Aerobic and electrochemical oxidative cross-dehydrogenative-coupling (CDC) reaction in an imidazolium-based ionic liquid.

The ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF(4)] has demonstrated high efficiency when applied as a solvent in the oxidative nitro-Mannich carbon--carbon bond formation. The copper-catalyzed cross-dehydrogenative coupling (CDC) between N-phenyltetrahydroisoquinoline and nitromethane in [BMIm][BF(4)] occurred with high yield under the described reaction conditions. Both the ionic liquid and copper catalyst were recycled nine times with almost no lost of activity. The electrochemical behavior of the tertiary amine substrate and beta-nitroamine product was investigated employing [BMIm][BF(4)] as electrolyte solvent. The potentiostatic electrolysis in ionic liquid afforded the desired product with a high yield. This result and the cyclic voltammetric investigation provide a better understanding of the reaction mechanism, which involves radical and iminium cation intermediates.