合成路线1

Treatment of hydroxylactone (I) with benzyl bromide and silver oxide gave the corresponding benzyl ether (II). Subsequent reduction of the lactone (II) with LiAlH4 afforded the linear diol (III). Tioether (IV) was prepared by treatment of (III) with diphenyl disulfide and tributylphosphine, and the remaining hydroxyl group of (IV) was then protected as the ketal (VI) using ethyl vinyl ether (V) and pyridinium tosylate. Oxidation of (VI) to sulfone (VII) was accomplished with m-chloroperbenzoic acid. Condensation of (VII) with 2-methyl-delta-valerolactone (VIII), followed by BF3 - Et2O-catalyzed cyclization furnished spiroketal (IX). Finally, the phenylsulfonyl group of (IX) was reductively removed by means of sodium amalgam.