175 research outputs found
Organocatalytic Approaches to Asymmetric Oxidation: Epoxidation of α-Branched Enals and α-Benzoyloxylation of Carbonyl Compounds
This work describes the development of enantioselective oxidation reactions of carbonyl compounds using covalent organocatalysis. In the first part, asymmetric epoxidation of α-branched α,β-unsaturated aldehydes with aqueous hydrogen peroxide is presented. An exceptionally synergistic combination of a primary cinchona alkaloid-derived amine and a chiral BINOL-derived phosphoric acid was found to promote the reaction with excellent enantiocontrol for a wide variety of α,β-disubstituted and α-monosubstituted enals. Conformational analysis of catalytically relevant intermediates using NMR and computational techniques enabled the rationalization of the absolute stereochemistry of products. The second part of this thesis describes a highly efficient direct catalytic asymmetric α-benzoyloxylation of cyclic ketones. The same primary amine paired with an inorganic acid was found to be an effective catalyst for a wide range of substrates. The methodology was applied to the first asymmetric synthesis of (+)-2β,4-dihydroxy-1,8-cineole, a predicted terpenoid metabolite in mammals. Preliminary investigations on the α-benzoyloxylation of α-branched aldehydes and α-branched enals using this catalytic system demonstrated significant potential of the method for the enantioselective formation of oxygenated quaternary stereocenters
Nucleophilic ring-opening of Methyl 1- Nitrocyclopropanecarboxylates
Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal
The Cinchona Primary Amine-Catalyzed Asymmetric Epoxidation and Hydroperoxidation of α,β-Unsaturated Carbonyl Compounds with Hydrogen Peroxide
Using cinchona alkaloid-derived primary amines as catalysts and aqueous hydrogen peroxide as the oxidant, we have developed highly enantioselective Weitz–Scheffer-type epoxidation and hydroperoxidation reactions of α,β-unsaturated carbonyl compounds (up to 99.5:0.5 er). In this article, we present our full studies on this family of reactions, employing acyclic enones, 5–15-membered cyclic enones, and α-branched enals as substrates. In addition to an expanded scope, synthetic applications of the products are presented. We also report detailed mechanistic investigations of the catalytic intermediates, structure–activity relationships of the cinchona amine catalyst, and rationalization of the absolute stereoselectivity by NMR spectroscopic studies and DFT calculations
Reactions of Donor-Acceptor Cyclopropanes with Naphthoquinones: Redox and Lewis Acid Catalysis Working in Concert
Reactions of 2-aryl cyclopropane dicarboxylates with
naphthoquinones are reported. The key feature was the use of
catalytic amounts of SnCl2, which acts as both electron donor and
Lewis acid. By an in-situ umpolung of naphthoquinone the formerly
electrophilic species is converted into a nucleophile that is able to
trigger the ring-opening of the three-membered ring with formation of
a new C-C bond. Treatment of these products with base under
oxidative conditions resulted - by losing methyl formate - in
cyclopentannulated products with fully conjugated π systems
exhibiting intensive absorptions in the visible range
Improving disk read performance through block-level replication into free space
Disk performance for random access fares significantly worse compared to
sequential access. Time required to transfer random blocks to or from disk is
dominated by seeking and rotational delay. To improve the throughput and
reduce the latency, one can apply techniques to increase the sequentiality of
disk accesses, such as block rearrangement and replication.
We introduce an approach to improve read performance by replicating
blocks into file system free space at the block level. This makes the replication
module independent of the file system and therefore easier to implement
and verify. A solution that requires no changes to the file system is
also easier to adopt. Supporting a new file system is a matter of writing a
user-space component that understands its free block data structures. We
implemented a prototype as a stacked device driver for Linux and evaluated
its performance on a number of workloads.Science, Faculty ofComputer Science, Department ofGraduat
ChemInform Abstract: A Mild Procedure for the Lewis Acid-Catalyzed Ring-Opening of Activated Cyclopropanes with Amine Nucleophiles.
ChemInform Abstract: Nucleophilic Addition of Phenol Derivatives to Methyl 1-Nitrocyclopropanecarboxylates.
ChemInform Abstract: The Cinchona Primary Amine-Catalyzed Asymmetric Epoxidation and Hydroperoxidation of α,β-Unsaturated Carbonyl Compounds with Hydrogen Peroxide.
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