Dehydrodimerization of imines via α-bromoimines using lithium diisopropylamide

α-Bromoimines were transformed into 1,4-diimines under soft conditions using lithium diisopropylamide in tetrahydrofuran.α-Bromoimines were transformed into 1,4-diimines using LDA in tetrahydrofuran     

Ionic equilibria in aqueous organic solvent mixtures the dissociation constants of acids and salts in tetrahydrofuran/water mixtures

The dissociation constants of several acids (perchloric, hydrochloric, phosphoric, acetic and benzoic acids) and of some sodium salts (chloride, acetate and benzoate) have been conductometrically determined in tetrahydrofuran/water mixtures up to a 90% of tetrahydrofuran in volume. The results demonstrate that conductometry can be successfully applied to determine the dissociation constants of salts and moderately weak and strong acids in the studied mixtures. The dissociation constants of the acids and some bases taken from the literature have been fitted to solvent composition through a previously derived equation, which is based on a preferential solvation model. The fitting parameters obtained allow calculation of the dissociation constant for any solvent composition inside the applicability solvent composition range. From the pK value, the pH of any buffered solution, such as those used in liquid chromatography, can be calculated for the particular tetrahydrofuran/ water composition of interest. Appreciable ion-pairing for sodium salts and strong acids has been observed for tetrahydrofuran contents higher than 60% in volume. Therefore, the accurate calculation of the pH values of buffers in tetrahydrofuran-rich solutions must take into account the pK values of the acid and salt.     

Radiation damage to DNA: electron scattering from the backbone subunits

In the context of damage to DNA by low energy electrons, we carry out calculations of electron scattering from tetrahydrofuran and phosphoric acid, models of the subunits in the DNA backbone, as a first step in simulating the electron capture process that occurs in the cell. In the case of tetrahydrofuran, we also compare with previous theoretical and experimental data. A comparison of the shape of the resonant structures to virtual orbitals is also performed to gain insight into the systematic connections with electron scattering from similar molecules and dissociative electron attachment experiments.     

Role of donor and secondary interactions in the structures and thermal properties of alkaline-earth and rare-earth metal pyrazolates

The addition of neutral coligands to reduce the aggregation and improve the volatility of potential heavy alkaline-earth metal chemical vapor deposition (CVD) precursors has typically resulted in liberation of the coligand upon heating. A new series of dinuclear alkaline-earth and rare-earth metal pyrazolates, bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)calcium] (1), bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)strontium] (2), and bis[bis(3,5-di-tert-butylpyrazolato)bis(tetrahydrofuran)barium] (3), have been obtained from our previous donor-free oligonuclear complexes [{M(3,5-tBu2pz)2}n] (5, M = Ca, n = 3; 6, M = Sr, n = 4; 7, M = Ba, n = 6) by treatment with tetrahydrofuran (THF). Compounds 1-3, as well as the europium analogue bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)europium(II)] (4), can also be prepared by direct reaction of the metals and pyrazole in THF and anhydrous liquid ammonia. Recrystallization from hexane led to single crystals of 2-4, while the powder diffraction pattern of 1 revealed it to be isostructural with the previously published bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)ytterbium(II)] (8), providing important insight into differences and similarities between the two groups of metals. Detailed structural analysis of the compounds reveals secondary interactions including pi-bonding and agostic interactions, which are considered essential in stabilizing the metal complexes. The direct comparison of structural features and thermal properties (as evaluated by thermogravimetric analysis and sublimation studies) of the donor-free oligonuclear and the donor-containing dinuclear species offers a better understanding of the role of donors and secondary interactions.     

Kinetics of the polymerization of tetrahydrofuran in the presence of water

The polymerization of tetrahydrofuran was studied with regard to the presence of polar and nonpolar compounds, or well-solvating and poorly solvating compounds, respectively. Tetrahydrofuran is highly nucleophilic, with a high solvation ability. It is capable of activating the native initiator itself and can be polymerized without any added cocatalyst. The addition of water to the tetrahydrofuran–initiator system decreases the polymerization rate. However, the dependence of the polymerization rate on the concentration of water in the dilute tetrahydrofuran runs through a maximum. The reaction rate is a function of the position of an equilibrium established during the solvation of initiator. All components of the system take part in the establishment of equilibrium.     

The liquid-liquid extraction using hydrophilic solvents occluded to an oil-adsorbent as an organic phase: extraction of 8-quinolinolato complexes of alkaline earth metals into tetrahydrofuran.

In order to use a hydrophilic solvent as an organic phase in liquid-liquid extraction by retaining it to a solid support, the occlusion and desorption of nine hydrophilic solvents, such as methanol, to three kinds of commercially available oil-adsorbent were examined. The combination of tetrahydrofuran and WOSEP made by fibrous polypropylene was finally selected, and was subjected to the extraction of alkaline Earth metals with 8-quinolinol. It was proved that Mg2+, Ca2+, and Sr2+ ions could be successfully extracted into the tetrahydrofuran phase in the form of 8-quinolinolato complexes, which could not be extracted into CHCl3.     

An Economic and Practical Synthesis of the 2-Tetrahydrofuranyl Ether Protective Group

Primary, secondary, and tertiary alcohols as well as phenols and carbohydrates are efficiently transformed into the corresponding 2-tetrahydrofuranyl ethers by a combination of Mn(0) powder and CCl₄ in tetrahydrofuran.     

Quantum chemical investigation by the AM1 method of the catalytic cyclodehydration of 1,4-butanediol

1,4-Butanediol is converted into tetrahydrofuran in the presence of silica gel at temperatures of 245–340°C. The mechanism of the conversion of 1,4-butanediol has been studied by the quantum chemical AM1 method with full optimization of the geometry. It was established that two parallel reactions are possible depending on the conformation of the molecule. The cyclodehydration reaction is effected by conversion of a semicyclic conformer of the protonated diol molecule at a basic center of the catalyst by a concerted mechanism. The heat of the reaction forming tetrahydrofuran is —161.768 kcal/mole.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 608–613, May, 1998.     

A Cascade “Prins‐Pinacol‐Type Rearrangement and C4‐OBn Participation” on Carbohydrate Substrates: Synthesis of Bridged Tricyclic Ketals,Annulated Sugars and C2‐Branched Heptoses

A “Prins pinacol type rearrangement followed by C4‐OBn participation” in a cascade manner has been observed while probing the fate of carbocation in some carbohydrate derived homoallylic alcohols in the Prins reaction. This has led to an easy access to tetrahydrofuran‐fused bridged bicyclic ketals (or tetrahydrofuran‐fused 1,6‐anhydro‐heptopyranose frameworks) which are further converted into some annulated sugars and C2‐branched heptoses.     

Direct catalytic oxidation of n-butane to to tetrahydrofuran

The feasibility of partially oxidizing n-butane to tetrahydrofuran in the presence of promoted V-P-O catalyst was demonstrated. Tetrahydrofuran formation was identified by means of chromatography and mass spectrometry. From the relationship between its concentration and reaction temperature tetrahydrofuran could be proposed as a possible intermediate in the transformation of n-butane into maleic anhydride.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 159–162, March–April, 1992.     

Comparative study of the high-temperature auto-ignition of cyclopentane and tetrahydrofuran

Cyclopentane (C₅H₁₀) and tetrahydrofuran (C₄H₈O) are both five-membered ring compounds. The present study compares the auto-ignition of cyclopentane and tetrahydrofuran in a high-pressure shock-tube (20 atm). Twelve different mixtures were investigated at two different fuel initial mole fractions (1% and 2%): at X_fuel = 1%, three equivalence ratios, kept constant between cyclopentane and tetrahydrofuran, were studied (0.5, 1, and 2), whereas three X_fuel/X_O2 were investigated when X_fuel = 2%. A detailed kinetic mechanism was developed to reproduce cyclopentane and tetrahydrofuran auto-ignition. The agreement between our experimental results and the modeling is very good. This mechanism was used to explain the similarities and differences observed between cyclopentane and tetrahydrofuran auto-ignition.     

Use of a database of plots of pesticide retention (R F) against mobile-phase composition.Part II. TLC as a pilot technique for transferring retention data to HPLC, and use of the data for preliminary fractionation of a mixture of pesticides by micropreparative column chromatography

Summary Relationships betweenR _F values and mobile-phase composition have been determined for moderately polar pesticides in normal-phase systems (NP) of the type silica-non-polar diluent (heptane)-polar modifier (ethyl acetate, tetrahydrofuran, or dioxane) and in reversed-phase systems (RP) of the type octadecyl silica-water-polar modifier (acetonitrile, methanol, or tetrahydrofuran). These relationships constitute a retention database which has enabled choice of the optimum conditions for preparative column chromatographic separation of pesticides into fractions; these were then applied to a silica plate and chromatographed. The plate was videoscanned, furnishing a real picture of the plate showing complete separation of the pesticide fractions.     

High-performance liquid chromatography of substituted p-benzoquinones and p-hydroquinones. II. Retention behavior, quantitative structure-retention relationships and octanol-water partition coefficients

The retention behavior of methoxy-substituted p-benzoquinones and the corresponding hydroquinones in reversed-phase chromatography was examined on octylsilica and two octadecylsilica stationary phases and with five hydroorganic mobile phases containing acetonitrile, methanol or tetrahydrofuran and additionally in most cases (NH3OH)3PO4 used as a reducing and buffering agent. The retention order of benzoquinones and hydroquinones was the same on each stationary phase with either methanol or acetonitrile as the organic modifier. On the other hand, minor differences in the retention order were observed with the various stationary phases. In all cases, satisfactory quantitative structure-retention relationships (QSRRs) were found and the data suggest that the differences in the retention behaviour of octadecylsilicas used in this study are silanophilic interactions which, together with solvophobic interaction contribute to the retention of these eluites. Further analysis showed that QSRRs of sterically crowded molecules must take into account reduced surface area available for binding. The retention data obtained with use of aqueous tetrahydrofuran as mobile phase failed to give rise to satisfactory QSRRs. This was attributed to selective solvation of eluite by tetrahydrofuran and/or nearly equipotent binding of eluite and tetrahydrofuran to stationary phase.     

Effective control of gas hydrate dissociation above the melting point of ice

Direct measurements of the dissociation behaviors of pure methane and ethane hydrates trapped in sintered tetrahydrofuran hydrate through a temperature ramping method showed that the tetrahydrofuran hydrate controls dissociation of the gas hydrates under thermodynamic instability at temperatures above the melting point of ice.     

新型键合型纤维素类手性固定相的制备及安息香分离

采用六亚甲基二异氰酸酯作为键合试剂,制备了键合型纤维素3,5-二甲基苯基氨基甲酸酯手性固定相。分别往正己烷/乙醇或正己烷/异丙醇中添加四氢呋喃和二氯甲烷,系统地考察了四氢呋喃和二氯甲烷的含量对安息香外消旋体拆分的影响。实验结果表明,安息香两对映体的容量因子随二者含量的增加而降低,但分离效果变化不大,分离因子均在1.2以上。所制备的CSP在采用含有高浓度四氢呋喃(23%)、二氯甲烷的流动相进行手性分离时仍具有良好的稳定性。与涂敷型固定相相比,流动相选择范围更广。     

Synthesis of 2,4- and 2,5-dialkyltetrahydrothiophenes

Summary Some 2,4- and 2,5-dialkyltetrahydrothiophenes were prepared by conversion of the corresponding tetrahydrofuran homologs into 1,4-dibromoalkanes and cyclization of the latter under the action of sodium sulfide into dialkyltetrahydrothiophenes.     

溶剂对脂肪酶降解高分子量PBS及改性共聚物的影响

采用固定化脂肪酶分别在四氢呋喃(THF)、甲苯及THF和甲苯的混合溶剂体系中, 对高分子量的PBS及PBS/CHDM共聚物进行了催化降解, 用GPC测定了降解产物的分子量, 用质谱(MS)对降解产物进行了分析, 用FTIR表征了产物化学结构. 研究结果表明, 在脂肪酶的作用下, 对M_n在10⁵以上的PBS, 在THF体系中可降解到1.4×10⁴, 而在甲苯体系中可降解到4×10⁴; 但在THF和甲苯的混合体系中, 可将M_n 10⁵以上的PBS和PBS/CHDM共聚物都可降解为0.1×10⁴以下的原料单体、一至四环状低聚物及少量线型低聚物. 分析了水含量对酶解反应的影响.     

Reaction of oxazirconacycloheptenes with aldehydes mediated by CuCl: one-pot synthesis of tetrahydrofuran derivatives from four different components involving two molecules of the same or different aldehydes, an ethylene and an alkyne

Reaction of zirconacyclopentenes with 2 equiv. of the same aldehydes in the presence of 1 equiv. of CuCl from −78 °C to room temperature afforded tetrahydrofuran derivatives in good isolated yields upon hydrolysis with aqueous 3 N HCl. Oxazirconacycloheptenes, generated in situ from zirconacyclopentenes with one aldehyde was found to be the reactive intermediate. When treated with a second aldehyde and CuCl, an oxazirconacycloheptene gave a tetrahydrofuran derivative comprised of four different components involving an alkyne, an ethylene and two different aldehydes, thus providing the first one-pot synthesis of important tetrahydrofuran derivatives from four components. When bulky aldehydes were used, hydrolysis of the above reaction mixtures afforded 2-hexen-1,6-diols, which could be quantitatively transformed to their corresponding tetrahydrofuran derivatives when treated with stronger aqueous acid (12 N HCl).     

Reductive cleavage of tetrahydrofuryl sulfur-substituted oxiranes: application to the formal synthesis of Kumausyne and Kumausallene

[reactions: see text] Readily available sulfinyl and sulfonyl tetrahydrofuran methanol derivatives have been transformed efficiently into a variety of substituted tetrahydrofuryl alcohols by treatment with (PhSe)2 in the presence of an excess of NaBH4. Alternatively, oxirane cleavage with MgI2 produces the related ketones, amenable to stereocontrolled reduction. This reductive cleavage methodology has been applied to short formal syntheses of trans-Kumausyne and Kumausallene.     

Deoxygenation/dimerization of sugar derivatives with BF3·Et2O-Et3SiH: synthesis of a β-isonucleoside

Lewis acid-Et₃SiH induced deoxygenation of anomeric carbon of sugars generates tetrahydrofuran derivatives, accompanied by hitherto unknown dimeric products. If the reagent addition steps are reversed, tetrahydrofuran derivatives are obtained as the sole products, while only the dimeric products are isolated if Et₃SiH is excluded. One of the deoxygenated products has been transformed into a β-isonucleoside.