Methyl 2-(8a-hydroxy-4a-methyl-8-methylenedecahydronaphthalen-2-yl)acrylate

The title compound, C16H24O3, was synthesized from ilicic acid which was isolated from the aerial part of Inula Viscosa (L) Aiton [or Dittrichia Viscosa (L) Greuter]. The molecule contains two fused six-membered rings both in chair conformations. In the crystal, molecules are linked into chains running parallel to the a axis by O—H⋯O hydrogen bonds.

The title compound, C 16 H 24 O 3 , was synthesized from ilicic acid which was isolated from the aerial part of Inula Viscosa (L) Aiton [or Dittrichia Viscosa (L) Greuter]. The molecule contains two fused six-membered rings both in chair conformations. In the crystal, molecules are linked into chains running parallel to the a axis by O-HÁ Á ÁO hydrogen bonds.

Comment
The Inula Viscosa (L) is widespread in Mediterranean area and extends to the Atlantic cost of Morocco. It is a well known medicinal plant (Shtacher & Kasshman, 1970;Chiappini et al., 1982) and has some pharmacological activities (Azoulay et al., 1986). This plant has been the subject of chemical investigation in terms of isolating sesquiterpene lactones (Bohlmann et al., 1977), sesquiterpene acids (Ceccherelli et al., 1988;Geissman & Toribio, 1967). The ilicic acid is one of the main components of the dichloromethane extract of the Inula Viscosa (L) Aiton or Dittrichia Viscosa (L) Greuter]. The literature report one article on the transformation of the ilicic acid (Barrero et al., 2009). In order to prepare products with high added value, that can be used in the pharmacologycal industry, we have studied the reactivity of this sesquiterpene acid. Thus, from this acid, we have prepared by the method of Barrero et al. (2009), 2-(4a,8-Dimethyl-1, 2,3,4,4 a,5,6,7-octahydro naphthalen-2-yl)-acrylic acid methyl ester. The epoxidation of the latter compound by metachloroperbenzoic acid (mCPBA), followed by the opening of the epoxide obtained by Bi(OTf) 3 leads to the title compound (I) with a yield of 50%.
The molecule is built up from two fused six-membered rings. The molecular structure of ( Fig. 1) shows the two rings to adopt a perfect chair conformation as indicated by Cremer & Pople (1975)

Experimental
To 1 g (4 mmol) of 2-(4a,8-Dimethyl-1,2,3,4,4a,5,6,7-octahydro-naphthalen-2-yl)-acrylic acid methyl ester dissolved in 40 ml of dichloromethane was added one equivalent of m-chloroperbenzoic acid at 70%. The reaction mixture was stirred at room temperature for 3 h, then treated three times with a solution of sodium bisulfite at 10%. The organic layer was then washed with distilled water three times until neutralization, dried over sodium sulfate, filtered and concentrated under reduced pressure. The residue obtained was chromatographed on silica gel eluting with hexane/ ethyl acetate (98/2) to give quantitatively the corresponding epoxide. 500 mg (1,89 mmol) of this epoxyde is dissolved with 5% of Para-toluene sulfonic acid (APTS) in 20 ml of dichloromethane. The reaction mixture was left stirring for a period of half an hour and then treated with 10 ml of a solution of sodium bicarbonate to 10%. The organic layer was dried filtered and concentrated under reduced pressure. Chromatography on silica gel, eluting with hexane/ethyl acetate (98/2) of the residue obtained, allowed us to obtain 250 mg (94.5 mmol) of the title compound which was recrystallized in dichloromethane.

Refinement
All H atoms were fixed geometrically and treated as riding with O-H = 0.82Å, C-H = 0.93 Å(aromatic), 0.96Å (methyl), 0.97 Å (methylene), 0.98Å (methine) with U iso (H) = 1.2U eq (C aromatic , C methylene , C methine ) or U iso (H) = 1.5U eq (O, supplementary materials sup-2 C methyl ). In the absence of significant anomalous scattering, the absolute configuration could not be determined and thus Friedel pairs were merged and any references to the Flack parameter were removed. Fig. 1. : Molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.