NEW METHODS FOR THE SYNTHESIS OF PIPERIDINE ALKALOIDS AND THEIR PRECURSORS USING ANODIC-OXIDATION AS A KEY REACTION

This article describes new methods to introduce a variety of substituents into the α, β or γ position of a piperidine ring by utilizing anodic oxidation as a key reaction. The following patterns of anodic oxidation were exploited to activate the α and β positions of N-methoxycarbonylpiperidines A; (1) anodic oxidation of A in methanol containing Et4NOTs to give the α-methoxylated products B, (2) anodic oxidation of A in acetic acid to give the α, β-bisacetoxylated products C, (3) anodic oxidation of A to afford β-halogenated α-hydroxy- or α-methoxy-piperidine derivatives D, and (4) anodic decarboxylation of pipecolinic acid derivatives to afford B or C. The position of A was activated by converting B or D into β, unsaturated α-methoxypiperidine derivatives E. The activated compounds B, C, D and E were used as useful precursors to introduce substituents into the desired positions of piperidine ring, and some alkaloids containing a piperidine skeleton such as coniine, optically active N-methylconiine, conhydrine, and eburnamonine were synthesized from these precursors. © 1990, The Society of Synthetic Organic Chemistry, Japan. All rights reserved.