Oxidative Reactions of Azines. 9. Cascade and Stage Oxidation of 1,4-Disubstituted 1,2,3,6-Tetrahydropyridines by Potassium Permanganate

A general scheme was developed for the cascade and stage oxidation of 1,4-disubstituted 1,2,3,6-tetrahydropyridines by potassium permanganate, based on the successive oxidation of the allylic triad of carbon atoms in the piperideine ring. In the case of 4-aryltetrahydropyridines 2-oxotetrahydropyridines are formed initially. 3,4-Dihydroxypiperidin-2-ones and finally 1-aminoalkan-3-ones are then formed. The oxidation of 4-methyl-substituted tetrahydropyridines to the analogous 1-aminoalkanones begins differently - with 3,4-dihydroxylation followed by lactamization of the piperidinediols.