(E)-Benzaldehyde O-{[3-(pyridin-3-yl)isoxazol-5-yl]methyl}oxime

The asymmetric unit of the title compound, C16H13N3O2, contains two independent molecules in which the pyridine and benzene rings form dihedral angles of 81.7 (2) and 79.8 (2)°, indicating the twist in the molecules. In the crystal, weak C—H⋯N interactions link molecules into chains along [100].

The asymmetric unit of the title compound, C 16 H 13 N 3 O 2 , contains two independent molecules in which the pyridine and benzene rings form dihedral angles of 81.7 (2) and 79.8 (2) , indicating the twist in the molecules. In the crystal, weak C-HÁ Á ÁN interactions link molecules into chains along [100].

Comment
The isoxazoles are five-membered heterocyclic systems with one oxygen atom and one nitrogen atom at adjacent positions. These compounds are used as intermediates in organic synthesis due to their easy transformation into important groups such as enamino ketones, enoximes, 1,3-dicarbonyl compounds, γ-amino alcohols, and β-hydroxy nitriles (Giomi et al., 2008;Chukanov & Reznikov, 2011).
They also have been widely used in the synthesis of nucleosides, alkaloids and other natural compounds. Many derivatives exhibit interesting applications in various fields such as agriculture, industry, and medicine. The wide spectrum of biological activities characteristic of these systems, comprises analgesic (Meyers et al., 2011), antifungal (Basappa et al., 2003), antiviral (Lee et al., 2009), anti-inflammatory (Talley et al., 2000), and antiobesity (Giomi et al., 2008) activities.
In our research group, we are interested in the synthesis of nitrogen containing compounds with potential biological activity such as isoxazoles and oximes. The (E)-benzaldehyde O-(3-(pyridin-3-yl)isoxazol-5-yl)methyl oxime, (I), is an isoxazole analogue exhibiting important antibiotic (Farrerons et al., 2003) and immunomodulator properties (Edgard et al., 2004). On the other hand, the oxime function is an important pharmacophore group present in a wide variety of biologically active compounds, such as 3-oxiconazole and cefuroxime. Compound I was synthesized via 1,3-dipolar cycloaddition of an alkyne and a nitrile oxide obtained by treatment of (E)-nicotinaldehyde oxime with NaOCl. The reaction proceeded with high regioselectivity affording only the 5-substituted isomer in 45% yield. The molecular structure of I is shown in Fig. 1. The asymmetric unit of (I) contains two independent molecules (1) and (2). In both molecules, the isoxazole and pyridine rings are almost coplanar (r.m.s. deviation of all non-hydrogen atoms = 0.0044 Å).

Refinement
The H-atoms were positioned geometrically [C-H= 0.95 Å for aromatic and C-H= 0.99 Å for methylene] and refined with U iso (H) 1.2 and 1.5 times U eq of the parent atom, respectively.

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 )
x y z U iso */U eq O1 0.42469 (12