The anodic cyanation of methanolic solutions of the 2-alkyl-N-phenylpiperidines 6bâd was performed in a flow cell equipped with a graphite felt anode. The reaction led to the formation of the 2-cyano-6-alkyl-N-phenylpiperidines 2bâd and proceeded with a high degree of regioselectivity. The 1H NMR spectra of the aminonitriles 2bâd showed an epimeric mixture at C-6. The major isomer has a trans configuration in which the cyano group is axial and the alkyl substituent is equatorial. Conversely, electrochemical oxidation of the 4-methyl-6-pentyl-N-phenylpiperidine 6e afforded the trisubstituted aminonitrile 2e as a single diastereomer (>98% de). The 4-cyanobutyl side chain was incorporated in a two-step procedure to yield dinitrile 4e. This latter compound was directly converted into spiropiperidine 5e by using the ThorpeâZiegler annulation procedure. The overall sequence (4 steps, 43%) allows the construction of the basic carbon framework of perhydrohistrionicotoxin.
在配有石墨毡阳极的流动池中,对 2-烷基-
N-苯基哌啶 6bâd 的
甲醇溶液进行了阳极
氰化反应。反应生成了 2-
氰基-6-烷基-
N-苯基哌啶 2bâd,并且具有高度的区域选择性。
氨基
硝酸酯 2bâd 的 1H NMR 光谱显示,C-6 处存在一种外延混合物。主要异构体具有反式构型,其中
氰基为轴向,烷基取代基为赤道向。相反,电
化学氧化 4-甲基-6-戊基-
N-苯基哌啶 6e 得到的三取代
氨基腈 2e 为单一非对映异构体(de>98%)。在两步法中加入 4-
氰基丁基侧链,得到二腈 4e。后一种化合物通过 ThorpeâZiegler 环化程序直接转化为螺
哌啶 5e。整个过程(4 个步骤,43%)构建了全氢双
硫仑毒素的基本碳框架。