Oxidation cyclischer α-Aminoketone Oxidation of Cyclic α-Aminoketones

The 1,2,3,4-tetrahydro-isoquinolin-4-one 4 reacts as an α-amino ketone with periodate to give various products, the major compound being 1-hydroxy-1,2-dihydro-3,4-isoquinolinedione 12. Upon stepwise oxidation with Hg(II)-EDTA the 4-hydroxyisoquinolinium ion 14 is detected as an intermediate and its further oxidation with periodate gives rise to an almost identical product spectrum. Because 12 represents a carbinolamide with an additional 4-carbonyl group, this type was examined first. Acid catalysis was used because the reactive species mostly are iminium ions. With cyclic 1,3dicarbonyl compounds, 1-substituted derivatives 17a, b are formed. With linear species 1-substitution is also observed, but the tautomeric forms 19a – c are obtained. The stable enones 24a, b result from alkyl ketones by ready autoxidation of the primary products. Base catalysis induces a ring contraction of 12 to the hydroxycarboxylic acid 25. Reaction of 12 with aniline and phenylhydrazine yields the easily oxidizable 1-substitution products 28 and 31.