Methyl 1-allyl-4-hydroxy-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylate

There are two independent molecules in the asymmetric unit of the title compound, C13H13NO5S, in both of which the ester substituent is nearly coplanar [C—C—C—O torsion angles = 2.7 (7) and −0.8 (7)°] with the planar fragment of the bicycle due to the formation of a strong O—H⋯O intramolecular hydrogen bond. The vinyl group at the ring N atom is approximately orthogonal to the heterocyclic mean plane [C—N—C—C torsion angles = 103.1 (6) and 98.2 (5)°]. The refinement was performed on a two-component, non-merohedrally twinned crystal [population ratio = 0.483 (3):0.517 (3).

There are two independent molecules in the asymmetric unit of the title compound, C 13 H 13 NO 5 S, in both of which the ester substituent is nearly coplanar [C-C-C-O torsion angles = 2.7 (7) and À0.8 (7) ] with the planar fragment of the bicycle due to the formation of a strong O-HÁ Á ÁO intramolecular hydrogen bond. The vinyl group at the ring N atom is approximately orthogonal to the heterocyclic mean plane [C-N-C-C torsion angles = 103.1 (6) and 98.2 (5) ]. The refinement was performed on a two-component, non-merohedrally twinned crystal [population ratio = 0.483 (3): 0.517 (3).

Comment
Oxicams are in integral part of the range of modern non-steroidal anti-inflammatory drugs (Kleemann et al., 2008). We have carried out the synthesis and studied the peculiarities of the spatial structure of methyl 4-hydroxy-1-methyl-2,2dioxo-1H-2λ 6 ,1-benzothiazine-3-carboxylate (I) being of interest as the initial product for obtaining 4-hydroxy-2,2dioxo-1H-2λ 6 ,1-benzothiazine-3-carboxamides. By now these compounds remain absolutely unstudied though they are isomers of oxicams and differ from them only by the reverse mutual arrangement of nitrogen and sulfur atoms in the thiazine cycle. Two molecules (IA and IB) are observed in asymmetric part of crystal unit cell.

Experimental
Triethylamine (1.54 ml, 11 mmol) was added to the solution of methyl N-allylanthranilate (1.91 g, 10 mmol) in CH 2 Cl 2 (20 ml). Chlorosulfonyl acetic acid ethyl ester (2.05 g, 11 mol) was then added dropwise with cooling and stirring and left at the room temperature for 5 h. The reaction mixture was diluted with a cold water and vigorously stirred. The organic layer was separated, dried over CaCl 2 , and the solvent was distilled off (finally under reduced pressure). The residue was treated with the solution of sodium methylate (prepared from metallic sodium (0.69 g, 30 mmol) and absolute MeOH (15 ml)), taken fo reflux, and then left for 10-12 h at the room temperature. The reaction mixture was diluted with cold water and acidified with 1 N HCl to pH 3. The precipitate was filtered, washed with water, and dried.

Refinement
The refinement was performed on a two-component, non-merohedral twinned crystal (Refined populations: 0.483 (3),0.517 (3) ). All hydrogen atoms were located from electron density difference maps and were refined in the riding motion approximation with U iso constrained to be 1.5 times U eq of the carrier atom for the methyl and hydroxyl supplementary materials groups and 1.2 times U eq of the carrier atom for the other atoms.

Figure 1
View of the title compound with atomic membering. All atoms are shown with displacement ellipsoids drawn at the 50% probability level.
Methyl 1-allyl-4-hydroxy-2,2-dioxo-1H-2λ 6 ,1-benzothiazine-3-carboxylate Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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.