合成路线1

Boron-catalyzed condensation of propionyl oxazolidinone (I) with acrolein (II) stereoselectively provided the aldol product (III), and further methanolysis afforded beta-hydroxy ester (IV). A second aldol condensation of (IV) with methacrolein (V) furnished a difficultly separable mixture of diols (VI). Conversion of (VI) to the corresponding acetonides by treatment with 2-methoxypropene (VII) allowed chromatographical separation of the required major isomer (VIII). Hydrolysis of the acetonide, followed by ring-closing metathesis of diene (XI) in the presence of Grubbs catalyst gave rise to cyclopentene (XII). Selective silylation of the less hindered allylic hydroxyl of (XII) with tert-butyldimethylsilyl chloride yielding (XIII) and subsequent oxidation of the remaining alcohol group with MnO2 then provided ketone (XIV). Conjugate addition of lithium di-n-butylcuprate to the unsaturated ketone, followed by phenylselenylation of the intermediate enolate with PhSeBr yielded alpha-selenyl ketone (XV). Oxidative elimination of the phenylselenyl group gave a (1:1) mixture of the required unsaturated ketone (XVII) and its exomethylene isomer (XVI). Isomerization of (XVI) to the desired endo isomer (XVII) was carried out by treatment with RhCl3.