Synthesis of the Side Chain via an Epoxide Intermediate

McChesney and his collaborators chose another approach, in which the easily accessible racemic trans epoxide 7.2.5 was opened by HCl to form chlorohydrin 7.2.6, which was then converted to the cis-epoxide 7.2.7 with basic Amberlite 400. Opening of the cis-epoxide 7.2.7 with ammonia in MeOH followed by methanolysis of the resulting amide and benzoylation gave racemic taxol side chain methyl ester 7.2.8 (255, 256). 

As an alternative functional group to an epoxide, cyclic sulfates and sulfites have also been used as intermediates to prepare the taxol side chain. Thus, asymmetric dihydroxylation of cis methyl cinnamate using AD-mix (3 gave the diol 7.2.12, which was converted to the cyclic sulfate 

13 with thionyl chloride followed by oxidation. The opening of 

13 with azide proceeded in a similar fashion to that of an epoxide, giving the azide 7.2.14, which was converted to the taxol side chain 7.2.15 (259). 

In another approach, commercially available ethyl fran.y-cinnamate was used as starting material, and similar chemistry to that described above was performed, except that the cyclic sulfite 7.2.16 was opened directly with azide instead of being oxidized to sulfate the resulting azidoalcohol 7.2.17 had the opposite stereochemistry at C-2. The stereochemistry at C-2 was inverted by the Mitsonobu procedure to give 

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