A procedure for the preparation of the title salts via regioselective halocyclization of 3-S-propargylthio-4Н-1,2,4-triazoles is reported. Stereoselectivity of electrophilic heterocyclization depends on the nature of the electrophilic reagent: bromination is better than iodobromination and iodination. The heterocyclization with tellurium tetrahalogenides leads to the formation of a mixture of geometric isomers of the salts. Their structure was confirmed by 1H NMR, 13C NMR, НМВС and single crystal X-ray diffraction analysis.

A convenient procedure for the regioselective preparation of [1,3]thiazolo[3,2-b][1,2,4]triazol-7-ium 10 and [1,2,4]triazolo[5,1-b][1,3]thiazin-4-ium salts 9 via regioselective electrophilic cyclization of 3-[(2-alken-1-yl)sulfanyl]-4H-1,2,4-triazoles 3 is reported. Direction of electrophilic heterocyclization strongly depends on nature of the alkenyl substitutent.

The reactions of [1,3]thiazolo[3,2-b][1,2,4]triazol-7-ium salts with nucleophiles were investigated. Theoretical investigation of reactivity descriptors and structural parameters of [1,3]thiazolo[3,2-b][1,2,4]triazol-7-ium cation was carried out, and the reactivity centers of the model salts were located. An efficient general method for the synthesis of novel poly-functional derivatives of symmetric triazoles from [1,3]thiazolo[3,2-b][1,2,4]triazol-7-ium halides was developed. The structures of the synthesized compounds were confirmed using proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance (13C NMR), Fourier-transform infrared spectroscopy (FTIR) and single-crystal X-ray analysis.

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The sources, describing cycloaddition reactions that lead to obtaining of substituted 1,2,4-triazoles and their fused derivatives were reviewed. The review article covers the literature data published in the period 2011-2021.Synthetic particularities of cycloaddition products, the optimization of reaction conditions, factors that influence on the direction of the reaction are reasonably mentioned. Cycloaddition reactions are presented as convenient method for obtaining of as functional 1,2,4-triazoles, as well as their fused derivatives. CONTENTS1. Introducrion 2. Cycloaddition reactions leading to formation of 1,2,4-triazole derivatives 3. Cycloaddition reactions leading to formation of fused derivatives of 1,2,4-triazole

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