%0 Journal Article
%A Vermeeren, Pascal
%A Hamlin, Trevor
%A Fernández López, Israel
%A Bickelhaupt, Matthias
%T How lewis acids catalyze diels–alder reactions
%D 2020
%@ 1433-7851
%U https://hdl.handle.net/20.500.14352/101614
%X The Lewis acid(LA)-catalyzed Diels–Alder reaction between isoprene and methyl acrylate was investigated quantum chemically using a combined density functional theory and coupled-cluster theory approach. Computed activation energies systematically decrease as the strength of the LA increases along the series I2 < SnCl4 < TiCl4 < ZnCl2 < BF3 < AlCl3. Emerging from our activation strain and Kohn–Sham molecular orbital bonding analysis was an unprecedented finding, namely that the LAs accelerate the Diels–Alder reaction by a diminished Pauli repulsion between the p-electron systems of the diene and dienophile. Our results oppose the widely accepted view that LAs catalyze the Diels–Alder reaction by enhancing the donor–acceptor [HOMOdiene–LUMOdienophile] interaction and constitute a novel physical mechanism for this indispensable textbook organic reaction.
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