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Novel Methods toward the Formation of Functionalized Cyclic Ethers and New Applications for Click Chemistry with Organic Peroxides
Cyclic ethers are valuable as synthetic reagents and as components of natural products, organic materials, and bioactive compounds, including a number of current therapeutics. Ethers are characteristically synthesized through Williamson etherification or an analogous process involving attack of a nucleophilic oxygen on an electrophilic carbon. In contrast, investigations of ether formation via intramolecular attack of a carbanion on an electrophilic oxygen have been mainly explored for the formation of epoxides through 3- exo cyclization of stabilized carbanions on an adjacent peroxide. Previous work in our lab has demonstrated that the synthesis of four-, five-, and six-membered oxacycles can be achieved through the intramolecular reaction of dialkyl peroxides with ketone enolates, leading us to hypothesize that this reaction could be extended to sulfone- and nitrile-stabilized carbanions. We now provide evidence for a new synthesis of nitrile- and sulfonyl-substituted oxacycles via intramolecular C-O bond formation involving reaction of peroxides with nitrile- and sulfone-stabilized carbanions. We found that sulfone- or nitrile-stabilized carbanions can be selectively generated in the presence of a peroxide under basic conditions and undergo immediate cyclization to form four-, five-, or six-membered cyclic ethers. The result provides a new approach for the synthesis of sulfonyl- or cyano-substituted oxetanes, tetrahydrofurans, or tetrahydropyrans. In a separate project, we explored copper-assisted azide-alkyne "click" chemistry of peroxide-containing substrates in the hopes of developing methods for achieving modular installation of peroxides on surfaces and nanoparticles. Our model investigations, conducted with simple peroxide-substituted alkynes and azides, indicated that click reactions could be accomplished and produce desired peroxy triazoles in good yields. Next, we extended our results to the surface functionalization of gold nanoparticles via click chemistry. Gold nanoparticles were successfully coated with azides, which could readily undergo click chemistry with our synthesized alkynyl peroxides, thus functionalizing the particle surface with peroxides. These peroxy functionalized materials are likely to release oxygen radicals on the surface in the presence of iron (II) species, which could provide significant utility in terms of both surface activation as well as antibacterial activity. Overall, our research has demonstrated the significance of peroxides and their use in organic synthesis and materials chemistry.
Horn, Alissa, "Novel Methods toward the Formation of Functionalized Cyclic Ethers and New Applications for Click Chemistry with Organic Peroxides" (2018). ETD collection for University of Nebraska - Lincoln. AAI13420068.