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The strategy used in our laboratory to synthesize diterpene natural compound-Taxol ( fig. 1-1 ) is a convergent approach. By synthesizing ring A and ring C with latent functions separately, followed by the coupling of ring A and ring C to form ring B and succeed the construction of the back bond structure of the target molecule. Together with the elaboration of the necessary functional groups with the correct stereochemistry the Taxol molecule could then be synthesized.
This dissertation describes the preparation of Ring A intermediate ( fig.A ) which will be used in the total synthesis of Taxol.
Firstly, the starting material, cyclopentene (I), was converted, by way of ozonolysis and aldol condensation into the compound-(II); After oxidation, protection of carbonyl group and reduction of formy1 group, the compound-(III) was obtained. Followed by bromination and the reaction with 1, 3-dithian, a white sulfonium salt compound-(IV) was formed, which was then subjected to [2,3]-sigmatropic rearrangement, desulfurization and reduction sequentially to yield compound-(V). Deprotection and cyano group introduction yielded compound-(VI). Finely, treatment of compound-(VI) with excess Dibal-H and protection of the resulting formy1 group to give the ring A intermediate (fig.A).
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