| Abstract
| - By means of low-temperature NMR spectroscopy, conformers (stereolabile atropisomers) due to therestricted rotation about the Ar−Ar and Ar−C(O)R bonds were detected in a number of acylphenylderivatives, substituted in positions 2 and 6 by the 3-isopropylphenyl moiety (compounds 1−3, R = H,Me, and t-Bu, respectively). The conformational assignment was accomplished on the basis of the symmetryof the low-temperature 13C NMR spectra with the added support of ab initio calculations. Theinterconversion 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 theasymmetric derivative 4, two enantiomers, generated by the restricted t-BuC(O)−Ar rotation, were foundsufficiently stable to allow their separation by means of the enantioselective HPLC technique at ambienttemperature and to obtain the corresponding CD spectra.
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