2-(3,4-Dimethoxyphenyl)-4-(thiophen-2-yl)-2,3-dihydro-1,5-benzothiazepine

In the title compound, C21H19NO2S2, the seven-membered thiazepine ring adopts a slightly distorted twist boat conformation. The dihedral angle between the benzene rings is 67.4 (2)°. The mean plane of the thiophene ring is twisted by 59.3 (2) and 87.7 (2)° from the mean planes of the benezene rings. In the crystal, inversion dimers linked by pairs of C—H⋯O hydrogen bonds generate R 2 2(20) loops.

In the title compound, C 21 H 19 NO 2 S 2 , the seven-membered thiazepine ring adopts a slightly distorted twist boat conformation. The dihedral angle between the benzene rings is 67.4 (2) . The mean plane of the thiophene ring is twisted by 59.3 (2) and 87.7 (2) from the mean planes of the benezene rings. In the crystal, inversion dimers linked by pairs of C-HÁ Á ÁO hydrogen bonds generate R 2 2 (20) loops.

Comment
Seven membered ring compounds are receiving significant attention because of the existence of their structural units in some natural products (Cutignano et al., 2003). Heterocycles containing the 1,4-thiazepine ring is one of important moieties in nitrogen and sulfur containing heterocycles and has been widely used as key building block for pharmaceutical agents as well as biologically active compounds. Benzothiazepine and its derivatives show a wide spectrum of pharmacological activities such as antifeedent, coronary vasodilatory, tranquilizer, antidepressant, CNS stimulant, antihypertensive, calcium channel blocker, antiulcer, calcium antagonist and antimicrobial agents (Sanjeeva et al., 2008). The C6-N12 is shorter than an usual C-N single bond [1.294 Å compared to 1.416 Å] and the C10-S9 bond is shorter than an usual C-S single bond [1.760 Å compared to 1.82 Å]. The bond lengths and angles do not show large deviations and are comparable with those reported for a similar structure (Manjula et al., 2013). The atoms C7, C8, C10 and C11 present in the central thiazepine ring forms a basal plane and the S9 atom as the bow, representing the boat conformation of thiazepine ring.
In the title compound, the dihedral angle between the mean planes of the benzene rings is 67.40°. The mean plane of the thiazepine ring is twisted by 36.17° and 77.93° from the mean planes of two benezene rings.

Experimental
A mixture of 2-aminothiophenol (4 mmol) with 3-(3,4-dimethoxyphenyl)-1-(thiophen-2-yl)prop-2-en-1-one (4 mmol) and 3-4 drops of conc. Hydrochloric acid in methanol (10 ml) was heated with stirring at 473 K for 4 h. The reaction was monitored by TLC (hexane/chloroform). After the completion of the reaction, the mixture was extracted in to ether (30 ml), washed successively with cold and dilute hydrochloric acid and water. The solvent was evaporated to dryness, the solid obtained was crystallized from 95° ethyl alcohol solution to get pale yellow needles of the title compound in 90° yield.

Refinement
All hydrogen atoms were located geometrically with C-H = 0.93-0.97) Å and allowed to ride on their parent atoms with U iso (H) = 1.2U eq (aromatic C).  ORTEP diagram of the title molecule with 50% probability ellipsoids.

Figure 2
Packing diagram of molecule, viewed along the crystallographic b axis. Dotted lines represents intermolecular hydrogen bonding.  Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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 S1 0.27208 (