rac-4,8-Divinylbicyclo[3.3.1]nonane-2,6-dione

The title compound, C13H16O2, is a chiral bicyclic structure composed of two fused cyclohexane rings possessing both boat and chair conformations. The molecules are packed in enantiopure columns which are pairwise linked forming an overall racemic solid; within the column pairs the packing is governed by weak dipole–dipole interactions stemming from stacked carbonyl functionalities (COcentroid–COcentroid distance = 3.290 Å).

The title compound, C 13 H 16 O 2 , is a chiral bicyclic structure composed of two fused cyclohexane rings possessing both boat and chair conformations. The molecules are packed in enantiopure columns which are pairwise linked forming an overall racemic solid; within the column pairs the packing is governed by weak dipole-dipole interactions stemming from stacked carbonyl functionalities (CO centroid -CO centroid distance = 3.290 Å ).

Comment
The hydrocarbon backbone of the title compound is a common motif in many biologically active compounds and its unique molecular shape has been utilized in the construction of different types of supramolecular architectures and inclusion complexes. Diols from this category of structures has with great success been exploited within the field of crystal engineering.
The title compound was obtained in the synthesis of a series of C 2 -symmetrically derivatized bicyclo[3.3.1]nonane-2,6-diones as a part of an ongoing project with the aim to study various supramolecular features of this class of compounds. The chiral bicyclic structure is composed of two merged cyclohexanes possessing both boat and chair conformations similar to the previously reported phenyl-substituted bicyclo[3.3.1]nonane-2,6-dione (Quast et al., 1999). The molecules are packed in column pairs which propagate in a unidirectional manner along the c axis. The column pairs are homochiral and generated by a two fold screw axis. The glide plane generates an over-all racemic structure comprised of parallel columns with alternating absolute stereochemistry. The formation of column pairs is governed by dipole-dipole interactions stemming from stacked carbonyl functionalities: centroid C2O1···centroid C2O1, 3.290 Å.

Experimental
A solution of LiCl in THF ( 0.5M, 12.5 mL, 6.25 mmol) was added to a round-bottom flask charged with CuCN (0.272 g, 3.04 mmol) and the mixture was stirred under argon at room temperature until all solid dissolved. The solution was cooled down to -30 °C and a solution of vinyl magnesium bromide in THF (0.7 M, 4.34 mL, 3.04 mmol) was added dropwise. The resulting dark brown mixture was warmed to -20 °C and stirred at this temperature for 30 minutes and then cooled to -78 °C.
A solution of bicyclo[3.3.1]nona-3,7-diene-2,6-dione (0.15g, 1.01 mmol) (Orentas et al., 2007) and trimethylsilylchloride (0.33 g, 3.04 mmol) in THF (3 mL) was added dropwise. The reaction mixture was stirred until the temperature reached -20 °C. The reaction was quenched with 10% HCl solution (20 mL) and stirred at room temperature until the intermediate silylenol ether was hydrolyzed (monitored by TLC). The mixture was diluted with water and extracted with EtOAc (3 x 20 mL). The combined organic phase was dried over Na 2 SO 4 and evaporated to dryness. The residue was purified by flash chromatography (10% ethyl acetate/petroleum ether) to afford the title compound as a coluorless solid in 70 % yield (144.4 mg). The product was recrystallised from petroleum ether to give colourless crystals suitable for X-ray diffraction analysis;

Refinement
The H atoms were positioned geometrically and treated as riding on their parent atoms with C-H distances of 0.93-0.97 Å and U iso (H) = 1.2U eq -1.5U eq . Equivalent reflections including Friedel pairs were merged prior to the final refinement. Fig. 1. The molecular structure of the title compound with atom labels and 30% probability displacement ellipsoids.