Dedicated to the 75^th anniversary of Uzhhorod National University Condensed heterocycles are well-known for their excellent biological effects and they are undeniably important compounds in organic chemistry. Electrophilic cyclization reactions are widely used for the synthesis of mono-heterocyclic compounds. This review highlights the utility of electrophilic cyclization reactions as an effective generic tool for the synthesis of various condensed heterocycles containing functional groups that are able to undergo further chemical transformations, such as nucleophilic substitution, elimination, re-cyclization, cleavage, etc. This review describes the reactions of unsaturated derivatives of different heterocycles with various electrophilic agents (halogens, arylsulfanyl chlorides, mineral acids) resulting in annulation of an additional partially saturated heterocycle. The electrophilic reaction conditions, plausible mechanisms and the use of such transformations in organic synthesis are also discussed. The review mainly focuses on research published since 2002 in order to establish the current state of the art in this area. 1 Introduction 2 Electrophilic Cyclization Pathways Involving a Nitrogen Nucleo­philic Center 3 Electrophilic Cyclization Pathways Involving a Chalcogen Nucleophilic Center 3.1 Sulfur Centers 3.2 Oxygen Centers 3.3 Selenium Centers 4 Strategies and Mechanisms 5 Conclusion Received: 16 February 2021 Accepted after revision: 09 April 2021 Publication Date: 19 May 2021 (online) © 2021. Thieme. All rights reserved Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

A procedure for the preparation of the title salts via regioselective halocyclization of 3- S -propargylthio-4 Н -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 ¹ H NMR, ¹³ C NMR, НМВС and single crystal X-ray diffraction analysis.