Redox Property of Enamines.

Abstract

Enamines are electron-rich compounds bearing intriguing redox properties. Herein, a series of secondary enamines condensed from primary amine and β-ketocarbonyls were synthesized and their electrochemical oxidation properties were systematically studied by cyclic voltammetry. Furthermore, theoretical calculation of oxidation potentials of enamines, particularly those catalytic intermediates, was also conducted to further broaden the scope investigated. Possible structural factors on oxidation and the nature of the resulted radical cation intermediates were revealed and discussed. Correlation of redox potentials with molecular properties such as highest occupied molecular orbital energies and natural population analysis charge were explored, and there appears no simple linear correlation. On the other hand, a good correlation with Mayr's nucleophilicity parameter N was noted among a range of catalytically relevant enamines. Spin population analysis disclosed that enamine radical cations mainly exhibit the carbon-center free radical feature. Taking experimental and computation data together, a comprehensive picture about the redox property of enamines is presented, which would provide guidance in the development of oxidative enamine catalysis and transformations.