Electrochemically induced oxidative S–O coupling: synthesis of sulfonates from sulfonyl hydrazides and N-hydroxyimides or N-hydroxybenzotriazoles†
The process of oxidative S–O coupling under the action of electric current was developed. Aryl, hetaryl and alkyl sulfonyl hydrazides and N-hydroxy compounds (N-hydroxyimides and N-hydroxybenzotriazoles) are applied as starting reagents for the preparation of sulfonates. The reaction is carried out under constant current conditions in an experimentally convenient undivided electrochemical cell equipped with a graphite anode and a stainless steel cathode under a high current density (60 mA cm−2). NH4Br in this process acts as a supporting electrolyte and participates in the oxidation of the starting compounds to form a coupling product. The developed strategy represents a quite atom-efficient approach: one partner loses two nitrogen and three hydrogen atoms, while another one loses only one hydrogen atom. Cyclic voltammetry and the control experiment allowed us to propose possible reaction pathways: generated through anodic oxidation molecular bromine or its higher oxidation state derivatives oxidize the starting compounds to form reactive species, which couple to form the S–O bond.