A solution of 5-3 (1.92 g, 5.91 mmol) in DMF (15 mL) was added with cesium carbonate (2.41 g, 7.39 mmol). The reaction mixture was heated at 50° C. for 60 min and added with 5-bromo-2-nitropyridine (24-1, 1.80 g). The reaction mixture was heated at 50° C. for 4.0 h. The solution was quenched with water (40 mL) and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure and the residue was purified by column chromatography (NH silica gel, hexane/ethyl acetate=3/1-1/3) to give 24 (1.76 g) in 67% yield: 1H NMR (500 MHz, DMSO-d6) δ 8.78 (d, 2 H), 8.42 (d, 1 H), 8.33 (d, 1 H), 7.96 (d, 2 H), 7.63 (m, 1 H), 7.21 (s, 1 H), 7.01 (s, 2 H), 2.08 (s, 6 H), ESI-MS=m/z 447.5 (M+H)+.
