Ethyl 4-(2-ethoxy-2-oxoethyl)-3-oxo-4,13-diazapentacyclo[11.8.0.02,11.05,10.014,19]henicosa-1,5(10),6,8,11,14(19),15,17,20-nonaene-12-carboxylate

In the title compound, C26H22N2O5, the system consisting of five fused rings, being essentially planar with an r.m.s. deviation from the least-squares plane of 0.049 (3) Å, makes a dihedral angle of 58.72 (12)° with the plane of the ethyl carboxylate group immediately attached to it, and a dihedral angle of 89.48 (14)° with the plane of the ethyl carboxylate group attached via the –CH2– bridge. Bond lengths indicate π-delocalization over the whole pentacyclic system. The molecular conformation is stabilized by a weak intramolecular C—H⋯O hydrogen bond. In the crystal, molecules form stacks along the b-axis direction, neighboring molecules within each stack being related by inversion and the shortest distance between the centroids of the pyridine rings within the stack being 3.667 (2) Å.

In the title compound, C 26 H 22 N 2 O 5 , the system consisting of five fused rings, being essentially planar with an r.m.s. deviation from the least-squares plane of 0.049 (3) Å , makes a dihedral angle of 58.72 (12) with the plane of the ethyl carboxylate group immediately attached to it, and a dihedral angle of 89.48 (14) with the plane of the ethyl carboxylate group attached via the -CH 2 -bridge. Bond lengths indicatedelocalization over the whole pentacyclic system. The molecular conformation is stabilized by a weak intramolecular C-HÁ Á ÁO hydrogen bond. In the crystal, molecules form stacks along the b-axis direction, neighboring molecules within each stack being related by inversion and the shortest distance between the centroids of the pyridine rings within the stack being 3.667 (2) Å .   Table 1 Hydrogen-bond geometry (Å , ).  The natural and many synthetic indolizines show a diversity of biological activity and are playing an increasingly important role in developing of new pharmaceuticals (Olden et al., 1991;Jaffrezou et al., 1992). The synthesis of these compounds has drawn much research interest (Liu et al., 2010). Indolizino[1,2-c]quinolin-6(5H)-one is an important annulated indolizines derivative. In our ongoing research work on the direct one pot syntheses of this class of compounds, we have prepared the title compound, (I), as one of the products. As part of this study, we have undertaken an X-ray crystallographic analysis of (I) in order to confirm its structure further.

Related literature
The bond lengths and angles of the title molecule ( are make dihedral angles with the pyrrole ring of 4.16 (12)° and 6.30 (13)°. The molecular conformation is stabilized by weak intramolecular C-H···O hydrogen bonds (Table 1). The packing of the title molecules via the π -π stacking interaction is shown in Fig.2, with a shortest intercentroid distance of 3.627 (2) Å.

Experimental
The compound (I) was prepared by the reaction of 1-(2-ethoxy-2-oxoethyl)quinolinium salt (2.0 mmol), tetrakispyridinecobalt(II) di(hydrochromate) [CoPy 4 ](HCrO 4 ) 2 (1.0 g) and potassium carbonate (3.0 mmol) mixed in 10 mL CH 3 CN and heated at reflux for 4 h. After the reaction was completed, the reaction mixture was purified by column chromatography on silica gel, and the product was isolated after evaporation of the solvent. Single crystals of (I) were obtained by slow evaporation from a petroleum ether-ethyl acetate (3:1) solvent system (yield 52%).

Refinement
The H atoms were geometrically placed and were treated as riding, with C-H = 0.93 Å.

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. Two reflections were omitted from the initial data set of 3811 reflections, thus 3809 is the correct number of reflections in the L.S. refinement procedure