C-13 and H-1 NMR of 2,6-diaryl-1-hydroxy piperidin-4-one oximes; substituent effects on cis/trans ratio and conformational equilibria

The reaction of substituted diarylidene acetones with hydroxylamine hydroch loride affords isomeric N-hydroxy diaryl piperidinone oximes as main produc ts. The structures as well as conformational equilibria of these products w ere established by H-1 and C-13 NMR spectroscopy and further studied by var iable temperature NMR. It was found that the cis/trans ratio of 2,6-substit uted piperidine derivatives depended on the position of the substituent on the aromatic ring. (C) 2000 Elsevier Science B.V. All rights reserved.