Methyl 6-ethoxy-3-phenyl-3a,4-dihydro-3H-chromeno[4,3-c]isoxazole-3a-carboxylate

In the title compound, C20H19NO5, the dihedral angle between the mean plane of the pyran ring (which has a half-chair conformation) and the benzene ring of the chromeno ring system is 7.21 (7)°. The dihedral angle between the mean plane of the chromeno ring system and the isoxazole ring is 21.78 (6)°, while the isoxazole ring forms a dihedral angle of 72.60 (8)° with the attached phenyl ring. In the crystal, molecules are linked via pairs of C—H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(10) ring motif. These dimers are linked via C—H⋯N hydrogen bonds, forming chains along [001].

In the title compound, C 20 H 19 NO 5 , the dihedral angle between the mean plane of the pyran ring (which has a half-chair conformation) and the benzene ring of the chromeno ring system is 7.21 (7) . The dihedral angle between the mean plane of the chromeno ring system and the isoxazole ring is 21.78 (6) , while the isoxazole ring forms a dihedral angle of 72.60 (8) with the attached phenyl ring. In the crystal, molecules are linked via pairs of C-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (10) ring motif. These dimers are linked via C-HÁ Á ÁN hydrogen bonds, forming chains along [001].
The molecular structure of the title molecule is illustrated in Fig. 1. In the chromeno ring system the pyran ring has a half chair conformation. Its mean plane makes a dihedral angle with the benzene ring of 7.21 (7)°. The dihedral angle between the mean plane of the chromeno ring system (fusion of benzene and pyran rings) and the isoxazole ring (O2/N1/C7-C9) is 21.78 (6)°. The isoxazole ring also forms a dihedral angle of 72.60 (8)° with the phenyl ring (C15-C20). The geometric parameters of the title molecule agree well with those reported for closely related structures (Gangadharan et al., 2011;Swaminathan et al., 2011).
In the crystal, molecules are linked via pairs of C-H···O hydrogen bonds to form inversion dimers with an R 2 2 (10) ring motif (Bernstein et al., 1995; Table 1 and Fig. 2). These dimers are linked via C-H···N hydrogen bonds to form chains along the c axis.

Experimental
At 283 -293 K, NCS (4 mmol) was added pinch wise over 3 h to a solution of ((E)-methyl2-((2ethoxy-6-((E)-(hydroxyimino)methyl)phenoxy)methyl) -3-phenylacrylate (2 mmol) in CCl 4 . After Et 3 N (4 mmol) was added to the reaction mixture which was stirred at room temperature for 2 h. After completion of the reaction, the mixture was evaporated under reduced pressure and the resulting crude mass was diluted with water (15 ml) and extracted with ethyl acetate (3 × 15 ml). The combined organic layers were washed with brine (2 × 10 ml) and dried over anhydrous Na 2 SO 4 . The organic layer was evaporated and purified by column chromatography (silica gel 60-120 mesh 7% EtOAc in hexanes) to provide the desired pure title product as a colourless solid. Crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of a solution in ethyl acetate.

Refinement
All the H atoms were placed in calculated positions and treated as riding atoms: C-H = 0.93-0.98 Å 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 molecule, with the atom numbering. Displacement ellipsoids are drawn at the 30% probability level.  A partial view of the crystal packing of the title compound. The C-H···O and C-H···N hydrogen bonds are shown as dashed lines (see Table 1 for details). 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.