Methyl 3-oxo-2,3-dihydro-1,2-benzothiazole-2-acetate 1,1-dioxide

The title molecule, C10H9NO5S, is composed of two essentially planar units with a dihedral angle of 89.16 (6)° between them. In the crystal structure, there are weak intermolecular C—H⋯O interactions resulting in dimeric pairs of molecules about inversion centres and chains of molecules extended along the a and c axes, thus stabilizing the structure. In addition, benzothiazole rings lying parallel to each other with centroid–centroid distances of 3.679 (2) and 3.999 (2) Å indicate the existence of π–π stacking interactions.

The title molecule, C 10 H 9 NO 5 S, is composed of two essentially planar units with a dihedral angle of 89.16 (6) between them. In the crystal structure, there are weak intermolecular C-HÁ Á ÁO interactions resulting in dimeric pairs of molecules about inversion centres and chains of molecules extended along the a and c axes, thus stabilizing the structure. In addition, benzothiazole rings lying parallel to each other with centroid-centroid distances of 3.679 (2) and 3.999 (2) Å indicate the existence ofstacking interactions.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH2607).

Comment
Saccharin derivatives are considered to be the most potent orally active human leucocyte elastase (HLE) inhibitors for the treatment of chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), cystic fibrosis, asthma and other inflammatory diseases (Kapui et al., 2003). Various biologically important saccharin skeletons and their N-alkyl derivatives were efficiently prepared (Xu et al., 2006) by chromium oxide-catalyzed oxidation of N-alkyl(omethyl)arenesulfonamides in acetonitrile besides the already developed methodology utilizing irradiation techniques for similar type of conversions (Masashi et al., 1999). In continuation to our research on benzene, 1,2-benzothiazine 1,1-dioxide and saccharin derivatives (Siddiqui et al., 2008;Siddiqui, Ahmad, Khan, Siddiqui & Weaver, 2007), we report herein the crystal structure of the title compound, (I).
The benzothiazole rings in (I) lie parallel to each other about the origin with the shortest distance between the centroids of the benzene rings of the adjacent molecules is 3.679 (2) Å which indicates the existence of π-π stacking interactions.

Experimental
The compound (I) was prepared following the prcedures reported earlier (Manjarrez et al., 1996). Crystals suitable for X-ray crystallography were grown from a solution of CH 3 OH by slow evaporation at 313 K.

Refinement
H-atoms were included in the refinements at geometrically idealized positions with aryl, methylene and methyl C-H distances 0.95, 0.99 and 0.98 Å, respectively, and U iso = 1.2 times U eq of the atoms to which they were bonded. The final difference map was free of any chemically significant features.
supplementary materials sup-2 Figures   Fig. 1. ORTEP-3 (Farrugia, 1997) drawing of (I) with displacement ellipsoids plotted at 50% probability level.  Methyl 3-oxo-2,3-dihydro-1,2-benzothiazole-2-acetate 1,1-dioxide 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 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.