1-Benzyl-4′,5′-diphenylpiperidine-3-spiro-3′-pyrrolidine-2′-spiro-3′′-indoline-4,2′′-dione

The asymmetric unit of the title compound, C34H31N3O2, consists of two independent molecules which differ slightly in the orientations of the phenyl rings with respect to the pyrrolidine ring. In both molecules, the piperidin-4-one ring adopts a chair conformation, whereas the pyrrolidine ring adopts an envelope conformation in one of the molecules and a twisted conformation in the other. An intramolecular C—H⋯O hydrogen bond is observed. The crystal packing is stabilized by intermolecular N—H⋯O hydrogen bonds and C—H⋯π interactions.

The asymmetric unit of the title compound, C 34 H 31 N 3 O 2 , consists of two independent molecules which differ slightly in the orientations of the phenyl rings with respect to the pyrrolidine ring. In both molecules, the piperidin-4-one ring adopts a chair conformation, whereas the pyrrolidine ring adopts an envelope conformation in one of the molecules and a twisted conformation in the other. An intramolecular C-HÁ Á ÁO hydrogen bond is observed. The crystal packing is stabilized by intermolecular N-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions.
SP thanks the CSIR for funding a major research project.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CI2737).

Comment
The development of new efficient methods to synthesize N-heterocycles with structural diversity is one of the major interests of modern synthetic organic chemists (Kirsch et al., 2004). Oxindole derivatives are known to possess a variety of biological activities (Klumpp et al., 1998) such as (i) a potent inhibitor of monoamine oxidase (MAO) in human urine and rat tissues (Glover et al., 1998) (ii) inhibition of several enzymes such as acetylcholinestrease (AChE) (Kumar et al., 1993) and atrial natriuretic peptide-stimulated guanylate cyclase and (iii) a potent antagonist of in vitro receptor binding by atrial natriuretic peptide (Medvedev et al., 1996) besides possessing a wide range of central nervous system activities (Bhattacharya et al., 1982). The derivatives of spirooxindole ring systems are used as antimicrobial, antitumour agents and as inhibitors of the human NKI receptor besides being found in a number of alkaloids like horsifiline, spirotryprostatin and (+)elacomine (Hilton et al., 2000). Our interest in preparing pharmacologically active pyrrolidines led us to the title compound, and we have undertaken X-ray crystal structure determination of these compounds in order to establish their conformations.
The asymmetric unit of the title compound contains two independent molecules, and these pair has almost identical geometry ( Fig. 1 and Fig. 2). In both the molecules, the bond lengths and bond angles show normal values and agree with each other (Allen et al., 1987). The sums of the angles at atoms N2 and N5 of the pyrrolidine rings 342.3 and 333.4°, respectively, are in accordance with sp 3 -hybridization, and sums of the angles at atoms N3 and N6 of the indolin-2-one moiety 360 and 359.8° confirms the sp 2 -hybridization (Govind et al., 2004;Kumar et al., 2006;Jeyabharathi et al., 2001).
In one of the independent molecules the pyrrolidine ring (in ring N5/C55/C48/C39/C62, C55 is the flap atom) adopts an envelope conformation and in the other it exhibits a twisted conformation. In the indolin-2-one ring systems, the benzene and pyrrole rings are individually planar and make dihedral angles of 3.8 (2) and 1.7 (2)°, while atoms O2 and O4 deviate from the pyrrole ring of the indolin-2-one system by -0.224 (5) and 0.117 (5) Å, respectively, because of the different interactions in which these O atoms are involved ( Table 1). The orientations of the phenyl groups with respect to the pyrrolidine ring differ slightly in the two independent molecules. N-H···O hydrogen bonds between the two molecules in the asymmetric unit generate an R 2 2 (8) graph set motif (Table   1 and Fig. 3). In addition, a C-H···π interaction (Table 1) is also found.

Experimental
A mixture of 1-benzyl-4-piperidinone (0.2 g, 0.001 mol), isatin (0.156 g, 0.001 mol) and phenylglycine (0.320 g, 0.002 mol) in methanol-water (2:1, 30 ml) were refluxed in a water bath for 24 h. After completion of the reaction as monitored by TLC, the excess solvent was removed under vacuum and the residue subjected to flash column chromatography using petroleum ether-ethyl acetate mixture (8:2 v/v) as eluent (yield: 0.220 g, 41%; m.p. 464-465 K) supplementary materials sup-2 Refinement H atoms attached to N2 and N5 are located in a difference map and refined with an N-H distance restraint of 0.82 (2)Å.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 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.