Highly Regioselective Organocatalyzed Synthesis of Pyrazoles from Diazoacetates and Carbonyl Compounds

A general, organocatalytic inverse-electron-demand [3+2] cycloaddition reaction between a range of carbonyl compounds and diazoacetates has been developed. This reaction is catalyzed by secondary amines as a green promoter to generate substituted pyrazoles with high levels of regioselectivity. It is noteworthy that this [3+2] cycloaddition reaction proceeds efficiently at room temperature with a simple and inexpensive catalyst. Considering the large variety and ready availability of the starting materials (e.g. ketones, -ketoesters, -diketones, and aldehydes), as well as the operational simplicity of this process, a convenient, practical, and highly modular pyrazole synthesis has been developed. We believe that this work will arouse more research interest in the organocatalytic synthesis of other biologically active heterocycles. Such studies are currently underway in our laboratory.