DMF‐Catalyzed Direct and Regioselective C–H Functionalization: Electrophilic/Nucleophilic 4‐Halogenation of 3‐Oxypyrazoles

Abstract

Abstract A novel, straightforward, and highly regioselective 4‐chlorination of 3‐oxypyrazole derivatives in boiling thionyl chloride (SOCl 2 ) in the presence of catalytic N , N ‐dimethylformamide (DMF) has been developed. This reaction likely proceeds through a DMF‐catalyzed electrophilic/nucleophilic chlorination mechanism and involves electrophilic attack by SOCl 2 and nucleophilic substitution by Cl – as the key steps. Based on this mechanism, the corresponding 4‐bromination and 4‐iodination of 3‐oxypyrazoles have also been achieved in good yield by adding Br – and I – , respectively, to the reaction system. This halogenation method enables quick access to many original 4‐halo‐3‐oxypyrazole series.