Corymbolone

The title compound, C15H24O2 [systematic name: (4S,4aR,6R,8aR)-4a-hydroxy-4,8a-dimethyl-6-(prop-1-en-2-yl)octahydronaphthalen-1(2H)-one], features two edge-shared six-membered rings with the hydroxyl and methyl substituents at this bridge being trans. One adopts a flattened chair conformation with the C atoms bearing the carbonyl and methyl substituents lying 0.5227 (16) and 0.6621 (15) Å, respectively, above and below the mean plane through the remaining four C atoms (r.m.s. deviation = 0.0145 Å). The second ring, bearing the prop-1-en-2-yl group, has a chair conformation. Supramolecular helical chains along the b axis are found in the crystal packing, which are sustained by hydroxy–carbonyl O—H⋯O hydrogen bonding.


Structural commentary
The title compound, corymbolone, was first characterised in 1985(Garbarino et al., 1985, and more recently synthesized in racemic form (Ferraz et al., 2006). In the present study, it was isolated from the product mixture that resulted from aerial oxidation of α-guaiene.
The molecular structure of the title molecule, Fig. 1, features two fused six-membered rings. The C2,C3,C5 and C6 atoms of the C1-C6 ring are planar with a r.m.s. deviation of 0.0145 Å, and with the C1 and C4 atoms lying 0.5227 (16) and 0.6621 (15) Å above and below this plane, respectively, so that the conformation of the ring is best described as being a flattened chair. By contrast, the C5-C10 ring closely approximates a chair conformation. With respect to the C1-C6 ring the C1-carbonyl, C4-methyl, C5-hydroxyl and C6-methyl groups have equatorial (eq), axial (ax), ax and eq dispositions, respectively. For the C5-C10 ring, the C5-hydroxyl, C6-methyl and C9-prop-1-en-2-yl groups have have ax, ax and eq dispositions, respectively.
The most prominent feature of the crystal packing is the formation of hydroxyl-O-H···O(carbonyl) hydrogen bonding that leads to helical supramolecular chains along the b axis (Table 1 and Fig. 2).

Synthesis and crystallization
Air was slowly bubbled through a neat solution of α-guaiene (7.0 g, 34.3 mmol) and after 21 days the crude mixture of products was subjected to column chromatography with a gradient of 100% hexane to 100% EtOAc. The product (0.12 g, 1.5%) at Rf 0.07 (10% EtOAc/hexane) was collected as a white crystalline solid and recrystallized from hexane to afford block-like colourless crystals of corymboline. M.p. 408-409 K; Lit. M.p. 409-410 K (Garbarino et al., 1985).
Spectroscopic data for the title compound are available in the archived CIF.

Refinement
The hydroxy-H atom was located in a difference Fourier map and freely refined. C-bound H-atoms were placed in  The molecular structure of the title molecule, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.  (67). All other physical and spectral data were identical to those previously reported by Garbarino et al. (1985). 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 > σ(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 O1 −0.00899 (