Synthesis, Conformational Analysis, and Biological Evaluation of Heteroaromatic Taxanes.

The asymmetric syntheses of heteroaromatic 3-[(tert-butyldimethylsilyl)oxy]-2-azetidinones 12-16 via chiral ester enolate-imine cyclocondensation chemistry are described. The azetidinones contain heteroaromatic moieties which, in certain cases, contribute to a decrease in enantioselectivity due to possible alternate coordinations in the transition states. The (3R,4S)-3-[(tert-butyldimethylsilyl)oxy]-4-heteroaryl-2-azetidinones were subsequently converted to the heteroaromatic taxanes 31-36 and 43-45.