Synthesis of new zwitterionic benzoyl(5-(halomethyl)-5-methyl-5,6-dihydrothiazolo[2,3-b][1,3,4]thiadiazole-4-ium-2-yl) amides

Synthesis of 5-(benzoylamino)-2-(methallylsulfanyl)-1,3,4-thiadiazole (2) was carried out by interaction of 5-amino-1,3,4-thiadiazole-2-thion with methallyl chloride in ethanol in the presence of sodium ethylate and subsequent acylation of the amino group with benzoyl chloride. It has been shown for the first time that electrophilic cyclization of thiadiazole (2) under action of iodine and bromine in dichloromethane proceeds to form the corresponding derivatives of 2-benzoylamino-5-halomethyl-5-methyl-5,6-dihydrothiazolo[2,3- b ][1,3,4]thiadiazolium. Upon further isolation of the reaction products from acetone solutions, dehydrohalogenation occurs with the formation of zwitterionic benzoyl(5-(halomethyl)-5-methyl-5,6-dihydrothiazolo[2,3- b ][1,3,4]thiadiazol-4-ium-2-yl)amides. The structure of the obtained compounds has been studied by GCMS, 1H and 13C NMR methods. Furthermore, the crystal structure of compound 5a has been characterized by X-ray diffraction analysis. From the X-ray data performed on an automatic four-circle D8 Quest Bruker diffractometer (MoKα radiation, λ = 0.71073 Å, graphite monochromator) at 293 K it follows that compound 5a crystallizes in a monoclinic crystal lattice. The unit cell consists of four C13H12N3IS2O units. Parameters of the zwitterion 5a cell: a = 9.768(5), b = 10.984(5), c = 14.299(6) Å; β = 101.54(2) deg.; V = 1503.2(12) Å3. The crystal structure of compound 5a is formed due to intra- and intermolecular short contacts S1···O1 (2.44 Å), O1···C4 (2.44 Å), as well as a large number of weak hydrogen bonds N···H-C, S···H-C, O···H-C in the range of 2.35-2.97 Å. The iodine atom of the iodomethylene substituent is located above the condensed heterocyclic system, forming a single weak intramolecular contact I1···C1 (3.66 Å) with the bridging carbon atom of the thiazolo-thiadiazole system. Complete tables of coordinates of atoms, bond lengths and valence angles for structure 5a are deposited in the Cambridge Structural Data Bank (No. 2168623; deposit@ccdc.cam.ac.uk; https://www.ccdc.cam.ac.uk ).