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A divergent route for the synthesis of new derivatives of 4,11-diaminoanthra[2,3-b]thiophene-5,10-dione was developed based on the introduction of cyclic amines to the terminal positions of 4,11-aminoalkyl groups. Modification of the side chains of anthra[2,3-b]-thiophene-5,10-dione increases the affinity of ligands to DNA duplex and decreases the affinity to G-quadruplexes. An analysis of the structure–activity relationship showed that 2-(piperidin-1-yl)ethylamine is the most promising side chain fragment for the development of new double-stranded DNA ligands. The ability of new ligands to bind to DNA duplex correlates with inhibition of tumor cell growth, which indicates the prospects for a further search for new antitumor compounds or chemical probes for duplex-forming nucleic acid sequences among 4,11-diaminoanthra[2,3-b]thiophene-5,10-diones.

The microreview is devoted to novel and modified methods for the synthesis of 1-benzothiophene-3-carboxylic acid derivatives including both the assembly of the heterocyclic core and the functionalization of position 3 of benzothiophene. The review covers key studies published since 2015.

Methods have been developed for the synthesis of anthra[2,3-b]thiophene-3(2)-carboxylic acids and their derivatives through modifications of 4,11-dibutoxy-3-methylanthra[2,3-b]thiophene-5,10-dione. A scheme involving methyl group transformations was proposed for the preparation of dibutoxyanthra[2,3-b]thiophene-3-carboxylic acid, including reactions of radical halogenation, hydrolysis, and oxidation of a 3-formyl derivative. 4,11-Dihydroxy-3-methylanthra[2,3-b]thiophene-2-carboxylic acid was synthesized from the appropriate carbonitrile, obtained by Rosenmund–von Braun reaction from 2-bromo-4,11-dibutoxy-3-methylanthra[2,3-b]-thiophene-5,10-dione.

3-carboxylate by using vicarious substitution of hydrogen, followed by intramolecular reductive heterocyclization. Some chemical properties of the target compound were characterized. As observed for the first time in the series of linear hetaryl-fused anthraquinones, the alkylation of hydroxy groups in naphtho[2,3-f]indole-5,10-diones gave not only 4,11-dialkoxy derivatives, but also the isomeric 5,10-dialkoxy derivatives of naphtho[2,3-f]indole-4,11-dione.

In this microreview, recent advances in the development of methods for indole cyclization, leading to indole-3-carboxylic acid derivatives, are highlighted. Selected works published since 2013 are covered.

We have developed an effective method for the synthesis of 4,11-diaminoanthra[2,3-b]furan-5,10-dione and 4,11-diaminoanthra[2,3-b]-thiophene-5,10-dione derivatives based on the substitution of 4,11-alkoxy groups with n-butylamine and subsequent oxidative dealkylation of n-butylamino groups via treatment with tetrabutylammonium hydroxide in DMSO.

The synthesis of anthrafurandiones, by means of which it is possible to obtain a series of previously unknown 2-substituted derivatives of 4,11-dimethoxy-5,10-dioxoanthra[2,3-b]furan-3-carboxylic acids after protection of the hydroxy groups of the initial 2,3-dibromoquinizarin, was optimized. Unlike most of the analogs, 4,11-dimethoxy-5,10-dioxo-2-(trifluoromethyl)anthra[2,3-b]furan-3-carboxylic acid ester is best synthesized from 2,3-dibromoquinizarin with subsequent methylation of the hydroxy groups. The heterocyclic ring of this ester was found to have low stability during the action of alkalis. This, together with the side deacetylation of the intermediate, is probably the main reason for its low yield at the heterocyclization stage.

Derivatives of anthra[2,3-b]furan-5,10-diones hold promise for various fields of science and technology, especially in the search for biologically active compounds. This review covers all currently known methods for the cyclization of linear anthrafurandiones, the first examples of which were synthesized approximately 30 years ago. The material has been arranged mainly in the order of increasing degree of substitution in anthrafurandiones. All the literature methods for functional group transformations providing access to a range of anthrafurandiones unavailable by direct heterocyclization have been considered separately.

A new method was developed for the synthesis of 4,11-dimethoxyanthra[2,3-b]furan-5,10-dione and some of its previously unknown derivatives. The method was based on heterocyclization of 2-(3-halo-anthraquinon-2-yl)formylacetic acid derivatives by the action of bases, leading to methyl 4,11-dimethoxy-5,10-dioxoanthra[2,3-b]furan-3-carboxylate. Subsequent acid hydrolysis of the ester group and decarboxylation of the obtained acid gave 4,11-dimethoxyanthra[2,3-b]furan-5,10-dione. The low yield of the target compound was probably due to heterocycle instability in the 5,10-dioxo-anthra[2,3-b]furan-3-carboxylic acid derivatives in basic medium.

A new method was developed for synthesis of anthra[2,3-b]furan-5,10-dione derivatives. The key compound for annelation of the furan fragment to the anthraquinone chromophor is the previously unknown analog of salicylaldehyde, 1,4-dimethoxy-3-formyl-2-hydroxyanthraquinone, which we have synthesized by the Miller–Loudon–Schneider reaction. A chain of sequential transformations was used for its conversion into the target 4,11-dihydroxyanthra[2,3-b]furan-5,10-dione (furanoquinizarine): O-alkylation of the starting formylhydroxyanthraquinone with bromoacetic acid esters, cyclo-dehydration of the 3-formylanthraquinon-2-ylacetic acid esters in the presence of bases, hydrolysis of the obtained esters to 4,11-dimethoxy-5,10-dioxo-5,10-dihydroanthra[2,3-b]furan-2-carboxylic acid, its decarboxylation, and demethylation of the obtained 4,11-dimethoxyanthra[2,3-b]furan-5,10-dione.

A previously unknown recyclization of an 11-acyldipyrido[1,2-a:1′,2′-c]imidazolium cation to 8-formyl-9-methyl(aryl)pyrido[1,2-a]benzimidazoles has been discovered. The proposed reaction mechanism includes a selective opening of one of the pyridinium rings and the formation of a benzaldehyde fragment via condensation of the intermediate with the participation of the acyl group.

A convenient method of synthesis of 2-(methoxycarbonylmethylene)-substituted imidazolidines and imidazolidinium bromides, and also of bicyclic diazo compounds has been developed starting from methyl bromopropiolate and ethylenediamine and its derivatives.

The reaction of methyl bromopropiolate with Β-amino alcohols containing a primary amino group generally results in the formation of 2-(methoxycarbonylmethyl)-δ2-1,3-oxazolines, while in the reaction with N-methyl- and N,N-dimethyl-substituted Β-aminoalcohols, 2-(methoxycarbonylmethylene)-1,3-oxazolidines, or their salts are formed.