Silicon-tethered intramolecular nucleophilic additions of a hydroxymethyl unit to ketones in β-hydroxyketones have been developed. The product obtained by this protocol was successfully converted to chiral A-ring moieties of Taxol™. Also developed was a promising silicon-tethered intramolecular α-alkylation reaction of the cyclic hydroxyketone.
preparations of the taxolA-ringfragment are described: one via organocatalyzed α-aminoxylation and the other via Sharpless asymmetric dihydroxylation (SAD). The former approach affords the A-ringfragment in 10 steps, and the latter approach involves eight steps to afford the new A-ringfragment in 91% ee, which is made enantiomerically pure through recrystallization. The new A-ringfragment bearing a bromoalkene