Conformational study of some 3t, 5t-Dimethyl -N-nitroso-2r, 6c-diarylpiperidin-4-one oximes using NMR spectra

Stereochemistry of 3t,5t-Dimethyl-N-nitroso-2r,6c-bis(o-chlorophenyl) piperidin-4-one oxime (1) and 3t,5t-Dimethyl-N-nitroso-2r,6c-bis(p-chlorophenyl) piperidin-4-one oxime (2) has been studied using H-1, C-13 and two-dimensional NMR spectra. Analysis of the spectral data shows that both the compounds seem to exist largely in boat conformations with one aryl group in the flagpole position and also among the two methyl groups one is in axial and other one is in equatorial orientations. Analysis on the reported spectral data on 3t-alkyl-N-nitroso-2r,6c-diphenylpiperidin-4-one oximes suggests that these compounds largely exist in boat conformations with one phenyl group in the flagpole position. Chair conformation with axial substituents may contribute and their order of stability depends on the nature of alkyl substituent at C-3. The relative populations of the conformations have been supported by the observed vicinal coupling constants and NOEs in their NOESY spectra. (C) 2019 Elsevier B.V. All rights reserved.