| The chemistry of N-heterocyclic carbenes (NHCs) and their transition-metal complexes have attracted much attention because these carbenes are readily generated from the corresponding imidazolium salts and act as efficient ligands in a great variety of catalytic processes. The thesis has reviewed the synthesis of N-heterocyclic carbenes (NHCs) and their transition-metal complexes and their catalytic application in achiral and chiral organic transformations. As good chiral sources, proline and their derivatives have been widely applied in asymmetric catalysis. However, there is no N-heterocyclic carbenes (NHCs) synthesized from proline. After N-tosylation, reduction, O-tosylation, iodination and coupling with 1-substituted imidazole, L-proline was transformed to three series of novel chiral imidazolium salts modificated by TsCl, MesCl or benzoyl choloride, one of which reacted with [Rh(COD)Cl]2 affording a NHC-Rh complex. The imidazolium salts and NHC-Rh complex were then tested for the catalytic aryl transfer of arylboronic acids to aldehydes to synthesize diarylmethanols. Aryl transfer of arylboronic acids to aldehydes to synthesize diarylmethanols is a user-friedly method, and has not been catalyzed by chiral NHC ligands in literature. The active catalysts either generated in situ or pre-synthesized afford the corresponding secondary alcohols in excellent yields and around 20% ee value, suggesting further structural modifications will be necessary to increase enantioselectivity. The results also reveal the wide scope of this method that is compatible with with a wide scope of organic groups. |
