Convenient synthesis and NMR spectral studies of variously substituted N-methylpiperidin-4-one-O-benzyloximes

摘要

A series of variously substituted N-methylpi-peridin-4-one-O-benzyloximes were synthesized by three different methods.Among them,the direct conversion of 2,6-diarylpiperidin-4-ones into the corresponding oxime ethers(method A)was proved to be better than the other two methods in the sense of good yield,convenience,easy work-up and quick reaction time.All the synthesized compounds are characterized by IR,Mass and NMR(~1H NMR,~(13)C NMR,~1H-~1H COSY,~1H-~(13)C COSY and HMBC)spectral studies.The conformational preference of the synthesized oxime ethers with/without alkyl and aryl substituents at C-3/C-5 and C-2/C-6 is discussed using the spectral data.The observed chemical shifts and coupling constants suggest that the synthesized oxime ethers adopt chair conformation with equatorial orientation of all the substituents,whereas 1-methyl-3-isopropyl-2,6-diph-enylpiperidin-4-one-O-benzyloxime also exists in boat conformation.Based on the NMR data,the effects of ox-imination on ring carbons and their associated protons and alkyl substituents are discussed.In addition,the effect of NMe group on the 2,6-diarylpiperidin-4-one-O-benzyloxi-mes was also studied.