Development of an asymmetric NHC-catalyzed cascade reaction and studies towards the asymmetric aminomethylation of enals
Date
2015
Authors
Ozboya, Kerem, author
Rovis, Tomislav, advisor
Henry, Charles, committee member
McNally, Andrew, committee member
Kennan, Alan, committee member
Inamine, Julia, committee member
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Abstract
A cascade reaction is developed to form complex cyclopentanones using an asymmetric Michael/Benzoin sequence. This reaction employs simple aliphatic aldehydes and ketoesters in conjunction with a chiral amine catalyst and a chiral NHC catalyst. Further investigation reveals a surprising interplay between these two catalysts. This relationship is manifested in a pseudo-dynamic kinetic resolution, which is responsible for the high diastereoselectivity observed. Subsequent work details the discovery of the aminomethylation of enals using NHC catalysis. This reaction utilizes an iminium source as well as cinnamaldehyde derivatives to form gamma-amino butyrate derivatives. Rendering this reaction asymmetric has proven a challenge, despite extensive effort to resolve these issues. In the course of these studies, an unexpected NHC-catalyzed Morita-Baylis-Hillman reaction was observed. Optimal conditions for this reaction were established, proving access to useful amino-enals. In an effort to design suitable catalysts for the asymmetric aminomethylation reaction, a strategy for the late-stage manipulation of NHC catalysts was developed. Key to this strategy is the `protection' of the triazolium salt by reduction to the triazoline. An aryl C-Br bond is then exploited for cross-coupling reactions, building a small library of new catalysts. The triazolium salt is then recovered by oxidation with a trityl salt.
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Subject
NHC
organocatalysis
organic synthesis
asymmetric catalysis