Chapter 24, Problem 24.48P

Interpretation Introduction

(a)

Interpretation:

For the given Diels-Alder reaction, the mechanism and the major product are to be drawn, paying attention to regiochemistry.

Concept introduction:

The Diels-Alder reaction (also known as [4+2] cycloaddition) joins a conjugated diene and a dienophile (an alkene or an alkyne) via the formation of two new sigma bonds. The product is a six-membered ring. The Diels-Alder reaction is concerted, that is, the process of bond breaking and bond formation occurs simultaneously. For a Diels-Alder reaction to take place, the diene must be able to achieve the s-cis conformation. Diels-Alder reactions cannot take place with the diene in the s-trans conformation. Electron-donating groups attached to the diene and electron-withdrawing groups attached to the dienophile facilitate the reaction. These reactions are highly regioselective and stereospecific. Substituents that are cis to each other about the carbon-carbon double bond of the dienophile end up cis to each other in the new ring that is produced. Otherwise, the substituents end up trans to each other in the ring. Substituents attached to the terminal carbons of the diene end up cis to each other in the new ring that is produced if the double bonds of the diene are both cis or both trans. Otherwise, the substituents end up trans to each other in the ring. When the diene and dienophile are both unsymmetric, two isomeric products can be produced.

Interpretation Introduction

(b)

Interpretation:

For the given Diels-Alder reaction, the mechanism and the major product are to be drawn, paying attention to regiochemistry.

Concept introduction:

The Diels-Alder reaction (also known as [4+2] cycloaddition) joins a conjugated diene and a dienophile (an alkene or an alkyne) via the formation of two new sigma bonds. The product is a six-membered ring. The Diels-Alder reaction is concerted, that is, the process of bond breaking and bond formation occurs simultaneously. For a Diels-Alder reaction to take place, the diene must be able to achieve the s-cis conformation. Diels-Alder reactions cannot take place with the diene in the s-trans conformation. Electron-donating groups attached to the diene and electron-withdrawing groups attached to the dienophile facilitate the reaction. These reactions are highly regioselective and stereospecific. Substituents that are cis to each other about the carbon-carbon double bond of the dienophile end up cis to each other in the new ring that is produced. Otherwise, the substituents end up trans to each other in the ring. Substituents attached to the terminal carbons of the diene end up cis to each other in the new ring that is produced if the double bonds of the diene are both cis or both trans. Otherwise, the substituents end up trans to each other in the ring. When the diene and dienophile are both unsymmetric, two isomeric products can be produced.