What makes a good diene and dienophile

Likewise, if the terminal carbons of the diene bear substituents, their relative configuration will be retained in the adduct. Using the earlier terminology, we could say that bonding to both the diene and the dienophile is syn. An alternative description, however, refers to the planar nature of both reactants and terms the bonding in each case to be suprafacial i. This stereospecificity also confirms the synchronous nature of the 1,4-bonding that takes place.

The essential characteristics of the Diels-Alder cycloaddition reaction may be summarized as follows:. These features are illustrated by the following eight examples, one of which does not give a Diels-Alder cycloaddition. There is no reaction in example D because this diene cannot adopt an s-cis orientation.

In example B the the same cyclic compound acts as both the diene colored blue and the dienophile colored red. The adduct has three rings, two of which are the five-membered rings present in the reactant, and the third is the new six-membered ring shaded light yellow. Example C has an alkyne as a dienophile colored red , so the adduct retains a double bond at that location. This double bond could still serve as a dienophile, but in the present case the diene is sufficiently hindered to retard a second cycloaddition.

The quinone dienophile in reaction F has two dienophilic double bonds. However, the double bond with two methyl substituents is less reactive than the unsubstituted dienophile due in part to the electron donating properties of the methyl groups and in part to steric hindrance. In all cases the configuration of the reactant is preserved in the adduct. Of the following dienes, which are S-trans and which are s-cis?

Skip to main content. Search for:. The Diels-Alder reaction We end this chapter with a discussion of a type of reaction that is different from anything we have seen before. In the Diels-Alder cycloaddition reaction, a conjugated diene reacts with an alkene to form a ring structure.

In a Diels-Alder reaction, the alkene reacting partner is referred to as the dienophile. Essentially, this process involves overlap of the 2p orbitals on carbons 1 and 4 of the diene with 2p orbitals on the two sp 2 -hybridized carbons of the dienophile.

Both of these new overlaps end up forming new sigma bonds, and a new pi bond is formed between carbon 2 and 3 of the diene. Corey, J. Payette, H. Yamamoto, J. Gotoh, Y. Hayashi, Org. Hayashi, S. Samanta, H. Gotoh, H. Ishikawa, Angew. Loh, Org. Nakashima, H. Fan, L.

Lin, J. Liu, Y. Huang, X. Feng, Eur. Berkessel, N. Vogl, Eur. The cycloadducts can be converted directly to the corresponding dihydropyrones and dihydropyridones.

Huang, V. Rawal, Org. Dai, D. 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. As we just mentioned above, electron-withdrawing groups increase the reactivity of the dienophile.

A few more points about the stereochemistry of the Diels-Alder reaction depending on the structure of the diene and the dienophile. First, 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. This indicates that Diels-Alder is a stereospecific reaction:. If the diene is cyclic as well, then bicyclic compounds are formed. The main concept here is the endo-exo isomerism. In the endo product, the substituents of the dienophile are pointing towards the larger bridge, while in the exo isomer, they are pointing away from the larger bridge:.

You can read more details such as the transition state and the endo-exo definition when acyclic dienes are reacted here.