Crystal structure of (1S,3R,8R,10S)-2,2-dichloro-10-hydroxy-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodecan-9-one

The asymmetric unit of title compound contains two independent molecules which are built from three fused rings: a heptane ring, a cyclohexyl ring bearing a ketone and an alcohol group, and a three-membered cyclopropane ring bearing two Cl atoms. In the crystal, the molecules are linked by O—H⋯O and C—H⋯O hydrogen bonds, forming chains propagating along [100].


Structural commentary
There are two molecules (A and B) in the asymmetric unit of the title compound, Fig. 1, both having the same the absolute configuration: (1S,3R,8R,10S) and (1AS,3AR,8AR,10AS). The compound is built up from three fused rings: a sevenmembered heptane ring, a six-membered cyclohexyl ring bearing a ketone and alcohol groups, and a three-membered propane ring bearing two Cl atoms (Fig. 1). In molecule B (Fig. 2), there is positional disorder affecting the location of atom C6 which is split over two positions, C6a and C6b. In both molecules, the six-membered rings display a conformation intermediate between boat and twist-boat with puckering parameters = 89.73 and '2 = 198.07 for molecule A and = 91.78 and '2 = 210.97 for molecule B. The seven-membered cycloheptane ring in molecule A displays a conformation intermediate between boat and twist-boat with puckering parameters q2 = 1.151 (5) and q3 = 0.030 (5) Å . Owing to the disorder observed in molecule B within the seven-membered ring, the conformation of this ring is intermediate between boat and twist-boat [q2 = 1.194 (5), q3 = 0.00 (4) Å ] or chair and twist-chair [q2 = 0.363 (5), q3 = 0.784 (5) Å ], depending on the position of atom C6a or C6b.

Supramolecular features
The two independent molecules are connected through O-HÁ Á ÁO hydrogen bonds, involving the hydroxyl and the ketone O atoms, forming an A-B dimer with an R 2 2 (10) ring motif ( Fig. 3 and Table 1). The A molecules of these dimers are linked via a C-HÁ Á ÁO hydrogen bond forming chains propagating along the a axis direction ( Fig. 3 and Table 1).

Figure 3
Partial crystal packing of the title compound (molecule A blue, molecule B red), viewed along the c axis, showing the formation of the hydrogenbonded chain parallel to the a-axis direction. The hydrogen bonds are shown as dashed lines (see Table 1; H atom as balls) and H atoms not involved in these interactions have been omitted for clarity.

Synthesis and crystallization
To a solution of 0.4 g (1.319 mmol) of (1S,3R,8S,9R,10S)-2,2dichloro-3,7,7,10-tetramethyl-9,10-epoxytricyclo[6.4.0.0 1,3 ]dodecane (Sbai et al., 2002) in acetone (8 ml), 3 ml of an aqueous solution of CrO 3 (1 g, 10 mmol) was added at 273 K. The mixture was stirred at room temperature for 30 min and cooled to 273 K in an ice bath and 1.5 ml of an aqueous solution of CrO 3 (0,5 g, 5 mmol) was added dropwise. The ice bath was removed and the mixture was stirred at room temperature for 1 h. The reaction mixture was extracted with dichloromethane (3 Â 30 ml) and the organic layers were dried over anhydrous Na 2 SO 4 and the solvent was removed under reduced pressure. The crude product was then purified on silica gel chromatography (230-400 mesh) using hexane/ ethyl acetate (95:5) as eluent to give the title compound (yield 53%). Colourless plate-like crystals were obtained from a petroleum ether solution, by slow evaporation of the solvent at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The OH and C-bound H atoms were included in calculated positions and refined as riding: O-H = 0.84, C-H = 0.98-1.00 Å with U iso (H) = 1.5U eq (O and C-methyl) and 1.2U eq (C) for other H atoms. The disordered cycloheptane ring in molecule B was refined by splitting atoms C6a, C14a and C15a over two positions. The occupancy factors were initially refined and once the occupancy was correctly evaluated the values were held fixed with ratio 0.54:0.46. Atoms C5a and C7a were also split (C5a/C5b and C7a/C7b) and constrained to occupy the same site using EXYZ and EADP commands allowing then to locate the H atoms.   PRO (Agilent, 2014); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and PLATON (Spek, 2009). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.