16. Conjugated Systems

As many as 18 different Diels–Alder products can be obtained by heating a mixture of 1,3-butadiene and 2-methyl-1,3-butadiene. Identify the products.

Diene A participates in a fast and efficient Diels–Alder reaction with maleic anhydride, the powerful dienophile from Assessment 22.9. However, the related diene B does not undergo a Diels–Alder reaction. Why?

In each Diels–Alder reaction shown, predict the product that will result.

(c)

Predict the products of the following proposed Diels–Alder reactions. Include stereochemistry where appropriate.

(e)

(f)

Which of the following dienes can undergo the Diels-Alder reaction?

Predict the products of the following proposed Diels–Alder reactions.

(b)

Predict the products of the following proposed Diels–Alder reactions.

(a)

The highly reactive triple bond of benzyne is a powerful dienophile. Predict the product of the Diels–Alder reaction of benzyne (from chlorobenzene and NaOH, heated) with cyclopentadiene.

Which of the following is the product of the intramolecular Diels-Alder reaction between $C_{6}H{O}_2$ (a 1,3-diene tethered to a dienophile via a five-carbon chain)?

What are the products of the following reactions?

d.

Assuming the diene approaches the dienophile from the top, predict the product of the following Diels–Alder reactions.

(c)

What stereochemical result would you expect if the Diels–Alder reaction with the free α,β- unsaturated ketone was faster than reaction with the iminium-bound alkene?

What two products are formed from each of the following reactions?

b.

By forming a Lewis acid–Lewis base complex with the dienophile, Lewis acids are able to increase the rate of Diels–Alder reactions. Why might this be true?

Predict the products of the following proposed Diels–Alder reactions. Include stereochemistry where appropriate.

(a)