Catalysts For Asymmetric Epoxidation Research Articles

Trifluoromethyl Ketone Galactose Catalyst for Asymmetric Epoxidation: Experimental and Theoretical Model

AbstractSince the introduction of the Shi catalyst, the organocatalytic epoxidation of olefins has become an area of continued research interest. To explore the possibility of enhancing the efficiency and stability of the catalyst, the synthesis of a galactose‐derived trifluoromethyl ketone, and its use for stereoselective epoxidation reaction that exploits a transitory dioxirane as active species are herein reported. The trifluoromethyl ketone was built on the C6 of a protected d‐galactopyranose. The organocatalyst was obtained smoothly in a few steps, and when utilized for stereoselective epoxidation exhibited excellent stability as no chemical alterations were observed during the reaction. The stereoselectivity, although sometimes moderate, appears surprisingly high considering the conformational freedom of the trifluoromethyl ketone moiety.DFT calculations were performed to investigate the interactions involved in regulating the observed selectivities. Moreover, a new mnemonic model has been developed to serve as a fast‐predicting tool for epoxidation of new substrates.

Dehydrogenation Based Asymmetric Epoxidation of Arylalkanes to Chiral Epoxides

Comprehensive SummaryWe report herein a formal asymmetric epoxidation of arylalkanes enabled by a one‐pot dual‐catalysts system comprising a pincer Ir catalyst for alkane dehydrogenation‐alkene isomerization (AD‐ISO) and a chiral ketone catalyst for asymmetric alkene epoxidation. This protocol provides a catalytic method for the synthesis of aryl epoxides in useful yields with high regio‐ and stereoselectivity directly from readily available alkyl arenes. Stereospecific derivatizations of the epoxidation product allow access to various enantioenriched compounds.

Chiral porous poly(ionic liquid)s: Facile one-pot, one-step synthesis and efficient heterogeneous catalysts for asymmetric epoxidation of olefins

Ionic liquids are potential media/solvents for asymmetric synthesis when combined with chiral catalysts, while most reported catalysts are homogenous, making them difficult to separate from the reaction systems. Herein, chiral porous poly(ionic liquid)s (CPPILs) containing chiral salen Mn(III) complex have been successfully synthesized through a simple and one-pot route involving simultaneously occurred Friedel-Crafts alkylation and quaternization. These CPPILs possess large specific surface area, plentiful micro/meso-porosity, and abundant ionic active sites. Consequently, CPPILs can serve as highly efficient heterogeneous catalysts for asymmetric epoxidation of styrene. Excellent catalytic performance with yield of epoxides and enantiomeric excess value comparable with or even higher than that of the homogeneous system was achieved. The high catalytic activity can be further expanded to various substrates of unfunctionalized olefins. These catalysts are stable and could be recycled at least five times without significant loss of reactivity and enantioselectivity.

Chiral C2-Symmetric Aminomethylbinaphthol as Synergistic Catalyst for Asymmetric Epoxidation of Alkylidenemalononitriles: Easy Access to Chiral Spirooxindoles

Chiral C2-symmetric 3,3'-bis((R,R)-2-naphthylethylaminomethyl)-(R)-binaphthol (AMB4) functions as an efficient organocatalyst for the asymmetric epoxidation of various alkylidenemalononitriles. The spiro-epoxyoxindole products obtained from isatilidenemalononitriles were easily transformed to the corresponding chiral dihydroquinoxalinyl spirooxindoles.

Retraction: Synthesis of a novel type of chiral salen Mn(iii) complex immobilized on crystalline zinc poly(styrene-phenylvinylphosphonate)-phosphate (ZnPS-PVPP) as effective catalysts for asymmetric epoxidation of unfunctionalized olefins

Retraction for ‘Synthesis of a novel type of chiral salen Mn(iii) complex immobilized on crystalline zinc poly(styrene-phenylvinylphosphonate)-phosphate (ZnPS-PVPP) as effective catalysts for asymmetric epoxidation of unfunctionalized olefins’ by Jing Huang et al., Catal. Sci. Technol., 2011, 1, 1472–1482, DOI: 10.1039/C1CY00285F

Retraction: A series of novel types of immobilized chiral salen Mn(iii) on different organic polymer–inorganic hybrid crystalline zinc phosphonate–phosphate act as catalysts for asymmetric epoxidation of unfunctionalized olefins

Retraction for ‘A series of novel types of immobilized chiral salen Mn(iii) on different organic polymer–inorganic hybrid crystalline zinc phosphonate–phosphate act as catalysts for asymmetric epoxidation of unfunctionalized olefins’ by Jing Huang et al., Catal. Sci. Technol., 2012, 2, 1040–1050, DOI: 10.1039/C2CY00502F.

Oligomeric (Salen)Mn(III) Complexes Featuring Tartrate Linkers Immobilized over Layered Double Hydroxide for Catalytically Asymmetric Epoxidation of Unfunctionalized Olefins.

A series of oligomeric (salen)Mn(III) complexes featuring tartrate linkers were prepared and immobilized over layered double hydroxide, and then used as catalysts for asymmetric epoxidation of unfunctionalized olefins. Comprehensive characterizations including 1H NMR, FT-IR, UV-Vis, elemental analysis, GPC, and ICP-AES were used to illustrate structures of oligomeric (salen)Mn(III) complexes, while powdered XRD, nitrogen physisorption, together with XPS studies provided further details to detect structures of heterogeneous catalysts. Interestingly, scanning electron microscopy found an interesting morphology change during modification of layered supporting material. Catalytic experiments indicated that configuration of major epoxide products was determined by salen chirality more than that of tartrate linker, but enantioselectivity (e.e. values) could be enhanced when tartrate and salen showed identical chiral configurations. Furthermore, the (R,R)-salen moieties linked with (R,R)-tartrate spacers usually offered higher enantioselectivity compared to other combinations. Lastly, Zn(II)/Al(III) layered double hydroxide played as a rigid supporting material in catalysis, showing positive chiral induction and high recycling potential in catalytic reactions.

Recent Developments in Heterogeneous Catalyzed Epoxidation of Styrene to Styrene Oxide

AbstractEpoxidation of styrene under heterogeneous catalyzed conditions provides environmentally friendly routes to produce styrene oxide, an important synthetic intermediate for synthesis of perfumes, epoxy resins, plasticizers, drugs, sweeteners and fine chemicals. The present review explores epoxidation of styrene under heterogeneous catalysed conditions using a variety of catalysts such as metal nanoparticles, metal oxides (of group 12 and 13 metals, transition metals, rare earth metals), transition metals and complexes, polyoxometallates, microporous and mesoporous materials (zeolites, modified zeolites, organic/inorganic porous hybrid materials, porous metal oxides, SBA 15) and polymers using hydrogen peroxide (H2O2), tert‐butyl hydroperoxide (TBHP), air or oxygen as oxidants.The use of salen based transition metal complexes and of chiral porphyrins as catalysts in asymmetric epoxidation of styrene is also reviewed. The reaction mechanism studies of most of these reactions suggest an intermediate formation of a reactive metal‐oxygen species, by interactions between the catalyst and oxidant.

Safe and Scalable Aerobic Oxidation by 2-Azaadamantan-2-ol (AZADOL)/NOx Catalysis: Large-Scale Preparation of Shi’s Catalyst

A method for safe and scalable aerobic alcohol oxidation using 2-azaadamantan-2-ol (AZADOL), an azaadamantane-type hydroxylamine catalyst, with a NOx cocatalyst in a conventional batch reactor has been developed. The use of 2 mol % AZADOL and 10 mol % NaNO2 was determined to promote aerobic alcohol oxidation quantitatively within a reasonable time (8 h). Safety is ensured by controlling the reaction temperature below the flash point of the acetic acid solvent. The robustness of the developed method is demonstrated by the 500 g scale oxidation of diacetone fructose into Shi’s catalyst for asymmetric epoxidation.

Chiral salen Mn (III) immobilized on ZnPS-PVPA through alkoxyl-triazole for superior performance catalyst in asymmetric epoxidation of unfunctionalized olefins

Chiral salen Mn (III) catalysts anchored onto ZnPS-PVPA via click chemistry are prepared and applied in asymmetric epoxidations of unfunctionalized olefins. Superior catalytic performances (conv%, up to >99; ee%, up to >99) are achieved in the epoxidations of α-methylstyrene, styrene, indene and 1-octene. According to 6-cyano-2,2-dimethylchromene and 6-nitro-2,2-dimethylchromene, configuration of epoxides are reversed. And then the catalysts are selective in not only oxidative systems, but also substrates. Moreover, superior reusability (yield, 82%; ee, 86%) after recycling for nine times could also be obtained, which provide the potential application in industry.

Chiral porphyrin imine manganese complex as catalyst for asymmetric epoxidation of styrene derivatives.

New chiral porphyrin imine was synthesized from (S)-3-benzyl-2-methyl-4-phenylbutanal according to dipyrromethane method using trifluoroacetic acid, BF3 etherate, and p-chloranil. Manganese complex of this chiral porphyrin imine ligand was used as catalyst in the asymmetric epoxidation of styrene derivatives possessing different substituents. Styrene derivatives possessing electron withdrawing groups gave the corresponding chiral epoxides in high yield up to 98% and ee up to 99%. The mechanism for the catalytic asymmetric epoxidation was also discussed based on transfer of oxygen.

Chiral MnIII (Salen) Covalently Bonded on Modified ZPS-PVPA and ZPS-IPPA as Efficient Catalysts for Enantioselective Epoxidation of Unfunctionalized Olefins.

Chiral MnIII (salen) complex supported on modified ZPS-PVPA (zirconium poly(styrene-phenylvinylphosphonate)) and ZPS-IPPA (zirconium poly(styrene-isopropenyl phosphonate)) were prepared using –CH2Cl as a reactive surface modifier by a covalent grafting method. The supported catalysts showed higher chiral induction (ee: 72%–83%) compared with the corresponding homogeneous catalyst (ee: 54%) for asymmetric epoxidation of α-methylstrene in the presence of 4-phenylpyridine N-oxide (PPNO) as axial base using NaClO as an oxidant. ZPS-PVPA-based catalyst 1, with a larger pore diameter and surface area, was found to be more active than ZPS-IPPA-based catalyst 2. In addition, bulkier alkene-like indene, was efficiently epoxidized with these supported catalysts (ee: 96%–99%), the results were much higher than those for the homogeneous system (ee: 65%). Moreover, the prepared catalysts were relatively stable and can be recycled at least eight times without significant loss of activity and enantioselectivity.

A novel chiral manganese-tetraamide macrocycle complex covalently attached to magnetite as recyclable catalyst for aerobic asymmetric epoxidation of olefins

A novel Mn complex containing N4-tetradentate tetraamide macrocyclic ligand (L) derived from chiral diethyl-2,3-benzylidene-l-tartrate and polyamidoamine dendrimer on Fe3O4@SiO2 surface was synthesized. The nanocomposite particles were investigated by SEM, XRD, VSM, EPR and FTIR. The nanocomposite showed high catalytic activity and selectivity for the epoxidation of linear terminal, cyclic and most of the aromatic olefins by O2 in the presence of isobutyraldehyde under mild conditions; epoxide selectivity 87–100%, enantiomeric excess 53–100%. The catalyst could be separated and recovered from the reaction system by applying an external magnetic field and reused for four cycles without the loss of activity after each cycle. Total TON of 16957 was obtained after four cycles.

ChemInform Abstract: Design of a New Bimetallic Catalyst for Asymmetric Epoxidation and Sulfoxidation.

A new chiral tethered 8-quinolinol-based ligand class is developed. The binuclear titanium complex of the ligand operates through a novel mechanism allowing for the regio- and stereoselective epoxidation of primary and tertiary homoallylic alcohols (up to 98% ee), as well as first examples of 2-allylic phenols (up to 92% ee). The new catalyst system also promotes the asymmetric oxidation of γ-hydroxypropyl sulfides giving an important class of chiral sulfoxides that have been inaccessible to date (up to 95% ee).

A Bimetallic Titanium Catalyst for Asymmetric Epoxidation and Sulfoxidation

A Bimetallic Titanium Catalyst for Asymmetric Epoxidation and Sulfoxidation

ChemInform Abstract: Chiral Octahedral Complexes of Co(III) as Catalysts for Asymmetric Epoxidation of Chalcones under Phase Transfer Conditions.

AbstractThe same type of catalyst is found to catalyze the coupling of the obtained epoxide (IIIa) with CO2.

Design of a New Bimetallic Catalyst for Asymmetric Epoxidation and Sulfoxidation.

A new chiral tethered 8-quinolinol-based ligand class is developed. The binuclear titanium complex of the ligand operates through a novel mechanism allowing for the regio- and stereoselective epoxidation of primary and tertiary homoallylic alcohols (up to 98% ee), as well as first examples of 2-allylic phenols (up to 92% ee). The new catalyst system also promotes the asymmetric oxidation of γ-hydroxypropyl sulfides giving an important class of chiral sulfoxides that have been inaccessible to date (up to 95% ee).

Olefin epoxidation by a (salen)Mn(iii) catalyst covalently grafted on glass beads

A newly synthesized robust (salen)Mn(iii) monolayer on glass bead substrates provides an active catalyst for asymmetric epoxidation of 6-cyano-2,2-dimethylchromene, cis-β-ethylstyrene, 1,2-dihydronaphthalene and indene.

Chiral octahedral complexes of Co(iii) as catalysts for asymmetric epoxidation of chalcones under phase transfer conditions

Stereochemically inert and positively charged chiral complexes of Co(iii) were shown to catalyze the asymmetric epoxidation of chalcones with H2O2 under phase transfer conditions.

Ionic liquid-functionalized graphene oxide as an efficient support for the chiral salen Mn(iii) complex in asymmetric epoxidation of unfunctionalized olefins

Chiral salen Mn(iii) complex covalently grafted on IL-functionalized GO sheet, was a highly efficient, universal and reusable catalyst for asymmetric epoxidation of unfunctionalized olefins using aqueous NaOCl as an oxidant.