Recent Advances in Iminium‐Salt‐Catalysed Asymmetric Epoxidation

Abstract

The research in this thesis depicts some of the most current developments in the area of asymmetric epoxidation of alkenes using chiral iminium salt catalysts. The first chapter reviews past and present developments in; catalytic asymmetric epoxidation, and covers the application of this reaction towards the kinetic resolution of racemic olefins.Chapter two is separated into two key areas; (i) asymmetric epoxidation as a tool in the kinetic resolution of racemic chromene substrates, and (ii) investigations into the asymmetric epoxidation of new N-protected dihydroquinoline substrates. In the first part of chapter two, the first examples of kinetic resolution in epoxidation reactions using iminium salt catalysts are reported, providing up to 98% ee in the epoxidation of racemic cis-chromenes.The second part of chapter two details the first known examples of asymmetric epoxidation upon nitrogen-protected dihydroquinoline substrates, affording enantioselectivities as high as 73% ee.In both parts of chapter two, non-aqueous epoxidation conditions were employed using Page's dihydroisoquinolinium iminium salt catalyst. The later part of chapter two introduces a biphenylazepinium iminium salt catalyst used under aqueous epoxidation conditions. Chapter three includes experimental data for all the compounds mentioned in chapter two, with chapter four containing HPLC traces to show determination of enantiomeric excess of epoxides, and enantioenriched alkene traces.iii ACKNOWLEDGEMENTS

Green Organocatalytic Oxidative Methods using Activated Ketones

“…Furthermore, a new familyo fc arbohydrate-based dihydroisoquinolinium salts 14 and 16 has been reported,a nd most recently,B ulman Page and co-workersh ave developed the first examples of the asymmetrice poxidation of dihydroquinoline substrates with iminium salt catalysts (Scheme 12). [48][49][50] Except for the use of chiral dioxiranes and oxaziridines, some recent examples of asymmetrice poxidation by using peracids have been presented by Miller and co-workers, by which excellent results in the electrophilic epoxidation of olefins by utilizing tripeptide 17 as the catalysta nd H 2 O 2 as the oxidant could be achieved (Scheme 13). [51][52][53] The crucial interaction between the substrate and the catalysthas been identifiedb yu sing different catalysts such as 18.…”

“…More recently, in 2013, Bulman Page managed to extend the use of catalyst 15 in heterogeneous catalysis, while showing the first results of kinetic resolution in the epoxidation reaction by employing iminium salt catalysis, by which enantiomeric excess values of up to 99 % for the epoxidation of racemic cis ‐chromenes could be achieved (Scheme ). Furthermore, a new family of carbohydrate‐based dihydroisoquinolinium salts 14 and 16 has been reported, and most recently, Bulman Page and co‐workers have developed the first examples of the asymmetric epoxidation of dihydroquinoline substrates with iminium salt catalysts (Scheme ) . Except for the use of chiral dioxiranes and oxaziridines, some recent examples of asymmetric epoxidation by using peracids have been presented by Miller and co‐workers, by which excellent results in the electrophilic epoxidation of olefins by utilizing tripeptide 17 as the catalyst and H 2 O 2 as the oxidant could be achieved (Scheme ) .…”

Synergistic Ammonium (Hypo)Iodite/Imine Catalysis for the Asymmetric α-Hydroxylation of β-Ketoesters

“…This observation rules out a mechanism proceeding via (our initially targeted) in situ formation of 2 as the active O-transfer reagent. In addition, these reported iminium-salt-catalyzed oxidations mainly used non-oxidizable counteranions, 21 which is in sharp contrast to our reaction where the presence of an oxidizable anion is crucial (vide infra).…”

An Overview of Saturated Cyclic Ethers: Biological Profiles and Synthetic Strategies

“…Due to the high need for enantiomerically pure epoxides, numerous powerful and efficient catalytic asymmetric reactions have been introduced and developed to generate epoxides [49]. Among these processes, Sharpless asymmetric epoxidation (SAE), Jecobsen–Katsuki epoxidation, Shi epoxidation, etc., are classic, powerful, and still popular [50,51,52].…”