[Synthesis]
General procedure for the synthesis of 4-hydroxy-1,5-naphthyridine (ZS96) from 2,2-dimethyl-5-((pyridin-3-ylamino)methylene)-1,3-dioxane-4,6-dione: ZS95 (100 mg, 0.403 mmol) was dissolved in diphenyl ether (3.0 mL) and refluxed for 50 min on a Bunsen burner. After completion of the reaction, the mixture was cooled to room temperature, the precipitate was collected by filtration and washed with hexane. The crude product was dried and purified by sublimation at 210 °C and 20 mbar to give white crystals ZS96 (40 mg, 68% yield).ZS96 sublimated slowly over 200 °C. IR (ATR, cm-1): 3012 (m), 2925 (s), 2855 (s), 2077 (w), 1975 (w), 1623 ( s), 1583 (m), 1559 (m), 1502 (s), 1461 (m), 1421 (m), 1328 (w), 1192 (w), 1137 (w), 1073 (w), 977 (w), 885 (w), 818 (w), 779 (w), 724 (w), 682 (w), 590 (w), 546 (w) , 481 (w).1H NMR (500 MHz, CDCl3 + d-TFA, δ): 9.15 (dd, J = 8.8, 1.2 Hz, 1H), 9.12-9.10 (m, 1H), 8.51 (d, J = 7.4 Hz, 1H), 8.41 (dd, J = 8.9, 5.4 Hz, 1H), 7.19 (d, J = 7.4 Hz, 1H). 13C NMR (125 MHz, CDCl3 + d-TFA, δ): 173.25, 147.30, 144.98, 142.03, 131.98, 131.43, 121.01, 116.06. HRMS: m/z 147.05496 [M+H]+, corresponds to molecular formula C8H6N2O (calculation error: -2.22 ppm). |