Crystal structure of rac-2,3-diphenyl-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-one 1-oxide

In the title compound, the thiazine ring exhibits an envelope conformation, with the S atom forming the flap of the envelope. In this racemate crystal, homochiral molecules form slabs parallel to (010) of thickness b/2 which then stack with alternating chirality in the b-axis direction. The stacking is aided by edge-to-face interactions between the phenyl rings of racemic molecules.


Structural commentary
The crystal structure of this racemic compound shows a thiazine ring in an envelope pucker with puckering amplitude of 0.718 (3) Å (Fig. 1). The oxygen on sulfur is pseudo-axial on ISSN 2056-9890 the thiazine ring. The two phenyl rings, on two adjacent atoms of the thiazine ring, are perpendicular to each other with an angle of 89.47 (19) between their planes. The oxygen on sulfur and the phenyl ring on C2 are trans to each other.

Supramolecular features
The crystal consists of a racemic mixture of the title compound. The two phenyl groups and one of the two oxygen atoms participate in intermolecular interactions (Table 1). The molecules of single chirality form slabs in the ac plane aided by edge-to-face interactions, with inter-centroid distance of 5.195 (3) Å , in the a-axis direction and with C-HÁ Á ÁO hydrogen-bonds (Table 1) in the c-axis direction (Fig. 2). Along the b-axis direction, these slabs stack with alternating chirality, stabilized once again byedge-to-face interactions with inter-centroid distances of 5.021 (3) Å .

Synthesis and crystallization
A 5 mL round-bottom flask was charged with 50.5 mg of 2,3diphenyl-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-one and 1.5 mL of methanol and stirred. A solution of 85.6 mg Oxone 1 and 0.74 mL distilled water was added dropwise and the mixture was stirred until the reaction was complete as determined by TLC. The solids were dissolved by addition of 7.4 mL distilled water. The solution was extracted with 7.4 mL dichloromethane. The organic layer was washed with distilled water and then with sat. sodium chloride. The solution was dried over Na 2 SO 4 and concentrated under vacuum to a crude solid. This was chromatographed on flash silica gel, eluting with 70% ethyl acetate/hexanes, 100% ethyl acetate, and 100% acetone, giving 37.5 mg product (70% yield), m.p.: 396-400 K, R f = 0.23 (EtOAc). Crystals for X-ray crystallography were grown by slow evaporation from ethanol solution.

Figure 2
Packing viewed down the c axis. Alternating slabs of enantiomers along the b-axis direction are differentiated by the color scheme.

Computing details
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009). Special details Experimental. 1. SADABS was used for absorption correction. R(int) was 0.0424 before and 0.0268 after correction. The Ratio of minimum to maximum transmission is 0.6364. The λ/2 correction factor is 0.0015. 2. The data collection nominally covered a full sphere of reciprocal space by a combination of 4 sets of ω scans each set at different φ and/or 2θ angles and each scan (5 s exposure) covering -0.300° degrees in ω. The crystal to detector distance was 5.82 cm. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.