The regio- and stereoselectivity of the Diels-Alder reaction can be influenced by the electronic and steric properties of the dienes and dienophiles involved:
Electron-donating groups on the diene and electron-withdrawing groups on the dienophile enhance the reactivity (increase the reaction rate) and direct the reaction toward the most stable, electron-rich double bond in conjugated dienes.
Steric effects can influence the approach of the dienophile, resulting in the preferential formation of endo over exo products.