Crystal structure of (R)-6′-bromo-3,3-dimethyl-3′,4′-dihydro-2′H-spiro[cyclohexane-1,3′-1,2,4-benzothiadiazine] 1′,1′-dioxide

In the title compound, the mean plane of the cyclohexane ring is almost normal to the benzene ring and to the mean plane of the 1,2,4-thiadiazinane ring. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming chains along [10], which are in turn linked via C—H⋯π interactions, forming sheets parallel to (010).

In the title compound, C 14 H 19 BrN 2 O 2 S, the 1,2,4-thiadiazinane ring adopts an envelope conformation with the N atom (attached to the sulfonyl group) as the flap, while the cyclohexane ring adopts a chair conformation. The mean plane of the cyclohexane ring is almost normal to the benzene ring and the mean plane of the 1,2,4-thiadiazinane ring, making dihedral angles of 70.4 (2) and 71.43 (19) , respectively. Furthermore, the dihedral angle between the benzene ring and the mean plane of the 1,2,4-thiadiazinane ring is 4.91 (18) . The molecular structure is stabilized by an intramolecular C-HÁ Á ÁO hydrogen bond, which encloses an S(6) ring motif. In the crystal, molecules are linked by N-HÁ Á ÁO hydrogen bonds into chains along [101], forming a C(6) graph-set motif. These chains are interconnected via C-HÁ Á Á interactions, leading to chains along [101], so finally forming sheets parallel to (010).
In view of their broad spectrum of biological activities, and in a continuation of our work on this class of compound, we have synthesized the title compound, (1), and report herein on its spectroscopic analysis and crystal structure.

Supramolecular features
In the crystal, molecules are linked by N-HÁ Á ÁO hydrogen bonds (Table 1 and Fig. 2), forming chains with a C(6) graphset motif along [101]. The chains are linked via structuredirecting C-HÁ Á Á interactions, leading to the formation of C(6) chains along [101]. These interactions lead to the formation of sheets parallel to (010) ( Table 1 and Fig. 2).

Figure 2
A view along the a axis of the crystal packing of the title compound. Hydrogen bonds are shown as thin blue lines (see Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity). Table 1 Hydrogen-bond geometry (Å , ).
Cg is the centroid of the C1-C6 ring.

Synthesis and crystallization
To a cooled solution of 2-amino-4-bromobenzene sulfonamide (5 g, 19.9 mmol) and anhydrous magnesium sulfate (MgSO 4 ; 3.5 g, 29.88 mmol) in dry toluene (60 ml), 3,3-dimethylcyclohexanone (22 mmol) was added followed by slow addition of polyphosphoric acid anhydride (T3P; 19 ml, 29.88 mmol, 50% solution in ethyl acetate). The reaction mixture was then refluxed in a sealed tube at 393 K for 6 h. It was cooled to 283 K and neutralized with saturated sodium bicarbonate solution (100 ml). The crude product was extracted with ethyl acetate (100 ml) and was finally washed with brine solution (50 ml). The organic phase was dried over anhydrous sodium sulfate and concentrated to give the crude product as a brown solid. It was then dissolved in a minimum amount of ethyl acetate (25 ml) and stirred for 1h in an ice-cooled bath, filtered and washed with cold ethyl acetate (10 ml Â 2) to give pure compound (1) (4.5 g, 75% yield) as a white solid. Colourless prisms of the title compound were obtained by slow evaporation of a solution of the compound in ethyl acetate.

Spectroscopic characterization
The IR spectra of the title compound exhibits strong bands at 1374 cm À1 due to asymmetric (S O) stretching and a band at 1165 cm À1 due to symmetric (S O) stretching. Further, a single band appearing at 3110 cm À1 is due to the secondary N-H group of the sulfonamide, and a band at 3308 cm À1 confirms the cyclization of sulfonamide through condensation with the ketone. Appearance of bands in the range of 2970-2815 cm À1 is assigned to the C-H stretching is due to the presence of the saturated hydrocarbons.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The NH hydrogens were located in a difference Fourier map. N-and C-bound H atoms were included in calculated positions (N-H = 0.86 and C-H = 0.93-0.97 Å ) and allowed to ride on their parent atoms, with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (N,C) for other H atoms.  Data collection: APEX2 (Bruker, 2009); cell refinement: APEX2 and SAINT-Plus (Bruker, 2009); data reduction: SAINT-Plus and XPREP (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Special details
Experimental. Melting points were determined in open capillaries and are uncorrected. The molecular structures of the synthesized compounds were established using IR, 1 H NMR, 13 C NMR and LC-MS studies. Solid state FT-IR Spectra were recorded as KBr discs on Jasco FT-IR Spectrometer. 1 H NMR and 13 C NMR were recorded in DMSO at 399.13 MHz and 75.50 MHz respectively on Bruker model avance II. All the chemical shifts were reported in parts per million (ppm) using tetramethyl silane (TMS) as an internal standard. Mass spectra of the compounds were recordedon Shimadzu LC-2010EV with ESI probe. 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 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.