The introduction of enantioselectivity into zinc catalyzed homoaldol reactions is described. Coordinating ligands such as bis-oxazolines and beta-amino alcohols inhibit the addition of zinc homoenolates to aldehydes while Lewis acids such as titanium (IV) isopropoxide and boron trifluoroetherate promote this reaction. Notably, the addition of zinc homoenolates to benzaldehyde mediated by chiral titanium (IV) alkoxides yields homoaldol adducts with moderate enantioselectivity. / The development of titanium catalysis of the homoaldol addition of silyloxyalkoxycyclopropanes to aldehydes is also described. The methodology features alkoxytitanium (IV) triflates as catalysts, which mediate homoenolate addition to a range of carbonyl substrates. The preparation of such titanium triflates by a new procedure, namely the treatment of titanium (IV) alkoxides with trimethylsilyltriflate, affords more reactive catalysts than those prepared by conventional methods. In addition, the catalyst system is stable at elevated temperatures for an extended period of time. / Titanium (IV) triflates derived from a variety of alkoxide ligands as well as ligands with sulfide linkages are effective catalysts for this reaction. Efforts directed towards extending this catalytic process to a highly enantioselective protocol are detailed. Moderate enantioselectivity is obtained in homoaldol reactions mediated by a tridentate alkoxide derived titanium tiflate.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.30701 |
| Date | January 1999 |
| Creators | Martins, Evelyn O. |
| Contributors | Gleason, Janet L. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001745084, proquestno: MQ64405, Theses scanned by UMI/ProQuest. |
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