(3-Methyl-3a,4,7,7a-tetrahydro-5H-4,7-methanoisoxazolo[4,5-d][1,2]oxazin-5-yl)(phenyl)methanone

The title compound, C14H14N2O3, is the exo isomer with a syn arrangement of two O atoms in the isoxazole and oxazine rings. The dihedral angle between the isoxazole and phenyl rings is 60.38 (4)°. In the crystal, weak C—H⋯O hydrogen bonds link the molecules, forming a three-dimensional network. The isoxazole O atom is an acceptor for three of these hydrogen bonds.


Comment
We have previously investigated the 1,3-dipolar cycloaddition reactions of symmetrical and unsymmetrical bicyclic alkenes (Yip et al., 2001;Mayo et al., 2001). When expanding this study on N-acyl-2-oxa-3-azanorborn-5-enes, the bicyclic alkene (III) reacts (see Fig. 1) with acetonitrile oxide (II) (generated in situ) in toluene, to give the cycloadducts (IV) and (V) as regioisomers in the ratio of 70:30 respectively (ratio was determined by isolated yields). The stereochemistry and regiochemistry of the major product (IV) was determined by this single-crystal X-ray analysis.
Although different stereoisomers (exo and endo) could be formed, only the exo stereoisomer was formed with a mixture of the corresponding regioisomers. The major product obtained was found to be the syn isomer (two O atoms in the rings are on the same side of the molecule).
The molecular structure of the title compound is shown in Fig. 2. The dihedral angle between the isoxazole ring [C4/C5/C6/O2/N2 with r.m.s. deviation 0.0013 Å] and the phenyl ring (C9-C14) is 60.38 (4)°. In the crystal, weak C-H···O hydrogen bonds link molecules forming a three-dimensional network (Fig. 3). The isoxazole O atom is an acceptor for three of these hydrogen bonds. We have prepared by a similar method and carried out the structure determination of a related cycloadduct (Lough et al., 2014)

Refinement
Hydrogen atoms were placed in calculated positions with C-H distances of 0.95-1.00 Å and included in the refinement in a riding-model approximation with U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ).  The reaction scheme.

Figure 2
The molecular structure of the title compound showing 30% probability ellipsoids.  Part of the crystal structure with weak hydrogen bonds shown as dashed lines. 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.