Organoboron compounds are highly valued synthetic intermediates due to their diverse array of reactivity, which is often utilized in the synthesis of valuable organic molecules. For this reason, there is significant interest in the development of novel borylation protocols, especially those whose products are suitable for further synthetic transformations towards valuable classes of compounds. Research in organoboron synthesis has been geared heavily toward transition metal-catalyzed addition to double and triple bonds, though an increasing number of publications detail transition metal-free borylation techniques involving substrate-mediated activation of a diboron reagent. This dissertation describes the author's contributions to the development of both a transition metal-catalyzed diboration and a transition metal-free protoboration.
A transition metal-free diboration of alkynamides is described in Chapter 1 which uses the unsymmetrical, differentially protected diboron reagent, pinBBdan. The method installs both boron moieties in a regio- and stereoselective fashion. The products have synthetic value because they are shown to have chemoselectivity in downstream cross-coupling reactions; chemoselectivity is made possible by to the significant difference in Lewis acidity of the pinacol and diaminonapthalene-protected boron centers. This method allows for facile synthesis of tetrasubstituted alkenes with a set geometry about the double bond.
A protoboration of allenes employing a Cu(II) catalyst under aqueous and atmospheric conditions is described. Though Cu(I)-catalyzed allene protoboration is well-described in the literature, this is the first report of an analogous Cu(II)-mediated process. The selectivity of the reaction is ligand-controlled, and moderate to good regioselectivities and yields can be achieved through use of a triphenylphosphine as ligand. The method is an environmentally friendly and facile means by which to borylate a challenging cumulated substrate. / Ph. D. / Organoboron compounds are valuable because of their ability to undergo a wide variety of chemical transformations, and they are often used as intermediates in the synthesis of challenging target molecules. In order for this reactivity to be exploited, methods must exist for the efficient synthesis of the desired boron-containing compound. This dissertation describes the author’s contributions to the development of two new methods by which to synthesize organoboron products. The first method involves installation of two differently ligated boron moieties onto an alkynamide substrate to produce a single, uncommon trans isomer as product. A synthetic application of these diboration products is described. The second method involves installation of a single boron moiety into allenes. Though the same overall transformation has been achieved in the literature with use of highly air-sensitive catalysts and organic solvents, the described method entails use of air-stable CuSO4 as catalyst and water as solvent. Therefore, the method is operationally simple and environmentally friendly relative to previously described methods.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/85003 |
| Date | 11 September 2018 |
| Creators | Snead, Russell Franklin |
| Contributors | Chemistry, Santos, Webster L., Kingston, David G. I., Tanko, James M., Carlier, Paul R. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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