Crystal structure of ethyl 1′,1′′-dimethyl-2′′,3-dioxo-3H-dispiro[benzo[b]thiophene-2,3′-pyrrolidine-2′,3′′-indoline]-4′-carboxylate

In the title compound, C23H22N2O4S, the pyrrolidine ring has an envelope conformation with the spiro C atom, shared with the indoline ring system, as the flap. The mean planes of the benzothiophene and indoline ring systems are inclined to the mean plane of the pyrrolidine ring by 88.81 (8) and 79.48 (8)°, respectively, and to each other by 68.12 (5)°. In the crystal, molecules are linked via C—H⋯O hydrogen bonds, forming chains propagating along [001].


S1. Comment
Indole compounds can be used as bioactive drugs (Stevenson et al., 2000). Indole derivatives exhibit antiallergic, central nervous system depressant and muscle relaxant properties (Harris & Uhle, 1960;Ho et al., 1986). In view of this biological importance, the crystal structure of the title compound was determined and the results are presented here.
The X-ray analysis confirms the molecular structure and atom connectivity as illustrated in Fig In the crystal, hydrogen-bonded chains running along [001] are generated by connecting neighbouring molecules via C-H···O hydrogen bonds (Table 1 and Fig. 2).

S2. Experimental
(E)-ethyl 2-(3-oxobenzo[b]thiophen-2(3H)-ylidene) acetate (1.0 mmol), N-methyl isatin (1.1 mmol) and sarcosine (1.1 mmol) were refluxed in methanol (20ml) until completion of the reaction monitored by TLC analysis. After completion of the reaction the solvent was evaporated under reduced pressure. The crude reaction mixture was dissolved in dichloromethane (2 × 50 ml) and washed with water followed by brine solution. The organic layer was separated and dried over sodium sulfate. After filtration the organic solvent was evaporated under reduced pressure. The product was separated by column chromatography using hexane and ethyl acetate (9:1) as an eluent to give a colourless solid. The product was dissolved in chloroform (3 ml) and heated for 2 min. The resulting solution was subjected to crystallization by slow evaporation of the solvent giving in single crystals suitable for X-ray crystallographic studies.

S3. Refinement
All H atoms were fixed geometrically and allowed to ride on their parent C atom: C-H = 0.93-0.98 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The crystal packing of the title compound viewed along the b axis. Dashed lines shows the intermolecular C-H···O hydrogen bonds. H atoms not involved in hydrogen bonding have been omitted for clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.40 e Å −3 Δρ min = −0.20 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008(Sheldrick, , 2015, Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0025 (2) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.