Ethyl 4-oxo-2,3,4,9-tetrahydro-1H-carbazole-3-carboxylate

In the title compound, C15H15NO3, the carbazole skeleton includes an ethoxycarbonyl group at the 3-position. In the indole ring system, the benzene and pyrrole rings are nearly coplanar, forming a dihedral angle of 0.89 (4)°. The cyclohexenone ring has an envelope conformation. In the crystal, intermolecular N—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three dimensional network. A weak C—H⋯π interaction is also observed.

In the title compound, C 15 H 15 NO 3 , the carbazole skeleton includes an ethoxycarbonyl group at the 3-position. In the indole ring system, the benzene and pyrrole rings are nearly coplanar, forming a dihedral angle of 0.89 (4) . The cyclohexenone ring has an envelope conformation. In the crystal, intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link the molecules into a three dimensional network. A weak C-HÁ Á Á interaction is also observed.

Comment
Tetrahydrocarbazole systems are present in the framework of a number of indole-type alkaloids of biological interest (Saxton, 1983). The structures of tricyclic, tetracyclic and pentacyclic ring systems with dithiolane and other substituents of the tetrahydrocarbazole core, have been reported previously (Hökelek et al., 1994;Patır et al., 1997;Hökelek et al., 1998;Hökelek et al., 1999;Hökelek & Patır, 1999). Although 4-oxo-tetrahydrocarbazoles rarely occur in nature, they have been increasingly important intermediates in the syntheses of indole or carbazole alkaloids and various biologically active heterocyclic compounds because of their unique structures. For instance, 4-oxo-tetrahydrocarbazole was used in the syntheses of antiemetic drugs, central nervous system active drugs and NPY-1 antagonists (Kumar et al., 2008). They have also been used in the syntheses of indole alkaloids (Ergün et al., 2002). Tetrahydrocarbazolone based antitumor active compounds and inhibitors of HIV integrase were synthesized from 4-oxo-tetrahydrocarbazoles (Li & Vince, 2006). The present study was undertaken to ascertain the crystal structure of the title compound, (I).
The molecule of the title compound contains a carbazole skeleton with an ethoxycarbonyl group at the 3 position, ( In the crystal, intermolecular N-H···O and C-H···O hydrogen bonds link the molecules into a three dimensional network (Table 1 and Fig. 2). There also exists a weak C-H···π interaction (Table 1).

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 > 2sigma(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.