Tetrahydrofuran Ring Opening Research Articles

How Topological Differences between Two Oxide Surfaces Determine Selectivity—The Case of the Dehydra-Decyclization of Tetrahydrofuran

Production of butadiene from biomass-based tetrahydrofuran (THF) is explored as an alternative to the existing petroleum-based processes. Metal oxide catalysts have been shown to exhibit varying product selectivities when reacted with THF. Among those oxides, ZrO2 showed the highest selectivity for butadiene. In contrast, Al2O3 showed the highest selectivity for the competing retro-Prins products, C3H6 and HCHO. The reasons behind the varying selectivity across oxides are unclear. In this work, we employ periodic density functional theory and mean-field microkinetic modeling to investigate the mechanism of the reaction of THF to butadiene and retro-Prins products on t-ZrO2 (101) (dry and hydrous) and on γ-Al2O3 (110). Our simulations reproduce the experimental selectivity trends. High selectivity for butadiene is promoted by the presence of neighboring Lewis acid metal sites that facilitate E1cB hydroxyl elimination from a 3-butenoxide intermediate; on hydrous Al2O3; where such neighboring Lewis acid centers are not available, the butenoxide undergoes E2 elimination and retro-Prins products ensue. The THF ring opening is rate-determining on ZrO2, whereas the γ-proton elimination that yields the 3-butenoxide intermediate is rate controlling on hydroxylated Al2O3. We conclude that the local topology around the active site greatly influences the mechanism and selectivity.

Difluorocarbene‐Induced Ring Opening of Tetrahydrofuran with TMSCF2Br for Difluoromethoxybutylation of N‐Aryl‐N‐hydroxylamines

AbstractIn this work, a novel difluorocarbene‐induced ring opening of THF with TMSCF2Br for difluoromethoxybutylation of N‐aryl‐N‐hydroxylamines under mild conditions is reported. The mechanism study revealed that THF was intermolecular activated by difluorocarbene, then the formed oxonium ylide was nucleophilic attacked by N‐aryl‐N‐hydroxylamines.

An Overview of the One-pot Synthesis of Imidazolines

One-pot syntheses are a simple, efficient and easy methodology, which are widely used for the synthesis of organic compounds. Imidazoline is a valuable heterocyclic moiety used as a synthetic intermediate, chiral auxiliary, chiral catalyst and a ligand for asymmetric catalysis. Imidazole is a fundamental unit of biomolecules that can be easily prepared from imidazolines. The one-pot method is an impressive approach to synthesize organic compounds as it minimizes the reaction time, separation procedures, and ecological impact. Many significant one-pot methods such as N-bromosuccinimide mediated reaction, ring-opening of tetrahydrofuran, triflic anhydrate mediated reaction, etc. were reported for imidazoline synthesis. This review describes an overview of the one-pot synthesis of imidazolines and covers literature up to 2020.

An Overview of the One-pot Synthesis of Imidazolines

One-pot syntheses are a simple, efficient and easy methodology, which are widely used for the synthesis of organic compounds. Imidazoline is a valuable heterocyclic moiety used as a synthetic intermediate, chiral auxiliary, chiral catalyst and a ligand for asymmetric catalysis. Imidazole is a fundamental unit of biomolecules that can be easily prepared from imidazolines. The one-pot method is an impressive approach to synthesize organic compounds as it minimizes the reaction time, separation procedures, and ecological impact. Many significant one-pot methods such as N-bromosuccinimide mediated reaction, ring-opening of tetrahydrofuran, triflic anhydrate mediated reaction, etc. were reported for imidazoline synthesis. This review describes an overview of the one-pot synthesis of imidazolines and covers literature up to 2020.

One-pot synthesis of imidazolinium salts via the ring opening of tetrahydrofuran.

A new one-pot synthesis of C2-hydroxypropyl-substituted imidazolinium salts via the ring opening of tetrahydrofuran (THF) with N,N'-disubstituted diamines has been developed. Preliminary studies of the reaction mechanism suggest the CO2-promoted oxidative ring opening of THF followed by Hg(ii)-mediated oxidation of an imidazolidine intermediate. These novel C2-substituted imidazolinium salts have shown to be active catalysts for the aza-Diels-Alder reactions.

Synthetic studies towards 1α-hydroxysolasodine from diosgenin and the unexpected tetrahydrofuran ring opening in the Birch reduction process

The synthesis of 1α-hydroxysolasodine from diosgenin was attempted. The Pd/C catalyst mediated dehydrogenation of diosgenin generated the 1,4,6-trien-3-one (3), which was reacted with Ac2O in pyridine in the presence of a catalytic amount of POCl3 followed by hydrolysis to give the 22-hydroxyfurostan (4) in 65% yield. Conversion of the primary 26-OH group into the azide and simultaneously 22-OH dehydration were achieved in one step by Mitsunobu reaction. Treatment of the (25R)-26-azidofurosta-1,4,6,20(22)-tetraen-3-one (5) with chlorotrimethylsilane (TMSCl)/NaI/MeCN and cyclisation in situ provided the (22R,25R)-spirosola-1,4,6-trien-3-one (6) in good yield. Stereoselective and regioselective epoxidation of trienone (6) with 30% H2O2 and 5% NaOH in methanol gave the 1α,2α-epoxy-(22R,25R)-spirosola-4,6-dien-3-one (7). Birch reduction of the epoxide (7) with Li/NH3 in THF followed by the treatment with NH4Cl, however, failed to generate the expected 1α-hydroxysolasodine, but provided a tetrahydrofuran ring opening product, (22S,25R)-1α,16β-dihydroxy-22,26-epiminocholest-4-en-3-one (8). Compounds 3 and 5–8 as well as solasodine were evaluated for their cell growth inhibitory activities against human prostate cancer PC3, human cervical carcinoma Hela, and human hepatoma HepG2 cells. At the concentration of 10μM, only epoxide 7 displayed moderate inhibitory rates towards these cells (40–54%).

An elusive hydridoaluminum(I) complex for facile C-H and C-O bond activation of ethers and access to its isolable hydridogallium(I) analogue: syntheses, structures, and theoretical studies.

The reaction of AlBr3 with 1 molar equiv of the chelating bis(N-heterocyclic carbene) ligand bis(N-Dipp-imidazole-2-ylidene)methylene (bisNHC, 1) affords [(bisNHC)AlBr2](+)Br(-) (2) as an ion pair in high yield, representing the first example of a bisNHC-Al(III) complex. Debromination of the latter with 1 molar equiv of K2Fe(CO)4 in tetrahydrofuran (THF) furnishes smoothly, in a redox reaction, the (bisNHC)(Br)Al[Fe(CO)4] complex 3, in which the Al(I) center is stabilized by the Fe(CO)4 moiety through Al(I):→Fe(0) coordination. Strikingly, the Br/H ligand exchange reactions of 3 using potassium hydride as a hydride source in THF or tetrahydropyran (THP) do not yield the anticipated hydridoaluminum(I) complex (bisNHC)Al(H)[Fe(CO)4] (4a) but instead lead to (bisNHC)Al(2-cyclo-OC4H7)[Fe(CO)4] (4) and (bisNHC)Al(2-cyclo-OC5H9)[Fe(CO)4] (5), respectively. The latter are generated via C-H bond activation at the α-carbon positions of THF and THP, respectively, in good yields with concomitant elimination of dihydrogen. This is the first example whereby a low-valent main-group hydrido complex facilitates metalation of sp(3) C-H bonds. Interestingly, when K[BHR3] (R = Et, sBu) is employed as a hydride source to react with 3 in THF, the reaction affords (bisNHC)Al(OnBu)[Fe(CO)4] (6) as the sole product through C-O bond activation and ring opening of THF. The mechanisms for these novel C-H and C-O bond activations mediated by the elusive hydridoaluminum(I) complex 4a were elucidated by density functional theory (DFT) calculations. In contrast, the analogous hydridogallium(I) complex (bisNHC)Ga(H)[Fe(CO)4] (9) can be obtained directly in high yield by the reaction of the (bisNHC)Ga(Cl)[Fe(CO)4] precursor 8 with 1 molar equiv of K[BHR3] (R = Et, sBu) in THF at room temperature. The isolation of 9 and its inertness toward cyclic ethers might be attributed to the higher electronegativity of gallium versus aluminum. The stronger Ga(I)-H bond, in turn, hampers α-C-H metalation or C-O bond cleavage in cyclic ethers, the latter of which is supported by DFT calculations.

Gold-catalyzed Synthesis of 4-(2-Oxoalkoxy)butyl Methanesulfonates via Ring-opening of Tetrahydrofuran

Abstract A variety of terminal alkynes were converted into the corresponding 4-(2-oxoalkoxy)butyl methanesulfonates via a gold-catalyzed intermolecular oxidation reaction using 8-ethylquinoline N-oxide as the oxidant and THF as the solvent. This reaction is proposed to proceed through the ring-opening of THF via an α-oxo gold carbene intermediate.

Mn-catalyzed three-component reactions of imines/nitriles, Grignard reagents, and tetrahydrofuran: an expedient access to 1,5-amino/keto alcohols.

An expedient Mn-catalyzed three-component synthesis of 1,5-amino/keto alcohols from Grignard reagents, imines/nitriles, and tetrahydrofuran (THF) is described, which deviates from the classic Grignard addition to imines/nitriles in THF solvent. THF is split and "sewn" in an unprecedented manner in the reaction, leading to the formation of two geminal C-C bonds via C-H and C-O cleavage. Mechanistic experiments and DFT calculations reveal radical and organo-Mn intermediates in the catalytic cycle and the α-arylative ring-opening of THF as the key reaction step.

A DFT study of furan hydrogenation and ring opening on Pd(111)

The reaction energies and the corresponding energy barriers of hydrogenation and ring opening of furan on Pd(111) for the formation of tetrahydrofuran (THF), 1-butanol and small hydrocarbons were studied using density functional theory (DFT). THF forms via sequential hydrogenation of carbon atoms of the furan ring in the order of α-carbon, adjacent β-carbon, second β-carbon, and the remaining α-carbon. Upon hydrogenation of the α-carbon of furan, ring opening becomes facile. Thus, hydrofuran (HF) is a reactive intermediate in both hydrogenation and ring opening. The fate of HF determines the selectivity of the overall reaction. A simple kinetic analysis indicates that coverage effects are important and the hydrogen partial pressure is a key factor in controlling selectivity. Dihydrofuran (DHF) was found to be a stable intermediate, consistent with experimental findings. Once DHF is formed, ring opening is not favored due to the high energy barriers of ring opening of DHF, trihydrofuran (TriHF) and THF. 1-Butanol is a thermodynamically favored product, while THF is kinetically preferred. Our theoretical work agrees well with experimental observations that 1-butanol is a major product at high temperatures whereas THF is a major product at low temperatures. Insights gained into selectivity toward ring hydrogenation and ring opening can assist future studies in catalyst selection.

Tetrahydrofuran ring opening and unexpected oxidation of the furyl ring in the reaction of bis(2-furyl) ditelluride with iodine and triphenylphosphine

The reaction of bis(2-furyl) ditelluride Fu2Te2 (1) with iodine in diethyl ether under ambient conditions expectedly yields FuTeI (2). The in situ reaction of 2 with triphenylphosphine affords Ph3PTe(Fu)I (3), which was characterized in the solid state by single crystal X-ray crystallography. The crystal structure of 3 shows linear P–Te–I backbone and T-shaped coordination around the tellurium atom. In the solid lattice, 3 exists as discrete molecules, which are lined together by a H⋯I hydrogen bonding network. There is no evidence of the secondary bonding Te⋯I or I⋯I interactions, which are typical for many tellurium–iodine compounds. When this two-step reaction of Fu2Te2 with I2 and PPh3 is carried out in tetrahydrofuran, a mixture of products is obtained. The main products, which were identified by single-crystal X-ray crystallography, are {Ph3P(C4H5O2)}2[TeI4] (4), {Ph3P(CH2)4PPh3}[TeI4]·2CH2Cl2 (5·2CH2Cl2), Fu2Te (6), (CH2)4TeI2 (7), Ph3PO, and elemental tellurium. The formation of the products has been discussed in terms of THF ring opening, abstraction of tellurium by PPh3, and the conversion of the furyl ring in FuTeI into a lactone ring due to the presence of atmospheric moisture.

Silyl Effects on 1,3-Diphosphacyclobutane-2,4-diyl: Ring-Opening of Tetrahydrofuran and Promotion of Reductive PC Cleavage

Mind your "P"s: Silylated P-heterocyclic biradicals activated tetrahydrofuran to give the corresponding 4-siloxybutyl-substituted 1,3-diphosphacyclobutane-2,4-diyls via ring-opening of the solvent molecule. Reductive P-C bond cleavage was found as an alternative approach to 1,3-diphosphacyclobuten-4-yl anion. Redox properties of the new P-heterocyclic biradicals were discussed in terms of hitherto unknown substituent effects.

Catalyst studies on the ring opening of tetrahydrofuran–dimethanol to 1,2,6-hexanetriol

The metal catalyzed hydrogenolysis of the biomass-derived THF–dimethanol to 1,2,6-hexanetriol using heterogeneous catalysts was investigated. Bimetallic Rh–Re catalysts (4wt% Rh and a Re/Rh (mol. ratio of 0.5) on a silica support gave the best performance and 1,2,6-hexanetriol was obtained in 84% selectivity at 31% conversion (120°C, 80bar, 4h); the selectivity reaches a maximum of 92% at 80°C. The product distribution at prolonged reaction times or higher temperatures or both shows the formation of diols and mono-alcohols, indicating that the 1,2,6-hexanetriol is prone to subsequent hydrodeoxygenation reactions. Different silica supports were investigated and optimal results were obtained with an amorphous silica featuring an intermediate surface area and an average mesopore size of about 6nm. TPR and XPS surface analysis support the presence of mixed Rh and Re particles. The redox Reδ+/ReTotal surface ratio correlates with the conversion in a volcano type dependency. Both gas phase as well as Rh200Re1OH cluster DFT calculations support an acid–metal bifunctional mechanism and explain the products distribution.

Tetrahydrofuran ring opening and related reactions with an N-heterocyclic carbene–boryl trifluoromethanesulfonate

Reaction of the triflate group in dipp-Imd-BH(2)OTf with nucleophiles generally occurs by direct substitution to give products dipp-Imd-BH(2)Nu. In contrast, reaction of this boryl triflate with aryloxides (ArO(-)) in THF resulted in insertion of THF with ring opening in between the NHC-boryl electrophile and the aryloxide to give products dipp-Imd-BH(2)O(CH(2))(4)OAr. The incorporation of THF was observed with other nucleophiles such as ethylthiolate and trimethylsilanolate whose conjugate acids have pK(a) values similar to that of phenol. The cleavage of ethyl acetate and oxetane is reported as well. A possible mechanism is proposed.

Copolymerization of Carbon–carbon Double-bond Monomer (Styrene) with Cyclic Monomer (Tetrahydrofuran)

We reported in this work that the cationic copolymerization in one step takes place between carbon–carbon double-bond monomer styrene with cyclic monomer tetrahydrofuran. The comonomers studied belong to different families: vinylic and cyclic ether. The reaction is initiated with maghnite-H+ an acid exchanged montmorillonite as acid solid ecocatalyst. Maghnite-H+ is already used as catalyst for polymerization of many vinylic and heterocyclic monomers. The oxonium ion of tetrahydrofuran and carbonium ion of styrene propagated the reaction of copolymerization. The acetic anhydride is essential for the maintenance of the ring opening of tetrahydrofuran and the entry in copolymerization. The temperature was kept constant at 40°C in oil bath heating for 6 hours. A typical reaction product was analyzed by 1H-NMR, 13C-NMR and IR and the formation of the copolymer was confirmed. The reaction was proved by matched with analysis. The maghnite-H+ allowed us to obtain extremely pure copolymer in good yield by following a simples operational conditions. © 2012 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Tetrahydrofuran in TiCl4/THF/MgCl2: a Non-Innocent Ligand for Supported Ziegler–Natta Polymerization Catalysts

While Ziegler–Natta (ZN) polymerization is one of the most important catalytic industrial processes, the atomic-scale nature of the catalytically active surface species remains unknown. Coupling high-resolution solid-state NMR spectroscopy with periodic density functional theory (DFT) calculations, we demonstrate that the major surface species in the ZN precatalyst corresponds to an alkoxy Ti(IV) surface species, which probably results from the ring-opening of tetrahydrofuran (THF) on a cationic Ti(IV) species.

Application of Solid-State Molybdenum Sulfide Clusters with an Octahedral Metal Framework to Catalysis: Ring-Opening of Tetrahydrofuran to Butyraldehyde

Solid-state molybdenum sulfide clusters with an octahedral metal framework, the superconducting Chevrel phases, are applied to catalysis. The cluster of copper salt, Cu x Mo6S8 (x = 2.94), stored in air is treated in a hydrogen stream above 300 °C. The activated cluster exhibits catalytic activity for the ring-opening of tetrahydrofuran, yielding butyraldehyde. Cyclic ethers such as trimethylene oxide and tetrahydropyran are also converted to the corresponding aldehydes. The cluster contains nonstoichiometric defects of sulfur atoms. Oxygen atoms are incorporated at the sulfur-deficient sites upon storage in air, but they are removed from the sites by the activation in a hydrogen stream. The resulting coordinatively unsaturated molybdenum atoms are catalytically active for the ring-opening reaction. The molybdenum atom in an intermediate oxidation state around 2+ is moderately coordinated by the oxygen of tetrahydrofuran and favorably releases the produced aldehyde. The neutral cluster Mo6S8, which has such sulfur-deficient sites, also catalyzes the reaction.

Ring-opening of tetrahydrofuran with PCl3 catalysed by an ortho-xylidenedizinc complex

The reaction of 1,2-o-xylyl dichloride with activated zinc in THF gives the organozinc compound [(μ-o-xyl)Zn2Cl2(THF)4], 1, where xyl = (2-methanidylphenyl)methanide. The compound is stable in the solid state but undergoes a slow decomposition in solution to generate the μ4-oxo cluster [(μ-o-xyl)2Zn4(μ-Cl)2(μ4-O)(THF)4], 3, which has been characterised in the solid state by single-crystal X-ray techniques. The organozinc complex 1 catalyses the ring-opening of THF in the presence of PCl3 to give a mixture of the two compounds [Cl(CH2)4O]PCl2 and [Cl(CH2)4O]2PCl.

Formation of 4-N-Arylamino-1-butanol Derivatives from Aromatic Nitro Compounds via a Novel Palladium-Catalyzed Tetrahydrofuran Ring-Opening Reaction

4-N-Arylamino-1-butanol derivatives are produced via a palladium-catalyzed tetrahydrofuran ring-opening reaction. This reaction occurs during the reduction of aromatic nitro groups with polymethylhydrosiloxane (PMHS) and potassium fluoride in the presence of hydrogen peroxide. This represents a novel route for the synthesis of 4-N-arylamino-1-butanols.

Synthesis and Investigation of [B20H17O(CH2)5]3–, a Novel Solvent Complex of the [B20H18]4–Ion

Reaction of the [trans-B(20)H(18)](2-) ion with the n-butoxide ion, formed in situ from reaction of n-butanol and NaH, in tetrahydropyran (THP) produces in good yield an unexpected and isolable solvent-coordinated polyhedral borane anion, [ae-B(20)H(17)O(CH(2))(5)](3-). The anticipated product of nucleophilic attack, [ae-B(20)H(17)On-Bu](4-), is not observed under the reaction conditions. The solvent-coordinated product is also formed in the presence of either ethoxide or carbamate ion but is not observed if the ethoxide or carbamate ion is not present in stoichiometric amounts. In the presence of the n-butanethiol anion, the coordinated THP ring undergoes a ring-opening reaction, yielding the [ae-B(20)H(17)O(CH(2))(5)Sn-Bu](4-) anion. Ring opening is also observed in the presence of the ethoxide ion in refluxing THP. Isolation of the previously proposed analogous solvent-coordinated tetrahydrofuran (THF) product, [ae-B(20)H(17)O(CH(2))(4)](3-), was unsuccessful; however, the product resulting from ring opening of THF by the n-butanethiol anion is reported.