Catalytic aziridinations and daisy chain polymer syntheses
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Methodological development toward the synthesis of useful molecular building blocks serves as a powerful toolbox for complex molecule syntheses and is essential in scientific fields such as biomedical and pharmaceutical research. Discovery of new reagents, catalysts, and synthetic strategies is particularly important for improving the efficiency of currently available methods in organic syntheses. Aziridines have been recognized as versatile precursors to many organic molecules due to their ability to undergo ring-opening reactions to deliver a wide range of nitrogen-containing compounds. In this dissertation, syntheses of aziridines from the reaction of imines with diazo compounds via two distinct catalytic methods were presented. The first part involved the use of viologens and pyridinium salts as a class of potential ionic organocatalysts in the reactions of imines with phenyldiazomethane. Substituted aziridines with 2,3-cis configurations were obtained as the predominant products in high yields and stereoselectivities. The second part described the synthesis of optically active aziridines by a Corey-Chaykovsky-type reaction via sulfur ylide addition to chiral N-tert-butanesulfinyl imines. The reactions were found to provide 2,3-trans-aziridines selectively and quantitative yields were obtained in most cases. The diastereoselectivity between the two trans-aziridines was found to vary significantly depending upon the type of solvents and sulfides employed in the reactions. As a synthetic approach toward mechanically interlocked daisy chain polymers, several 1,10-phenanthroline-copper complex-based rotaxanes were synthesized. A study on the dethreading and rethreading processes of these rotaxanes upon removal and addition of copper(I) was discussed in the third part of this dissertation. The preliminary results of using these rotaxanes incorporated with internal olefin functionalities in entropy-driven ring-opening metathesis polymerization (ED-ROMP) reactions were also presented.