9β-Hydroxy-6,9-dimethyl-3-methylene-3a,4,8,9,9a,9b-hexahydroazuleno[4,5-b]furan-2(3H)-one

The title compound, C15H18O3, was synthesized from 9α-hydroxyparthenolide (9α-hydroxy-4,8-dimethyl-12-methylen-3,14-dioxa-tricyclo[9.3.0.02,4]tetradec-7-en-13-one), which was isolated from the chloroform extract of the aerial parts of Anvillea radiata. The seven-membered ring of the title compound shows a chair conformation, while the five-membered rings exibit different conformations, viz a twisted one for the lactone ring and an envelope conformation for the other five-membered ring with the C atom closest to the hydroxy group forming the flap. In the crystal, O—H⋯O hydrogen bonds connect molecules into dimers that are interconnected by C—H⋯O interactions, producing supramolecular chains along the b axis.

The title compound, C 15 H 18 O 3 , was synthesized from 9hydroxyparthenolide (9-hydroxy-4,8-dimethyl-12-methylen-3,14-dioxa-tricyclo[9.3.0.0 2,4 ]tetradec-7-en-13-one), which was isolated from the chloroform extract of the aerial parts of Anvillea radiata. The seven-membered ring of the title compound shows a chair conformation, while the fivemembered rings exibit different conformations, viz a twisted one for the lactone ring and an envelope conformation for the other five-membered ring with the C atom closest to the hydroxy group forming the flap. In the crystal, O-HÁ Á ÁO hydrogen bonds connect molecules into dimers that are interconnected by C-HÁ Á ÁO interactions, producing supramolecular chains along the b axis.

Comment
Anvillea radiata is a plant that grows in northern Africa and particularly found in the two Maghreb countries, Morocco and Algeria. This plant is used in traditional local medicine for the treatment of dysentery, gastric-intestinal disorders (Bellakhdar, 1997), hypoglycemic activity (Qureshi et al., 1990), and has been reported to have antitumoral activity (Abdel Sattar et al., 1996). In our study of different Moroccan endemic plants, we have demonstrated that the aerial parts of Anvillea radiata could be used as a renewable source of 9-hydroxyparthenolide (El Hassany, et al., 2004). In order to prepare products with high added value that can be used in pharmacology and cosmetics industry, we studied the chemical reactivity of this major constituent of Anvillea radiata. Thus, treatment of this sesquiterpene with Bi(OTf) 3 in dichloromethane (El Haib et al., 2011) leads to the litle compound with a yield of 60%. The crystal structure of (I) is reported herein.
The molecule contains three fused rings which exhibit different conformations. The molecular structure of (I), Fig.1, shows the lactone ring to adopt a twisted conformation, as indicated by Cremer & Pople (1975) (Table 1).

Experimental
Bi(OTf) 3 (39 mg, 6 x 10 -2 mmol) was added to a stirred solution of 9β-hydroxyparthenolide (600 mg, 2.27 mmol) in dichloromethane (10 ml). The reaction mixture is left stirring for three hours at room temperature. After completion of the reaction, a saturated solution of NaHCO 3 was added and the resulting mixture is extracted three times (3 x 20 mL) with dichloromethane. The organic phases are combined and dried over Na 2 SO 4 and evaporated under vacuum. Chromatography of the residue obtained on a column of silica gel eluting with hexane -ethyl acetate (85/15) allowed the isolation of the title compound (334 mg, 1.35 mmol) with a yield of 60%. Recrystallization from ethyl acetate at room temperature yielded single crystals of the title compound.

Refinement
All H atoms were fixed geometrically and treated as riding with C-H = 0.96 Å (methyl), 0.97 Å (methylene), 0.98 Å (methine) with U iso (H) = 1.2U eq (methylene, methine) or U iso (H) = 1.5U eq (methyl, OH). In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined and thus the Friedel pairs were merged and any references to the Flack parameter were removed.  9β- 4,8,9,9a,

Special details
Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

CrysAlisPro (Agilent Technologies, 2010)
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.