Believes versus evidence-based regio-orientation in the structure assignment of pyrazolo[1,5-a]pyrimidines

Abstract

This review aims to focus and highlight the regio-orientation and regioselectivity of the reactions of 3(5)-aminopyrazoles with 1,3-bielectrophilic reagents that lead to the formation of pyrazolo[1,5-a]pyrimidines. To clarify the significance of regio-orientation, reactions of 3(5)-aminopyrazoles with symmetric 1,3-bielectrophilic reagents such as acetylacetone and malononitrile are also included. The comparable nucleophilicity of the exocyclic NH2 group and endocyclic NH in 3(5)-aminopyrazoles is considered as it causes literature controversy associated with regio-orientation of the substituents on the pyrimidine ring of pyrazolo[1,5-a]pyrimidine when unsymmetrical 1,3-bielectrophilic reagent reacts with 3(5)-aminopyrazole. To the best of our knowledge, this review would be the first collective and confined report to the regio-orientation of pyrazolo[1,5-a]pyrimidines.