A borderline case between meso and stable C1: an axially chiral, yet configurationally semi-stable biphenyl with two oppositely configured [10]paracyclophane portions |
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Authors: | Gerhard Bringmann Tobias A.M. Gulder Dirk Kuckling Werner Tochtermann |
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Affiliation: | a Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany b Institut für Organische Chemie, Universität Kiel, Olshausenstraße 40, D-24098 Kiel, Germany |
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Abstract: | The synthesis of the bi[10]paracyclophanes 2 and 4 from the meso-configured bioxepine 3 is described. These compounds are stereochemically remarkable: the biaryl axis that connects the constitutionally identical, but oppositely configured planar-chiral paracyclophane portions, is configurationally semi-stable. Thus, 2 is an unprecedented borderline case of a (planar-chiral)-(axially chiral)-(planar-chiral) molecule that is right in between a meso-compound (as a macroscopical result of the—albeit slow—rotation about the central C,C-bond) and C1-symmetry (with respect to the existence of separable—even though configurationally unstable—discrete atropo-enantiomers). Despite their restricted configurational stability, these atropo-enantiomers were resolved on a chiral phase at 5 °C and were stereochemically assigned by LC-CD coupling, in combination with quantum chemical CD calculations. |
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Keywords: | Cyclophanes Circular dichroism (CD) Quantum chemical CD calculations Planar chirality Axial chirality |
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