4-Amino-3-pyrazolin-5-ones synthesis

A few other methods of preparing 4-amino-3-pyrazolin-5-ones have been reported but none has been used extensively. Methylation of the N-2 of 2-pyrazolin-5-ones, the classical 3-pyrazolin-5-one synthesis, has been reported only once.536 Emerson and co-workers426 have hydrolyzed iminotoluquinone substituted by antipyrine to give the... 

Pyrazolines substituted at position 4 or 5 with hydroxy or amino groups readily eliminate a molecule of water or amine yielding pyrazoles. The 4-substituted derivatives are relatively more stable than the 5-substituted ones, because for the last group the lone pair at N-1 assists the elimination (407) -> (408) -> (409). The sulfonyl group at position 1 is also easily eliminated and this property is taken advantage of in Dorn s elegant synthesis of 3-aminopyrazole (Section 4.04.3.3.1). 

Several methods for the synthesis of 5-imino-2-pyrazolines depend upon the amination of a pyrazole ring. 5-Chloropyrazoles react with aniline to give the corresponding 5-amino compound.826,1002 The chloropyrazoles can be prepared and amination accomplished in one... 

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... 

Derivatives of Y-hydroxyacetylenic acids, which are useful intermediates in the synthesis of butenolides, are prepared from propiolic acid and ester anions. Alk-2-ynoic and 2-allenic esters are prepared by the oxidation of 3,4-disubstituted 2-pyrazolin-5-ones with lead(iv) tetra-acetate in the absence and presence of BF3 respectively. Py-Unsaturated esters are produced in high yield by the palladium-catalysed decarboxylation-carbonylation of allylic carbonates. Magnesium enolates of esters react with nitriles to give (Z)-3-amino-alk-2-enoates. Enol lactones react with diethyl methoxycarbonylmethylphosphonate to give cyclic unsaturated keto-esters (Scheme 66). ... 

SCHEME 4 Synthesis of N-amino-3-chloro-4-(3,5-diaryl-2-pyrazoline-2-yl-)-azetidine-2-ones. 

---