Ethyl 2-amino-7,7-dimethyl-2′,5-dioxospiro[5,6,7,8-tetrahydro-4H-chromene-4,3′(2′H)-1H-indole]-3-carboxylate

In the molecule of the title compound, C21H22N2O5, the indole system and the spiro-pyran ring are almost planar [maximum deviations of 0.0447 (17) and 0.0781 (17) Å, respectively]; the dihedral angle between them is 84.6 (3)°. The remaining six-membered ring adopts a twisted conformation. Intramolecular N—H⋯O hydrogen bonds occur. In the crystal structure, interamolecular N—H⋯O and C—H⋯O hydrogen bonds link the molecules.

In the molecule of the title compound, C 21 H 22 N 2 O 5 , the indole system and the spiro-pyran ring are almost planar [maximum deviations of 0.0447 (17) and 0.0781 (17) Å , respectively]; the dihedral angle between them is 84.6 (3) . The remaining sixmembered ring adopts a twisted conformation. Intramolecular N-HÁ Á ÁO hydrogen bonds occur. In the crystal structure, interamolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link the molecules.

Comment
The indole nucleus is the well known heterocycle (da Silva et al., 2001). Compounds carrying the indole moiety exhibit antibacterial and fungicidal activities (Joshi & Chand, 1982). Spirooxindole ring systems are found in a number of alkaloids like horsifiline, spirotryprostatin and elacomine (Abdel-Rahman et al., 2004). As a part of our programme devoted to the preparation of heterocyclic compounds involving indole derivatives (Zhu et al., 2007), we have synthesized a series of spirooxindoles via reactions of substituted isatins together with malononitrile (or ethyl 2-cyanoacetate) and enaminones .
We report herein the crystal structure of the title compound, (I).

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.