Alkyne Synthesis from 5-Pyrazolone Derivatives (2025)

The alkyne functional group is characterized by a π-electron rich, sp-hybridized carbon-carbon triple bond (C≡C). The two π bonds make alkynes valuable intermediates in modern organic synthesis, allowing complex molecule construction by cross coupling or cycloaddition. Notably, alkynes play a central role in “Click” cycloadditions, which efficiently construct useful 1,2,3-triazoles by coupling an alkyne and an azide in the presence of a copper(I) catalyst. Despite their versatility, there are few practical syntheses to construct the alkyne triple bond without halogenated hydrocarbons or toxic materials. 5-pyrazolone derivatives, readily obtained from the action of hydrazine hydrate on β-keto esters, provide a promising scaffold for alkyne synthesis, including cyclic alkynes. Our research has focused on developing new methodology for the synthesis of alkynes from 5-pyrazolone derivatives, using the elimination of N2 gas to drive the reaction irreversibly forward.