Showing structure for (4r,4as,5s,8ar,9ar)-9a-ethoxy-3,4a-dimethyl-4-{[(2z)-2-methylbut-2-enoyl]oxy}-2-oxo-4h,5h,6h,7h,8h,8ah,9h-naphtho[2,3-b]furan-5-carboxylic acid