Synthesis and study of the structure of iodine-containing imidazo[2,1-b][1,3]thiazinium systems

Heterocyclization of S-alkenyl derivatives of 1-methylimidazole-2-thiol (1-methyl-2-prenyl-sulfanylimidazole (1), 1-methyl-2-cinnamylsulfanylimidazole (4), and 2-(3-butenyl)sulfanyl-1-methyl-imidazole (7)) has been studied for the first time under the action of iodine (iodocyclization) in various solvents (chloroform, dichloro-methane, glacial acetic acid), and at different substrate and iodine ratios (1 : 1, 1 : 2). It has been found that the interaction of compounds 1, 4, 7 with iodine proceeds regioselectively, regardless of the reaction conditions, and it is accompanied by the linear annelation of the thiazinium ring and formation of a bicyclic fused heterocyclic system. As a result, new iodine-containing imidazo[2,1- b ][1,3]thiazinium systems have been synthesized - 6-iodo-1,5,5-trimethyl-6,7-dihydro-5 H -imidazo[2,1- b ][1,3]hiazinium polyiodide / iodide (2, 3), 6-iodo-1-methyl-5-phenyl-6,7-dihydro-5 H -imidazo[2,1- b ][1,3]thiazinium triiodide / iodide (5, 6), and 6-iodomethyl-1-methyl-6,7-dihydro-5 H -imidazo[2,1- b ][1,3]thiazinium iodide (9). The structure of the synthesized compounds has been studied and proved by 1H and 13C NMR spectroscopy. The evidence for heterocyclization reactions of alkenyl sulfides 1, 4, and 7 is the absence of signals for the alkenyl protons and the presence of a more complex splitting pattern of signals for the thiazinium ring protons in the 1H NMR spectra of heterocyclization products. The structures of polyiodide 2 and triiodide 5 have been unambiguously established and characterized by X-ray diffraction analysis. According to the X-ray analysis data, the cell of polyiodide 2 contains two heterocyclic cations, a triiodide anion, and an iodide anion. In the triiodide crystal 5 heterocyclic cations correspond to two types of crystallographically independent triiodide anions: one cell contains eight molecules of a heterocyclic cation and eight triiodide anions. The structural organization in the crystals is due to short contacts between atoms: I(4)∙∙∙H(3) (2.95 Å), I(4)∙∙∙I(1) (3.57 Å), H(8a)∙∙∙I(2) (3.13 Å) (in crystal 2), I(2)∙∙∙I(4) (3.95 Å), I(5)∙∙∙H(5) (3.14 Å), I(4)∙∙∙H(7a) (3.12 Å), I(4)∙∙∙H(7b) (3.17 Å) (in crystal 5).