Recent Advances in the Microwave and Ultrasound-Assisted Synthesis of Pyrazole Scaffolds

Pyrazoles are well-known five-membered heterocyclic compounds and are found in a wide variety of synthetic and natural compounds. Compounds carrying pyrazole scaffolds exhibit a wide range of biological activities such as anticancer, antimicrobial, anticonvulsant, antioxidant, analgesic and anti-inflammatory effects. Pharmaceuticals with many different activities in the pyrazole structure are currently on the market (e.g., celecoxib, lonazolac, tepoxalin, rimonabant, pyrazofurin, epirizole). The pyrazole ring contains the N-N double bond, which is thought to have a key role in biological activity, and compounds with this bond are difficult to produce by organisms, so their relative abundance is very low in nature. For this reason, many studies have been carried out on this structure and it has been revealed that the structure has a unique effect spectrum. Microwave-assisted synthesis has opened up some new opportunities compared to conventional synthesis. It is possible to use less solvent and reduce processing time with microwave synthesis. In addition, better selectivity and thermal stability are provided by microwave synthesis. Ultrasound-assisted synthesis is often used to enhance conventional solvent extraction, while microwaves reveal bioactive compounds by heating without any solvent. In the traditional method of pyrazole synthesis; polar solvents, acidic and basic catalysts are needed in large quantities in the synthesis of pyrazole scaffolds. This review aims to summarize the recent advancements in the synthesis methods of a pyrazole ring with nontraditional methods. Therefore this article will provide readers with a new perspective on the synthesis of pyrazole scaffolds as an environmentally friendly alternative.