Methyl 4-anilino-2′,5-dioxo-1′,2′-dihydro-5H-spiro[furan-2,3′-indole]-3-carboxylate

In the title compound, C19H14N2O5, the spiro junction links an oxindole moeity and a furan ring, which subtend a dihedral angle of 83.49 (6)°. The molecular structure features an N—H⋯O hydrogen bond, which generates an S(6) ring motif. The crystal packing is governed by two N—H⋯O interactions, one of which generates a centrosymmetric R 2 2(14) dimer. The other N—H⋯O interaction along with a C—H⋯O hydrogen bond contributes to the formation of a C 2 2[R 2 2(9)] dimeric chain running along the b-axis direction.

In the title compound, C 19 H 14 N 2 O 5 , the spiro junction links an oxindole moeity and a furan ring, which subtend a dihedral angle of 83.49 (6) . The molecular structure features an N-HÁ Á ÁO hydrogen bond, which generates an S(6) ring motif. The crystal packing is governed by two N-HÁ Á ÁO interactions, one of which generates a centrosymmetric R 2 2 (14) dimer. The other N-HÁ Á ÁO interaction along with a C-HÁ Á ÁO hydrogen bond contributes to the formation of a C 2 2 [R 2 2 (9)] dimeric chain running along the b-axis direction.
The bond lengths and angles in the title compound are within normal ranges except those at the spiro junction which reflects the presence of bulky subsituents. The dihedral angle between the five (C5/C6/N1/C7/C8) and six membered (C1-C6) rings in the indole group is 4.15 (8)°. The indole moeity is orthogonal to the furan ring as indicated by the dihedral angle of 83.49 (6)° between them.
The furan ring in the structure adopts a twisted conformation with a psuedo-twofold axis passing through the C8 atom and C9-C10 bond. The puckering parameters (Cremer & Pople, 1975) for the furan ring are q 2 = 0.0810 (14)Å, φ 2 = 310.9 (10)°. The benzene ring is bisectionally oriented to the furan ring, the dihedral angle between them being 52.80 (8)°. The title compound exihibits structural similarities with an already reported related structure (Gayathri et al.,

Experimental
Isatin (1 mmol), aromatic amine (1 mmol), and dimethyl acetylene dicarboxylate (1 mmol) were stirred at room temperature in methanol in the presence of triethylamine (20 mol%) for 4 hrs to give the spirolactones which was filtered out and recrystallized from methanol to afford the pure product (85% yield) as yellow solid.

Refinement
Positions of the H atoms were localized from the difference electron density maps and their distances were geometrically constrained. The H atoms of amine groups were refined freely with U iso (H) = 1.2U eq (N). The atoms bound to the C atoms were treated as riding atoms with d(C-H) = 0.93Å and U iso (H) = 1.    Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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.