After degassing into 1,4-dioxane (0.1 M) under nitrogen atmosphere, m-bromobenzoic acid (1 eq.), pinacol ester of bisboronic acid (1.5 eq.) and potassium acetate (4.4 eq.) were added. The mixture was degassed again followed by the addition of PdCl2 (dppf) (5%). The resulting solution was heated to 110°C for overnight reaction. Upon completion of the reaction, the solvent was removed under vacuum to give a dark colloidal residue. This residue was dissolved in ethyl acetate and water to separate the organic layer. The aqueous phase was further extracted with ethyl acetate (2×). The combined organic layers were washed with 2M HCl, dried over MgSO4 and concentrated in vacuum to give a dark brown product. To purify the product, column chromatography (petroleum ether/ethyl acetate elution) was used. The 3-carboxyphenylboronic acid pinacol ester prepared by Suzuki coupling reaction was a light brown solid in 89% yield.1H NMR (400 MHz, CDCl3) δ 8.57 (s, 1H), 8.19 (ddd, J = 21.9, 1.18, 10.1 Hz, 1H), 8.09-7.98 (m, 1H), 7.57-7.38 (m, 1H), 1.37 (m, 1H), 7.57-7.38 (m, 1H). 1H), 1.37 (s, 12H).13C NMR (101 MHz, CDCl3) δ 171.66, 139.98, 136.60, 132.84, 128.71, 127.93, 84.21, 24.89.LCMS (ESI) m/z 249.2 [M + H]+.
