8-(Biphenyl-4-yl)-8-hydroxypentacyclo[5.4.0.02,6.03,10.05,9]undecan-11-one ethylene ketal

The title compound, C25H24O3, synthesized as a potential chiral catalyst, exhibits a range of C—C bond lengths in the pentacycloundecane cage between 1.5144 (18) and 1.5856 (16) Å. The two benzene rings are not planar with respect to each other, but rather are twisted at a torsion angle of 34.67 (17)°. The molecule has an intramolecular O—H⋯O interaction and participates in two C—H⋯O intermolecular interactions to form a one-dimensional chain.

The title compound, C 25 H 24 O 3 , synthesized as a potential chiral catalyst, exhibits a range of C-C bond lengths in the pentacycloundecane cage between 1.5144 (18) and 1.5856 (16) Å . The two benzene rings are not planar with respect to each other, but rather are twisted at a torsion angle of 34.67 (17) . The molecule has an intramolecular O-HÁ Á ÁO interaction and participates in two C-HÁ Á ÁO intermolecular interactions to form a one-dimensional chain.

Comment
The molecule was synthesized as part of an ongoing study into the synthesis of chiral cage ligands for applications in asymmetric catalysis. The title molecule, which exists as a racemic mixture, has the potential to be a very unique ligand once it is resolved into an enantiopure compound.
A number of publications have focused on the molecular geometries of PCU cage derivatives as well as the bond lengths which deviate from the normal value of 1.54 Å (Flippen-Anderson et al., 1991;Linden et al.,2005;Kruger et al., 2005, 2006, Boyle et al., 2007. Certain bonds in the cage skeleton are longer (e.g. C9-C10, 1.5922 Å) while others are significantly shorter (e.g. C1-C11, 1.5106 Å). The molecule (I) consists of a large hydrophobic hydrocarbon skeleton as well as a hydrophilic ketal group and hydroxyl moiety. The two aromatic rings attached to C8 are not planar with respect to each other, but rather twisted at a torsion angle of 34.67 (17)° as expected due to steric factors. Fig. 1 shows the molecular structure and the numbering scheme employed.
The molecule exhibits intramolecular hydrogen bonding (Fig. 2) between the hydroxyl group and the ketal group (O3-H3H···O2). There is no intermolecular hydrogen bonding present in the structure, however a complex network of weak Van der Waals interactions between neighbouring molecules (Fig. 3) results in a layered packing effect with alternating hydrophilic and hydrophobic layers made up of the hydrophobic cage molecules and aromatic moeties, and the hydrophilic hydroxyl and ketal groups, respectively (Fig. 4).

Experimental
A solution of 4-bromobiphenyl in dry THF (3 mol eq) was cooled to −78°C using a dry-ice-acetone bath. Butyllithium solution (15% in hexane, 1.2 mole equivalents relative to bromobiphenyl) was added and the solution stirred for 10 minutes.