Peculiarities of the three-dimensional structures of isomers of 1,2,5-trimethyl-4-amino(amido)piperidines from the 1H and 13C NMR spectra

The three-dimensional structures of seven 1,2,5-trimethyl-4-amino(amido)piperidines were studied by means of the ¹H and ¹³C NMR spectra. The ³J_HH values and the ¹³C chemical shifts indicate that the substituents in the piperidine ring of all of the 2c,5c,4r isomers have a 2e,4e,5a orientation, while those in the piperidine ring of all of the 2c,5t,4r isomers have a 2e,4e,5e orientation. The conformational change (as a result of ring conversion) 2e,4a,5e 2a,4e,5a was observed for the 2t,5c,4r isomers on passing from the corresponding amine to the amide; this change is associated with striving of the more bulky amide substituent to become equatorially oriented. Retarded rotation about the C₍₄₎-N bond was observed in the 2c,5t,4r isomer of the 4-(N-phenylbenzamido) derivative; this is explained by steric hindrance due to the 5e-CH₃ group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 54–57, January, 1988.The authors thank I. I. Chervin for assistance in recording the NMR spectra with a WM-400 spectrometer.