Halogenations of 3-Aryl-1H-pyrazol-5-amines

Abstract

AbstractA direct C–H halogenation of 3-aryl-1H-pyrazol-5-amines using N-halogenosuccinimides (NXS; X = Br, I, Cl) in dimethyl sulfoxide at room temperature has been developed. This transformation provides an effective metal-free protocol for the synthesis of novel 4-halogenated pyrazole derivatives with moderate to excellent yields. The method utilizes NXS reagents as cheap and safe halogenating reagents under simple and mild reaction conditions, it has broad substrate scope, and can be used for gram-scale synthesis. The utility of this procedure is established by further transformations of the 4-halogenated products. Mechanism studies show that DMSO plays a dual role of catalyst and solvent.