Crystal structure of (4bS,8aR)-1-isopropyl-4b,8,8-trimethyl-7-oxo-4b,7,8,8a,9,10-hexahydrophenanthren-2-yl acetate

The title compound, (4bS,8aR)-1-isopropyl-4 b,8,8-trimethyl-7-oxo-4 b,7,8,8a,9,10-hexahydrophenanthren-2-yl acetate, was prepared by a direct acetylation reaction of naturally occurring totarolenone. In the crystal, molecules are linked to each other by C—H⋯O hydrogen bonds and C—H⋯π interactions, forming sheets parallel to the bc plane.


Chemical context
Diterpene phenols are a family of natural products isolated from a variety of terrestrial plant sources. They exhibit a wide variety of interesting biological activities such as antitumour (Iwamoto et al., 2003;Son et al. 2005), antimicrobial (Yoshikawa et al., 2008;Pereda-Miranda et al., 1992), antiviral (Yang et al., 2011;Wen et al., 2007) and anti-inflammatory (Chen et al. 2013). In addition, derivatives of diterpene phenol natural products have been studied extensively as potential chemotherapeutic agents (Areche et al., 2007;Yang et al. 2001).

Supramolecular features
In the crystal, molecules are linked by C-HÁ Á ÁO and C-HÁ Á Á interactions, forming layers parallel to the bc plane (Table 1 and Fig. 3).

Synthesis and crystallization
A solution of totarolenone 1 (300 mg, 1.041 mmol) in acetic anhydride (10 mL) and sodium acetate (290 mg) was heated under reflux for 24 h. After cooling, the solution was extracted with ether (3 Â 20 mL). The organic layer was washed with water, dried on anhydrous Na 2 SO 4 and evaporated under reduced pressure. The obtained residue was chromatographed on silica gel column using hexane and ethyl acetate (95/5) as eluent, to give compound 2. The molecular structure of the title compound with the atom-numbering scheme. The displacement ellipsoids are drawn at the 30% probability level. Only the major disorder components are shown. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
A view along the a axis of the crystal packing of the title compound, showing the C-HÁ Á ÁO hydrogen bonds (orange dashed lines) and C-HÁ Á Á interactions (green dashed lines). For clarity, only the H atoms involved in these interactions have been included.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in calculated positions and refined in the riding model: C-H = 0.95-1.00 Å with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl). The carbonyl O atom is disordered over two sites having occupancies of 0.63 (7) and 0.37 (7). Atom C6 atom of the cyclohexene ring is disordered over two sites with an occupancy ratio of 0.793 (14):0.207 (14). The absolute structure was reliably determined based on the value of the Flack parameter [0.02 (5)].

Funding information
Funding for this research was provided by: Cadi Ayyad University.

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.