Reaction Steps
Stannane 3a (4.25 g., 9.68 mmol, 1.5 equiv.) and triflate 2 (1.80 g., 6.44 mmol, 1 equiv.) are suspended in 17 mL of DMF. Bis(triphenylphosphine)palladium dichloride (0.68 g., 0.969 mmol, 0.15 equiv.) and LiCl (0.82 g., 19.3 mmol, 3 equiv.) are added and the mixture is heated to 150° C. After 45 min., more bis(triphenylphospine)palladium dichloride (0.2 g., 0.285 mmol, 0.04 equiv.), more LiCl (0.4 g., 9.42 mmol, 1.46 equiv.), and more stannane 3a (0.8 g., 1.82 mmol, 0.28 equiv.) is added, and heating is continued for 2 hours. (The reaction generally turns from yellow-brown to black when complete.) The mixture is allowed to cool to room temperature, and 15 mL of aqueous saturated KF and 10 mL of ether are added. The mixture is stirred for 30 min., and then filtered through celite to remove the tin salts. The filter cake is washed with EtOAc and ether, and the combined filtrates are washed with water, followed by 3% aqueous ammonia solution and then brine. The organic phase is dried (MgSO4) and then concentrated in vacuo. Chromatography on silica gel using 25%, 50% then 75% methylene chloride/hexane affords 2-methoxy-3'-carboethoxy-[1,1'-biphenyl]-6-carboxaldehyde (4a) (1.72 g., 6.06 mmol, 94%) as a slightly yellow oil which crystallizes on standing: mp=67°-69° C.; UVmax (CHCl3) 242 nm (ε=15819), 324 nm (ε=3953); 1H NMR (300 MHz, CDCl3) δ9.70 (s, 1H, CHO), 8.09 (ddd, J=2, 2, 7 Hz, 1H, ArH), 7.99 (s, 1H, ArH), 7.62 (dd, J=2, 8 Hz, 1H, ArH), 7.49 (m, 3H, ArH), 7.19 (dd, J=2, 8 Hz, 1H, ArH), 4.37 (q, J=7 Hz, 2H, CO2CH2), 3.76 (s, 3H, OCH3), 1.34 (t, J=7 Hz, 3H, CO2CH2CH3); 13C NMR (75 MHz, CDCl3 ) δ191.93 (C=O), 166.31 (C=O), 156.98, 135.27, 133.73, 133.57, 131.92, 130.42, 129.17, 129.09, 128.09,119.30, 115.95, 61.14, 56.06, 14.32; IR (film) 2980, 2940, 2838, 1718, 1694, 1468, 1294, 1260, 1234, 1110, 794 cm- 1 ; MS (DCI) m/e 285 (MH+), 239 (M--C2H5O). Anal. Calcd for C17H16O4.0.25 H2O: C, 70.69; H, 5.76. Found: C, 70.64; H, 5.59.
