Development of highly modular ligands for use in asymmetric transition-metal catalyzed reactions

Detta är en avhandling från Stockholm : Institutionen för organisk kemi

Sammanfattning: The synthesis and evaluation of ligands for use in asymmetric transition metal catalyzed reactions is a widely used concept to achieve improved enantioselectivity in a variety of different transformations. The present thesis decribes the synthesis of a number of different oxazoline-based ligands and their use in titanum-catalyzed addition of diethyl zinc to aliphatic and aromatic aldehydes. Interestingly, the presence of catalytic amounts of titanium in our system was sufficient to achieve effective catalysis in contrast to what has been previously reported concerning titanium-catalyzed addition of diethyl zinc to aldehydes.The synthesis and evaluation of a library of novel dipeptide-like ligands are described and these ligands were employed in connection with ruthenium-catalyzed transfer hydrogenation of aromatic ketones. Excellent enantioselectivities and yields were obtained.Furthermore, the novel concept of forming the ligand and catalyst in situ in a one-pot system was explored. In addition to significant simplification, this approach resulted in improvements in both enantioselectivity (minor) and reaction rate (2-3 fold) compared to previously studied procedures.The surprizing influence of alkali salts on ruthenium-catalyzed transfer hydrogenation involving these dipeptide-like ligands are described and discussed. In the presence of these additives the ruthenium-catalyzed transfer hydrogenation performed with higher enantioselecitvity and reactivity.Finally, mechanistic studies concerning ruthenium-catalyzed transfer hydrogenation involving the dipeptide-like ligands are also described and discussed.

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