Current Organic Chemistry - Volume 25, Issue 1, 2021

Nitrogen, oxygen and sulfur-containing fused heterocycles are of great importance because of their exciting and diverse biological activities. The construction of the carbonnitrogen and carbon-oxygen through a multicomponent reaction approach by using ecofriendly reusable heterogeneous catalysts are of significant importance as it opens avenues for the introduction of nitrogen and oxygen in organic molecules. Thus, green methodologies have gained particular significance in this field; today, green chemistry is considered a tool for introducing sustainable concepts at the fundamental level. This review emphasizes and discusses the current progress on the applications of eco-friendly, recyclable heterogeneous catalysts for the synthesis of different heterocyclic fused systems and their green protocols. We paid particular attention to the specific integration of carbon-nitrogen, and carbon-oxygen bond-forming fused heterocycles by a one-pot approach by evaluating the literature between 2012 and the middle of 2020. The efficiency of the catalyst is assessed in terms of reaction time, yield and possible reusability. The MCR and heterogeneous catalyst strategies have demonstrated broader scope, economical and viability for the green and sustainable processes in the field of synthetic organic chemistry.

The benzo[b]thiophene nucleus is ubiquitous in biologically and pharmaceutically important compounds. These moieties are highly important in materials science. The synthesis of benzothiophene as a privileged structure has readily become a subject of great interest and actively pursued in recent years. This review focuses on facile and convenient methods of synthesis of benzo[b]thiophene based molecules through different transition metals catalyzed reactions.

In the past several decades, hypervalent iodine chemistry has witnessed prosperous development as hypervalent iodine reagents have been widely used in various organic transformations. Specifically, hypervalent iodine reagents have been vastly used in various bondforming reactions. Among these oxidative coupling reactions, the reactions involving the formation of C-N bond have been extensively explored to construct various heterocyclic skeletons and synthesize various useful building blocks. This review article is to summarize all the transformations in which carbon-nitrogen bond formation occurred by using hypervalent iodine reagents under metal-free conditions.

Dihydro[1,3]oxazines are an important class of heterocyclic compounds having a wide range of biological and material properties. Medicinally, they possess diverse pharmacological activities, such as bactericidal, fungicidal, microbiocidal, antitumor, anti-HIV, and anti-inflammatory agents. Apart from being biologically active, they are materially useful for making polybenzoxazines. Polybenzoxazines are a novel class of non-conjugated thermosetting materials that belong to the family of addition-curable phenolic resins. They have lucrative properties such as small shrinkage in curing, low water absorption, good thermal stability, and there is no release of volatile materials during cure, and no need for catalyst and inexpensive raw materials. Further, the flexibility in designing a monomer gives polybenzoxazines an additional edge over ordinary phenolic resins. This review briefly describes the syntheses, including eco-friendly strategies, and biological and material significance of various dihydro[1,3]oxazine derivatives.

Reactions in water have demonstrated numerous surprising results. The effects of water in these reactions may include significant physical and chemical interactions with the substrates and catalysts through polar effects and hydrogen bonding ability. In some instances, water is also able to interact with the intermediates of reactions and possibly with the transition states of chemical processes. Organic synthesis in water encourages the researchers to follow the principles of green chemistry. Among heterocyclic compounds, quinoline scaffold has become an important motif for the development of new drugs. They are widely found in pharmaceuticals as well as in agrochemical industry. Over the last few decades, numerous reports have been documented to access quinoline derivatives with structural diversity, either by new annulation or by ring functionalization. This review summarizes an overview of the synthesis and functionalisation of quinoline scaffolds in an aqueous medium. This method may encourage researchers to adopt green chemistry and to apply these environmentally safe methods in designing important heterocyclic cores.

Metal-free organocatalysts are becoming an important tool for the sustainable development of various bioactive heterocycles. On the other hand, during the last two decades, calix[n]arenes have been gaining considerable attention due to their wide range of applicability in the field of supramolecular chemistry. Recently, sulfonic acid functionalized calix[n] arenes are being employed as an efficient alternative catalyst for the synthesis of various bioactive scaffolds. In this review, we have summarized the catalytic efficiency of p-sulfonic acid calix[n]arenes for the synthesis of diverse, biologically promising scaffolds under various reaction conditions. There is no such review available in the literature showing the catalytic applicability of p-sulfonic acid calix[n]arenes. Therefore, it is strongly believed that this review will surely attract those researchers who are interested in this fascinating organocatalyst.