(1S,3R,8R,9R,10S)-2,2-Dibromo-3,7,7,10-tetramethyl-9β,10β-epoxy-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodecane

The title compound, C16H24Br2O, was synthesized from β-himachalene (3,5,5,9-tetramethyl-2,4a,5,6,7,8-hexahydro-1H-benzocycloheptene), which was isolated from the essential oil of the Atlas cedar (Cedrus atlantica). The molecule contains fused six- and seven-membered rings, each linked to a three-membered ring. The six-membered ring has a half-chair conformation, while the seven-membered ring displays a chair conformation. The dihedral angle between the mean planes through the six- and seven-membered rings is 39.55 (12)°. The two three-membered rings, linked to the six- and seven-membered rings, are nearly perpendicular to the six-membered ring, making dihedral angles of 78.6 (2) and 80.5 (2)°, respectively. The absolute structure was established unambiguously from anomalous dispersion effects. In the crystal, each molecule is linked to its symmetry-equivalent partner by C—H⋯O hydrogen bonds, forming zigzag chains parallel to [100].

The title compound, C 16 H 24 Br 2 O, was synthesized fromhimachalene (3,5,5,4a,5,6,7,, which was isolated from the essential oil of the Atlas cedar (Cedrus atlantica). The molecule contains fused six-and seven-membered rings, each linked to a three-membered ring. The six-membered ring has a halfchair conformation, while the seven-membered ring displays a chair conformation. The dihedral angle between the mean planes through the six-and seven-membered rings is 39.55 (12) . The two three-membered rings, linked to the six-and seven-membered rings, are nearly perpendicular to the six-membered ring, making dihedral angles of 78.6 (2) and 80.5 (2) , respectively. The absolute structure was established unambiguously from anomalous dispersion effects. In the crystal, each molecule is linked to its symmetry-equivalent partner by C-HÁ Á ÁO hydrogen bonds, forming zigzag chains parallel to [100].
In the crystal, each molecule is linked to its symmetry equivalent partner by C9-H9···O1 non classic hydrogen-bond as shown in Fig.2 and Table 2. The present structure is similar to that of C 16 H 24 OCl 2 published, in a previous work, by Benharref et al. (2010).

Refinement
All H atoms were fixed geometrically and treated as riding with C-H = 0.96 Å (methyl),0.97 Å (methylene), 0.98 Å (methine) with U iso (H) = 1.2Ueq(methylene, methine) or U iso (H) = 1.5Ueq(methyl). The space group is not centro symmetric and the polar axis restraint is generated automatically by SHELXL program. The Friedel opposites reflections are not merged.

Special details
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 > σ(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 C1 0.4959 (