A diastereomer of methyl (1R,3′S)-1′,1′′-dimethyl-2,2′′-dioxo-2H-dispiro[acenaphthylene-1,2′-pyrrolidine-3′,3′′-indoline]-4′-carboxylate

In the title compound, C26H22N2O4, the central pyrrolidine ring adopts a twist conformation and the cyclopentane ring of the dihydroacenapthylene group adopts an envelope conformation with the spiro C atom as the flap. The naphthalene ring system of the dihydroacenaphthylene group forms dihedral angles of 83.4 (9) and 61.3 (7)°, respectively, with the mean planes of the pyrrolidine and indole rings. The crystal packing is stabilized by intermolecular C—H⋯O hydrogen bonds. The title compound is a diastereomer of a previously reported structure.


Experimental
A mixture of 1 eq of (E)-methyl 2-(1-methyl-2-oxoindolin-3-ylidene) acetate, 1 eq of isatin and 1.5 eq of acenaphthylene-1,2-dione were dissolved in acetonitrile. This reaction mixture was refluxed at 353K for 8 hours. The reaction mixture was monitored for completion by thin layer chromatography. Upon completion, the the product was dried and purified by coloumn chromatography using ethyl acetate and hexane (1:9) as an elutent to affored pure dispiro oxindole.
Yield (78%). Single crystals suitable for X-ray diffraction were obtained by slow evaporation of a solution of the title compound in ethyl acetate at room temperature.

Refinement
All H atoms were fixed geometrically and allowed to ride on their parent C atoms, with C-H distances fixed in the range 0.93-0.98 Å with U iso (H) = 1.5U eq (C) for methyl H 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. H atoms are presented as small spheres of arbitrary radius.  The molecular packing viewed down the b axis. Dashed lines shows the intermolecular C-H···O hydrogen bonds.

Methyl (1R,3′S)-1′,1′′-dimethyl-2,2′′-dioxo-2H-dispiro[acenaphthylene-1,2′-pyrrolidine-3′,3′′-indoline]-4′
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.