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

Abstract

Abstract The 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.

Keywords

• calixarene bis‐nosylates
• cyclic voltammetry
• DC‐polarography
• electrochemical generation of sulfinates
• in‐situ EPR spectroelectrochemistry
• quantum chemical calculations