E. Lukyanenko, A. A. Borisenko, G. Grishina
Apr 1, 2004
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Chemistry of Heterocyclic Compounds
Abstract
We have shown that previously unknown optically pure trans-(3R,4R) isomers 4a-d with diastereomeric excess de > 99% and the diastereomeric pair of cis-(3S,4R),-(3R,4S) isomers 3a-d with de < 71% of N-[(1S)-1-phenylethyl]-4-amino-1,3-dialkylpiperidine are formed in 46%-90% yield by sequential lithiation and alkylation by alkyl halides of the chiral imines 1a,b, with formation of Z-(3S)-3-alkyland Z-(3R)-3-alkylimines 2a-d followed by their reduction by sodium borohydride in ethanol. The entire reaction sequence is carried out with no isolation of intermediates. The cis isomers 3a-d and the trans isomers 4a-d were separated by column chromatography on aluminum oxide; their structure and diastereomeric purity were established from elemental analysis, chromatomass spectrometry, and H, C NMR spectra. The cis and trans structure of isomers 3a-d and 4a-d was established by analysis of the vicinal spin–spin coupling constants for the 3-H and 4-H protons of the piperidine ring, using high-resolution one-dimensional and two-dimensional H NMR spectroscopy. Formation of only the