endo-3,3-Dimethyl-4-oxobicyclo[3.1.0]hexan-2-yl methanesulfonate

The relative configuration of the endo isomer of the title compound, C9H14O4S, has been established and the conformation of the diastereoisomer is discussed. The five-membered ring adopts an envelope conformation. The conformation of the methanesulfonate substituent is stabilized by intermolecular C—H⋯O hydrogen bonds. The crystal packing results in alternating layers of polar methanesulfonates and stacked bicyclohexanyl rings parallel to ab.

The relative configuration of the endo isomer of the title compound, C 9 H 14 O 4 S, has been established and the conformation of the diastereoisomer is discussed. The fivemembered ring adopts an envelope conformation. The conformation of the methanesulfonate substituent is stabilized by intermolecular C-HÁ Á ÁO hydrogen bonds. The crystal packing results in alternating layers of polar methanesulfonates and stacked bicyclohexanyl rings parallel to ab.
The X-ray crystallography study reported here determined the relative stereochemistry of the endo diasteroisomer : C(1) S, C(4) R, and C(5) R. The compound crystallizing in a centrosymetric space group, one obtains the racemic mixture The five-membered ring C1-C5 adopts an envelope conformation. Puckering parameter Phi is 260.1 (8)° and close to the expected value of k x 36° (Cremer & Pople, 1975), suggesting that the presence of a sp 2 carbon (C2) in the five-membered ring does not significantly distort its conformation. The observed values of torsion angles defining the C1-C5 ring (Table   1)  Packing is also reinforced by van der Waals interactions resulting in alterning layers of polar methanesulfonates and stacked bicyclohexanyl rings parallel to the ab cell planes.

Experimental
Synthesis of the compound will be detailed elsewhere.
Crystals were obtained by evaporation at 5°C of solutions in diethylether.

Refinement
All H atoms were placed at idealized positions and allowed to ride on their parent atoms, with C-H = 0.97 Å and U iso (H) = 1.2U eq (C) for methylene groups and U iso (H) = 1.5U eq (C) for the methyl group.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 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 C1 0.1819 (