Degree Granting Department
carbene, catalysis, cobalt, cyclopropanation, diazo, porphyrin
Metal-catalyzed cyclopropanation of olefins with diazo reagents has attracted research interest because of its fundamental and practical importance. The resulting cyclopropyl units are recurrent motifs in biologically important molecules and can serve as versatile precursors in organic synthesis. Since they were first introduced in 2004, Co(II) complexes of D2-symmetric chiral amidoporphyrins [Co(D2-Por*)] have emerged as a new class of catalysts for asymmetric cyclopropanation. These metalloradical catalysts have been shown to be highly effective for asymmetric intermolecular cyclopropanation of a broad scope of substrates with different classes of carbene sources, particularly including electron-deficient olefins and acceptor/acceptor-substituted diazo reagents, with excellent diastereoselectivity and enantioselectivity.
This dissertation focuses on exploring the Co(II)-based metalloradical catalyzed enantioselective cyclization reactions. It includes expanding families of catalysts, types of reactions and classes of substrates. With the developed novel approach for chiral porphyrin ligands, a new family of catalysts bearing different electronic and steric characters was synthesized. They turned out to be better catalysts for metalloradical cyclization in many cases, for instance, enantioselectivity of intramolecular cyclopropanation reached up to 99% with new catalyst. Besides the catalyst synthesis, more challenging diazo reagents were successfully employed in both intra- and intermolecular cyclopropanation for direct synthesis of highly functionalized cyclopropanes. Moreover, a tandem radical cyclization process beyond cyclopropanation was discovered, dihydrofuran was generated in a highly selective manner. Last but not least, we developed some novel applications of cyclopropane products, which could potentially lead to more exciting works.
Scholar Commons Citation
Xu, Xue, "Asymmetric Intra- and Intermolecular Cyclopropanation by Co(II)- Based Metalloradical Catalysis" (2012). USF Tampa Graduate Theses and Dissertations.