Electrochemical oxidation of ferrocenylsubstituted 1,4-dihydropyridines

Abstract

1-p-Ferrocenylphenyl- and 4-ferrocenylsubstituted Hantzsch esters were subjected to electrochemical oxidation using a graphite cyclic rotating disk electrode in acetonitrile medium; in each case the initial response was one-electron oxidation of the ferrocenyl substituent to give a ferrocenium cation, which was followed by a two-electron electrochemical oxidation of the dihydropyridine ring involving intermediate deprotonation of the latter and formation of a ferroceniumpyridinium dication. We have also detected for the first time at room temperature relatively stable cation radicals of 2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine containing a cationic ferrocenium substituent in the 4-position; these proved to be more stable than cation radicals of dihydropyridines containing ferrocenyl substituents attached to the nitrogen atom.