合成路线1

The sodium salt of L-phenylalanine (I) was condensed with pivalaldehyde (II) in boiling pentane to afford imine (III). Subsequent reaction of (III) with benzyl chloroformate generated oxazolidinone (IV) as a 9:1 mixture of diastereoisomers, which were separated chromatographically. The required cis compound was treated with allyl bromide (V) in the presence of potassium hexamethyldisilazide in THF at -78 C to provide (VI) as the major isomer. Aldehyde (VII) was then obtained by ozonolysis of (VI) at -78 C. Reductive amination of (VII) with L-homophenylalanine methyl ester (VIII) using NaBH3CN yielded the corresponding amine (IX) which, upon heating in toluene in the presence of 1-hydroxybenzotriazole, afforded pyrrolidinone (X). Reduction of the ester function of (X) with Ca(BH4)2 gave alcohol (XI), which was finally oxidized under Swern conditions to the target aldehyde.