Crystal structure of (1R,2S,4R,7R,8S,9R)-3,3-dichloro-8,9-epoxy-4,8,12,12-tetramethyltricyclo[5.5.0.02,4]dodecane

The title compound, C16H24Cl2O, is built up from two fused six- and seven-membered rings which bear a dichlorocyclopropane group and an epoxy group, respectively. In the molecule, the six-membered ring adopts an envelope configuration with the C atom linking the epoxy ring at the flap, while the seven-membered ring adopts a boat–sofa conformation.

Supporting information for this paper is available from the IUCr electronic archives (Reference: XU5855). Epoxides are valuable intermediates frequently used as versatile building blocks in organic synthesis (Qu et al., 2009).
Because of their widespread occurrence, biological and synthetic utilities, the synthesis of new epoxides has grown significantly.
In the aim of preparing new epoxides from natural products, we recently synthetise γ-Epoxyhimachalene 1 (scheme 1) from naturally occurred sesquiterpene γ-himachalene without crystallographic evidence of its absolute configuration as the product was oily. We therefore decided to transform it into a solid derivative by [2+1] cycloaddition reaction of a dihalocarbene on the remaining cyclohexenic double bond.
The structure of the newly prepared 2 (scheme 2) has been established from its 1 H and 13 C NMR spectral data. An X-ray structure analysis has allowed us to determine unambiguously its stereochemistry and deduce the absolute configuration of its oily precursor γ-Epoxyhimachalene 1.

S2. Structural commentary
Compound 2 is built up from two fused 6 and 7 membered rings ( Fig. 1). The seven membered ring is bearing an epoxy group whereas the 6 membered ring bears a dichlorocyclopropane. In the seven membered ring, the puckering parameters

Figure 1
Displacement ellipsoid plot of the title compound.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.6765 (