Current Organic Chemistry - Volume 25, Issue 13, 2021

Tandem and domino reactions constitute economic methodologies to prepare complex molecules starting from simple materials. Especially, combining these powerful procedures to asymmetric catalysis allows direct access to many elaborated chiral products, including important key intermediates in total syntheses of important biologically active compounds. A range of various types of chiral organocatalysts have already been successfully applied to such syntheses. This review presents major developments in the total synthesis of bioactive products based on the use of enantioselective organocatalytic domino/tandem reactions as key steps. It is divided into three parts, dealing successively with syntheses based on organocatalytic asymmetric Michael-initiated domino reactions as key steps; aldol-initiated domino/tandem reactions and other domino reactions.

Microwave (MW)-assistance may be a powerful tool in the Hirao P–C coupling reactions of vinyl/aryl halides with dialkyl phosphites in the presence of Pd-catalysts/Pligands elaborated forty years ago. This review surveys the development of this reaction by showing the expansion of the reagents and catalysts, as well as the information accumulated. The stress was laid on the “green” aspects, the simplification of the catalyst systems, and the reliable mechanistic details in order to be able to establish the optimum conditions. The best protocol involves the use of some excess of the >P(O)H reagent to ensure the PdII→Pd⁰ reduction and, via its trivalent tautomeric form (>POH), also the P-ligand. The overall rate is the result of two factors, the activity of the catalyst complex formed, and the reactivity of the reactants in the P–C coupling reactions. The nature of the aryl substituents in Ar2P(O)H influences both components. NiII salts may also be used as the catalyst precursor, however, despite the Pd^II→Pd⁰→Pd^II route, in this case, a Ni^II→Ni^IV→Ni^II sequence was proved.

Polysaccharide-based materials have been widely used as the first-choice candidates for various applications, especially in the field of biomaterials. The primary reasons for this are the sustainable nature of these materials and their high bioavailability. Their ability to be easily chemically modified enables them to be utilized in various avenues, with oxidation of the backbone being one of the most common chemical modifications. Additionally, these materials degrade via different pathways (enzymatically and chemically) and are hence ideal candidates for biomedical applications. This review summarizes the recent progress made with different oxidized polysaccharides and their potential applications to the field of biomaterials.

Asymmetric organic synthesis is of paramount importance in the development of drugs. Asymmetric addition reactions such as aldol reaction, Michael addition, and Mannich addition reactions are important carbon-carbon bond-forming reactions and have been employed in the synthesis of a broad range of biologically important molecules. Many of these reactions have been developed under solvent-free conditions or in greener solvents like water. Several reactions have been developed at room temperature or by using a non-conventional energy source such as microwave irradiation. Several greener catalysts have been developed for such reactions. The present review article discusses the application of green chemistry parameters in the development of selected asymmetric addition reactions leading to biologically important molecules during the last ten years. Asymmetric aldol reactions, asymmetric Michael reactions, and different asymmetric addition reactions involving imines such as Mannich reaction, aza-benzoin reaction, etc. in aqueous media or under solvent-free conditions have been reviewed. Application of different types of catalysts such as prolinamides, 1,2-diamines, polymer and magnetic nanoparticle-supported chiral catalysts is demonstrated.

The use of natural and environment-friendly energy sources for the betterment of the living society has become an active concern in both government and public sectors. Due to this, responsible use of global resources has become a growing concern among people. Similarly, in the chemical industry especially in pharmaceutical fields, there is constant pressure in reducing hazardous organic solvents and environmentally detrimental laboratory materials. The use of ionic liquids for the efficient synthesis of a wide array of fundamentally important structural motifs has gained tremendous importance in the scientific era. In this review, the synthesis of two such medicinally relevant moieties, namely, triazole and pyrazole, in green and sustainable ionic liquid have been discussed.

Abstract: Ultrasonication, nowadays, is well-regarded as an effective green tool in implementing a plethora of organic transformations. The last decade has seen quite useful applications of ultrasound irradiation in synthetic organic chemistry. Ultrasound has already come out as a unique technique in green chemistry practice for its inherent properties of minimizing wastes and reducing energy and time, thereby increasing the product yields with higher purities under milder reaction conditions. The present review summarizes ultrasound-promoted useful organic transformations involving both carbon-carbon and carbon-heteroatom (N, O, S) bond-forming reactions in the absence or presence of varying catalytic systems, reported during the period 2016-2020.

Recent years have witnessed a rapid development of environmentally sustainable organic processes that can stop the eventual depletion of our eco-system with wider implications on the day-to-day practice in academic laboratories and industries. The use of biocompatible raw materials as a catalyst, solvent, and synthetic precursors; continuous attempt to design ideal synthetic processes, and use of energy-efficient strategy, such as multicomponent reactions have potential to achieve sustainable organic synthesis. The aim of this review was to discuss the applications of nature’s chiral pool, such as amino acids, carbohydrates, and their readily accessible derivatives as a catalyst, solvent, and raw materials for the synthesis of diverse molecular targets.

Most of the biologically active microbial natural products and their analogs bear a complex molecular architecture. The semisynthetic modifications and stereospecific diversity- oriented synthesis of these native natural products to generate analogs are difficult and time-consuming. Mutasynthesis is a powerful tool that utilizes the microorganism's genetic and metabolic engineering skills to produce derivatives of complex natural products of microbial origin. Mutasynthesis is based on the cellular uptake of chemically modified intermediates from the culture media and their addition to the secondary metabolism by mutant microorganisms. This review will describe the importance of mutasynthesis in the generation of complex microbial secondary metabolites. We have covered a literature search on mutasynthesis over the last ten years (2011-2020) in this review.