The general procedure for the synthesis of 2-furanboronic acid from 2-(furan-2-yl)-6-methyl-1,3,6,2-dioxaborolane-4,8-dione was as follows: a solution of MIDA borate (5 mmol) in THF (50 mL) was added to a 100 mL flask fitted with a stir bar under an ambient atmosphere followed by the addition of an aqueous 1.0 M NaOH solution (15 mL ). The reaction mixture was stirred vigorously for 20 minutes. Upon completion, the mixture was transferred to a partition funnel and diluted with ether (50 mL) and 0.5 M pH 7 sodium phosphate buffer (50 mL). The phases were separated after sufficient shaking. The aqueous phase was extracted with a solvent mixture of THF/ether (1:1, 2 x 25 mL). The organic phases were combined, dried with anhydrous MgSO4, filtered and concentrated in vacuum. The residual solvent was co-evaporated with acetonitrile and the resulting solid was dried under vacuum at about 1 Torr for 30 min. The resulting boric acid was analyzed by 1H-NMR to be >95% pure and was immediately used in the subsequent cross coupling reaction. Specific examples are as follows: 2-furanboronic acid (0.531 g, 95% yield) was obtained as an off-white solid using MIDA borate (1.127 g, 5.002 mmol) following the general procedure described above.TLC (unfolding reagent: ethyl acetate) Rf = 0.46, stained with potassium permanganate to develop color.1H-NMR (500 MHz, DMSO-d6:D2O 1H-NMR (500 MHz, DMSO-d6:D2O 95:5, with TMS) δ 7.81 (dd, J = 1.5, 5.5 Hz, 1H), 7.07 (dd, J = 3.0, 0.5 Hz, 1H), 6.48 (dd, J = 3.5, 2.0 Hz, 1H). 13C-NMR (125 MHz, DMSO-d6:D2O 95:5, with TMS) δ 146.4, 121.5, 110.3. 121.5, 110.3. HRMS (EI+) calculated value C4H3O3B [M]+: 112.0332, measured value: 112.0332.
