2,10-Bis(3-bromophenyl)-3,7,11,15-tetraoxa-8,16-diazatricyclo[12.2.1.16,9]octadeca-1(16),6(18),8,14(17)-tetraene

The title compound, C24H20Br2N2O4, is an 18-membered tricycle including two isoxazole rings. The asymmetric unit contains one half of the formula unit; a centre of inversion is located at the centroid of the compound. The dihedral angle between adjacent isoxazole and benzene rings is 84.0 (2)°. The compound displays intra- and intermolecular π–π stacking interactions between the isoxazole rings, the shortest centroid–centroid distances being 3.837 (3) and 3.634 (3) Å, respectively. The molecules are stacked in columns along the a axis with short Br⋯Br contacts [3.508 (1) Å].

The title compound, C 24 H 20 Br 2 N 2 O 4 , is an 18-membered tricycle including two isoxazole rings. The asymmetric unit contains one half of the formula unit; a centre of inversion is located at the centroid of the compound. The dihedral angle between adjacent isoxazole and benzene rings is 84.0 (2) . The compound displays intra-and intermolecularstacking interactions between the isoxazole rings, the shortest centroid-centroid distances being 3.837 (3) and 3.634 (3) Å , respectively. The molecules are stacked in columns along the a axis with short BrÁ Á ÁBr contacts [3.508 (1) Å ].

Related literature
For the biological activity of isoxazole derivatives, see: Kim et al. (1994Kim et al. ( , 1997; Lang & Lin (1984). For the syntheses of various pyrano [3,4-c]isoxzole derivatives, see: Kim et al. (1999).  et al., 1994, 1997Lang & Lin, 1984). Recently we reported that the syntheses of various pyrano [3,4-c]isoxzole derivatives by means of the intramolecular 1,3-dipolar cycloaddition of a nitrile oxide containing an alkyne moiety within the structure and that these fused isoxazoles displayed fungicidal activities against some plant pathogens (Kim et al., 1999). During the chromatographic purification of the crude product, we isolated an unexpected macrocylic isoxazole compound which was formed by intermolecular cycloaddition process.

Crystal data
The asymmetric unit of the title compound, C 24 H 20 Br 2 N 2 O 4 , contains one half of the formula unit; a centre of inversion is located at the midpoint of the compound (Fig. 1). The C7 and C11 atoms lie in the isoxazole ring plane with the largest deviation of 0.055 (9) Å (C7) from the least-squares plane of the isoxazole ring. The compound displays intra-and intermolecular π-π interactions between the isoxazole rings (the symmetry operations for second planes: -x,-y,-z and -x,1 -y,-z, respectively), the shortest centroid-centroid distance being 3.837 (3) Å and 3.634 (3) Å, respectively. The parallel planes are shifted for 1.048 Å and 1.936 Å, respectively (Fig. 2). There may also be weak intermolecular π-π interactions between adjacent benzene rings, with a shortest centroid-centroid distance of 4.453 (4) Å. The molecules are stacked in columns along the a axis and the Br···Br contacts are present. The shortest Br1···Br1 a [symmetry code: (a) 2 -x,-y,1 -z] distance is 3.508 (1) Å.

Experimental
A mixture of 1-bromo-3-[1-(but-3-ynyloxy)-2-nitroethyl]benzene (1.49 g, 5 mmol), phenyl isocyanate (2.97 g, 25 mmol) and Et 3 N (51 mg, 0.5 mmol) in dry benzene (30 ml) was stirred for 12 h at 25 °C under nitrogen atmosphere. Water (1 ml) was added and the mixture was stirred for 2 h at which time the solids were removed by vacuum filtration. The filtrate was dried (MgSO 4 ) and concentrated in vacuo to give crude product, which was column chromatographed (SiO 2 ) by eluting with a mixture of n-hexane/EtOAc (10:1) to afford the title compound (34 mg, 1.2%) as a white solid. Crystals suitable for X-ray analysis were obtained by slow evaporation from an n-hexane/EtOAc solution. Mp 231 °C. 1 H NMR (600 MHz,  71, 164.13, 141.11, 131.00, 129.98, 128.74, 124.43, 122.61, 98.90, 74.22, 67.40, 27.91. supplementary materials sup-2 Refinement H atoms were positioned geometrically and allowed to ride on their respective parent atoms [C-H = 0.95 (CH, sp 2 ), 1.00 (CH, sp 3 ) or 0.99 Å (CH 2 ) and U iso (H) = 1.2U eq (C)]. The highest peak (1.25 e Å -3 ) and the deepest hole (-1.87 e Å -3 ) in the difference Fourier map are located 1.46 Å and 0.89 Å from the Br1 atom, respectively. Fig. 1. The structure of the title compound, with displacement ellipsoids drawn at the 50% probability level for non-H atoms [Symmetry code: (i) -x, -y, -z].  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 Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq