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The annular tautomerism of the curcuminoid NH-pyrazoles

AuthorsCornago, Pilar; Cabildo, Pilar; Claramunt, Rosa M.; Bouissane, L.; Pinilla, Elena; Torres, M. R.; Elguero, José
Issue Date2009
PublisherRoyal Society of Chemistry (UK)
CitationNew Journal of Chemistry 33: 125- 135 (2009)
AbstractThe structures of four NH-pyrazoles, (E)-3,5-bis[β-(4-hydroxy-3- methoxyphenyl)-ethenyl]-1H-pyrazole (3), (E)-3(5)-[β-(4-hydroxy-3- methoxyphenyl)-ethenyl]-5(3)-methyl-1H-pyrazole (4), (E)-3(5)-[β-(4- hydroxy-3-methoxyphenyl)-ethenyl]-4,5(3)-dimethyl-1H-pyrazole (5) and (E)-3(5)-[β-(3,4-dimethoxyphenyl)-ethenyl]-4-methyl-5(3) -phenyl-1H-pyrazole (8), have been determined by X-ray crystallography. Compounds that have a phenol residue crystallize forming sheets that are stabilized by a complex pattern of hydrogen bonds between a unique tautomer (4), or by a 2: 1 mixture of both tautomers (5) (these tautomers being identical in the case of 3). Pyrazole 8, which lacks OH groups, crystallizes in cyclic dimers that are stabilized by N-H⋯N hydrogen bonds. The tautomerism in solution and in the solid state was determined by 13C and 15N CPMAS NMR spectroscopy. For compounds 4, 5 and 8, the solid state results agree with those observed by crystallography; the most abundant tautomer in solution coincides with the tautomer present in the solid state (4 and 8) or with the most abundant tautomer in the crystal (5). © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Publisher version (URL)http://dx.doi.org/10.1039/b812018h
Identifiersdoi: 10.1039/b812018h
issn: 1144-0546
e-issn: 1369-9261
Appears in Collections:(IQM) Artículos
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