Ionic Liquids: Promising But Challenging Solvents for the Synthesis of N-Heterocycles

The use of ionic liquids to replace organic solvents in metal catalyzed reactions has recently gained much attention and great progress has been accomplished in this area in the last years. Therefore, considerable attention has been paid on the use of ionic liquids in chemical research. As the interest for environment increases and environmental laws become more stringent, the need to replace existing processes with new more sustainable technologies becomes a primary objective. The efficiency of a chemical synthesis can be nowadays measured, not only by parameters like selectivity and overall yield, but also by its raw material, time, human resources and energy requirements, as well as the toxicity and hazard of the chemicals and the protocols involved. Modern synthetic chemistry is benefited as ionic liquid methodology provided an environmentally benign approach. The multicomponent reactions in the presence of task-specific ionic liquids are used not only as environmentally benign reaction media, but also as catalysts. In comparison to traditional processes the use of ionic liquids resulted in improved, complimentary or alternative selectivities in organic synthesis. This review focuses on the advances in the development of innovative applications of ILs for the synthesis of N-heterocycles.