合成路线1

A new synthesis of (3R,4S)-1-benzyl-4-phenyl-3-(triethylsilyloxy)azetidin-2-one (XIII), a precursor of the side chain of paclitaxel, has been described: The reaction of ethyl L-tartrate (I) with benzaldehyde and TsOH followed, by reduction with LiAlH4 and AlCl3 gives the monobenzylated tretraol (II), which is submitted to an oxidative cleavage of the alpha-diol bond with NaIO4 to yield the aldehyde (III). Reaction of (III) with benzylamine affords the imine (IV), which is submitted to a Grignard addition of phenylmagnesium bromide in ether providing a 1:9 mixture of aminoalcohols (VI) and (VII) separated by chromatography. Oxidation of the desired major isomer (VII) with CrO3/H2SO4 gives the corresponding acid (VIII), which is then esterified with TMS-Cl in refluxing methanol to the methyl ester (IX). Deprotection of compound (IX) by hydrogenolysis with reluxing HCO2H over Pd/C yields 3(S)-amino-2(R)-hydroxy-3-phenylpropionic acid methyl ester (X), which is silylated at the OH group of with TES-Cl and TEA in ether/THF to afford the silyl ether (XI). Cyclization of (XI) by means of LHMDS in THF provides the beta-lactam (XII), which is finally benzoylated with benzoyl chloride and TEA in the usual way.