Governing organic reactions through secondary orbital interactions. Semiempirical and density functional theory study of catalyzed cycloaddition reactions between pyrrole and ether dienophiles

Abstract

A combination of density functional and semiempirical computational studies of cycloaddition reactions with an activated pyrrole and a specially designed dienophile were performed to study electronic interactions and rearrangements that govern cycloaddition reactions. Several very simple principles, such as bond order, uniformity, and secondary orbital interactions were used to follow the reaction paths and the reaction outcomes were determined. It was demonstrated that the localization of double bonds in the ring would increase the reactivity. The reaction should proceed through the transition state that will have the most uniform ring bond order distribution. It was also demonstrated that secondary orbital interactions between reactants, such as hydrogen bonding, could be the curtailing factor that determines the reaction outcome. To obtain a better understanding of the reaction transformations, nonbonding interactions in the reactants’ complexes and their isomeric transition states were discussed.