Conformational studies by dynamic NMR. 93.(1) Stereomutation,enantioseparation, and absolute configuration of the atropisomers of diarylbicyclononanes |
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Authors: | Casarini Daniele Rosini Carlo Grilli Stefano Lunazzi Lodovico Mazzanti Andrea |
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Institution: | Department of Chemistry, University of Basilicata, Via N. Sauro 85, 85100 Potenza, Italy. mazzand@ms.fci.unibo.it |
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Abstract: | The structure of 9-(4-methoxyphenyl)-9-(3-methylphenyl) bicyclo3.3.1]nonane (1) has been determined by single-crystal X-ray diffraction, and the rotation barriers about the two aryl-C9 bonds have been measured by variable temperature NMR spectroscopy in solution. In the case of 9-(4-methoxyphenyl)-9-(1-naphthyl)bicyclo3.3.1]nonane (3), the barrier involving the naphthyl-C9 rotation was found to be so high as to allow the physical separation of the two atropisomers by enantioselective HPLC at ambient temperature: the absolute configuration could be established on the basis of the corresponding CD spectra. It was also observed that the Ar-C9 rotation barriers of monoaryl-substituted nonanes are much lower than those of the corresponding diaryl-substituted nonanes. |
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