Ethyl 2-benzoyl-6-methylindolizine-7-carboxylate

The title compound, C19H17NO3, was synthesized using a tandem annulation reaction between 4-benzoyl-1H-pyrrole-2-carbaldehyde and (E)-ethyl 4-bromobut-2-enoate under mild conditions. The dihedral angle between the benzene ring and the indolizine ring system is 41.73 (4)°.

The author thank Dr Qing Feng Wang, Taishan University, for the data collection.

Comment
Indolizines have attracted considerable attention from medicinal and organic chemists because of the interesting similarities and diversions in structure to indole 2009a, 2011. Synthetic indolizines play important roles as calcium entry blockers, potential central nervous system depressants, 5-HT3 receptor antagonist, histamine H3 receptor antagonists, cardiovascular agents, and PLA2 inhibitors. They have also drawn much attention owing to their possible usage as dyes and chemosensors. The title indolizine (I) (Fig. 1) was synthesized in order to study its biological properties. (I) was screened for anticancer activities and found to be inactive. We report here the crystal structure of the title compound. In the title compound, C 19 H 17 NO 3 , all bond lengths and angles show normal values (Ge et al., 2009b).
The dihedral angle between the benzene and indolizine rings is 41.73 (4)°.

Experimental
To a 50 ml round-bottomed flask were added 4-benzoyl-1H-pyrrole-2-carbaldehyde (1.00 mmol), (E)-ethyl 4-bromobut-2-enoate (2.00 mmol), potassium carbonate (0.28 g, 2.05 mmol) and dry DMF (10 ml). The mixture was stirred at room temperature for 8 h. The solvent was removed under reduced pressure and an product was isolated by column chromatography on silica gel (yield 76%). Crystals of (I) suitable for X-ray diffraction were obtained by allowing a refluxed solution of the product in ethyl acetate to cool slowly to room temperature (without temperature control) and allowing the solvent to evaporate for 10 d.

Refinement
All H atoms were placed in geometrically calculated positions and refined using a riding model with C-H = 0.97 Å (for CH 2 groups),0.96 Å (for CH 3 groups) and 0.93 Å (for aromatic protons), their isotropic displacement parameters were set to 1.2 times (1.5 times for CH 3 groups) the equivalent displacement parameter of their parent atoms.

Computing details
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).  The molecular structure of (I), showing displacement ellipsoids drawn at the 50% probability level. 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.