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Enantiopure Chiral Concave N‐Heterocyclic Carbene Precursors
Author(s) -
Reimers Tim,
Haberhauer Gebhard,
Benkhäuser Christian,
Schmidtchen Franz P.,
Lützen Arne,
Lüning Ulrich
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201300830
Subject(s) - enantiopure drug , chemistry , alkene , metathesis , carbene , ring (chemistry) , stereochemistry , ring closing metathesis , organic chemistry , enantioselective synthesis , catalysis , polymer , polymerization
Abstract Chiral concave imidazolinium salts 4· Cl – with different ring sizes were synthesized as precursors of chiral concave N‐heterocyclic carbenes, starting from di‐ ortho ‐substituted anilines 5 and 2,7‐disubstituted aminonaphthalenes 6 . The terminal alkene groups of the substituents were cyclized by ring‐closing metathesis to give bimacrocyclic axially chiral concave imidazolinium salts 14· Cl – , and, after hydrogenation of the double bonds, 4· Cl – . The overall yields of bimacrocycles 4b· Cl – and 4c· Cl – were 54 and 39 %, starting from amino‐substituted arenes 5 and 6 , respectively. Racemic mixtures of the three concave NHC precursors 4a – c· Cl – were separated by chiral HPLC techniques, and their absolute stereochemistry was assigned by comparison of simulated and experimental CD spectra.