Regioselective Synthesis of N -Vinyl Pyrazoles from Vinyl Sulfonium Salts with Diazo Compounds.

Herein, we develop a base-promoted regioselective synthesis of N -vinyl pyrazoles from vinyl sulfonium salts with diazo compounds. This metal-free synthetic protocol provides an efficient and practical approach to diverse N -vinyl pyrazoles in good to excellent yields under mild conditions. The reaction appears to experience a [3 + 2] annulation of vinyl sulfonium salts and diazo anions rather than diazo compounds, followed by N -vinylation.