There are many sources of the information regarding the historical background and the current applications. Try searching "diels alder" and "Woodward-Hoffmann rules". Roald Hoffmann received the 1981 Nobel Prize in Chemistry for his work in forumuating rules that govern the reaction symmetry of the Diels-Alder type.
Here is a review article that I found fascinating:
Stocking, Emily M.; Williams, Robert M., "Chemistry and Biology of Biosynthetic Diels-Alder Reactions", Angew. Chem. Int. Ed. 2003, 42, 3078-3115.