4-(2-Nitrobenzyl)-3-phenyl-3,4-dihydro-2H-1,4-benzoxazin-2-ol

The title compound, C21H18N2O4, crystallizes with two independent molecules (A and B) in the asymmetric unit. In both molecules the oxazine ring has an envelope conformation with the hydroxyl-substituted C atom as the flap. The nitrobenzyl ring and the phenyl ring are almost normal to the mean plane of the benzooxazine ring system with dihdral angles of 85.72 (15) and 82.69 (15)°, respectively, in molecule A, and 85.79 (15) and 87.72 (15)°, respectively, in molecule B. The main difference in the conformation of the two molecules concerns the dihedral angle between the nitrobenzyl ring and the phenyl ring, viz. 79.67 (18) in molecule A and 71.13 (18)° in molecule B. In the crystal, the A and B molecules are linked by an O—H⋯O hydrogen bond. These units are then linked via C—H⋯O hydrogen bonds, forming sheets lying parallel to (010). Further C—H⋯O hydrogen bonds link the sheets to form a three-dimensional network. There are also O—H⋯π and C—H⋯π interactions present, reinforcing the three-dimensional structure.

The title compound, C 21 H 18 N 2 O 4 , crystallizes with two independent molecules (A and B) in the asymmetric unit. In both molecules the oxazine ring has an envelope conformation with the hydroxyl-substituted C atom as the flap. The nitrobenzyl ring and the phenyl ring are almost normal to the mean plane of the benzooxazine ring system with dihdral angles of 85.72 (15) and 82.69 (15) , respectively, in molecule A, and 85.79 (15) and 87.72 (15) , respectively, in molecule B. The main difference in the conformation of the two molecules concerns the dihedral angle between the nitrobenzyl ring and the phenyl ring, viz. 79.67 (18) in molecule A and 71.13 (18) in molecule B. In the crystal, the A and B molecules are linked by an O-HÁ Á ÁO hydrogen bond. These units are then linked via C-HÁ Á ÁO hydrogen bonds, forming sheets lying parallel to (010). Further C-HÁ Á ÁO hydrogen bonds link the sheets to form a three-dimensional network. There are also O-HÁ Á Á and C-HÁ Á Á interactions present, reinforcing the threedimensional structure.  Table 1 Hydrogen-bond geometry (Å , ).

S1. Comment
Numerous natural and synthetic substances that have the core "1,4-benzoxazine" have been used in different fields of medicine. The 1,4-benzoxazine structure is an integral part of several naturally occurring substances. For example, various glycosides of the 2-hydroxy-2H-1,4-benzoxazine skeletons have been found to occur in gramineous plants such as maize, wheat, rye, and rice, and have been suggested to act as plant resistance factors against microbial diseases and insects (Ozden et al., 1992;Hartenstein & Sicker, 1994). Moreover, 3,4-Dihydro-2H-1,4-benzoxazines have received a great deal of attention due to their wide range of biological and therapeutical properties (Ilas et al., 2005). For example they have been investigated as antihypertensive agents (Touzeau et al., 2003), neuroprotective antioxidants (Largeron et al., 1999) and prostaglandin D 2 receptor antagonists (Torisu et al., 2004). Herein, we report our results about the synthesis and the crystallographic study of 4-(2-nitrobenzyl)-3-phenyl-3,4-dihydro-2H-benzo[b][1,4]oxazin-2-ol, (I). The molecular geometry and the atom-numbering scheme of asymetric unit are shown in Fig. 1. The asymetric unit contents two molecule of (I). The crystal packing can be described as alternating connected layers parallel to the (001) plane along the c axis ( Fig. 2 Fig. 2). These interactions link the molecules within the layers and also link the layers together and reinforcing the cohesion of the structure.

S3. Refinement
All H atoms were localized on Fourier maps but introduced in calculated positions and treated as riding on their parent atoms (C and O) with C-H = 0.97 Å (methylene); C-H = 0.93 Å (aromatic) or C-H = 0.98 Å (methine); O-H = 0.82 Å and with U iso (H) = 1.2 U eq (C aryl ; C methine or C methylene )and U iso (H) = 1.5 U eq (O hydroxy ). In the absence of significant supporting information sup-2 Acta Cryst. (2014). E70, o863-o864 anomalous scattering effects Friedel pairs have been merged. The number of Friedel pairs is 2686.

Figure 1
The title molecule (Farrugia, 2012) with the atomic labelling scheme. The displacement parameters are drawn at the 50% probability level.

4-(2-Nitrobenzyl)-3-phenyl-3,4-dihydro-2H-1,4-benzoxazin-2-ol
Crystal data 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
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