Draw the structures of the diene and the dienophile that reacted to form the Diels-Alder product shown.
Of the diene and product shown. diene dienophile
As we know, the diels-alder reaction is reversible. Here the HOMO of diene reacts with the LUMO of dienophile. For a good diels-alder reaction diene should be more electron rich and dienophile should be electron deficient. So, it requires diene should attach with some electon donating group and dienophile should attach with some electron withdrawing group.
In diels-alder reaction, 3 pi bond take part and form 2 sigma bond and one pi bond.
So to do retro diels-alder reaction, start putting curly arrow from the pi bond (clock wise or anticlockwise manner). Here 2 sigma bond and 1 pi bond produces 3 pi bond. Mechanism of retro diels alder is,