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

The title compound, C(15)H(18)O(3), was synthesized from 9α-hy-droxy-parthenolide (9α-hy-droxy-4,8-dimethyl-12-methylen-3,14-dioxa-tricyclo-[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 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 mol-ecules into dimers that are inter-connected by C-H⋯O inter-actions, producing supramolecular chains along the b axis.