8a-Methyl-5,6,8,8a,9,10-hexahydro-10,12a-epoxyisoindolo[1,2-a]isoquinolinium iodide

The title compound, C17H18NO+·I−, is an adduct resulting from an intramolecular Diels–Alder reaction of methallyl chloride with 3,4-dihydro-1-furylisoquinoline. The cation comprises a fused pentacyclic system containing three five-membered rings (dihydropyrrole, dihydrofuran and tetrahydrofuran) and two six-membered rings (tetrahydropyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered tetrahydropyridine ring adopts the unsymmetrical half-boat conformation. In the crystal, cations and iodide anions are bound by weak intermolecular hydrogen-bonding interactions into a three-dimensional framework.

The title compound, C 17 H 18 NO + ÁI À , is an adduct resulting from an intramolecular Diels-Alder reaction of methallyl chloride with 3,4-dihydro-1-furylisoquinoline. The cation comprises a fused pentacyclic system containing three fivemembered rings (dihydropyrrole, dihydrofuran and tetrahydrofuran) and two six-membered rings (tetrahydropyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered tetrahydropyridine ring adopts the unsymmetrical half-boat conformation. In the crystal, cations and iodide anions are bound by weak intermolecular hydrogen-bonding interactions into a three-dimensional framework.

Comment
Recently our group has proposed an efficient approach (Zubkov et al., 2009) to potentially bioactive substances -hydrogenated isoindolo[2,1-a]isoquinolines using commercially available furfurals and phenethylamines as starting materials (Boltukhina et al., 2006). The intramolecular furan Diels-Alder reaction (IMDAF) (Zubkov et al., 2004) between unsaturated acid derivatives and the furan core of the amines was the key step of the transformations mentioned above.
Trying to apply our chemistry to target natural products, we were attracted to isoindoloisoquinoline alkaloids. Today, there are three known natural alkaloids containing the isoindolo[2,1-a]isoquinoline skeleton -Nuevamine, Jamtine (and its N-oxide) and Hirsutine (Rasheed et al., 1991).
This work realizes aforementioned approach and describes the structure of an alkaloid-like IMDAF product I containing the nodal iminium nitrogen atom (Tagmazyan et al., 1976;Ahmad et al., 1987).
The five-membered rings have usual envelope conformations, and the central six-membered tetrahydropyridine ring adopts the unsymmetrical half-boat conformation. The nitrogen N7 atom has a trigonal-planar geometry (sum of the bond angles is 359.5°). The dihedral angle between the planes of the dihydropyrrole (N7/C8/C12A/C12B) and benzene rings is 20.1 (1)°.
The cation of I possesses three asymmetric centers at the C8A, C10 and C12A carbon atoms and can have potentially eight diastereomers. The crystal of I is racemic and consists of enantiomeric pairs with the following relative configuration of the centers: rac-8 AR*,10R*,12 AR*.
The crystal packing of the cations of I is stacking along the b axis ( Fig. 2). In the crystal, the cations and iodide anions are bound by the weak intermolecular hydrogen bonding interactions into 3-dimensional framework (Fig. 2, Table 1).

Experimental
Potassium iodide (3.1 g, 11 mmol) and methallylchloride (0.8 ml, 8.25 mmol) were added to a solution of 1-furyl-3,4-dihydroisoquinoline (1.08 g, 5.5 mmol) in dioxane (50 ml). The reaction mixture was refluxed for 5 h (monitoring by TLC until disappearance of the starting compound sport). At the end of the reaction, solvent was removed under reduced pressure and the residue was crystallized from ethyl acetate-ethanol mixture to give 0.35 g of isoquinolinium iodide as brown prisms ( Fig. 3). Yield is 17%. The single crystals of product I were obtained by slow crystallization from acetonitrile (yield 73%