This little snippet of a reaction was taken from an old exam for the course that I am studying for right now.  It involves a diels alder reaction between a cyclopentadiene and Maleic anhydride.  Here the diene is the cyclopentadiene (this molecule goes through diels alder reactions with itself so it is necessary to heat it above 160*C to reverse the reaction) and the dienophile as the Maleic anhydride.  This is the first step where the reaction goes as a 4π+2π endo reaction as a pericyclic reaction.  Then the second step will remove the diester as it also reduces the C=O into alcohols.  Then the final step involves turning the alkene into a 1,2-diiodine when the alkene gets halogenated, and then intramolecularly the alcohol attaches to the other point of halogenation.