Electrochemical cascade pyrazole annulation and C-H halogenation for the synthesis of 4-halopyrazoles

The synthesis of 4-halo-functionalized pyrazoles by electrochemical cascade reactions between N,N-dimethyl enaminones and proper hydrazine reagents in the presence of a halogen source is realized at room temperature. The work provides tunable and efficient accesses to 4-chloro- and 4-bromopyrazoles in aqueous THF (tetrahydrofuran) without using any transition metal reagent.