Elevating pyrrole derivative synthesis: a three-component revolution

Pyrrole is an essential chemical with considerable relevance as a pharmaceutical framework for many biologically necessary medications. The growing demand for biologically active compounds calls for a simple one-pot method for generating novel pyrrole derivatives. Nots surprisingly, several multicomponent reactions (MCRs) aim to synthesize pyrrole derivatives. However, this review presents the three-component synthesis of pyrrole derivatives, highlighting the significance of multicomponent reaction in synthesizing eclectic multi-functionalised pyrrole covering the selected literature on the three-component synthesis of substituted pyrrole from 2016 to late 2023. Furthermore, this article classifies the reactions based on the starting material with functional groups involved in the pyrrole ring formation.

Coumarin-Synthetic Methodologies, Pharmacology, and Application as Natural Fluorophore

Coumarins are secondary metabolites made up of benzene and α-pyrone rings fused together that can potentially treat various ailments, including cancer, metabolic, and degenerative disorders. Coumarins are a diverse category of both naturally occurring as well as synthesized compounds with numerous biological and therapeutic properties. Coumarins as fluorophores play a key role in fluorescent labeling of biomolecules, metal ion detection, microenvironment polarity detection, and pH detection. This review provides a detailed insight into the characteristics of coumarins as well as their biosynthesis in plants and metabolic pathways. Various synthetic strategies for coumarin core involving both conventional and green methods have been discussed comparing advantages and disadvantages of each method. Conventional methods discussed are Pechmann, Knoevenagel, Perkin, Wittig, Kostanecki, Buchwald-Hartwig, and metal-induced coupling reactions such as Heck and Suzuki, as well as green approaches involving microwave or ultrasound energy. Various pharmacological applications of coumarin derivatives are discussed in detail. The structural features and conditions responsible for influencing the fluorescence of coumarin core are also elaborated.

DMSO promoted catalyst-free oxidative C-N/C-O couplings towards synthesis of imidazoles and oxazoles

Dimethyl sulfoxide (DMSO)-promoted catalyst-free oxidative C-N coupling and C-O coupling under oxidant-free conditions are outlined. This protocol is operationally simple and leads to various functionalized substituted imidazoles or oxazoles in good yields. To date, a very limited number of oxidation protocols have been established, where DMSO acts solely as a catalyst or an oxidant or both. In this report, DMSO is not only used as a C-N/C-O coupling agent but is also used as the oxidant required for these oxidative transformations. Hence, our demonstrated DMSO-promoted catalyst-free coupling transformation has the ability to lead to a new dimension in the field of oxidative coupling.

Hydrotrope assisted green synthesis of dicoumarols and in silico and in vitro antibacterial, antioxidant and xanthine oxidase inhibition studies

Aqueous hydrotrope has been employed for the first time to synthesize heteroaryl dicoumarols by condensation of 4-hydroxycoumarin and different heterocyclic aldehydes. This method is highly efficient and green, and the same aqueous hydrotropic solution can be used up to five times without any considerable loss of yield in the product. The synthesized compounds showed good antibacterial potential against Gram-positive (Staphylococcus aureus/NTCC 0997 and B. oceanisediminis) and Gram-negative (Escherichia coli/D0157:H7 and E. coli rosetta) bacterial strains using the Resazurin microtiter plate visual method. The MIC value of 312 µg/ml for compounds 3b, 3k and 3l for S. aureus while 39 µg/ml for compounds 3a, 3b and 3k for E. coli and 625 µg/ml for 3a and 3b for B. oceanisediminis was observed. The compounds were screened via computational methods like molecular docking studies and molecular dynamic simulations with PDB Id's 2W9S and 2EX6. Antioxidant activity was assessed using DPPH and H2O2 assays. Five compounds with the best binding score in molecular docking with XO (PDB ID: 1FIQ) have been tested in an in-vitro study using an enzyme inhibition assay. Novel compound 3b gave the IC50 value of 0.28 µg/ml, comparable to the standard drug Allopurinol.Communicated by Ramaswamy H. Sarma.

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.

Visible Light-Mediated C(sp2)-H Selenylation of Amino Pyrazole and Amino Uracils in the Presence of Rose Bengal as an Organophotocatalyst

Herein, we report an efficient methodology for the synthesis of alkyl, benzyl, and phenyl selenoethers of aminopyrazoles and aminouracils by C(sp²)-H functionalization in the presence of visible light and Rose Bengal as an organophotocatalyst. The reaction of amino pyrazole/iosothiazole/isoxazole or amino uracils with 0.5 equivalent of diphenyl/dibenzyl/diethyl diselenides in the presence of visible light in acetonitrile medium and a catalytic amount of Rose Bengal provided the corresponding phenyl, benzyl, or ethyl selenoethers in good to very good yields. We have also utilized some of the selenylated aminopyrazoles for the preparation of pyrazole-fused dihydropyrimidines tethered with arylselenoethers by a catalyst-free one-pot three-component reaction. The notable features of this methodology are metal-free reaction conditions, good to very good yields, use of an organic photocatalyst, and wide substrate scope; it is also applicable to gram-scale synthesis and provides selenoethers of medicinally important heterocycles such amio-pyrazole, isoxazole, isothiazole, and uracils.

Convenient one-pot synthesis of 1,2,4-oxadiazoles and 2,4,6-triarylpyridines using graphene oxide (GO) as a metal-free catalyst: importance of dual catalytic activity

A convenient and efficient process for the synthesis of 3,5-disubstituted 1,2,4-oxadiazoles and 2,4,6-triarylpyridines has been described using an inexpensive, environmentally benign, metal-free heterogeneous carbocatalyst, graphene oxide (GO). GO plays a dual role of an oxidizing agent and solid acid catalyst for synthesizing 1,2,4-oxadiazoles and triarylpyridines. This dual catalytic activity of GO is due to the presence of oxygenated functional groups which are distributed on the nanosheets of graphene oxide. A broad scope of substrate applicability and good sustainability is offered in this developed protocol. The results of a few control experiments reveal a plausible mechanism and the role of GO as a catalyst was confirmed by FTIR, XRD, SEM, and HR-TEM analysis.

Reactions involving aryl methyl ketone and molecular iodine: a powerful tool in the one-pot synthesis of heterocycles

The preparation of heterocyclic compounds has attracted great attention in organic chemistry because of their extensive application in the field of bioactive molecules, materials science, and natural products.

One-pot synthesis of pyrimidine linked naphthoquinone-fused pyrroles by iodine-mediated multicomponent reactions

Herein we report iodine-mediated multicomponent reactions for the synthesis of naphthoquinone-fused pyrroles tethered with a pyrimidine moiety. The reaction of aryl methyl ketones (3) or terminal aryl alkynes (5) in the presence of molecular iodine in DMSO medium followed by sequential addition of barbituric acids (2) and 2-amino-1,4-naphthoquinone (1) provides the corresponding three-component hybrid molecules 4 having naphthoquinone-fused pyrroles tethered with a barbituric acid moiety. This three-component reaction proceeds via metal-free C-H oxidation followed by multi-component cyclization forming three new bonds (2 C-C, 1 C-N) in one pot. Alternatively, the same molecules can also be prepared from the reaction of arylglyoxals, 2-aminonaphthoquinone, and barbituric acids in the presence of a catalytic amount of iodine in methanol medium under reflux conditions. The salient features of these methodologies are: one-pot metal-free method, good yields, wide substrate scope, easy purification of products, and the presence of medicinally important naphthoquinone, pyrrole and pyrimidine moieties in the products.

Synthesis of Sulfamate-Fused 2-Aminopyrroles via an Isocyanide-Based Three Component [1+2+2] Annulation

An efficient preparation of sulfamate-fused 2-aminopyrroles was achieved through an isocyanide-based three-component [1+2+2] annulation of isocyanides, dialkyl acetylenedicarboxylates, and sulfamate-derived cyclic imines in good to excellent yields (up to 99 %). This reaction proceeds smoothly without any activation or modification of substances under neutral and metal-free conditions. The reaction could also be conveniently performed on a gram scale.

Recent applications of thiourea-based organocatalysts in asymmetric multicomponent reactions (AMCRs)

This review describes the recent applications of thiourea-based organocatalysts in asymmetric multicomponent reactions.

Microwave assisted synthesis of β-keto thioethers and furan derivatives by thiol directed multicomponent reactions

A series of β-keto thioethers tethered with cyclic-1,3-dicarbonyls (4) and a tetra-substituted furan derivative (5) has been prepared by multicomponent reaction under microwave heating conditions.

I2/DMSO mediated multicomponent reaction for the synthesis of 2-arylbenzo[d]imidazo[2,1-b] thiazole derivatives

Synthesis of a series of 2-arylbenzo[d]imidazo[2,1-b] thiazoles tethered with barbituric acid moiety has been reported from the three component reaction of 2-aminobenzothiazoles, barbituric acids and terminal aryl acetylenes or aryl methyl ketones in the presence of I2 in DMSO medium. Both conventional and microwave heating conditions can be used for this multicomponent reaction. The salient features of this methodology are: (i) formation of one C-C and two C-N bonds in one-pot under metal-free oxidation followed by cyclization, (ii) selective formation of the fused imidazole ring, (iii) wide substrate scope, (iv) easy purification of the products, (v) products having more than one pharmaceutically important motifs and (vi) gram scale synthesis possible.

Acetic acid mediated regioselective synthesis of 2,4,5-trisubstituted thiazoles by a domino multicomponent reaction

Acetic acid mediated regioselective synthesis of novel 2,4,5-trisubstituted thiazole derivatives has been reported by a domino reaction of thiosemicarbazide and aldehydes/ketones/isatin, to generate thiosemicarbazones (in situ) followed by addition of arylglyoxal and active methylene/activated C–H acids/pyrazole/indole in ethanol at 80 °C.

Iodine–DMSO-promoted divergent reactivities of arylacetylenes

An unprecedented set of efficient, economical, atom-economic and exceedingly selective I₂–DMSO-promoted methods is described for the generation of different structures.

Lemon juice mediated multicomponent reactions for the synthesis of fused imidazoles

A green approach for the synthesis of diverse medicinally important tricyclic fused imidazoles has been described using one-pot multicomponent reactions in lemon juice as a biocatalyst as well as the reaction medium.

The synthesis of HMF-based α-amino phosphonatesviaone-pot Kabachnik–Fields reaction

The first use of biomass-derived HMF in the one-pot Kabachnik–Fields reaction is reported here. A wide range of furan-based α-amino phosphonates were prepared in moderate to excellent yields under mild, effective and environmentally-benign conditions: iodine as a non-metal catalyst, biobased 2-MeTHF as the solvent and room or moderate temperature. The hydroxymethyl group of HMF persists in the Kabachnik–Fields products, widening the scope of further modification and derivatization compared to those arising from furfural. Issues involving the diastereoselectivity and double Kabachnik–Fields condensation were also faced.

A mild and efficient one-pot protocol for the synthesis of α-amino phosphonates directly from 5-HMF was described.