Date on Master's Thesis/Doctoral Dissertation
Hammond, Gerald B.
Heterocyclic compounds--Synthesis; Heterocyclic chemistry
Our research mainly focused on three parts related to the rapid construction of N-heterocycles and the search for ionic reaction promoters. First, N-heterocycles of different ring sizes and with different substitution patterns constitute extremely important structure classes (e.g., alkaloids) in the search for bioactivity. A contemporary challenge in organic synthesis is the mapping of new chemical spaces through tandem or cascade reactions in an atom economical fashion. Our strategy to access these biologically important heterocycles is through a cyclization-triggered tandem addition to alkynes catalyzed by readily available alkynophilic coinage metals like copper. In this manner, a variety of functional groups could be introduced to the ring system through a carbon-carbon forming reaction. Second, in chemistry, a promoter is defined as a substance added to a catalyst to improve its performance in a chemical reaction. Promoters interact with active components of catalysts and thereby alter their chemical effect on the catalyzed substance. In our studies, we found KCTf3 is an ideal promoter that is readily available and able to tolerate harsh reaction conditions. When KCTf3 is added to reaction system, a reshuffling of ions occurs and a CTf3- reactive cationic species will be generated in situ, which improves the efficiency of a reaction. Third, silver-mediated halogen abstraction is the most preferred method to generate cationic gold from a gold catalyst precursor. However, the use of silver activators is problematic because of its high cost, generation of unwanted side reactions and Au-Ag intermediates. We found that a gold phthalimide complex (L-Au-Pht) could be easily synthesized, and upon contact with either a Brønsted acid or a Lewis acid it generates an active gold phthalimide complex that not only avoid problems caused by silver promoters but also yields an efficient and highly reactive gold catalyst for the most popular types of gold-catalyzed reactions, including X-H (X = O, N, C) additions to C-C unsaturated compounds (alkyne/allene/alkene), and cycloisomerizations .
Han, Junbin, "Synthesis of N-heterocycles through cyclization-triggered tandem additions to alkynes and the study of promoters in ionic reactions." (2014). Electronic Theses and Dissertations. Paper 568.