Methyl 4-hydroxy-2-isopropyl-1,1-dioxo-2H-1,2-benzothiazine-3-carboxylate

In the crystal structure of the title molecule, C13H15NO5S, the S and N atoms of the thiazine ring exihibit the maximum deviations from the least-squares plane of 0.3008 (6) and 0.3280 (7) Å, respectively. The ring therefore adopts a half chair conformation. The thiazine ring is twisted by an angle of 13.29 (7)° with respect to the aromatic ring. The isopropyl substituent is oriented at a dihedral angle of 53.2 (12)° with respect to the thiazine ring. An intramolecular O—H⋯O hydrogen bond occurs. Intermolecular hydrogen bonding is observed in the crystal structure.

The title compound, I, is varied in structure with respect to III only concerning the alkyl group attached to the nitrogen atom of the thiazine ring. The characteristic intramolecular O-H···O hydrogen bond is observed in the structure of I as for II and III forming a six membered S 1 1 (6) ring (C7/C8/C9/O4 H3O/O3) system (Bernstein, et al., 1995). The observed ring is inclined at dihedral angles of 18.9 (4)° and 16.1 (4)° with respect to the thiazine (C1/C6/C7/C8/N1/S1) and aromatic (C1/C2/C3/C4/C5/C6) rings. The isopropyl group is oriented at a dihedral angle of 53.2 (1)° relative to the thiazine ring.
The dihedral angle between the thiazine and aromatic ring is 13.29 (7)°. Alongwith the O-H···O type hydrogen bonding interaction the molecule is connected to it's neighboring symmetry equivalents by additional weak C-H···O type interactions producing a three dimensional network (Fig. 2. Tab. 1).

Experimental
The synthesis of the titled compound has already been published (Arshad et al., 2011). Recrystallization from methanol under slow evaporation of the solvent leads to the formation of crystals suitable for structural analysis.

Refinement
Carbon bound H atoms were positioned geometrically with C-H = 0.93 Å and 0.98Å for aromatic and C11 carbon atoms, respectively, and were refined using a riding model with U iso (H) = 1.2 U eq (C). Similarly, H atoms of methyl groups were positioned geometrically with C-H = 0.96 Å and were refined using a riding model with U iso (H) = 1.5 U eq (C). The H atom of the hydroxyl group was located from the difference map with O-H= 0.88 (2)Å and was refined with U iso (H) = 1.5 U eq (O).  Methyl 4-hydroxy-2-isopropyl-1,1-dioxo-2H-1,2-benzothiazine-3-carboxylate

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 > 2σ(F 2 ) is used only for calculating Rfactors(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.