Pyrazine Radical Cations as a Catalyst for the Aerobic Oxidation of Amines

An efficient and green synthetic method for the preparation of N,N-disubstituted tetramethylpyrazinium radical cations was developed, which does not require any solvent or strong alkylating agents. The investigation by UV/Vis and electron paramagnetic resonance (EPR) spectroscopy proved the stability of the prepared radical cation. Moreover, it was shown for the first time that the prepared N,N-disubstituted tetramethylpyrazine can act as a powerful metal-free catalyst for the selective oxidative homocoupling of amines to the corresponding imines under solvent-free conditions. Furthermore, oxygen or even air can be employed as an efficient oxidative reagent.