Intramolecular arene hydroxylation versus intermolecular olefin epoxidation by (mu-eta2:eta2-peroxo)dicopper(II) complex supported by dinucleating ligand

A discrete (mu-eta2:eta2-peroxo)Cu(II)2 complex, [Cu2(O2)(H-L)]2+, is capable of performing not only intramolecular hydroxylation of a m-xylyl linker of a dinucleating ligand but also intermolecular epoxidation of styrene via electrophilic reaction to the C=C bond and hydroxylation of THF by H-atom abstraction.     

Intramolecular SNAr reactions in a large-ring ketocalix[6]arene

Ketocalix[6]arene 2e was prepared by CrO3 oxidation of the methylene groups of 2a, followed by hydrolysis of the acetate groups. 2e undergoes intramolecular SNAr reactions under the usual methylation conditions (MeI, base), yielding mono- and dixanthone calixarene derivatives.     

Intramolecular direct arylation in an A,C-functionalized calix[4]arene

A recently developed efficient method for intramolecular direct arylation is employed on a doubly functionalized calix[4]arene fixed in the cone conformation. The reaction takes place in high yield leading to meta substituted calix[4]arenes. The functionalities are located at two opposite aromatic rings and the two possible diastereomers are obtained in a 1:1 ratio. Full sets of data including crystal structures for both isomers are presented. The NMR data reveal that even at temperatures up to 120 degrees C both isomers are fixed in a flattened cone conformation with the substituted aromatic units pointing outwards.     

Intramolecular hydrogen bonding effect on metal ion complexation of homooxacalix[4]arene bearing tetraamides

N,N-Dipentylamido homooxacalix[4]arene (3) in the C-1,2-alternate conformation provided Pb²⁺ ion selectivity over other metal cations. N-Monopentylamido homooxacalix[4]arene in C-1,2-alternate conformation has an intramolecular hydrogen bonding, causing decrease of the metal ion complex ability.     

Intramolecular epoxidation with the H2O2/ortho ester system

Intramolecular epoxidation is shown to occur when trimethyl ortho oleate is treated with H₂O₂.     

Thermal risk assessment for the epoxidation of linseed oil by classical Prisleschajew epoxidation and by direct epoxidation by H2O2 on alumina

Journal of Thermal Analysis and Calorimetry - Substitution of fossil feedstock by vegetable oils is growing due to environmental constraints and oil depletion. Among the different valorization...     

Intramolecular Pd-catalyzed carbocyclization, Heck reactions, and aryl-radical cyclizations with planar chiral arene tricarbonyl chromium complexes

(o-butenylhalobenzene)Cr(CO)(3) complexes were synthesized by diastereoselectve allylmetal additions to o-halo benzaldehyde complexes. The addition of allylZnBr proved particularly convenient and clean. The complexes undergo intramolecular Pd-catalyzed cyclizations (Heck reactions) without decomplexation and/or alkene isomerization. In complexes with a benzylic stereogenic center, the diastereoselectivity of the alkene carbopalladation is governed by the planar chirality of the complex rather than by the benzylic stereogenic center in the side chain. This reaction outcome can be rationalized by the geometry of the arene plane vs that of the Pd coordination plane in the transition step of the alkene carbopalladation step. An alternative cyclization procedure involves the generation of a Cr(CO)(3)-coordinated arene radical from the bromo and iodo complexes. Intramolecular aryl-radical cyclization affords indan complexes. The transition metal arene pi-bond remains intact during this process.     

Alkyl Ammonium Ion Selectivity of Hexahomotrioxacalix[3]arene Triamide Derivative having the Intramolecular Hydrogen-Bonding Group

The lower rim functionalized hexahomotrioxacalix[3]arene triamide 4 with cone-conformation was synthesized from triol 1 by a stepwise reaction. The different extractability for alkali metal ions, transition metal ions, and alkyl ammonium ions from water into dichloromethane is discussed. Due to the strong intramolecular hydrogen bonding between the neighboring NH and CO groups in triamide 4, its affinity to metal cations was weakened. Triamide 4 shows a single selectivity to n-BuNH₃⁺. The anion complexation of triamide 4 was also studied by ¹H NMR titration experiments. Triamide 4 binds halides through the intermolecular hydrogen bonding among the NH hydrogens of amide in a 1:1 fashion in CDCl₃. The association constants calculated from these changes in chemical shifts of the amide protons are K_a = 223 M⁻¹ for Cl⁻ and K_a = 71.7 M⁻¹ for Br⁻. Triamide 4 shows a preference for Cl⁻ complexation than Br⁻ complexation.     

Alkyl Ammonium Ion Selectivity of Hexahomotrioxacalix[3]arene Triamide Derivative having the Intramolecular Hydrogen-Bonding Group

The lower rim functionalized hexahomotrioxacalix[3]arene triamide 4 with cone-conformation was synthesized from triol 1 by a stepwise reaction. The different extractability for alkali metal ions, transition metal ions, and alkyl ammonium ions from water into dichloromethane is discussed. Due to the strong intramolecular hydrogen bonding between the neighboring NH and CO groups in triamide 4, its affinity to metal cations was weakened. Triamide 4 shows a single selectivity to n-BuNH ₃ ⁺ . The anion complexation of triamide 4 was also studied by ¹H NMR titration experiments. Triamide 4 binds halides through the intermolecular hydrogen bonding among the NH hydrogens of amide in a 1:1 fashion in CDCl₃. The association constants calculated from these changes in chemical shifts of the amide protons are K _a = 223 M^?1 for Cl^? and K _a = 71.7 M^?1 for Br^?. Triamide 4 shows a preference for Cl^? complexation than Br^? complexation.     

Alkene epoxidation catalysed by binuclear manganese complexes

Binuclear manganese(II) complexes with macrocyclic ligands have been synthesized by template Schiff base condensation of diethylenetriamine and pentane-2,4-dione or 1,3-diphenyl-propane-1,3-dione. Catalytic epoxidation of simple olefins with hydrogen peroxide and t-BHP were studied using the above manganese complexes in the presence of a base. The influence of reaction temperature, the additive methanol and the cocatalyst had been investigated. The major products of the oxidations were the epoxides. The new manganese complexes showed significant catalytic activities for the epoxidation of alkenes using hydrogen peroxide as oxidant and ammonium acetate as cocatalyst.     

Mechanism of olefin epoxidation by a mono-oxygenase model

Kinetic data suggest that the rate determining step in the epoxidation of cyclohexene by Mn-TPP and sodium hypochlorite is the conversion of a Mn(III)-species into an oxo-manganese(V)-species.     

Kinetics of epoxidation by a Musa paradisiaca chloroperoxidase

Epoxidations of indene, styrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 4-bromostyrene, and naphthalene using Musa paradisiaca plant juice chloroperoxidase in the presence of H₂O₂ and t-butyl peroxide as oxidants have been studied. The steady-state kinetic parameters, K_m and k_cat of the enzyme for the above substrates have been determined. The temperature and pH optima of the epoxidation are 25°C and 6.2, respectively. The yield of styrene oxide in the presence of H₂O₂ was 44%. The results show that M. paradisiaca plant juice chloroperoxidase is a potential biocatalyst for organic epoxidation reactions.     

Control of ethylene epoxidation selectivity by surface oxametallacycles

Surface science experiments, DFT calculations, and kinetic isotope effect data are utilized to understand the elementary steps that govern the selectivity of silver catalysts for the partial oxidation of ethylene to produce ethylene oxide. It is proposed that selective and unselective pathways proceed via a common intermediate, the surface oxametallacycle. The structures of the transition states leading from this intermediate to selective and unselective products are calculated. From the calculated Gibbs free energies of activation for competing pathways, it is possible to predict selectivity to ethylene oxide as well as the magnitude of the kinetic isotope effect. The proposed mechanism is qualitatively and quantitatively in accord with experimental results.     

Enantioselective epoxidation of conjugated cis-enynes by chiral dioxirane

This paper describes a highly chemo- and enantioselective epoxidation of conjugated cis-enynes using readily available glucose-derived ketone 2 as catalyst and Oxone as oxidant to form cis-propargyl epoxides in high ee's. The interaction between the alkyne group of the substrate and the oxazolidinone moiety of the ketone catalyst as well as the interactions between the substituents on enynes and the oxazolidinone moiety of the ketone catalyst are important for the stereodifferentiation.     

The stereospecific epoxidation of olefins catalysed by ruthenium

Epoxidation of olefins by sodium periodate is effected by the catalysis of RuCl₃, (H₂O)_n associated with bipyridyl. The reaction is stereospecific for both cis and trans alkenes.     

Enantioselective epoxidation of terminal olefins by chiral dioxirane

[see reaction]. This paper describes an enantioselective epoxidation of terminal olefins using chiral ketone 3 as catalyst and Oxone as oxidant. Up to 85% ee has been obtained.     

Effective asymmetric epoxidation of styrenes by chiral dioxirane

High enantioselectivity (80-92% enantiomeric excess (ee)) has been obtained for the epoxidation of various styrenes using an easily prepared ketone (4) catalyst.