How Important is the Metal-free Catalytic Knoevenagel Reaction in Medicinal Chemistry? An Updated Review

The Knoevenagel condensation is a powerful and primary step for the development of carbon-carbon bond transformations. These condensations offer versatile products/ intermediates for diverse uses in polymers, cosmetics, chemical industries, and medicinal chemistry. Various homogenous and heterogenous catalysts have been found to promote the Knoevenagel condensation reaction, both environmentally and economically. Due to their attractive use in the production of pharmaceutical drugs, they are proven to be the main force that drives the synthesis involving numerous multi-component and multistep reactions. The present study, therefore, aims to summarise reported Knoevenagel condensation reactions using metal-free catalysts resulting in pharmaceutically useful compounds with anti-cancer, anti-tumor, anti-oxidant, anti-malarial, anti-diabetic, and anti- bacterial activities. By considering factors like their structure-activity relationships (SARs), the reaction conditions, and the steps involved, as well as the advantages and limitations of the particular approach, we also provide a general framework and direction in order to achieve superior characteristics of the catalyst.