New oxidative reactions of 1,2,3,6-tetrahydropyridines: imination, lactamination and decyclisation in the presence of potassium permanganate

A novel oxidative imination reaction of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine 1a by 4-nitroaniline/potassium permanganate has been found to occur yielding 2-(4-nitrophenyl)imino-1,2,5,6-tetrahydropyridine 4; in the absence of nitroaniline the shorter reaction time allows the reaction to be stopped at the unsaturated lactam 5 formation stage; the oxidation of 1a hydrochloride leads to 1-(N-formyl-N-methyl)amino-3-phenylpropan-2-one 6 via decyclisation–elimination steps, providing a new method for N-formyl-substituted aminoketone synthesis.