Crystal structure of 2,3-diphenyl-2,3-dihydro-4H-1,3-benzothiazin-4-one 1-oxide

The crystal structure of the sulfoxide of 2,3-diphenyl-2,3-dihydro-4H-1,3-benzothiazin-4-one, which belongs to a bioactive family of compounds, exhibits a screw-boat pucker for the thiazine ring. C—H⋯O hydrogen-bond and van der Waals interactions stabilize the crystal lattice.


Supramolecular features
The crystal lattice has layers of molecules comprising alternating enantiomers, extending along the a-axis direction and lying in the ac plane. The layers are linked across the b-cell direction through intermolecular C1-HÁ Á ÁO2 i hydrogen bonds (Fig. 2, Table 1) between molecules of the same chirality [symmetry code: (i) Àx + 1 2 , y À 3 2 , Àz + 1 2 ]. While C-HÁ Á ÁO interactions are also present in our two earlier structures (Yennawar et al., 2014;Yennawar, Yang & Silverberg, 2016), the differences in either the donor C or acceptor O atoms make them unique in each case. In the present structure, the chiral C atom donates the proton to the O atom at position 4 (Á Á ÁO-C) of the thiazine ring, while in our 2016 structure, the acceptor O atom was the one at position 1 (Á Á ÁO-S). In the 2014 structure, the two benzene-ring C atoms are the donors to the only O atom (Á Á ÁO-C) on the thiazine ring.

Figure 2
Crystal packing diagram showing C-HÁ Á ÁO contacts as dotted red lines between molecules of (I) which form chains along the b-axis direction.

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.
0.1212 g of triphenyltin chloride and 2.0 ml of acetone and stirred. The contents of the 2 ml vial were added to the 10 ml flask and the vial was rinsed with an additional 0.5 ml of acetone, giving a clear solution, which was stirred for 2 h and then allowed to stand without stirring for 3 d. The solution was filtered through Celite and then concentrated under vacuum, giving a white solid. The solid was recrystallized from cyclohexane to give a yellow solid (yield 0.0755 g, 72%). Crystals suitable for X-ray analysis were obtained by slow evaporation from an acetone solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were placed geometrically and allowed to ride on their parent C atoms during refinement, with C-H distances of 0.98 (methine) or 0.93 Å (aromatic) and with U iso (H) = 1.2U eq (C). Although of no particular significance in this racemic compound, the enantiomer chosen was the C1(S) one.

Special details
Experimental. 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 (10 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.