Synthesis of Aminopyrazoles from Isoxazoles: Comparison of Preparative Methods by in situ NMR Analysis

A single-step method and a two-step method for the synthesis of aminopyrazoles from isoxazoles are presented and compared. Based on in situ NMR monitoring, both processes proceed through a ketonitrile. In the single-step process, hydrazine serves to both open the isoxazole to the unisolated ketonitrile intermediate and form the aminopyrazole. The two-step process involves ring opening of the isoxazole by deprotonation with hydroxide to generate the ketonitrile followed by the addition of acetic acid and hydrazine to form the aminopyrazole.