Synthesis, spectral and single crystal X-ray diffraction studies of novel O-(Carboalkoxy)methyl oxime ethers of 3-alkyl and 3,5-dialkyl-1-methyl-2,6-diphenylpiperidin-4-ones

A series of novel O-(Carboalkoxy)methyl oxime ether derivatives of 3-alkyl and 3,5-dialkyl-1-methyl-2,6-diphenylpiperidin-4-ones were synthesized and characterized through FT-IR, Mass, 1H NMR, 13C NMR, 1H1H COSY, 1H13C COSY and NOESY spectral techniques. The stereocontrolled formation of E-isomer exclusively in all the cases was confirmed by NMR spectral analysis. A1,3 strain induced epimerization of C5 carbon in the case of compounds 18 and 23 was also observed. The preferred conformation of compounds 16, 17, 20, 21, 22 and 25 was found to be chair and for compounds 19 & 24 it was boat while compounds 18 and 23 adopt a twist boat conformation as observed by 1H NMR and NOESY spectra. The solid state geometry of compound 16 was established by single crystal X-ray diffraction analysis.