8a-Methyl-5,6,8,8a,9,10-hexa-hydro-10,12a-epoxy-isoindolo[1,2-a] isoquinolinium iodide

The title compound, C17H18NO+· I-, is an adduct resulting from an intra-molecular Diels-Alder reaction of methallyl chloride with 3,4-dihydro-1-furylisoquinoline. The cation comprises a fused penta-cyclic system containing three five-membered rings (dihydro-pyrrole, dihydro-furan and tetra-hydro-furan) and two six-membered rings (tetra-hydro-pyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered tetra-hydro-pyridine ring adopts the unsymmetrical half-boat conformation. In the crystal, cations and iodide anions are bound by weak inter-molecular hydrogen-bonding inter-actions into a three-dimensional framework.