Synthesis of 3-Aryl-Substituted 4-Aminopyrazoles from Acetophenones

A synthetic methodology for a protecting-group-free formation of 3-aryl-substituted 4-aminopyrazoles from acetophenones via a telescoped oximation and hydrazine condensation of 1,3-ketoaldehydes to generate nitrosopyrazoles, and copper-catalyzed NaBH4 reduction of the nitroso group, was demonstrated. The synthesis tolerates a broad scope of substrates with a variety of substituents on the phenyl ring to afford the desired products.