(4S)-5′-Chloro-3,7,7-trimethyl-5,6,7,8-tetrahydro-4H-spiro[1,2-oxazolo[5,4-b]quinoline-4,3′-indole]-2′,5-dione

In the title compound, C20H18ClN3O3, the five- and six-membered heterocycles fused through a spiro C atom are inclined to each other at an angle of 87.4 (1)°. In the tricyclic ring system, the cyclohexene ring adopts an envelope conformation with the spiro atom as the flap. In the crystal, two sets of N—H⋯O hydrogen bonds link the molecules into columns containing centrosymmetric R 2 2(7) ring motifs and propagating along the b-axis direction.

In the title compound, C 20 H 18 ClN 3 O 3 , the five-and sixmembered heterocycles fused through a spiro C atom are inclined to each other at an angle of 87.4 (1) . In the tricyclic ring system, the cyclohexene ring adopts an envelope conformation with the spiro atom as the flap. In the crystal, two sets of N-HÁ Á ÁO hydrogen bonds link the molecules into columns containing centrosymmetric R 2 2 (7) ring motifs and propagating along the b-axis direction.

Comment
A large number of natural products contain the quinoline and indole heterocycles, and they are found in numerous commercial products, including pharmaceuticals, fragrances and dyes (Padwa et al., 1999). In view of the above importance, crystallographic study of the title compound (I) has been carried out to establish its molecular structure.
In (I) (Fig. 1), the indole ring adopts slightly envelope conformation on atom C7. The sum of the bond angle around atom N3 (360°) of the quinoline ring indicates sp 2 hybridization. The quinoline group and indole ring are in axial orientation with the dihedral angle between them as 87.39 (1)°. The indole and quinoline ring systems are planar and keto atoms O1 and O3 deviate from the attached ring system by -0.024 (1) and -0.012 (2) Å, respectively.

Experimental
A reaction mixture of 5-chloro isatin (1 mmol), 5,5-dimethylcyclohexane-1,3 dione (1 mmol) and 5-amino-3-methylisoxazole (1 mmol) in 5 ml of ethanol was heated up to 80°C for 6-10 h. The reaction was monitored by TLC. Then, the reaction mixture was filtered hot and the resulting solid products were washed with ethanol, dried in an air and recrystallized from ethanol.

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.