The bi[10]paracyclophane (-)-6b with two chiral planes and one chiral axis has been synthesized in enantiomerically pure form. Its absolute configuration was determined by quantum chemical calculation of the circular dichroism and comparison with the experimental CD spectrum. (C) 1999 Elsevier Science Ltd. All rights reserved.
A borderline case between meso and stable C1: an axially chiral, yet configurationally semi-stable biphenyl with two oppositely configured [10]paracyclophane portions
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 Cl-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 degrees C and were stereochemically assigned by LC-CD coupling, in combination with quantum chemical CD calculations. (c) 2005 Elsevier Ltd. All rights reserved.