Investigation of transannular cycloaddition reactions involving furanoxonium ions using DFT calculations. Implications for the origin of plumarellide and rameswaralide and related polycyclic metabolites isolated from corals.

DFT calculations probing potential (4 + 2) and (4 + 3) cycloaddition pathways leading to the polycyclic ring systems found in the coral secondary metabolites plumarellide, mandapamate and rameswaralide are described. Formation of plumarellide and mandapamate via stepwise intramolecular cycloaddition of a furanoxonium ion onto a 1,3-diene is shown to be viable. The calculations also predict the outcome of related cyclisations involving model systems.