By means of low temperature NMR spectroscopy the conformers (stereolabile atropisomers) due to the restricted rotation about the Ar-Ar and Ar-C(O)R bonds were detected in a number of acylphenyl derivatives, substituted in the positions 2 and 6 by the 3-isopropyl phenyl moiety (compounds 1-3, R = H, Me, t-Bu, respectively). The conformational assignment was accomplished on the basis of the symmetry of the low temperature 13C NMR spectra with the added support of ab-initio calculations. The interconversion barriers were also determined by complete line shape simulation of the NMR spectra and the experimental values were satisfactorily reproduced by ab-initio calculations. In the case of the asymmetric derivative 4, two enantiomers, generated by the restricted t-BuC(O)-Ar rotation, were found sufficiently stable as to allow their separation by means of the enantioselective HPLC technique at ambient temperature and to obtain the corresponding CD spectra.

Conformational Consequences of the Dynamic Processes in the Stereolabile Atropisomers of Acyl-Substituted Meta-Terphenyl Derivatives

LUNAZZI, LODOVICO;MAZZANTI, ANDREA;MINZONI, MIRKO
2007

Abstract

By means of low temperature NMR spectroscopy the conformers (stereolabile atropisomers) due to the restricted rotation about the Ar-Ar and Ar-C(O)R bonds were detected in a number of acylphenyl derivatives, substituted in the positions 2 and 6 by the 3-isopropyl phenyl moiety (compounds 1-3, R = H, Me, t-Bu, respectively). The conformational assignment was accomplished on the basis of the symmetry of the low temperature 13C NMR spectra with the added support of ab-initio calculations. The interconversion barriers were also determined by complete line shape simulation of the NMR spectra and the experimental values were satisfactorily reproduced by ab-initio calculations. In the case of the asymmetric derivative 4, two enantiomers, generated by the restricted t-BuC(O)-Ar rotation, were found sufficiently stable as to allow their separation by means of the enantioselective HPLC technique at ambient temperature and to obtain the corresponding CD spectra.
L. Lunazzi; A. Mazzanti; M. Minzoni
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/47449
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