Synthesis and Applications of Carbohydrate-Based Organocatalysts

Organocatalysis is a very useful tool for the asymmetric synthesis of biologically or pharmacologically active compounds because it avoids the use of noxious metals, which are difficult to eliminate from the target products. Moreover, in many cases, the organocatalysed reactions can be performed in benign solvents and do not require anhydrous conditions. It is well-known that most of the above-mentioned reactions are promoted by a simple aminoacid, l-proline, or, to a lesser extent, by the more complex cinchona alkaloids. However, during the past three decades, other enantiopure natural compounds, the carbohydrates, have been employed as organocatalysts. In the present exhaustive review, the detailed preparation of all the sugar-based organocatalysts as well as their catalytic properties are described.

A comprehensive survey upon diverse and prolific applications of chitosan-based catalytic systems in one-pot multi-component synthesis of heterocyclic rings

Heterocyclic compounds are among the most prestigious and valuable chemical molecules with diverse and magnificent applications in various sciences. Due to the remarkable and numerous properties of the heterocyclic frameworks, the development of efficient and convenient synthetic methods for the preparation of such outstanding compounds is of great importance. Undoubtedly, catalysis has a conspicuous role in modern chemical synthesis and green chemistry. Therefore, when designing a chemical reaction, choosing and or preparing powerful and environmentally benign simple catalysts or complicated catalytic systems for an acceleration of the chemical reaction is a pivotal part of work for synthetic chemists. Chitosan, as a biocompatible and biodegradable pseudo-natural polysaccharide is one of the excellent choices for the preparation of suitable catalytic systems due to its unique properties. In this review paper, every effort has been made to cover all research articles in the field of one-pot synthesis of heterocyclic frameworks in the presence of chitosan-based catalytic systems, which were published roughly by the first quarter of 2020. It is hoped that this review paper can be a little help to synthetic scientists, methodologists, and catalyst designers, both on the laboratory and industrial scales.

Valorization of Waste: Sustainable Organocatalysts from Renewable Resources

One of the greatest challenges facing our society is to reconcile our need to develop efficient and sophisticated chemical processes with the limited resources of our planet and its restricted ability to adsorb pollution. Organocatalysis has allowed many issues to be addressed in the development of sophisticated, but less polluting, processes. However, minimizing waste also means an efficient utilization of raw and renewable materials. Waste biomass represents an alternative to conventional petroleum-based chemical manufacturing and is a highly attractive renewable resource for the production of chemicals and high-value-added organocatalysts. Recent achievements in the use of renewable biomass feedstocks for the synthesis of organocatalysts are presented. Their application in synthetic methodologies, including multicomponent reactions, which are performed under solvent-free conditions or in eco-friendly reaction media, as well as recycling and reusing the organocatalysts, is illustrated. A few pioneering examples that demonstrate the potential of these promoters in asymmetric synthesis have also been documented. In particular, this review covers examples on the use of hetero- and homogeneous organocatalysts derived from 1) waste biopolymers, such as chitosan, alginic acid, and cellulose; ii) renewable platform molecules, such as levoglucosenone, isosorbide, mannose, d-glucosamine, and lecithin; 3) terpenes and rosin, such as pinane, isosteviol, and abietic acid; and iv) natural proteins (gelatin, bovine tendons, silk fibroin proteins).

Chitosan: A Natural and Sustainable Polymeric Organocatalyst for C-C Bond Formation During the Synthesis of 5-amino-2,3-dihydrobenzo[d] thiazole-4,6-dicarbonitriles

Background:

A green, recyclable and reusable chitosan catalyst has been utilized for the synthesis of 5-amino-2,3-dihydrobenzo[d]thiazole-4,6-dicarbonitrile and its derivatives.

Methods and Results:

Three-component reaction protocol incorporates the reaction of aldehydes, malononitrile and rhodanine derivatives. This is examined as an efficient route for the synthesis of dicarbonitriles utilizing a green, biodegradable, environmentally benign, and easily available chitosan catalyst. In the reported protocol, catalyst can be recycled and not any substantial dropping in its catalytic activity during the recycling steps was obtained.

Conclusion:

A green and environmentally benign, one pot three-component protocol has been illustrated for the synthesis of 5-amino-2,3-dihydrobenzo[d]thiazole-4,6-dicarbonitrile derivatives. Adequately yield products were gained via the natural catalytic approach with the recyclability of the catalyst. The use of chitosan represents this procedure as an attractive substitute for the synthesis of biaryls complex by multicomponent reaction condition.

ZnO nanoparticle–β-cyclodextrin: a recyclable heterogeneous catalyst for the synthesis of 3-aryl-4H-benzo[1,4]thiazin-2-amine in water

ZnO nanoparticles and β-cyclodextrin was used as a green catalytic system for the synthesis of benzo[1,4]thiazin-2-amine via a one-pot, three-component reaction of an o-amino thiophenol, aldehydes and isocyanides in excellent yields at 60 °C in water.

S-Nanoparticle/SDS: an efficient and recyclable catalytic system for synthesis of substituted 4H-pyrido[1,2-a]pyrimidines in aqueous admicellar medium

A green protocol has been described for the synthesis of 4H-pyrido[1,2-a]pyrimidines under admicellar catalysis by S₈ NPs.

Molecular iodine catalysed domino cyclization in aqueous medium: a simple and efficient synthetic route to 1,4-dihydropyridazines

An efficient protocol has been developed for the synthesis of dihydropyridazines using molecular iodine as green catalyst.

Meglumine catalyzed expeditious four-component domino protocol for synthesis of pyrazolopyranopyrimidines in aqueous medium

Meglumine has been found to be an efficient catalyst for the synthesis of structurally diverse tricyclic fused pyrazolopyranopyrimidines by one-pot, four-component reaction of ethyl acetoacetate, hydrazine hydrate, aromatic aldehydes and barbituric acid in water.