(1S,3R,8R,10R)-2,2-Dibromo-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodecan-9-one

The title compound, C16H24Br2O was synthesized by three steps from β-himachalene (3,5,5,9-tetramethyl-2,4a,5,6,7,8-hexahydro-1H-benzocycloheptene), which was isolated from essential oil of the Atlas cedar (Cedrus atlantica). The molecule is built up from a seven-membered ring to which a six- and a three-membered ring are fused. The six-membered ring shows a chair conformation. One C atom in the seven-membered ring and two methyl groups attached to the ring are disordered over two sets of sites, with an occupancy ratio of 0.658 (7):0.342 (7).

The title compound, C 16 H 24 Br 2 O was synthesized by three steps from -himachalene (3,5,5,9-tetramethyl-2,4a,5,6,7,8hexahydro-1H-benzocycloheptene), which was isolated from essential oil of the Atlas cedar (Cedrus atlantica). The molecule is built up from a seven-membered ring to which a six-and a three-membered ring are fused. The six-membered ring shows a chair conformation. One C atom in the sevenmembered ring and two methyl groups attached to the ring are disordered over two sets of sites, with an occupancy ratio of 0.658 (7):0.342 (7).

Comment
With the aim exploiting the Moroccan floral inheritance, in particular plants which contain essential oils, we have directed our research endeavours towards the oil of the Atlas Cedar (Cedrus atlantica). The main constituent of this oil is β-himachalene (El Haib et al., 2011). The reactivity of this sesquiterpene has been studied extensively by our team (El Jamili et al., 2002;Benharref et al., 2013;Ourhriss et al. (2013), in order to prepare new products having olfactive properieties suitable for the perfume or cosmetics industry. In this work we present the crystal structure of the title compound, (1S, 3R, 8R, 10R)-2, 2-dibromo-3,7, 7,10-tetramethyltricyclo[6.4.0.0 1 , 3 ]dodecan-9-one. The molecule is built up from two fused seven and six-membered rings and a three-membered ring attached to the seven-membered ring as shown in Fig. 1. The six-membered ring has a chair conformation as indicated by the total puckering amplitude QT = 0.527 (3) Å and spherical polar angle θ = 167.9 (3)° with φ = 99.3 (17)° (Cremer & Pople, 1975). Owing to the presence of Br atoms, the absolute configuration could be successfully confirmed as C1(S), C3(R), C8(R) and C10(R).

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) = 1.2U eq (methylene, methine) or U iso (H) = 1.5U eq (methyl). The C6 carbon atom is disordered over two positions inducing a disorder of the two methyl groups C14 and C15 attached to C7. The occupancy factor for these sites was refined.

Computing details
Data    (2) Special details Experimental. ′Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. CrysAlisPro (Agilent Technologies, 2013 ) 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. (