Why does the reaction of (Z)-butenedioic acid (fumaric acid) with 1,3-cyclopentadiene

give only one product?
I don't know where to start.
Thanks.

1 answer

First, your nomenclature. Maleic acid is the cis-(Z)-2-butenedioic acid and fumaric acid is the trans-(E)-2-butenedioic acid. So unsure of your conformation, I will assume Maleic acid.

Maleic acid reacts as a dienophile in the above reaction. cyclopentadiene (obviously) is the diene. A diene and dienophile react in what is known as the Diels-Alder reaction. In this case, since maleic acid is symmetrical, it only adds in one orientation to the diene, giving you a heterocyclic compund with only one possible conformation.