Structure of 4,6-dimethylisothiazolo[5,4-b]pyridin-3(2H)-one and its 2-[4-(2-methylphenyl) piperazin-1-ylmethyl] derivative

The crystal and molecular structures of 4,6-dimethylisothiazolo5,4-b]pyridin-3(2H)-one, C₈H₈N₂OS, 1, and its 2-4-(2-methylphenyl)piperazin-1-ylmethyl] derivative, C₂₀H₂₄N₄OS, 2c, are described. These compounds crystallize in the monoclinic system in the space group P2 ₁/c. The cell constants for compound 1 are a = 5.049(1), b = 14.897(1), c = 11.330(1) Å, = 98.07(1)°, Z = 4, T = 293 K, and D _cal = 1.419 g cm^–3, and for compound 2c are a = 15.525(1), b = 12.021(1), c = 10.911(1) Å, = 106.42(1)°, Z = 4, T = 293 K, and D _cal = 1.253 g cm^–3 The structures were solved by direct methods and refined to R values of 0.0411 and 0.0380 for 1640 and 3504 reflections for 1 and 2c, respectively. The analysis of the geometry and difference electron density map reveal that the dimethylisothiazolopyridine 1 exists in the amino tautomeric form in the crystalline state. The conformation of the o-methylphenylpiperazine part of the molecule 2c strongly depends on the substituents effect in the phenyl ring and is very similar to those observed in crystals for other investigated arylopiperazine derivatives of the isothiazolopyridine.