1,6-Naphthyridin-5-amine was synthesized as follows: 5-azido-1,6-diazaphthalene (3.2 g, 18.7 mmol) was dissolved in methanol (30 mL) and stirred at room temperature. Stannous chloride dihydrate (21 g, 93.6 mmol) and concentrated hydrochloric acid (10 mL) were sequentially added to the solution, followed by heating and refluxing the reaction mixture for 5 hours. Upon completion of the reaction, the mixture was cooled to room temperature and neutralized with saturated sodium bicarbonate solution to pH 7-8. The reaction mixture was filtered and the aqueous phase was extracted with ethyl acetate (5 x 30 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and the solvent was concentrated under reduced pressure to afford 1,6-naphthyridin-5-amine as a light yellow solid (2.20 g, 81% yield), which was used directly in the next step of the reaction. Mass spectrum (ESI MS): m/z 146 [M + H]+. 1H NMR (400 MHz, CDCl3) δ 8.91 (dd, J = 1.6, 4.8 Hz, 1H), 8.62 (d, J = 8.0 Hz, 1H), 8.00 (d, J = 6.0 Hz, 1H), 7.47 (dd, J = 4.8, 8.0 Hz, 1H). 7.09 (br, 2H), 6.98 (d, J = 6.0 Hz, 1H).
