Crystal structure and computational study of 3,4-dihy-droxy-3-hy-droxy-methyl-9-methyl-6-methyl-idene-3a,4,5,6,6a,9,9a,9b-octa-hydro-azuleno[4,5-b]furan-2,8(3H,7H)-dione.

In the mol-ecule of title compound, C15H20O6, also known as cynarinin A, the cyclo-pentane ring having twist conformation and a γ-lactone ring assuming an envelope conformation are trans- and cis-fused, respectively, to a cyclo-heptane ring adopting a twist-chair conformation. In the crystal, O-H⋯O hydrogen bonds link neighbouring mol-ecules, forming a three-dimensional network. Theoretical calculations of the mol-ecular structure using the CNDO approximation and MOPAC PM3 geometry optimization are in satisfactory agreement with the results of the X-ray structure analysis.