A highly efficient PASE approach to a new class of polycyclic purine derivatives has been proposed. The strategy includes a consecutive reduction, auto-aromatization, and heterocyclization of the initial nitrobenzimidazopyrimidines obtained by a three-component condensation. It was shown that reduction of nitrobenzimidazopyrimidines by metals in acidic media was more efficient than heterogeneous hydro­genation. Novel derivatives of benz[4,5]imidazo[1,2-a]purines were obtained­ in good yields and the proposed structure was confirmed by X-ray crystal structure analysis. The obtained convergent benzimidazopurines combine two relevant medicinal chemistry scaffolds – benz­imidazole and purine.

Nitrogen-containing heterocyclic compounds are the basis of many natural and synthetic biologically active substances. 1 More than two-thirds of the known drugs used in clinical practice contain heterocyclic and, above all, nitrogen-containing fragments within their structure. Over the past decades, the chemistry of aza-heterocycles has received considerable attention due to the wide spectrum of their biological activity and numerous therapeutic applications in medicine.Of nitrogenous heterocycles, azoloazines containing fragments similar to the natural heterocycles purines and pyrimidines are currently of great practical importance. Thus, non-natural nucleosides abacavir, famciclovir, remdesivir are known, which are the products of structural modifications of all the components of the nucleotide exhibiting excellent indicators of antiviral action (Fig. 1). [2][3][4] In addition to the generally accepted nucleoside forms, the azoloazines themselves are relevant in the search for means of combating diseases on a global scale. Nitroazolo- [5,1-c][1,2,4]triazines and nitroazolo [1,5-a]pyrimidines, a new family of antiviral compounds has been found. 5 The

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The nucleophilic substitution of the nitro group of 4-alkyl-6-nitro-4,7-dihydro-1,2,4-triazolo[5,1-c][1,2,4]triazine-7-ones on the example of interaction with morpholine was studied. It is established that under the action of excess cycloalkylimine at room temperature the unusual easy disclosure of triazine cycle with the formation of sterically hindered hydrazones occurs which are the key intermediates for further transformations. The carrying of reaction at elevated temperatures leads to the formation of products of substitution of the nitro group with the amine and also with morpholyl hydrazones which are the products of hydrolysis of amides of hydrazones and subsequent decarboxylation. Thus, the nucleophilic substitution of the nitro group in the described triazolotriazines ows through the ANRORC mechanism.

This review is focused on the synthetic strategies to heterocyclic C-nucleosides and covers the literature from 2011 to 2021. The main attention is paid to the following three approaches: the direct C-C coupling of a carbohydrate moiety with a preformed aglycon unit, the construction of a (pseudo)sugar residue on a pre-formed aglycon, and the construction of an aglycon on a pre-formed (pseudo)sugar. In each Section, the literature data are categorized in terms of the size of aglycon from simple to complex, the advantages and drawbacks of the reviewed approaches are discussed.