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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 31, Number 2
JKCSEZ 31(2)
April 20, 1987 

The Importance of π-Nonbonded Secondary Orbital Interaction on the Stereoselectivity in the (4+2) Cycloaddition Reactions of Allene Compounds

알렌화합물의 (4+2) 고리화반응에서 입체 선택성에 대한 π-비결합 2차 궤도함수 상호작용의 중요성
Ikchoon Lee, Keun Bae Rhyu, Byung Choon Lee

이익춘, 유근배, 이병춘
시클로로펜타디엔과 메틸기로 치환된 알렌의 산 및 에스테르간의 (4+2)고리화반응에서 입체 선택성을 π-비결합상호작용(π-NBI)을 적용하여 고찰하였다. 열반응에서는 diene(LUMO)-dienophile (HOMO)만을 고려한 2-FMO방법이, 산촉매반응에서는 diene (HOMO)-dienophile (LUMO)상호작용만을 고려한 2-FMO방법이 이들의 입체선택성의 결정에 중요하였다. cumulated diene계의 친디엔체에서 메틸 치환기는 알렌구조와 through-bond 상호작용에 의해 π-isoconjugate diene 구조를 형성하여 컨쥬게이션기로 작용하며 FMO의 에너지에 narrowing effect를 주고 있으나 이같은 π-isoconjugated diene 구조를 만들 수 없는 친디엔체에서는 메틸기가 단순히 전자주는기로 작용한다. 열반응에서 입체선택성은 에틸렌 분자와 마찬가지로 메틸 치환기의 π-비결합 2차궤도 상호작용(π-NSOI)에 의해서 좌우되었다.

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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