Ethyl 5-amino-1-[(4-methylphenyl)sulfonyl]-1H-pyrazole-4-carboxylate

In the title molecule, C13H15N3O4S, the benzene and pyrazole rings are inclined to each other at 77.48 (3)°. Two amino H atoms are involved in bifurcated hydrogen bonds, viz. intramolecular N—H⋯O and intermolecular N—H⋯O(N). The intermolecular hydrogen bonds link the molecules related by translation in [100] into chains. A short distance of 3.680 (3) Å between the centroids of benzene and pyrazole rings from neighbouring molecules shows the presence of π–π interactions, which link the hydrogen-bonded chains into layers parallel to the ab plane.


Comment
During the course of our studies directed toward exploring the synthetic potential of 2,3-dihydroprazoles and thiazoles for synthesizing of novel antibacterial agents (Elgazwy, Ismail et al., 2012), we have recently reported various successful approaches for synthesis of 3,5-diaryl-4,5-dihydropyrazole analogues by the reaction of chalcones with thiosemicarbazide or with hydrazine hydrate in the presence of acetic acid (Elgazwy, Soliman et al., 2012). In conjunction with this work, we report here the title compound (I).
In (I) (Fig. 1), the benzene and pyrazole rings form a dihedral angle of 77.48 (3)°. Each amino hydrogen is involved in bifurcated hydrogen bond (one intra-and one intermolecular, Table 1), as was implied by the broad and downfield-shifted peak of the ethyoxy protons in the 1 H NMR. The intermolecular interactions, for which the acceptors are a tosyl oxygen and a pyrazole nitrogen, link the molecules related by translation parallel to the a axis. Short distance of 3.680 (3) Å between the centroids of benzene and pyrazole rings from the neighboring molecules shows a presence of π-π interactions, which link further hydrogen-bonded chains into layers parallel to ab plane.

Experimental
The reaction of unsaturated ketones of (E)-ethyl 2-cyano-3-ethoxyacrylate with 4-methylbenzenesulfonohydrazide was conducted in the presence of ethanol at reflux for 16 h. The 4,5-dihydro-1H-pyrazole analogues were obtained regiospecifically with satisfactory yields (60-96%). In most cases, N-1 was substituted by a strongly electronwithdrawing group that hindered the elimination of water and a subsequent aromatization of the pyrazole ring. For the title compound, we further employed an ethyl carboxylate at C-4 and an amino group at C-5. Pyrazoles showed sets of 1 H and 13 C NMR data that corresponded to the proposed structures. Compound (3) showed 1 H NMR chemical shifts as a characteristic AB system. The 13 C NMR spectra showed typical chemical shifts of 4,5-dihydro-1H-pyrazole rings on average at δ 157.0 (C-3), 46.4 (C-4), 88.4 (C-5). It is noteworthy that C-5 showed similar chemical shifts for series (3-

Refinement
The amino H atoms were located on a difference map and isotropically refined. C-bound H atoms were geometrically positioned (C-H 0.95-0.99 Å), and refined using a riding model, with U iso (H) fixed to 1.2 -1.5 × U(eq) of the parent atom.

Figure 1
The molecular structure of (I) showing the atomic numbering and 50% probabilty displacement ellipsoids.  Rms deviation of fitted atoms = 0.0150 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.