Starting from D-(-)-ribose, a tricyclic natural product-like scaffold suitable for combinatorial derivatization was synthesized via an intramolecular hetero-Diels-Alder reaction. Lithium perchlorate was found to enhance the reaction rate and, at the same time, had a pronounced influence on the chemoselectivity of the reaction. The stereochemical course of the reaction, however, was not influenced by the Lewis acid.