Melvin D. Rozeboom

Regioselectivities of Diels-Alder cycloadditions to methoxy-substituted quinones

Abstract Diels-Alder cycloadducts of unsymmetrical electron-rich dienes and methoxybenzoquinones or naphthoquinones produce adducts in which the more nucleophilic diene terminus becomes bonded to the non-methoxylated carbon. These results support the “secondary orbital”, but not the “schizophrenic”, model for donor substituent effects on regioselectivity.

On the mechanism of regioselectivity control by donor substituents on electrophilic alkenes: applications to quinone cycloadditionregioselectivity

Abstract Donor substitution on alkenes slightly increases the LUMO coefficient at the site of substitution. However, nucleophiles preferentially attack the unsubstituted terminus of the alkene due to direct repulsive interactions between the nucleophile and the substituent. Secondary orbital interactions make the terminus remote from the site of substitution the most electrophilic. LUMO coefficients, or equivalent spectroscopic measures, esr hyperfine coupling in the esr spectra of radical anions, are appropriate for prediction of reactivities of unsubstituted positions but not substituted ones.