Crystal structure of 2-benzylamino-4-p-tolyl-6,7-dihydro-5H-cyclopenta[b]pyridine-3-carbonitrile

In the crystal of the title compound, molecules are linked by pairs of N—H⋯Nnitrile hydrogen bonds, forming inversion dimers with an (12) ring motif. The dimers are linked by C—H⋯π and π–π interactions [centroid–centroid distance = 3.7211 (12) Å], forming a three-dimensional framework.


Chemical context
The pyridine nucleus is prevalent in numerous natural products and is extremely important in the chemistry of biological systems (Bringmann et al., 2004). Many naturally occurring and synthetic compounds containing the pyridine scaffold possess interesting pharmacological properties (Temple et al., 1992). Among them, 2-amino-3-cyanopyridines have been identified as IKK-inhibitors (Murata et al., 2003). The above observations prompted us to synthesize the title compound, which contains a pyridine 3-carbonitrile group, and we report herein on its crystal structure.

Structural commentary
The molecular structure of the title compound is shown Fig. 1. As expected, the pyridine ring (N1/C2-C6) is almost planar (r.m.s. deviation = 0.009 Å ). The cyclopentane ring fused with the pyridine ring adopts an envelope conformation with atom C8 as the flap, deviating by 0.3505 (1)Å from the mean plane defined by atoms (C5/C6/C7/C9). In the CH 2 -NH 2 chain, the C-N bond lengths [C2-N3 = 1.349 (3) and N3-C21 = 1.437 (3) Å ] are comparable with those reported for a similar structure (Nagalakshmi et al., 2014). The endocyclic angle at C5 is contracted to 118.73 (19) while that at C6 is expanded to 126.2 (2) , due to the fusion of the five-and six-membered rings. Steric hindrance rotates the benzyl ring (C22-C27) out of the plane of the central pyridine ring by 81.87 (14) . This twist may be due to the non-bonded interactions between one of the ortho-H atoms of the benzene ring and atom H21B of the CH 2 -NH 2 chain. The benzyl and and p-tolyl (C41-C46) rings are inclined to one another by 56.18 (15) , while the ptolyl ring is inclined to the pyridine ring by 47.60 (11) .

Synthesis and crystallization
A mixture of cyclopentanone (1 mmol) 1, 4-methylbenzaldehyde (1 mmol), malononitrile (1 mmol) and benzylamine were taken in ethanol (10 mL) to which ptoluenesulfonic acid (p-TSA) (1 mmol) was added. The reac-tion mixture was heated under reflux for 2-3 h. The reaction progress was monitored by thin layer chromatography. After completion of the reaction, the mixture was poured into crushed ice and extracted with ethyl acetate. The excess solvent was removed under vacuum and the residue was subjected to column chromatography using a petroleum ether/ The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view along the c axis of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines (see Table 1 for details) and H atoms not involved in hydrogen bonding have been omitted for clarity.
ethyl acetate mixture (97:3 v/v) as eluent to obtain the pure product. The product was recrystallized from ethyl acetate, affording colourless crystals of the title compound (yield: 70%, m.p.: 434 K).