Recent developments in the solvent-free synthesis of heterocycles

Heterocyclic molecules exhibit significant importance as they possess pharmacological, biological, and industrial applications. Although several excellent synthetic routes have been established for heterocyclic molecules, sustainable synthetic procedures such as microwave, ultrasound, grinding, photochemical, and thermodynamic route maps are needed to be explored further. Furthermore, these techniques become more eco-compatible when they produce value-added products in the absence of solvent. The advantages of these methodologies are to generate a library of small molecules, which will eventually combine to form complex bioactive molecules. In this review, we have emphasized recent studies (2010 to 2022) on the solvent-free conditions of various heterocycles (N, O, S), which have been synthesized via oxidation, reduction, condensation, and conjugated reactions. In this literature survey, glimpses of methodologies with their advantages, mechanistic considerations, and limitations are highlighted. These sustainable, and economically feasible routes will pave the way for a revolutionary corridor in the near future. We have emphasized recent studies (2010 to 2022) on the solvent-free conditions of various heterocycles (N, O, S), which have been synthesized via oxidation, reduction, condensation, and conjugated reactions.