Silica-supported Lewis acids are good catalysts for Diels−Alder reactions between furan and acrylonitrile and methyl acrylate at room temperature. When 2,5-dimethylfuran is used as the diene, yields of the Diels−Alder adducts with methyl acrylate are lower, due in part to the appearance of aromatization products. The use of microwave activation results in some cases in good yields of aromatic products and, as such, constitutes a good synthetic route to polysubstituted aromatic compounds. Computational studies on the reaction mechanism and the role of the catalyst on the product distribution show that “hard” Lewis acids, such as aluminum derivatives, make ring-opening of the adduct much easier, affording aromatic products. The theoretical results are in excellent agreement with the relative reactivity observed for the different dienes and dienophiles.