EPR studies on carboxylic esters, 23 [1]. Preparation of new dialkyl azulenedicarboxylates and EPR-spectroscopic study of their radical anions

Abstract

Abstract Selected dialkyl azulenedicarboxylates were prepared by carbo-bromination of alkyl azulenemonocarboxylates and subsequent alcoholysis or by alkoxycarbonylcarbene insertion of ethyl indane-2-carboxylate. The electrochemical behavior of the diesters was studied by means of differential pulse polarography and cyclovoltammetry. In-situ electroreduction of the azulenedicarboxylic esters led to the corresponding radical anions, the EPR spectra of which were recorded. For certain radical anions a rearrangement under migration of the functional group from the 5- into the 6-position was observed. The spin density distribution in these non-alternant π-electron systems as determined from the proton hyperfine structure (hfs) coupling constants was compared with the results of MO calculations and discussed with respect to the influence of substituents.