Chapter 24, Problem 24.44P

Interpretation Introduction

(a)

Interpretation:

The mechanism and major product for the given Diels-Alder reaction is to be drawn.

Concept introduction:

The Diels–Alder reaction joins a conjugated diene and a dienophile (either an alkene or an alkyne) via the formation of two new $\text{σ}$ bonds. The product is a six-membered ring of carbon atoms. For a Diels–Alder reaction to take place, the diene must be able to attain the $\text{s-cis}$ conformation. Diels–Alder reactions cannot take place with the diene in the $\text{s-trans}$ conformation. Standard Diels–Alder reactions are facilitated by electrondonating groups attached to the diene and electron-withdrawing groups attached to the dienophile. Substituents that are cis to each other about the C=C double bond of the dienophile end up cis to each other in the new ring that is produced.

Answer to Problem 24.44P

The mechanism and major product for the given Diels-Alder reaction is:

The $\text{Cl-C=C-C}$ configurations along the diene skeleton are different, one is cis and the other is trans thus produced two enetiomers:

Explanation of Solution

The given reaction is:

Here the diene is in trans configuration. For a Diels–Alder reaction to take place, the diene must be able to attain the $\text{s-cis}$ conformation, the reaction cannot take place with the diene in the $\text{s-trans}$ conformation. The trans to cis conformational change is possible through rotation around C-C single bond. The product formed when the diene changes its conformation to cis is:

Each end carbon in the diene becomes a chiral center, noted with an asterisk. The $\text{Cl-C=C-C}$ configurations along the diene skeleton are different, one is cis and the other is trans, so the two Cl atoms will be trans to each other with respect to the six-membered ring in the product, thus two enantiomers are produced as shown below:

Conclusion

The mechanism and major product for the given Diels-Alder reaction is drawn from the structures of given reactants with stereochemistry.

Interpretation Introduction

(b)

Interpretation:

The mechanism and major product for the given Diels-Alder reaction is to be drawn.

Concept introduction:

The Diels–Alder reaction joins a conjugated diene and a dienophile (either an alkene or an alkyne) via the formation of two new $\text{σ}$ bonds. The product is a six-membered ring of carbon atoms. For a Diels–Alder reaction to take place, the diene must be able to attain the $\text{s-cis}$ conformation. Diels–Alder reactions cannot take place with the diene in the $\text{s-trans}$ conformation. Standard Diels–Alder reactions are facilitated by electrondonating groups attached to the diene and electron-withdrawing groups attached to the dienophile. Substituents that are cis to each other about the C=C double bond of the dienophile end up cis to each other in the new ring that is produced.

Answer to Problem 24.44P

The mechanism and major product for the given Diels-Alder reaction is:

The $\text{CN-C=C-CN}$ configuration is trans, and therefore, the two CN groups will be trans to each other thus, produced two enantiomers:

Explanation of Solution

The given reaction is:

Here the cycloaddition, Diels-Alder reaction forms the six-membered ring product as:

In the above reaction, two carbons in the dienophile become chiral centers, noted with an asterisk.

The $\text{CN-C=C-CN}$ configuration is trans, and therefore, the two CN groups will be trans to each other thus, produced two enantiomers:

Conclusion

The mechanism and major product for the given Diels-Alder reaction is drawn from the structures of given reactants with stereochemistry.

Interpretation Introduction

(c)

Interpretation:

The mechanism and major product for the given Diels-Alder reaction is to be drawn.

Concept introduction:

The Diels–Alder reaction joins a conjugated diene and a dienophile (either an alkene or an alkyne) via the formation of two new $\text{σ}$ bonds. The product is a six-membered ring of carbon atoms. For a Diels–Alder reaction to take place, the diene must be able to attain the $\text{s-cis}$ conformation. Diels–Alder reactions cannot take place with the diene in the $\text{s-trans}$ conformation. Standard Diels–Alder reactions are facilitated by electrondonating groups attached to the diene and electron-withdrawing groups attached to the dienophile. Substituents that are cis to each other about the C=C double bond of the dienophile end up cis to each other in the new ring that is produced.

Answer to Problem 24.44P

The mechanism and major product for the given Diels-Alder reaction is:

The $\text{CN-C=C-CN}$ configuration is cis, and therefore, the two CN groups will be cis to each other:

Explanation of Solution

The given reaction is:

Here the cycloaddition, Diels-Alder reaction forms the six-membered ring product as:

The $\text{CN-C=C-CN}$ configuration is cis, and therefore, the two CN groups will be cis to each other with respect to the six-membered ring in the product.

Conclusion

The mechanism and major product for the given Diels-Alder reaction is drawn from the structures of given reactants with stereochemistry.

Interpretation Introduction

(d)

Interpretation:

The mechanism and major product for the given Diels-Alder reaction is to be drawn.

Concept introduction:

The Diels–Alder reaction joins a conjugated diene and a dienophile (either an alkene or an alkyne) via the formation of two new $\text{σ}$ bonds. The product is a six-membered ring of carbon atoms. For a Diels–Alder reaction to take place, the diene must be able to attain the $\text{s-cis}$ conformation. Diels–Alder reactions cannot take place with the diene in the $\text{s-trans}$ conformation. Standard Diels–Alder reactions are facilitated by electrondonating groups attached to the diene and electron-withdrawing groups attached to the dienophile. Substituents that are cis to each other about the C=C double bond of the dienophile end up cis to each other in the new ring that is produced.

Diels–Alder reactions tend to favor an endo product over an exo product

Answer to Problem 24.44P

The mechanism and major product for the given Diels-Alder reaction is:

Diels–Alder reactions tend to favor an endo product over an exo product:

Explanation of Solution

The given reaction is:

Here the cycloaddition, Diels-Alder reaction forms the bicyclic compound as product:

Here, it is noticed that two carbons of the diene and two carbons of the dienophile become chiral centers, noted with an asterisk.

The $\text{C-C=C-C}$ configurations along the diene skeleton are the same, cis, so the two bonds to the ${\text{CH}}_{\text{2}}$ group will be cis to each other with respect to the six-membered ring in the product. The $\text{CN-C=C-CN}$ configuration in the dienophile is cis, and therefore, the two CN groups will be cis to each other with respect to the six-membered ring in the product. Overall, two diasteromers will be produced, and the endo product will be the major product:

Conclusion

The mechanism and major product for the given Diels-Alder reaction is drawn from the structures of given reactants with stereochemistry.