1-Allyl-3-benzyl-1H-benzimidazol-2(3H)-one

In the title compound, C17H16N2O, the fused benzimidazol-2(3H)-one system is essentially planar, the largest deviation from the mean plane being 0.006 (2) Å for the carbonyl C atom. Its mean plane is almost perpendicular to the benzyl plane and to the allyl group, making dihedral angles of 80.6 (1) and 77.4 (3)°, respectively. The benzyl group and the allyl subsituent lie on opposite sides of the fused ring system. In the crystal, molecules are linked by bifurcated C—H⋯O hydrogen bonds in which the carbonyl O atom acts as accepter to two aromatic C—H groups, forming a two-dimensional network parallel to (001).

In the title compound, C 17 H 16 N 2 O, the fused benzimidazol-2(3H)-one system is essentially planar, the largest deviation from the mean plane being 0.006 (2) Å for the carbonyl C atom. Its mean plane is almost perpendicular to the benzyl plane and to the allyl group, making dihedral angles of 80.6 (1) and 77.4 (3) , respectively. The benzyl group and the allyl subsituent lie on opposite sides of the fused ring system. In the crystal, molecules are linked by bifurcated C-HÁ Á ÁO hydrogen bonds in which the carbonyl O atom acts as accepter to two aromatic C-H groups, forming a twodimensional network parallel to (001).
In continuation of our research work devoted to the development of substituted benzimidazol-2-one derivatives (Belaziz et al., 2012(Belaziz et al., , 2013, we reported a synthesis of new benzimidazol-2-one derivative differently substituted by action of allylbromide with 1-benzyl -1H-benzo[d]imidazol-2(3H)-one in the presence of a catalytic quantity of tetra-n-butylammonium bromide under mild conditions to obtain disubstituted compound (Scheme 1).
In the crystal, the molecules are linked by C3-H3···O1 and C14-H14···O1 hydrogen bonds in the way to build twodimensional network as shown in Fig. 2 and Table 2.

Experimental
To 1H-benzo[d]imidazol-2(3H)-one (0.2 g, 1.49 mmol), potassium carbonate (0.41 g, 2.98 mmol) and tetra-n-butylammonium bromide (0.05 g, 0.15 mmol) in DMF (20 ml) was added benzylchloride (0.22 g, 1.79 mmol). Stirring was continued at room temperature for 6 h. The resulting salt was removed by filtration and the filtrate concentrated under reduced pressure. The residue was separated by chromatography on a column of silica gel with ethyl acetate/hexane (1/2) as eluent. The compound was recrystallized from ethanol to give colorless crystals. To the compound obtained (1-benzylbenzimidazol-2-one (0.15 g, 0.67 mmol) was added allylbromide (0.10 g, 0.87 mmol) in DMF (10 ml), and potassium carbonate (0.18 g, 1.33 mmol) and tetra-n-butylammonium bromide (0.02 g, 0.07 mmol). Stirring was continued at room temperature for 12 h. The formed salt was removed by filtration and the filtrate concentrated under reduced pressure. The residue was separated by chromatography on a column of silica gel with ethyl acetate/hexane (1/1)

Refinement
All H atoms could be located in a difference Fourier map. However, they were placed in calculated positions with C-H = 0.93 Å (aromatic, olefinic), and C-H = 0.97 Å (methylene) and refined as riding on their parent atoms with U iso (H) = 1.2 U eq (C).

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. 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.