Crystal structure of pseudoguainolide

The lactone ring in the title mol­ecule, C15H22O3 (systematic name: 3,4a,8-tri­methyl­dodeca­hydro­azuleno[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-methyl­ene C-C bond. The seven-membered ring is based on a twisted boat conformation. No specific inter­actions are noted in the the crystal packing