Cascade and stepwise oxidation of 4-phenyl- and 4-(γ-pyridyl)tetrahydropyridines

A general cascade and stepwise oxidation scheme for 4-aryl-substituted 1,2,3,6-tetrahydropyridines with KMnO₄ is described, which includes the consecutive oxidative transformation of the carbon triad in the substrate allylamine fragment, yielding tetrahydropyridin-2-ones, 3,4-dihydroxypiperidin-2-ones and, finally, 1-formylamino-3-arylpropan-3-ones