1,3-Dipolar Cycloadditions of Carbonyl Ylides to Aldimines: Scope, Limitations and Asymmetric Cycloadditions

The development of a diastereoselective 1,3‐dipolar cycloaddition of carbonyl ylides and imines for the synthesis of α‐hydroxy‐β‐amino esters is described. The methodology is successfully applied to chiral α‐methylbenzylimines affording enantiomerically pure syn‐β‐amino alcohols, which is exemplified with a short asymmetric synthesis of the paclitaxel side‐chain. The use of chiral Rh(II) carboxylate catalysts for the development of a catalytic enantioselective 1,3‐dipolar cycloaddition is also described, affording syn‐β‐amino alcohols in modest enantiomeric purity (e.r. up to 82:18).