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 Title: Investigations of transition state geometry in the intramolecular aldol reaction and the intramolecular reaction of allylsilanes with aldehydes Author(s): Henke, Brad Richard Doctoral Committee Chair(s): Deuman, Scott E. Department / Program: Chemistry Discipline: Chemistry Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Organic Abstract: Investigations into factors which influence the transition state geometry of the aldol reaction are described. Synthesis of two bicyclic model systems designed to study base-catalyzed intramolecular aldol reactions are reported, along with the effects that various metal counterions, solvents, and additives have on the stereochemical course of cyclization in these models. These models are the first to provide data concerning the factors which influence the preference for an open versus closed transition state in the absence of extraneous steric bias. Results indicate that coordination ability of the metal counterion is a major factor in influencing transition state geometry. In addition, synthesis of two model systems designed to study Lewis acid-catalyzed reactions of enolsilanes with acetals are described. The influence of change in Lewis acid and solvent on the stereochemical course of reaction are reported. Cyclizations in these model systems are highly selective and relatively insensitive to the Lewis acid and are interpreted in terms of reaction through an S$\sb{\rm N}$2 mechanism, with a possible change in mechanism when $\rm BF\sb3{\cdot}Et\sb2 O$ is used.Studies on the stereochemical course of the intramolecular allylsilane-aldehyde reaction catalyzed by SnCl$\sb4$ are also discussed. These investigations were performed on a model system designed to unambiguously correlate transition state geometry with product stereochemistry in the absence of steric bias. The influence of concentration, stoichiometry of reagents, presence of "spectator ligands" on SnCl$\sb4$, and solvent on the stereochemical course of addition have been documented. The nature of the aldehyde-SnCl$\sb4$ complex is implicated as the origin of these effects. In addition, the X-ray crystal structure of the complex between 4-t-butylbenzaldehyde and SnCl$\sb4$ is reported and shows a 1:2 (tin:ligand) stoichiometry with cis coordination around the tin atom. The solution behavior of this complex was also studied using variable temperature $\sp1$H and $\sp{13}$C NMR techniques; the results show the stoichiometry of the complex to be 1:2 in solution. Issue Date: 1989 Type: Text Language: English URI: http://hdl.handle.net/2142/21519 Rights Information: Copyright 1989 Henke, Brad Richard Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9010880 OCLC Identifier: (UMI)AAI9010880
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