The reactivity of 3,5-dimethylidene-2,2,6,6-tetramethyl-4-oxopiperidin-1-oxyl and its diamagneticN-methyl analog in nucleophilic addition of amines and diels—Alder dimerization

3,5-Dimethylidene-1,2,2,6,6-pentamethyl-4-oxopiperidine was shown by the kinetic method to be less reactive than 3,5-dimethylidene-2,2,6,6-tetramethyl-4-oxopiperidin-1-oxyl in the nucleophilic addition of secondary amines and Diels—Alder dimerization. According to the quantum-chemical AM1 calculations, this is due to the difference in the structures of the activated complexes (in the reactions with amines) and to the “press” effect created by theN-methyl group that impedes the necessary cycle flattening (in the Diels—Alder reaction).