Electrochemical reduction of 3-iminoindolenine derivatives in dimethylformamide

Abstract

The electrochemical behaviour of 3-iminoindolenine derivatives (Ia−g) in DMF solution was studied by polarography, cyclic voltammetry, controlled-potential coulometry and ultraviolet spectroscopy. In aprotic medium (DMF with KClO4 as background electrolyte) compounds (Ia−g) are reduced at a mercury dropping electrode in two-electron steps. The potentials of the first reversible step have been correlated with the Hammett constants. In the presence of 3,4-dimethylphenol the first wave grows in height at the expense of the second until with sufficient protonating agent only one wave of two-electron height is observed. On addition of benzoic or monochloroacetic acid as protonating agent, the two normal waves of aprotic medium are gradually replaced by a single two-electron wave at less negative potentials. The electrochemical reduction products of compounds (Ia−g) are 3-aminoindole derivatives (IIa−g). A multi-step scheme for the electrochemical reduction of (Ia−g) is suggested to explain the various experimental results obtained.