4- Amino-1,2-dihydropyrazol-3-ones, reaction

From ethyl 2-cyanoacetate. 5-Aminopyrazol-3-ones can be conveniently prepared from /7-keto esters with hydrazines. Thus, heating ethyl 2-cyanoacetate 142 with (4-ferf-butylphenyl)hydrazine 143 in ethanolic sodium ethoxide afforded 5-amino-2-(4-ferf-butylphenyl)-2,4-dihydropyrazol-3-one 144 (01JMC3730) (Scheme 33). The reaction that takes place under acidic conditions, between ethyl 2-cyanoacetate 142 and 2-hydrazino-6-oxopyrimidine-5-carbonitrile 145 in boiling acetic... 

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