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Updated: Jun 17, 2026
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Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
Published on: June 21, 2017
Oriented electric fields accelerate Diels-Alder reactions and control the endo/exo selectivity
Rinat Meir1, Hui Chen, Wenzhen Lai
1Institute of Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
Summary
External electric fields (EEFs) can catalyze or inhibit Diels-Alder reactions by 4-6 orders of magnitude. The EEF
Area of Science:
- Physical Chemistry
- Organic Chemistry
- Computational Chemistry
Background:
- Diels-Alder reactions are crucial in organic synthesis.
- Controlling reaction rates and selectivity is a key challenge.
- External electric fields (EEFs) offer a novel approach to influence chemical reactivity.
Purpose of the Study:
- To investigate the catalytic and inhibitory effects of EEFs on Diels-Alder reactions.
- To explore the influence of EEF orientation on reaction rates and selectivity.
- To understand the mechanism of EEF control over Diels-Alder reactions.
Main Methods:
- Computational modeling using valence bond diagram.
- Simulation of Diels-Alder reactions under various EEF conditions.
- Analysis of reaction pathways and transition states.
Main Results:
- EEFs aligned with the reaction axis significantly lower activation barriers, enhancing reaction rates by 4-6 orders of magnitude.
- Reversing EEF orientation inhibits the reaction.
- Perpendicular EEFs can control endo/exo selectivity by influencing molecular dipoles.
- A crossover to a stepwise mechanism with a zwitterionic intermediate occurs at critical EEF strengths.
Conclusions:
- EEFs act as tunable catalysts/inhibitors for Diels-Alder reactions.
- A selection rule for EEF effects is proposed: alignment with electron flow lowers barriers.
- EEF control over selectivity is independent of secondary orbital interactions.
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01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
01:29Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
01:29Diels–Alder Reaction: Characteristics of Dienes
The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that influence the rate of the reaction.
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...
01:28Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
01:24Diels–Alder Reaction: Characteristics of Dienophiles
In a Diels–Alder reaction, the diene is usually an electron-rich system and acts as a nucleophile, whereas the dienophile is electron-deficient and functions as an electrophile. Much like the diene, the nature of the dienophile significantly impacts the outcome of the reaction.
Characteristics of Dienophiles
Generally, the best dienophiles are alkenes containing electron-withdrawing substituents such as carbonyl, nitrile, and nitro groups. The feasibility of a Diels–Alder reaction depends on...
Characteristics of Dienophiles
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01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.