Answer:
See explanation below
Explanation:
First of all, a Diels Alder reaction is very useful to synthetize rings of 6 carbons. In order to do this, we need two reactants. A dienophile and a conjugate diene.
The conjugate diene, is usually a 4 or 5 carbons, with two double bonds, both conjugate and the dienophile, usually have one double bond and an withdrawing atractor group on 1 carbon.
We already have the product here, which is a ring of 6 carbons, with a double bond and chlorine in two carbons. The only way to do this is putting a conjugate diene of 4 carbons, and a dienophile with 3 carbons and 2 chlorines.
The mechanism of reaction is in the attached picture.
Hope this helps