We have used quantum chemical calculations to explore the mechanism, regio-, and stereoselectivity of the intramolecular oxidopyrylium–alkene cycloadditions used in two recently reported total syntheses of the diterpenoid (+)-intricarene, and possibly also occurring during its biosynthesis. We addressed: (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.
Wang, S. C.; Tantillo, D. J. J. Org. Chem. 2008, 73, 1516-1523: "Theoretical Studies on Synthetic and Biosynthetic Oxidopyrylium–Alkene Cycloadditions. Pericyclic Pathways to Intricarene"
