Palladium N-heterocyclic carbene catalyzed regioselective C–H halogenation of 1-aryl-3-methyl-1H-pyrazol-5(4H)-ones using N-halosuccinimides (NXS)

Abstract

A novel palladium N-heterocyclic carbene [Pd(NHC)Cl₂] complex of vitamin B₁ was synthesized and characterized by ¹H NMR, EDX, FT-IR and UV–visible spectroscopy. The complex was used as a catalyst for regioselective ortho-C–H chlorination/bromination of 1-aryl-3-methyl-1H-pyrazol-5(4H)-ones via C–H bond activation utilizing Ag₂O as the effective terminal additive. The catalyst was easy to prepare, efficient and found to be highly regioselective, affording the target products in moderate to excellent yields.