Synthesis
Preparation of Intermediate I-04a: Ethyl 1-methyl-3-n-propyl-pyrazole-5-carboxylate (11 g, 56.12 mmol) was dissolved in 6 M hydrochloric acid solution (121 mL) and heated to 100°C for overnight reaction. Upon completion of the reaction, the mixture was concentrated under vacuum and subsequently extracted with ethyl acetate (EA) and the organic layer was washed with water. Finally, the organic layer was concentrated in vacuum to afford the target product 1-methyl-3-propyl-1H-pyrazole-5-carboxylic acid (I-04a) (9.4 g, 98% yield).ESI-MS (M + 1): 169; calculated value C8H12N2O2: 168.1.
References
[1] Patent: WO2014/131855, 2014, A1. Location in patent: Page/Page column 80
[2] Patent: WO2016/20307, 2016, A1. Location in patent: Page/Page column 50
[3] Patent: US2008/194529, 2008, A1. Location in patent: Page/Page column 56-57
[4] Patent: WO2015/114647, 2015, A1. Location in patent: Page/Page column 46; 47
[5] Patent: US5250534, 1993, A
