Enantiopure Aromatic Saddles Bearing the Fenestrindane Core

The synthesis of
enantiomerically pure, configurationally stable
fenestrindane-based polyaromatic compounds with saddle-like structures
is reported. Seven racemic fenestrane synthetic precursors were first
screened by chiral HPLC for resolvability into enantiomers. Among
the three resolvable precursors, a tribenzofenestrene derivative was
resolved on a semipreparative scale, and the absolute configuration
of the more slowly eluting enantiomer was established by X-ray crystallography.
The enantiopure tribenzofenestrenes were then separately converted,
in six steps, to the saddle-shaped fenestrindane derivatives in optically
pure form. The two enantiomeric pairs of saddles were characterized
by 1H and 13C NMR spectroscopy, mass spectrometry,
and circular dichroism spectroscopy. All new compounds reported herein
represent the first enantiopure non-natural carbocyclic fenestranes
isolated to date.