Recent Developments in the Chemistry of Pyrazoles

The pyrazole motif has been found to be amenable to extensive, wide-ranging applications. A long-standing history of success has been achieved in the pharmaceutical field. More recent exploits have seen exciting developments in the areas of metal-organic frameworks, liquid crystals, and electroluminescence to name but a few. Such diverse applications have resulted in a demand for access to evermore complex examples of this diazole, which has driven synthetic chemists to develop a multitude of novel methods. In particular, modern methods have strived to overcome limitations in regioselectivity that are associated with classical methods. They have also sought to install significant molecular complexity within a single transformation to avoid lengthy functionalization sequences. As highlighted in this review, covering advances in the synthesis and application of pyrazoles in the past two decades, significant progress has been made in the use of metal catalysis, cycloaddition reactions, and multicomponent reactions for the construction of 5-membered heterocycles.