Crystal structure of 1-benzyl-4-(4-chlorophenyl)-2-imino-1,2,5,6,7,8,9,10-octahydrocycloocta[b]pyridine-3-carbonitrile

The title compound comprises a 2-iminopyridine ring fused with a cyclooctane ring, which adopts a twist boat–chair conformation. Intermolecular C—H⋯N interactions form (14) ring motifs and molecules are further connected by weak C—H⋯π interactions.


Chemical context
Schiff bases are compounds carrying an imine or azomethine (-C N-) functional group. They have gained importance in the medicinal and pharmaceutical fields due to their broad spectrum of biological activity, including anti-inflammatory, analgesic, antimicrobial, anticonvulsant, antitubercular (Aboul-Fadl et al., 2003), anticancer, antioxidant and antihelminthic, among others. Schiff base derivatives are present in a number of processes, which prompted researchers to design novel heterocyclic/aryl Schiff bases with the aim of developing new environmentally friendly technologies (Bhattacharya et al., 2003). Schiff bases are also used as ligands for catalysts, intermediates in organic synthesis, dyes, pigments, and polymer stabilizers (Dhar & Taploo, 1982).
Iminopyridine complexes can be useful catalysts, and pyridones have been investigated extensively as valuable building blocks for many fused heterocyclic systems (Johns et al., 2003) displaying a wide range of biological and pharmacological activities. They exhibit, for example, antiproliferative and antitubolin activities (Magedov et al., 2008). Many pyridin-2one and 3-cyano-2-iminopyridine derivatives also exhibit antiproliferative activity (McNamara & Cook, 1987). As part of our studies in this area, the title compound was synthesized ISSN 1600-5368 and we report herein on the molecular and crystal structures of this compound.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The cyclooctane ring adopts a twist boat-chair conformation (Wiberg, 2003), as found in similar structures (Vishnupriya et al., 2014a,b). As expected, the pyridine ring (atoms C1-C5/N3) is almost planar, with an r.m.s. deviation of 0.002 Å . The chlorobenzene (C31-C36) and phenyl (C13-C18) rings are almost planar, with r.m.s. deviations of 0.005 and 0.004 Å , respectively. The sum of the angles around atom N3 is 359.8 , indicating that atom N3 is sp 2 -hybridized. The C2-C38 N2 bond angle of 176.07 (19) shows the linearity of the cyano group, a feature systematically observed in carbonitrile compounds. Nitrile atoms C38 and N2 are displaced from the mean plane of the pyridine ring by 0.0258 (1) and 0.0363 (1) Å , respectively. The imino C1 N1 bond length is 1.286 (2) Å . The imino group is nearly coplanar with the pyridine ring, as indicated by the N1 C1-N3-C5 torsion angle of À178.89 (14) . The chlorobenzene ring is attached to the pyridine ring with a C2 C3-C31 . . . C36 torsion angle of 100.99 (19) , indicating a (+)anticlinal conformation. The C33 . . . C34 . . . C35 bond angle of 121.11 (15) deviates from 120 due to the presence of the chlorine substituent. The chlorine atom bonded to C34 deviates by 0.0446 (1) Å from the mean plane of the phenyl ring. The chlorine is attached to the benzene ring with a C32 . . . C33 . . . C34-Cl1 torsion angle of 178.95 (13) . In the pyridine ring, the formal double bonds [C4 C5 = 1.375 (2) and C2 C3 = 1.369 (2) Å ] are longer than standard C C bonds (1.34 Å ), while the other bond lengths are slightly shorter than standard C-C and C-N bond lengths, evidencing that there is a homo-conjugation effect for this ring.

Supramolecular features
In the crystal, pairs of C-HÁ Á ÁN interactions form R 2 2 (14) ring motifs (Bernstein et al., 1995), and the resulting dimers are further connected through weak C-HÁ Á Á interactions involving the phenyl ring as acceptor (Table 1 and Fig. 2). The resulting supramolecular structure is a two-dimensional framework parallel to the crystallographic ab plane.

Database survey
Similar structures reported in the literature are 2-methoxy-4-(2-methoxyphenyl)-5, 6,7,8,9,10-hexahydrocycloocta[b]pyridine-3-carbonitrile (Vishnupriya et al., 2014a) and 4-(2fluorophenyl)-2-methoxy-5,6,7,8,9,10-hexahydrocycloocta[b]pyridine-3-carbonitrile (Vishnupriya et al., 2014b). In the structure reported here, the twisted conformation of the cyclooctane ring and the planar conformation of the pyridine are similar to those found in the related structures. However, the C NH functional group present in the title compound allows the formation of C-HÁ Á ÁN hydrogen bonds, which are not present in the above-cited compounds. In the title compound, the bond lengths in the central pyridine ring span the range 1.369-1.447 Å , which compares well with the ranges observed in the similar structures (1.314-1.400 Å ), but these bonds are systematically longer in the title compound, due to the substitution of the pyridine N atom by a benzyl group.
Cg1 is the centroid of the phenyl ring.

Figure 2
Partial packing diagram of the title compound. Dashed lines represent intermolecular hydrogen bonds and C-HÁ Á Á contacts. For clarity, H atoms not involved in hydrogen bonding have been omitted. and p-toluenesulfonic acid (0.5 mmol) was added. The reaction mixture was refluxed for 2-3 h. After completion of the reaction (followed by thin-layer chromatography), the mixture was poured into crushed ice and extracted with ethyl acetate. The excess of solvent was removed under reduced pressure and the residue was chromatographed using a petroleum ether/ethyl acetate mixture (97:3 v/v) as eluent, to afford the pure product. The product was recrystallized from ethyl acetate, affording colourless crystals (m.p. 493 K; yield 71%).

Refinement
C-bound H atoms were placed in calculated positions and allowed to ride on their carrier atoms, with C-H = 0.93 (aromatic CH) or 0.97 Å (methylene CH 2 ). Imine atom H1 was found in a difference map and refined freely, with the N-H distance restrained to 0.84 (2) Å . Isotropic displacement parameters for H atoms were calculated as U iso (H) = 1.2U eq (C) for CH and CH 2 groups, while the U iso factor for H1 was refined. Crystal data, data collection and structure refinement details are summarized in Table 2. Computer programs: APEX2 and SAINT (Bruker, 2004), SHELXS97 and SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).