Synthesis and Reaction Mechanisms for the Construction of Pyrrolo[1,2-a]quinoxalines and Pyrrolo[1,2-a]quinoxalin-4(5H)-ones

Abstract

Pyrrolo[1,2-a]quinoxalines and pyrrolo[1,2-a]quinoxalin-4(5H)-ones are recognized as important tricyclic scaffolds due to their diverse pharmacological activities, including anticancer, anti-fungi, anti-tuberculosis, and antimalarial, as well as their roles as 5-HT3 receptor agonists and kinase inhibitors targeting CK2 and AKT, and others. Developing efficient and reliable synthetic approaches to access these compounds remains an attractive goal in contemporary medicinal chemistry and drug discovery. This review highlights recent advances in the synthesis of pyrrolo[1,2-a]quinoxalines and pyrrolo[1,2-a]quinoxalin-4(5H)-ones, particularly focusing on strategies that maintain the A and C-rings while constructing the B-ring through the formation of a-, b-, and c-bonds. The information collected describes the two key components of the synthesis process 1-(2-substitued-phenyl)-1H-pyrrole and aldehyde or its surrogate. This review also briefly summarizes the reaction mechanisms for the formation of tricyclic skeletons to determine the key factors governing the issues of productivity and regioselectivity. Through analysis of the advantages and disadvantages of existing synthetic methods, we predict that A-ring formation strategy-based pyrrolo[1,2-a]quinoxaline reactions will be developed in the future. We hope that this review will motivate the search for novel strategies to synthesize pyrrolo[1,2-a]quinoxalines and pyrrolo[1,2-a]quinoxalin-4(5H)-ones, accessing tricyclic skeletons that may have potential applications in medicinal chemistry, materials science, and many branches of chemistry.