2-(1-Benzothiophen-2-yl)-4H-1,3,4-oxadiazin-5(6H)-one

In the title compound, C11H8N2O2S, the oxadiazinone ring is nearly planar [maximum deviation = 0.016 (4) Å], and is approximately coplanar with the benzothiophene ring system [dihedral angle = 3.1 (5)°]. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming chains running along the b-axis direction.


Comment
Noncompetitive α-amino-3-hydroxy-5-methyl-4-isoxazolepropanoic acid (AMPA) receptor antagonists have actively been explored, driven by the belief that such drugs would exercise effectiveness independent of glutamatelevels and the synaptic membrane polarization state, with minor influence on normal glutamatergic activity compared with competitive antagonists (De Sarro et al., 2005). Commercially available 2,4-diphenyl-4H-1,3,4-oxadiazin-5-one was selected as a suitable starting compound with a novel structure versus other HTS (high throughput screening) hit compounds and known noncompetitive AMPA antagonists (Shigeki et al., 2012). The title compound is a new oxadiazin compound with a similar structure to it. We synthesized it and report here its crystal structure.
The molecular structure of the title compound is shown in Fig. 1. The benzothiophene ring makes a dihedral angle of 3.1 (5)° to oxadiazin ring.
As shown in Figure 2, the molecules are linked by N-H···O and weak S···S (Table 1) bonds into a three-dimensional network, which consolidate the crystal packing.

N′-(2-chloroacetyl)benzo[b]
thiophene-2-carbohydrazide (0.27 g, 1 mmol) was dissolved in 10 ml acetonitrile, after which potassium carbonate (0.28 g, 2.0 mmol) was added and the mixture was refluxed for 3 h under heating. The reaction solution was left and cooled to room temperature, evaporated, diluted with EtOAc, washed with water and brine, and then dried over MgSO 4 . After the drying agent was filtered off, the product was evaporated and the resulting crystalline residues were recrystallized from n-hexane and EtOAc to give the compound (0.19 g, 0.8 mmol, 80.0%) as a yellow crystal suitable for X-ray analysis.

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

Figure 2
A packing diagram of (I). Intermolecular hydrogen bonds are shown as dashed lines. 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 > σ(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.