Conformational studies by dynamic nuclear magnetic resonance. Part 17. Stereodynamic processes in hindered piperidyl-amides and -amidines

Abstract

It has been shown that molecules containing hindered piperidyl rings can have planar or perpendicular conformations depending on the functional group attached to nitrogen. In addition, we have shown that when the group is CRNPh (amidines) the molecule may switch from a planar to a perpendicular conformation depending on the steric hindrance generated by alkyl substituents. Also, the position of the 2,6-cis-methyls in the dimethylpiperidyl ring (axial or equatorial) depends on the overall molecular conformation (planar or perpendicular). Finally, in at least one case we demonstrated that the dynamic motion usually observed is rotation at the NC bond, as previously assumed, in that only at lower temperature could a second motion (ring reversal or nitrogen inversion) be detected.