Symmetry in Asymmetric Catalysis and Hydrogen Bond-Based Self-Assembly : Synthesis and Investigations

Sammanfattning: The thesis elaborates on four different projects focusing on synthesizing symmetry-related molecules and investigating their performance as catalysts for asymmetric catalysis or as monomers for hydrogen bond-based self-assembly.Chapter 2 describes a new method to desymmetrize a meso-ligand. Two pseudo-Cs-symmetric bissalen complexes from a meso bissalen ligand and two different pairs of metal ions were designed and synthesized. The resulting complexes catalyzed asymmetric ring-opening of meso-epoxides with up to 76% ee of the product, indicating a new approach to applying meso-ligand in asymmetric catalysis. Chapters 3 and 4 deal with the synthesis of a C3-symmetric tricyclic trilactam and its derivatives as monomers for hydrogen bond-based self-assembly. In Chapter 3, we have accomplished the racemic and enantiomeric syntheses of the unfunctionalized trilactam that had been attempted for a long time. Solid-state hydrogen bond-based self-assembly of the two trilactams was revealed by single-crystal X-ray diffraction. Due to the poor solubility of the unsubstituted trilactams in non-polar solvents, the studies on their self-assembly in solution were hindered. In Chapter 4, we turned our efforts towards the synthesis of a more lipophilic trilactam, aiming to study its self-assembly in non-polar solvents. Many functionalizations of different intermediates involved in the synthesis of the unfunctionalized trilactam were attempted but failed to result in the lipophilic trilactam. An unexpected oxidative rearrangement of an α,β-unsaturated-γ-lactam was discovered during the attempts towards the lipophilic trilactam. Substrate scope screening of the reaction and DFT calculation of the possible transition state of the rearrangement step indicated an important role played by the β-substituent of the unsaturated γ-lactam.Chapter 5 presents two different approaches aiming at increasing the biocompatibility of a C2-symmetric molecule as a monomer for hydrogen bond-based self-assembly, i.e., increasing the hydrophilicity of the monomer while keeping its lipophilicity. The approach where we tried to improve the hydrophilicity of the monomer by complexing it with cyclodextrins did not work well. The effect of cyclodextrin complexation on the hydrophilicity of the monomer was limited. The other approach, where PEG groups were installed on the side chain of the monomer, worked very well. The resulting monomer could get dissolved in water and extracted back to organic solvents. 1H NMR spectra of the PEGylated monomer in toluene-d6 and C6D6 indicated the formation of a self-assembled aggregate.