Allyl Ethers Research Articles

Nickel-Catalyzed Phosphine Free Direct N-Alkylation of Amides with Alcohols.

Herein, we developed an operational simple, practical, and selective Ni-catalyzed synthesis of secondary amides. Application of renewable alcohols, earth-abundant and nonprecious nickel catalyst facilitates the transformations, releasing water as byproduct. The catalytic system is tolerant to a variety of functional groups including nitrile, allylic ether, and alkene and could be extended to the synthesis of bis-amide, antiemetic drug Tigan, and dopamine D2 receptor antagonist Itopride. Preliminary mechanistic studies revealed the participation of a benzylic C-H bond in the rate-determining step.

(NHC)NiH‐Catalyzed Regiodivergent Cross‐Hydroalkenylation of Vinyl Ethers with α‐Olefins: Syntheses of 1,2‐ and 1,3‐Disubstituted Allyl Ethers

Cross-hydroalkenylation of a vinyl ether (1) with an α-olefin (2) was first achieved by a set of [NHC-Ni(allyl)]BArF (NHC=N-heterocyclic carbene) catalysts. Both 1,2- and 1,3-disubstituted allyl ethers were obtained, highly selectively, by using NHCs of different sizes. In contrast, the chemoselectivity (i.e., 1 as acceptor and 2 as donor) was controlled mostly by electronic effects through the catalyst-substrate interaction. Sterically bulkier alkenes (2) were used as preferred donors compared to smaller alkenes. This electronic effect also served as a basis for the first tail-to-head cross-hydroalkenylations of 1 with either a vinyl silane or boronic ester.

(NHC)NiH‐Catalyzed Regiodivergent Cross‐Hydroalkenylation of Vinyl Ethers with α‐Olefins: Syntheses of 1,2‐ and 1,3‐Disubstituted Allyl Ethers

AbstractCross‐hydroalkenylation of a vinyl ether (1) with an α‐olefin (2) was first achieved by a set of [NHC‐Ni(allyl)]BArF (NHC=N‐heterocyclic carbene) catalysts. Both 1,2‐ and 1,3‐disubstituted allyl ethers were obtained, highly selectively, by using NHCs of different sizes. In contrast, the chemoselectivity (i.e., 1 as acceptor and 2 as donor) was controlled mostly by electronic effects through the catalyst–substrate interaction. Sterically bulkier alkenes (2) were used as preferred donors compared to smaller alkenes. This electronic effect also served as a basis for the first tail‐to‐head cross‐hydroalkenylations of 1 with either a vinyl silane or boronic ester.

Amine Induced Retardation of the Radical-Mediated Thiol-Ene Reaction via the Formation of Metastable Disulfide Radical Anions.

The effect of amines on the kinetics and efficacy of radical-mediated thiol-ene coupling (TEC) reactions was investigated. By varying the thiol reactant and amine additive, it was shown that amines retard thiyl radical-mediated reactions when the amine is adequately basic enough to deprotonate the thiol affording the thiolate anion, e.g., when the weakly basic amine tetramethylethylenediamine was incorporated in the TEC reaction between butyl 2-mercaptoacetate and an allyl ether at 5 mol %, the final conversion was reduced from quantitative to <40%. Alternatively, no effect is observed when the less acidic thiol butyl 3-mercaptopropionate is employed. The thiolate anion was established as the retarding species through the introduction of ammonium and thiolate salt additives into TEC formulations. The formation of a two-sulfur three-electron bonded disulfide radical anion (DRA) species by the reaction of a thiyl radical with a thiolate anion was determined as the cause for the reduction in catalytic radicals and the TEC rate. Thermodynamic and kinetic trends in DRA formations were computed using density functional theory and by modeling the reaction as an associative electron transfer process. These trends correlate well with the experimental retardation trends of various thiolate anions in TEC reactions.

Synthesis of 2-substituted hydroquinone derivatives from 1,4-benzoquinone and allyl ethers

B-Alkylpinacolboranes, derived from rhodium-catalyzed hydroboration of allyl ethers with pinacolborane, react with 1,4-benzoquinone under acidic, oxidizing conditions, to afford, after subsequent hydrogenation, 2-substituted hydroquinones in isolated, purified yields of about 50% based on 1,4-benzoquinone. The product hydroquinones have potential use as precursors to poly(arylene ether) and related aromatic polymers.

Computational study of the thermal decomposition and the thermochemistry of allyl ethers and allyl sulfides

In spite of the several experimental and computational studies on the thermal decomposition of allyl ethers and allyl sulfides, there are still disagreements on aspects of the reaction mechanism, such as the true nature of the transition states and the grade of synchronicity of the reactions. This work presents a computational study of the gas-phase thermolysis reaction of allyl ethers and allyl sulfides substituted at α-carbon, at the M05-2X/6-31+G(d,p) level of theory and a temperature range from 586.15 to 673.15 K. The substituent groups were methyl, ethyl, n-propyl, i-propyl, allyl, benzyl and acetonyl. It was found that the sulfides react faster than the homologous ethers and that the substituent groups with the capacity of delocalize charge increase the reaction rate. Through natural bond orbital calculations, the transition states were characterized. The synchronicities and atomic charges of the studied reactions were determined. A computational study at the G3 level of theory on the thermochemistry of allyl ethers and sulfides was also carried out.

Bioaccumulation of Polybrominated Diphenyl Ethers and Alternative Halogenated Flame Retardants in a Vegetation-Caribou-Wolf Food Chain of the Canadian Arctic.

The trophodynamics of halogenated flame retardants (HFRs) including polybrominated diphenyl ethers (PBDEs) and alternative HFRs were investigated in the terrestrial, vegetation-caribou-wolf food chain in the Bathurst Region of northern Canada. The greatest concentrations in vegetation (geometric mean of lichens, moss, grasses, willow, and mushrooms) were of the order 2,4,6-tribromophenyl allyl ether (TBP-AE) (10 ng g-1 lw) > BDE47 (5.5 ng g-1 lw) > BDE99 (3.9 ng g-1 lw) > BDE100 (0.82 ng g-1 lw) > 1,2,3,4,5-pentabromobenzene (PBBz) (0.72 ng g-1 lw). Bioconcentration among types of vegetation was consistent, though it was typically greatest in rootless vegetation (lichens, moss). Biomagnification was limited in mammals; only BDE197, BDE206-208 and ∑PBDE biomagnified to caribou from vegetation [biomagnification factors (BMFs) = 2.0-5.1]. Wolves biomagnified BDE28/33, BDE153, BDE154, BDE206, BDE207, and ∑PBDE significantly from caribou (BMFs = 2.9-17) but neither mammal biomagnified any alternative HFRs. Only concentrations of BDE28/33, BDE198, nonaBDEs, and ∑PBDE increased with trophic level, though the magnitude of biomagnification was low relative to legacy, recalcitrant organochlorine contaminants [trophic magnification factors (TMFs) = 1.3-1.8]. Despite bioaccumulation in vegetation and mammals, the contaminants investigated here exhibited limited biomagnification potential and remained at low parts per billion concentrations in wolves.

Carboxylate-directed C-H allylation with allyl alcohols or ethers.

A [Ru(p-cymene)Cl2]2 catalyst activates allyl alcohols and ethers for the regioselective ortho-C-H allylation of aromatic and heteroaromatic carboxylates. The reaction is orthogonal to most C-H functionalisations with allyl alcohols in that allyl arenes rather than carbonyl compounds are obtained. A wide range of substrates are thus smoothly transformed to allylarenes at 50 °C in phosphate-buffered 2,2,2-trichloroethanol. The reaction concept combines the use of abundant reagents and directing groups in a sustainable, waste-minimised method for C-C bond formation.

Hydrosilylation of Allyl Ethers in the Presence of Supported Sulfur-Containing Platinum(II) Complexes

Hydrosilylation of allyl ethyl, allyl butyl, allyl glycidyl, allyl benzyl, and allyl phenyl ethers by 1,1,3,3-tetramethyldisiloxane in the presence of supported sulfur-containing platinum(II) complexes with the general formula [{SiO2}O2Si(Me)(CH2)3SR]2PtCl2 (R = Bu, Hex, Bn; {SiO2} is silica surface) and side processes have been studied.

Versatile etherification of alcohols with allyl alcohol by a titanium oxide-supported molybdenum oxide catalyst: gradual generation from titanium oxide and molybdenum oxide

A sustainable method to synthesize allyl ethers from allyl alcohol by the simple mixing of TiO2 and MoO3 catalysts.

Iridium‐Catalyzed Dynamic Kinetic Stereoselective Allylic Etherification of Achmatowicz Rearrangement Products

AbstractWe recently developed a novel Ir‐catalyzed dynamic kinetic isomerization reaction for Achmatowicz rearrangement products. In this update, we show that products derived from the Achmatowicz rearrangement can also undergo Ir‐catalyzed dynamic kinetic allylic etherification in the presence of an appropriate ligand and additive to afford useful intermediates for the synthesis of carbohydrates. The addition of the triphenyl phosphite ligand shuts down the isomerization pathway and promotes the allylic etherification pathway. The addition of diphenyl phosphate improved the diastereoselectivity for the addition reaction. Interestingly, opposite diastereoselectivity was observed for sterically demanding alcohol nucleophiles compared to less sterically demanding alcohol nucleophiles. The method was also applied to the synthesis of several 2,3‐dideoxypyranosides.magnified image

Waste-water treatment plants are implicated as an important source of flame retardants in insectivorous tree swallows (Tachicyneta bicolor)

Wastewater treatment plants (WWTPs) are an important source of anthropogenic chemicals, including organic flame retardants (FRs). Limited studies indicate birds can be exposed to FRs by feeding from waters receiving WWTP effluent or in fields receiving biosolids. Expanding on our earlier study, 47 legacy and 18 new FR contaminants were characterized in the eggs of insectivorous tree swallows (Tachycineta bicolor) feeding in water bodies receiving effluent from two WWTPs and compared to those from a reference site 19 km downstream of the nearest WWTP. Of the FRs measured, polybrominated diphenyl ethers (PBDEs) dominated the FR profile, specifically BDE-47, -99, -100, -153, -154, with considerably lower concentrations of hexabromocyclododecane (HBCDD), BDE-183 and BDE-209; each detected in 96–100% of the eggs overall except HBCDD (83%). FR concentrations were usually significantly greater in eggs from the secondary WWTP versus the tertiary WWTP and/or reference site. Despite low detection rates, concentrations of new FRs, specifically pentabromobenzyl acrylate (PBBA), 1,2,-bis-(2,4,6-tribromophenoxy)ethane (BTBPE), bis(2-ethylhexyl)-tetrabromophthalate (BEHTBP), tetrabromo-o-chlorotoluene (TBCT), hexabromobenzene (HBB), α- and β-1,2-dibromo-4-(1,2-dibromoethyl)-cyclohexane (DBE-DBCH), were greater than HBCDD or BDE-209. Additional evidence that WWTPs are an important source of exposure to new FR contaminants for birds utilizing associated water bodies is that only the WTTP eggs, not the reference eggs, had measureable concentrations of PBBA, TBCT, BEHTBP, HBB, α-DBE-DBCH, 2,2′,4,5,5′-pentabromobiphenyl (BB-101), pentabromoethyl benzene (PBEB), 2,4,6-tribromophenyl allyl ether (TBPAE), and tetrabromo-p-xylene (pTBX). Our study suggests that WWTPs are an important source of legacy and new FR contaminants for birds consuming prey that are associated with WWTP out-flows.

Adsorbed Conformations of PCE Superplasticizers in Cement Pore Solution Unraveled by Molecular Dynamics Simulations

The conformations of polycarboxylate ether (PCE) type superplasticizer polymers adsorbed on the surface of MgO in cement pore solution are simulated by molecular dynamics (MD). Three types of PCEs commonly applied to concrete are simulated, namely a methacrylate type PCE (PCEM-P), an allyl ether type PCE (PCEA-P), and an isoprenyl ether type PCE (PCEI-P) with ethylene oxide (EO) unit numbers (P) of 25, 34 and 25, respectively. It is observed that the adsorbed layer thickness is inversely proportional to the experimentally measured adsorbed amount at the initial paste flow of 26 ± 0.5 cm. Simulation results indicate that the adsorbed layer thickness is sensitive to the initial polymer orientations against the model MgO surface. I.e., polymer molecules initially placed parallel/perpendicularly against the MgO surface gradually forms a train shaped or a loop and tail adsorption profile, respectively. As a result, the loop and tail shaped conformation gives a higher layer thickness.

Bioactive products from singlet oxygen photooxygenation of cannabinoids

Photooxygenation of Δ8 tetrahydrocannabinol (Δ8-THC), Δ9 tetrahydrocannabinol (Δ9-THC), Δ9 tetrahydrocannabinolic acid (Δ9-THCA) and some derivatives (acetate, tosylate and methyl ether) yielded 24 oxygenated derivatives, 18 of which were new and 6 were previously reported, including allyl alcohols, ethers, quinones, hydroperoxides, and epoxides. Testing these compounds for their modulatory effect on cannabinoid receptors CB1 and CB2 led to the identification of 7 and 21 as CB1 partial agonists with Ki values of 0.043 μM and 0.048 μM, respectively and 23 as a cannabinoid with high binding affinity for CB2 with Ki value of 0.0095 μM, but much less affinity towards CB1 (Ki 0.467 μM). The synthesized compounds showed cytotoxic activity against cancer cell lines (SK-MEL, KB, BT-549, and SK-OV-3) with IC50 values ranging from 4.2 to 8.5 μg/mL. Several of those compounds showed antimicrobial, antimalarial and antileishmanial activities, with compound 14 being the most potent against various pathogens.

Pd-Catalyzed Enantio- and Regioselective Formation of Allylic Aryl Ethers.

A general methodology for the synthesis of enantioenriched tertiary allylic aryl ethers through Pd-catalyzed decarboxylative reactions of vinyl cyclic carbonates and phenols is presented. Switching of the regioselectivity toward the formation of linear products by a judicious choice of the ligand is also reported.

Minimally Invasive Hemostatic Materials: Tackling a Dilemma of Fluidity and Adhesion by Photopolymerization in situ

Hemostasis in vivo is a key to success in minimally invasive surgery (MIS). However, solid hemostatic materials cannot pass through the sheath tube of the MIS apparatus, while liquid ones are restricted by their low adhesion, which leads to them peeling off of tissue. To tackle the dilemma of fluidity and adhesion, a formulation containing a multifunctional sucrose allyl ether (SAE) monomer and an alpha-hydroxyketone liquid photoinitiator (HMPP) was applied as a lead hemostatic material for MIS. Real-time infrared results showed that SAE initiated by HMPP can rapidly polymerize into a transparent crosslinking membrane. Quantum chemistry showed that this occurs via a free radical addition reaction mechanism. Thermodynamic properties, such as reaction driving force and enthalpy change, were similar to those for a corresponding small molecular analogue, allyl methyl ether (AME), but the addition rate was lower than that for AME. The CC50 values of SAE and HMPP were also obtained by cell experiments. A hemostasis experiment in vivo was performed by comparing the formulation with chitosan and a traditional Chinese medicine (Yunnan Baiyao powder). The result showed that the formulation had a competitive advantage for use in MIS.

Epoxidation of unsaturated carbonyl compounds

Epoxidation of unsaturated carbonyl compounds by reaction with chloromethyl propargyl(allyl) ether in the presence of an alcoholate occurs exclusively at the carbonyl groups to form vinyl epoxides.

Effect of Chain Extender on Hydrogen Bond and Microphase Structure of Biodegradable Thermoplastic Polyurethanes

Thermomechanical properties of polyurethanes (PUs) strongly depend on the molecular interactions and microphase structure. In this work, two chain extenders with different ratios, flexile 1,4-butanediol (BDO) and branched trimethylolpropane mono allyl ether (TMPAE), are used to tune the molecular interactions and microphase structures of a series of biodegradable thermoplastic polyurethanes (TPUs). In TPUs, the biodegradable polycaprolactone (PCL, Mn of 2000) is used as soft segment while 1,6-diisocyanatohexane (HDI) and chain extenders are used as hard segment. Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscppy (1H-NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and mechanical tests were performed to characterize the bulk structure and properties of TPUs. Compared with BDO, the steric bulk of TMPAE is larger. The increment of TMPAE can help to increase the hydrogen bond content, microphase separation, and the elastic modulus ratio (R), which would strongly affect the thermomechanical property of the TPUs. The results of this work verify the importance of the structure of chain extender on the properties of TPUs. It provides valuable information for further understanding the structure-property relationships of these polyurethanes.

Atomistic dynamics simulation to solve conformation of model PCE superplasticisers in water and cement pore solution

The working mechanism of polycarboxylate ether (PCE) type superplasticisers in concrete was studied from the point of view of conformational changes of the polymer simulated by molecular dynamics in pure water and cement pore solution. Three typical types of PCEs, namely a methoxy polyethyleneglycol monomethacrylate–sodium methacrylate copolymer (PCEM), a polyethyleneglycol mono allyl ether–sodium maleate copolymer (PCEA) and a polyethyleneglycol mono (3-methyl-3-butenyl) ether–sodium acrylate copolymer (PCEI) were investigated using large-scale atomistic molecular dynamics simulations. It was observed that the PCE polymers which possess negatively charged backbones were stretched in water due to electrostatic repulsion. However, they were found to be significantly shrunken and distorted in synthetic cement pore solution, depending on the polyethylene glycol (PEG) density along the backbone, resulting in the aggregation of PEG side chains due to the salting-out effect.

Palladium-Catalyzed Mizoroki-Heck Reaction of Aryl Iodides with Allyl Aryl Ethers Using Imidazo[1, 5-a ]pyridines

We have demonstrated the Mizoroki–Heck reaction of aryl iodides with aryl allyl ethers using 1.5 mol% of imidazo[1, 5-a]pyridine–Pd catalytic system. Aryl cinnamyl ethers were obtained in moderate-to-high yield under mild reaction conditions.