Starting from symmetric bis‐ortho‐alkenyl‐substituted aniline 11 and unsymmetric bis‐alkenyl‐substituted aminonaphthalene 12, imidazolinium salt 17 has been prepared. Salt 17 was cyclized by ring‐closing metathesis, and hydrogenation gave axially chiral N‐heterocyclic carbene precursor 19. The configurational stability of 19 was proven by temperature‐dependent NMR studies and also by the use of Λ‐BINPHAT as a chiral shift reagent. Compound 19 was also characterized by single‐crystal X‐ray diffraction.
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.
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