Absolute configuration of (1R,3S,8R,11R)-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodec-9-en-11-ol

The absolute configuration of the title compound, C16H26O, was determined as (1R,3S,8R,11R) based mainly on the synthetic pathway but is also implied by the X-ray analysis. The molecule contains fused six- and seven-membered rings. Part of the seven-membered ring was refined as disordered over two sets of sites with the occupancy ratio fixed at 0.86:0.14. The disorder corresponds to a major chair conformation and a minor boat conforation. In the crysyal, O—H⋯O hydrogen bonds connect the molecules into chains parallel to the a axis.

In the crystal, the hydroxyl group is engaged in O-H···O hydrogen bonding with symmetry related molecules forming infinite chains parallel to the a axis (Fig. 2).

Experimental
To a cooled (273 K) solution of (I) (4.6 mmol) in 50 ml of a solvent mixture THF/H 2 O (4/1, v/v), NBS (9,16 mmol) was added in small portions, then mixture was kept under stirring at 273 K, for two hours. After completion of the reaction, a 15% sodium hydrogenocarbonate solution was added and the reaction mixture was taken up in ether, dried over anhydrous sodium sulfate, and concentrated. The crude product was purified by chromatography on silica gel (230-400 mesh) with Hexane/ethyl acetate (96:4) as eluent to give the title compound in 20% yield. X-ray quality crystals were obtained by slow evaporation from a petroleum ether solution of the title compound.
The C6 carbon atom is disordered over two positions inducing a disorder of the two methyl groups C14 and C15 attached to C7. This disorder was modelled using the tools available in SHELXL97 (Sheldrick, 2008). The two disordered fragment were included in two different parts, PART 1 and 2. The occupancy factor for the two sites was refined using the free variable restraining the sum of the occupancy factors to be equal to 1. The occupancies were ultimately fixed. To be able to calculate the disordered hydrogen atom positions, atom C5 was split in two identical positions which were restrained to have same coordinates and anisotropic thermal parameters by using the EXYZ and EADP instructions in SHELXL97 (Sheldrick, 2008). Windows (Farrugia, 2012) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figure 1
The asymmetric unit of (II) with displacement ellipsoids drawn at the 30% probability level. The dashed bonds represent the minor component of disorder. H atoms are represented as small spheres of arbitrary radii.

Special details
Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. CrysAlisPro (Agilent Technologies,2012) Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (