Terminal Epoxides Research Articles

Alkoxide-Initiated Regioselective Coupling of Carbon Disulfide and Terminal Epoxides for the Synthesis of Strongly Alternating Copolymers

The synthesis of highly regioregular and alternating polythiocarbonates from carbon disulfide and terminal epoxides has been achieved. The copolymerizations were performed under ambient and solvent-free conditions in the presence of LiOtBu (0.125–0.5 mol %) as initiator. At higher loadings the reaction pathway switched in favor to the catalytic formation of cyclic dithiocarbonates. Under optimized reaction conditions polymers with molecular weights up to 109 kg mol–1 were isolated. The NMR spectroscopic analysis of the polythiocarbonates revealed that 94% of backbone structure is formed by strongly alternating head-to-head arrangement of epoxypropane and 1,2-epoxybutane monomers, respectively, at a thiocarbonate group −CHR–OC(S)O–CHR– and tail-to-tail arrangement at a trithiocarbonate group −CH2–SC(S)S–CH2–. Atactic polymers were obtained using racemic mixtures of the epoxides, but an isotactic polymer was obtained when chiral (R)-epoxypropane was converted. A mechanism is proposed which rationalizes the ...

Transformation of Carbon Dioxide into Oxazolidinones and Cyclic Carbonates Catalyzed by Rare‐Earth‐Metal Phenolates

AbstractRare‐earth‐metal complexes stabilized by amine‐bridged tri(phenolato) ligands were developed, and their activities in catalyzing transformations of CO2 were studied. A series of terminal epoxides and challenging disubstituted epoxides were converted into the respective cyclic carbonates in the presence of CO2 in yields of 58 to 96 %. In addition, these rare‐earth‐metal complexes also showed good activities in catalyzing three‐component reactions of anilines, epoxides, and CO2, which generated 5‐substituted‐3‐aryl‐2‐oxazolidines in yields of 48 to 96 %, as a useful strategy to construct oxazolidinones.

Development of Highly Active and Regioselective Catalysts for the Copolymerization of Epoxides with Cyclic Anhydrides: An Unanticipated Effect of Electronic Variation.

Recent developments in polyester synthesis have established several systems based on zinc, chromium, cobalt, and aluminum catalysts for the ring-opening alternating copolymerization of epoxides with cyclic anhydrides. However, to date, regioselective processes for this copolymerization have remained relatively unexplored. Herein we report the development of a highly active, regioselective system for the copolymerization of a variety of terminal epoxides and cyclic anhydrides. Unexpectedly, electron withdrawing substituents on the salen framework resulted in a more redox stable Co(III) species and longer catalyst lifetime. Using enantiopure propylene oxide, we synthesized semicrystalline polyesters via the copolymerization of a range of epoxide/anhydride monomer pairs.

Regio‐ and Stereoselective Synthesis of Dithiocarbonates under Ambient and Solvent‐Free Conditions

AbstractHerein, we report on the utilization of readily available lithium tert‐butoxide as an efficient catalyst for the addition of carbon disulfide to terminal and internal epoxides under ambient conditions. Notably, the reaction proceeds regio‐ and stereoselectively. By applying the optimized conditions, 14 terminal and internal epoxides were converted. The desired cyclic dithiocarbonates were isolated in yields up to 95 % after simple filtration over silica. NMR spectroscopy experiments to identify the mode of activation were performed, and they indicated activation of carbon disulfide by the catalyst. The reaction of cis‐2,3‐butyleneoxide gave only the trans‐dithiocarbonate, whereas the conversion of (R)‐propylen oxide gave the respective thiocarbonate stereoselectively as one enantiomer (>99 % ee) in 87 % yield.

Dinuclear Aluminum Poly(phenolate) Complexes as Efficient Catalysts for Cyclic Carbonate Synthesis

A series of dinuclear aluminum complexes 1–4 stabilized by amine-bridged poly(phenolato) ligands have been synthesized, which are highly active in catalyzing the cycloaddition of epoxides and CO2. In the presence of 0.3 mol % complex 3 and 0.9 mol % NBu4Br at 1 bar CO2 pressure, terminal epoxides bearing different functional groups were converted to cyclic carbonates in 60–97% yields. Complex 3 is one of the rare examples of Al-based catalysts capable of promoting the cycloaddition at 1 bar pressure of CO2. Moreover, reactions of more challenging disubstituted epoxides also proceeded at an elevated pressure of 10 bar and afforded cyclic carbonates in 52–90% yields.

Eric N. Jacobsen

Eric N. Jacobsen

ChemInform Abstract: Metal‐Catalyzed Directed Regio‐ and Enantioselective Ring‐Opening of Epoxides

AbstractReview: 48 refs.

Highly Active and Robust Metalloporphyrin Catalysts for the Synthesis of Cyclic Carbonates from a Broad Range of Epoxides and Carbon Dioxide.

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso-phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent-free conditions. The meta-substituted catalysts exhibited high catalytic performance, whereas the para- and ortho-substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta-substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h(-1) at 170 °C) at an initial CO2 pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides.

An efficient ternary catalyst ZnBr2/K2CO3/[Bmim]Br for chemical fixation of CO2 into cyclic carbonates at ambient conditions

A simple, readily available and recyclable ternary catalytic system of ZnBr2/K2CO3/[Bmim]Br was developed for the efficient conversion of CO2 and epoxides (both internal and terminal epoxides) to cyclic carbonates under very mild conditions (room temperature, 1atm) with excellent yields (>90% for 18 examples). The catalytic activity would not be affected by CO2 in the presence of small amount of water and air. The reactions would even be carried out under CO2 partial pressure as low as 0.5atm, giving carbonate in good yield. This process has been repeated 5 times without any obvious decrease in catalytic activity. The influences of the type of catalyst, catalyst loading, CO2 pressure, reaction time, and temperature on the reaction yields have been investigated. The possible reaction mechanism was proposed based on the reaction results.

Chemical fixation of CO2 to cyclic carbonates using Al(III) β-aminoalcohol based efficient catalysts: An experimental and computational studies

A series of Al(III) unsymmetrical β-aminoalcohol based complexes 1–6 were synthesized via metalation of the corresponding ligands 1′–6′ those were prepared by the reaction of benzylamine with readily available epoxides viz., styrene oxide, 1,2-epoxy-3-phenoxypropane, 4-tertbutylphenyl glycidyl ether, 4-chlorophenyl glycidyl ether, glycidyl 2-methylphenyl ether and 1,2-epoxyhexane. Among these complexes, the complex 2 was found to be most effective in the cycloaddition of aryloxy/aliphatic terminal epoxides with CO2 under atmospheric pressure to get corresponding cyclic carbonates with high conversion and selectivity (up to >99%) in the presence of tetrabutylammonium bromide as a co-catalyst. The DFT calculations revealed the important role played by counter-ion in the co-catalyst during cycloaddition reaction of CO2 with the substituted epoxides.

DFT studies on the origin of regioselective ring-opening of terminal epoxides during copolymerization with CO2

This report presents a detailed density functional theory (DFT) study on the difference in regioselectivity for the copolymerization reactions of styrene oxide versus propylene oxide with CO2 utilizing binary (salen)cobalt(III) catalyst systems. This study focuses on the discrepancy of regioselective ring-opening of two terminal epoxides during the copolymerization with CO2. It was found that the nucleophilic ring-opening of styrene oxide occurred predominantly at the methine C α -O bond due to the election delocalization of phenyl group to stabilize the transition state for the methine C―O bond cleavage.

ChemInform Abstract: Utility of Unsaturated Terminal Epoxides in Cyclopropane Synthesis

AbstractReview: 79 refs.

Metal-Catalyzed Directed Regio- and Enantioselective Ring-Opening of Epoxides.

Control of regio- and stereoselectivity of chemical reactions is the central theme in synthetic chemistry. Regioselective and enantiospecific ring opening of readily available enantioenriched epoxides precursors provides a straightforward access to diverse highly functionalized molecules which can serve as chiral building blocks for synthesis of biologically active compounds. However, prior to our research work, the scope of catalytic highly regioselective ring opening of epoxides is limited to structurally or electronically biased epoxides, such as terminal and aromatic epoxides. Regioselective ring-opening of epoxides with substituents on both sides demonstrating similar steric and electronic effects is still a formidable challenge for organic chemists. To address this challenge, our approach is to use the readily available functional moiety incorporated in an epoxide as a directing group to realize the regioselective nucleophilic attack on the oxirane ring. Alternatively, asymmetric ring-opening of epoxides can also provide the ring-opening products in highly enantioenriched form. However, excellent results are usually obtained in the case of the kinetic resolution of terminal epoxides or the desymmetrization of meso-epoxides. In these cases, the issue of regiocontrol of the ring-opening is circumvented or minimized. Based on our successful results of regioselective ring-opening of functionalized epoxides by implementing the directed ring-opening strategy, we also investigated the enantioselective ring-opening of internal epoxides bearing a functional moiety as directing group. This Account summarizes our research on metal-catalyzed directed ring-opening reactions of epoxides, which encompasses the following breakthroughs: (1) highly regioselective ring-opening of various substrates including epoxy allylic alcohols, epoxy homoallylic alcohols and epoxy allylic sulfonamides with a variety of N-, O-, and halide-nucleophiles catalyzed by W-, Mo-, or Ni-salt; (2) first kinetic resolutions of epoxy allylic alcohols, epoxy homoallylic alcohols, and epoxy allylic sulfonamides with various amines as nucleophiles, which were catalyzed by W-bishydroxamic acid (W-BHA), nickel-BINAM, and Gd-N,N'-dioxide catalytic system, respectively; (3) successful implementation of the strategy of combined asymmetric syntheses by the combination of the enantioselective epoxidation and the enantioselective ring-opening of 2,3-epoxy alcohols establishing a new entry to prepare amino alcohols in regio-, diastereo-, and enantiomerically pure form.

Synthesis of Cyclic Carbonates Catalysed by Chromium and Aluminium Salphen Complexes.

Chromium and aluminium salphen complexes have been found to display remarkable catalytic activity in the synthesis of cyclic carbonates from a range of epoxides and carbon dioxide. The Al(salphen) complex is more reactive towards terminal epoxides at ambient temperature and pressure, whereas the Cr(salphen) complex exhibits higher catalytic activity towards more challenging internal epoxides at elevated temperature and pressure.

Structure-Activity Relationships for DNA Damage by Alkenylbenzenes in Turkey Egg Fetal Liver.

Certain alkenylbenzenes (AB), flavoring chemicals naturally occurring in spices and herbs, are established to be cytotoxic and hepatocarcinogenic in rodents. The purpose of the present study was to determine the DNA damaging potential of key representatives of this class using the Turkey Egg Genotoxicity Assay. Medium white turkey eggs with 22- to 24-day-old fetuses received three injections of nine AB with different carcinogenic potentials: safrole (1, 2 mg/egg), methyl eugenol (2, 4 mg/egg), estragole (20, 40 mg/egg), myristicin (25, 50 mg/egg), elemicin (20, 50 mg/egg), anethole (5, 10 mg/egg), methyl isoeugenol (40, 80 mg/egg), eugenol (1, 2.5 mg/egg), and isoeugenol (1, 4 mg/egg). Three hours after the last injection, fetal livers were harvested for measurement of DNA strand breaks, using the comet assay and DNA adducts formation, using the nucleotide(3) (2)P-postlabeling assay. Estragole, myristicin, and elemicin induced DNA stand breaks. These compounds as well as safrole, methyl eugenol and anethole, at the highest doses tested, induced DNA adduct formation. Methyl isoeugenol, eugenol, and isoeugenol did not induce genotoxicity. The genotoxic AB all had the structural features of either a double bond in the alkenyl side chain at the terminal 2',3'-position, favorable to formation of proximate carcinogenic 1'-hydroxymetabolite or terminal epoxide, or the absence of a free phenolic hydroxyl group crucial for formation of a nontoxic glucuronide conjugate. In contrast, methyl isoeugenol, eugenol and isoeugenol, which were nongenotoxic, possessed chemical features, unfavorable to activation.

Chiral Cobalt(III) Complexes as Bifunctional Brønsted Acid–Lewis Base Catalysts for the Preparation of Cyclic Organic Carbonates

Stereochemically inert cationic cobalt(III) complexes were shown to be one-component catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa carbon dioxide pressure. The optimal catalyst possessed an iodide counter anion and could be recycled. A catalytic cycle is proposed in which the ligand of the cobalt complexes acts as a hydrogen-bond donor, activating the epoxide towards ring opening by the halide anion and activating the carbon dioxide for subsequent reaction with the halo-alkoxide. No kinetic resolution was observed when terminal epoxides were used as substrates, but chalcone oxide underwent kinetic resolution.

Robust Zinc Complexes that Contain Pyrrolidine‐Based Ligands as Recyclable Catalysts for the Synthesis of Cyclic Carbonates from Carbon Dioxide and Epoxides

AbstractNew zinc catalysts bearing ligands that contain a pyrrolidine scaffold were synthesized and tested successfully in the coupling of CO2 with terminal and internal epoxides. These catalysts provide excellent activity and total selectivity to the corresponding cyclic carbonates, even for challenging substrates such as cyclohexene oxide, trans‐1,2‐epoxybutane, and methyl epoxioleate. The robustness of the most active catalytic system was demonstrated by turnover numbers of up to 1840 for propylene oxide. The recycling of this catalytic system was performed up to five times without relevant loss of activity using this substrate.

ChemInform Abstract: Robust Bifunctional Aluminium—Salen Catalysts for the Preparation of Cyclic Carbonates from Carbon Dioxide and Epoxides.

AbstractThe title reaction applies only to terminal epoxides and the catalysts can be recovered and reused for 3 catalytic cycles without significant loss of the catalytic activity.

Highly Efficient Polymer-Supported Catalytic System for the Valorization of Carbon Dioxide.

Polydibenzo-18-crown-6 was utilized as a co-catalyst and polymeric support in combination with potassium iodide for the synthesis of cyclic carbonates from carbon dioxide and epoxides under mild and solvent-free conditions. The efficiency of this catalytic system can be easily increased by loading the polymer with KI prior to the reaction. The influence of various reaction parameters were studied thoroughly. The scope and limitation of the catalyst system was studied at 80 °C and 100 °C. A large number of terminal epoxides (14) were converted to the desired cyclic carbonates in yields up to 99%. We could successfully recover and reuse the catalyst >20 times with excellent yields up to 99%. Although, we observed that the activity gradually decreased after repetitive cycles. This decrease was attributed to KI leaching and partial degradation caused by mechanical stirring. This assumption is supported by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Utility of Unsaturated Terminal Epoxides in Cyclopropane Synthesis

Developments in the synthesis of bicyclo[n.1.0]alkanes by lithium 2,2,6,6-tetramethylpiperidide-induced intramolecular cyclopropanation of unsaturated terminal epoxides are reviewed. The main alternative intramolecular cyclopropanation strategies are also briefly discussed to put the epoxide chemistry in perspective. Terminal epoxide (or chlorohydrin) precursors possessing a tethered alkene undergo intramolecular cyclopropanation with complete stereoselectivity and in generally good to excellent yields to give cyclopropyl alcohols; application of this cyclopropanation methodology in the synthesis of natural products is also reviewed. Keywords: Cyclopropanes, epoxide, intramolecular cyclopropanation, lithium 2, 2, 6, 6-tetramethylpiperidide, total synthesis.