Furan and maleimide undergo a Diels–Alder reaction at 25 °C to give the endo isomer of t...

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.

(a) Draw and label the endo and exo isomers of the Diels–Alder adduct of furan and maleimide.

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

(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.

(d) Explain why the endo isomer predominates when the reaction takes place at 25 °C and why the exo isomer predominates at 90 °C.