Microwave-mediated Synthesis of Medium Ring-sized Heterocyclic Compounds

Many medium ring-sized heterocyclic motifs are found in naturally occurring compounds of significant biological activity which led to the investigation of the biological activity of simpler heterocyclic compounds accommodating these ring systems. Therefore, the development of newer synthetic methodologies to access such ring systems has remained an important activity over the last few decades. However, common methods of their synthesis are usually associated with thermodynamic disadvantages. Many metal-mediated transformations e.g., Heck reaction, Suzuki reaction, etc. tend to overcome some of these effects but at the cost of environmental disadvantages. In recent years, several green chemical techniques have found useful applications in the synthesis of such ring systems. In particular, the use of microwave technology has provided better opportunities. The present review attempts to highlight many synthetic approaches developed for the synthesis of such heterocyclic scaffolds of pharmacological interest involving condensation reaction, coupling reaction, Multi-component reaction, Cyclo-addition reaction, Dipolar cycloaddition reaction, etc. An emphasis has also been given on the distinct advantages offered by microwave application over classical approaches, wherever such knowledge is available.