Synthesis of 3-substituted and 3,4-disubstituted pyrazolin-5-ones

The synthesis of 3-substituted and 3,4-disubstituted pyrazolin-5-ones from acylated ethyl acetoacetates and diethyl malonates is described. The reaction of acylated ethyl acetoacetates and diethyl acetylmalonate with hydrazine (98%) gave 3-substituted pyrazolin-5-ones and malonyldihydrazide, respectively, following a deacetylation–condensation sequence. The reaction of ethyl 2-acetyl-3-hydroxy-2-butenoate and diethyl 2-(1-hydroxyethylidene)malonate with hydrazine monohydrochloride yielded ethyl 3,5-dimethyl-1H-pyrazole-4-carboxylate and 4-ethoxycarbonyl-3-methylpyrazolin-5-one, respectively, following a dehydration–cyclocondensation sequence, in high yields.