91Ó°ÊÓ

Diels-Alder reactions constitute reactions that are used to generate six-membered rings comprising controlled stereochemistry.These reactions are termed [4+2] cycloaddition reactions.

The diene must comprise an s-cis conformation for the reaction to happen. In the final product the electron-withdrawing group is found in the stereochemical position near to the diene’s central atoms.

(a)

In the reaction, the cyclopentadiene is the diene and the other compound is the dienophile. Cyclopentadiene is found in the cis-form in the Diels-Alder reaction. The NO₂ is the electron withdrawing group in the dienophile. It will occupy the endo position in the product. The stereochemistry and the reaction can be given as:

Major product of the Diels-Alder reaction in reaction a

(b)

In the following reaction, (Z)-3-methoxypenta-1,3-diene is a diene and benzoquinone is a deienophile. Due to syn addition, the substituents on the diene and dienophile present on the same side will be cis on the product. The electron-withdrawing group in the dienophile is the C=O group that will occupy the endo position.

The reaction along with the stereochemistry can be given as:

Major product of the Diels-Alder reaction in reaction b

(c)

In the following reaction, (1E, 3E)-1,4-diphenylbuta-1,3-diene is the diene and furan-2,5-dione is the dienophile. The electron-withdrawing group, C=O group occupy the endo position. The reaction and the stereochemistry can be given as:

Major product of the Diels-Alder reaction in reaction c