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A green protocol has been developed for the synthesis of simple coumarins and linear pyrano[2,3-f] and [3,2-f]indoles by the reaction of phenol derivatives with β-ketoesters under ball milling at ambient temperature in the presence of methanesulfonic acid.

A different type of MnO

Received: 20.10.2020. Accepted: 19.12.2020. Published:30.12.2020. An electron-deficient series of 1,2,4‑triazines and quinazoline have been used for cross-dehydrogenative coupling with 1,3‑dihydroxy and 1,3‑dimethoxyxanthones to give stable nucleophilic addition products. The adducts and their subsequent oxidation products were obtained in good yields and the structures of the compounds were confirmed by 1H NMR spectroscopy. These results expand the scope of the methodology of nucleophilic substitution of hydrogen with the participation of xanthones with azines. Moreover, this methodology makes it possible to obtain new organic materials based on xanthones, which have a wide spectrum of biological activity. This work was finantionally supported by the Presidential Council on Grants NSh-2700.2020.3 and Ministry of Science and Higher Education of the Russian Federation (project FEUZ-2020-005).

This review summarizes and systematizes the literature on the anti-HIV activity of plant coumarins with emphasis on isolation and the mechanism of their antiviral action. This review summarizes the information on the anti-HIV properties of simple coumarins as well as annulated furano- and pyranocoumarins and shows that coumarins of plant origin can act by several mechanisms: inhibition of HIV reverse transcriptase and integrase, inhibition of cellular factors that regulate HIV-1 replication, and transmission of viral particles from infected macrophages to healthy ones. It is important to note that some pyranocoumarins are able to act through several mechanisms or bind to several sites, which ensures the resistance of these compounds to HIV mutations. Here we review the last two decades of research on the anti-HIV activity of naturally occurring coumarins.

The chemical equivalence of the hydroxy groups in the 5,7-dihydroxycoumarin core has challenged synthetic chemists to develop short and efficient strategies for the selective modification of one of the hydroxy groups leaving the second intact. Over the past 100 years, chemists have proposed various approaches to distinguishing between these two groups according to their reactivity. While the early syntheses included simple nonselective reactions of both hydroxy groups and the subsequent separation of mixtures of the 5-O- and 7-O-isomers formed, recent sophisticated approaches often include the introduction of protective groups for selective directing reactions or the completely controlled construction of the 5,7-dihydroxycoumarin framework by Horner–Wadsworth–Emmons reaction. This review discusses in detail approaches towards unsymmetrically substituted 5,7-dihydroxycoumarins as well as factors influencing 5-O vs. 7-O regioselectivity of reactions of 5,7-dihydroxycoumarins. This review covers all the literature since 1921 with an emphasis on recent works. This critical review may facilitate the synthesis of new drug candidates as well as the total synthesis of natural products.1 Introduction2 O-Modification of 5,7-Dihydroxycoumarins2.1 Alkylation/Alkenylation2.2 Acylation2.3 Sulfonylation2.4 Silylation2.5 Acylation Followed by Alkylation3 Other Approaches3.1 Synthesis from Substituted Phloroglucinol3.2 Synthesis from Derivatives of 2-Acylphloroglucinol4 Conclusion

1-Nicotinoylbenzotriazole (NicBt) was uncovered as an efficient protecting agent for the site-selective acylation of resorcinol-type phenolic groups with almost equal reactivity. The use of NicBt allows selective protection of the 7-OH group in 5,7-dihydroxycoumarins in one simple scalable step, while combination of the nicotinoylation with tosylation–denicotinoylation or silylation–denicotinoylation yields 5-OH-protected 5,7-dihydroxycoumarins. Furthermore, nicotinoylated 5,7-dihydroxycoumarins proved useful in a gram-scale three-step preparation of a 2,2-dimethylpyrano[2,3-f]coumarin, a key intermediate for the synthesis of calanolide A, an HIV reverse transcriptase and Mycobacterium tuberculosis inhibitor, and its active analogues.

A series of coumarin-pyridine-based push-pull fluorophores were prepared starting from 1,2,4-triazines by using direct C-H functionalization (SNH-reaction)–Diels-Alder–retro Diels-Alder domino reaction sequence. This efficient synthetic strategy allowed to obtain a series of 19 coumarin-pyridine fluorophores. Their photophysical properties were studied. While pyridine-substituted derivatives of 4-alkylcoumarins may be considered as alternative to coumarin dyes characterized by emission maxima mainly in a visible region with wavelengths of 402–415 nm, absorption in the UV range at 210–307 nm, and good photoluminescence quantum yields of 6–19%, all the derivatives of 4-phenylcoumarin did not exhibit any noticeable fluorescence. More detailed photophysical studies were carried out for two the most representative derivatives of 4-alkyl-coumarin-pyridines to demonstrate their positive solvatochromism, and the collected data were analyzed by using Lippert-Mataga equation, as well as Kosower and Dimroth/Reichardt scales. The obtained results demonstrate that the combining two chromophore systems, such as 2,5-diarylpyridine and coumarin ones, is promising in terms of improving the photophysical properties of the new coumarin-pyridine hybrid compounds.

This review summarizes the data on the synthesis and modification of various triazine derivatives using a copper additive as catalyst or mediator. The first part is devoted to the synthesis of 1,3,5-, 1,2,4- and 1,2,3-triazines from suitable amidine, hydrazide, hydrazone, azide, and amide derivatives and 1,3-dipoles as well as via ring extension of pyrazole, while the second part discusses modification of triazines using Sandmeyer, Sonogashira, Liebeskind-Srogl, Ullmann, and other types of reactions.

A new synthetic protocol for nucleophilic substitution of hydrogen­ in quinoxalones and pteridinones by the action of 5,7-di­hydroxycoumarins and related m-dihydroxybenzene compounds has been developed. The C–C coupling reaction proved to proceed smoothly under rather mild conditions, thus giving the corresponding C–H functionalized products in good yields. The advantages of this environmentally benign protocol are high regio- and chemoselectivity, and an easy workup procedure. Direct incorporation of the coumarin moiety into the pyrazine ring in pteridines or quinoxalines provides a short pathway to pyrazine-coumarin hybrid compounds.

Natural stilbenes are of significant interest for their wide range of biological activity and other prospects for the development of medical and bioorganic chemistry. The most well-known of stilbenoids is resveratrol, which is produced by some plants in response to mechanical damage or injured by microorganisms and bacteria. Resveratrolis interesting for the chemical and biological industry for its wide spectrum of biological activity. However, it cannot be considered as a medicine because of its poor bioavailability and fast metabolism. The synthesis of a close analog such as 3,3',4,4',5,5'-hexamethoxystilbene (HMS) and coupling of its with an azaheterocyclic compounds, will provide a new series of compounds with potential biological activity against socially significant compounds.

A new method for the direct metal-free C–H functionalization of electron-deficient triazines with fragments of naturally occurring and synthetic 5,7-dihydroxycoumarins is reported. It has been found that the reaction of 5,7-dihydroxycoumarins with triazines proceeds under mild conditions, showing a high chemo- and regioselectivity.

This article presents the optimized procedure for the annulation of the pyran ring in acridone derivatives, which makes it possible to obtain acronycine and its derivatives in high yield, without using complicated chromatographic purification methods.This article presents the optimized procedure for the annulation of the pyran ring in acridone derivatives, which makes it possible to obtain acronycine and its derivatives in high yield, without using complicated chromatographic purification methods.

Operationally simple and convenient synthesis of selectively protected derivatives of 5,7-dihydroxycoumarins was proposed. The proposed method is based on the reaction of the coumarins with nicotinoyl azide yielding 7-nicotinoyloxy derivatives of the coumarins. This approach can significantly improve the procedure for preparing the dimethylpyranocoumarins, an important semiproduct for synthesis of anti-HIV agents.

This review is devoted to dehydrogenative C(sp2)–C(sp2) cross-coupling reactions. In the review we discussed the reactions of aromatic N-heterocycles with such reagents as amides and aldehydes, alkenes, aromatic and heterocyclic compounds with the formation of the corresponding C–H/C–H coupling products. The review is focused on mechanism as well as scope and limitations of dehydrogenative cross-coupling reactions.

A new approach was developed for nucleophilic substitution of hydrogen in quinazoline derivatives under the action of 5,7-dimethoxycoumarins. Such reactions provide direct synthetic route avoiding pre-functionalization of the C–H bond. The advantages of this environmentally benign approach are high regio- and chemoselectivity, and an easy workup procedure.