Crystal structure of 5-chloro-1,3-bis[2-(2-oxo-1,3-oxazolidin-3-yl)ethyl]-1H-benzimidazol-2(3H)-one

In the title compound, C17H19ClN4O5, the benzimidazole fused-ring system is essentially planar, the maximum deviation from the mean plane being 0.06 (1) Å. Both oxazolidine rings are nearly planar, the maximum deviations from the mean planes are 0.071 (13) and 0.070 (10) Å. The dihedral angle between the mean planes of the oxazolidine rings is 69.9 (7)°. The benzimidazole mean plane makes the dihedral angles of 43.9 (6) and 45.6 (6)° with the two oxazolidine rings. In the crystal, the molecules are linked together by weak C—H⋯O hydrogen bonds building zigzag tapes running along the c axis. The Cl atom is split over two positions with an occupancy ratio of 0.567 (7):0.433 (7). This means that the reaction yields two isomers, A and B; the A component has the Cl-atom substituent in the 5-position of the benzimidazolone ring and the B component has the Cl atom in the 6-position. The two isomers form the disordered co-crystal, with a nearly half Cl atom in each of them, as indicated by the occupancy ratio. The crystal structure was refined as an inversion twin.

Supporting information for this paper is available from the IUCr electronic archives (Reference: XU5863).

S1. Comment
Benzimidazol-2-one derivatives are useful heterocyclic building blocks and are prominent structural elements of compounds demonstrating a wide variety of pharmacological and biochemical properties (Gribkoff et al., 1994;Olesen et al., 1994;Soderlind et al., 1999).
Also, oxazolidin-2-ones are a very important class of heterocyclic compounds and their derivatives have attracted attention in various areas of drug development for antibacterial activity (Diekema & Jones, 2000;Mukhtar & Wright, 2005). Some oxazolidin-2-ones have been used as chiral auxiliaries in a wide range of asymmetric reactions (Evans et al., 1993;Matsunaga et al., 2005). In a previous study, we reacted 1H-benzo[d]imidazol-2(3H)-one with bis(2-chloroethyl)amine hydrochloride in the presence of a catalytic quantity of tetra-n-butylammonium bromide to form 1,3-bis(2-(2- (Ouzidan et al., 2011). The study is extended to the synthesis of the 5-chloro analog to furnish the title compound (Scheme 1).
The molecule of title compound is build up from a fused five-and six-membered rings linked through ethyl groups, on opposite side, to two 2-oxo-oxazolidin-3-yl rings as shown in Fig. 1. The chlorine in 5-chloro-benzo[d]imidazol-2(3H)one is splited in two positions with an occupancy ratio of Cl1B = 0.567 (7) and Cl1A = 0.433 (7). As a matter of fact, we have two isomers that form a disordered co-crystal, like in the 5-Chloro-1- (Dardouri et al., 2011), but with a nearly half chlorine atom in each of them as shown in the occupancy ratio of Cl1A and Cl1B. The fused rings system (N2N3C6 -C12) is essentially planar with the largest deviation from the mean plane being 0.06 (1) Å at C8 atom. The benzimidazole plane makes dihedral angles of 43.9 (6)° and 45.6 (6)° with the two 2-oxo-oxazolidin-3-yl rings, (O1N1C1-C3) and (O5N4C15-C17), respectively. The dihedral angle between the two 2-oxo-oxazolidin-3-yl rings is of 69.9 (7)°. In the crystal, the molecules are linked together by C4-H4A···O2 and C14-H14A···O4 hydrogen bonds in the way to build a zigzag tape along c axis as shown in Fig. 2 and Table 2.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. In the molecule there is a pseudo center of symmetry but the results of the structure refinement in the centro symmetric Pbcn space group are not satisfactory. The absolute structure cannot be determined reliably and the structure is refined as a 2-component inversion twin.
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), and C-H = 0.97 Å (methylene) and refined as riding on their parent atoms with U iso (H) = 1.2 U eq (C).