Regio- and stereochemistry in the aza-Diels–Alder reaction of an azoalkene with furan and 2,3-dihydrofuran: a molecular electron density theory study

Abstract

In the present work, a molecular electron density theory (MEDT) study is carried out to shed light on the regio- and stereochemistry in two Diels–Alder (DA) reactions explored experimentally by Lemos and coworkers. These reactions involve the aza-Diels–Alder (ADA) reaction of an azoalkene AA with both furan FU and dihydrofuran DHFU in the presence of dichloromethane at room temperature. The regiochemistry of the obtained cycloadducts is completely opposite in the considered ADA reactions. The results of the local reactivity indices analysis based on the Parr functions confirmed the regiochemistry experimentally observed. Exploration of potential energy surfaces (PESs) indicated that the formation of endo adducts, P-1n and PDH-2n, are more favorable than exo ones. It was found that the electrostatic as well as the stabilizing π···π stacking interactions between two interacting fragments in the transition states associated with the endo attack can be considered as the origin of the endo stereochemistry predominance.