Looking at the big picture in activation strain model/energy decomposition analysis: the case of the ortho – para regioselectivity rule in Diels–Alder reactions

GRIMBLAT, NICOLÁS; SAROTTI, ARIEL M.

ORGANIC & BIOMOLECULAR CHEMISTRY

ROYAL SOC CHEMISTRY

Año: 2020 vol. 18 p. 1104 - 1111

1477-0520

The regioselectivity of the Diels-Alder reaction is predicted by the ortho-para rule which has been explained from FMO theory. Using DFT calculations, the activation-strain model and energy decomposition analysis we studied the reaction of methyl acrylate with four unsymmetrical dienes. We found that if the analysis is carried out considering the TS structures, the selectivity would not be explained by the interaction energy as expected consider the FMO arguments. However, a thorough analysis along the reaction path revealed that the interaction energy is responsible for the regioselectivity. A deeper analysis with the EDA model showed that the term that accounts for the HOMO-LUMO interactions favors the ortho/para adduct, as predicted by FMO arguments.