Fe-Catalyzed Domino Intramolecular Nucleophilic Substitution of 4-Hydroxychromen-2-one and Pyran-2-one/Ring Opening of Activated Arene: An Easy Access to 2,3-Disubstituted Furo[3,2,-c]coumarins and Furo[3,2,-c]pyran-4-ones via Nonsymmetric Triarylmethanes

Multi-Auto-Tandem Reaction to Access Site-Specific Functionalized Tricyclic Furo[3,2-c]coumarins and Naphtho[2,3-b]furan-4,9-diones

A three-component multi-auto-tandem reaction for the construction of site-specific tricyclic furo[3,2-c]coumarins via the formation of C-C, C-O, and C-S bonds in one step from 4-hydroxycoumarins/4-hydroxy-2-pyrones, ynals, and sodium sulfinates is reported. This cascade reaction efficiently produces a variety of rare C-2-functionalized furo[3,2-c]coumarins in moderate to good yields under straightforward reaction conditions. Furthermore, this protocol can be extended to a three-component coupling involving 2-hydroxy-1,4-naphthoquinone, ynals, and sodium sulfinates, yielding tricyclic naphtho[2,3-b]furan-4,9-dione derivatives. Notably, the carbonyl group and the α-position of ynals act as C-2 synthons in the specific multi-auto-tandem reaction, enabling the two aforementioned types of multicomponent transformations.

Modular access to furo[3,2-c]chromen-4-ones via Yb(OTf)3-catalyzed [3 + 2] annulation of 4-hydroxycoumarins with β-nitroalkenes

A facile and efficient strategy for modular access to furo[3,2-c]chromen-4-ones using 4-hydroxycoumarin and β-nitroalkenes via Lewis acid-catalyzed formal [3 + 2] annulation protocol is described. This reaction proceeds via cascade Michael addition/nucleophilic addition/elimination in the presence of Yb(OTf)3, which involves the formation of two new σ (C-C and C-O) bonds for the construction of a novel furan ring in a single operation. This protocol affords a variety of functional groups, thereby providing a practical and efficient method for the fabrication of a furo[3,2-c]chromen-4-one framework.

Synthesis of arene-functionalized fused heterocyclic scaffolds via a regioselective cascade 1,4-conjugate addition/5-exo-dig annulation strategy

Facile access to furan fused heterocyclic scaffolds through a regioselective cascade reaction of propargylamines with 4-hydroxy-2H-pyran-2-ones and 4-hydroxy-6-methylpyridin-2(1H)-one has been achieved. This cascade reaction presumably involves the formation of ortho-alkynyl quinone methide (o-AQM), 1,4-conjugate addition, followed by regioselective 5-exo-dig annulation, and a 1,3-H shift process. Moreover, the reaction provides a new and efficient method for the synthesis of highly sterically congested 3-phenolic furo[3,2-c]pyran-4-ones and furo[3,2-c]pyridin-4(5H)-ones by the formation of a furan ring from readily available starting materials in good to high yields (50-82%) with broad functional group compatibility in a single step. Significantly, the strategy described here is easily scalable and several useful synthetic transformations of the prepared arene-functionalized 4H-furo[3,2-c]pyran-4-ones were also performed.

Sc(OTf)3-Mediated One-Pot Synthesis of Coumarin-Fused Furans: A Thiol-Dependent Reaction for the Easy Access of 2-Phenyl-4H-furo[3,2-c]chromen-4-ones

Herein, we report a simple and efficient method for the preparation of novel thioether-linked coumarin-fused furans from the one-pot three-component reaction of arylglyoxal, 4-hydroxycoumarin, and various aromatic thiols in the presence of Sc(OTf)₃ as a catalyst. This methodology is also applicable to cyclic 1,3-dicarbonyls such as cyclohexane-1,3-dione and dimedone. Depending upon the thiols, this methodology can either give a three-component thioether-linked coumarin-fused furan (4) or a two-component furocoumarin product (5). Wide substrate scope, good to excellent yields, and products having more than one pharmaceutically important motif are the salient features of this methodology.

One-Pot Synthesis of 4H-Pyrano[3,2-c]coumarin Derivatives Catalyzed by Deep Eutectic Solvent

4H-Pyrano[3,2-c]coumarin derivatives are an important class of pharmaceutical compounds that are expensive to prepare by previously reported methods. An efficient and green method was developed to obtain these derivatives using the deep eutectic solvent (DES) zinc chloride/acetamide (n:n = 1:4), which acted as both the catalyst and the solvent for the reaction. An aromatic aldehyde, 4-hydroxycoumarin, and cyanoacetate were used as the substrates. The DES, substrate molar ratio, diluent type, temperature, and reaction time were optimized to obtain the 4H-pyrano[3,2-c]coumarin derivatives from a range of aromatic aldehydes in a single step in moderate to high yields and under mild reaction conditions.

Strategies for the synthesis of furo-pyranones and their application in the total synthesis of related natural products

The furo-pyranone framework is widely present in the molecular structure of various biologically potent natural products and un-natural small molecules, and it represents a valuable target in synthetic organic chemistry and medicinal chemistry.

Furo[3,2-c]coumarins carrying carbon substituents at C-2 and/or C-3. Isolation, biological activity, synthesis and reaction mechanisms

The isolation, biological activity and synthesis of natural furo[3,2-c]coumarins are presented, covering mainly the developments in the last 35 years. The most relevant approaches toward the synthesis of 2-substituted, 3-substituted and 2,3-disubstituted heterocycles are also discussed, with emphasis on the efficiency of the processes and their mechanisms.