Green Synthesis of Pyrazoles: Recent Developments in Aqueous Methods

Organic syntheses by adopting green protocols such as sonochemical procedures, microwave technologies, solvent-free conditions, green solvents, heterogeneous catalysis particularly nanocatalysts, ionic liquids have replaced traditional procedures due to concerns pertaining especially to the environment. The heterocycle, pyrazole, due to its multifaceted applications, has been the target of chemists and therefore various synthetic approaches have been developed to synthesize pyrazole-containing molecules. In the present compilation, we have summarized recent water-based research work on the synthesis of pyrazoles. 1 Introduction 2 Synthesis of Polyfunctionalized Pyrazoles 3 Synthesis of Fused Pyrazoles in Water without Catalyst 3.1 Fused [5-5]System (3 Heteroatoms): Furo[2,3-c]pyrazoles 3.2 Fused [5-6]System (3 Heteroatoms): Pyrano[2,3-c]pyrazoles 3.3 Fused [5-6-6]System (3 Heteroatoms): Pyrazolo[3,4-b]quinolones 4 Synthesis of Fused Pyrazoles in Water Using Catalyst 4.1 Fused [5-5]System (3 Heteroatoms): Furo[2,3-c]pyrazoles 4.2 Fused [5-6]System (3 Heteroatoms): Pyrano[2,3-c]pyrazoles 4.3 Fused [5-6-6]System (2 Heteroatoms): Pyrazolo[1,2-b]phthalazines 4.4 Fused [5-6-6]System (3 Heteroatoms): Benzopyranopyrazoles 4.5 Fused [5-6-6]System (5 Heteroatoms): Pyrazolo[4',3':5,6]pyrido[2,3-d]pyrimidines and Pyrazolo[4',3':5,6]pyrano[2,3-d]pyrimidines 5 Conclusions