General procedure for the synthesis of diethyl [2,2'-bipyridine]-5,5'-dicarboxylate from ethanol and 2,2'-bipyridine-5,5'-dicarboxylic acid: 2,2'-bipyridine-5,5'-dicarboxylic acid (200 mg, 0.82 mmol) and anhydrous ethanol (13 mL) were added to a dry flask with stirring under an ice bath. Thionyl chloride (1.3 mL) was slowly added dropwise, followed by installation of a reflux condenser and heating to reflux. After 24 hours of reaction, the reaction mixture was cooled in an ice bath and saturated sodium carbonate solution (20 mL) was added dropwise to quench the reaction. The aqueous phase was extracted with dichloromethane (4 x 20 mL), the organic phases were combined and dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: 1:1 dichloromethane/hexane solvent mixture of 3% acetone) to afford diethyl [2,2'-bipyridyl]-5,5'-dicarboxylate (190 mg, 77% yield) as a white solid.1H NMR (500 MHz, CDCl3) δ 9.32 (dd, J = 0.5, 2.0 Hz, 1H), 8.59 (dd, J = 0.5, 8.5 Hz, 1H), 8.46 (dd, J = 2.0, 8.5 Hz, 1H), 4.47 (q, J = 7.5 Hz, 2H), 1.46 (t, J = 7.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 165.2, 158.3, 150.6, 138.1, 126.6, 121.3, 61.6, 14.3; HRMS (ESI) m/z 301.1193 [C16H17N2O4 (M + H)+ calculated value 301.1183].
