Synthesis of pyrazolyl-2-pyrazolines by treatment of 3-(3-aryl-3- oxopropenyl)chromen-4-ones with hydrazine and their oxidation to bis(pyrazoles)

A. Lévai, Artur M S Silva, Diana C G A Pinto, José A S Cavaleiro, Ibon Alkorta, José Elguero, J. Jekó́

Research output: Contribution to journalArticle

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Abstract

The synthesis of several 1-acetyl-3-aryl-5-[3-(2-hydroxyphenyl)pyrazol-4- yl]-2-pyrazolines 3a-3h has been accomplished by treatment of the 3-(3-aryl-3-oxopropenyl)chromen-4-ones 1a-h with hydrazine hydrate in hot acetic acid. The 1-acetyl-3-aryl-5-(3-chromonyl)-2-pyrazolines 2a-2f were also obtained as by-products. Oxidation of the 1-acetyl-4-pyrazolyl-2-pyrazolines 3a-3f with DDQ gave the 3(5)-aryl-5(3)-[3-(2-hydroxyphenyl)pyrazol-4-yl] pyrazoles 5a-5f. The oxidation of the 2-pyrazoline rings was accompanied by N-deacylation. The reaction mechanisms of both transformations are discussed, the first one being supported by experimental results. The structures of all new derivatives were established by NMR and the evidence of prototropic tautomerism is carefully discussed. Theoretical calculations of energies and of the 1H and 13C NMR chemical shifts of the possible tautomeric forms of 5(3)-[3-(2-hydroxyphenyl)pyrazol-4-yl]-3(5)-(4-methoxyphenyl)pyrazole (5c), by B3LYP and GIAO, showed that compounds of this type probably exist as mixtures of two tautomers.

Original languageEnglish
Pages (from-to)4672-4679
Number of pages8
JournalEuropean Journal of Organic Chemistry
Issue number22
DOIs
Publication statusPublished - Nov 12 2004

Fingerprint

hydrazine
Pyrazoles
Acetic Acid
Nuclear magnetic resonance
Oxidation
Chemical shift
Byproducts
Derivatives
Proton Magnetic Resonance Spectroscopy
3-pyrazolyl 2-pyrazoline
pyrazole
Carbon-13 Magnetic Resonance Spectroscopy

Keywords

  • 4-Pyrazolyl-2- pyrazolines
  • B3LYP
  • Bispyrazoles
  • Chromones
  • GIAO
  • NMR spectroscopy

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

Synthesis of pyrazolyl-2-pyrazolines by treatment of 3-(3-aryl-3- oxopropenyl)chromen-4-ones with hydrazine and their oxidation to bis(pyrazoles). / Lévai, A.; Silva, Artur M S; Pinto, Diana C G A; Cavaleiro, José A S; Alkorta, Ibon; Elguero, José; Jekó́, J.

In: European Journal of Organic Chemistry, No. 22, 12.11.2004, p. 4672-4679.

Research output: Contribution to journalArticle

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AU - Pinto, Diana C G A

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