rac-3-(4-Chlorophenyl)-3a,4-dihydro-3H-chromeno[4,3-c]isoxazole-3a-carbonitrile

The title compound, C17H11ClN2O2, which contains two stereogenic C atoms, crystallizes in a centrosymmetric space group as a racemate. The pyran ring and the 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 4.17 (5)°. The molecular conformation features a weak C—H⋯O contact. In the crystal, C—H⋯O hydrogen bonds link the molecules, forming chains along the a-axis direction.

The title compound, C 17 H 11 ClN 2 O 2 , which contains two stereogenic C atoms, crystallizes in a centrosymmetric space group as a racemate. The pyran ring and the 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 4.17 (5) . The molecular conformation features a weak C-HÁ Á ÁO contact. In the crystal, C-HÁ Á ÁO hydrogen bonds link the molecules, forming chains along the a-axis direction.

Comment
As a continuation of our research related to isoxazole containing chromenoisoxazole moiety, we analysed the crystal structure of rac-6- 3a,4,isoxazole-3a-carbonitrile (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 conformations.
The dihedral angle between the pyran and the benzene rings (C1-C6) is 4.17 (5)°. The dihedral angle between the chromeno ring (fusion of benzene and pyran rings) and isoxazole ring is 13.42 (5)°. In the chromenoisoxazole moiety, the dihedral angle between the benzene and isoxazole ring is 10.83 (5)° and the dihedral angle between the pyran and isoxazole ring is 14.81 (5) The molecular structure is stabilized by C-H···O intramolecular interaction and the crystal packing is stabilized by C-H···O hydrogen bonds (Table 1).

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.

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.