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

In the title compound, C18H15N3O3, the dihedral angle between the mean planes of the quinoline and indole ring systems [r.m.s. deviations = 0.189 (2) and 0.027 (2) Å, respectively] is 88.65 (5)°. The cyclohexene ring of the quinoline ring system adopts an envelope conformation with the central –CH2– C atom as the flap. In the crystal, molecules are linked by two pairs of N—H⋯O hydrogen bonds, forming inversion dimers, and enclosing R 2 2(14) ring motifs. This arrangement results in the formation of chains propagating along [100].

In the title compound, C 18 H 15 N 3 O 3 , the dihedral angle between the mean planes of the quinoline and indole ring systems [r.m.s. deviations = 0.189 (2) and 0.027 (2) Å , respectively] is 88.65 (5) . The cyclohexene ring of the quinoline ring system adopts an envelope conformation with the central -CH 2 -C atom as the flap. In the crystal, molecules are linked by two pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers, and enclosing R 2 2 (14) ring motifs. This arrangement results in the formation of chains propagating along [100].

Comment
A large number of natural products contain the quinoline and indole heterocycles, and are found in numerous commercial products, including pharmaceuticals, fragrances and dyes (Padwa et al., 1999). In view of the above importance we have synthesized the title compound and report herein on its crystal structure.
The molecular structure of the title molecule is shown in Fig. 1. The quinoline group and indoline ring mean planes [r.m.s = 0.189 (2) and 0.027 (2) Å, respectively] are in axial orientations with a dihedral angle of 88.65 (5)°. The indole ring adopts an almost planar conformation with a maximum deviation 0.0486 (4) Å for the spiro C atom, C10. The quinoline ring system has an envelope conformation with the puckering parameters (Cremer & Pople, 1975) and the asymmetry parameters (Nardelli,1983) are: q 2 = 0.3087 (2) Å, φ 2 = 209.3 (3)° and the closest pucker descriptor is an envelope on atom C6 of the cyclohexene ring. The sum of the bond angles around atoms N2 and N3 (360 °) of both the quinoline and indole rings indicates sp 2 hybridization. The keto atoms O3 and O2 deviate from the attached ring system of indole and quinoline by -0.032 (1) and -0.021 (1) Å, respectively.
In the crystal, molecules are linked by two pairs of N-H···O hydrogen bonds (Table 1) Table 1).

Experimental
A mixture of isatin (1 mmol), cyclohexane-1,3 dione (1 mmol) and 5-Amino-3-methylisoxazole (1 mmol) in 5 ml of ethanol was heated to 353 K for 6-10 h. The reaction was monitored by TLC. When finished the reaction mixture was filtered hot and the resulting solid products were washed with ethanol, dried in air and recrystallized from ethanol, giving colourless block-like crystals.

Refinement
N and C-bound H atoms were positioned geometrically and allowed to ride on their parent atoms: N-H = 0.86 Å, C-H = 0.93, 0.97 and 0.96 Å for CH, CH 2 and CH 3 H atoms, respectively, with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (N,C) for other H atoms.  The molecular structure of the title molecule, with atom labelling. The displacement ellipsoids are drawn at the 30% probability level.  A partial view along the b-axis of the crystal packing of the title compound. It shows the two R 2 2 (14) inversion dimer formations due to the presence of two pairs of N-H···O hydrogen bonds (dashed lines; see Table 1 for details).  The crystal packing of the title compound viewed along the a-axis. The hydrogen bonds are shown as dashed lines (see Table 1 for details; C-bound H atoms have been omitted for clarity). 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.75216 (16