Diethyl 1-acetyl-4′-(4-chlorophenyl)-5′-(4-nitrophenyl)-2-oxospiro[indoline-3,3′-pyrrolidine]-2′,2′-dicarboxylate

In the title compound, C31H28ClN3O8, the pyrrolidine ring exhibits an envelope conformation, with the spiro C atom located at the flap position. A spiro junction links the oxindole ring system and the pyrrolidine ring. The planar oxindole ring system is twisted with respect to the nitrobenzene and chlorobenzene rings, with dihedral angles of 62.34 (11) and 75.93 (9)°, respectively. In the crystal, a weak C—H⋯O interaction links the molecules into chains and two intramolecular C—H⋯O close contacts are seen.

In the title compound, C 31 H 28 ClN 3 O 8 , the pyrrolidine ring exhibits an envelope conformation, with the spiro C atom located at the flap position. A spiro junction links the oxindole ring system and the pyrrolidine ring. The planar oxindole ring system is twisted with respect to the nitrobenzene and chlorobenzene rings, with dihedral angles of 62.34 (11) and 75.93 (9) , respectively. In the crystal, a weak C-HÁ Á ÁO interaction links the molecules into chains and two intramolecular C-HÁ Á ÁO close contacts are seen.

D-HÁ
The diffraction data were collected at the Centre for Test and Analysis, Chengdu Branch, Chinese Academy of Sciences. The author acknowledges financial support from China West Normal University.

Comment
The spirooxindole-pyrrolidine unit is a privileged heterocyclic motif that forms the core of a large family of alkaloid natural products with strong bioactivity profiles and interesting structural properties such as alstonia muelleriana and horsfiline (Garnick & Lequesne, 1978;Jossang et al., 1991). Pyrrolidine-containing compounds are of significant importance because of their biological activities and widespread employment in catalysis (Grigg et al., 1995;Witherup et al., 1995;Kravchenko et al., 2005). Oxindole derivatives are of importance in the total synthesis of indole and oxindole alkaloids such as potent inhibitors of monoamine oxidase (MAO) in human urine and rat tissues (Glover et al., 1998) and atrial natriuretic peptidestimulated guanylate cyclase and a potent antagonist of in vitro receptor binding by atrial natriuretic peptide besides possessing a wide range of central nervous system activities (Bhattacharya et al., 1982). We report herein the crystal structure of the title compound.
The molecular structure of (I) is shown in Fig. 1. In the molecule, the pyrrolidine ring exhibits an envelope conformation.
The crystal packing is stabilized by C-H···O hydrogen bonding (Table 1).
Experimental 1-acetyl-3-(4-chlorobenzylidene)indolin-2-one (0.09 g, 0.3 mmol), diethyl 2-aminomalonate (0.035 g, 0.2 mmol) and 4-nitrobenzaldehyde (0.036 g, 0.24 mmol) were dissolved in dichloromethane (2 ml). To the stirred mixture, acetic acid (0.006 g, 0.1 mmol) was added. After the mixture had been stirred at 273 K for 24 h, the reaction was quenched with a saturated solution of sodium bicarbonate (5 ml). The mixture was extracted with diethyl ether, removal of solvent under reduced pressure, the residue was purified through column chromatography on silica gel to give target compound. Colourless single crystals suitable for X-ray diffraction were obtained by recrystallization from ethanol.

Refinement
One ethyl group is disordered over two sites, occupancies were refined to 0.663 (5):0.337 (5). Imino H atoms were located in a difference Fourier map and were refined isotropically. The carbon-bound H atoms were placed in calculated positions, with C-H = 0.93-0.98 Å, and refined using a riding model, U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of (I) with 30% probability displacement ellipsoids (arbitrary spheres for H atoms). The minor disordered component is omitted for clarity.

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 > σ(F 2 ) is used only for calculating Rfactors(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. (2)