccant was removed by filtration and the filtrate was concentrated under reduced pressure. The crude product was purified by fast column chromatography with an eluent gradient of 0-30% ethyl acetate/hexane to afford methyl 4-boronic acid pinacol ester phenylacetate as a colorless, clear liquid (4.93 g, 70% yield). The product was confirmed by NMR hydrogen spectrum (1H NMR, 400 MHz, DMSO-d6): δ 7.68-7.58 (m, 2H), 7.35-7.23 (m, 2H), 3.71 (s, 2H), 3.61 (s, 3H), 1.29 (s, 12H); NMR carbon spectrum (13C NMR, 101 MHz, DMSO-d6) δ 171.29, 137.72, 134.45, 128.86, 83.56, 82.79, 51.68, 40.23, 24.62; mass spectrum (EIMS) m/z 276 ([M]+).
References
[1] Patent: WO2006/46593, 2006, A1. Location in patent: Page/Page column 180-181
[2] Patent: WO2006/109633, 2006, A1. Location in patent: Page/Page column 155-156
[3] Chemical Communications, 2015, vol. 51, # 77, p. 14505 - 14508
[4] Journal of Organic Chemistry, 2006, vol. 71, # 15, p. 5594 - 5598
[5] Angewandte Chemie - International Edition, 2014, vol. 53, # 45, p. 12077 - 12080
