(−)-(1S,5R)-2-Oxabicyclo[3.3.1]nonan-3-one

In the title compound, C8H12O2, the cyclohexane ring exhibits a chair conformation and the δ-lactone ring is axially bonded to the cyclohexane ring. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, resulting in ribbons extending along [010].

In the title compound, C 8 H 12 O 2 , the cyclohexane ring exhibits a chair conformation and the -lactone ring is axially bonded to the cyclohexane ring. In the crystal, molecules are linked by C-HÁ Á ÁO hydrogen bonds, resulting in ribbons extending along [010].

Comment
The titled compound, C 8 H 12 O 2 , was prepared in a three step synthesis (Fig. 2). Racemic diethyl 2-(3oxocyclohexyl)malonate (1) was synthesized as a product of Michael addition of diethyl malonate to cyclohex-2-en-1-one. The molecular structure of the title compound is shown in Fig. 1. Bond lengths and angles in (-)-3 are similar to those observed in related structures [Yokoyama et al., 2003;Schmidt et al., 1998;Finet et al., 2007]. As in these related structures, in (-)-3 the cyclohexane ring reveals chair conformation ( Fig. 1) and the δ-lactone ring is axially bonded to the cyclohexane ring.

Experimental
Crystals suitable for X-ray structure analysis were obtained directly after purification by column chromatography by slow evaporation of the eluent (petroleum ether : aceton : iso-propanol : ethyl acetate (40:1:3:1) v/v) at room temperature.

Refinement
All H atoms were placed at calculated positions and were treated as riding atoms, with C-H distances of 0.99 -1.00 Å.
The absolute configuration of (-)-3 was choosen on the basis of known absolute configuration of particular substrates: The absolute configuration of (-)-1 was confirmed by comparison of its optical rotation with the literature data [Wascholowski et al., 2008;Tzvetkov et al., 2006;Xu et al., 2002]. The absolute configuration of the carbon atom bearing hydroxyl group in product (+)-2 was determined using the Mosher's ester [Olejniczak, 2010]. Fig. 1. Selected view of (-)-3 (30% probability thermal ellipsoids).

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.