2′-Methyl-3,5-diphenylspiro[4,6-dioxa-2-azabicyclo[3.2.0]hept-2-ene-7,4′-isoquinoline]-1′,3′(2′H,4′H)-dione

In the title compound, C25H18N2O4, the tetrahydropyridine ring adopts a distorted envelope conformation with the spiro C atom at the flap position [deviation = 0.470 (2) Å]. The dihydro–oxazole ring is planar (r.m.s. deviation = 0.013 Å) and it makes dihedral angles of 73.43 (8) and 4.24 (8)° with the two attached phenyl rings. The dihedral angle between oxetane and oxazole planes is 67.44 (9)°. In the crystal structure, C—H⋯O hydrogen bonds link neighbouring molecules into zigzag chains along the b axis and these chains are linked via C—H⋯π interactions.

In the title compound, C 25 H 18 N 2 O 4 , the tetrahydropyridine ring adopts a distorted envelope conformation with the spiro C atom at the flap position [deviation = 0.470 (2) Å ]. The dihydro-oxazole ring is planar (r.m.s. deviation = 0.013 Å ) and it makes dihedral angles of 73.43 (8) and 4.24 (8) with the two attached phenyl rings. The dihedral angle between oxetane and oxazole planes is 67.44 (9) . In the crystal structure, C-HÁ Á ÁO hydrogen bonds link neighbouring molecules into zigzag chains along the b axis and these chains are linked via C-HÁ Á Á interactions.

Experimental
The title compound was obtained from the reaction between 1,3,4(2H)-isoquinolinetrione (189 mg, 1 mmol) and 2,5-diphenyloxazole (440 mg, 2 mmol). The compound was purified by flash column chromatography in ethyl acetate and petroleum ether. X-ray quality single crystals of the title compound were obtained by slow evaporation of a chloroform solution.

Refinement
All the H atoms were located in a difference Fourier map [C-H = 0.95 (2)-1.021 (18) Å] and allowed to refine freely. The highest residual electron density peak is located at 0.75 Å from H10A and the deepest hole is located at 0.86 Å from C18.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
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.