Construction Of Catalytic System Based On β-cyclodextrin

Cyclodextin is a kind of oligomer which has been widely studied in the supramolecular chemistry field. Due to its hydrophobic cavity and hydrophilic external cavity, cyclodextin can form stable molecular assembly with organic molecules through a variety of molecular inter-atomic forces such as van der waals force, hydrophobic inteactions. At the same time, the hydroxyl of cycledextrin can easily be converted into other function groups, so the particular function group with special catalytic activity can be bonded to cyclodextrin. Based on the above ideas,herein, we design and construct a supramolecular catalytic system.The asymmetric catalytic Michael addition reaction has been studied for decades of years. L-Proline and its pyrrolidine-based derivatives have been thoroughly investigated and have shown to be effective asymmetric catalysts for the Michael additions. However, these organocatalysts still have some drawbacks in which a high catalyst loading is generally required and they are hard to be recoved. Traditional proline derivatives design ideas have no space to be left after several years of development. Therefore, we try to prepare catalysts based on a new catalyst design concept in this research. The chiral pyrrolidine functional group was covalently conjugated to cyclodextrin to assemble a new type of supramolecular system for catalytic asymmetric Michael addition. Good results are obtained(ee=90.9%) in the catalytic evaluation. On the basis of experimental results, quantitative calculation method was employed to investigate the chiral induction mechanism. It was found that the transition state of S product could build more hydrogen bonds with chiral side chain, substrates and cyclodextrin hydroxyl making it to be the advantage reaction path. The theoretical calculation results are in agreement with the experimental results.The configuration of the modified β-cyclodextrin was studied via 2DNMR and the result of ROESY showed the chiral pyrrolidine group could enter the cavity of theβ-cyclodextrin. The results of quantum calculation(PM6) showed the lowest energy conformation is the self-inclusion conformation.