- Lewis Acid-Catalyzed Nitrone Cycloadditions to Bidentate and Tridentate α,β-Unsaturated Ketones. High Rate Acceleration, Absolutely endo-Selective and Regioselective Reactions
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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
- Kanemasa, Shuji,Uemura, Takashi,Wada, Eiji
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p. 7889 - 7892
(2007/10/02)
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