Crystal structures of ethyl (2S*,2′R*)-1′-methyl-2′′,3-dioxo-2,3-dihydrodispiro[1-benzothiophene-2,3′-pyrrolidine-2′,3′′-indoline]-4′-carboxylate and ethyl (2S*,2′R*)-5′′-chloro-1′-methyl-2′′,3-dioxo-2,3-dihydrodispiro[1-benzothiophene-2,3′-pyrrolidine-2′,3′′-indoline]-4′-carboxylate

The title compounds, (I) and (II), are dispiro-indole-pyrrolidine-benzothiophene derivatives, with (II) having a chlorine substituent on the oxoindole unit. As a result, the conformation of the two molecules differs in the angle of inclination of the indole moiety with respect to the benzothiophene ring system, with a dihedral angle of 71.59 (5) in (I) and 82.27 (7)° in (II).

for (I), and by 81.99 (10) and 88.79 (10) for (II). In both compounds, the ethoxycarbonyl group occupies an equatorial position with an extended conformation. The overall conformation of the two molecules differs in the angle of inclination of the indole unit with respect to the benzothiophene ring system, with a dihedral angle between the planes of 71.59 (5) in (I) and 82.27 (7) in (II). In the crystal of (I), molecules are linked via pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers enclosing R 2 2 (14) loops. The dimers are linked via C-HÁ Á ÁO and bifurcated C-HÁ Á ÁO(O) hydrogen bonds, forming sheets lying parallel to (100). In the crystal of (II), molecules are again linked via pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers but enclosing smaller R 2 2 (8) loops. Here, the dimers are linked by C-HÁ Á ÁO hydrogen bonds, forming ribbons propagating along [010].

Chemical context
The spiro-indole-pyrrolidine ring system is a frequently encountered structural motif in many biologically important and pharmacologically relevant alkaloids, such as vincrinstine, vinblastine and spirotypostatins (Cordell, 1981). Highly functionalized pyrrolidines have gained much interest in the past few years as they constitute the main structural element of many natural and synthetic pharmacologically active compounds (Waldmann, 1995). Optically active pyrrolidines have been used as intermediates, chiral ligands or auxiliaries in controlled asymmetric synthesis (Suzuki et al., 1994;Huryn et al., 1991). In view of this importance, the title compounds were synthesized and we report herein on their molecular and crystal structures.
The molecular structure of the compound (II) is illustrated in Fig. 2. The overall geometry of the molecule is similar to that of (II). The pyrrolidine ring (N2/C8-C11) also adopts a twist conformation on the C8-C11 bond, and the fivemembered ring (N1/C11-C14) of the oxindole moiety has an r.m.s. deviation = 0.042 Å . The mean plane of the benzothiophene ring system (S1/C1-C8; r.m.s. deviation = 0.034 Å ) and the mean plane of the indole ring system (N1/C11-C18; r.m.s. deviation = 0.069 Å ) are inclined to one another by 82.27 (7) , and are both almost normal to the mean plane of the pyrrolidine ring (N2/C8-C11) with dihedral angles of 88.79 (10) and 81.99 (10) , respectively.
Molecules (I) and (II) differ only in the presence of a chloride atom at position 5 in the oxoindole unit in (II). The conformation of the two molecules differ in the angle of inclination of the indole moiety with respect to the benzothiophene ring system, with a dihedral angle of 71.59 (5) in (I) and 82.27 (7) in (II). This is illustrated in Fig. 3, which shows a view of the superposition of the two molecules (Mercury; Macrae et al., 2008). There is also a small difference in the orientation of the ester function, the C20-O4-C21-C22 torsion angle being 173.44 (19)  The molecular structure of molecule (I), with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 2
The molecular structure of molecule (II), with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.
In the crystal of (II), molecules are again linked via pairs of N--HÁ Á ÁO hydrogen bonds, forming inversion dimers but enclosing smaller R 2 2 (8) loops (Table 2

Synthesis and crystallization
The two compounds were prepared in a similar manner using isatin (1.1 mmol) for (I) and 5-chloro isatin (1.1 mmol) for (II). A mixture of (E)-ethyl 2-(3-oxobenzo[b]thiophen-2(3H)ylidene) acetate (1.0 mmol) and the relevant isatin together with sarcosine (1.1 mmol) was refluxed in methanol (20 ml) until completion of the reaction, as evidenced by TLC analysis. After completion of the reaction, the solvent was evaporated under reduced pressure. The crude reaction mixture was dissolved in dichloromethane (2 Â 50 ml) and washed with water followed by brine solution. The organic layer was separated and dried over sodium sulfate. After filtration, the solvent was evaporation under reduced pressure. The product was separated by column chromatography using hexane and ethyl acetate (9:1) as eluent to give a white solid. This was dissolved in chloroform (3 ml) and heated for 2 min. The resulting solutions were allowed to evaporate slowly at room temperature and yielded colourless block-like crystals of compounds (I) and (II). The crystal packing of compound (I), viewed along the a axis. The hydrogen bonds are shown as dashed lines (see Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity).

Figure 5
A partial view along the a axis of the crystal packing of compound (II). The hydrogen bonds are shown as dashed lines (see Table 2 for details; H atoms not involved in hydrogen bonding have been omitted for clarity).

Hydrogen-bond geometry (Å, º)
Cg is the centroid of the C1-C6 ring. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.29 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.