Tetyana V. Beryozkina

Solvent-dependent transformations of polysubstituted 2-acetyl-2,5-dihydrothiophenes to the corresponding 2-hydroxy- or deacetylated derivatives are described. The treatment of a methanolic solution of the dihydrothiophene substrates with sodium methoxide afforded the deacylated products. Conversely, the treatment with sodium ethoxide in an oxygen saturated ethanolic solution produced 2-hydroxy substituted 2,5-dihydrothiophenes.

An azide-free approach toward N -sulfonyl amidines, including phosphorus-containing derivatives based on the reactions of thioamides and thiophosphonyl diamides with iminoiodinanes, was developed.

Heterocyclic compounds containing two exocyclic double bonds are underrepresented in the literature compared with aromatic heterocycles. However, over the past decade, there has been a growing interest among organic chemists, both in Russia and globally, in developing effective methods for the synthesis (or generation) of heterocycles that incorporate two or more exocyclic double bonds. Exocyclic bonds are involved in chemical reactions that yield products of various structural forms, including spirocyclic compounds, condensed heterocycles and indolones featuring a C3 quaternary stereocentre. Among these compounds, compounds with diverse biological activities were identified. Currently available reviews focus on specific types of heterocycles or particular scaffolds, or address catalytic reactions only. This review summarizes and systematizes the literature concerning the synthesis, properties, and biological activities of five-membered heterocycles containing two exocyclic conjugated bonds such as C=C and C=C, C=C and C=N, C=C and C=O, C=O and C=N, and C=C and C=S, with a primary focus on materials published between 2016 and 2025. The bibliography includes 218 references. Keywords: heterocycles, furans, pyrroles, indoles

Metal-free reactions of thioacetamide derivatives with N-sulfonyliminoiodinane, affording isothiazoles under mild conditions, are described. 2-Substituted thioacetamides modified with an enamine moiety undergo reactions with iminoiodinane to form 4,5-disubstituted isothiazoles in 72-93% yields. Reactions of (het)arylidene-substituted 2-thioacetamides and iminoiodinane with subsequent one-pot oxidation of the formed sulfonylisothiazolines afford 3,4,5-trisubstituted isothiazoles in 44-96% yields. A scale-up synthesis of the developed methods was performed. The photophysical properties of the new isothiazoles were investigated, and UV- or blue-light-shifted fluorescence has been detected (QY up to 11%).

Transition metal-catalyzed and noncatalytic reactions of acrylic thioamides with N-sulfonyliminoiodinanes enabling the selective synthesis under mild conditions of a series of fully decorated S- and N,S-containing heterocycles are described. Fine-tuning of the thioamide structure allows selective preparation in good yields of ortho-fused thiophenes, 1,2-thiazines, and spiro-fused isothiazolines. A one-pot thermally induced rearrangement of sulfonylisothiazolines was discovered as a complementary route to thiophenes.

The chemistry of heterocyclic compounds has traditionally been and remains a bright area of chemical science in Russia. This is due to the fact that many heterocycles find the widest application. These compounds are the key structural fragments of most drugs, plant protection agents. Many natural compounds are also derivatives of heterocycles. At present, more than half of the hundreds of millions of known chemical compounds are heterocycles. This collective review is devoted to the achievements of Russian chemists in this field over the last 15–20 years. The review presents the achievements of leading heterocyclists representing both RAS institutes and university science. It is worth noting the wide scope of the review, both in terms of the geography of author teams, covering the whole of our large country, and in terms of the diversity of research areas. Practically all major types of heterocycles are represented in the review. The special attention is focused on the practical applications of heterocycles in the design of new drugs and biologically active compounds, high-energy molecules, materials for organic electronics and photovoltaics, new ligands for coordination chemistry, and many other rapidly developing areas. These practical advances would not be possible without the development of new fundamental transformations in heterocyclic chemistry. Bibliography — 2237 references.

Catalyst-controlled regioselective and diastereoselective reactions of thioamides with diazoamides and 1-sulfonyl-1,2,3-triazoles was developed. Enantioselective and gram-scale syntheses were performed.

A novel and efficient base-catalyzed, transition-metal-free method for the synthesis of diheterocyclic compounds connected by an amidine linker, including apart from the common 1,2,3-triazole ring, either an additional pyrimidinedione, 4-nitroimidazole, isoxazole, 1,3,4-triazole, 2-oxochromone or thiazole ring, has been developed. The process was facilitated by a strong base and includes the cycloaddition reaction of 3,3-diaminoacrylonitriles (2-cyanoacetamidines) to heterocyclic azides followed by a Cornforth-type rearrangement to the final products. The reaction is tolerant to various N-monosubstituted 3,3-diaminoacrylonitriles and to different heterocyclic azides. The developed method has a broad scope and can be applied to obtain a variety of N-heteroaryl-1,2,3-triazole-4-carbimidamides with alkyl, allyl, propargyl, benzyl, cycloalkyl, and indolyl substituents at the N¹ position .

It was shown that the reaction of 2-cyanothioacetamides with hydrazine involves both cyano- and thioamide groups, and 3,5-diaminopyrazoles are formed. In the reaction of 2-cyano-3-(dimethylamino)-N,N-dimethylprop-2-enethioamides with hydrazine and its derivatives, the interaction proceeds with the participation of cyano- and enamine groups, not affecting the thiocarbamoyl group, and leads to the formation of 4-thiocarbamoylpyrazoles. A synthesis method has been developed and a series of 1-substituted-4-thiocarbamoyl pyrazoles has been thus synthesized. The structure of the reaction products was studied using NMR spectroscopy and mass spectrometry and confirmed by X-ray diffraction analysis.

An efficient base-catalyzed, metal-free method for thesynthesisof 5-amino-1,2,3-triazole-4-N-sulfonyl- and arylimidamides,directed by the structure of the amidine group, has been developed.It is based on a previously unknown tandem process involving cycloadditionreaction to 3,3-diaminoacrylonitriles (2-cyanoacetamidines) with aryl(alkyl)sulfonylor aryl azides and Cornforth-type rearrangement. During the reactionoptimization, different factors were found to facilitate the titlereaction, which include the use of a strong base and N-mono- or N,N & PRIME;-disubstituted3,3-diaminoacrylonitriles. The reaction is tolerant to variously N-monosubstituted and N,N & PRIME;-disubstituted 3,3-diaminoacrylonitriles and to various aryl-and aryl/alkyl sulfonyl azides. The developed method has a broad scopeand can be applied to obtain a variety of 5-amino-1,2,3-triazole-4-carbimidamidesbearing at the N-1 position alkyl, allyl, propargyl, benzyl,cycloalkyl, and heteroaryl substituents and sulfonyl and aryl substituentsat the amidine group. Post-cyclization reactions of prepared 5-amino-1,2,3-triazoleswith DMF-DMA DMA-DMF leads to 1,2,3-triazolo[4,5-d]pyrimidines, 8-aza purine analogues demonstrating the applicabilityof the prepared compounds in organic synthesis.