Master of Science (MS)
Silane reagents play important roles in many areas of organic synthesis. This is primarily due to the ability of silanes to bond to more ligands than the traditional four to become hypervalent (i.e. penta- or hexavalent). This hypervalency causes the silicon center to become more Lewis Acidic and causes the formation of carbon nucleophiles from organosilane ligands. These nucleophiles have been used to perform many cross-coupling reactions with organohalide reagents. The research presented in this thesis reports the utility of silane reagents in cross-coupling reactions of Grignard reagents with alkyl halides. This cross coupling was desirable because the silane should act as a mediator, being reformed in the reaction process. Also, similar transformations mediated by metal catalysts suffer from poor reactivity, low yields, and undesired side reactions. Although the results from this study do not show marked improvement over couplings formed in the absence of silane reagents, analysis of the deficiencies of silane-mediated cross-coupling reactions are made as well as proposals for future research. The first indium trichloride catalyzed deoxygenative alkylations of alcohol derivatives using a step-wise reaction plan are reported herein as well as the first study of the possible chiral transfer in the transformation from a C-O bond to a C-C bond via InCl3 mediated alkylative deoxygenation upon the silyl ether derivatives of chiral alcohols. This chiral transfer was believed to take place because of a possible concerted mechanism. Results of this research indicated that chiral transfer does not occur in these types of reactions under the conditions explored due to the formation of a carbocation intermediate in the mechanism. The reactivity observed in the deoxygenative alkylations of a range of alcohols is similar to that of other non-concerted substitution reactions such as preference for 2°, benzylic, and 3° alcohol precursor starting material. Based upon the discoveries made in this line of research, a reasonable mechanism for the InCl3-catalyzed deoxygenative alkylation of alcohol derivatives was found.
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Dupre, Andrea S., "The roles of silanes as coupling reagents and in deoxygenative alkylations" (2003). LSU Master's Theses. 928.
David A. Spivak