Electrocatalytic three-component synthesis of 4-halopyrazoles with sodium halide as the halogen source.

The first example of the electrocatalytic multicomponent synthesis of 4-chloro/bromo/iodopyrazoles from hydrazines, acetylacetones and sodium halides under chemical oxidant- and external electrolyte-free conditions has been developed. Sodium halides played a dual role as a halogenation reagent and a supporting electrolyte. Mechanism studies revealed that the bromination reaction proceeded <i>via</i> an ionic pathway, whereas both chlorination and iodination proceeded <i>via</i> a radical pathway.