rac-Methyl 3-(2-methoxyphenyl)-1-phenyl-3,3a,4,9b-tetrahydro-1H-chromeno[4,3-c]isoxazole-3a-carboxylate

The title compound, C25H23NO5, comprising two stereogenic carbon atoms of the same configuration, crystallizes in a centrosymmetric space group as a racemate. The six-membered pyran ring and the five-membered isoxazole ring adopt sofa and twisted conformations, respectively. The dihedral angle between the benzene ring and the mean plane through the near coplanar atoms of the pyran ring is 10.73 (7)°. The crystal structure features C—H⋯O hydrogen bonds.

The title compound, C 25 H 23 NO 5 , comprising two stereogenic carbon atoms of the same configuration, crystallizes in a centrosymmetric space group as a racemate. The sixmembered pyran ring and the five-membered isoxazole ring adopt sofa and twisted conformations, respectively. The dihedral angle between the benzene ring and the mean plane through the near coplanar atoms of the pyran ring is 10.73 (7) . The crystal structure features C-HÁ Á ÁO hydrogen bonds.
In the chromenoisoxazole moiety, the dihedral angle between the benzene and isoxazole ring is 56.88 (6)°. The dihedral angle between the pyran and isoxazole ring is 56.27 (6)°. The sum of the bond angles around N1 [334.55 (39)°] indicates sp3 hybridization (Beddoes et al.,1986). The unit cell contains no residual solvent accessible voids, if the voids in the dry crystals ever contained solvent, though generally solvent loss from organic crystals is associated with either a total loss of crystallinity or at least a degradation of the crystal quality. In this case the crystals remained glass-clear.
The geometric parameters of the title compound ( Fig. 1) agree well with the reported similar structures (Kanchanadevi et al., 2011;Swaminathan et al., 2012).
The molecular structure is stabilized by C-H··· O intramolecular interactions and the crystal packing is via C-H··· O hydrogen bonds (Table 1, Fig. 2).

Experimental
A mixture of (E)-methyl 2-((2-formylphenoxy)methyl)-3-(2-methoxyphenyl)acrylate (2 mmol, 0.65 g) and N-phenylhydroxylamine (3 mmol, 0.33 g) in ethanol (10 mL) was refluxed for 6 h. After the completion of the reaction as indicated by TLC, the reaction mixture was concentrated and the resulting crude mass was diluted with water (15 mL) and extracted with ethyl acetate (3 × 15 mL). The combined organic layer was washed with brine (3 × 15 mL) and dried over anhydrous Na 2 SO 4 , solvent was removed under reduced pressure. The crude mass was purified by column chromatography on silica gel (Acme 100-200 mesh), using ethyl acetate-hexane (0.5: 9.5) to afford the pure compound as a colourless solid in 91% yield.

Refinement
Hydrogen atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93 -0.97 Å and U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2 U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound showing the atom-numbering scheme and displacement ellipsoids drawn at the 20% probability level.  The crystal packing of the title compound. Hydrogen bonds are shown by dashed lines. 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.