STUDIES DIRECTED TOWARD THE TRIPLY-CONVERGENT TOTAL SYNTHESIS OF CEPHALOTAXINE
Abstract
Studies directed toward an original synthesis of cephalotaxine and 11-hydroxycephalotaxine are described. This new convergent approach involves a late intramolecular acylnitroso (4+2) cycloaddition. It required raising the oxidation level of a fragile piperonal substructure to the desired carboxylic acid, precursor of the requisite hydroxamic acid, which proved synthetically impractical. New preparations of the $\beta$,$\gamma$-dihydroxylated vinyl sulfone moiety are reported. However, elimination of a chiral sulfoxide failed to induce asymmetry and produced only the racemic vinylsulfone. The effect of another vinyl sulfone, lacking $\beta$-functionality, on the conjugate addition and the gain in stability of the ensuing adducts were investigated. Finally, elimination of an allylic phenylsulfone by "self-immolation" of an intermediate ortho-lithiophenylsulfone afforded the corresponding diene on a variety of substrates.
Degree
Ph.D.
Subject Area
Organic chemistry
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