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<H1>Pyrylium-ylide approach to the taxane core structure</H1>
<h2>Philip Magnus </h2>
<ADDRESS>Department of Chemistry and Biochemistry, University of Texas at
Austin, Austin, Texas 78712. </ADDRESS>
<hr>The use of a pyrylium-cyclization
controls the absolute stereochemistry of the crucial C-19 methyl group and hence
all of the other stereogenic centres. The heterocyclic oxido-bridge imposes a
rigid comformational lock, thus enabling complete sterechemical control.
Eventually, the oxido bridge must be eliminated, and in this process the
oxidation state is transposed with the formation of the 4,5-double bond. This
is, of course, ideally placed for the insertion of the oxetane ring. This
lecture will describe the results we have obtained using this unique strategy.
<hr>
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