Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

Denisa Tarabová; Stanislava Soralová; Martin Breza; Marek Fronc; Wolfgang Holzer; Viktor Milata

doi:10.3762/bjoc.10.70

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

Beilstein J Org Chem. 2014 Apr 1:10:752-60. doi: 10.3762/bjoc.10.70. eCollection 2014.

Authors

Denisa Tarabová¹, Stanislava Soralová², Martin Breza³, Marek Fronc³, Wolfgang Holzer⁴, Viktor Milata¹

Affiliations

¹ Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, SK-812 37 Bratislava, Slovakia.
² Department of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, SK-812 37 Bratislava, Slovakia ; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Comenius University in Bratislava, Odbojárov 10, SK-832 32 Bratislava, Slovakia.
³ Department of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, SK-812 37 Bratislava, Slovakia.
⁴ Department of Drug and Natural Product Synthesis, Vienna University, Althanstrasse 14, A-1090 Vienna, Austria.

Abstract

Activated enol ethers derived from esters or the dinitrile of malonic acid, or from pentane-2,4-dione were treated with hydrazine hydrate. The structures of the obtained products - pyrazoles 5 - were studied with a focus on tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arrangement of the formally equivalent subunits.

Keywords: NMR; bis-enehydrazines; enol ethers; pyrazole; tautomerism.