Recent Green Methods for Quinoxaline Synthesis

Quinoxaline represents an important class of bicyclic nitrogen-containing fused heterocyclic compounds. A combination of benzene and pyrazine rings makes a stable structure, with broad popularity in material science, catalysis, and microbiology. A number of various synthetic methods have emerged for their synthesis, driven by their versatile biological importance. However, most of these approaches are promoted by transition metal catalysts. In recent years, the pursuit of transition-metal-free green synthetic strategies has heightened. In this review, we aimed to highlight the most critical aspects of these synthetic protocols, mechanisms, capabilities, and limitations are summarized. Maximalization of the resource efficiency in the synthetic technique, promotion of chemical process sustainability, energy saving, low toxicity of both reagents and product, in addition to hazards, pollution, cost, and purification challenges minimization, are the key advantages of utilizing the transition metal-free catalysts. In summary, we highlight quinoxaline green and metal-free synthetic methods, with a focus on advancements of the last ten years and the potential pharmacological applications in the future.