5,9-Dihy-droxy-9-methyl-3,6-dimethyl-ene-3a,4,5,6,6a,7,8,9,9a,9b-deca-hydro-azuleno[4,5-b]furan-2(3H)-one.

The title compound, C(15)H(20)O(4), was synthesized from 9α-hy-droxy-parthenolide (9α-hy-droxy-4,8-dimethyl-12-methyl-ene-3,14-dioxatricyclo-[9.3.0.0(2,4)]tetra-dec-7-en-13-one), which was isolated from the chloro-form extract of the aerial parts of Anvillea radiata. The seven-membered ring has a chair conformation, while the five-membered rings display twisted conformations. The dihedral angle between the seven-membered ring and the lactone ring is 21.69 (10)°. In the crystal, mol-ecules are linked into chains propagating along the c axis by inter-molecular O-H⋯O hydrogen bonds; an intra-molecular O-H⋯O link also occurs.