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

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.