| In the first part of the work, a new axially chiral monodentate phosphine with an atropisomeric structure was designed, synthesized, and resolved. The chirality is derived from restricted rotation about a central Caryl-N imide bond, resulting in enantiomeric atropisomers that are stable and separable at temperature in excess of 120°C. Specific rotation was measured by a polarimeter and the absolute configuration was determined by X-ray crystallography. The chirally pure phosphine was evaluated in various asymmetric reactions. In the well studied Pd-catalyzed allylic alkylation, the reaction conditions were optimized and the catalyst was able to induce moderate enantioselectivity up to 55% ee. Other efforts, including incorporation of atropisomers into polymers, were also tried.; In the second part of the work, molecularly imprinted polymers (MIPs) were prepared, using D,L-phenylalanine anilide and chirally pure L-phenylalanine anilide as templates. Methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were used as the functional monomer and the crosslinking agent, respectively. A D,L-PheNHPh imprinted racemic polymer was enantioselectively modified by diazomethane in presence of pure L-isomer. This method to produce a chiral surface has the advantage as the kinetic resolution in that high selectivity could be achieved by pushing the reaction to completion. Using the same method to chemically modify an L-imprinted polymer greatly enhanced its binding selectivity. Another sub-project was to demonstrate that MIPs could be used in measuring enantiomeric excess (ee). The L-PheNHPh imprinted polymer was chosen as the MIP system. The results showed that utilizing MIPs to measure ee was accurate and rapid, as the ee values can be calculated from straightforward concentration measurements. The MIP-based assay also had the advantage of being easily tailored for different substrates. Finally, a new way to prepare MIP particles with homogeneous size and shape was tried. Divinylbenzene cores of 2 μm were prepared by precipitation polymerization then coated with an MIP layer. Future work includes rebinding studies to test these MIP particles. |
