Synthesis of Novel 5,6-Disubstituted Pyrrolo [2,3-d]Pyrimidine-2,4-Diones Via One-Pot Three-Component Reactions

Autocatalytic and DMSO-promoted regioselective synthesis of pyrimidine-fused quinolines from anilines and barbituric acids

Autocatalytic and DMSO-participating regioselective synthesis of N,N-disubstituted pyrimido[4,5-b]quinoline-2,4(1H,3H)-diones from anilines and barbituric acids has been achieved. In this newly developed one-pot tandem reaction, DMSO serves as a solvent cum methine source. Additionally, barbituric acid plays a dual role by acting as a substrate and a catalyst, making this reaction an environmentally benign approach to accessing valuable heterocycles. This method offers an auto-catalytic, additive-free, and operationally simple approach with a wide substrate scope and excellent tolerance for various functional groups. Furthermore, a few controlled experiments were conducted to gain insight into the reaction mechanism. Moreover, large-scale experiments have further enriched this methodology.

Sustainable Green Synthesis of Pyrimidine Derivatives: Review on Multicomponent Synthesis, Catalysts and Techniques

"The founder of green chemistry explains how chemicals manufacturing must change to support a sustainable future." In this review, Green chemistry is considered in the synthesis of heterocycles compounds containing Pyrimidine nuclei using different catalyzes, solvents, and techniques for the synthesis of pyrimidine derivatives that achieve sustainability. The mentioned fused heterocycles are classified according to the type of ring system. The yield of the target molecules reported in the review is given in the reaction's last step.

Synthesis of 3,4-Dihydropyrimidin(thio)one Containing Scaffold: Biginelli-like Reactions

The interest in 3,4-dihydropyrimidine-2(1H)-(thio)ones is increasing every day, mainly due to their paramount biological relevance. The Biginelli reaction is the classical approach to reaching these scaffolds, although the product diversity suffers from some limitations. In order to overcome these restrictions, two main approaches have been devised. The first one involves the modification of the conventional components of the Biginelli reaction and the second one refers to the postmodification of the Biginelli products. Both strategies have been extensively revised in this manuscript. Regarding the first one, initially, the modification of one of the components was covered. Although examples of modifications of the three of them were described, by far the modification of the keto ester counterpart was the most popular approach, and a wide variety of different enolizable carbonylic compounds were used; moreover, changes in two or the three components were also described, broadening the substitution of the final dihydropyrimidines. Together with these modifications, the use of Biginelli adducts as a starting point for further modification was also a very useful strategy to decorate the final heterocyclic structure.

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.

Synthesis Strategies and Medicinal Value of Pyrrole and its Fused Heterocyclic Compounds

For several decades, interest in pyrrole and pyrrolopyrimidine derivatives increases owing to their biological importance, such as anti-tumor, anti-microbial, anti-inflammatory, anti-diabetic, anti-histaminic, anti-malarial, anti-Parkinson, antioxidant and anti-viral, specially recently against COVID-19. These tremendous biological features motivated scientists to discover more pyrrole and fused pyrrole derivatives, owing to the great importance of the pyrrole nucleus as a pharmacophore in many drugs, and motivated us to present this article, highlighting on the different synthetic pathways of pyrrole and its fused compounds specially pyrrolopyrimidine, as well as their medicinal value from 2017 till 2021.

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

Microwave-assisted (MWA) multicomponent reactions (MCRs) have successfully emerged as one of the useful tools in the synthesis of biologically relevant heterocycles. These reactions are strategically employed for the generation of a variety of heterocycles along with multiple point diversifications. Over the last few decades classical MCRs such as Ugi, Biginelli, etc. have witnessed enhanced yield and efficiency with microwave assistance. The highlights of MWA-MCRs are high yields, reduced reaction time, selectivity, atom economy and simpler purification techniques, such an approach can accelerate the drug discovery process. The present review focuses on the recent advances in MWA-MCRs and their mechanistic insights over the past decade and shed light on its advantage over the conventional approach.

Hydrogen Peroxide-Mediated Rapid Room Temperature Metal-Free C(sp2)-H Thiocyanation of Amino Pyrazoles, Amino Uracils, and Enamines

A rapid metal- and additive-free room temperature method for C(sp²)-H thiocyanation of aminopyrazoles, aminoisoxazole, aminoisothiazole, amino uracils, and aliphatic enamines has been developed in an aqueous medium using hydrogen peroxide as a benign oxidant and ammonium thiocyanate as a thiocyanating agent. On the other hand, the reaction of hydrogen peroxide and ammonium thiocyanate followed by one-pot addition of NaOH provides the corresponding disulfides in the case of amino azoles, and pyrimidine-fused 2-amino thiazoles were observed in the case of aminouracils. The salient features of this method are the use of an eco-friendly oxidant, reaction tunability to access different products, wide substrate scope, and good to very good yields.

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.

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.

A green method for the synthesis of pyrrole derivatives using arylglyoxals, 1,3-diketones and enaminoketones in water or water-ethanol mixture as solvent

Three-component reaction between arylglyoxals, 1,3-dicetones and enaminoketones leads to new polyfunctionalized tetraone derivatives which may be easily converted to polyfunctionalized pyrroles. Reactions were conducted in water or water-ethanol mixture as green solvents, and all products were isolated by simple washing of the resulting solids with diethyl ether.

A Critical Review on Advances in the Multicomponent Synthesis of Pyrroles

Nitrogen containing heterocyclic compounds are biologically significant molecules. This is especially true for pyrrole a five membered nitrogen containing aromatic molecule, which is present as a key structural motif in a large number of drugs and lead molecules. This review aims to provide an overview of the multi-component reaction (MCR) based methodologies used for the synthesis of pyrrole and its derivatives, focusing particularly on eco-friendly methods that avoid the use of hazardous reagents, solvents and catalysts are deemed especially relevant to the disciplines of medicinal chemistry and drug discovery.

Synthesis of Pyrimidine Fused Quinolines by Ligand-Free Copper-Catalyzed Domino Reactions

Herein, we report two novel methods for the synthesis of pyrimidine fused quinolines using a one-pot C-C and C-N bond forming strategy from the reaction of 6-aminouracils with 2-bromobenzaldehydes or 2-bromobenzyl bromide derivatives in the presence of 10 mol % CuCl₂ without using any ligand. The reaction of 2-bromobenzaldehyde or its derivatives with 6-aminouracils in the presence of K₂CO₃ as base and a catalytic amount of CuCl₂ in DMF medium under microwave heating conditions provides corresponding pyrimidine fused quinoline derivatives in good yields within 30 min. Alternatively, pyrimidine fused quinoline derivatives have been synthesized from the reaction of 2-bromobenzyl bromides with 6-aminouracil derivatives in the presence of molecular oxygen, CuCl₂ (10 mol %), and K₂CO₃ as base in DMF under reflux conditions. Structures of all the products were unambiguously confirmed by spectroscopic techniques and by recording single crystal XRD of 3a.

The Rigidins: Isolation, Bioactivity, and Total Synthesis-Novel Pyrrolo[2,3-d]Pyrimidine Analogues Using Multicomponent Reactions

Rigidins (2-6) are pyrrolopyrimidine alkaloids isolated from marine tunicates. Since their isolation, refinement of their total syntheses, and biochemical evaluation, interest toward this pyrrolo[2,3-d]pyrimidine scaffold as a medicinal candidate has been triggered. The derivatization of these natural products has led to the discovery of a novel range of 7-deazahypoxanthines, which exhibit extremely potent anticancer activity in human cancer cell lines. A major breakthrough toward the synthesis of rigidin and various rigidin analogues has been the application of multicomponent reactions (MCRs). The rapid assembly of molecular diversity and flexibility displayed by MCRs makes it an attractive strategy for the preparation of rigidin-inspired small molecules. Furthermore, a number of rigidin-like 7-deazaxanthine compounds have been reported in the literature and the popularity of implementing MCRs to construct these 7-deazaxanthines is highlighted here. It is our hope that the synthetic methods described in this chapter will result in the further generation of rigidin-inspired compounds that will move on from being "hits" into "leads" in the medicinal chemistry drug discovery pipeline and potentially into anticancer therapeutics.

Synthesis of fused pyrroles containing 4-hydroxycoumarins by regioselective metal-free multicomponent reactions

Two novel methods have been developed for the synthesis of chromone, flavone and coumarin fused pyrroles by one-pot three component reactions.

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.