cycloaddition reactions of nitrile oxides to chiral 3-acryloyl-2-oxazolidinones lead to highly diastereoselective formation of 2-isoxazolines. The magnesium ion serves to fix the α,β-unsaturated moiety through chelation to effect chiral shielding. These asymmetric reactions provide the first successful examples of Lewisacid-mediated stereocontrol of nitrile oxide cycloaddition reactions to electron-deficient