Sulfur-mediated annulation of 1,2-phenylenediamines towards benzofuro- and benzothieno-quinoxalines

Metal-free construction of dihydropyrazino[2,3-b]indoles from 2-aminoacetophenones, isocyanates and 1,2-diamines

A Brønsted acid/iodine co-mediated approach to construct dihydropyrazino[2,3-b]indoles in 2-MeTHF as a green solvent at room temperature was established. A wide range of diversely substituted dihydropyrazino[2,3-b]indoles (42 examples, 61-85% yields) were synthesized under mild conditions, even on a gram scale. This protocol features organocatalysts, an eco-friendly solvent, mild conditions, readily accessible substrates, broad substrate scope and simple work-up.

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.