The Electronic Structures and Dienophilicities in the Diels-Alder Reaction of Methyl α, β -Unsaturated Carboxylates

Abstract

Molecular orbital calculation based on the orthogonal atomic orbitals has been carried out on seven methyl α, β -unsaturated carboxylates in order to elucidate the remarkable differences in their reactivity as dienophiles in the Diels-Alder addition to methyl trans-9, trans-11-octadecadienoate shown in Table 2. Calculated results are summarized in Table 1. It is found that the frontier electronic densities of the highest occupied orbitals at the reaction centers have a good linear relationship with the logarithm of the rate constants. Plots of the correlation for dicarboxylates and for monocalboxylates fall on two different but parallel lines as shown in Fig.1. The correlation of the chemical reactivity with the electronic structure has been discussed on the basis of the experimental results.