Thioanalogues of N-1-methylanabasine and nicotine – Synthesis and structure

The synthesis, spectral characteristics and structures of N-1-methyl-6-(pyridin-3-yl)piperidine-2-thione (1) (thioanalogue of N-1-methylanabasine) and N-1-methyl-(5-pyridin-3-yl)pyrrolidine-2-thione (2) (thioanalogue of nicotine) are reported. Both compounds were obtained using Lawesson’s reagent. The structures of compounds 1 and 2 are confirmed by NMR, IR, UV and mass spectroscopy, as well as, by X-ray diffraction analysis. Pyridine ring of compound 1 adopts a pseudo-axial orientation in solution, as well as in a solid state. A substantial lengthening of the CS bond in the crystals of 1 is interpreted as a sign of an enhanced electron delocalization within the thiolactam group due to the presence of several CH groups in the nearest vicinity of the sulfur atom. In the crystals of 2, which differ from 1 in that the relatively puckered piperidine-2-thione moiety is replaced by the flat pyrrolidine-2-thione ring, no short CH⋯S(C) contacts are observed. Instead, the packing is governed by stacking interactions between pyridine rings. The pyrrolidine and pyridine rings in 2 are nearly perpendicular to each other and the pyrrolidine moiety adopts a flattened half-chair conformation.