Spiro[1.3-dioxolane-2.6'(3'H)-naphtho[2.3-c]furan]-9'-carboxylic acid. 1'.3'a.5'.7'.8'.8'a.9'.9'a-octahydro-1'-methyl-3'-oxo-. phenylmethyl ester. (1'R.3'aR.8'aS.9'S.9'aR)-