Synthesis
A. 6-Hydroxypyridazine-3-carboxylic acid (5.00 g, 31.6 mmol) was dissolved in methanol and thionyl chloride (0.36 mL, 0.59 g, 4.94 mmol) was added slowly. The reaction mixture was heated to reflux at 80 °C for 16 hours. After completion of the reaction, it was cooled to room temperature and the product crystallized. The crystals were collected by filtration and washed with cold methanol. The mother liquor was combined, concentrated and crystallized again to give methyl 6-oxo-1,6-dihydropyridazine-3-carboxylate in a total yield of 4.954 g (100% yield).
References
[1] Patent: WO2006/34440, 2006, A2. Location in patent: Page/Page column 43
[2] Patent: US2011/257173, 2011, A1. Location in patent: Page/Page column 19; 21
[3] Patent: US2011/105509, 2011, A1. Location in patent: Page/Page column 30; 31; 32
[4] Patent: US2016/376283, 2016, A1. Location in patent: Paragraph 1225; 1227
[5] Patent: WO2004/89939, 2004, A1. Location in patent: Page 40-41
