3-Allyl-6-bromo-1H-imidazo[4,5-b]pyridin-2(3H)-one

In the molecule of the title compound, C9H8BrN3O, the fused-ring system is almost planar, the largest deviation from the mean plane being 0.008 (3) Å. The plane through the atoms forming the allyl group is roughly perpendicular to the imidazo[4,5-b]pyridin-2-one system, as indicated by the dihedral angle between them of 70.28 (11)°. In the crystal, each molecule is linked to its symmetry equivalent about the center of inversion by a pair of strong N—H⋯O hydrogen bond, forming inversion dimers.

In the molecule of the title compound, C 9 H 8 BrN 3 O, the fusedring system is almost planar, the largest deviation from the mean plane being 0.008 (3) Å . The plane through the atoms forming the allyl group is roughly perpendicular to the imidazo [4,5-b]pyridin-2-one system, as indicated by the dihedral angle between them of 70.28 (11) . In the crystal, each molecule is linked to its symmetry equivalent about the center of inversion by a pair of strong N-HÁ Á ÁO hydrogen bond, forming inversion dimers.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: SJ5172). Imidazopyridine molecules are important pharmacophores, which have proven to be useful for a number of biologically relevant targets. The compounds derived from the imidazopyridine system have recently been evaluated as antagonists of various biological receptors, including angiotensin-II (Chen & Dost 1992;Cappelli et al., 2006), platelet activating factor (Weier et al., (1993(Weier et al., ( , 1994, and metabotropic glutamate subtype V (Kulkarni & Newman, 2007). Recently, a series of imidazo[4,5-b] pyridine derivatives as orally bioavailable Aurora A inhibitors with excellent potencies were reported (Bavetsias et al., 2007(Bavetsias et al., , 2010. Hence, the synthesis of imidazo [4,5-b]pyridine derivatives is currently of great interest. Despite the importance of these intermediates, the methodology available for the synthesis was generally target-specific and restrictive in its scope.
The two fused five and six-membered rings building the molecule are nearly planar with the maximum deviation of 0.008 (3)Å from C1 (Fig. 1). The dihedral angle between the imidazo[4,5-b]pyridin-2-one system and the plane through the atoms forming the allyl group is about 70.28 (11)°. The allyl group is nearly perpendicular to the imidazo[4,5-b]pyridin-2-one system and the torsion angle N2-C7-C8-C9 is in the range of -131.6 (5)°. In the crystal, each molecule is linked to its symmetry equivalent about an inversion center by a strong N-H···O hydrogen bond to form a pseudo dimers as shown in Fig.2 and Table 1.

Experimental
To a stirred solution of 6-bromo-1,3-dihydro-imidazo[4,5 -b-]pyridin-2-one (0.2 g; 93.4 mmol), K 2 CO 3 (0.38 g; 2.8 mmol), and tetra n-butyl ammonium bromide (0.03 g; 9.34 10-5 mol)in DMF, allyllbromide (0.097 ml; 1.12 mmol) was added dropwise. Later the mixture was heated under reflux for 24 h. After completion of reaction (monitored by TLC), the salt was filtered and the solvent was removed under reduced pressure. The resulting residue was purified by column chromatography on silica gel using (ethylacetate/hexane) (1/1) as eluent. The crystals were obtained by dissolving 80 mg of product in 4 mL of methanol at about 353 K, followed by a slow evaporation of the solvent.

Refinement
H atoms were located in a difference map and treated as riding with C-H = 0.93 Å, 0.97, Å, and 0.86 Å for aromatic, methylene and -NH * respectively. All H atoms had U iso (H) = 1.2 U eq (aromatic, methylene, -NH).  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 Rfactors(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.