Abstract
Quinoxalines, also known as benzo[a]pyrazines, constitute an important class of nitrogen-containing heterocyclic compounds as a result of their widespread prevalence in natural products, biologically active synthetic drug candidates, and optoelectronic materials. Owing to their importance and chemists' ever-increasing imagination of new transformations of these products, tremendous efforts have been dedicated to finding more efficient approaches toward the synthesis of quinoxaline rings. The last decades have witnessed a marvellous outburst in modifying organic synthetic methods to create them sustainable for the betterment of our environment. The exploitation of transition-metal-free catalysis in organic synthesis leads to a new frontier to access biologically active heterocycles and provides an alternative method from the perspective of green and sustainable chemistry. Despite notable developments achieved in transition-metal catalyzed synthesis, the high cost involved in the preparation of the catalyst, toxicity, and difficulty in removing it from the final products constitute disadvantageous effects on the atom economy and eco-friendly nature of the transformation. In this review article, we have summarized the recent progress achieved in the synthesis of quinoxalines under transition-metal-free conditions and cover the reports from 2015 to date. This aspect is presented alongside the mechanistic rationalization and limitations of the reaction methodologies. The scopes of future developments are also highlighted.
Highlights
Nitrogen-containing heterocycles, of natural and synthetic origin, represent a huge family of indispensable structural motifs and have attracted enormous attention in synthetic and medicinal chemistry as well as in material sciences owing to Biplob Borah was born in 1995 in Garukhunda, a small village in the Nagaon district of Assam, India
Despite notable developments achieved in transition-metal catalyzed synthesis, the high cost involved in the preparation of the catalyst, toxicity, and difficulty in removing it from the final products constitute disadvantageous effects on the atom economy and eco-friendly nature of the transformation
Considering the great importance of the quinoxaline framework in many branches of chemistry including natural products chemistry, drug discovery, medicinal chemistry, material science, and agrochemical area, tremendous efforts have been dedicated toward their synthesis
Summary
Nitrogen-containing heterocycles, of natural and synthetic origin, represent a huge family of indispensable structural motifs and have attracted enormous attention in synthetic and medicinal chemistry as well as in material sciences owing to Biplob Borah was born in 1995 in Garukhunda, a small village in the Nagaon district of Assam, India. His research interests include stereoselective synthesis of natural products, development of novel methodologies for asymmetric synthesis, multicomponent reactions, and 1,3-dipolar cycloaddition reactions Review their wide-ranging chemical landscape and proli c bioactivity pro les.[1] Among various nitrogen heterocycles, quinoxalines and their derivatives have been considered as versatile and privileged structural scaffolds in synthetic and medicinal chemistry.[2] These well-established nitrogen-containing bicyclic heterocycles mainly consist of a benzene ring fused with a pyrazine ring in their structure. Several synthetic quinoxaline-based compounds M, N, O, P, and Q exhibited potent pharmacological activities such as antitumor,[36] anticancer,[37] antiproliferative,[38] anti-in ammatory,[39] and folate cycle inhibitors[40] respectively Despite these wide-ranging biological activities, a diverse molecular structure that featured the quinoxaline framework has been established as potential fragments in diverse areas of materials science. On behalf of a clear and understanding overview, the article is organized based on the different types of substrates used rather than compiled in chronological order
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