Switch From Pauli-Lowering to LUMO-Lowering Catalysis in Bronsted Acid-Catalyzed Aza-Diels-Alder Reactions.

ABSTRACT: Brønsted acid-catalyzed inverse-electron demand (IED) aza-Diels-Alder reactions between 2-aza-dienes and ethylene were studied using quantum chemical calculations. The computed activation energy systematically decreases as the basic sites of the diene progressively become protonated. Our activation strain and Kohn-Sham molecular orbital analyses traced the origin of this enhanced reactivity to i) "Pauli-lowering catalysis" for mono-protonated 2-aza-dienes due to the induction of an asynchronous, but still concerted, reaction pathway that reduces the Pauli repulsion between the reactants; and ii) "LUMO-lowering catalysis" for multi-protonated 2-aza-dienes due to their highly stabilized LUMO(s) and more concerted synchronous reaction path that facilitates more efficient orbital overlaps in I

SUBMITTER: Yu S 

PROVIDER: S-EPMC8340067 | biostudies-literature | 2021 Aug

REPOSITORIES: biostudies-literature