6a-Nitro-6-phenyl-6,6a,6b,7,8,9,10,12a-octahydrospiro[chromeno[3,4-a]indolizine-12,3′-indolin]-2′-one

In the title compound, C28H25N3O4, the central pyrrolidine ring adopts adopts an envelope conformation with the N atom as the flap and the piperidine ring adopts a chair conformation. The pendant pyrrolidine ring is almost planar (r.m.s. deviation = 0.008 Å). An intramolecular C—H⋯O interaction closes an S(6) ring. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds generate R 2 2(8) loops.

In the title compound, C 28 H 25 N 3 O 4 , the central pyrrolidine ring adopts adopts an envelope conformation with the N atom as the flap and the piperidine ring adopts a chair conformation. The pendant pyrrolidine ring is almost planar (r.m.s. deviation = 0.008 Å ). An intramolecular C-HÁ Á ÁO interaction closes an S(6) ring. In the crystal, inversion dimers linked by pairs of N-HÁ Á ÁO hydrogen bonds generate R 2 2 (8) loops.
The other pyrrolidine ring (N3/C21/C22/C27/C28) makes a dihedral angle of 39.60 (9)° with the pyran ring, it makes a dihedral angle of 88.12 (9)° with the piperidine ring which shows that they are almost at right angles to each other. The dihedral angle between the pyran ring and the piperidine ring is 57.58 (9)° . The oxygen atom O4 attached with pyrrolidine ring deviates by -0.0736 (1)Å. The nitrogroup attached with the pyrrolidine ring makes a diherdal angle of 88.81 (2)° which shows it is in orthogonal orientation . The crystal packing features N-H···O hydrogen bonds and an intramolecular C-H···O hydrogen bond is also observed.

Experimental
To a solution of isatin (1 equiv) and piperidine-2-carboxylic acid (1.4 equiv) in dry toluene, was added 3-nitro-2phenyl-2H-chromene (1equiv) under nitrogen atmosphere. The reaction mixture was refluxed f or 24h in Dean-Stark apparatus to give the cycloadducts. After completion of the reaction as indicated by TLC, the solvent was evaporated under reduced pressure. The crude product was extracted with dichloromethane. The organic layer was dried with anhydrous sodium sulphate and concentrated in vacuo. Then the crude product was purified by column chromatography using hexane/EtOAc (7:3) as eluent. Colourless blocks were obtained by slow evaporation of a solution of the title compound in ethyl acetate at room temperature.

Refinement
The hydrogen atoms were placed in calculated positions and treated as riding atoms: C-H = 0.93 Å to 0.97 Å, and N-H =0.86 Å with Uiso(H) = 1.5Ueq(C) for methyl H atoms and = 1.2Ueq(C) for other H atoms.

Figure 1
The molecular structure of the title compound, showing displacement ellipsoids drawn at the 30% probability level.
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.