Herein we describe quantum chemical calculations (B3LYP) on the intramolecular oxidopyrylium−alkene cycloadditions used in two recently reported total syntheses of (+)-intricarene, and possibly alsooccurring during its biosynthesis. Using theory, we address (1) the necessity of enzyme intervention ifthis reaction occurs in Nature and (2) the effects of substituents attached to the oxidopyrylium and alkenegroups on the activation barriers for cycloaddition.