(6aS*,6bS*,11R*,11aR*)-6-(2-Furyl-methyl)-5,12-dioxo-5,6,6a,6b,7,11,11a,12-octa-hydro-furo[3',2':5,6]isoindolo[2,1-a]quinazoline-11-carb-oxy-lic acid.

The title compound, C(23)H(18)N(2)O(6), is the product of an intra-molecular thermal cyclo-addition within 1-malein-2-[(E)-2-(2-fur-yl)vin-yl]-4-oxo-3,4-dihydro-quinazoline. The mol-ecule comprises a previously unknown fused penta-cyclic system containing two five-membered rings (2-pyrrolidinone and furan) and three six-membered rings (benzene, 2,3-dihydro-4-pyrimidinone and dihydro-cyclo-hexa-ne). The central five-membered pyrrolidinone ring has the usual envelope conformation. The six-membered dihydro-pyrimidinone and dihydro-cyclo-hexane rings adopt a half-boat and a half-chair conformation, respectively. The dihedral angle between the planes of the terminal benzene and furan rings is 45.99 (7)°. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into centrosymmetric dimers. Weak C-H⋯O hydrogen bonds consolidate further the crystal packing, which exhibits π-π inter-actions, with a short distance of 3.556 (3) Å between the centroids of benzene rings of neighbouring mol-ecules.