tert-Butyl 4-{5-[3-(trifluoromethoxy)phenyl]-1,2,4-oxadiazol-3-yl}piperazine-1-carboxylate

In the title compound, C18H21F3N4O4, the piperazine ring adopts a chair conformation and the dihedral angle between the oxadiazole and benzene rings is 6.45 (14)°. The C atoms and their attached H atoms in the piperazine ring are disordered, with site-occupation factors of 0.576 (12) and 0.424 (12). In the crystal, molecules are linked through weak C—H⋯O interactions, generating an R 2 2(12) motif. Further, secondary C—H⋯O intermolecular interactions link the molecules into C(6) chains along [100].

In the title compound, C 18 H 21 F 3 N 4 O 4 , the piperazine ring adopts a chair conformation and the dihedral angle between the oxadiazole and benzene rings is 6.45 (14) . The C atoms and their attached H atoms in the piperazine ring are disordered, with site-occupation factors of 0.576 (12) and 0.424 (12). In the crystal, molecules are linked through weak C-HÁ Á ÁO interactions, generating an R 2 2 (12) motif. Further, secondary C-HÁ Á ÁO intermolecular interactions link the molecules into C(6) chains along [100].
Data collection: APEX2 (Bruker, 2009); cell refinement: APEX2 and SAINT-Plus (Bruker, 2009); data reduction: SAINT-Plus and XPREP (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97. moiety for the pharmaceutical industry (Nicolaides et al., 1998). As a consequence of these, oxadiazoles have often been the target of numerous drug discovery programs as anti-inflammatory agents, anti-tumor agents, potential anticancer agents, Histamine H3 receptor antagonists as potent inhibitors of MIF biological function, and bell-tryptase inhibitors, In addition to these, 1,2,4-oxadiazoles are widely used as hydrolysis resisting amide bioisosteres in the development of peptidomimetics (Kemnitzer et al.,2009). Also, oxadiazoles exhibit wide range of antibacterial, antifungal and activities against Gram-positive and Gram-negative bacteria. Keeping this in mind, the crystal structure of the title compound was determined.
In the crystal structure of the title compound, C 18 H 21 F 3 N 4 O 4 , the piperazine ring adopts chair conformation, and the molecule is almost planar with the dihedral angle between the oxadiazole and the benzene ring is 6.45 (14) o . In the structure, the molecules are linked through weak C10A-H10C···O4 interactions generating a R 2 2 (12) motif. Further, C17 -H17A···O4 intermolecular interactions link the molecules into C(6) chains along [100].

Experimental
To a solution of 1-N-carbidamide (2.14 mmol) in 5 ml N,N-dimethylformamide was added 3-trifluoromethoxy benzoic acid (2.36 mmol) and propylphosphonic anhydride (4.72 mmol). The reaction mixture was heated at 150°C for 12 h (reaction was monitored by TLC). The reaction mixture was poured to ice cold water. The solid obtained was filtered and washed with water. The crude product was purified by column chromatography using pet ether-ethyl acetate as the eluent.
Colourless prisms were obtained from slow evaporation of the solution of the compound in a mixture of pet ether and ethyl acetate (1:2).

Refinement
All H atoms were positioned geometrically, with C-H = 0.93 Å for aromatic H, C-H = 0.97 Å for methylene H and C -H = 0.96 Å for methyl H, and refined using a riding model with U iso (H) = 1.5Ueq(C) for methyl H and U iso (H) = 1.2Ueq(C) for all other H.
The C10, C11 C12 and C13 carbon atoms of a piperazine ring in the molecules were disordered over two sites and refined with site occupancy factors 0.576 (12)

Figure 1
Molecular structure of the title compound, showing displacement ellipsoids drawn at the 50% probability level.  Packing of molecules in the crystal structure along a axis.  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 Occ. (