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, C(20)H(23)N(3)OS, (II), and C(20)H(21)N(3)OS, (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) A between pyridine rings. In the crystal structure of (III), the molecules are linked by C-H...O hydrogen bonds and C-H...pi interactions.