Cyclopropanation Reactions of Enones with Lithiated Sulfoximines: Application to the Asymmetric Synthesis of Chiral Cyclopropanes.
Stabilized lithiated sulfoximines 2 and 9 undergo highly diastereoselective Michael reactions with acyclic enones under kinetically controlled conditions. At rt the initially formed anionic Michael adducts undergo intramolecular displacement of the sulfonimidoyl group, with inversion of stereochemistry at the carbon bearing the nucleofuge, to give cyclopropanes. Lithiated sulfoximines derived from S-alkyl sulfoximines give mixtures of 1,2- and 1,4-adducts with enones under kinetically controlled conditions. However, at rt the 1,2-adducts are in equilibrium with their corresponding 1,4-adducts. The 1,4-adducts are formed in a highly diastereoselective manner and are rapidly converted to diastereomerically pure cyclopropanes in good to excellent yields. Optically active versions of these sulfoximines give cyclopropanes in high enantiomeric purities.
Pyne
Stephen G.
SG
Department of Chemistry, University of Wollongong, Wollongong, New South Wales, 2522, Australia and Department of Chemistry, University of Western Australia, Nedlands, Western Australia, 6009 Australia.
Dong
Zemin
Z
Skelton
Brian W.
BW
White
Allan H.
AH