Chapter 20.5, Problem 20.9P

Interpretation Introduction

Interpretation: The diene and the dienophile that might be used to prepare the given racemic Diels-Alder adduct have to be found.

Concept Introduction:

Diels-Alder reaction:

It is the reaction of conjugated dienes with double or triple bonded compounds which are known as “dienophiles”. The reaction is a $4+2$ cycloaddition reaction that results in the formation of a six membered cyclic product which is known as “adduct”.

Example:

Diels-Alder reaction to form bicyclic system:

The Diels-Alder adduct formed in the Diels-Alder reaction can also be a bicyclic system which will be obtained when cylopentadiene is used as the diene as shown here:

In this reaction, the cylopentadiene acts as both diene and dienophile and formed a bicyclic system. When it is heated to ${\text{170}}^{\text{o}}\text{C}$, a reverse Diels-Alder reaction takes place in which the bicyclic system will be decomposed and gives back the cylopentadiene.

Racemic mixture in Diels-alder reaction:

In the Diels-alder reaction, the formation of two new sigma bonds results in the formation of two new chiral centres that are enantiomers to each other. So, the Diels-alder adduct is the mixture of two enantiomers and therefore it is being a racemic Diels-alder adduct.