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.