Highly Diastereoselective Enolate Addition of O-Protected α-Hydroxyacetate to (<i>S</i><i>_R</i>)-<i>tert-</i>Butanesulfinylimines: Synthesis of Taxol Side Chain

The taxol side chain (SR,2R,3S)-N-tert-butanesulfinyl-O-Boc-3-phenylisoserine benzyl ester 4c was synthesized through a lithium enolate addition of O-Boc-α-hydroxyacetate benzyl ester 5c to benzylidene (SR)-tert-butanesulfinamide 6a in excellent yield and diastereoselectivity. By similar approach, a series of enantiopure 3-substituted isoserine benzyl esters 4 useful for the semi-syntheses of taxol derivatives were also prepared in high to excellent yields and diastereoselectivities. The diastereoselective addition mechanism was discussed on the basis of the experimental observation.