Regioselective Synthesis of 5-Substituted Pyrazoles

Copper(I)-Catalysed Reaction of Hydrazonyl Chlorides with Homopropargylic Alcohols: Regioselective Synthesis of 5-Substituted Pyrazoles: A. Silvani, M. Manenti, G. Molteni
Synthesis 2022, DOI: 10.1055/s-0042-1751770


5-Hydroxyethyl-substituted pyrazoles are interesting scaffolds for drug discovery and medicinal chemistry applications, and novel straightforward synthetic routes to these compounds are highly desirable. 1,3-Dipolar cycloadditions are well-established reactions for the synthesis of a broad range of 5-membered heterocycles, but their use for the direct synthesis of 5-hydroxyethyl-pyrazoles is a challenging endeavor, which was recently addressed by the group of Professor Giorgio Molteni (Università degli Studi di Milano, Italy) who developed an efficient method based on the copper(I)-catalyzed reaction of hydrazonyl chlorides with homopropargylic alcohols.


Professor Molteni said: “We believe that intramolecular complexation of copper(I) by carbinol oxygen could lead to the formation of a dinuclear copper(I) intermediate, which would explain both the novel, regioselective synthesis of 5-substituted pyrazoles and the different kinetic behavior of alkynes that do not contain an hydroxyl group.”

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