Synthesis
Ethyl 3-pyridazinone-6-carboxylate (1.17 g, 6.96 mmol) was used as a raw material, which was dissolved in phosphoryl chloride (12 mL) and the reaction was heated at 100 °C for 2 hours. Upon completion of the reaction, the mixture was cooled to room temperature and subsequently concentrated under reduced pressure to about 3 mL. The concentrated residue was slowly poured into ice water and slowly neutralized with 10% aqueous sodium hydroxide solution under ice bath conditions. The neutralized mixture was extracted with ethyl acetate. The organic layer was washed with saturated aqueous sodium chloride solution and subsequently dried with anhydrous magnesium sulfate. The dried organic phase was evaporated under reduced pressure to give the crude product. The crude product was purified by rapid chromatography on silica gel (200-300 mesh, eluent ratio hexane: ethyl acetate = 3:1) to afford ethyl 6-chloropyridazine 3-carboxylate (892 mg, yield 68.7%) as a white solid. The melting point was measured to be 145.6-146.7 °C (literature values 154-155 °C [56]).
References
[1] European Journal of Medicinal Chemistry, 2017, vol. 137, p. 598 - 611
[2] Patent: CN106187910, 2016, A. Location in patent: Paragraph 0242; 0243
[3] Nippon Kagaku Zasshi, 1957, vol. 78, p. 577,579, 580
[4] Chem.Abstr., 1959, p. 5275
[5] Bulletin de la Societe Chimique de France, 1959, p. 1793,1796
