Crystal structure of (Z)-3-(4-methoxybenzylidene)-2,3-dihydrobenzo[b][1,4]thiazepin-4(5H)-one

In the title compound, C17H15NO2S, the two C atoms linking the S and carbonyl C atoms of the seven-membered thiazepine ring are disordered over two sites, with occupancies of 0.511 (4) and 0.489 (4); both disorder components adopt distorted twist-boat conformations. In the crystal, N—H⋯O and C—H⋯O hydrogen bonds link inverted-related molecules into dimers, incorporating R 1 2(6) and R 2 2(8) ring motifs; the acceptor carbonyl O atom is bifurcated. These dimers are further linked by C—H⋯O hydrogen bonds, forming supramolecular tapes running along the a axis.


S1. Structural commentary
The title compound is used as an intermediate for the synthesis of dosulepin, which is an antidepressant of the tricyclic family. Dosulepin prevents reabsorbing of serotonin and noradrenaline in the brain, helps to prolong the mood lightening effect of any released noradrenaline and serotonin, thus relieving depression. Dibenzo[c,e]thiazepin derivatives exhibit chiroptical properties (Tomascovic et al., 2000). Dibenzo[b,e]thiazepin-5,5-dioxide derivatives possess antihistaminic and antiallergenic activities (Rajsner et al., 1971). Benzene thiazepin derivatives are identified as a type of effective antihistaminic compounds (Metys et al., 1965). In view of this biological importance, the crystal structure of the title compound has been carried out and the results are presented here. Fig. 1 shows a displacement ellipsoid plot of (I), with the atom numbering scheme. The geometric parameters of the title molecule agree well with those reported for similar structures Lakshmanan et al., 2012).
The sum of angles at N1 atom of the thiazepin ring (359.9°) is in accordance with sp 2 hybridization. Both the major and minor conformers of the disorderd thiazepine ring adopt distorted twist-boat conformations.

S2. Synthesis and crystallization
A mixture of (Z)-methyl 2-(bromomethyl)-3-(4-methoxyphenyl)acrylate (2 mmol) and o-aminothiophenol (2 mmol) in the presence of potassium tert-butoxide (4.8 mmol) in dry THF (10 ml) was stirred at room temperature for 1 h. After the completion of the reaction as indicated by TLC, the reaction mixture was concentrated and the resulting crude mass was diluted with water (20 ml) and extracted with ethyl acetate (3 x 20 ml). The organic layer was washed with brine (2 x 20 ml) and dried over anhydrous sodium sulfate. It was then concentrated to successfully provide the crude final product [1,4] thiazepin-4(5H)-one). This was purified by column chromatography on silica gel with ethylacetate/hexane 1:19 as eluent to afford the title compound in good yield (47 %).
Single crystals suitable for X-ray diffraction were obtained by slow evaporation of its ethylacetate solution at room temperature.

S3. Refinement
Atoms C1   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.25 e Å −3 Δρ min = −0.34 e Å −3 Special details 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (