Abstract
Recently reported syntheses of 3(5)-aminopyrazoles, 4-aminopyrazoles, and 1-aminopyrazoles as well as of diaminopyrazoles and their general pattern of reactivity towards mono- and bidentate electrophiles have been surveyed. Emphasis has also been laid on techniques for ascertaining the site selectivity in reactions with electrophiles, including single crystal X-ray structure analysis, 1 H- 15 N HMBC, and NOE intensity difference experiments as well as other modern 2D NMR techniques. Some thermally induced cycloadditions have also been treated.
Highlights
The chemistry of aminopyrazoles has been extensively investigated in the past.[1]
It has been reported that 5-substituted aminopyrazoles 62 were formed via gently heating βketoamides 60 with aryl or alkylhydrazines and Lawesson’s reagents (LR)
Reaction of arylhydrazononitrile with functionally substituted alkylhalides This synthesis has recently been developed initially by Goncalves et al.[58] who reported that mesoxalonitrile arylhydrazones 75a reacted with functionally substituted hydrazines in triethylamine solutions to yield 4-aminopyrazole-5-carbonitriles 77a
Summary
The chemistry of aminopyrazoles has been extensively investigated in the past.[1]. The considerable biological and medicinal activities of pyrazoles[2] and azolopyrazoles,[3] for which aminopyrazoles are preferred precursors, have stimulated these investigations. These topics to our knowledge have not been surveyed These are generally obtained from either reaction of hydrazines with α,β-unsaturated nitriles,14-16 3-oxoalkenonitriles and hydrazines[17,18,19,20] or reaction of hydrazonoyl halides with active methylenenitriles.[21] In addition, several other novel routes have been recently reported. Aminopyrazole itself was prepared via reacting acrylonitrile (4) with hydrazine hydrate and subsequent cyclization of 5 to yield 6 and dehydrogenation of the latter affording 7.22 Compound 7 was directly obtained from reaction 8 and hydrazine (Scheme 1).[23]. Treatment of with Bredereck’s reagent afforded that was hydrolysed in 2N HCl to yield The latter reacted with hydrazines in the presence of organic acids in THF to yield 30 (Scheme 7).[37]
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