Reusable nano-catalyzed green protocols for the synthesis of quinoxalines: an overview

Heterocyclic compounds are very widely distributed in nature and are essential for life activities. They play a vital role in the metabolism of all living cells, for example, vitamins and co-enzyme precursors thiamine, riboflavin etc. Quinoxalines are a class of N-heterocycles that are present in a variety of natural and synthetic compounds. The distinct pharmacological activities of quinoxalines have attracted medicinal chemists considerably over the past few decades. Quinoxaline-based compounds possess extensive potential applications as medicinal drugs, presently; more than fifteen drugs are available for the treatment of different diseases. Diverse synthetic protocols have been developed via a one-pot approach using efficient catalysts, reagents, and nano-composites/nanocatalysts etc. But the use of homogeneous and transition metal-based catalysts suffers some demerits such as low atom economy, recovery of catalysts, harsh reaction conditions, extended reaction period, expensive catalysts, the formation of by-products, and unsatisfactory yield of products as well as toxic solvents. These drawbacks have shifted the attention of chemists/researchers to develop green and efficient protocols for synthesizing quinoxaline derivatives. In this context, many efficient methods have been developed for the synthesis of quinoxalines using nanocatalysts or nanostructures. In this review, we have summarized the recent progress (till 2023) in the nano-catalyzed synthesis of quinoxalines using condensation of o-phenylenediamine with diketone/other reagents with plausible mechanistic details. With this review, we hope that some more efficient ways of synthesizing quinoxalines can be developed by synthetic chemists.

An overview of quinoxaline synthesis by green methods: recent reports

Quinoxalines and their derivatives belong to an important class of bicyclic aromatic heterocyclic system, also known as benzopyrazines, containing a benzene ring and a pyrazine ring. They have attracted considerable attention over the years due to their potential biological and pharmaceutical properties. A wide range of synthetic strategies is reported in this significant area of research. The present review showcases recent research advances in the synthesis of quinoxaline derivatives following environmentally benign approaches.

Copper(0)/Selectfluor System-Promoted Oxidative Carbon-Carbon Bond Cleavage/Annulation of o-Aryl Chalcones: An Unexpected Synthesis of 9,10-Phenanthraquinone Derivatives

A general and efficient protocol for the synthesis of 9,10-phenanthraquinone derivatives has been successfully developed involving a copper(0)/Selectfluor system-promoted oxidative carbon-carbon bond cleavage/annulation of o-aryl chalcones. A variety of substituted 9,10-phenanthraquinones were synthesized in moderate to good yields under mild reaction conditions.

Reaction control in heterogeneous catalysis using montmorillonite: switching between acid-catalysed and red-ox processes

For a montmorillonite clay modified with a super-acid (CF₃SO₃H), two different modes of behaviour can take place simply by a judicious choice of reaction conditions.

The Fault in Their Shapes: Investigating the Surface-Plasmon-Resonance-Mediated Catalytic Activities of Silver Quasi-Spheres, Cubes, Triangular Prisms, and Wires

The surface-plasmon-resonance (SPR)-mediated catalytic activities of Ag and Au nanoparticles have emerged a relatively new frontier in catalysis in which visible light can be employed as an eco-friendly energy input to drive chemical reactions. Although this phenomenon has been reported for a variety of transformations, the effect of the nanoparticle shape and crystalline structure on the activities remains unclear. In this paper, we investigated the SPR-mediated catalytic activity of Ag quasi-spheres, cubes, triangular prisms, and wires toward the oxidation of p-aminothiophenol to p,p'-dimercaptoazobenzene by activated O2. The activities at 632.8 nm excitation followed the order triangular prisms and quasi-spheres > wires ≫ cubes. These results indicated that the shape, optical properties, and crystal structure played an important role in the detected SPR-mediated activities.

Recent developments in one-pot tandem oxidation process coupling reactions

The recent additions to the tandem oxidation process (TOP) research area are reviewed.

l-Proline mediated synthesis of quinoxalines; evaluation of cytotoxic and antimicrobial activity

A simple, greener and highly efficient method for the synthesis of functionalized quinoxalines has been developed employing l-proline as a catalyst in water. The newly synthesized quinoxaline–sulphonamide conjugates exhibited significant cytotoxic and antimicrobial activities.