REACTIVITY OF DIENOPHILES FREE

If the diene is cyclic as well, then bicyclic compounds are formed. This indicates that Diels-Alder is a stereospecific reaction: Some of the commonly used dienophiles are shown below:Ī few more points about the stereochemistry of the Diels-Alder reaction depending on the structure of the diene and the dienophile.įirst, remember that if there are two groups on the dienophile, the product will have them cis or trans exactly as they initially appear in the dienophile. Therefore, electron-donating groups on the diene increase its reactivity, while electron-withdrawing groups on the dienophile lower the LUMO energy level, thus support this electron flow as well.Īs we just mentioned above, electron-withdrawing groups increase the reactivity of the dienophile. Even though it is a concerted mechanism, one can imagine the electron flow being initiated from the highest occupied molecular orbitals (HOMO) of the diene and goes to the lowest occupied molecular orbitals (LUMO) of the dienophile.

This is a result of the HOMO-LUMO interaction in the Diels-Alder reaction. Remember that electron-donating groups increase the reactivity of the diene: The second factor is the electronic effect. Cyclic dienes produce bridged bicyclic compounds: These conformations are two extremes as the locked trans dienes do not react in the Diels-Alder while the cyclic cis dienes are so reactive that they may react with themselves.įor example, cyclopentadiene dimerizes because one molecule acts as the diene and the other as the dienophile.

REACTIVITY OF DIENOPHILES FREE

Cyclic dienes, on the other hand, are locked whether they are cis or trans since there is no free rotation about the sigma bond: However, these are conformations since they interconvert through a rotation abound the sigma bond between the two double bonds and we call them s- cis and s- trans:Īcyclic dienes usually prefer the s- trans conformation. Conjugated dienes can also be in cis and trans geometry. We are not talking about the traditional cis and trans isomerism of the alkenes. The first thing to remember here is that it can only react in the cis conformation. First, a reminder that the Diels-Alder reaction is a type of a pericyclic reaction between a conjugated diene (two double bonds) and a dienophile (an alkene with an electron-withdrawing group). In reality, this system is two five‐membered rings, a cyclopentene ring and a cyclopentane ring, which are sharing two sides (the “carbon bridge”).In this post, we will discuss the reactivity and specifics of the diene and the dienophile in the Diels-Alder reaction. The previous diagram shows what appears to be a cyclohexene ring with a carbon bridge connecting the third and sixth carbons. If the diene is a ring structure, the Diels‐Alder reaction produces a bicyclic ring system.Ī bicyclic ring system has two carbon rings that share common sides. An example of this stereospecificity is the reaction of 1,3‐butadiene with cis‐diethylmaleate.īecause the reaction is basically a concerted cyclization, the diene must react in the cis conformation. The original stereochemistry of the diene and the dienophile are preserved during this syn‐addition reaction. The Diels‐Alder reaction is very ste‐reospecific. Electron‐supplying groups on the diene make the electrons of the π system more available for reaction.ĭiels‐Alder stereochemistry. A good dienophile generally has one or more electron‐withdrawing carbonyl groupsĪttached to it. Simple alkenes and alkynes are not good dienophiles. Instead, this reaction proceeds by a pericyclic process, a mechanism of just one step, involving a cyclic redistribution of bonding electrons. The mechanism for the Diels‐Alder reaction shows that it does not run via a carbocation intermediate. The Diels‐Alder reaction is favored by the presence of electron‐withdrawing groups on the diene and electron‐releasing groups on the dienophile, which is a group or bond that is attracted to a diene. A typical example is the reaction of 1,3‐butadiene with maleic anhydride. This reaction produces a 1,4‐addition product. The Diels‐Alder reaction is a cycloaddition reaction between a conjugated diene and an alkene.

Cahn‐Ingold‐Prelog RS Notational System.

Racemic Mixtures: Resolving Enantiomers.

Cyclohydrocarbons: Reactivity, Stresses of Small Rings.

Alkynes: Molecular and Structural Formulas.

Alkenes: Oxidation and Cleavage Reactions.

Alkenes: Electrophilic Addition Reactions.

Alkenes: Catalytic Addition of Hydrogen.

Alkenes: Hydration (Direct Addition of Water).

Alkenes: Molecular and Structural Formulas.

Alkanes: Molecular and Structural Formulas.

Brønsted‐Lowry Theory of Acids and Bases.

Reactivity of dienophiles