(4R*,4aR*,7aS*)-5-Oxo-6-phenyl-4a,5,6,7,7a,8-hexahydro-4H-furo[2,3-f]isoindole-4-carboxylic acid

The asymmetric unit of the title compound, C17H15NO4, contains two independent molecules with similar geometric parameters. In both molecules, the conformation of the cyclohexene ring is half-chair, while the pyrrolidinone ring adopts an envelope conformation with the γ-carbon atom of the α-pyrrolidinone ring as the flap. In the crystal, O—H⋯O hydrogen bonds between the carboxylic and carbonyl groups link alternate independent molecules into chains propagating in the b-axis direction. The crystal packing also features weak C—H⋯π interactions.

The asymmetric unit of the title compound, C 17 H 15 NO 4 , contains two independent molecules with similar geometric parameters. In both molecules, the conformation of the cyclohexene ring is half-chair, while the pyrrolidinone ring adopts an envelope conformation with the -carbon atom of the -pyrrolidinone ring as the flap. In the crystal, O-HÁ Á ÁO hydrogen bonds between the carboxylic and carbonyl groups link alternate independent molecules into chains propagating in the b-axis direction. The crystal packing also features weak C-HÁ Á Á interactions.
Cg1 and Cg2 are the centroids of the C13A-C18A and O1A-C5A rings, respectively. Symmetry codes: (i) Àx þ 1 2 ; y þ 1 2 ; z; (ii) x þ 1 2 ; y; Àz þ 3 2 ; (iii) Àx; y À 1 2 ; Àz þ 3 2 ; (iv) x À 1 2 ; y; Àz þ 3 2 . Recently, the researchers attention was drawn to such class of compounds as heterolignans ( Figure 1) (Ramos et al., 1999). The best known heterolignan is azatoxin, which has antineoplastic activity (Leteurtre et al., 1992). In addition, it should be noted that a number heterolignans show anticancer, antirheumatic and antiasthmatic activity (Iwasaki et al., 1996;Ducharme et al., 1994). There are two important aspects of the synthesis of these compounds. First, as biological activity investigations have shown, the replacement of carbon atoms by heteroatoms in the cycle, or the replacement of benzene fragments by heterocycles, has little effect on biological activity. Second, from the synthetic point of view Cheteroatom bonds are easier accesible than C-C bonds. In addition to this, structural variability and synthetic availability of heterocycles are significantly higher than benzene fragments.

D-HÁ
Considering mentioned above, synthesis of lignan analogues or their synthetic precursors, including those with furan cycles, are contemporary tasks. It was found that in the reaction of maleic anhydride and [3-(2-furyl)-2-propenyl]-phenylamine the furane cycle persists and exocyclic double bond reacts. Furoisoindole system with carboxyl group in the sixmembered ring is formed. It should be noted that earlier furoisoindole system used to be obtained by the Domino Wittig-Diels-Alder reaction (Patre et al., 2007) and palladium-catalyzed tandem cyclization of allenes with heteroarylhalides (Ohno et al., 2005).
The structure displays O-H···O hydrogen bonding between acid carboxyl and carbonyl groups, which connects molecules into chains propagating in b-axis direction ( Figure 3). The crystal packing exhibits weak intermolecular C-H···π interactions.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.