4- Amido-3-pyrazolin-5-ones

Synthesis of 4-amino-2-pyrazolin-5-ones is usually achieved by treatment of an a-amido-/3-aldehydo- or /9-ketoester with hydrazines according to the classical method for preparation of 2-pyrazolin-5-ones. Variants on this procedure consist of using an a-amidoester which has /9-substituents whose reaction is equivalent to that of a /9-carbonyl substituent. Such compounds are D-benzylpenicilloic acid a-methyl ester,1027 ethyl phenylpenaldate243 and the acetal of an a-amido-/9-formyl ester.59,243 Cornforth has isomerized 2-phenyl-4-hydrazino-methylidyneoxazolidone to 4-benzamido-2-pyrazolin-5-one. The same compound was obtained by treatment of 1-ethoxyvinyl-2-phenyl-oxazolidone with phenylhydrazine.319... 

Most 4-amido-3-pyrazolin-5-ones have been prepared either by acylation of secondary amines537 618,1471 (4-alkylimino-3-pyrazol-idinones) or by acylation of the primary amine1471 followed by alkylation.537 Shimidzu1297 has reported the replacement of a methyl group by a cyano group and conversion of this to a thiourea (eq. 198). 

Dihlmann371 has determined the Rt values of 4-amino- and 4-amido-3-pyrazolin-5-ones by using butanol-acetic acid-water as solvent and ferric chloride or p-dimethylaminobenzaldehyde as developer. 

TABLE XXIV. 3-Pyrazolin-5-ones. Imino, Amino, Amido, Azo, Aminoazo, and Hydrazido Substituents... 

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