Diels‐Alder Reaction of Oxazolidine‐fused Butadienes Toward Alkenes: Shedding Light on the Energetics, Selectivities, and Molecular Mechanistic Aspects by a Density Functional Theory Study

Abstract

AbstractThis work comprehensively studies the underlying features of a Diels‐Alder (DA) reaction between an electron‐rich diene D‐1 and an electron‐deficient dienophile Dph‐2. The DA reaction studied takes place along the complete C4‐C5 regioselectivity and a high exo‐stereoselectivity. Based on the kinetics analyses, the evaluated regioselectivity, , and exo‐stereoselectivity, , represent an excellent agreement with the experimental outcomes. This DA reaction also displays a high polarity caused by a strong nucleophilic and a strong electrophilic character of, respectively, D‐1 and Dph‐2. A prediction of the C4‐C5 regioselectivity is made possible by analysis of the Parr functions values estimated at the reactive sites of reactants. The origin of the exo‐stereoselectivity predominance over the endo one was well discussed employing an activation‐strain model and a natural bond orbital analysis. The molecular mechanistic considerations elucidate that formation of both C4‐C5 and C1‐C6 single bonds takes place via C‐to‐C coupling of the corresponding pseudoradical centers.