合成路线1

In a different synthetic strategy, the known Garner's aldehyde (I) is subjected to a Wittig reaction with phosphorane (II) to give the unsaturated ester (III), which is subsequently hydrogenated, producing (IV) as an inseparable mixture of diastereoisomers. Oxazolidine hydrolysis in (IV), followed by cyclization under acidic conditions leads to lactone (V). This is then converted to the thiolactone (VI) upon treatment with Lawesson's reagent in hot toluene. Condensation of thiolactone (VI) with the Wittig reagent (VII), followed by double bond isomerization in the presence of DBU furnishes the dihydropyran derivative (VIII). Stereoselective hydrogenation of the double bond of (VIII) with PtO2 gives rise to the desired all-cis isomer (IX). The methyl vester group of (IX) is then reduced to aldehyde (X) by means of DIBAL in cold toluene.