(4R)-10α-Acetoxy-4β-(3-furyl)-1,4,4a,5,6,7,8,9,10,11,12,12bβ-dodecahydro-4aβ,7,9,9-tetramethyl-2,13-dioxo-7β,11β-methano-2H-cycloocta[f][2]benzopyran-8β-acetic acid methyl ester