Electrochemical, EPR, and quantum chemical study of reductive cleavage of cone‐Calix[4]arene nosylates – New electrosynthetic approach

Abstract

AbstractThe mechanism of electrochemical reduction of a series of six cone‐calix[4]arene‐bis‐nosylates (4‐nitrophenylsulfonate aryl esters) was investigated on mercury electrodes using DC‐polarography and cyclic voltammetry (CV) combined with in situ electron paramagnetic resonance (EPR)‐spectroelectrochemistry in aprotic dimethylformamide. Model compounds – expected fragments and products ‐ were studied for comparison. The experimental results are supported by quantum chemical calculations. All calix[4]arene‐bis‐nosylates are reduced in a first reversible step to bis‐(radical anion) by two simultaneous one‐electron transfers. Each of the two electrons is unpaired and separately localized on two nosylate groups.In the second reduction step next 2×2 electrons are transferred and both sulfonate ester groups are cleaved to two 4‐nitro‐benzenesulfinate ions and a calixarene bis‐phenolate (95%). This electroreductive generation of arylsulfinate anions is a significant finding from the electrosynthetic point of view. Activated arylsulfinates, the synthesis of which is generally difficult, can be easily prepared by electrochemical reduction of the nosyl esters.