ALDER-ENE REACTION

Alder-Ene Reaction
Ene Reaction

The four-electron system including an alkene π-bond and an allylic C-H σ-bond can participate in a pericyclic reaction in which the double bond shifts and new C-H and C-C σ-bonds are formed. This allylic system reacts similarly to a diene in a Diels-Alder Reaction, while in this case the other partner is called an enophile, analogous to the dienophile in the Diels-Alder. The Alder-Ene Reaction requires higher temperatures because of the higher activation energy and stereoelectronic requirement of breaking the allylic C-H σ-bond.

The enophile can also be an aldehyde, ketone or imine, in which case β-hydroxy- or β-aminoolefins are obtained. These compounds may be unstable under the reaction conditions, so that at elevated temperature (>400°C) the reverse reaction takes place - the Retro-Ene Reaction.

While mechanistically different, the Ene reaction can produce a result similar to the Prins Reaction.

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Mechanism of the Alder-Ene Reaction

Also like the Diels-Alder, some Ene Reactions can be catalyzed by Lewis Acids. Lewis-Acid catalyzed Ene Reactions are not necessarily concerted (for example: Iron(III) Chloride Catalysis of the Acetal-Ene Reaction).

Recent Literature

Formaldehyde Encapsulated in Zeolite: A Long-Lived, Highly Activated One-Carbon Electrophile to Carbonyl-Ene Reactions

Ytterbium(III) Triflate/TMSCl: Efficient Catalyst for Imino Ene Reaction

Asymmetric Carbonyl-Ene Reaction Catalyzed by Chiral N,N′-Dioxide-Nickel(II) Complex: Remarkably Broad Substrate Scope

Highly Enantioselective Carbonyl-ene Reactions Catalyzed by a Hindered Silyl-Salen-Cobalt Complex

Highly Enantioselective and Anti-Diastereoselective Catalytic Intermolecular Glyoxylate-Ene Reactions: Effect of the Geometrical Isomers of Alkenes

Steric acceleration of an uncatalysed ene reaction at room temperature

Iron(III) Chloride Catalysis of the Acetal-Ene Reaction

Direct Synthesis of β-Alkyl N-Aryl Aza Baylis-Hillman Adducts via Nitroso-Ene Reaction

Regioselective Ene-Type Allylic Chlorination of Electron-Rich Alkenes by Activated DMSO

Ene Reaction of Arynes with Alkynes

2-Methylenetetrahydropyrans: Efficient Partners in the Carbonyl Ene Reaction

Confined Acid-Catalyzed Asymmetric Carbonyl-Ene Cyclization