ABSTRACT
Quinolines are a prominent heterocyclic motif and crucial building blocks in creating physiologically active compounds. Due to the fast development of novel medicines with a quinoline nucleus, numerous research papers have been published in a short amount of time. Therefore, to comprehend the present state of the quinoline nucleus in medicinal chemistry science, it is necessary to combine new information with older data. So far, several traditional synthesis techniques have been reported in the literature to synthesize this scaffold. Pfitzinger, Gould–Jacob, Friedlander, Skraup, Doebner–von Miller, and Conrad–Limpach are examples of old synthetic methods. However, they need expensive and demanding conditions, such as high temperature, the use of non-biodegradable chemical compounds degrade the ecosystem, create irritation or harm as pollutants, and represent a threat to the environment. However, traditional synthesis processes need a difficult and time-consuming apparatus set-up, resulting in high costs and pollutants. As a result, scientists are presently developing new and innovative techniques to decrease the use of chemicals, solvents, and catalysts, which are detrimental to both humans and the environment. Therefore, we have attempted to shed light in this current review on various reactions to produce quinolines and their derivatives using various green synthetic methods.