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Title Synthesis and Functionalization of Heterocycles via Non-Covalent Catalysis
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Publication Date
Degree PhD
Discipline/Department Chemistry
Degree Level doctoral
University/Publisher The Ohio State University
Abstract Hydrogen-bond donor (HBD) catalysis has emerged as a remarkable platform for the activation of reactants through non-covalent interactions. This class of organocatalysts provides a sustainable alternative to transition metal catalysis and avoids the difficulties associated with trace metal removal. Classically, HBD catalyst interactions proceed in two major pathways: direct activation or anion recognition. Enhanced HBD catalysts that display improved performance under both modes of action allow for the discovery of new reactivity patterns that have previously been unattainable. Two new classes of elegantly designed non-covalent catalysts have been explored in the synthesis and functionalization of heterocycles.Boronate ureas, an internal Lewis acid assisted urea, are particularly well suited for the direct activation of molecules containing nitro-functionality. Donor-acceptor cyclopropanes are useful building blocks in synthetic chemistry due to the electronic nature of the strained ring and the intrinsic functionality. Boronate ureas were applied toward development of the first cycloaddition of nitrones with nitrocyclopropane carboxylates in the presence of an enhanced non-covalent catalyst. The highly functionalized 1,2-oxazinane core synthesized in this single step is a prominent scaffold in many bioactive targets. With this strategy, a small library of oxazinane products has been synthesized in up to 99% yield and 4:1 dr. A second class of enhanced catalysts, silanediols, have a propensity to recognize the ether functionality. This molecular recognition was exploited in the context of direct epoxide activation for carbon dioxide fixation. Typically, with organocatalytic cyclic carbonate formation, very few types of functional groups are able to affect this transformation under mild conditions; often, high temperatures, long reaction times, and high pressures of carbon dioxide are necessary for desired product formation. With only 10 mol % of a silanediol-tetrabutylammonium iodide co-catalyst system, this transformation can be accomplished at room temperature using only one bar of carbon dioxide.Having established the ability of silanediols to work in tandem with anions, chiral silanediols were investigated in enantioselective anion-binding catalysis to construct chromanones. To date, introduction of carbonyl-containing nucleophiles in an intermolecular fashion has only been performed racemically. However, the unique chemical environment accessible with novel chiral silanediols is able to control carbon-carbon bond formation between silyl ketene acetals and benzopyrylium salts generated in situ from chromone derivatives. When coupled with recrystallization, synthetically useful enantioselectivities of up to 74% can be obtained. Importantly, this is the first example of anion-binding catalysis utilizing the benzopyrylium ions of chromenones, as well as an innovative strategy to incorporate complex alkyl functionality directly into the scaffold of chromanones.
Subjects/Keywords Organic Chemistry; organocatalysis; hydrogen bond donor catalysis; silanediols; boronate ureas; oxazinanes; carbonates; chromanones; asymmetric catalysis
Contributors Mattson, Anita (Advisor)
Language en
Rights unrestricted ; This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.
Country of Publication us
Format application/pdf
Record ID oai:etd.ohiolink.edu:osu1467277822
Repository ohiolink
Date Indexed 2016-12-22
Grantor The Ohio State University

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…Dioxide Fixation .............................................. 50 2.1 Silanediols as a Scaffold for Hydrogen Bond Donor Catalysis .............................. 50 2.1.1 Stability of the Silanediol Functional Group…

…50 2.1.2 Molecular Recognition Properties of Silanediols ............................................. 52 2.1.3 Silanediols as Hydrogen Bond Donor Catalysts............................................... 53 2.2 Carbon Dioxide as a Chemical…

…57 2.2.3 Use of Si-OH Bonds in CO2 Fixation............................................................... 62 2.3 Silanediols in Cyclic Carbonate Formation ............................................................ 63 2.3.1 Reaction…

…Chapter 3: Enantioselective Chromenone Functionalization ............................................ 84 3.1 Silanediols as Enantioselective Anion-Binding Catalysts ...................................... 84 3.1.1 Enantioselective Anion-Binding…

…Catalysis ....................................................... 84 3.1.2 Silanediols in Anion-Binding Activation of Substrates ................................... 91 3.2 2-Alkyl-Chroman-4-one Synthesis…

…22 Figure 1.10 Absolute Configuration ................................................................................. 24 Figure 2.1 Stability of Silanediols

…104 Scheme 3.16 Reactivity with BINOL-Silanediols .......................................................... 105 Scheme 3.17 Reactivity of Novel VANOL-Silanediols ................................................. 106 Scheme 3.18 Influence…

…of Silyl Group on VANOL-Silanediols..................................... 107 Scheme 3.19 Reactivity of 3,3'-substituted BINOL-Silanediol ...................................... 109 Scheme 3.20 Positive Control Experiments…

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