5-Amino-6-benzoyl-8-nitro-2,3-dihydro-1H-spiro[imidazo[1,2-a]pyridine-7,3′-indolin]-2′-one dimethyl sulfoxide monosolvate

In the title compound C21H17N5O4·C2H6OS, the central six-membered ring derived from 1,4-dihydropyridine adopts a distorted boat conformation with a small puckering amplitude of 0.127 (3) Å. The sums of bond angles around the pyridine N atom [358.7 (2)°] and the other imidazolidine N atom [60 (2)°] indicate that these atoms are in sp2 hybridization, leading to an essentially planar imidazolidine ring. The last heterocycle, an oxindole moiety, is also nearly planar with an r.m.s. deviation of 0.0185 (1) Å. The amine NH2 group forms an intramolecular hydrogen bond with the benzoyl group, giving a S(6) motif. In the crystal, N—H⋯O hydrogen bonds lead to the formation of chains along the c-axis direction. Within the chains there are further N—H⋯O and C—H⋯O hydrogen bonds enclosing R 2 2(14) ring motifs. The chains are linked via N—H⋯O and C—H⋯O hydrogen bonds involving the dimethyl sulfoxide solvent molecule which acts as both an acceptor and a donor..

In the title compound C 21 H 17 N 5 O 4 ÁC 2 H 6 OS, the central sixmembered ring derived from 1,4-dihydropyridine adopts a distorted boat conformation with a small puckering amplitude of 0.127 (3) Å . The sums of bond angles around the pyridine N atom [358.7 (2) ] and the other imidazolidine N atom [60 (2) ] indicate that these atoms are in sp 2 hybridization, leading to an essentially planar imidazolidine ring. The last heterocycle, an oxindole moiety, is also nearly planar with an r.m.s. deviation of 0.0185 (1) Å . The amine NH 2 group forms an intramolecular hydrogen bond with the benzoyl group, giving a S(6) motif. In the crystal, N-HÁ Á ÁO hydrogen bonds lead to the formation of chains along the c-axis direction. Within the chains there are further N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds enclosing R 2 2 (14) ring motifs. The chains are linked via N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds involving the dimethyl sulfoxide solvent molecule which acts as both an acceptor and a donor..

Synthesis and crystallization
A mixture of benzoylacetonitrile (1.0 mmol), isatin (1.0 mmol) and 2-(nitromethylene) imidazolidine was dissolved in 10 ml of EtOH, and triethylamine (1.0 mmol) was added. The reaction mixture was refluxed for 45 min. After completion of the reaction, as evident from TLC, the precipitated solid product was filtered and dried to obtain pure pale brown solid.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were placed in calculated positions and allowed to ride on their carrier atoms with C-H = 0.93 (aromatic CH), 0.96 (methyl CH 3 ) or 0.97 Å (methylene CH 2 ), and N-H = 0.86 Å. Isotropic displacement parameters for H atoms were calculated as U iso = 1.5U eq (C) for CH 3 groups and U iso = 1.2U eq (carrier atom) for all other H atoms.

Results and discussion
Our interest in preparing pharmacologically active pyridine-related compounds (Suresh et al., 2013) led us to the title compound, derived from a 1,4-dihydropyridine, and we have undertaken X-ray crystal structure determination of this compound in order to establish its molecular conformation.
In the title compound ( Fig. 1 benzene ring, and the strain is taken up by the angular distortion rather than by bond length distortions (Allen, 1981 124.9 (2)°.

Figure 1
The molecular structure of the title compound, showing 20% probability displacement ellipsoids. All H atoms are omitted for clarity. Partial packing diagram of the title compound. Dashed bonds represent inter-molecular hydrogen bonds.