Novel perfluoroalkyl‐substituted pyrazoles. 1. Hydroxypyrazoles

Abstract

Addition of methylhydrazine to a variety of haloalkyl‐substituted α,β‐unsaturated esters gives 1,5‐disubstituted 3‐hydroxypyrazoles, in contrast to the more common synthesis from β‐ketoesters, which gives 1,3‐disubstituted 5‐hydroxypyrazoles. This reaction is used to prepare several novel pyrazoles bearing haloalkyl substituents. Criteria for assignment of structures have been developed based on physical and spectroscopic properties of the isomers. The regiochemical preference in this addition is considered on the basis of steric, electronic, and mechanistic factors. Copyright © 1993 Journal of Heterocyclic Chemistry