Theoretical studies on synthetic and biosynthetic oxidopyrylium-alkene cycloadditions: pericyclic pathways to intricarene

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