Graphene oxide as an acid catalyst for the room temperature ring opening of epoxides

The minute amount of hydrogen sulfate groups introduced into the graphene oxide (GO) obtained by Hummers oxidation of graphite renders this material as a highly efficient, recyclable acid catalyst for the ring opening of epoxides with methanol and other primary alcohols as nucleophile and solvent.     

Mild and Efficient Ring Opening of Epoxides Catalyzed by Potassium Dodecatungstocobaltate(III)

Summary. Efficient ring opening of epoxides under mild conditions is reported. Potassium dodecatungstocobaltate(III) trihydrate was used as an efficient catalyst for the alcoholysis and acetolysis of epoxides. Conversion of epoxides to thiiranes was also performed efficiently in the presence of this catalyst.     

Cobalt complexes appended with p- and m-carboxylates: two unique {Co(3+)-Cd2+} networks and their regioselective and size-selective heterogeneous catalysis

Co(3+) complexes appended with arylcarboxylate groups act as molecular building blocks to afford {Co(3+)-Cd(2+)} networks. These networks function as the heterogeneous and reusable catalysts for regio- and stereoselective ring opening of epoxides and size-selective cyanation of aldehydes.     

Enantioselective Ring Opening of Epoxides with 4-Methoxyphenol Catalyzed by Gallium Heterobimetallic Complexes: An Efficient Method for the Synthesis of Optically Active 1,2-Diol Monoethers

Useful chiral building blocks such as 1,2-diols can be obtained by the enantioselective ring opening of achiral epoxides with oxygen nucleophiles. The ring opening is carried out effectively (up to 94 % ee) with 4-methoxyphenol and catalytic amounts of gallium complexes. The novel complex GaSO 1 displays a particularly high catalytic activity.     

Synthesis of 1,2-azidoalcohols from epoxides using a task-specific protic ionic liquid: 1-hydrogen-3-methylimidazolium azide

A task-specific ionic liquid as an environmentally eco-friendly green catalyst has been synthesized and used in the ring opening of epoxides under green conditions. In order to use protic ionic liquids (PIL), we decided to synthesize 1,2-azidoalcohols via a ring opening reaction of epoxides with 1-hydrogen-3-methylimidazolium azide ([Hmim]N₃), which actually acts as a solvent, a reagent and an activator of the epoxide ring. The reaction was carried out in short times (50–70 min) at 70 °C to give 1,2-azidoalcohol in 80–94% isolated yields.     

A DFT Study on the Mechanism of the Cycloaddition Reaction of CO2 to Epoxides Catalyzed by Zn(Salphen) Complexes

The reaction mechanism for the Zn(salphen)/NBu₄X (X=Br, I) mediated cycloaddition of CO₂ to a series of epoxides, affording five‐membered cyclic carbonate products has been investigated in detail by using DFT methods. The ring‐opening step of the process was examined and the preference for opening at the methylene (C_β) or methine carbon (C_α) was established. Furthermore, calculations were performed to clarify the reasons for the lethargic behavior of internal epoxides in the presence of the binary catalyst. Also, the CO₂ insertion and the ring‐closing steps have been explored for six differently substituted epoxides and proved to be significantly more challenging compared with the ring‐opening step. The computational findings should allow the design and application of more efficient catalysts for organic carbonate formation.     

Formation of enantiopure 5-substituted oxazolidinones through enzyme-catalysed kinetic resolution of epoxides

Halohydrin dehalogenase from Agrobacterium radiobacter catalyzed the enantioselective ring opening of terminal epoxides with cyanate as a nucleophile, yielding 5-substituted oxazolidinones in high yields and with high enantiopurity (69-98% ee). This is the first example of the biocatalytic conversion of a range of epoxides to the corresponding oxazolidinones.     

Rhodium-catalyzed ring opening of vinyl epoxides with alcohols and aromatic amines

[Rh(CO)(2)Cl](2) is an effective catalyst for the ring opening of vinyl epoxides with alcohols and aromatic amines under neutral conditions at room temperature. The reaction occurs with excellent diastereo- and regioselectivity (>20:1) giving the trans-1,2-amino alcohols or alkoxy alcohols for a wide range of substrates. The regio- and stereochemistry of these reactions is complementary to that typically obtained with palladium-catalyzed ring openings of vinyl epoxides.     

The Generation of (Samarium) Thiolates from Aryl Thiocyanates and Their Reaction with Epoxides: A Route to β-Hydroxy Sulfides

This investigation describes the reduction of an aryl thiocyanate with samarium(II) iodide, followed by reaction with various epoxides, to produce β-hydroxy sulfides. This method of ring opening of epoxides provides a substantial improvement in reaction time and convenience over existing methods while maintaining good regioselectivity and excellent yield.     

Synthesis of optically active 2-hydroxy monoesters via-kinetic resolution and asymmetric cyclization catalyzed by heterometallic chiral (salen) Co complex

The binuclear chiral (salen) Co complexes bearing Lewis acids of Al and Ga catalyze regio- and enantioselective ring opening of terminal epoxides with carboxylic acids. The ring opened product of epichlorohydrin with carboxylic acids followed by cyclization step in the presence of catalyst and base represent straightforward, efficient methods for the synthesis of enatiomerically enriched (>99% ee) valuable terminal epoxides. Strong synergistic effects of different Lewis acid of Co-Al and Co-Ga were exhibited in the catalytic process.     

Conversion of epoxides into halohydrins with elemental halogen catalyzed by thiourea

A highly regioselective method for the synthesis of β-iodohydrins and β-bromohydrins by the direct ring opening of epoxides with elemental halogen in the presence of thiourea is described. This method occurs under neutral and mild conditions with high yields in various solvents even when sensitive functional groups are present.     

Theoretical study concerning the reactivity of imine derivatives of polycyclic aromatic hydrocarbons

The opening reaction of N-protonated polycyclic aromatic hydrocarbon imines has been computed by means of ab initio, density functional, and semiempirical methods of calculation. Imines are predicted to be more stable than the corresponding O-protonated derivatives, epoxides and diol epoxides. On the other hand, the activated N-methanesulfonylbenzene imine presented more favorable DeltaE( not equal ) and DeltaE(r) for ring opening due to the effect of hydrogen-bond interactions. Anti and syn trans-diol benzene imines did not show a different behavior from the unsubstituted imine. According to these calculations, bay-region, fjord-region, and bay-region methyl-substituted compounds opened more easily among the imine derivatives, following the same reactivity pattern as the oxygen analogs. The exothermicity of the opening process correlated with the charge delocalization in the resulting carbocation.     

Alumina-supported metal(II) Schiff base complexes as heterogeneous catalysts in the high-regioselective cleavage of epoxides to halohydrins by using elemental halogen

A highly regioselective method for the synthesis of β-iodohydrins and β-bromohydrins through direct ring opening of epoxides with elemental halogen in the presence of alumina-supported Schiff base complexes of Mn(II), Co(II), Ni(II) and Cu(II) as new catalysts is described. This method is regioselective under mild conditions in various aprotic solvents with high yields, even when sensitive functional groups are present. The catalysts are easily recovered and can be reused several times.     

Highly reactive and enantioselective kinetic resolution of terminal epoxides with H2O and HCl catalyzed by new chiral (salen)Co complex linked with Al

The asymmetric hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by new easily synthesized dimeric chiral (salen)Co bearing Al, provides a practical and straightforward method for the synthesis of enantiomerically enriched terminal epoxides (>99% ee) and diols. An inorganic acid, HCl is applied first time for the asymmetric ring opening reaction of terminal epoxides. Reactions are conveniently carried out at room temperature under an air atmosphere.     

Ring Expansion of Epoxides under Brønsted Base Catalysis: Formal [3+2] Cycloaddition of β,γ‐Epoxy Esters with Imines Providing 2,4,5‐Trisubstituted 1,3‐Oxazolidines

A novel ring‐expansion reaction of epoxides under Brønsted base catalysis was developed. The formal [3+2] cycloaddition reaction of β,γ‐epoxy esters with imines proceeds in the presence of triazabicyclodecene (TBD) as a superior Brønsted base catalyst to afford 2,4,5‐trisubstituted 1,3‐oxazolidines in a highly diastereoselective manner. This reaction involves the ring opening of the epoxides with the aid of the Brønsted base catalyst to generate α,β‐unsaturated esters having an alkoxide at the allylic position, which would formally serve as a synthetic equivalent of the 1,3‐dipole, followed by a cycloaddition reaction with imines in a stepwise fashion. This methodology enables the facile synthesis of enantioenriched 1,3‐oxazolidines from easily accessible enantioenriched epoxides.     

Microwave-assisted polymerization of higher alkylene oxides

Homopolymers and block copolymers of higher epoxides (butene oxide and hexene oxide) are synthesized using 1-alkanols and PEG-MME 1100 as initiators by anionic ring opening polymerization in bulk employing controlled microwave heating in sealed vessels. The selectivity of polymerization of higher epoxides and the effect of different reaction parameters on the formation of side products is discussed. A procedure for the generation of fairly clean homopolymers and multiblock copolymers (giving bottle-brush and cone type of structures) is developed.     

A new dinuclear chiral salen complexes for asymmetric ring opening and closing reactions: Synthesis of valuable chiral intermediates

A new dinuclear chiral Co(salen) complexes bearing group 13 metals have been synthesized and characterized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides with H₂O, chloride ions and carboxylic acids and consequently provide enantiomerically enriched terminal epoxides (>99% ee). It also catalyzes the asymmetric cyclization of ring opened product, to prepare optically pure terminal epoxides in one step. The homogeneous dinuclear chiral Co(salen) have been covalently immobilized on MCM-41. The potential benefits of heterogenization include facilitation of catalyst separation and recyclability requiring very simple techniques. The system described is very efficient.     

Aluminium triflate: a remarkable Lewis acid catalyst for the ring opening of epoxides by alcohols

Al(OTf)3 was found to be an extremely effective catalyst (at ppm levels) for ring opening reactions of epoxides using a range of alcohols.     

环氧乙烷亲核开环的区域选择性规则在有机化学教学中的应用

环氧乙烷亲核开环的区域选择性规则是有机化学中典型脂肪三元杂环亲核性开环的选择性规则,具有普遍性。本文以非对称环氧乙烷的亲核性开环为核心,从开环反应过渡态稳定性的角度讨论了决定环氧乙烷亲核开环区域选择性的原因。介绍了该区域选择性规则在经过三元杂环正离子中间体的非对称烯烃亲电加成反应区域选择性教学中的应用。加强学生对不同反应的机理和选择性的联系,起到教学中融会贯通的作用,可以提高教学效率和效果。     

Allyltin tribromide: A versatile reagent involved in the ring-opening of epoxides

This paper presents a versatile reagent for epoxide cleavage. The allyltin tribromide could act as a novel and easily prepared allylation reagent and halide atom donor to convert epoxides to the corresponding homoallyl alcohols and halohydrins in high yields with excellent regioselectivities under mild reaction conditions, respectively. It could also act as a Lewis acid to catalyze the ring opening reactions of epoxides with alcohols.