合成路线1

The ozonolysis of the terminal double bond of cyclic carbonate (XVII) with O3 in methanol/NaOH followed by oxidation of the resulting aldehyde with KMnO4 and methylation with diazomethane gives the ester (XVIII), which is submitted to a Dieckman cyclization by means of lithium diisopropylamide (LDA) in THF, yielding the tetracyclic ester (XIX). The protection of the free hydroxy group of (XIX) with 2-methoxypropene and p-toluenesulfonic acid affords the enol ester (XX), which is decarboxylated with potassium phenylthiolate in hot DMF, affording the tetracyclic ketone (XXI). Selective deprotection of (XXI) in acidic medium gives the hydroxy ketone (XXII), which is protected again with a stronger protecting group, benzyloxymethyl chloride (BOMCl) ethyl(diisopropyl)amine, giving the ketone (XXIII). Enolization of (XXIII) with trimethylsilyl chloride (TMSCl) and LDA yields the enol-silyl ether (XXIV), which is oxidized with m-chloroperbenzoic acid (MCPBA) in hexane to the alpha-silyloxy ketone (XXV). The Grignard reaction of (XXV) with methylmagnesium bromide affords the tertiary alcohol (XXVI), which is dehydrated with the Burgess' reagent to the methylene compound (XXVII). This compound is either mesylated with mesyl chloride and osmylated with OsO4 to the monomesylated triol (XXVIII), or osmylated with OsO4 followed by silylation with TMSCl, tosylated with p-toluenesulfonyl chloride and desilylated to give the monotosylated triol (XXIX). Both compounds (XXVIII) and (XXIX) are cyclized by means of 1,8 diazabicyclo[5.4.0]undec-7-ene (DBU) in hot toluene to the hydroxyoxetane (XXX), which is acetylated with acetic anhydride in dimethylaminopyridine (DMAP) to the acetoxyoxetane (XXXI). Selective desilylation of (XXXI) with HF in pyridine yields the secondary alcohol (XXXII).