Crystal structure of ethyl 2′′,3-dioxo-7′,7a’-dihydro-1′H,3H,3′H-dispiro[benzo[b]thiophene-2,6′-pyrrolo[1,2-c]thiazole-5′,3′′-indoline]-7′-carboxylate

In the title compound, C23H20N2O4S2, the central pyrrolidine ring adopts an envelope conformation with the spiro C atom, shared with the benzothiophene ring system, as the flap. The thiazole ring has a twisted conformation on the S—C bond, where the C atom is that closest to methine C atom. The mean planes of the benzothiophene and indoline ring systems are inclined to the mean plane of the central pyrrolidine ring by 82.75 (8) and 80.03 (8)°, respectively, and to each other by 61.49 (6)°. In the crystal, molecules are linked via pairs of N—H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif. The dimers are linked via C—H⋯O and C—H⋯N hydrogen bonds, forming a three-dimensional structure. The ethoxycarbonyl group is disordered over two orientations, with an occupancy ratio of 0.717 (12):0.283 (12).

The molecular structure of the title compound as illustrated in Fig In the crystal, molecules are linked via C-H···O, C-H···N, N-H···O intermolecular hydrogen bonds (Table 1 and Fig. 2).

S2. Experimental
A reaction mixture of (E)-ethyl 2-(3-oxobenzo[b]thiophen-2(3H)-ylidene) acetate (1.0 mmol), isatin (1.1 mmol) and thiazolidine-4-carboxylic acid (1.1 mmol) was refluxed in methanol (20 ml) 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 supporting information sup-2 Acta Cryst. (2015). E71, o148-o149 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 two minutes. The solution was then subjected to crystallization by slow evaporation of the solvent resulting in single crystals suitable for X-ray crystallographic studies.

S3. Refinement
Atoms C1, C2 and O2 are disordered over two positions (C1A/C1B, C2A/C2B & O2/O2A) with a refined occupancy ratio of 0.716 (12) : 0.284 (12). The O-C and C-C distances of the disordered atoms were restrained to be equal. The displacement parameters of the disordered atoms were restrained to be equal for bonded atoms. The NH H atom was located in a difference Fourier map and freely refined. The C-bound H atoms were fixed geometrically and allowed to ride on their parent C atoms: C-H = 0.93-0.97 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  The molecular packing of the title compound viewed along the b axis. Dashed lines show the C-H···N, C-H···O and C -H···N hydrogen bonds (Table 1)  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.26 e Å −3 Δρ min = −0.27 e Å −3 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (