Cycloaddition to Conjugated Dienes The Diels-Alder Reaction

b Cycloaddition to Conjugated Dienes The Diels-Alder Reaction 

Conjugated dienes undergo another type of 1,4-addition when they react with alkenes (or alkynes). The simplest example is the addition of ethylene to 1,3-butadiene to give cyclohexene. 

This reaction is an example of a cycloaddition reaction, an addition that results in a cyclic product. This cycloaddition, which converts three tt bonds to two a bonds and one new tt bond, is called the Diels-Alder reaction, after its discoverers, Otto Diels and Kurt Alder. It is so useful for making cyclic compounds that it earned the 1950 Nobel Prize in chemistry for its discoverers. As with hydroboration (Sec. 3.13), this reaction is concerted. All bond-breaking and bond-making occur at the same time. 

The two reactants are a diene and a dlenophile (diene lover). The simple example in eq. 3.35 is not typical of most Diels-Alder reactions because it proceeds oiJy under pressure and not in good yield. However, this type of reaction gives excellent yields at moderate temperatures if the dienophile has electron-withdrawing groups attached, as in the following examples  

How could a Diels-Alder reaction be used to synthesize the following compound  

---