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Surprisingly Difficult Resolution of N ‐Methylated Cationic [4]Helicenes
Author(s) -
Mehanthalie,
Grass Stéphane,
Lacour Jérôme
Publication year - 2012
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.22032
Subject(s) - chemistry , diastereomer , enantiopure drug , enantiomer , cationic polymerization , chirality (physics) , adduct , resolution (logic) , stereochemistry , chromatography , organic chemistry , enantioselective synthesis , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , artificial intelligence , quark , computer science , catalysis
1,13‐Dimethoxyquinacridinium ions of type 3 are highly configurationally stable [4]helicenes that can be synthesized in racemic form in a single step from tris(2,6‐dimethoxyphenyl)methylium ion. Previously, it had been shown that the single enantiomers can be routinely obtained from racemic mixtures through Pummerer fragmentations of diastereomerically pure sulfoxide adducts that release the enantiopure cations after a C–C bond rupture. This resolution protocol is readily performed because of a (normally) large retention difference of the diastereomers over silica gel. Herein, we report that it is not always the case. Introduction of N ‐methyl side chain(s) at the periphery of the helical quinacridinium cations, which are needed for photophysical and biological studies, has a large negative effect of this separation. Instead of simple, rapid, and multigram separations by flash chromatography , extensive semi‐preparative high‐performance liquid chromatography sequences are now required. Chirality 24:928–935, 2012 . © 2012 Wiley Periodicals, Inc.