Showing papers on "Tetrahydrofuran published in 1993"
TL;DR: In this article, an improved synthesis of the title compounds was reported, and the N,N'-dialkylthioureas 1 with 3-hydroxy-2-butanone gave the imidazole-2(3H)-thiones 2 which on treatment with potassium in boiling tetrahydrofuran give the IMidazol-2ylidenes 3 in excellent yields
Abstract: An improved synthesis of the title compounds is reported. Reaction of the N,N'-dialkylthioureas 1 with 3-hydroxy-2-butanone gives the imidazole-2(3H)-thiones 2 which on treatment with potassium in boiling tetrahydrofuran give the imidazol-2-ylidenes 3 in excellent yields
502 citations
TL;DR: In this article, it was shown that the presence of water, methanol, or ethyl acetate in the solvent had little effect on the Mn of the polymer obtained, because of the high chemoselectivity of the reaction of bis(cyclic carbonate and amine.
Abstract: Bis(cyclic Carbonate)s 1 were prepared by the reaction of bis(epoxide)s and atmospheric pressure of CO2 in the presence of sodium iodide and triphenylphosphine as catalysts at 100°C in high yield. Polyaddition of 1 and hexamethylenediamine (2a) or dodecamethylenediamine (2b) in dimethylsulfoxide or N,N-dimethylacetamide (DMAc) at 70 or 100°C for 24 h afforded corresponding poly(hydroxyurethane)s with Mn 20,000–30,000. When ethylenediamine (2c) or 1,3-propanediamine (2d) was used as a diamine, poly(hydroxyurethane)s with lower molecular weight were obtained. The presence of water, methanol, or ethyl acetate in the solvent had little effect on the Mn of the polymer obtained, because of the high chemoselectivity of the reaction of the five-membered cyclic carbonate and amine. Polyaddition of bis(cyclic carbonate) bearing ester groups and 2a also afforded the corresponding poly(hydroxyurethane) without aminolysis of the ester groups. Poly(hydroxyurethane) 3 obtained from the bis(cyclic carbonate) derived from bisphenol A was less soluble in organic solvents than model polyurethane 8 having no hydroxy groups obtained from 4,4′-isopropylidenebis(2-hydroxyethoxybenzene) and hexamethylene diisocyanate, and was thermally stable as well as 8.3 easily undertook crosslinking at room temperature by the treatment with hexamethylene diisocyanate or aluminium triisopropoxide in DMAc or tetrahydrofuran. The gel crosslinked by aluminium triisopropoxide regenerated the original polymer at room temperature by treatment with 1.5 equiv of 1.2M HCl in N-methylpyrollidinone for 1 h. © 1993 John Wiley & Sons, Inc.
215 citations
TL;DR: A series of single crystals of tetrakis as discussed by the authors have been prepared where the monoanion is a hexanuclear chalcohalide rhenium cluster and the neutral guest molecules are dimethylformamide (DMF) in 2a and 2b (triclinic modification), tetrahydrofuran (THF), and dioxane in 2d).
Abstract: A series of single crystals of tetrakis[3,4,3',4'-bis(ethylenedithio)-2,2',5,5'-tetrathiafulvalene] Re 6 Se 5 Cl 9 .-guest] (2a-d) have been prepared where the monoanion is a hexanuclear chalcohalide rhenium cluster and the neutral guest molecules are dimethylformamide (DMF) in 2a (monoclinic modification) and 2b (triclinic modification), tetrahydrofuran (THF) in 2c, and dioxane in 2d. All four compounds present the same basic structural organization in which conducting organic cation radical slabs are sandwichdn by inorganic cluster monoanion layers
112 citations
TL;DR: In this article, the EPR spectra of solutions of a nitroxide-labeled poly(N-isopropylacrylamide) (PNIPAM-T/880, M v 2.9×10 6 ; labeled poly- 4-amino-2,2,6,6-tetramethylpiperidine 1-oxide (TEMPO); label content, 1×10 -5 mol g -1 ) were recorded in mixtures of water and THF in order to investigate the phenomenon of cononsolvency exhibited
Abstract: The EPR spectra of solutions of a nitroxide-labeled poly(N-isopropylacrylamide) (PNIPAM-T/880, M v 2.9×10 6 ; labeled poly- 4-amino-2,2,6,6-tetramethylpiperidine 1-oxide (TEMPO); label content, 1×10 -5 mol g -1 ) were recorded in mixtures of water and THF in order to investigate the phenomenon of cononsolvency exhibited by the PNIPAM/water/THF ternary system. A detailed line-shape analyse of the EPR signals was carried out for spectra recorded at constant temperature as a function of solvent composition and as a function of temperature (-10 to +95 o C) for several water/THF mixtures
105 citations
TL;DR: In this paper, strong bases (lithium diisopropylamide (LDA) or BuLi) convert cyclosporin A (CS) to hexalithio derivative containing a Li alkoxide, four Li azaenolate, and one Li enolate units.
Abstract: Strong bases (lithium diisopropylamide (LDA) or BuLi) convert cyclosporin A (CS) to hexalithio derivative containing a Li alkoxide, four Li azaenolate, and one Li enolate units. The Li6 compound is solubilized in tetrahydrofuran (THF) by addition of excess LDA or LiCl. Reactions with electrophiles (alkyl halides, aldehydes, ClCO2R, CO2, (RS)2, D2O) at low temperatures give products containing new side chains in amino-acid residue 3 of the cyclic undecapeptide (see 1–13, Schemes 1, and 2, and Figs. 1 and 2) in moderate to high yields and, with Re- or Si-selectivities, depending upon the conditions of lithiation of up to 7:1, Pure CS derivatives (Scheme 2, Table 1 in the Exper. Part) can be isolated by column chromatography. N-Alkylations or cleavage of the peptide backbone by carbonyl addition occur only at higher temperatures and/or with prolonged reaction times (see 14 and 15 in Scheme 4). Very little or no epimerization of stereogenic centers occurs under the conditions employed. Possible reasons for the feasibility of these surprizing conversions of CS are discussed (Schemes 4 and 5 and Fig. 3). For comparision, [MeAla3]CS (2b) and [D-MeAla3]CS (2a) were also prepared by conventional peptide synthesis in solution (Schemes 6 and 7). Their 1H- and 13C-NMR spectra are compared with those of CS (Table 2 in the Exper. Part).
95 citations
TL;DR: A kinetic study of the reduction of ferrate ion under basic conditions has been completed in this article, where it was shown that a typical aliphatic ether, tetrahydrofuran, is oxidized at a rate comparable to that of a typical ferrate atom.
Abstract: A kinetic study of the reduction of ferrate ion under basic conditions has been completed. The observation that a typical aliphatic ether, tetrahydrofuran, is oxidized at a rate comparable to that ...
87 citations
TL;DR: In this paper, the crystal structures of α-metalated amines are determined, as are α-lithiated halides and ethers, in order to determine whether they are carbenoids.
Abstract: In order to determine whether α-metalated (lithiated) amines are carbenoids, as are α-lithiated halides and ethers, we have determined the crystal structures of the title compounds. In [α-(dimethylamino)benzyllithium–diethyl ether]2 ([9 · OEt2]2) lithium bridges the anionic carbon and the nitrogen atom which corresponds to the most stable calculated model structure of LiCH2NH2. The C–N bond is only slightly (≈ 3 pm) elongated (compared to the neutral species). If one of the N-methyl groups in [9 7dot; OEt2]2 is replaced by a pivaloyl group as in (S)-α-(methylpivaloylamino)benzyllithium – (–)-sparteine (10 dot; sparteine), a five-membered ring chelate is formed with Li being bound to the benzylic carbon atom and the oxygen atom of the pivaloyl group. In agreement with model calculations avoidance of the bridged structure as in [9 · OEt2]2 is compensated energetically by the chelate. Again a very small C–N bond elongation (≈ 3 pm) is observed. In [3-iodo-2-lithio-1-methylindole – 2 THF]2 ([12 · 2 THF]2) lithium again does not bridge to the indole nitrogen atom because it is a weak donor. The C–N bond length to the anionic C atom is slightly longer (2–3 pm) than in the non-lithiated compound. Other α-lithiated amines, which have been published, although not analyzed so far under this particular aspect, show also a marginal C–N bond lengthening. However, since α-lithiated amines – in contrast to α-lithiated halides and ethers – until now have not been reported in the literature to react with nucleophiles RLi, there is no need to include them into the group of the above mentioned carbenoids – at least not to date.
81 citations
01 Jan 1993
TL;DR: In this article, electron paramagnetic resonance (EPR) spectra of solutions of a nitroxide-labeled poly (N-isopropylacrylamide) (PNIPAM-T/880, M, 2.9 X 106; label, 4-amino-2,2,6,6-tetramethylpiperidine l-oxide (TEMPO); label content, 1 X 1W mol g-'1 were recorded in mixtures of water and tetrahydrofuran (THF) in order to
Abstract: The electron paramagnetic resonance (EPR) spectra of solutions of a nitroxide-labeled poly- (N-isopropylacrylamide) (PNIPAM-T/880, M, 2.9 X 106; label, 4-amino-2,2,6,6-tetramethylpiperidine l-oxide (TEMPO); label content, 1 X 1W mol g-'1 were recorded in mixtures of water and tetrahydrofuran (THF) in order to investigate the phenomenon of cononsolvency exhibited by the PNIPAM/water/THF ternary system. A detailed line-shape analysis of the EPR signals was carried out for spectra recorded at constant temperature as a function of solvent composition and as a function of temperature (-10 to +35 "C) for several water/THF mixtures. Changes in the rotational correlation time and in the isotropic hyperfine coupling constant of the label were correlated to the macroscopic polymer phase-separation process. The data support a model involving preferential water adsorption along the polymer chains in mixed water/THF solutions. This situation was compared to that offered by the PNIPAMIwaterlmethanol system, another ternary mixture which exhibita the phenomenon of cononsolvency. Differences between the two systems are described. They are interpreted in terms of the relative hydrogen-bonding abilities of the two organic cononsolventa.
77 citations
TL;DR: In this article, the preparation of N,N'-bis-tert-butoxycarbonylthiourea from thIourea and di-TERT-butyl dicarbonate in tetrahydrofuran is described.
77 citations
TL;DR: The chemical modifications and immobilization of cytochrome c were able to change its biocatalytic activity and stability in the organic solvent system, and the best catalytic efficiency was obtained in a system containing 50% tetrahydrofuran in phosphate buffer.
53 citations
TL;DR: In this article, surface-lithiated polysulfone membranes can be derivatized, potentially with a wide variety of functional groups, using n-butyllithium and tetrahydrofuran (THF).
Abstract: Polysulfone membranes were modified heterogeneously by lithiation, using n-butyllithium and low concentrations of tetrahydrofuran (THF). The effects of various conditions of reactant concentration, temperature, and time were determined quantitatively. The degree of substitution was measured by XPS and FTIR, using the carbonyl absorption band of lithium-activated membranes that had been converted to ones containing acyl fluoride substituents. The optimum conditions for membrane functionalization were 0.2M n-butyllithium in hexane at room temperature. The reaction rate increased substantially in the presence of 2% THF. The surface-lithiated membranes can be derivatized, potentially with a wide variety of functional groups. © 1993 John Wiley & Sons, Inc.
TL;DR: In this paper, the enantiomeric silane (2R,3S)-1a undergoes BF 3 -OEt 2 -promoted additions with (S)-2-(benzyloxy)propanal.
Abstract: Methyl α-methyl-β-(dimethylphenylsilyl)-(E)-hex-4-enoates (2S,3R)-1a undergo BF 3 -OEt 2 -promoted additions with (S)-2-(benzyloxy)propanal (2) producing nearly enantiomerically pure cis-2,5-substituted tetrahydrofurans 3 whereas the reactions run under chelation controlled conditions employing SnCl 4 resulted in the formation of the complementary trans-2,5-disubstituted tetrahydrofuran. Additions to the enantiomeric silane (2R,3S)-1b utilizing BF 3 -OEt 2 or SnCl 4 afforded the cis-2,5-disubstituted furan stereochemistry in both cases
Patent•
06 May 1993TL;DR: In this article, a CO2 absorption activator was proposed for deacidification of gases containing CO2 and optionally other acid gas compounds, particularly H2 S and/or COS.
Abstract: Liquid absorbing acid gas compounds presenting an improved CO2 absorption capacity, said absorbing liquid containing one or a plurality of tertiary alkanolamines and a CO2 absorption activator. The activator is comprised of at least one amino compound selected among polyalkylene-polyamines, alkylenediamines or cycloalkylenediamines, the aminoalkylated compounds of heterocycles such as piperazine, piperidine, furan, thiophene, tetrahydrofuran and tetrahydrothiophene, the alkoxyalkylamines and the alkylmono-alkanolamines having an alkyl residue in at least C2. Application of said absorbent liquid to the deacidification of gases containing CO2 and optionally other acid gas compounds, particularly H2 S and/or COS.
TL;DR: In this article, the reduction of disubstituted naphthalene derivatives by potassium-graphite intercalate C8K was reported, carried out at 0 °C in tetrahydrofuran.
Abstract: The reduction of disubstituted naphthalene derivatives by potassium–graphite intercalate C8K is reported. The reduction is carried out at 0 °C in tetrahydrofuran. The C8K–ether system suggests an alternative route for the Birch type reaction and the mechanism is discussed vis-a-vis the reaction in liquid ammonia.
TL;DR: The lithiation of different phenone imines with an excess of lithium powder and a catalytic amount (8 mol %) of naphthalene in the presence of several carbonyl compounds in tetrahydrofuran at temperatures ranging between −78 and 20°C leads, after hydrolysis with water, to the corresponding 1,2-aminoalcohols 3 in moderate yields.
TL;DR: In this article, the X-ray-structure determination confirms that 2 is the first contact ion pair of a lithium diorganophosphide without Li-P contact, which makes the (2-NC5H4)2P ion a versatile ligand for III/V precursors.
Abstract: [Li{(2-NC5H4)2P}{thf}]2(thf = tetrahydrofuran) and [AlMe2{(2-NC5H4)2P}]3 are obtained in high yield by treating (2-NC5H4)2PH 1, with BunLi and Me3Al, respectively; the X-ray-structure determination confirms that 2 is the first contact ion pair of a lithium diorganophosphide without Li–P contact, which makes the (2-NC5H4)2P– ion a versatile ligand for III/V precursors (already established in 3).
TL;DR: The photolysis of catena-poly (phenyl-4-phenylphenylsilicon) at λinc = 365-400 nm leads to products (probably free radicals) which are oxidized by diphenyliodonium ions.
TL;DR: The authors showed that β-ptopiolactone, contrary to larger lactones, is less basic (6 kcal/mol) than the corresponding aliphatic ester, which is a consequence of substantial hybridization changes upon cyclization.
Abstract: Ab initio calculations, at different levels of accuracy, have been performed for different cyclic oxygen bases (2-oxetanone, γ-butyrolactone, oxetane, and tetrahydrofuran), for the corresponding acyclic counterparts (methyl acetate, ethyl acetate, methyl propionate, methyl ethyl ether, dimethyl ether, and methyl propyl ether), and for their protonated species. The gas-phase proton affinities for some of these species were reinvestigated by FT-ICR techniques. Our results show that β-ptopiolactone, contrary to larger lactones, is less basic (6 kcal/mol) than the corresponding aliphatic ester. This is a consequence of substantial hybridization changes upon cyclization, which for five-membered (or larger) systems are quite small
TL;DR: In this paper, structural studies by X-ray crystallography have been carried out on the complexes [BiPhCl2(thf), [NBu4n]2[Bi2Ph2Br6]4 and [NEt4][BiPh2I2]6.
Abstract: Structural studies by X-ray crystallography have been carried out on the complexes [BiPhCl2(thf)]1(thf = tetrahydrofuran), [NBu4n]2[Bi2Ph2Br6]4 and [NEt4][BiPh2I2]6. Complex 1 comprises a chloridebridged polymeric chain with each bismuth centre in a square-based pyramidal co-ordination environment. A phenyl group occupies the apical site whilst the four basal positions are occupied by three chlorine atoms, one terminal and two bridging, and the oxygen of a co-ordinated thf molecule. The chloride bridges are quite asymmetric and a comparison is made with the increasing trend towards symmetric bridges found in the previously characterised bromide and iodide derivatives. The structure of the anionic part of 4 comprises a centrosymmetric [Bi2Ph2Br6]2– dianion with a planar Bi2Br6 unit and trans phenyl groups with each bismuth centre also adopting a square-based pyramidal co-ordination geometry with apical phenyls. Comparisons are made with similar bismuth, antimony and tellurium complexes and the differences discussed. The structure of the anion of 6 can be described as disphenoidal or equatorially vacant, trigonal bipyramidal with axial iodides and equatorial phenyls. This is similar to the previously known bromide complex except that 6 exists in the solid state as a weakly bound centrosymmetric dimer. All of the above structures are compared with those of related compounds and the various trends which are apparent are discussed.
TL;DR: In this article, a dialkylsulfonio-methylation has been observed on the treatment of the 7,8-C2B9H12(-) ion with formaldehyde and dialkyl sulfides in aqueous acidic medium.
Abstract: Dialkylsulfonio-methylation has been observed on the treatment of the 7,8-C2B9H12(-) ion with formaldehyde and dialkyl sulfides in aqueous acidic medium. Four zwitterions of the type 9-R2S-CH2-7,8-C2B9H11 were formed with dimethyl and diethyl sulfide, tetrahydrothiophene and thioxane. In contrast, dialkyl ethers (diethyl ether, tetrahydrofuran, dioxane) afforded low amounts of the 10-R2O-7,8-C2B9H11 zwitterions, with the carborane 4,5- C2B7H13 being the principal product. Using acetaldehyde instead of formaldehyde, moderate yields of the 10-R2O- and high yields of the 10-R2S-7,8-C2B9H11 derivatives were obtained. With tertiary amines, only corresponding ammonium salts precipitated. Possible reaction pathways for these transformations are discussed and compared with the specific degradation of the 7,8-C2B9H12(-) ion to the arachno-4,5- C2B7H13 carborane.
TL;DR: In this article, the reaction of 3-chloro-2-chloromethylpropene and carbonyl compounds with an excess of lithium powder in the presence of a catalytic amount of naphthalene (6%) in tetrahydrofuran at −78 to 20°C leads, after hydrolysis, to the corresponding methylenic 1,5-diols 3 in a Barbier-type process.
TL;DR: In this article, a series of polymers with various combinations of these substituents, as well as the end members of the series, poly(diphenylsiloxane) and poly(di(p-tolyl) siloxane).
TL;DR: In this article, the reduction power of AHTEA complex in tetrahydrofuran toward 59 selected organic compounds containing representative functional groups under practical conditions (tetrahydrafuran, room temperature, the quantitative amount of reagent to compound) has been investigated.
Abstract: The addition of triethylamine to a solution of aluminum hydride in tetrahydrofuran (THF), which was prepared by the addition of a calculated amount of hydrogen chloride in diethyl ether to solutions of sodium aluminum hydride in THF, provides very stable solutions of aluminum hydride-triethylamine complex (AHTEA). The reducing power of AHTEA complex in tetrahydrofuran toward 59 selected organic compounds containing representative functional groups under practical conditions (tetrahydrofuran, room temperature, the quantitative amount of reagent to compound) has been investigated. In this way, we have established that quantitative reduction of various organic functionalities can be readily achieved using the calculated quantity of AHTEA to avoid the use of excess reagent
TL;DR: The primary chemical equilibria which define autoprotolysis in aqueous binary solvents have been elucidated and the constants of these equilibrium values were computed in this paper.
Abstract: The primary chemical equilibria which define autoprotolysis in aqueous binary solvents have been elucidated and the constants of these equilibria computed for aqueous solvent mixtures of methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol, acetonitrile, acetone, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, and formic acid. The values of these constants explain the different behaviors of the diverse binary solvents. From these fundamental constants, the plan value at any solvent composition of any of the binary solvents studied can be accurately computed
TL;DR: In this article, the stepwise formation of two distinct bimetallic titanium/magnesium complexes during the reduction of TiCl3 (or TiCl4) by magnesium in tetrahydrofuran (THF) has been identified.
TL;DR: Isothiocyanats were prepared in quantitative yields from the reaction of nitrile oxides with thiourea in tetrahydrofuran at room temperature in this paper.
TL;DR: In this paper, the reaction of lanthanoid metals with hexachloroethane in tetrahydrofuran under ultrasonication conditions gives LnCl3(thf)n(Ln = La, Nd, Sm, n= 2; Ln = Gd, Yb, n = 3.
Abstract: Reaction of lanthanoid metals with hexachloroethane in tetrahydrofuran under ultrasonication conditions gives LnCl3(thf)n(Ln = La, Nd, Sm, n= 2; Ln = Gd, Yb, n= 3; Ln = Er, n= 3.5, thf = tetrahydrofuran) in good yield; the X-ray crystal structure of [YbCl3(thf)2]2, derived from YbCl3(thf)3 by prolonged treatment with pentane, reveals a chloride-bridged octahedral dimer with trans thf ligands.
TL;DR: In this article, an 8:1 tetramer/dimer equilibrium in tetrahydrofuran-d 8 at -90 o C (1.6 M solution) was found.
Abstract: Vinyllithium (ViLi; isotopically labeled with 6 Li) is an 8:1 tetramer/dimer equilibrium in tetrahydrofuran-d 8 (THF-d 8 ) at -90 o C (1.6 M solution). In the presence of equilmolar amounts of TMEDA (tetramethylethylenediamine), the tretramer:dimer ratio is 1:13 in THF-d 8 at -80 o C (1.9 M solution). Dynamic NMR phenomena are observed in the ViLi tetramer: at -90 o C in THF-d 8 , a static aggregate is found, whereas at -60 o C rapid intraaggravate exchange of the four lithium sites indicates a fluxional tetramer
TL;DR: A series of manganese(IV) complexes, [Mn (R, R′-L)2]·nS (R or R′ = H, Cl, Br, CH3O; n = 1 2, 1, 3/2, 2; S = H2O, THF (THF = tetrahydrofuran)) where H2(R,R′-l) denotes o-(salicylideneaminomethyl)phenol) with the substituent R on the salicylideamino ring
Abstract: A series of manganese(IV) complexes, [Mn (R, R′-L)2]·nS (R or R′ = H, Cl, Br, CH3O; n = 1/2, 1, 3/2, 2; S = H2O, THF (THF = tetrahydrofuran)) where H2(R, R′-L) denotes o-(salicylideneaminomethyl)phenol with the substituent R on the salicylideneamino ring and the R′ on the aminomethylphenol ring, have been prepared and characterized by infrared and electronic spectra, magnetic moments, cyclic voltammetry, and spectroelectrochemical experiment. The molecular structure of [Mn (5-Cl′-L)2]·2THF has been determined by X-ray crystallography. The ligands act as meridional tridentate ONO donors and the complex has an MnO4N2 coordination sphere. The spectral, magnetic, and electrochemical properties are discussed in relation to the molecular structure.
TL;DR: In this paper, a single-crystal X-ray study of (Me3Si)3CLi·tmen (tmen =N,N, N′,N′-tetramethylethylenediamine) was conducted.
Abstract: A single-crystal X-ray study of (Me3Si)3CLi·tmen (tmen =N,N,N′,N′-tetramethylethylenediamine) shows that it crystallises with the ionic structure [Li(tmen)2][Li{C(SiMe3)3}2] but that the anions pack with different orientations from those in crystalline [Li(thf)4][Li{C(SiMe3)3}2](thf = tetrahydrofuran). The 1H, 7Li, 13C and 29Si NMR spectra of (Me3Si)3CLi·2thf and (Me3Si)3CLi·tmen in thf and toluene, and 7Li, 13C and 29Si NMR spectra of the solids are described. Spectra obtained from solutions below ca. 25 °C show the presence of ion pairs [Li(thf)4][Li{C(SiMe3)3}2] or [Li(tmen)2][Li{C(SiMe3)3}2], together with further species which appear to be different in thf and toluene. Spectra from solutions at higher temperatures show inter-species exchange on the NMR timescale.