Crystal structure of ethyl 2-{4-[(5-chloro-1-benzofuran-2-yl)methyl]-3-methyl-6-oxo-1,6-dihydropyridazin-1-yl}acetate

In the title compound, C18H17ClN2O4, the dihedral angle between the benzofuran ring system [maximum deviation 0.014 (2) Å] and the oxopyradizine ring is 73.33 (8)°. The structure is characterized by disorder of the ethyl group, which is split into two parts, with a major component of 0.57 (3), and the acetate carbonyl O atom, which is statistically disordered. In the crystal, the molecules are linked by C—H⋯O interactions, forming a three-dimensional network.

In continuation of this line of research (Taoufik et al., 1984;Benchat et al., 1998;Abourichaa et al., 2003), we have developed a new pyridazin-3(2H)-one derivative. It will be subjected to further pharmacological investigations, especially tests of anticancer activity. Compound (I) is stable at room temperature, and its structure has been determined by NMR ( 1 H and 13 C). In this paper we wish to report the crystal structure determination of the title compound possessing the biologically active pyridazinone ring.
The molecule of the title compound is build up from 5-chlorobenzofuran-2-yl linked, via -CH 2 -group, to sixmembered heterocyclic ring which is related to acetate group as shown in Fig. 1. The benzofuran system is virtually planar with the largest deviation from the mean plane being -0.014 (2) Å at C4, and makes dihedral angle of 73.33 (8)° with the mean plane through the oxopyridazin (C10-C13,N1,N2) ring. Non classical C-H···O hydrogen bonds link the molecules into a three-dimensional network.

S3. Refinement
The H atoms were located in a difference map and treated as riding with C-H = 0.93 Å (aromatic), C-H = 0.97 Å (methylene) and C-H = 0.96 Å (methyl), and with U iso (H) = 1.2 U eq (aromatic and methylene) and U iso (H) = 1.5 U eq for methyl. This structure is characterized by a partial disorder at the acetate group, with the ethyl group split into two parts.
The major component had a site occupancy factor = 0.57 (3). The carbonyl-O3 was statistically disordered. Owing to poor agreement, the (0 0 2) reflection was omitted from the final cycles of refinement. Molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small circles.

Figure 2
Crystal packing in the structure of the title compound, showing molecules linked by C-H···O hydrogen bonds (dashed lines). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.043 Δρ max = 0.25 e Å −3 Δρ min = −0.34 e Å −3 Absolute structure: Flack & Bernardinelli (2000), 2104 Friedel pairs Absolute structure parameter: 0.02 (7) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (