合成路线1

The acylation of 3-hydroxypiperidine with tosyl chloride followed by oxidation of the OH group with CrO3 and H2SO4 gives 1-tosylpiperidine-3-one (II), which is converted into the enol triflate (III) by reaction with LHMDS and PhN(SO2CF3)2 in THF. The condensation of (III) with 1-(tert-butoxycarbonyl)-2-vinylpiperidine (IV) by means of Pd(OAc)2 affords the diene (V), which is selectively deprotected with NaOH in methanol to afford the piperidine (VI). The condensation of (VI) with silylated methyl propenoate (VII) by means of triethylamine in dichloromethane gives the nonisolated intermediate (VIII) that cyclizes to the tetracyclic compound (IX) (as major isomer). The reaction of (IX) with HF and pyridine in refluxing dichloromethane affords the silylated tetracyclic ketone (X) (as major isomer), which is desilylated with KF, KHCO3 and H2O2 in refluxing methanol/THF providing the tetracyclic hydroxyketone (XI) (as major isomer), separated by column chromatography. Elimination of the OH group of (XI) with C6F5OC(S)-Cl, Bu3SnH and AIBN in refluxing benzdene yields the tetracyclic ketone (XII), which is finally reduced with LiAlH4 in THF.