Lewis Acid-Catalyzed Nitrone Cycloadditions to Bidentate and Tridentate α,β-Unsaturated Ketones. High Rate Acceleration, Absolutely endo-Selective and Regioselective Reactions

Article abstract of DOI:10.1016/S0040-4039(00)74770-8

α,β-Unsaturated ketone dipolarophiles having bidentate or tridentate ligand structures, such as (E)-1-benzyloxy- and (E)-1-(2-phenylthioethoxy)-3-penten-2-one, are activated by a Lewis acid catalyst in 1,3-dipolar cycloadditions of nitrones.Dichlorodiisopropoxytitanium and chlorotriisopropoxytitanium are especially effective.Lewis acid-mediated enhancement of stereo- and regioselectivity have been attained for the first time in intermolecular nitrone cycloadditions.Formations of dipolarophile/Lewis acid complexes is responsible for the remarkable Lewis acid catalysis. Keywords: Nitrone, Dipolar cycloaddition, Lewis acid, Stereocontrol, Regiocontrol, Bidentate and tridentate enone