The reaction of alkyl 4-amino-2,6-diaryl-1,2,3,6-tetrahydropyridine-5-carboxylates with hydrazine hydrate results in the formation of 1-ammonio-2-aryl-4-imino-1,2,3,4-tetrahydropyridine 6-oxides, with elimination of one aryl group and the ester alkoxy group.