5-Amino-5′-bromo-6-(4-methylbenzoyl)-8-nitro-2,3-dihydro-1H-spiro[imidazo[1,2-a]pyridine-7,3′-indolin]-2′-one including an unknown solvate

In the title compound, C22H18BrN5O4, the central six-membered ring, derived from 1,4-dihydropyridine, adopts a distorted boat conformation with a puckering amplitude of 0.197 (3) Å, the imidazole ring adopts a twisted conformation with a puckering amplitude of 0.113 (3) Å, and the oxindole moiety is planar with an r.m.s. deviation of 0.0125 Å. Two intramolecular N—H⋯O hydrogen bonds are formed, each closing an S(6) loop. In the crystal, strong N—H⋯O hydrogen bonds lead to the formation of zigzag chains along the c axis. These are consolidated in the three-dimensional crystal packing by weak N—H⋯O hydrogen bonding, as well as by C—H⋯O, C—H⋯Br and C—H⋯π interactions. A small region of electron density well removed from the main molecule was removed with the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155] following unsuccessful attempts to model it as a plausible solvent molecule. The unit-cell characteristics do not take into account this feature of the structure.

In the title compound, C 22 H 18 BrN 5 O 4 , the central sixmembered ring, derived from 1,4-dihydropyridine, adopts a distorted boat conformation with a puckering amplitude of 0.197 (3) Å , the imidazole ring adopts a twisted conformation with a puckering amplitude of 0.113 (3) Å , and the oxindole moiety is planar with an r.m.s. deviation of 0.0125 Å . Two intramolecular N-HÁ Á ÁO hydrogen bonds are formed, each closing an S(6) loop. In the crystal, strong N-HÁ Á ÁO hydrogen bonds lead to the formation of zigzag chains along the c axis. These are consolidated in the three-dimensional crystal packing by weak N-HÁ Á ÁO hydrogen bonding, as well as by C-HÁ Á ÁO, C-HÁ Á ÁBr and C-HÁ Á Á interactions. A small region of electron density well removed from the main molecule was removed with the SQUEEZE procedure in PLATON [Spek (2009). Acta Cryst. D65,[148][149][150][151][152][153][154][155] following unsuccessful attempts to model it as a plausible solvent molecule. The unit-cell characteristics do not take into account this feature of the structure.

Structural commentary
Our interest in preparing pharmacologically active pyridine-related compounds (Nagalakshmi et al., 2014) led us to the title compound, derived from a 1,4-dihydropyridine. We have undertaken an X-ray crystal structure determination of this compound in order to establish its molecular conformation.

Synthesis and crystallization
A mixture of 4-methylbenzoylacetonitrile (1.0 mmol), 5-bromoisatin (1.0 mmol) and 2-(nitromethylene)imidazolidine were dissolved in 10 ml of EtOH and triethylamine (1.0 mmol) was added and the reaction mixture was heated to reflux 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. Yield 91 %. Melting point 530 K. supporting information sup-2 . E70, o816-o817

Refinement
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. A small region of electron density well removed from the main molecule and appearing disordered was removed with PLATON SQUEEZE [Spek (2009). Acta Cryst. D65,[148][149][150][151][152][153][154][155] following unsuccessful attempts to model it as plausible solvent molecule.

Figure 1
The molecular structure of (I), showing 20% probability displacement ellipsoids and the atom-numbering scheme. Hatoms are omitted for clarity.  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 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.