Synthesis
General procedure for the synthesis of ethyl 3,5-dimethyl-1H-4-pyrazolecarboxylate from ethyl bisacetoacetate: To a solution of ethyl bisacetoacetate (4.6 g, 26.7 mmol) in ethanol (50 mL) was added hydrazine hydrochloride (1.8 g, 26.7 mmol). The reaction mixture was heated to reflux and kept for 2 hours. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. The resulting residue was washed with ethyl acetate to afford ethyl 3,5-dimethyl-1H-4-pyrazolecarboxylate as a colorless solid (3.1 g, 69% yield), which was pure enough to be used directly in the subsequent reaction.
References
[1] Patent: WO2014/49133, 2014, A1. Location in patent: Page/Page column 44
[2] Justus Liebigs Annalen der Chemie, 1894, vol. 279, p. 237
[3] Archiv der Pharmazie (Weinheim, Germany), 1926, p. 346
[4] Zeitschrift fur Physikalische Chemie, 2013, vol. 227, # 6-7, p. 841 - 856
[5] Journal of Organic Chemistry, 2018, vol. 83, # 12, p. 6454 - 6465
