Organic Chemistry/Introduction to reactions/Diels-Alder reaction
The Diels-Alder reaction, named after the German chemists who developed it, is a method for producing simple ring compounds.
Mechanism of a reaction between a diene and a dienophile
In the Diels-Alder reaction, a conjugated diene reacts with a dienophile. The dienophile is named for its affinity to react with the diene.
Because dienes and dienophiles are often gases, this reaction usually takes place in a sealed container at elevated pressure and temperature. The temperature required by this reaction can be reduced by the presence of electron-witdrawing groups attached to the dienophile.
In some cases, such as furan and maleic anhydride, or cyclopentadiene and acrolein, the reaction will take place at room temperature in an ethoxyethane solution.
The reaction shown above is highly unlikely due to the lack of substituents on the diene and dienophile. The dienophile will usually have a carbonyl, nitro, or other electron-withdrawing group attached. Any substituents attached to the diene or dienophile will end up in the final product.
Notice that the product retains the same basic cyclohexene structure. The substituents simply extend from the ring.
Alkynes can also react as dienophiles.
Diels-Alder reactions can sometimes reverse themselves through Retro-Diels-Alder reactions. For example, dicyclopentadiene can be cracked to form 1,3-cyclopentadiene by thermal dissociation. Retro reactions occur under situations where the fragments are stable by themselves.
Read more about Kurt Alder and Otto Diels in the Wikipedia.