This page focuses on the Diels-Alder reaction, a type of pericyclic reaction called a [4+2] cycloaddition.
Reaction of 1,3-butadiene with (E)-1,2-dichloroethene
Reaction of 1,3-butadiene with an alkyne
Reaction of cyclopenta-1,3-diene with a cis alkene. Note the endo product formation.
Reaction of dicyclopentadiene to form 2 molecules of cyclopentadiene