Synthesis and Stereochemistry of Novel Propeller-shaped Ligands and their Use in Asymetric Carbon-Carbon Bond-forming Reactions

Novel types of chiral ligands for asymmetric catalysis will be synthesized and tested in various carbon-carbon bond-forming reactions. The access to enantiomerically pure reactants is a permanent challenge in synthetic organic chemistry, the more as the today`s legal regulations permit only the application of enantiomerically pure compounds in many fields of biology and medicine. While in the past optical resolution procedures of racemic mixtures have been the general method for obtaining pure enantiomers, methods of asymmetric synthesis with chiral auxiliaries are well established at now and permit the enantioselective generation of intermediates in antibiotics and natural products synthesis. Particularly the asymmetric catalysis using chiral transition metal complexes has come to the fore and now provides one of the most cost-effective and environmentally friendly methods for the production of a truly vast array of structurally diverse, enantiomerically pure compounds. However, despite the impressive number of efficient asymmetric transformations which have been developed so far, there are still reaction types which either cannot be catalyzed with known catalysts or deserving further improvement. It is the aim of the present project to work out synthetic pathways to a new family of chiral ligands which differ significantly from the previous ones in terms of symmetry and complexation mode. Both will influence the reactivity and stereoselectivity of the catalysts derived thereof. Structur elucidation of catalytic intermediates by crystal structure analysis and modern nuclear magnetic resonance techniques and applying calculation methods will give insight into geometry and the electronic and steric effects influencing the course of the reaction. This knowledge will enable us to prepare "tailor-made" ligands specifically designed and optimized for a substrate of interest and opening eventually also the way to new reaction types to be catalyzed.