Ionic liquid-assisted approaches in the synthesis of nitrogen-containing heterocycles: A focus on 3- to 6-membered rings

• Heterocyclic chemistry finds broad uses in biology, pharma, and industry. • ILs are important for their stability, eco-friendliness, and recyclability. • ILs enhance yield, and efficiency in nitrogen-heterocycle synthesis. • IL-based catalysis drives sustainable, efficient, and eco-friendly synthesis. Nitrogen-containing heterocyclic compounds represent one of the most significant groups in traditional organic chemistry. Many pharmaceuticals, designed to replicate the bioactivity of natural compounds, contain these nitrogen-based heterocyclic compounds. Organic chemists have invested substantial effort into creating these compounds, focusing on innovative and efficient synthetic methods. Ionic liquids (ILs) are highly valued in organic synthesis due to their unique characteristics, such as a wide liquid range, superior solvating properties, low vapour pressure, non-flammability, eco-friendliness, and high thermal stability. They also enhance reaction rates and are easily recyclable. Their dual role as both catalysts and reaction media has drawn significant attention from chemists. With about 4000 research papers published annually, ILs continue to be a major focus of scientific exploration, particularly in the synthesis of nitrogen-containing heterocyclic compounds. This review aims to portray the synthesis of nitrogen-containing heterocyclic compounds (3-membered to 6-membered) assisted by ionic liquids.