Ethyl 5-(4-aminophenyl)isoxazole-3-carboxylate

The asymmetric unit of the title compound, C12H12N2O3, contains two molecules in which the benzene and isoxazole rings are almost coplanar, the dihedral angles between their mean planes being 1.76 (9) and 5.85 (8)°. The two molecules interact with each other via N—H⋯N and N—H⋯O hydrogen bonds, which link the molecules into layers parallel to the ac plane. The layers stack in a parallel mode with an interlayer distance of 3.36 (7) Å.

The asymmetric unit of the title compound, C 12 H 12 N 2 O 3 , contains two molecules in which the benzene and isoxazole rings are almost coplanar, the dihedral angles between their mean planes being 1.76 (9) and 5.85 (8) . The two molecules interact with each other via N-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds, which link the molecules into layers parallel to the ac plane. The layers stack in a parallel mode with an interlayer distance of 3.36 (7) Å .
Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97. Isoxazoles are important compounds possessing pharmaceutical properties. Extensive investigation on the crystal structures of isoxazoles helps disclose their structure-activity relationship (Veronese et al. (1997); Becht et al. (2006); Andrzejak et al. (2011)). In a continuation of our research (Qi et al. (2011)), herein, we report the crystal structure of the title isoxazole derivative. The asymmetric unit of the title compound, C 12 H 12 N 2 O 3 , contains two planar molecules. In the molecular structure, (I) (Fig. 1), the dihedral angle between the isoxazole ring C7/C8/C9/N2/O1 and phenyl ring C1/C2/C3/C4/C5/C6 is 1.76 (9)° for molecule 1. The amino-group of the benzene ring is nearly into the same plane (r.m.s. deviation = 0.034 Å) as is usual for amino groups attached to aromatic rings. The COOEt group of the isoxazole ring is also in the same plane. The dihedral angle between the carboxylate and the isoxazole ring is 0.92 (13)°. For molecule 2, the dihedral angle for the isoxazole ring C19/C20/C21/N4/O4 and phenyl ring C13/C14/C15/C16/C17/C18 is 5.85 (8)°, which is slightly larger than molecule 1. The carboxylate group also has a little distortion with the larger dihedral angle between the carboxylate and the isoxazole ring being 1.58 (11)°. The two molecules interact with each other by strong N-H···N and N-H···O hydrogen bonds, which link the molecules into a layer (Fig. 2, Table 1). The layers then stack in parallel mode with the interlayer distance of 3.36 (7) Å.

Experimental
After a reaction of 4-nitroacetophenone and diethyl oxalate in a basic solution of ethanol for 2hrs, then add acetic acid to neutralize the solution from former reaction to obtain yellow solids. The solids were collected and reacted with hydroxylamine hydrochloride in ethanol at reflux for 4 hrs to form yellow products which were then reduced with stannous chloride in ethyl acetate to yield the title compound.

Refinement
H atoms were placed in geometrically idealized positions, and refined as riding on their parent atoms, with C-H distances fixed to 0.93 Å (aromatic CH), 0.97 (CH 2 ) with U iso = 1.2Ueq(C) and 0.96 Å (methyl CH 3 ) with U iso = 1.5Ueq(C). The N-H distances are fixed to 0.86 Å (U iso = 1.5Ueq(N)).

Computing details
Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).  The molecular structure of the title compound, with atom labels and 30% probability displacement ellipsoids for non-H atoms.  Intermolecular N-H···N and N-H···O contacts forming a supramolecular sheet.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.18 e Å −3 Δρ min = −0.20 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0095 (16) 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.