Deoxygenation Of Epoxides Research Articles

PPh3-Promoted Direct Deoxygenation of Epoxides to Alkenes.

Deoxygenation of epoxides into alkenes is one of the most important strategies in organic synthesis, biomass conversions, and medicinal chemistry. Although metal-catalyzed direct deoxygenation provides one of the most commonly encountered protocols for the conversion of epoxides to alkenes, the requirement of expensive catalysts and extra reductants has largely limited their universal applicability. Herein, we report an efficient PPh3-promoted metal-free strategy for deoxygenation of epoxides to generate alkene derivatives. The success of deoxyalkenylation of epoxides bearing a wide range of functional groups to give terminal, 1,1-disubstituted, and 1,2-disubstituted alkenes manifests the powerfulness and versatility of this strategy. Moreover, gram-scale synthesis with excellent yield and modification of biologically active molecules exemplifies its generality and practicability.

Deoxygenation of Epoxides with Hexamethyldigermane Catalyzed by Au Nanoparticles on TiO2

AbstractMono‐ and disubstituted epoxides undergo quantitative deoxygenation into the corresponding alkenes by hexamethyldigermane (Me3GeGeMe3) in the presence of 1 mol% of supported Au nanoparticles on TiO2, with digermane being transformed into the corresponding digermoxane. Tri‐ and tetrasubstituted epoxides react either poorly or remain intact, allowing thus the selective intermolecular deoxygenation of a monosubstituted epoxide in the presence of a highly substituted one. Stereoisotopic studies and Hammett‐type kinetics indicate a dipolar transition state of the deoxygenation process, whose degree of polarity profile depends on the substituents. For alkyl‐substituted epoxides the deoxygenation is almost stereospecific (retention of configuration), while for the aryl‐substituted ones, in which the dipolar character is more profound, substantial loss of stereospecificity is observed.

Clean protocol for deoxygenation of epoxides to alkenes via catalytic hydrogenation using gold

Au NP catalyst combined with triethylphosphite, P(OEt)3, is remarkably more reactive than solely Au NPs for the selective deoxygenation of epoxides to alkenes.

Deoxygenation of Epoxides with Carbon Monoxide.

The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer‐iridium(I) complex in combination with a Lewis acid co‐catalyst to achieve a pre‐activation of the epoxide substrate, as well as the elimination of CO2 from a γ‐2‐iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate‐dependent change in the mechanism for the epoxide C−O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.

Inverting isomers.

An unexpected epoxide deoxygenation reaction was observed to occur with inversion of stereochemistry and has enabled development of a method for alkene isomerization.

Nickel-catalyzed deoxygenation of oxiranes: Conversion of epoxides to alkenes

Deoxygenation of epoxides takes place under the catalysis of nickel in the presence of diethylzinc as a deoxygenation agent to yield alkenes. Epoxides with a wide variety of substitution patterns are deoxygenated in this catalytic system to give terminal, 1,1-disubstituted, 1,2-disubstituted, trisubstituted, and tetrasubstituted alkenes in high yields. Reactions of 1,2-disubstituted epoxides we examined proceeded in an E-stereoselective manner. High compatibility with other functional groups through this transformation was also observed.

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO2 and Epoxides.

A series of iron(III) chloride and iron(III) μ-oxo compounds supported by tetradentate amino-bis(phenolate) ligands containing a homopiperazinyl backbone were prepared and characterized by electronic absorption spectroscopy, magnetic moment measurement, and MALDI-TOF mass spectrometry. The solid-state structures of three iron(III) μ-oxo compounds were determined by single crystal X-ray diffraction and revealed oxo-bridged bimetallic species with Fe-O-Fe angles between 171.7 and 180°, with the iron centers in distorted square pyramidal environments. Variable temperature magnetic measurements show the oxo complexes exhibit strong antiferromagnetic coupling between two high-spin S = 5/2 iron(III) centers. The oxo complexes exhibit poor activity for the reaction of carbon dioxide and epoxides in the presence of a cocatalyst, under solvent free conditions to yield cyclic carbonates. The least active iron oxo compound bears tert-butyl groups on the phenolate donors, and we propose that steric congestion around the iron center reduces catalytic activity in this case. We provide evidence that an epoxide deoxygenation step occurs when employing monometallic iron(III) chlorido species as catalysts. This affords the corresponding μ-oxo compounds which can then enter their own catalytic cycle. Deoxygenation of epoxides during their catalytic reactions with carbon dioxide is frequently overlooked and should be considered as an additional mechanistic pathway when investigating catalysts.

Oxidoperoxidomolybdenum(vi) complexes with acylpyrazolonate ligands: synthesis, structure and catalytic properties.

Oxidoperoxido-molybdenum(vi) complexes containing acylpyrazolonate ligands were obtained by reaction of [Mo(O)(O)2(H2O)n] with the corresponding acylpyrazolone compounds HQR. Complexes Ph4P[Mo(O)(O2)2(QR)] (R = neopentyl, 1; perfluoroethyl, 2; hexyl, 3; phenyl, 4; naphthyl, 5; methyl, 6; cyclohexyl, 7; ethylcyclopentyl, 8) were obtained if the reaction was carried out with one equivalent of HQR in the presence of Ph4PCl. Alternatively, neutral complexes [Mo(O)(O2)(QR)2] (R = neopentyl, 9; hexyl, 10; cyclohexyl, 11) were formed when two equivalents of HQR were used in the reaction. These complexes were isolated in good yields as yellow or yellow-orange crystalline solids and were spectroscopically (IR, 1H, 13C{1H} and 31P{1H} NMR), theoretically (DFT) and structurally characterised (X-ray for 1, 2, 9 and 10). Compounds 1 and 9 were selected to investigate their catalytic behaviour in epoxidation of selected alkenes and oxidation of selected sulphides, while 10 and 11 were tested as catalyst precursors in the deoxygenation of selected epoxide substrates to alkenes, using PPh3 as the oxygen-acceptor. Complexes Ph4P[Mo(O)(O2)2(QR)] were shown to be poor catalyst precursors in oxidation reactions, while the activity of [Mo(O)(O2)(QR)2] species is good in all the studied reactions and comparable to related oxidoperoxido-molybdenum(vi) complexes. Complex [Mo(O)2(QC6)2], 12, was obtained by treatment of 10 with one equivalent of PPh3, demonstrating that the first step in the epoxide deoxygenation mechanism was the oxygen atom transfer toward the phosphane.

Mo-catalyzed deoxygenation of epoxides to alkenes

A Mo(VI)-catalyzed deoxygenation of epoxides to alkenes has been achieved using a sacrificial alcohol as a reductant. The MoO2(dtc)2 (dtc=diethyl dithiocarbamate) was proved to be a better catalyst than the other molybdenum based catalysts examined. Of the reducing agents examined, secondary alcohol, 2,4-dimethyl-3-pentanol was the most efficient and proved to be a better potential hydrogen donor. The reaction is very clean and the product yield ranges from moderate to excellent, with almost no byproduct(s) detected except, 2,4-dimethyl-3-pentanone, which is the oxidized product of 2,4-dimethyl-3-pentanol. [Display omitted]

Molybdenum-Catalyzed Deoxygenation of Epoxides

Molybdenum-Catalyzed Deoxygenation of Epoxides

Molybdenum‐Catalyzed Stereospecific Deoxygenation of Epoxides to Alkenes

AbstractMild and simple catalytic systems consisting of molybdenum(VI) dichloride dioxide [MoO2Cl2] as a catalyst and a phosphine as reductant have been developed for the stereospecific deoxygenation of epoxides to alkenes. The reactions using 1,2‐bis(diphenylphosphino)ethane (dppe) and triphenylphosphine (PPh3) proceed with retention and inversion of stereochemistry, respectively. The mild reaction tolerates the presence of various functional groups and affords stereodefined substituted olefins in good yields.magnified image

Regioselective and Stereospecific Copper-Catalyzed Deoxygenation of Epoxides to Alkenes.

Two copper salts (Cu(CF3CO2)2 and IMesCuCl) were identified as earth-abundant, inexpensive, but effective metal catalysts together with diazo malonate for chemo-/regioselective and stereospecific deoxygenation of various epoxides with tolerance of common functional groups (alkene, ketone, ester, p-methoxybenzyl, benzyl, tert-butyldimethylsilyl, and triisopropylsilyl). In particular, the unprecedented regioselectivity allowed for the first time monodeoxygenation of diepoxides to alkenyl epoxides. Density functional theory mechanistic studies showed that the deoxygenation occurred by collapsing the free ylide, unfavoring the possible intuitive pathway via cycloreversion of possible oxetane.

ChemInform Abstract: An Efficient Protocol for the Eliminative Deoxygenation of Aliphatic and Aromatic Epoxides to Olefins with Polyphosphoric Acid as a Promoter.

AbstractThis method allows the chemo‐ and stereoselective deoxygenation of a wide variety of epoxides under eco‐friendly conditions in short reaction times.

An efficient protocol for the eliminative deoxygenation of aliphatic and aromatic epoxides to olefins with polyphosphoric acid as a promoter

An efficient eliminative deoxygenation reaction is reported for the conversion of aliphatic and aromatic epoxides to olefins. Polyphosphoric acid (PPA) is used in 30mol% as a promoter to afford the products in excellent yield (85–96%) at 50°C under neat condition. Our method has advantages such as inexpensive reagents, high yield, stereoselective product in short reaction time under eco-friendly reaction conditions.

Mild and Efficient Reductive Deoxygenation of Epoxides to Olefins with Tin(II) Chloride/Sodium Iodide as a Novel Reagent

A highly efficient and green protocol is reported for the reductive deoxygenation of organic epoxides to olefins using tin(II) chloride/sodium iodide as a novel reagent. The reaction gives an excellent yield (85–96%) in ethanol under reflux within 2–10 minutes, without affecting other functional groups. The advantages of our method are the use of inexpensive reagents, the eco-friendly and green reaction conditions, and the short reaction times and high yields.

Deoxygenation of Epoxides to Alkenes under Rhenium Catalysis

Key words deoxygenation - rhenium catalysis - stereospecific reaction - epoxides

Copper Nanocrystal Plane Effect on Stereoselectivity of Catalytic Deoxygenation of Aromatic Epoxides

Previous studies have shown that crystal planes of heterogeneous catalysts could display enhanced activity, such that higher turnover or chemoselectivity could be achieved. Here we report an example where the reaction stereoselectivity was significantly affected by the catalyst crystal planes. In copper-catalyzed deoxygenation reaction of aromatic epoxides, copper cubes, wires, and plates gave the olefin products with different cis/trans selectivities, whereas homogeneous copper catalysts showed poor selectivity. Scanning tunneling microscope and density functional theory studies revealed that the different adsorption mode and higher adsorption strength of epoxide oxygen on Cu{100} plane were responsible for the observed variation of selectivity. The copper-catalyzed deoxygenation reaction provided new practical access to cis-olefins from readily available aromatic epoxides. Our work also indicated that nanocrystal catalysts may provide useful stereochemical control in organic reactions.

ChemInform Abstract: A New Entry to Sonochemical/Efficient Agitation Switching: Alkene Formation Through Epoxide Deoxygenation.

AbstractAn electrochemical synthesis of cyclic carbonates from epoxides is reported.

Noble-Metal-Free Deoxygenation of Epoxides: Titanium Dioxide as a Photocatalytically Regenerable Electron-Transfer Catalyst

Catalytic deoxygenation of epoxides into the corresponding alkenes is a very important reaction in organic synthesis. Early reported systems, however, require noble metals, high reaction temperatures (>373 K), or toxic reducing agents. Here, we report a noble-metal-free heterogeneous catalytic system driven with alcohol as a reducing agent at room temperature. Photoirradiation (λ <420 nm) of semiconductor titanium dioxide (TiO2) with alcohol promotes efficient and selective deoxygenation of epoxides into alkenes. This noble-metal-free catalytic deoxygenation is facilitated by the combination of electron transfer from surface Ti3+ atoms on TiO2 to epoxides, which promotes deoxygenation of epoxides, and photocatalytic action of TiO2, which regenerates oxidized surface Ti atoms with alcohol as a reducing agent.

ChemInform Abstract: Concerted Two‐Electron Transfer and High Selectivity of TiO2 in Photocatalyzed Deoxygenation of Epoxides.

AbstractIt is shown, that the concerted multi‐electron transfer is the dominant pathway in the photocatalytic deoxygenation of epoxides on a pristine TiO2 surface to give the corresponding alkenes.