Current Organic Chemistry - Volume 24, Issue 22, 2020

Microwave Mediated Organic Synthesis (MMOS) is typical on the proficient heat shift carried out by dielectric heating, which in turn, is primarily dependent on the capability of the reagent or solvent to take up microwave energy. The employment of microwave energy has witnessed a fast expansion in the past two decades, with novel and pioneering applications in peptide and organic synthesis, material sciences, polymer chemistry, biochemical processes and nanotechnology. This review summarizes current MW- mediated catalytic reactions in use for the synthesis of a diversity of N-heterocycles by Multi- Component Reactions (MCRs) and a variety of miscellaneous reactions. In addition, the review addresses some aspects of the use of nanoparticles for a diversity of applications in microwave chemistry.

Green chemistry plays an important role in the development of sustainable production systems which involves tremendous research efforts on the design of synthetic and analytical techniques through resource-efficient ways. The improvement in synthetic reaction performances encourages the modern society to minimize energy and reagent consumption and waste generation. Explosion of the chemicals are referred as extremely toxic substances and have been allied with major harmful health effects, though no cure has been established due to the lack of curative therapeutic approaches. In view of the facts, green chemistry strategies trigger a new hope in the synthesis of safer biologically active compounds to meet the demands of disease free environment. Here, we highlighted the development of various compounds and greener techniques such as ultrasoundassisted method, microwave-assisted method, green solvent reactions, solvent free reactions, biomolecules and nanoformulations as a new healthy approach.

The literature survey reveals that the individual coumarin and heterocyclic molecules have biological and pharmaceutical activities. Moreover, integrated coumarinfused heterocyclic compounds have shown interesting biological and physiochemical properties and thus, designing and development of coumarin-fused heterocyclic molecules are of great interest in the field of synthetic organic chemistry. Several coumarin-fused heterocyclic molecules have been synthesized by using different strategies such as multistep method, one-pot multi-component protocol, coupling and condensation method. The wide applications of integrated coumarin-fused heterocyclic molecules stimulated interest among researchers to develop different methodologies for the synthesis of novel fused molecules. As a consequence, several research articles, papers and review articles have been published in the literature. In this review article, we have presented various methods for the synthesis of different class of coumarin-fused heterocyclic molecules and their applications in chemical, optical, pharmaceutical and other useful applications.

Carbonylation reactions with carbon monoxide (CO) provide efficient and attractive routes for the synthesis of bulk and fine chemicals. However, the practice of using a large excess of an inflammable, lethal and greenhouse CO gas is always a concern in this chemistry. The development of CO surrogates has gained substantial interest and become a green alternative to gaseous CO. Many of the recent studies have focused on the development of other benign and safe reagents to work as a CO source in carbonylation reactions, and the assortment of feasible CO surrogates for specific reaction can be accomplished by the literature data. This review describes the recent developments in palladium-catalyzed carbonyl insertions without the direct use of gaseous CO.

Coumarin-linked heterocycles represent privileged structural subunits and are welldistributed in naturally occurring compounds with immense biological activities. Multicomponent reactions (MCRs) are becoming a valuable tool for synthesizing structurally diverse molecular entities. On the other hand, the last year has seen a tremendous outburst in modifying chemical processes to make them sustainable for the betterment of our environment. The application of aqueous medium in organic synthesis is fulfilling some of the goals of ‘green and sustainable chemistry’ as it has some advantages over the traditional synthetic methods in terms of reaction rates, yields, purity of the products, product selectivity, etc. Hence, significant progress has been made in recent years. In the present review, we provide an overview of the recent developments of multicomponent synthesis of biologically relevant coumarin linked and fused heterocyclic compounds carried out from 2015 till today in an aqueous medium.

The annulative π-extension (APEX) reactions through C-H bond activation has tremendous potential to access fused aromatic systems from relatively simple aromatic compounds in a single step. This state-of-the-art technique has the ability to streamline the synthesis of functionalized materials useful in material science, biomedical research, agroand pharmaceutical industries. Furthermore, C-H activation strategy does not require prefunctionalization steps, which allows for the late-stage modification of the functional molecule with requisite molecular properties. Owing to their unique photophysical properties, carbazoles are widely used in photovoltaic cells, biomedical imaging, fluorescent polymer, etc. It is also ubiquitously found in many natural products, agrochemicals and privileged medicinal scaffolds. Hence, direct conversion of easily accessible indole to carbazole remains an active research area. In the last decades, significant advancement has been made to access carbazole moiety directly from indole through cascade C-H activation. The underlying mechanism behind this cascade π-extension strategy is the facile electrophilic metalation at the C-3 position of the indole moiety, 1,2- migration and electro cyclization. In this review, we will discuss recent literature reports for the palladium-catalyzed π-extension of indole to carbazole moiety through C-H bond activation.

Heterocyclic compounds are the largely diverse organic molecules and find prevalent applications in the fine chemical industry, medicinal chemistry and agricultural science. They are also among the most commonly bearing frameworks in numerous drugs and pharmaceutical substances. Therefore, the development of convenient, efficient and environmentally benign methods to produce various types of heterocyclic compounds is an attractive area of research. For the synthesis and functionalization of heterocycles, enormous achievements have been attributed over the past decades. Recently, ironcatalyzed reactions have accomplished a noteworthy development in the synthesis of heterocycles. This review highlights some remarkable achievements in the iron-catalyzed synthesis of heterocyclic compounds published in the last five years.

Indole moiety is often found in different classes of pharmaceutically active molecules having various biological activities including anticancer, anti-viral, anti-psychotic, antihypertensive, anti-migraine, anti-arthritis and analgesic activities. Due to enormous applications of indole derivatives in pharmaceutical chemistry, a number of conventional synthetic methods as well as green methodology have been developed for their synthesis. Green methodology has many advantages including high yields, short reaction time, and inexpensive reagents, highly efficient and environmentally benign over conventional methods. Currently, the researchers in academia as well as in pharmaceutical industries have been developing various methods for the chemical synthesis of indole based compounds via green approaches to overcome the drawbacks of conventional methods. This review reflects the last ten years developments of the various greener methods for the synthesis of indole derivatives by using microwave, ionic liquids, water, ultrasound, nanocatalyst, green catalyst, multicomponent reaction and solvent-free reactions etc. (please see the scheme below). Furthermore, the applications of green chemistry towards developments of indole containing pharmaceuticals and their biological studies have been represented in this review.