How Lewis Acids Catalyze Diels–Alder Reactions?
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Lewis acids catalyze Diels-Alder reactions by lowering the activation energy and increasing the reaction rate. This is achieved through various mechanisms. One mechanism is the diminished Pauli repulsion between the π-electron systems of the diene and dienophile, which is facilitated by the Lewis acid . Another mechanism involves increasing the asynchronicity of the reaction to relieve the destabilizing Pauli repulsion between the closed-shell filled π-orbitals of the diene and dienophile . Additionally, Lewis acids can promote the participation of 3-alkyl and 3-phenyl 2H-azirines in hetero Diels-Alder reactions, bypassing the need for an electron-withdrawing carboxyl moiety at the 3-position of the 2H-azirine . The specific Lewis acid used can also affect the regioselectivity of the reaction, leading to the formation of different cyclohexene derivatives . Overall, Lewis acids play a crucial role in catalyzing Diels-Alder reactions by influencing the reaction pathway and reducing the energy barrier.
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| Lewis acids catalyze Diels-Alder reactions by reducing the Pauli repulsion between the π-electron systems of the diene and dienophile, contrary to the widely accepted view. | |
| Lewis acids, such as BF3·OEt2, catalyze Diels–Alder reactions of 1,2-naphthoquinones, providing access to cis-tetrahydrophenanthrene derivatives without rapid adduct aromatization. | |
| Lewis acids catalyze Diels-Alder reactions by promoting the reaction between dienyl phosphate esters and α,β-unsaturated carbonyl compounds, resulting in the formation of cyclohexene derivatives. |
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