rac-Methyl 3-(2-methoxyphenyl)-3a,4-dihydro-3H-chromeno[4,3-c]isoxazole-3a-carboxylate

The title compound, C19H17NO5, comprising two stereogenic C atoms of the same configuration, crystallizes in a centrosymmetric space group as a racemate. The pyran ring adopts a half-chair conformation, while the isoxazole ring adopts an envelope conformation with the C atom bonded to the methoxyphenyl group as the flap. The dihedral angle between the mean plane of the pyran ring and the adjacent benzene ring is 5.86 (5)°. In the crystal, molecules are linked by a weak C—H⋯O hydrogen bond, forming a chain along the a axis.

The title compound, C 19 H 17 NO 5 , comprising two stereogenic C atoms of the same configuration, crystallizes in a centrosymmetric space group as a racemate. The pyran ring adopts a half-chair conformation, while the isoxazole ring adopts an envelope conformation with the C atom bonded to the methoxyphenyl group as the flap. The dihedral angle between the mean plane of the pyran ring and the adjacent benzene ring is 5.86 (5) . In the crystal, molecules are linked by a weak C-HÁ Á ÁO hydrogen bond, forming a chain along the a axis.

Comment
As a continuation of our research related to isoxazole containing chromenoisoxazole moiety, we analyzed the crystal structure of rac-methyl 3-(2-methoxyphenyl)-1-phenyl-3,3a,4,9b-tetrahydro-1H-chromeno[4,3-c]isoxazole-3a-carboxylate (Paramasivam et al., 2012). The present compound exhibits the pronounced similarity to the previous ones, either in bond lengths and angles as well as in molecular conformation. Isoxazole derivative is used for the treatment of rheumatoid arthritis (Rozman et al., 2002) whereas benzopyran derivatives exhibit anti-depressant activities (Winn et al., 1976) and in the treatment of impulsive-disorder disease (Caine, 1993). On this grounds, the title compound was chosen for X-ray structure analysis (Fig. 1).

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

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.