7-[2-(3-Furyl)ethyl]-7,8-dimethyl-3,5,6,6a,7,8,9,10-octahydro-1H-naphtho[1,8a-c]furan-3-one

In the title molecule, C20H26O3, a clerodane diterpenoid isolated from Dodonaea viscosa, the trans-fused six-membered rings of the decaline system display chair conformations. The five-membered lactone ring adopts an envelope conformation and the five-membered furan ring is essentially planar with a maximum deviation of 0.0052 (12) Å.

In the title molecule, C 20 H 26 O 3 , a clerodane diterpenoid isolated from Dodonaea viscosa, the trans-fused sixmembered rings of the decaline system display chair conformations. The five-membered lactone ring adopts an envelope conformation and the five-membered furan ring is essentially planar with a maximum deviation of 0.0052 (12) Å .

Comment
In continuation of our work on Natural Product chemistry (Arfan et al., 2010) and in view of the important role played by natural products in medicinal chemistry (Khan et al., 2005), the plant Dodonaea viscosa has been subjected to phytochemical investigation which resulted in the isolation of the title compound.
The title molecule ( Fig. 1) is chiral, but its absolute configuration could not be determined from the crystallographic data. However, the absolute stereochemistry of the compound was established from NMR and literature data (Jefferies et al., 1967). The molecule has four chiral centers and the two trans fused cyclohexyl rings of decaline, C7-C14 and C13-C18, adopt chair conformations. The five-membered lactone ring adopts a C13-envelope conformation with C13 0.625 (3) Å out of the plane formed by the rest of the ring atoms. The five-membered furan ring is essentially planar with maximum deviation of any atom from the plane being 0.0052 (12) Å for C2. There are no significant hydrogen bonds or π-π interactions between the molecules although there may be a weak C-H···π interaction linking neighbouring molecules; C2-H2···C1 3.747 (3)Å (under 1/2 + x, 1.5 -y, 1 -z). This leads to zigzag chains running parallel to the a axis (Fig. 2).

Experimental
The whole plant of Dodonaea viscosa (50 kg) was powdered and extracted with methanol (100 L × 3) at room temperature and the residue (1 kg) was separated under vacuum. The residue was suspended in water and extracted with n-hexane, chloroform, ethyl acetate and n-butanol, respectively. The chloroform fraction (500 g) was subjected repeatedly to column chromatography on silica gel using petroleum ether with a gradient of 15% ethyl acetate to yield the title compound (2 g).
Colourless crystals suitable for X-ray crystallographic analysis were obtained from an ether-chloroform mixture(1:1) by slow evaporation of the solvent at room temperature.