Preparation of enantiopure biimidazoline ligands and their use in asymmetric catalysis

Abstract

A convenient new method for the preparation of 2,2'-biimidazolines is reported. Amino alcohols were reacted with dimethyl oxalate, and the product hydroxy amides converted into chloroamides by reaction with thionyl chloride. Treatment with PCl5, followed by diamines (ethanediamine, propane-1,3-diamine, 2,2-dimethylpropane-1,3-diamine) furnished a series of enantiopure tricyclic biimidazolines. Complexes of two of the ligands with PdCl2 were prepared and their X-ray crystal structures were determined. The biimidazolines were tested as ligands for asymmetric Pd-catalysed allylations. Moderate enantioselectivity (up to 80% ee) was found for the reaction of dimethyl malonate with diphenylallyl acetate, with the 5,7,5 fused tricyclic systems outperforming the 5,6,5 analogues. The corresponding reaction of pentenyl acetate gave lower enantioselectivity (44-57% ee), and proved very sensitive to the donor strength of the ligands, the stronger donors giving lower yields. The results provide a further demonstration of the value of the 'tunability' of imidazoline ligands.

Vicinal Diamino Functionalities as Privileged Structural Elements in Biologically Active Compounds and Exploitation of their Synthetic Chemistry

“…Overall, the majority of the preparations of these compounds have focused on condensation reactions of diamines with dialdehydes or other appropriate electrophiles. A notable exception was reported by Casey and co-workers (78). Two equivalents of chiral vicinal amino alcohols were treated with dimethyl oxalate to form the diamide.…”

Synthesis and Application of Diphenyl Sulfide Linked Bis(imidazoline) Ligands: Dramatic Electronic Effect of Ligands on Catalytic Behavior

“…In this case, the Hendrickson reagent cannot be used for the nucleophiles of the corresponding diamines (instead of the sulfonamides in 4), as they may destroy the reagent. Finally, desired ligands 1g-i with electron-donating substituents were synthesized following Casey's procedure [8] by using bis(β-hydroxy amide) 8 as precursor (Scheme 2), which was the intermediate in our bis(oxazoline) preparation.…”

Synthesis, spectral analysis, and in vitro microbiological evaluation of ethyl 7,9-diaryl-1, 4-diazaspiro[4.5]dec-9-ene-6- carboxylates as a new class of antibacterial and antifungal agents

“…The importance of the imidazoline unit rests on its presence in many biologically active compounds [1,2]. Imidazoline units are also used in organic synthesis as synthetic intermediates [3,4], chiral auxiliaries [5], chiral catalysts [6], and ligands for asymmetric catalysis [7]. Like imidazole, imidazoline-based compounds have been used as N-heterocyclic carbene ligands [8] with various transition metals, for example, in the commercially available second generation Grubbs' catalyst.…”