Fused heterocyclic systems with 1,2,4‐triazole scaffold arouse great interest from researchers in the branch of heterocyclic and medical chemistry because of their wide biological activities as they are considered as fungicidal, antimicrobial, analgesic, bronchodilators, antioxidant, anti‐inflammatory agents, and they are G‐quadruple stabilizers; the molecular docking data for coumarin‐containing 1,2,4‐triazoles indicate their ability to act as a urease inhibitor. Therefore, the present review aims to investigate new trends in the chemistry of heterocycles incorporating thiazolo[3,2‐b][1,2,4]triazoles, thiazolo[2,3‐c][1,2,4]triazoles, thiazino[5,1‐b][1,2,4]triazoles, thiazino[3,4‐b][1,2,4]triazoles, triazolothiazepines, and their biological characteristics. The main sections discuss: (a) the synthetic routes to the production of substituted fused heterocyclic systems, which include condensation reactions, multiple bond annulation, and the reactions of electrophilic heterocyclization. (b) Description of chemical and biological characteristics of these fused heterocycles.

A facile access to novel condensed system of [1,3]thiazolo[2′,3′:3,4][1,2,4]triazolo[1,5-a]pyrimidine is presented. This protocol consists of bromine-assisted direct electrophilic heterocyclization of 3-Nallylamine-5,6-dihydro[1,3]thiazolo[2,3-c] [1,2,4]triazole. The bromination took place in acetic acid and gave a good yield of the target product, which was dehydrobrominated by sodium acetate action.

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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.

The development of methods of obtaining new condensed heterocyclic compounds from 1,2,4-triazolethiones is an urgent problem, since these compounds possess a broad spectrum of physiological activity as analgetic, vasodilating, anti-inflammatory, and bactericidal agents and show tranquilizing action [1-3]; they are used as highly effective additives to photomaterial [4], and also are inhibitors of corrosion of nonferrous metals and alloys based on them [5].