2-(3,4-Dimethyl-5,5-dioxo-2H,4H-pyrazolo[4,3-c][1,2]benzothiazin-2-yl)acetic acid

In the title molecule, C13H13N3O4S, the heterocyclic thiazine ring adopts a half-chair conformation in which the S and an adjacent C atom are displaced by 0.919 (3) and 0.300 (4) Å, respectively, on the same side of the mean plane formed by the remaining ring atoms. The mean planes of the benzene and pyrazole rings are inclined at a dihedral angle of 18.32 (12)° with respect to each other. The acetate group is oriented at 80.75 (8)° with respect to the pyrazole ring. The crystal structure is stabilized by O—H⋯N and C—H⋯O hydrogen bonds, resulting in fused eight- and seven-membered rings with R 2 2(8) and R 2 2(7) graph-set motifs, respectively.

In the title molecule, C 13 H 13 N 3 O 4 S, the heterocyclic thiazine ring adopts a half-chair conformation in which the S and an adjacent C atom are displaced by 0.919 (3) and 0.300 (4) Å , respectively, on the same side of the mean plane formed by the remaining ring atoms. The mean planes of the benzene and pyrazole rings are inclined at a dihedral angle of 18.32 (12) with respect to each other. The acetate group is oriented at 80.75 (8) with respect to the pyrazole ring. The crystal structure is stabilized by O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds, resulting in fused eight-and seven-membered rings with R 2 2 (8) and R 2 2 (7) graph-set motifs, respectively.
The bond distances and angles in the title compound ( Fig. 1) agree very well with the corresponding bond distances and angles reported in closely related compounds (Siddiqui et al., 2008;2009). The heterocyclic thiazine ring adopts a twist chair conformation with atoms S1 and C1 displaced by 0.919 (3) and 0.300 (4) Å, respectively, on the same side of the mean plane formed by the remaining ring atoms (r.m.s. deviation 0.012 for N1/C6-C8 atoms). The mean-plane of the benzene ring C1-C6 makes a dihedral angle 18.32 (12)° with the mean-plane of the pyrazolyl ring (N2/N3/C7/C8/C10).
The mean-plane of the acetate group (O3/O4/C12/C13) lies at 80.75 (8)° with respect to the pyrazolyl ring. The crystal structure is stabilized by intermolecular hydrogen bonding interactions ( Fig. 2 and Table 1). The hydrogen bonds O4-H4O···N2 and C12-H12B···O3 result in eight membered rings with a R 2 2 (8) motif while C5-H5···O4 hydrogen bonding results in a seven membered ring with a R 2 2 (7) motif (Bernstein et al., 1995); both rings are fused together and result in chains of molecules along the b-axis in a zigzag fashion. Moreover, C9-H9A···O2 interactions link the title molecules into chains along the b-axis further consolidating the crystal packing.

Refinement
All H atoms were positioned geometrically and refined using a riding model, with O-H = 0.84 Å and C-H = 0.95, 0.98 and 0.99 Å, for aryl, methyl and methylene H-atoms, respectively. The U iso (H) were included at 1.5U eq (O) or 1.2U eq (C).  1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.  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.