![]() A striking number of organocatalysts have been developed over the years to increase the reactivity and selectivity of the DA reaction. ![]() Since its discovery in 1928, it has paved the way for a convenient procedure to create sixâmembered rings, with up to four stereocenters, becoming the gold standard for many applications ranging from the synthesis of natural products to the industrial production of relevant compounds in the pharmaceutical field. The DielsâAlder (DA) cycloaddition reaction is of paramount importance in synthetic organic chemistry. These findings again demonstrate the generality of the Pauli repulsionâlowering catalysis concept. Notably, the reactivity can be further enhanced on going from a Period 3 to a Period 5 LA, as these species amplify the asynchronicity of the DielsâAlder reaction due to a stronger binding to the dienophile. Our detailed activation strain and KohnâSham molecular orbital analyses reveal that these LAs lower the DielsâAlder reaction barrier by increasing the asynchronicity of the reaction to relieve the otherwise destabilizing Pauli repulsion between the closedâshell filled Ïâorbitals of diene and dienophile. The reaction barriers systematically increase from halogen ![]() The catalytic effect of various weakly interacting Lewis acids (LAs) across the periodic table, based on hydrogen (Groupâ 1), pnictogen (Groupâ 15), chalcogen (Groupâ 16), and halogen (Groupâ 17) bonds, on the DielsâAlder cycloaddition reaction between 1,3âbutadiene and methyl acrylate was studied quantum chemically by using relativistic density functional theory.
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