The three-ring eudesmanolide, C15H16O3, is a natural product isolated from Dicoma anomala Sond. (Asteraceae). The compound contains an endo–exo cross conjugated methylenecyclohexenone
ring with an envelope conformation transfused
with cyclohexane and trans-annelated with an -
methylene -lactone. The absolute structure was assigned by optical rotation measurements compared to those from the synthetic compound with known stereochemistry. The crystal packing is consolidated by C—H...O interactions.