Cargando…

Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles

(1)H and (13)C NMR spectra of eleven 2-phenacylbenzoxazoles (ketimine form) show that their CDCl(3)-solutions contains also (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenols (enolimine form). Intramolecular hydrogen bonding in the latter tautomer was found to be significantly weaker than that one in resp...

Descripción completa

Detalles Bibliográficos
Autores principales: Skotnicka, Agnieszka, Kolehmainen, Erkki, Czeleń, Przemysław, Valkonen, Arto, Gawinecki, Ryszard
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Molecular Diversity Preservation International (MDPI) 2013
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3634406/
https://www.ncbi.nlm.nih.gov/pubmed/23439552
http://dx.doi.org/10.3390/ijms14034444
_version_ 1782267096526225408
author Skotnicka, Agnieszka
Kolehmainen, Erkki
Czeleń, Przemysław
Valkonen, Arto
Gawinecki, Ryszard
author_facet Skotnicka, Agnieszka
Kolehmainen, Erkki
Czeleń, Przemysław
Valkonen, Arto
Gawinecki, Ryszard
author_sort Skotnicka, Agnieszka
collection PubMed
description (1)H and (13)C NMR spectra of eleven 2-phenacylbenzoxazoles (ketimine form) show that their CDCl(3)-solutions contains also (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenols (enolimine form). Intramolecular hydrogen bonding in the latter tautomer was found to be significantly weaker than that one in respective (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines. Integrals of the (1)H NMR signals were used to evaluate the molar ratio of the tautomers. Strong electron-donating substituents were found to stabilize the ketimine tautomer. pK(T) (negative logarithm of the equilibrium constant, K(T) = [ketimine]/[enolimine]) was found to be linearly dependent on the Hammett substituent constant σ. The results of the MP2 ab initio calculations reveal enolimine including an intramolecular OH···N hydrogen bond to be the most stable form both with electron-donor and electron-acceptor substituents. The stability of ketimines is an intermediate of those found for enolimines and enaminones i.e., (E)-2-(benzo[d]oxazol-2(3H)-ylidene)-1-phenylethanones. (13)C CPMAS NMR spectral data reveal that in the crystalline state the ketimine tautomer is predominant in p-NMe(2) substituted congener. On the other hand, enolimine forms were detected there when the substituent has less electron-donating character or when it is an electron-acceptor by character.
format Online
Article
Text
id pubmed-3634406
institution National Center for Biotechnology Information
language English
publishDate 2013
publisher Molecular Diversity Preservation International (MDPI)
record_format MEDLINE/PubMed
spelling pubmed-36344062013-05-02 Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles Skotnicka, Agnieszka Kolehmainen, Erkki Czeleń, Przemysław Valkonen, Arto Gawinecki, Ryszard Int J Mol Sci Article (1)H and (13)C NMR spectra of eleven 2-phenacylbenzoxazoles (ketimine form) show that their CDCl(3)-solutions contains also (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenols (enolimine form). Intramolecular hydrogen bonding in the latter tautomer was found to be significantly weaker than that one in respective (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines. Integrals of the (1)H NMR signals were used to evaluate the molar ratio of the tautomers. Strong electron-donating substituents were found to stabilize the ketimine tautomer. pK(T) (negative logarithm of the equilibrium constant, K(T) = [ketimine]/[enolimine]) was found to be linearly dependent on the Hammett substituent constant σ. The results of the MP2 ab initio calculations reveal enolimine including an intramolecular OH···N hydrogen bond to be the most stable form both with electron-donor and electron-acceptor substituents. The stability of ketimines is an intermediate of those found for enolimines and enaminones i.e., (E)-2-(benzo[d]oxazol-2(3H)-ylidene)-1-phenylethanones. (13)C CPMAS NMR spectral data reveal that in the crystalline state the ketimine tautomer is predominant in p-NMe(2) substituted congener. On the other hand, enolimine forms were detected there when the substituent has less electron-donating character or when it is an electron-acceptor by character. Molecular Diversity Preservation International (MDPI) 2013-02-25 /pmc/articles/PMC3634406/ /pubmed/23439552 http://dx.doi.org/10.3390/ijms14034444 Text en © 2013 by the authors; licensee MDPI, Basel, Switzerland. http://creativecommons.org/licenses/by/3.0 This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).
spellingShingle Article
Skotnicka, Agnieszka
Kolehmainen, Erkki
Czeleń, Przemysław
Valkonen, Arto
Gawinecki, Ryszard
Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles
title Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles
title_full Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles
title_fullStr Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles
title_full_unstemmed Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles
title_short Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles
title_sort synthesis and structural characterization of substituted 2-phenacylbenzoxazoles
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3634406/
https://www.ncbi.nlm.nih.gov/pubmed/23439552
http://dx.doi.org/10.3390/ijms14034444
work_keys_str_mv AT skotnickaagnieszka synthesisandstructuralcharacterizationofsubstituted2phenacylbenzoxazoles
AT kolehmainenerkki synthesisandstructuralcharacterizationofsubstituted2phenacylbenzoxazoles
AT czelenprzemysław synthesisandstructuralcharacterizationofsubstituted2phenacylbenzoxazoles
AT valkonenarto synthesisandstructuralcharacterizationofsubstituted2phenacylbenzoxazoles
AT gawineckiryszard synthesisandstructuralcharacterizationofsubstituted2phenacylbenzoxazoles