a. A mixture of 2,3-diaminopyridine (5.0 g, 45.9 mmol), glycerol (21.1 g, 229 mmol), sodium 3-nitrobenzenesulfonate (20.6 g, 91.7 mmol), and sulfuric acid (20 mL) was added to water (30 mL), and the reaction was stirred for 16 hours at 135°C. Upon completion of the reaction, the mixture was cooled to room temperature and subsequently slowly poured into an ice-water mixture (150 g). After adjusting the pH of the mixture to neutral with base, it was extracted with ethyl acetate (3 x 100 mL). The organic layers were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography using petroleum ether/ethyl acetate (2:1, v/v) as eluent to afford 1,7-naphthyridin-8-amine as a yellow solid (2.6 g, 39% yield). eSI MS: m/z 146.1 [M + H]+.
