16. Conjugated Systems

Which dienophile in each pair is more reactive in a Diels–Alder reaction?

1.

Which dienophile in each pair is more reactive in a Diels–Alder reaction?

2.

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

(a)

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

(b)

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

(a)

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

(d)

Predict the products of the following Diels–Alder reactions.

(c)

(d)

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.

Provide a mechanism of the Diels–Alder reaction shown and predict the regioisomer that will form.

While not covered explicitly in this chapter, the ene reaction occurs similarly to the Diels–Alder reaction but replaces the electrons from one bond in the diene with the electrons in a C―H bond. Draw the mechanism for the following reaction. [Number the carbons and draw in the hydrogens of the product. And, of course, make a note of bonds formed and bonds broken.]

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?

Predict the product of the following Diels–Alder reactions. Where a racemic mixture is produced, show both enantiomers and explain how each is formed.

(d)

Figure 22.16(a) <IMAGE> shows a unique example where the Diels–Alder reaction gives a single product (no enantiomers) regardless of whether the diene attacks the dienophile from the top or bottom.

(a) Show the product of the diene attacking from the bottom and confirm that the same product is obtained.

(b) What is special about this product that makes this true?

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

(c)