CYCLOPROPANATION REACTIONS OF ENONES WITH LITHIATED SULFOXIMINES - APPLICATION TO THE ASYMMETRIC-SYNTHESIS OF CHIRAL CYCLOPROPANES

Stabilized lithiated sulfoximines 2 and 9 undergo highly diastereosele ctive Michael reactions with acyclic enones under kinetically controll ed conditions. At rt the initially formed anionic Michael adducts unde rgo intramolecular displacement of the sulfonimidoyl group, with inver sion of stereochemistry at the carbon bearing the nucleofuge, to give cyclopropanes. Lithiated sulfoximines derived from S-alkyl sulfoximine s give mixtures of 1,2- and 1,4-adducts with enones under kinetically controlled conditions. However, at rt the 1,2-adducts are in equilibri um with their corresponding 1,4-adducts. The 1,4-adducts are formed in a highly diastereoselective manner and are rapidly converted to diast ereomerically pure cyclopropanes in good to excellent yields. Opticall y active versions of these sulfoximines give cyclopropanes in high ena ntiomeric purities.