Theoretical Analysis of Substituted Diels - Alder Reagents to Determine the Polar or Non Polar Character of the Reaction

The non-polar character of Diels-Alder (DA) reactions using 1- and 2-substituted butadienes and ethylene is discussed. Linear correlations between variations in the energy barrier and the electrophilicity index have been obtained. The charge transfer (CT) process in the cycloaddition reactions depends on the substitution pattern on almost all ethylene reagents. The current work stresses that a polar DA reaction will occur when only the ethylene is substituted by electronwithdrawing (EW) groups increasing its electrophilicity or when both DA reagents are being activated by EW and electron-releasing (ER) groups, enhancing their electrophilic and nucleophilic nature.