The site-selective acylation of a steroidal natural product 19-hydroxydehydroepiandrosterone catalyzed by 1,1′-Bi(2-napthol)-derived (BINOL) chiral phosphoric acids (CPAs) is described. Systematic ...

Site-Selective Acylation of Natural Products with BINOL-Derived Phosphoric Acids

Coumarin-pyridine push-pull fluorophores: Synthesis and photophysical studies.

Coumarin-pyridine push-pull fluorophores: Synthesis and photophysical studies

Mechanochemical synthesis of coumarins via Pechmann condensation under solvent-free conditions: An easy access to coumarins and annulated pyrano[2,3-f] and [3,2-f]indoles

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 	Introduction 2 	O-Modification of 5,7-Dihydroxycoumarins 2.1 	Alkylation/Alkenylation 2.2 	Acylation 2.3 	Sulfonylation 2.4 	Silylation 2.5 	Acylation Followed by Alkylation 3 	Other Approaches 3.1 	Synthesis from Substituted Phloroglucinol 3.2 	Synthesis from Derivatives of 2-Acylphloroglucinol 4 	Conclusion

Synthetic Approaches to Unsymmetrically Substituted 5,7-Dihydroxycoumarins

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.

1-Nicotinoylbenzotriazole: A Convenient Tool for Site-Selective Protection of 5,7-Dihydroxycoumarins

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.

New approach to the synthesis of biologically active derivatives of pyranocoumarins

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.

Synthesis of azaheterocyclic derivatives of 5,7-dimethoxycoumarins by CH/CH functionalization with quinazolines

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.

Anna K. Inyutina

Papers

1-Nicotinoylbenzotriazole: A Convenient Tool for Site-Selective Protection of 5,7-Dihydroxycoumarins

Synthetic Approaches to Unsymmetrically Substituted 5,7-Dihydroxycoumarins

New approach to the synthesis of biologically active derivatives of pyranocoumarins

Synthesis of azaheterocyclic derivatives of 5,7-dimethoxycoumarins by CH/CH functionalization with quinazolines

Optimization of pyran ring annulation in the synthesis of acronycine and its derivatives