Concentration dependence of the rate of prototropic rearrangement of azoles in hexamethylphosphoric triamide

Kalikhman, I. D.; Лопырев, В. А.; Shibanova, E. F.; Pestunovich, V. A.; Воронков, М. Г.

doi:10.1007/bf00923674

Cited by 7 publications

(6 citation statements)

References 2 publications

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“…Recent studies on tautomerism in pyrazoles based on NMR spectroscopy are mostly follow-ups to the fundamental studies disclosed in the past century, to a large extent from the valuable contributions of Elguero et al [39,[86][87][88][89][90][91][92][93][94][95][96][97]. The main conclusions of these pioneering studies were that, for pyrazole itself, in solution, a tautomeric equilibrium is observed, meaning that pyrazole exists as a mixture of two identical tautomers, with interconversion rates high enough to be undetected in the NMR time scale [89].…”

Section: Experimental Studiesmentioning

confidence: 99%

Revisiting the Structure and Chemistry of 3(5)-Substituted Pyrazoles

2019

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Pyrazoles are known as versatile scaffolds in organic synthesis and medicinal chemistry, often used as starting materials for the preparation of more complex heterocyclic systems with relevance in the pharmaceutical field. Pyrazoles are also interesting compounds from a structural viewpoint, mainly because they exhibit tautomerism. This phenomenon may influence their reactivity, with possible impact on the synthetic strategies where pyrazoles take part, as well as on the biological activities of targets bearing a pyrazole moiety, since a change in structure translates into changes in properties. Investigations of the structure of pyrazoles that unravel the tautomeric and conformational preferences are therefore of upmost relevance. 3(5)-Aminopyrazoles are largely explored as precursors in the synthesis of condensed heterocyclic systems, namely pyrazolo[1,5-a]pyrimidines. However, the information available in the literature concerning the structure and chemistry of 3(5)-aminopyrazoles is scarce and disperse. We provide a revision of data on the present subject, based on investigations using theoretical and experimental methods, together with the applications of the compounds in synthesis. It is expected that the combined information will contribute to a deeper understanding of structure/reactivity relationships in this class of heterocycles, with a positive impact in the design of synthetic methods, where they take part.

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Section: Experimental Studiesmentioning

confidence: 99%

Revisiting the Structure and Chemistry of 3(5)-Substituted Pyrazoles

2019

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“…A. Shainyan, V. I. Meshcheryakov), can serve as a convenient method for the production of N-unsubstituted 1H-1,2,3-triazole 130 on account of the simple elimination of the highly nucleofugic CF 3 SO 2 group [344]. V. A. Lopyrev and coworkers realized a targeted synthesis of functionally substituted 1,2,4-triazoles and studied their acid-base characteristics and synthetic potential [346][347][348][349][350][351][352][353][354][355][356]. Methods were developed for the synthesis of various derivatives of amino-and diamino-1,2,4-triazoles, including fluorine-substituted 1H-1,2,4-triazole-3-amines 133 [346,354] Polyfluoroalkyl-1,3,4-oxadiazoles, which are of great practical interest, were synthesized and investigated [346,[355][356][357][358].…”

Section: Triazoles and Thiadiazolesmentioning

confidence: 99%

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

Nedolya

2008

Chem Heterocycl Comp

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“…HMPA was introduced in 1968 by Creagh and Truitt to study by 1 H NMR the tautomerism of 1 H ‐1,2,4‐triazole (see also) and then in 1977 extended by Chenon et al . to 1 H ‐pyrazoles and 13 C NMR.…”

Section: Resultsmentioning

confidence: 99%

“…HMPA was introduced in 1968 by Creagh and Truitt [45] to study by 1 H NMR the tautomerism of 1H-1,2,4-triazole (see also [46] ) and then in 1977 extended by Chenon et al [47] to 1Hpyrazoles and 13 C NMR. Our first use of this solvent was reported in 1991 and concerns the use of 13 C NMR spectroscopy to study the tautomerism of 1H-pyrazoles [48] followed by a 1 H, 13 C, and 15 N NMR study of other 1H-pyrazoles.…”

Section: Resultsmentioning

confidence: 99%

The structure of azines derived from C‐formyl‐1H‐imidazoles in solution and in the solid state: tautomerism, configurational and conformational studies

Pinto

Silva

et al. 2013

Magnetic Reson in Chemistry

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The structures of three azines derived from 2‐formylimidazole, 4(5)‐formylimidazole, and 4(5)‐formyl‐5(4)‐methylimidazole have been determined in solution and in the solid state. Density Functional Theory (DFT) Polarizable Continuum Model (PCM) calculations (geometries, energies, and chemical shifts), NMR [solution and cross polarization magic‐angle spinning (CPMAS)], and X‐ray crystallography [azine of 4(5)‐formylimidazole] have been used. The configuration around the central C = N bonds has been determined and some insights about prototropic tautomerism and conformation have been gained. Copyright © 2013 John Wiley & Sons, Ltd.

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Concentration dependence of the rate of prototropic rearrangement of azoles in hexamethylphosphoric triamide

Cited by 7 publications

References 2 publications

Revisiting the Structure and Chemistry of 3(5)-Substituted Pyrazoles

Revisiting the Structure and Chemistry of 3(5)-Substituted Pyrazoles

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The structure of azines derived from C‐formyl‐1H‐imidazoles in solution and in the solid state: tautomerism, configurational and conformational studies

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