Abstract
The title compound, C(20)H(32)O(2) (systematic name: 3-ethenyl-3,4a,7,7,10a-penta-methyl-dodeca-hydro-9H-benzo[f]chromen-9-one), was isolated from Sideritis perfoliata. In the crystal, mol-ecules pack in helical supra-molecular chains along the 2(1) screw axis running parallel to the a axis, bound by C-H⋯O hydrogen bonds. These chains are efficiently inter-locked in the other two unit-cell directions via van der Waals inter-actions. Hirshfeld surface analysis shows that van der Waals inter-actions constitute the major contribution to the inter-molecular inter-actions, with H⋯H contacts accounting for 86.0% of the surface.