4-Methyl-3-phenyl-2,4-dihydropyrazolo[4,3-c][1,2]benzothiazine 5,5-dioxide1

In the title molecule, C16H13N3O2S, the heterocyclic thiazine ring adopts a twist chair conformation with the S atom and an adjacent C atom displaced by 0.946 (5) and 0.405 (6) Å, respectively, on the same side of the mean plane formed by the remaining ring atoms. The mean planes of the benzene rings make dihedral angles of 16.61 (10) and 15.32 (10)° with the mean plane of the pyrazole ring. The molecular structure is consolidated by intramolecular C—H⋯N interactions and the crystal packing is stabilized by N—H⋯O and C—H⋯N hydrogen bonds. The crystal studied was an inversion twin with the refined ratio of the twin components being 0.53 (11):0.47 (11).

In the title molecule, C 16 H 13 N 3 O 2 S, the heterocyclic thiazine ring adopts a twist chair conformation with the S atom and an adjacent C atom displaced by 0.946 (5) and 0.405 (6) Å , respectively, on the same side of the mean plane formed by the remaining ring atoms. The mean planes of the benzene rings make dihedral angles of 16.61 (10) and 15.32 (10) with the mean plane of the pyrazole ring. The molecular structure is consolidated by intramolecular C-HÁ Á ÁN interactions and the crystal packing is stabilized by N-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds. The crystal studied was an inversion twin with the refined ratio of the twin components being 0.53 (11):0.47 (11).

Related literature
For the biological activity of related compounds, see: Turck et al. (1996); Silverstein et al. (2000); Lombardino et al. (1973); Zinnes et al. (1973); Ahmad et al. (2010a,b). For related structures, see: Siddiqui et al. (2008Siddiqui et al. ( , 2009  Among the broad class of heterocyclic compounds, pyrazole and benzothiazine nuclei are well known for their biological activity potential. Oxicam drugs are benzothiazine based potent anti-inflammatory and analgesic drugs (Turck et al. 1996;Lombardino et al., 1973;Zinnes et al., 1973), whereas celecoxib, an anti-inflammatory drug and selective inhibitor of cox-2 enzyme, contains pyrazole fragment (Silverstein et al., 2000). Keeping in view these facts and figures, we have prepared some pyrazolobenzothiazines which contain both of these medicinally important heterocycles fused with eachother (Ahmad et al., 2010a & b). We report here the crystal structure of the title compound.
The bond distances and angles in the title compound ( Fig. 1) agree very well with the corresponding bond distances and angles observed in closely related structures (Siddiqui et al., 2008;2009). The heterocyclic thiazine ring adopts a twist chair conformation with atoms S1 and C1 displaced by 0.946 (5) and 0.405 (6) Å, respectively, on the same side from the mean plane formed by the remaining ring atoms (N1/C6-C8). The mean planes of the benzene rings C1-C6 and C11-C16 make dihedral angles 16.61 (10) and 15.32 (10)°, respectively, with the mean-plane of the pyrazole ring (N2/N3/C7/C8/C10).

Experimental
A mixture of 3-benzoyl-4-hydroxy-2-methyl-2H-1,2-benzothiazine 1,1-dioxide (5.0 g, 0.020 mol), hydrazine hydrate (5 ml) and ethanol (30 ml) was refluxed for 5 h followed by the removal of solvent under vacuum. The residue obtained was washed with cold water to get the title compound as a white crystalline product. Transparent crystals suitable for X-ray crystallographic studies were grown from a CHCl 3 solution at room temperature by slow evaporation.

Refinement
All H atoms were positioned geometrically and refined using a riding model, with N-H = 0.86 Å and C-H = 0.93 and 0.96 Å, for aryl and methyl type H-atoms, respectively. The U iso (H) were allowed at 1.2U eq (N/C). An absolute structure was not determined as the crystal was a racemic twin with BASF parameter refined to 0.53 (11); 1306 Friedel pairs of reflections were not merged. A low angle reflection (0 1 1) was omitted as it was hindered by the beam stop.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are presented as small spheres of arbitrary radius.    (11) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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.