The lactone ring in the title mol-ecule, C15H22O3 (systematic name: 3,4a,8-tri-methyl-dodeca-hydro-azuleno[6,5-b]furan-2,5-dione), assumes an envelope conformation with the methine C atom adjacent to the the methine C atom carrying the methyl substituent being the flap atom. The other five-membered ring adopts a twisted conformation with the twist being about the methine-methyl-ene C-C bond. The seven-membered ring is based on a twisted boat conformation. No specific inter-actions are noted in the the crystal packing.
Keywords: crystal structure; inula graveolens; plant extract.