2H-Pyrazol-3-ylamines as precursors for the synthesis of polyfunctionally substituted pyrazolo[1,5-a]pyrimidines

Abstract

Substituted aminopyrazoles (5a-d) were synthesized and reacted with bidentate electrophiles to afford pyrazolo [1,5-a]pyrimidines. The regioorientation of reagents has been determined by ( 15 N, 1 H) HMBC measurements as well as an X-ray crystal structure determination.

A facile environment-friendly one-pot two-step regioselective synthetic strategy for 3,7-diarylpyrazolo[1,5-a]pyrimidines related to zaleplon and 3,6-diarylpyrazolo[1,5-a]pyrimidine-7-amines assisted by KHSO $$_{4}$$ 4 in aqueous media

“…The structure of 7a was confirmed on the basis of the comparison of its spectral and analytical data with those reported [45] for 7-amino-3, 6-diphenylpyrazolo[1,5-a]pyrimidine. The C 2 -H protons in 7a-7c, 7e, 7f, 7h, 7i appeared as singlets at around 8.40 ppm, while those in 7d and 7g got mixed with C 5 -H proton signals and appeared as multiplet in the range 8.33-8.42 ppm and 8.35-8.37 ppm, respectively.…”

“…While the previously reported protocols [28,34,45] involve longer reaction time (8 h to overnight), use of toxic solvent (pyridine), and difficult work-up procedure, the synthetic methodology presented herein has the advantage of shorter reaction time (1-4 h for compounds 5 and 2-4.5 h for compounds 7), aqueous reaction media, and ease of isolation of practically pure precipitated product. In addition, the reaction is a one-pot two-step protocol.…”

Green Synthesis, Printing Performance, and Antibacterial Activity of Disperse Dyes Incorporating Arylazopyrazolopyrimidines

“…The structures of synthesized compounds were confirmed by a variety of spectroscopic techniques, including 1 H and 13 C NMR, mass spectroscopy, IR, and elemental analysis. Elnagdi et al 6,18–20 reported that the reaction of enaminoni-trile 1 with aromatic diazonium salts affords arylhydrazones 2 , which are readily converted into arylazoaminopyrazoles 3 . Our work wanted to determine if 4-arylazo-2H-pyr- azol-3-ylamine derivatives could be used as precursors to arylazo-pyrazolo[1,5-a]pyrimidin-7-ylamines (and pyrimi-din-7-ones).…”

“…15–17 Arylazopyrazolo[1,5-a]pyrimidines were prepared by condensing aminoarylazopyrazoles with β-bifunctional reagents using methodologies initially established in our laboratories. 18–20…”

Synthesis of spiro(cyclohexa-diene-pyrazolo[1,5-a]pyrimidine-4-ylidene)-malononitrile derivatives

“…The stability of compound 6 in this form supports the exclusion of any other expected isomeric forms. Furthermore, Elnagdi et al 38 reported recently, the reaction of 4-(arylazo)-5-ethyl-1H-pyrazol-3-ylamine with benzylidenemalononitrile in pyridine to afford pyrazolo[1,5-a]pyrimidines via the reaction of exocyclic amino function followed by cyclisation. The regioorientation of the reagents has been determined by 15 N, 1 H/HMBC measurements as well as an X-ray crystal structure.…”