Electrocyclization for the Synthesis of Mono‐ and Disulfonyl‐substituted Pyrazoles From Sulfonyl Hydrazines and 1,3‐Diketones

The tunable electrocyclic reactions for the synthesis of a series of mono‐ and disulfonyl‐substituted pyrazoles from sulfonyl hydrazines and 1,3‐diketones were investigated by utilizing inexpensive electrolytes under electrochemical conditions in an undivided cell. When nBu4NBF4 was used as an electrolyte, it afforded monosulfonyl‐substituted pyrazoles. By contrast, when NH4I was used as an electrolyte, it gave disulfonyl‐substituted pyrazoles. The mechanistic investigation shows that they all underwent a free radical process but formed N‐centered sulfonyl hydrazine radical and S‐centered sulfonyl radical in the synthesis of mono‐ and disulfonyl‐substituted pyrazoles, respectively. A highly atom‐economical reaction of sulfonyl hydrazines with 1,3‐diketones to prepare mono‐ and disulfonyl substituted pyrazoles chemoselectively under electrochemical conditions. A series of sulfonyl‐substituted pyrazoles were obtained in high yields and in a short reaction time without external heating. The one‐step reaction avoids the separation of intermediate compounds, showing a good practical value.