Browsing by Subject "Alcohols"
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Item Preparation of Substituted Enol Derivatives from Terminal Alkynes and Progress Toward the Total Synthesis of Nigricanoside A(2011-02-01) DeBergh, John Robbins; Ready, Joseph M.This manuscript consists of two chapters. The first chapter describes the preparation of stereodefined enol derivates of alpha-branched aldehydes from terminal alkynes. Specifically, alkenyl alanes, derived from the methylalumination of alkynes, are shown to be efficiently oxygenated with peroxyzinc species. The resulting metallo-enolate may be trapped with benzoic anhydride, acetic anhydride, and TESOTf to generate E-trisubstituted enol esters and silanes. Traditional approaches to these types of olefins involve enolization of aldehydes; these methods are often inefficient and generally afford mixtures of olefin stereoisomers. Therefore, the methodology presented Chapter One represents a conceptually novel and useful strategy. The development and scope of the methylalumination-oxygenation reaction is discussed along with applications of the enol derivatives in the context of asymmetric and natural product synthesis. Finally, the alkenyl alane intermediates are shown to be efficiently aminated to afford ene-hydrazine products. The second chapter involves the progress towards the asymmetric synthesis and structural assignment of nigricanoside A, a potent antimitotic glycolipid isolated from marine green algae. A convergent synthetic route is presented along with an analysis the natural product’s relative and absolute stereochemistry. Various diastereomers of orthogonally protected subunits of nigricanoside A were prepared through vinyl-metal additions to alpha-hydroxy aldehydes. The chapter includes attempts to join the subunits through etherification reactions as well as descriptions of future strategies to effect etherification.Item The Synthetic Utility of Enol Derivatives and the Directed Aryltitanation of Homoallylic and Allylic Alcohols(2012-07-20) Lee, Kathleen Marie Spivey; Ready, Joseph M.This dissertation is organized in three parts. First, enol derivatives represent important building blocks for organic synthesis. Often their olefin geometry directly translates into product diastero- and enantioselectivity. Thus, stereodefined enol benzoates are subjected to the Sharpless Asymmetric Dihydroxylation to form enantiomerically enriched alpha-hydroxy aldehydes. Due to their instability, these alpha-hydroxy aldehydes are further transformed in situ to demonstrate their utility in organic synthesis. The second and third parts address the carbometalation of two types of alkenes. While the carbometalation of alkynes is a widely used transformation, the corresponding transformation for alkenes is less developed. Directing groups, such as homoallylic and allylic alcohols, may help overcome the poor reactivity of alkenes towards carbometalation. Herein the alcohols direct a highly diastereoselective aryltitanation to the proximal carbon–carbon double bond. Reactions with homoallylic alcohols result in stereospecific aryl incorporation at the terminal carbon of the double bond while the reactions with the allylic alcohol incorporate the aryl group proximal to the alcohol and generate two new sp3 centers.Item Titanium-Mediated Carbometallation of Homoallylic Alcohols(2012-07-20) Peng, Bo; Ready, Joseph M.Addition of zinc dichloride as an additive allows for the titanium-mediated carbometalation of homoallylic alcohols with Grignard reagents. The zinc dichloride additive successfully inhibits the B-hydride elimination of the titanium intermediate. The unsaturated products are obtained in up to 90 percent yield and up to >20 to 1 ratio of the carbometallation to oxidative arylation products. Subsequent electrophilic trapping is possible with elemental halides to yield the respective halohydrin products or oxidation to yield the diol products. The reaction is tolerant of both alkyl and aryl substituents on the homoallylic alcohol. This reaction allows ready access to unsaturated secondary alcohols or further functionalized products from an initial homoallylic alcohol.