Thesis advisor: Kian L. Tan / Chapter 1. Directing groups are a powerful means of controlling the selectivity in reactions. The field of hydroformylation has used directing group strategies to control regio- and diastereoselectivity with much success. However, directing groups are inherently inefficient as they must be installed and removed from the molecule of interest, and generate a stoichiometric byproduct in the process. Strategies to solve this problem have included the use of exchange reactions that allow for transient binding of substrate to a molecule that can direct the course of the reaction. This allows the use of catalytic quantities of the directing functionality to effect the desired transformation, and obviates the need for installation and removal of the directing functionality in separate steps. Chapter 2. Our lab has developed a phosphorous based ligand that incorporates an N,O-acetal moiety that allows for reversible binding of both alcohol substrates and a metal catalyst. These ligands rapidly exchange with alcohols in the presence of catalytic amounts of p-TsOH. The racemic ligand was found to undergo epimerization on exchange with a chiral alcohol in an effort to isolate enantioenriched material. However, a strategy using a thermodynamic gearing effect of adjacent stereocenters was found to be successful in producing a chiral ligand. Chapter 3. Using catalytic quantities of our scaffolding ligand we are able to effect branch- and diastereoselective hydroformylation of homoallylic alcohols. We offer a model based on A1,3 strain for the origin of the diastereoselectivity, and tested substrates to lend support to the model. We also investigated the use of chiral scaffolding ligands in the enantioselective hydroformylation of homoallylic alcohols, and preliminary results show modest enantioselectivity. Chapter 4. We have expanded the substrate scope of our scaffolding ligand strategy to include the hydroformylation of allylic alcohols. We are able to produce β-hydroxy carbonyl compounds in good yields and with excellent selectivities, which offers an alternative to the formaldehyde aldol reaction. We show that our strategy is successful in the hydroformylation of trisubstituted olefins, which are a difficult class of hydroformylation substrates, where we are able to produce single diastereomers in good yields under mild conditions. We investigated the enantioselective hydroformylation of allylic alcohols and found that while racemization may be a problem with these substrates, in-situ hemi-acetal protection may offer a solution to the problem. / Thesis (PhD) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
| Identifer | oai:union.ndltd.org:BOSTON/oai:dlib.bc.edu:bc-ir_101844 |
| Date | January 2011 |
| Creators | Lightburn, Thomas Edward |
| Publisher | Boston College |
| Source Sets | Boston College |
| Language | English |
| Detected Language | English |
| Type | Text, thesis |
| Format | electronic, application/pdf |
| Rights | Copyright is held by the author, with all rights reserved, unless otherwise noted. |
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