Artículo
Atropisomerism in amidinoquinoxaline N-oxides: effect of the ring size and substituents on the enantiomerization barriers
Díaz, Jimena Estela
; Vanthuyne, Nicolas; Rispaud, Hélène; Roussel, Christian; Vega, Daniel Alberto
; Orelli, Liliana Raquel
Fecha de publicación:
01/2015
Editorial:
American Chemical Society
Revista:
Journal of Organic Chemistry
ISSN:
0022-3263
Idioma:
Inglés
Tipo de recurso:
Artículo publicado
Clasificación temática:
Resumen
The atropisomerism of novel 2,3-dihydro1H-pyrimido[1,2-a]quinoxaline 6-oxides 1 bearing dissymmetric (ortho-substituted) 5-aryl residues and the homologous 1,2-dihydroimidazo[1,2-a]quinoxaline 5-oxides 2 was investigated. The existence of a chiral axis was demonstrated for compound 1a by X-ray diffraction and by DFT calculations of the ground state geometry. The resolution of the atropisomeric enantiomers on chiral stationary phases is reported. The barriers to enantiomerization were determined by off-line racemization studies and/or by treatment of the plateau-shape chromatograms during chromatography on chiral support. A clear ring size effect was evidenced. In all cases, six-membered amidine derivatives 1 showed higher barriers than the corresponding lower homologues 2, which also display lower sensitivity to the substituent size. Transition states for the interconversion of the atropisomers were located using DFT calculations, and involved the interaction of the ortho substituent with the formally sp2 nitrogen in the amidine moiety. In contrast, in the most favoured enantiomerization transition state of the 2-nitro derivative the ortho substituent is close to the N-oxide group.
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Articulos(OCA HOUSSAY)
Articulos de OFICINA DE COORDINACION ADMINISTRATIVA HOUSSAY
Articulos de OFICINA DE COORDINACION ADMINISTRATIVA HOUSSAY
Citación
Díaz, Jimena Estela; Vanthuyne, Nicolas; Rispaud, Hélène; Roussel, Christian; Vega, Daniel Alberto; et al.; Atropisomerism in amidinoquinoxaline N-oxides: effect of the ring size and substituents on the enantiomerization barriers; American Chemical Society; Journal of Organic Chemistry; 80; 3; 1-2015; 1689-1695
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