1′-Methyl-4′-phenyl-2′′-sulfanylidenedispiro[indoline-3,2′-pyrrolidine-3′,5′′-1,3-thiazolidine]-2,4′′-dione

The title compound, C20H17N3O2S2, crystallizes with two molecules in the asymmetric unit. The pyrrolodine rings have envelope conformations in both molecules, the N atoms deviating by 0.574 (3) and 0.612 (2) Å from the mean planes through the other ring atoms. The 1′-methyl and 4′-phenyl groups on the pyrrolidine rings are substituted in equatorial positions. In the crystal, molecules are linked into a three-dimensional network by N—H⋯O, N—H⋯N and C—H⋯O and N—H⋯π hydrogen bonds.


Comment
Heterocyclic compounds are of interest because of their diverse biological activities (Chavan et al., 2001;Baldwin et al., 1994). Some received considerable attention because of their potential antimicrobial activity (Amal Raj et al., 2003), especially indoles and spiroindoles, which play important roles in medicinal chemistry (Mogilaiah et al., 2001). The spiropyrrolidinyloxindole ring system is a frequently observed structural motif in many of the pharmacologically relevant alkaloids (Hilton et al., 2000). The derivatives of spirooxindole possess wide range of biological properties such as antimicrobial, antitumoral, antibiotic agents and inhibitors of human NK-1 receptor (Okita & Isobe, 1994).
The title compound ( Fig. 1) crystallizes with two molecules (A and B) in the assymetric unit. Both these molecules contain a central of pyrrolidine ring, which is connected by two spiro junctions at the atoms C1 and C8 to a thiosolidine and oxindole rings, respectively. The pyrrolidine rings adopt an envelope conformation in both the molecules and the atoms N1A and N1B deviate -0.574 (3) and -0.612 (2) Å, respectively from the mean plane defined by the atoms C1, C2, C3 and C4.
The other two substituents, the phenyl ring and methyl groups are oriented equatorially to best plane of the pyrrolidine rings.
The dihedral angles between the pyrrolidine ring and the oxidole and the thiosolidines moieties are 84.7 (1) and 88.2 (1)°, respectively for molecule A and 81.8 (1)and 90.0 (1)°, respectively for molecule B. The packing diagram of the title molecule viewed down b axis is shown in Fig. 2. The molecules are linked to form a three-dimensional network by N-H···O, N-H···N and C-H···O intra and intermolecular hydrogen bonds. In addition there is an N-H···π weak interaction, Table 1.

Experimental
A mixture of 5-benzylidene-2-thioxo-1,3-thiazolidin-4-one (1 mmol), isatin (1 mmol) and sarcosine (1 mmol) were taken up in 20 ml of aqueous methanol and refluxed for 8 h on a water bath (Sampath et al., 2010). The resultant product was subjected to column chromatography to yield the title compound and it was crystallized using methanol by slow evaporation method.