Electrochemically induced oxidative S-O coupling: synthesis of sulfonates from sulfonyl hydrazides and -hydroxyimides or -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 ). NH 4 Br 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. A variety of sulfonates were synthesized from sulfonyl hydrazides and N -hydroxy compounds via electrochemically induced oxidative S-O bond formation.