Synthesis of N-aminopyrazoles by Fe(II)-catalyzed rearrangement of 4-hydrazonomethyl-substituted isoxazoles

A novel effective method is reported for the preparation of 1-amino-1H-pyrazole-4-carboxylic acid derivatives by Fe(II)-catalyzed rearrangement of isoxazoles having (2,4-dinitrophenylhydrazono)methyl substituent at C4. The reaction proceeds smoothly for both E and Z isomers of 4-(hydrazonomethyl)iso...

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Bibliographic Details
Published in:Tetrahedron 2018-10, Vol.74 (43), p.6288-6298
Main Authors: Galenko, Ekaterina E., Ivanov, Viktor K., Novikov, Mikhail S., Zolotarev, Andrey A., Khlebnikov, Alexander F.
Format: Article
Language:English
Subjects:
Fe-catalysis
Hydrazone
Isoxazole
N-aminopyrazole
Rearrangement
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Summary:A novel effective method is reported for the preparation of 1-amino-1H-pyrazole-4-carboxylic acid derivatives by Fe(II)-catalyzed rearrangement of isoxazoles having (2,4-dinitrophenylhydrazono)methyl substituent at C4. The reaction proceeds smoothly for both E and Z isomers of 4-(hydrazonomethyl)isoxazoles, and this means it is not necessary to separate mixtures of E/Z-isomers of the hydrazones prepared by reaction of 5-methoxy/pirrolidino-4-carbonylisoxazoles and 2,4-dinitrophenylhydrazine. The rearrangement proceeds via the formation of an aziridine intermediate which can be isolated in certain cases. The 2-nitro group in the synthesized 1-[(2,4-dinitrophenyl)amino]-1H-pyrazole-4-carboxylic esters can be selectively reduced in two steps via acylation of the amino group followed by hydrogenation-deacylation using H2-Pd/C. [Display omitted]
ISSN:0040-4020
1464-5416
DOI:10.1016/j.tet.2018.09.015