The introduction of microwave irradiation in organic synthesis has revolutionized traditional synthetic chemistry by enhancing efficiency, reducing reaction times, lowering costs, improving selectivity, increasing safety, and promoting sustainability. Consequently, microwave technology has become indispensable in diverse fields, including the synthesis of peptides, biologically active heterocycles, industrially valuable organic compounds, polymers, and materials science. The use of microwave heating has significantly advanced the synthesis of biologically relevant organic sulfides/thioethers and disulfides compared to conventional synthetic routes. These methods offer shorter reaction times, excellent yields, simple work-up procedures, and the use of green solvents or solvent-free and metal-free reaction conditions, making them more attractive from a green chemistry perspective. Moreover, microwave heating simplifies the solid-phase synthesis of disulfide-rich peptides, making it more viable, selective, and cost-effective. Notably, substantial progress has been made over the past two decades in synthesizing small molecules of both symmetrical and unsymmetrical organic sulfides and disulfides, including disulfide-containing therapeutic peptides, under microwave irradiation. This review provides an overview of recent advancements in the microwave-assisted synthesis of a wide variety of bioactive diaryl and aryl–alkyl sulfides and disulfides, including a disulfide-bridged cycloheptapeptide, along with critical discussions where necessary.

A unique nanocomposite, Cu-CuO@rGO-SiO 2 , exhibits enhanced catalytic activity in C–X (X = S, N, O) coupling reactions. The high performance presumably originates from synergism of different co-existing copper species spread over rGO-SiO 2 matrices.

Catalysis is an integral part of sustainable and green chemical processes. During the last two decades, the wonder 2D carbon material with honeycomb structure, graphene, and other functionalized graphenes have emerged as extremely versatile and robust nanomaterials in heterogeneous catalysis. The incredible catalytic efficacy of such carbon nanomaterials relies on their unique physicochemical properties, including large surface area, diverse catalytic active sites, multiple chemical functionalities, tunable electron density, synergistic effect, etc., making them noteworthy as metal-free catalysts and catalytic supports. The article presents an overview of the catalytic applications of various graphene-based nanomaterials (GBNs), either metal-free or embedded with metal/metal oxide NPs, in synthesizing medicinally privileged heterocyclic compounds. It also summarizes the general methodologies for preparing graphene and various GBNs, their chemical structures, characterization techniques, and discussions on the potential active sites that are responsible for wider catalytic activity. Overall discussions unequivocally establish a promising paradigm for uncovering more innovative graphene-based materials and their subsequent applications in diverse fields, including heterogeneous catalysis.

Heterocyclic moieties are ubiquitous in nature and the exploration of heterocyclic chemistry goes centuries back, which have coalesced into the invention of greener methodologies towards the synthesis of heterocycles of potential uses. Benzothiazine is an important class of heterocyclic molecule, in which a benzene ring is fused with a six–member N, S containing ring. Amongst the three possible isomers, 1,4–benzothiazines show a wide spectrum of pharmaceutical and biological activities like anti–inflammatory, anti–rheumatic, antihypertensive, andantipathogenic roles. In search of greener protocols,metal–free catalysts, and environmentally benign reaction conditions, a lot have been unboxed to date, and many other dimensions remain yet to be deciphered. This minireview is an attempt to classify various sustainable protocols for the synthesis of 1,4–benzothiazine scaffolds over the last decade based on the reacting components and pathways, along with the consideration of plausible mechanistic insights and critical analysis.

Since its inception in 1960s, the Tsuji-Trost reaction, an allylic substitution reaction with diverse nucleophiles such as phenols, amines, thiols, and active methylene compounds, has remained as one of the most useful and widely used organic reactions for the construction of C-C and C-heteroatom bonds. Allylic compounds such as allylic acetates, alcohols, halides, and carbonates undergo this transformation which plays an important role in the total synthesis of various natural products. The competence to incorporate synthetically demanding allylic functionalities makes it a beneficial tool for the synthesis of complex molecules. Over the last two decades, major advancements for this unique and facile Tsuji-Trost allylation reaction have been made with special emphasis to develop greener and sustainable protocols. This chapter presents an update on the significant progress focusing on the newly designed catalytic systems with high efficiency, the use of eco-friendly solvents or solvent-free conditions, low or room temperature conditions and waste management, along with future outlook.

The synthesis of triazole has been of immense interest due to their potential bioactivity. This chapter is primarily focused on the greener strategies involved in the synthesis of triazoles. Special emphasis has been given to processes that involve heterogeneous catalysis, combinatorial synthesis, solvent-free reactions, on-water reactions, microwave-assisted protocols, and reactions promoted by solid-surfaces, polymeric materials and carbonaceous nanomaterials. The diverse protocols involved in the synthesis of this moiety, their limitations and the use of metals other than copper are also discussed in detail.

A Ni-based ternary nanocomposite, Ni–rGO–zeolite, has been developed as an efficient and recyclable heterogeneous catalyst for on-water regioselective azide alkyne cycloaddition.

Heterogeneous catalysis represents one of the important areas in the field of organic synthesis. Major developments have been emerged during last few decades and polymer-supported catalysts have been employed successfully in various catalytic organic transformations. Ion-exchange resins and polypeptides are two important examples of such heterogeneous polymer-supported catalysts among others because of their easy accessibility, stability, recoverability and reusability. Cross-linked ion-exchange resins and polypeptides are highly insoluble, which make them better choice in terms of their easy separation from the reaction mixture and subsequent recyclability. The present review article provides an overview of different types of ion exchange resins as polymer-supported catalysts such as amberlite resin, polystyrene resin, polyionic gel-based systems, ion-exchange resins and prolineimmobilized species, PEG-bound poly (amino acid), amino acid anchored with Merrifild resin, amphiphilic block polypeptides etc. Their preparation, characterizations and catalytic applications in diverse organic transformations have been presented with critical analysis on their stability, mechanistic overview and suitability etc.

Organophosphorous compounds are of potential importance in diverse fields. They are often used as intermediates for making functionalized phosphine ligands as well as find vast applications in the areas of industrial, agricultural and biological chemistry. The microwave-assisted synthesis of C-P bonds has become increasingly popular because of its various advantages over conventional heating in the perspectives of green chemistry. This review article has primarily focused on the synthesis of various organophosphorous molecules via microwave promoted C-P cross-coupling reactions under metal-catalyzed or metal–free conditions over the last two decades. The synthesis of phosphine ligands on 4,4′-bisquinolone structural framework, disubstituted phosphinic acid esters, vinyl phosphines, aryl- and vinylphosphonates, sugar and nucleoside phosphonates, aminobisphosphonates, triphenyl phosphines, water-soluble tertiary phosphine oxides and many other potentially useful organophosphorous compounds have been illustrated critically. The Hirao reaction, Michaelis-Arbuzov reaction and Sandmeyer type of reactions are generally involved in creating C-P bonds. The role of various metal catalysts, solvents, bases, additives and temperature in different literatures are carefully discussed.

2D graphene-based nanomaterials used in sustainable catalysis have received notable attention because of their easy availability and vast catalytic potentials. Graphene is composed of sp2-C spread endlessly in a honeycomb fashion. Its oxidized form, that is, graphene oxide (GO) and other chemically modified graphenes (CMGs) have been often used as heterogeneous catalysts in organic reactions since the first application in 2010. GO possesses diverse oxygenated functional groups and bears excellent oxidizing as well as acidic properties. This chapter covers catalytic applications of GO and CMGs toward the synthesis of diverse heterocyclic compounds of biological relevance. Some specific and important heterocycles often used as suitable scaffolds including benzothiazines, quinoxalines, imidazopyridines, pyridine, di-, and tetra-hydropyridines. In most cases, the oxidative and acidic properties of GO nanosheets are prudently exploited to control selectivity and high yields. In some cases, the underlying mechanisms, as well as its impending outlook, are also discussed.

We report here selective formation of functionalized 1,4-dihydropyridines (DHP), acridinediones and polyhydroquinolines in high yields using amine-functionalized graphene oxide nanosheets (AFGONs) as the bifunctional catalyst. The method overcomes the limitations of previous protocols affording a mixture of DHP and pyridine derivatives using graphene oxide as the catalyst. The mild reaction conditions are found compatible with a wide range of functional groups. It is presumed that a cooperative effect between the acidic and basic functionalities present in AFGONs may have exerted high catalytic efficiency as well as prevented further oxidation to pyridine derivatives. A plausible mechanism is proposed on the basis of some control experiments. The reactions can be scaled up conveniently, and the catalyst can be recycled for five consecutive runs without loss of its activity.

Ionic liquids (ILs) are considered as highly useful materials for potential diverse uses such as greener and more convenient alternatives to volatile organic solvents, reagents, additives, ligands and co-solvents. Thermal stability, negligible vapor pressure and high polarity with ionic environments have possibly conferred some unique physico-chemical properties and a wider electrochemical window on ILs. More importantly, these properties are tuneable, depending on variations in alkyl chains and counter-anions. On the other hand, various transition-metal-catalyzed cross-coupling reactions constitute an important backbone of contemporary organic synthesis. A vast number of C–C and C-heteroatom cross-coupling reactions are reported in the presence of ILs, often showing better performance. The influence of IL on the action of a given catalyst or on the course of a reaction can be relatively complex, and is not understood well enough to be able to draw succinct conclusions. However, there are a few reports in the literature that help understand the role of actual and active catalytic species stabilized in an IL environment. Stabilization, which can be either helpful or detrimental to catalysis depends on specific circumstances. This review article is aimed primarily at summarizing the various applications of ILs during the past decade, focusing as far as possible on the task-specific properties of ILs in transition-metal-catalyzed C–C and C-heteroatom cross-coupling reactions. Several successful achievements and noteworthy progress in this field of research leads to the sensible conclusion that future prospects in this field of research are not only bright but promise new horizons.

A new 2D copper(I) coordination polymeric complex has been synthesized from CuI and 1-(1-{4-chlorophenylthio}propan-2-ylthio)-4-chlorobenzene ([(CuI)2{ArSCH2CH(CH3)SAr}2]n, Ar = 4-ClC6H4) and characterized by high resolution mass spectrometry (HRMS) and single crystal X-ray diffraction techniques. The complex has been employed as a suitable catalyst for a solvent-free, one-pot, three-component A3-coupling reaction. A variety of aromatic and aliphatic aldehydes, terminal alkynes and aliphatic cyclic secondary amines have been used to prepare a library of propargylamines using the 2D-Cu complex at significantly low concentration (0.2 mol%).