3,5-Disubstituted-1H-pyrazoles: sequential syntheses from N-acylbenzotriazoles, alkynes, and hydrazine in ionic liquid

Abstract

A new procedure that is free of copper and palladium has been developed for the sequential synthesis of 3,5-disubstituted-1H-pyrazoles using various N-acylbenzotriazoles, terminal alkynes, and hydrazine. In this process, N-acylbenzotriazoles react with terminal alkynes in 1-butyl-3-methyl-imidazolium tetrafluoroborate, catalyzed by zinc chloride, to produce α,β-unsaturated alkynones. These intermediates are then converted into pyrazoles through an in-situ reaction with hydrazine. Additionally, the ionic liquid can be recovered and reused without significant loss of efficiency.