The basic utility and application of the ruthenium tetroxide (RuO₄) oxidation of N-acyl amines and their related compounds including optically active substrates, are described. The oxidation of the acyclic and cyclic N-acyl amines was carried out at room temperature by the active RuO₄, which was generated in situ from a catalytic amount of ruthenium dioxide (RuO₂·xH₂O) and an excess of 10% aqueous sodium metaperiodate (NaIO₄) in a double layer system of ethyl acetate-water to afford the corresponding imides in good to excellent yields. Cyclic ene-carbamates were oxidized at their carbon-carbon double bond to give the w-(N-formylamino)carboxylic acids as the major products. The conventional double layer system of the reaction media was changed to a single layer aqueous system containing tert-butanol, in which oxidation directly cleaved the endo-cyclic C-N bond to produce w-amino acids as the sole open-ring products. The syntheses of baclofen, lycoperdic acid, optically active pyrrolidine-3-phosphonic acids and L-carnitine were accomplished using the RuO₄ oxidation as the key step.