Diastereoselective preparation of 2,4,6-trisubstituted-2′-cyanopiperidines: application to the construction of the carbon framework of perhydrohistrionicotoxin
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.
The fire ant venom alkaloid (′)-solenopsin A was prepared in 4 steps (34%) starting from the N-phenyl-2-undecyl piperidine (1c). The key step in this synthesis involved the dearomatization of the phenyl group of N-phenyl-2-methyl-6-undecyl-piperidine (9c), which was carried out under Birch conditions.
<i>N</i>-phenyl-substituted pyrrolidines, piperidines and azabicyclics by a tandem reduction-double reductive amination reaction
作者:Richard A. Bunce、Derrick M. Herron、Jason R. Lewis、Sharadsrikar V. Kotturi
DOI:10.1002/jhet.5570400115
日期:2003.1
formed in high yield and are easily purified. The method has also been extended to the synthesis of fused N-phenylazabicyclics from 2-(3-oxo-propyl)cycloalkanones. A high degree of diastereoselectivity for the trans-fused product is observed in substrates having an ester group α to the cycloalkanone carbonyl. Bicyclic precursors lacking this ester group give mixtures of cis and trans products. Finally