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KMID : 1059519870310020133
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Journal of the Korean Chemical Society
1987 Volume.31 No. 2 p.133 ~ p.142
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The Importance of π-Nonbonded Secondary Orbital Interaction on the Stereoselectivity in the (4+2) Cycloaddition Reactions of Allene Compounds
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Lee Ik-Choon
Rhyu Keun-Bae
Lee Byung-Choon
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Abstract
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Stereoselectivities of (4+2) cycloaddition reactions of cyclopentadiene with the methyl-substituted allenic acids and esters were investigated by application of π-nonbonded interaction (π-NBI) theory. 2-FMO method has been found to be adequate for determination of endo selectivities of diene(LUMO)-dienophile (LUMO) interaction in the thermal reactions and diene (HOMO)-dienophile (LUMO) interaction in the Lewis acid catalyzed reactions. π-isoconjugate diene structure was formed by through-bond interaction of allene moiety with methyl group in the cumulated diene system; the methyl substituent acts as a conjugative chain and causes inter-level narrowing effect of the FMO's. In dienophiles which do not form π-isoconjugate diene system, methyl group acts merely as an electron donating group. In thermal reactions, the stereoselectivities are controlled by π-nonbonded secondary orbital interaction (π-NSOI) of methyl substituent, which behaves similarly as an ethylene molecule.
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