Synthesis
A. Methyl 3,6-dichloropyridazine-4-carboxylate (2.00 g, 10.4 mmol) was dissolved in dioxane (9.0 mL) and 1M hydrochloric acid solution (10.4 mL) was added. The reaction mixture was stirred at 90°C for 20 hours. After completion of the reaction, the mixture was cooled to 0 °C and the precipitate was collected by filtration. The precipitate was washed with cold water followed by a small amount of pyridazine acid Z.1 to afford the target product 3-oxo-6-chloro-2,3-dihydropyridazine-4-carboxylic acid (955 mg, 53% yield). The product was confirmed by HPLC-MS analysis (MS (MH)+ = 173; retention time t Ret = 0.00min; analytical method: LCMSBAS1).
References
[1] Patent: WO2011/131741, 2011, A1. Location in patent: Page/Page column 62-63
[2] Patent: WO2011/144622, 2011, A1. Location in patent: Page/Page column 55
[3] Patent: US2012/94976, 2012, A1. Location in patent: Page/Page column 33-34
