Synthesis, 1D and 2D NMR spectral assignments, and stereochemical studies of some 4,8,9,10-tetraaryl-1,3-diazaadamantan-6-one oximes

Abstract

A series of 4,8,9,10-tetraaryl-1,3-diazaadamantan-6-one oximes (4a-4e) have been synthesized. 1H and 13C NMR spectra of these oximes were recorded. Chemical shifts have been assigned and the stereochemistry of the compounds was established using 1D and 2D NMR spectral data. A detailed spectral investigation was carried out for one of the representative compounds (4a) with COSY, NOESY, HMQC, HMBC, DEPT-135, and N NMR spectral data. The NMR result clearly indicated the twin chair conformation of the two piperidine rings. The NMR results proved the axial orientation of two aryl groups (C4 and C10) in one piperidine ring and equatorial orientation of two aryl groups (C8 and C9) in another piperidine ring. The effect of allylic (A1,3) interaction between the oxime hydroxyl group and H-5e has been observed. Long-range coupling between H-10e and H-2 which are in ‘W’ arrangement is noted.