A theoretical study on the hetero-Diels–Alder reaction of phosphorous substituted diaza- and oxaza-alkenes with olefins derivatives

Abstract

The reactivity, regio- and stereo-selectivity of the hetero-Diels–Alder reaction of 1,2-diaza- and 1,2-oxaza-1,3-butadiene derivatives with some olefins has been investigated using density functional theory (DFT) based reactivity indices and activation energy calculations at the B3LYP/cc-pVDZ level of theory. Four reactive pathways associated with ortho and meta regio- and endo and exo stereo-selectivity have been explored and characterized. Analysis of the results indicates that these reactions take place via an asynchronous concerted bond-formation process with a polar character. All of the studied processes predicted ortho regioselectivity and in the majority of them the endo approach appeared to be energetically favored, in agreement with experimental findings. Phosphonyl and phosphinyl groups increased the reactivity of the 1,2-oxaza-1,3-butadienes, shown by decreasing activation energies. DFT-based reactivity indices correctly explain the polar nature of these cycloaddition reactions.