Asymmetric Epoxidation Of Enones Research Articles

Asymmetric epoxidation of enones: effect of surfactants, radical scavengers and morphology of catalysts on reaction rates, chemical yields and enantioselectivities in phase-transfer catalysis

Highly enantioselective epoxidation of enones has been accomplished with asymmetric phase-transfer catalysis using Cinchona alkaloid-derived meta-dimer catalysts.

Asymmetric epoxidation of enones using cumyl hydroperoxide and in situ generated zinc complexes of chiral pyrrolidinyl alcohols

The homogeneous asymmetric epoxidation of a range of enones was carried out using cumyl hydroperoxide, diethylzinc, and chiral pyrrolidinyl alcohol-containing ligands to afford the corresponding epoxy ketones with enantioselectivities of ≤97% ee. Examination of the enantioselectivities obtained in the asymmetric epoxidation of enones using a range of chiral ligands indicated that synergy between the sterically bulky bicyclo[2.2.2]octane skeleton and the substituents attached to the carbinol moiety played an important role in determining the reaction enantioselectivity. The position and nature of the substituent on the aromatic ring of the enone also had a pronounced effect on the observed enantioselectivity.

Development of Selective Peptide Catalysts with Secondary Structural Frameworks.

Enzymes are biogenic catalysts that enable the vital activity of organisms. Enzymes promote reactions in a selective manner with a high level of substrate recognition ability. The development of such a sophisticated catalyst has been one of the goals for chemists. A synthetic peptide is the prime candidate to realize an enzyme-like catalyst. Considering that the catalytic function of enzymes derives from their molecular structures, the key for the creation of a peptide catalyst might be the introduction of a specific three-dimensional structure. Our motivation was to find a peptide catalyst with a versatile secondary structural framework and apply the peptide to a variety of selective reactions. Although helical-peptide-catalyzed asymmetric epoxidation of enones is popular, no other highly enantioselective reaction with a helical peptide has been reported. It was found that resin-supported α-helical polyleucine promoted asymmetric conjugate addition of a carbon nucleophile to enones via the formation of an iminium intermediate at the N-terminal amino group. By changing the helical chain to a repetitive Leu-Leu-Aib (Aib = α-aminoisobutyric acid) sequence and introducing a few amino acids to the N-terminus, a highly enantioselective peptide catalyst was obtained. The helical peptide catalyst was applicable for a tandem enamine/iminium-mediated reaction and asymmetric epoxidation of enones. Although the extension of the helical peptide to conjugate addition of a nucleophile to an enal was not successful simply by attaching proline to the N-terminus of the helix, the incorporation of a β-turn motif was effective to improve the catalytic performance. In the sequence of such a turn-helix-type peptide, the helical part was seemingly distant from the N-terminal amino group; however, the hydrophobicity, structure, and chirality of the helix largely affected the reaction. The turn-helix-type peptide promoted a wide range of asymmetric reactions: conjugated additions of hydride and carbon nucleophiles to enals via the iminium activation and α-oxyamination of aldehydes via the enamine activation. The peptides with turn-helix and helix frameworks were also employed for several reactions that were difficult to achieve with low-molecular-weight catalysts: enzyme-cocatalyzed asymmetric oxidation in water, diastereo- and enantioselective cyclopropanation, regioselective reduction of dienals, kinetic resolution of planar-chiral compounds, and desymmetrization to induce planar chirality. To explore other types of peptide catalysts, a combinatorial library screening was performed. On the way, it was revealed that a histidyl residue assisted to accelerate a reaction via reversible addition to an iminium intermediate. Through the screening of random peptide libraries, novel peptide sequences for efficient and enantioselective conjugate addition were discovered. Although we have no information about the molecular structure of the newly found peptides, they can be an entry point for establishing a versatile framework of peptide catalysts.

Front Cover Picture: Quest for Efficient Catalysts based on Zinctert-Butyl Peroxides for Asymmetric Epoxidation of Enones:C2-vs C1-Symmetric Auxiliaries (Adv. Synth. Catal. 6/2016)

Front Cover Picture: Quest for Efficient Catalysts based on Zinctert-Butyl Peroxides for Asymmetric Epoxidation of Enones:C2-vs C1-Symmetric Auxiliaries (Adv. Synth. Catal. 6/2016)

Chiral Ligand-controlled Catalytic Asymmetric Epoxidation of Enone with Hydroperoxide

Conjugate addition-type asymmetric epoxidation of an enone with lithium cumene hydroperoxide was mediated by a chiral ligand. The catalytic process was realized under conditions of a slow addition of cumene hydroperoxide.

Efficient asymmetric epoxidation of alpha,beta-unsaturated ketones using a soluble triblock polyethylene glycol-polyamino acid catalyst.

[reaction: see text]. Polyethylene glycol (PEG)-bound poly-L-leucine acts as a THF-soluble catalyst for the Juliá-Colonna asymmetric epoxidation of enones. Excellent enantioselectivities may be obtained even with short chain length polyleucine. FT-IR investigations have determined that the catalytically active polyleucine components of these copolymers have an alpha-helical structure.

The effect of the primary structure of the polypeptide catalyst on the enantioselectivity of the Juliá-Colonna asymmetric epoxidation of enones.

Epoxidation of chalcone (1), using basic hydrogen peroxide, catalysed by polypeptides with defined primary structures demonstrates that the residues in the chain near to the N-terminus determine the stereochemical outcome of the reaction.

Beta-peptides as catalysts: poly-beta-leucine as a catalyst for the Juliá-Colonna asymmetric epoxidation of enones.

Poly-beta-leucines have been evaluated as catalysts for the Juliá-Colonna asymmetric epoxidation of enones; the beta 3-isomer was found to be an effective catalyst for the epoxidation of chalcone (70% ee) and some analogues.

ChemInform Abstract: Remarkable Ligand Effect on the Enantioselectivity of the Chiral Lanthanum Complex‐Catalyzed Asymmetric Epoxidation of Enones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Asymmetric Epoxidation of Enones with Oxygen in the Presence of Diethylzinc and (R,R)‐N‐Methylpseudoephedrine.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Asymmetric Epoxidation of Enones With Oxygen in the Presence of Diethylzinc and (R,R)‐N‐Methylpseudoephedrine

An efficient method for the asymmetric epoxidation of α,β-unsaturated ketones 1 is embodied in their reaction with oxygen in the presence of diethylzinc and (R,R)-N-methyl-pseudoephedrine. It affords epoxides 2 in excellent yields, with complete diastereoselectivity, and with enantiomeric excesses of up to 92% ee. The enantiomerically pure amino alcohol employed can be recovered virtually quantitatively with unchanged optical purity.