3,4-Dihydro-1,4-benzothiazepin-5(2H)-one

In the molecule of the title compound, C9H9NOS, the seven-membered ring has a twist conformation. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link the molecules into centrosymmetric dimers.

In the molecule of the title compound, C 9 H 9 NOS, the sevenmembered ring has a twist conformation. In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into centrosymmetric dimers.
In the molecule of (I), (Fig. 1) the bond lengths and angles are within normal ranges (Allen et al., 1987). Ring A (C3-C8) is, of course, planar, while ring B (S/N/C1-C3/C8/C9) is not planar and has a twisted conformation.

Experimental
The title compound, (I), was prepared by the literature method with a minor change (Ishibashi et al., 2001). 2-Mercaptobenzoic acid methyl ester (3.3 g, 19.6 mmol) was added to the solution of sodium (0.5 g, 22.0 mmol) in ethanol (20 ml). The mixture was stirred at room temperature for 10 min, and then 2-oxazolidinone (1.7 g, 19.8 mmol) was added. The mixture was heated under reflux for 6 h. The solvent was evaporated off, water (15 ml) was added to the residue, and the whole mixture was extracted with ethyl acetate (15 ml×3). The combined ester layer was dried with sodium sulfate and evaporated.
The residue was recrystallized from ethanol and dried in vacuum at 323 K to give the title compound as a white solid (yield; 60%, m.p. 466-468 K) (Ishibashi et al., 2001, m.p. 465-466 K). Crystals of (I) suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

Refinement
H atoms were positioned geometrically, with N-H = 0.86 Å (for NH) and C-H = 0.93 and 0.97 Å for aromatic and methylene H, respectively, and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C,N). Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

Data collection
Enraf-Nonius CAD-4 diffractometer R int = 0.022 Radiation source: fine-focus sealed tube θ max = 26.0º Monochromator: graphite θ min = 1.7º T = 294(2) K h = 0→9 ω/2θ scans k = 0→10 Absorption correction: ψ scan (North et al., 1968) l = 0→29 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.