A Configurationally Stable Chiral Concave Imidazolinium Salt

Abstract

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.

Enantiopure Chiral Concave N‐Heterocyclic Carbene Precursors

“…[26] Motivated by the discovery that a change in the size of a concave N-heterocyclic carbene can influence its chemoselectivity, [23] new chiral bimacrocycles of varying sizes with nonamethylene (rac-4b·Cl -) and decamethylene chains (rac-4c·Cl -) were synthesized (Scheme 2). [26] Motivated by the discovery that a change in the size of a concave N-heterocyclic carbene can influence its chemoselectivity, [23] new chiral bimacrocycles of varying sizes with nonamethylene (rac-4b·Cl -) and decamethylene chains (rac-4c·Cl -) were synthesized (Scheme 2).…”

“…[26] based on high-performance liquid chromatography (HPLC) were successful. Two different approaches Scheme 2.…”

“…2,7-Dihydroxy-1-nitronaphthalene (7), [31] 2,6-bis(hex-5-enyloxy)aniline (5a), [24] and N-[2,6bis(pent-4-enyloxy)phenyl]-2-bromo-2-methylpropanamide (10a) [26] were synthesized according to literature procedures. 2,7-Dihydroxy-1-nitronaphthalene (7), [31] 2,6-bis(hex-5-enyloxy)aniline (5a), [24] and N-[2,6bis(pent-4-enyloxy)phenyl]-2-bromo-2-methylpropanamide (10a) [26] were synthesized according to literature procedures.…”

“…In our group, achiral concave Nheterocyclic carbenes have already been synthesized [24] and applied in both transition-metal catalysis [25] and organocatalysis. [26] In this paper, we present the synthesis of two new derivatives, 4b·Cland 4c·Cl -, with different ring sizes, the successful resolution of all three racemic chiral imidazolium salts 4·Cl -, and the assignment of the absolute configuration of the enantiopure bimacrocycles by circular dichroism analysis and calculation. [23] Furthermore, the challenge of synthesizing a configurationally stable axially chiral concave NHC precursor 4a·Clwas mastered.…”

“…[23] Furthermore, the challenge of synthesizing a configurationally stable axially chiral concave NHC precursor 4a·Clwas mastered. [26] In this paper, we present the synthesis of two new derivatives, 4b·Cland 4c·Cl -, with different ring sizes, the successful resolution of all three racemic chiral imidazolium salts 4·Cl -, and the assignment of the absolute configuration of the enantiopure bimacrocycles by circular dichroism analysis and calculation.…”