Furan and maleimide undergo the diels-alder reaction at 25 °c to give the endo product. when the reaction takes place at 90 °c, however, the major product is the exo isomer. further study shows that the endo product isomerizes to the exo product at 90 °c. draw the exo product of the diels-alder reaction of furan with maleimide.

see attached image

Explanation:

In organic chemistry, a product may be kinetically or thermodynamically favoured. A kinetically favours product forms faster, it may not necessarily be the more stable product. The thermodynamically favoured product forms at a slower rate but is more stable. Often times, the kinetically favoured product rearranges itself to form the thermodynamically favoured product at equilibrium. The endo product of the Diels Alder reaction mentioned in the question is first formed (kinetically favoured) but rearranges to form the exo product (thermodynamically favoured) at equilibrium. This is clear shown in the reaction mechanism attached below.