Three novel benzothia­zine-fused triazoles as potential centrally acting muscle relaxants

The structures of the novel triazolobenzothia­zines 2,4-di­hydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]thia­zin-1-one (IDPH-791), C₉H₇N₃OS, (I), a potential muscle relaxant, its benzoyl derivative, 2-(2-oxo-2-phenyl­ethyl)-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]thia­zin-1-one, C₂₀H₁₇N₃O₄S, (II), and the [beta]-keto ester derivative, ethyl 3-oxo-2-(1-oxo-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]thia­zin-2-yl)-3-phenylpropano­ate, C₁₇H₁₃N₃O₂S, (III), are the first examples of benzothia­zine-fused triazoles in the crystallographic literature. The heterocyclic thia­zine rings in all three structures adopt a distorted half-chair conformation. Com­pound (III) exists in the trans-[beta]-diketo form. Other than N-H...O hydrogen bonds in (I) forming dimers, no formal inter­molecular hydrogen bonds are involved in the crystal packing of any of the three structures, which is dominated by C-H...O/N and [pi]-[pi] stacking inter­actions.