archives@tulane.edu / The synthesis of cyclic polymers has become popularized due to improved synthetic chemistry increasing access to architecturally well-defined polymers. Since their discovery, many studies have been performed describing their physical properties in solution and bulk, and as confined thin films. Also, their electronic, biomedical, and self-assembly behavior has been characterized for advanced biomedical and industrial applications. Herein, some of the ongoing shortcomings within the cyclic polymer field are addressed by a detailed analysis of cyclic polymers synthesized through: 1) the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) “click” ring closure method, and; 2) the electrophilic zwitterionic ring expansion polymerization (eZREP). First, cyclic polystyrene synthesized via CuAAC is investigated to source potential impurities using a series of analytical tools including HPLC for fractionation and MALDI-ToF MS for characterization of the linear precursor and cyclic product. It was ascertained that the linear precursor undergoes uncatalyzed azide alkyne dimerization during storage, resulting in a linear dimer that retains an azide and alkyne group. Consequently, post-cyclization the sample has a high cyclic architectural purity with small amounts of cyclic dimers. With this same CuAAC cyclization, cyclic polycaprolactone was generated to fabricate thin films (~100 nm). The CuAAC cyclization was performed using an optimized synthesis, where the azide was coupled to the linear precursor directly prior to cyclization to minimize the opportunity for dimerization. Both the linear and cyclic polymers made stable as-cast films, but only the cyclic polymer maintained a stable film after recrystallization as demonstrated by its resistance to dewetting. Moreover, the linear polymer dewet after recrystallization regardless of end group, suggesting that architecture provides a larger influence on thin film stability than end group effects. Finally, towards understanding the ring expansion method, eZREP has been investigated to generate pure cyclic polyethers by polymerizing monosubstituted epoxides with B(C6F5)3. While the major component was the cyclic structure, in most cases, there was still a contribution of impurities arising from non-cyclic structures (e.g., tadpole and linear architectures). Using primarily MALDI-ToF MS, it was ascertained that most impurities had free hydroxyl groups that could be alkynylated, “clicked” onto a solid phase azidified resin, and then filtered to remove resin-bound impurities. This allowed for a facile method of making pure cyclic materials in two reactions (i.e. polymerization and “click” scavenging purification). Finally, the origin of the impurities was further explored, elucidating that when glycidyl ether-based monomers were polymerized, there was competition between the boron coordinating with the epoxide oxygen to polymerize, and boron coordination with the ether oxygen to generate non-cyclic derivatives. The polymerization was improved by using monomers that either did not contain the glycidyl ether oxygen (e.g. alkyl groups) or adding electron withdrawing groups to deactivate the glycidyl ether oxygen, yielding greater amounts of cyclic polymer and fewer side reactions. The goal of this work is to garner interest in cyclic polymers by increasing accessibility of these compounds by addressing the primary deficiencies of the CuAAC and eZREP methods for the synthesis of cyclic polymers, while bringing attention to the concern of cyclic polymer purity, arguably the largest concern within the cyclic polymer community. Through these advancements, continued efforts will be made to make novel cyclic materials for unique biomedical and industrial applications. / 1 / Farihah M Haque

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The use of a Nazarov cyclization for the diastereoselective synthesis of rocaglamide was studied. Chapter 1 discusses the biological activity of the rocaglamide family of natural products and details the previous synthetic work on these compounds. Chapter 2 discusses the approaches taken in the Magnus group for the total synthesis of rocaglamide. Several approaches to the natural product were undertaken. Using a novel acid bromide induced Nazarov cyclization, construction of the C-ring of the natural product was achieved. Attempts to construct the remainder of rocaglamide were ultimately unsuccessful. / text

The first chapter of this thesis represents the continued development of a general method for the formation of benzo-fused N-heterocycles by formal radical cyclization onto benzene rings. Important stages in this process involve 1) the copper-mediated coupling of various amino alcohols to protected p-iodophenols, 2) carbamate-protection of the resulting aryl secondary amine to allow the following oxidation step, 3) the oxidative formation of quinone ketals as radical acceptors, 4) the radical cyclization of pendant iodo-radical triggers onto the cross-conjugated ketone, and 5) the subsequent aromatization of the resulting products into benzo-fused N-heterocycles. Various protected 2,3-dihydroindolessome of which with 2-substitutionshave been synthesized using this methodology. For some examples, it was necessary to repeat the experiments of a previous group member to obtain publication-quality data. The second chapter describes a new methodology for the formation of regioselectively-substituted benzene rings. Various arene species have been synthesized in p-disubstituted, 1,2,4-trisubstituted and 1,2,3,4-tetrasubstituted arrays. Key steps in the methodology include 1) the synthesis of 1,4-diketones by alkylation of various aldehydes and their subsequent reduction and oxidation, 2) addition of organometallic alkenes to 1,4-diketones to form ring closing metathesis (RCM) precursors, and 3) RCM and subsequent aromatization of these cyclized products by double-dehydration to form the desired substituted benzenes. The macrocycle [12]-paracyclophane has also been synthesized using a modified version of the above methodology.

Treatment of thioanisole-substituted aryldiyne with 2 equiv. of N-Iodosuccinimide and 5 mol% of PPh3AuCl and 5 mol% AgSbF6 in refluxing dichloromethane gave 5-iodo benzo[b]naphtho[2,1-d]thiophene in good yields. This method tolerated various functional groups in alkyl and phenyl moiety. We also treatment thioanisole-substituted aryldiyne with 10 mo% of PdX2 and 3 equiv. CuX2 (X= Cl, Br),in reluxing THF gave in 5-position have halogen substitute benzo[b]naphtho[2,1-d]thiophene derivative.

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Thesis advisor: Xiao-Xiang Zhang / Thesis advisor: James Morken / This dissertation will present three projects focusing on the development of stereoselective radical cascade reactions via metalloradical catalysis (MRC) using Co(II) D2-symmetric chiral amidoporphyrins [Co(D2-Por*)] as the catalyst. The first project demonstrated the feasibility of applying MRC for asymmetric radical cascade processes by achieving an enantioselective radical bicyclization of 1,6-enynes with diazo compounds, which constructed multi-substituted cyclopropane-fused tetrahydrofurans bearing three contiguous stereogenic centers and one trisubstituted alkene. Detailed mechanistic studies including EPR studies and DFT calculation unveiled a radical-based stepwise mechanism. The synthetic utility of this reaction was demonstrated by a series of diastereoselective transformations of the bicyclic products. In the second project, this strategy was expanded to the application of Co(II)-based MRC to catalyze radical cascade reactions involving hydrogen-atom abstraction (HAA) process. A broad array of homopropargyl ethers reacted with diazo compounds to generate enantiomerically enriched ɑ,β-disubstituted tetrahydrofurans in good yields with high diastereoselectivities and enantioselectivities. The third project explored the utilization of the established strategy to accomplish more challenging bicyclization of 1,6,8-dienynes for the construction of cycloheptadiene-fused tetrahydrofurans in regio- and diastereoselective fashions. Such 5,7-fused ring system has been widely found in natural products and bioactive species. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.