Reaction Steps
Diester 6a (0.968 g., 2.95 mmol, 1 equiv.) is dissolved under argon in 9.8 mL of 1,2-dichloroethane. Dimethylboron bromide (1.16 mL, 11.9 mmol, 4.03 equiv. ) is added, the flask is sealed and the mixture allowed to stir for 21 hours at ambient temperature. Another 1.16 mL of dimethylboron bromide is added, and the mixture stirred, sealed under argon, for 3 days. The flask is cooled to 0° C., and 20 mL of saturated NaHCO3 is added with caution. The mixture is poured into 1N HCl, and extracted thrice with EtOAc. The combined extracts are washed with brine, dried (MgSO4), and evaporated. Chromatography using 10% EtOAc/hexane yields 2-hydroxy-3'-carboethoxy-(1,1'-biphenyl)-6-carboxylic acid, ethyl ester (7a) (0.659 g., 2.10 mmol, 71%) as a yellow oil: UVmax (CHCl3) 242 nm (ε=10155), 296 nm (ε=4591 ); 1H NMR (300 MHz, CDCl3) δ 8.09 (dd, J=2, 8 Hz, 1H, ArH), 7.96 (dd, J=2, 2 Hz, 1H, ArH), 7.57-7.45 (m, 3H, ArH), 7.33 (dd, J=8, 8 Hz, 1H, ArH), 7.14 (dd, J=2, 8 Hz, 1H, ArH), 4.98 (br, 1H, OH), 4.35 (q, J=7 Hz, 2H, CO2CH2), 3.99 (q, J=7 Hz, 2H, CO2CH2), 1.36 (t, J=7 Hz, 3H, CH2CH3), 0.95 (t, J=7 Hz, 3H, CH2CH3); 13C NMR (75 MHz, CDCl3) δ 167.18 (C=O), 166.13 (C=O), 153.18, 135.46, 134.13, 131.76, 131.25, 130.67, 129.42, 129.16, 129.03, 127.32, 122.42, 119.19, 61.21, 60.85, 14.30, 13.70; IR (film) 3406, 2982, 1718, 1296, 1236, 758 cm-1 ; MS (DCI) m/e 315 (MH+), 269 (M--C2H5O). HRMS Calcd for C18H18O5Na: 337.1052. Found: 337.1044.
