Enantioselective Total Synthesis of Taxol

Enantioselective total synthesis of taxol has been accomplished. Coupling reaction of the optically A-ring hydroxy aldehyde with the aromatic C-ring fragment followed by Lewis acid mediated eight-membered B-ring cyclization gave the desired ABC endo-tricarbocycle. The C-ring moiety of this product reduced under Birch conditions to the cyclohexadiene derivative, which was oxygenated by singlet oxygen the convex β-face to give the C4β,C7β-diol stereoselectively. For introduction of the C19-methyl, the ketone was prepared via cyclopropanation of the C-ring allylic alcohol or conjugate addition of cyano group to the C-ring enone. Reductive cleavage of the cyclopropane ring followed by isomerization of resulting enol to the corresponding ketone gave the crucial synthetic intermediate containing the C19-methyl group. Regioselective transformation of three hydroxyl groups of this intermediate, conversion of the4-carbonyl group to the allyl chloride, and introduction of the C10-oxygen functionality afforded a precursor D-ring construction. Dihydroxylation of the allyl chloride moiety followed by basic treatment of the resulting gave a fully functionalized taxol skeleton. Functional group manipulation of this product including of the C13 side chain provided (−)-taxol.