Mild and Efficient Flavin-Catalyzed H2O2Oxidation of Tertiary Amines to AmineN-Oxides

A mild and highly effective H2O2 oxidation of tertiary amines has been developed by the use of flavin catalysis. Eight aliphatic amines were oxidized to their corresponding N-oxides in fast and selective reactions. For all substrates a considerable rate enhancement was observed compared to the noncatalyzed reactions. The product N-oxides were isolated in good yields using this mild oxidation system based on the environmentally attractive oxidant H2O2. As the catalyst, an N1,N5-dialkylated flavin was used as an analogue of the biologically important flavin redox cofactor. The catalytic cycle proposed for the flavin catalysis accounts for the observation that, in addition to the hydrogen peroxide oxidant, molecular oxygen is required for the initiation of the process.