(S)-4-(2-Chloropropan-2-yl)-1-(2,2,2-trichloroethyl)cyclohexene

The title compound, C11H16Cl4, was synthesized by the reaction of (1S)-β-pinene with triethylamine in the presence of ZnCl2. The cyclohexene ring assumes a half-boat conformation. The crystal packing is governed only by van der Waals interactions. The structure, which has been refined in P21, presents a striking P21/m pseudosymmetry.

The title compound, C 11 H 16 Cl 4 , was synthesized by the reaction of (1S)--pinene with triethylamine in the presence of ZnCl 2 . The cyclohexene ring assumes a half-boat conformation. The crystal packing is governed only by van der Waals interactions. The structure, which has been refined in P2 1 , presents a striking P2 1 /m pseudosymmetry.

Comment
The research on polyhalogenated alkanes, lactams and lactones, which are versatile intermediates in the synthesis of natural products and bioactive molecules, has held the attention of chemists for many years (Delaude et al., 2004). Among others, the Kharasch reaction is an effective method for the formation of these polyhalogenated products. This process consists in the addition of a polyhalogenated alkane to an alkene and requires either a radical initiator or a transition metal catalyst (Borguet et al., 2007). In the course of our ongoing research program aimed at the synthesis of natural chlorinated compounds (Ziyat et al., 2002;Ziyat et al., 2004;Boualy et al., 2009), the title compound has been obtained and its crystal structure is reported herein.

Experimental
A mixture of (1S)-β-pinene (1 g, 7.34 mmol) and triethylamine (1 ml, 7.11 mmol) in carbon tetrachloride (15 ml) was added to a solution of ZnCl 2 in (1.1 g, 8.09 mmol) in water (15 ml) under stirring at room temperature. On completion of the reaction, the mixture was diluted with 25 ml of water, extracted with carbon tetrachloride (3 × 10 ml) and dried over Na 2 SO 4 .
The title compound was isolated as a white powder by column chromatography on silica gel using n-hexane as eluent (yield 90%; m. p. = 48 °C), but colourless single crystals suitable for X-ray analysis were obtained by slow evaporation of a

Refinement
The molecule contains one chiral carbon atom at C4. Irrespective of this it is possible to solve the structure in the higher symmetry P2 1 /m space group, but this forces the molecule to have a crystallographically imposed mirror symmetry passing through C1 and C4 of the cyclohexene ring, resulting in the C2 (sp 2 ) and C6 (sp 3 ) carbon atoms to be symmetry-related and disordered over two orientations. This disorder is totally absent in the noncentrosymmetric P2 1 space group. Moreover, refining in P2 1 /m results in significantly worse R values (R1 = 5.4%, wR2 = 18.2%). All H atoms were calculated geometrically and refined using a riding model, with C-H = 0.93-0.98 Å and with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C) for methyl H atoms.  Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level.

Special details
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 Rfactors(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