N-Hetereocyclic carbenes (NHC) have been intensively investigated since Ukai et al had reported the first NHC-catalyzed coupling of two equivalents of benzaldehyde, to form what is known as the benzoin product. A plethora of reports have since been published on NHC-catalyzed reactions, such as the cross-benzoin, Stetter, redox reactions, and many others. An attractive feature of NHCs is their ability to effect the umpolung (inversion of reactivity) of aldehydes. The efforts in the introduction of β,γ-unsaturated-α-ketoesters as acceptors for the Stetter reaction have led to the first highly enantioselective intermolecular Stetter reaction with β-aryl substituted Stetter acceptors (up to >99% ee). The synthetic applications of the Stetter adducts generated from the α-ketoester acceptors were demonstrated to give access to a diverse number of useful building blocks. Furthermore, the α-ketoester substrates were found to also be applicable for the cross-benzoin reaction. Through the development of a new electron-deficient, morpholine-based triazolium-derived carbene, a highly chemo- and enantioselective cross-benzoin reaction was achieved using aliphatic aldehydes and α-ketoesters. This methodology constitutes as the first highly enantioselective intermolecular cross-benzoin reaction with aliphatic aldehydes (up to 93% ee). In addition, a highly divergent synthesis of Stetter adducts and cross-benzoin products could be achieved in excellent regioselectivity.
Interested in utilizing NHCs as organocatalysts for the development of new reactions, tetrahydrofuran and prolinal derivatives were found to undergo efficient ring-expansions. This methodology gives access to highly functionalized lactones and lactams, which could serve as synthetically useful building blocks for the synthesis of natural products and biologically active compounds.
| Identifer | oai:union.ndltd.org:USASK/oai:ecommons.usask.ca:10388/ETD-2012-06-489 |
| Date | 2012 June 1900 |
| Contributors | Gravel, Michel |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text, thesis |
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