Show the product of the Diels–Alder dimerization of cyclobutadiene. (This reaction is similar to the dimerization of cyclopentadiene, discussed in Section 15-11.)

Furan and maleimide undergo a Diels–Alder reaction at 25 °C to give the endo isomer of the product. When the reaction takes place at 90 °C, however, the major product is the exo isomer. Further study shows that the endo isomer of the product isomerizes to the exo isomer at 90 °C.

b. Which isomer of the product would you usually expect from this reaction? Explain why this isomer is usually favored.

1,4-Benzoquinone is a good Diels–Alder dienophile. Predict the products of its reaction with

a. buta-1,3-diene

b. cyclopenta-1,3-diene

Cyclopentadiene can react with itself in a Diels–Alder reaction. Draw the endo and exo products.

Recall (Section 16-10) that two positions of anthracene sometimes react more like polyenes than like aromatic compounds.

b. The Diels–Alder reaction of anthracene with maleic anhydride is a common organic lab experiment. Predict the product of this Diels–Alder reaction.

Furan and maleimide undergo a Diels–Alder reaction at 25 °C to give the endo isomer of the product. When the reaction takes place at 90 °C, however, the major product is the exo isomer. Further study shows that the endo isomer of the product isomerizes to the exo isomer at 90 °C.

c. Examine your answer to (b) and determine whether this answer applies to a reaction that is kinetically controlled or one that is thermodynamically controlled, or both.

While attempting to recrystallize maleic anhydride, a student dissolved it in freshly distilled cyclopentadiene rather than in freshly distilled cyclopentane. Was her recrystallization successful?

What are the products of the following reactions?

a.