The general procedure for the synthesis of methyl cinnoline-6-carboxylate from methyl 4-chlorocinnoline-6-carboxylate was as follows: to a solution of methyl 4-chlorocinnoline-6-carboxylate (192 mg, 0.863 mmol) in dimethylsulfoxide (30 mL) was added sodium formate (70 mg, 1.04 mmol), tetrakis(triphenylphosphine)palladium(0) (198 mg, 0.702 mmol) and N,N-diisopropylethylamine (0.21 mL, 1.21 mmol). The reaction mixture was stirred at 90 °C for 1.5 hours. After completion of the reaction, it was cooled to room temperature, water was added and extracted with ethyl acetate. The organic layer was washed sequentially with water and brine, dried over anhydrous sodium sulfate and evaporated to remove the solvent. The resulting solid was washed with ether and subsequently purified by silica gel column chromatography (eluent: hexane-ethyl acetate) to afford methyl cinnoline-6-carboxylate (16 mg, 0.089 mmol, 10% yield). The product was characterized by 1H-NMR (CDCl3) with the following chemical shift δ (ppm): 4.03 (3H, s), 7.97 (1H, dd, J = 0.8, 6.0 Hz), 8.42 (1H, J = 0.8, 8.0 Hz), 8.59-8.63 (2H, m), and 9.43 (1H, dd, J = 0.8, 6.0 Hz).
