Chapter 24, Problem 24.14P

Interpretation Introduction

Interpretation:

By paying particular attention to stereochemistry, the major product of the Diels-Alder reaction is to be drawn.

Concept introduction:

A diene contributes four $\text{π}$ pi electrons from a pair of conjugated $\text{π}$ bonds. A dienophile contributes two $\text{π}$ electrons from a single $\text{π}$ bond. The Diels-Alder reaction proceeds through an aromatic transition state. For a Diels-Alder reaction to take place, the diene must be in the s-cis conformation. The electron-withdrawing substituents bonded directly to the dienophile carbons facilitate standard Diels-Alder reactions. The stereochemical configuration in the dienophile is conserved throughout the course of a Diels-Alder reaction. If the double bonds in the diene are either both trans or both cis, then the substituents at the ends of the diene become cis to each other with respect to the plane of the ring in the product. Conversely, if one of the dienes double bonds is cis and the other is trans then the two substituents become trans to each other in the product.

In a Diels-Alder reaction, the endo approach is generally favored over the exo approach, so the major product is usually endo.