Synthesis of 1,5-naphthyridine (4): To a round bottom flask was added 3-aminopyridine (1 g, 10.63 mmol), sodium m-nitrobenzenesulfonate (3.59 g, 15.95 mmol), glycerol (3.33 mL, 46.85 mmol), concentrated sulfuric acid (5.92 mL, 111.53 mmol) and water (3 mL). The reaction mixture was heated to 150 °C and stirred continuously for 2.5 hours. Upon completion of the reaction, it was cooled to room temperature and the pH was adjusted to 8 with 4 M sodium hydroxide solution, followed by extraction with ethyl acetate (5 x 30 mL). The organic phases were combined, washed with saturated saline, dried over anhydrous sodium sulfate and concentrated under reduced pressure. Purification by column chromatography (petroleum ether/ethyl acetate=1:1) afforded the target product 1,5-naphthyridine (622 mg, 45% yield) as a yellow solid. Melting point: 74~75°C (literature value 75°C). 1H NMR (400MHz, CDCl3): δ9.04-8.96 (m, 2H), 8.43 (d, J=8.4Hz, 2H), 7.66 (dd, J=8.4,4.1Hz, 2H).
