合成路线1

In an alternative, stereospecific synthesis of (X), Sharpless asymmetric epoxidation of 2-ethyl-2-propen-1-ol (XI) in the presence of (-)-diethyl tartrate provides the (R)-epoxide (XII). Ring opening of (XII) with sodium thiophenoxide produces diol (XIII), which is further protected with 1-methoxycyclohexene (VII), yielding ketal (XIV). Sulfide (XIV) is then oxidized with mCPBA to afford sulfoxide (XV) as a mixture of diastereoisomers. Pummerer rearrangement of sulfoxides (XV) in boiling Ac2O, followed by alkaline hydrolysis of the intermediate alpha-acetoxy sulfides furnishes aldehyde (XVI). Then, aldol condensation of aldehyde (XVI) with thiolactam (I) employing stannous triflate and N-ethylpiperidine gives adduct (XVII). Dehydration of alcohol (XVII) to the alpha,beta-unsaturated thiolactam (XVIII) is accomplished by tosylation with p-toluenesulfonic anhydride, followed by tosylate elimination in the presence of DBU. Desulfuration of thiolactam (XVIII) with deactivated Ra-Ni leads to (XIX). Then, hydrogenation of olefin (XIX) produces a mixture of epimers, from which the target isomer (X) can be isolated by column chromatography (7).