1246808-10-5Relevant articles and documents
Atropisomerism in amidinoquinoxaline N-oxides: Effect of the ring size and substituents on the enantiomerization barriers
Díaz, Jimena E.,Vanthuyne, Nicolas,Rispaud, Hélène,Roussel, Christian,Vega, Daniel,Orelli, Liliana R.
, p. 1689 - 1695 (2015/05/13)
The atropisomerism of novel 2,3-dihydro-1H-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-shaped 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 favored enantiomerization transition state of the 2-nitro derivative the ortho substituent is close to the N-oxide group. (Chemical Equation Presented).
New atropisomers derived from amidinoquinoxaline N-oxides: Synthesis and NMR characterization
Díaz, Jimena E.,García, Ma. Beatriz,Orelli, Liliana R.
experimental part, p. 50 - 56 (2011/01/06)
The complete 1H and 13C NMR characterization of some representative examples of five and six-membered amidinoquinoxaline N-oxides 1 with dissymmetric aryl substituents and their methiodides 2 is reported. Compounds 1 were synthesized
