Catalyst-free electrochemical sulfonylation of amines with sulfonyl hydrazide in aqueous medium

An efficient electrochemical sulfonylation of amines with sulfonyl hydrazides under exogenous-oxidant-free and catalyst-free conditions in aqueous medium was developed. A wide variety of sulfonamides were prepared via a simple electrochemical process from various cyclic or acyclic secondary amines, as well as more challenging free primary amines with equivalent amount of aryl/heteroaryl hydrazides in air under mild conditions. This protocol was found to be excellent in terms of facile scale-up, and to show great potential in the modification/synthesis of bioactive compounds. The reaction mechanism was investigated by a series of control experiments and CV studies, which indicated that the reaction might have gone through a radical pathway. Also, n-Bu₄NBr served both as a supporting electrolyte and a redox agent to yield sulfonyl radical species and sulfonyl cations from sulfonyl hydrazides.