(1S,2R,4'aβ,6S,7'S,9'aS)-6-(Acetyloxy)-4'a,5',6',7',8',9'-hexahydro-5'β-hydroxy-3,3-dimethyl-8'-ethylidene-1',9'-dioxospiro[cyclohexane-1,4'(3'H)-[1H-7,9a]methanocyclohepta[c]pyran]-2-carbaldehyde