4,6-Dimethyl-2-[(4-phenyl­piperidin-1-yl)meth­yl]isothia­zolo[5,4-b]pyridin-3(2H)-one and 4,6-dimethyl-2-[(4-phenyl-1,2,3,6-tetra­hydro­pyridin-1-yl)meth­yl]isothia­zolo[5,4-b]pyridin-3(2H)-one

In the crystal structures of the title compounds, C₂₀H₂₃N₃OS, (II), and C₂₀H₂₁N₃OS, (III), significant differences occur in the conformation of, respectively, the phenyl­piperidine and phenyl­tetra­hydro­pyridine substituents at the 2-position of the iso­thiazolo­pyridine system. The piperidine ring adopts a chair conformation, while the tetra­hydro­pyridine ring assumes a half-chair form. The phenyl­piperidine and phenyl­tetra­hydro­pyridine fragments exhibit different conformations resulting from the steric and conjugation effects in the phenyl ring, respectively. Theoretical calculations show that both conformations are energetically stable and correspond to a minimum of energy for the analyzed systems. The mol­ecular packing in (II) is influenced by [pi]-[pi] inter­actions of the iso­thiazolo­pyridine systems, with a shortest centroid-to-centroid separation of 3.5843 (11) Å between pyridine rings. In the crystal structure of (III), the mol­ecules are linked by C-H...O hydrogen bonds and C-H...[pi] inter­actions.