3-Ethyl-5-(4-methoxyphenoxy)-2-(pyridin-4-yl)-3H-imidazo[4,5-b]pyridine

In the title compound, C20H18N4O2, the imidazopyridine fused ring system is almost perpendicular to the benzene ring [dihedral angle = 87.6 (5)°]. The pyridine ring makes a dihedral angle of 35.5 (5)° with the mean plane of the imidazopyridine fragment. The crystal structure is stabilized by an aromatic π–π stacking interaction between the phenyl rings of neighbouring molecules [centroid–centroid distance = 3.772 (2) Å, interplanar distance = 3.546 (2) Å and slippage = 1.286 (2) Å].


Comment
Pyridine derivatives has numerous applications in medicinal chemistry (Passannanti et al., 1998). Furthermore, the imidazo[4,5-b]pyridine moiety is also an important heterocyclic nucleus which has been used extensively in medicinal chemistry. In fact, the heterocycles derived from these intermediates have been tested for their potential as anti-neuroinflammatory (Jiyeon et al., 2010). Pyridine-3-carboxamides have gained attention because of their diverse pharmacological properties such as anti-inflammatory (Abdel-Alim et al., 2005), anticancer (Girgis et al., 2006), cytoprotective (Slominska et al., 2008), and anxiolytic (Spanka et al., 2010) activities. Against this background, and in order to obtain detailed information on molecular conformations in the solid state, an X-ray study of the title compound was carried out.
The bond lengths and angles in (Fig. 1) agree with those observed in other imidazopyridine derivatives (Ouzidan et al., 2010). The imidazopyridine ring system is essentially planar, with maximum deviation of 0.013 (1)° for atom C1. The sum of bond angles around N2[359.2 (9)°] of the imidazole ring is in accordance with sp 3 hybridization (Beddoes et al., 1986). The imidazopyridine ring system makes dihedral angles of 35.5 (5) and 87.6 (5)°, respectively, with the pyridine and phenyl rings and also the dihedral angle between the pyridine and phenyl ring is 87.0 (6)°. It shows that the phenyl ring is perpendicular to both the imidazopyridine and pyridine rings. The atoms O1 and O2 are deviated by 0.039 (1) and -0.021 (1)Å from the leastsquares plane of the phenyl ring.
The molecules lack hydrogen bonding functionality and pack in layers parallel to the (100) planes. The crystal structure is stabilized by an aromatic π-π stacking interaction between the phenyl rings of adjacent molecules, with a Cg···Cg distance of 3.772 (2) Å and an interplanar distance of 3.546 (3) Å resulting in a slippage of 1.286 (3) Å (Cg is the centroid of the C14-C19 phenyl ring).
Experimental N-ethyl-6-(4-methoxyphenoxy)pyridin-2-amine (0.23 g, 1 mmol) and amide (0.12 g, 1 mmol) successively added to Al 3+ -Y in xylene at 145°C. After stirring for 16 h, the mixture was diluted with dichloromethane. After removing the catalyst by filtration, followed by solvent evaporation, the resulting crude product was finally purified by column chromatography (silica gel). Single crystals suitable for X-ray diffraction were obtained by slow evaporation of a solution of the title compound in ethylacetate at room temperature.

Refinement
All H atoms were fixed geometrically and allowed to ride on their parent C atoms, with C-H distances fixed in the range 0.93-0.97 Å with U iso (H) = 1.5U eq (C) for methyl H 1.2U eq (C) for other H atoms.  Fig. 1. The structure of showing the atom-numbering scheme. The displacement ellipsoids are drawn at the 30% probability level.