Phenyl(pyrrolo[2,1-a]isoquinolin-3-yl)methanone

In the title compound, C19H13NO, the fused isoquinoline–pyrrole system is planar (r.m.s. deviation = 0.0249] Å) and makes a dihedral angle of 53.73 (9)° with the phenyl ring. An intramolecular C—H⋯O interaction generates an S(6) ring motif.


Comment
The natural and many synthetic indolizines have a diversity of biological activity and are playing an increasingly important role in developing new pharmaceuticals [Olden et al., 1991;Jaffrezou et al., 1992]. Pyrrolo[2,1-a]-isoquinolines are 7,8benzo-fused indolizines and occur in several marine alkaloids. The synthesis of these structures is drawing much recent research interest [Verna et al., 2009]. In our research work on the direct one pot syntheses of pyrrolo[2,1-a]isoquinolines [Liu et al., 2010], 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. The bond lengths and angles of the title molecule ( Fig. 1) are within normal ranges (Allen et al., 1987). he fused isoquinoline-pyrrole moiety is planar. The dihedral angle between the isoquinoline-pyrrole fused ring and benzene ring is 53.73 (9)°. Although atoms C8, C11 and C19 attached to atom N are all of sp2 hybridization, their different environments cause slight differences in the N-C8, N-C11 and N-C19 bond lengths, and in the C19-N-C11, C19-N-C8 , C11-N-C8 and C10-C11-N angles (Table 1). An intramolecular C-H···O weak hydrogen bond generating an S(6) ring is observed ( Table 2). The crystal packing is stabilized by van der Waals forces.

Experimental
The compound (I) was prepared by the reaction of DMF solution of 2-(2-oxo-2-phenylethyl)isoquinolinium bromide with an excess amount of maleic acid in the presence of TPCD and potassium carbonate. After the reaction was completed, the mixture was isolated by chromatography on a silica gel column after evaporation of the solvent. Single crystals of (I) were obtained by slow evaporation from an petroleum ether-ethyl acetate(3:1) solvent system (yield 80%).

Refinement
The H atoms were geometrically placed and were treated as riding, with C-H = 0.93Å . Fig. 1. The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms.

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