Synthesis of Perfluoro- and 2-Trifluoromethylpentafluorodihydrofurans and Their Epoxy Derivatives

Perfluorotetrahydrofuran-2-carboxylic acid was converted through a series of transformations into perfluoro-2,3-dihydrofuran and perfluoro-2,5-dihydrofuran; likewise, from (2-perfluorotetrahydrofuryl)difluoroacetic acid 2-trifluoromethylpentafluoro-2,3-dihydrofuran was obtained. Perfluoro-2,3-dihydrofuran and 2-trifluoromethylpentafluoro-2,3-dihydrofuran underwent isomerization into perfluoro-2,5-dihydrofuran and 2-trifluoromethylpentafluoro-2,5-dihydrofuran by the action of cesium fluoride. Treatment of perfluoro-2,5-dihydrofuran with SbF₅ resulted in ring opening and formation of cis-perfluoro-2-butenoyl fluoride, while 2-trifluoromethylpentafluoro-2,3-dihydrofuran was converted into 2-trifluoromethylpentafluoro-2,5-dihydrofuran under the same conditions. Perfluoro-3,4-epoxytetrahydrofuran and 2-trifluoromethyl-3,4-epoxypentafluorotetrahydrofuran containing fused oxirane and tetrahydrofuran rings were synthesized by reactions of perfluoro-2,5-dihydrofuran and 2-trifluoromethylpentafluoro-2,5-dihydrofuran, respectively, with sodium hypochlorite.     

Characterization of Extra-framework Cations in Zeolites. A temperature-programmed desorption (TPD) study

We have investigated the interaction of a few 5-ring organic compounds (cyclopentane, cyclopentene, furan, 2-methylfuran, 2,5-dihydrofuran and tetrahydrofuran) with alkali-metal cation-exchanged faujasites (LSX, X and Y types) by means of temperature-programmed desorption (TPD). The desorption behavior at higher temperatures of all probe molecules on the sodium ion containing faujasites with different Si/Al ratios reflects the higher cation content of zeolites with greater aluminum content. Only the desorption profiles of tetrahydrofuran and 2,5-dihydrofuran show, depending on the kind of cation, additional desorption features at higher temperatures. Using a regularization method, desorption energy distribution functions for furan and tetrahydrofuran were calculated. The calculated desorption energy distributions clearly illustrate the very different adsorption behavior of furan and tetrahydrofuran which leads to large differences in the binding energies between the corresponding adsorption complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Efficient and mild synthesis of highly substituted 2,5-dihydrofuran and furan derivatives via stepwise reaction

An efficient and mild synthesis of highly substituted 2,5-dihydrofuran and furan derivatives from a variety of alkylidene malonates and 1,4-butyne-diol via one-pot reaction was applied. With various conditions of base amount, temperature and time applied to the reaction, the 2,5-dihydrofuran and the furan derivatives could be selectively obtained. Moreover, the formation of furan derivatives with 2,5-dihydrofuran derivatives as intermediates was also investigated. Some of these 2,5-dihydrofuran derivatives showed potent in vitro anti-tumor activities against HeLa cells.     

Catalytic synthesis of dihydrofurans (review)

Various methods for the preparation of 2,3-dihydrofuran, 2,5-dihydrofuran, 2-methylenetetrahydrofuran, and their alkyl and aryl derivatives are examined. The most promising method for the preparation of 2,3-dihydrofuran is the conversion of 1,4-butanediol on cobalt catalysts. 2,5-Dihydrofuran is obtained by dehydration of 2-butene-1,4-diol on Al₂O₃, cobalt-containing and other catalysts, while 2-methylenetetrahydrofuran is obtained by dehydrohalogenation of tetrahydrofurfuryl halides. The various methods for the isomerization of 2,5-dihydrofuran to 2,3-dihydrofuran are discussed. Examples of the application of dihydrofurans in organic synthesis are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1299–1311, October, 1982.     

Allenes—XXXV : The addition of allenic carbenes to oxygen heterocycles

Dimethylvinylidene carbene from 1-bromo-3-methylbutadiene and potassium t-butoxide adds to 2,5-dihydrofuran and 2,3-dihydropyran to give the corresponding allenic cyclopropanes. 1,4-Cycloaddition of the allenic carbene to furan followed by hydration during work up yields the bicyclic ketone 11.     

Liquid-phase hydroformylation of 2,3- and 2,5-dihydrofurans

The synthesis of 3-formyl derivatives of the tetrahydrofuran series was carried out by hydroformylation of 2,3-dihydrofuran and 2,5-dimethoxy-2,5-dihydrofuran in the presence of HRh(CO)(PPh₃)₃. The influence of the temperature, pressure, catalyst concentration, and the nature of the solvent on the conversion of dihydrofuran, the composition of aldehydes obtained and the selectivity of their formation was investigated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2569–2571, November, 1989.     

Transformations of heterocyclic compounds on membrane catalysts

The transformations of furan, -methylfuran, furfural, and 2,3-dihydrofuran on a palladium — nickel membrane catalyst at 50–300°C under conditions of diffusion of hydrogen through the catalyst were investigated. Under these conditions furan is hydrogenated to tetrahydrofuran in quantitative yield. Considerable amounts of furan, the hydrogenation of which in the presence of the above-named derivatives is inhibited, are detected in the catalyzate along with hydrogenation products in the transformations of -methylfuran, furfural, and 2,3-dihydrofuran.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 599–601, May, 1975.     

Reactivity of Cl–P+–Cl toward cyclic organic ethers

The dichlorophosphenium ion (Cl-P(+)-Cl) undergoes a variety of reactions with cyclic organic ethers in the gas phase in a Fourier-transform ion cyclotron resonance mass spectrometer. Most of the reactions are initiated by Cl-P(+)-Cl-induced heterolytic C-O bond cleavage. However, the observed final products depend on the exact structure of the ether. For saturated ethers, e.g., tetrahydropyran, tetrahydrofuran, and 2-methyltetrahydrofuran, the most abundant ionic product corresponds to hydroxide abstraction by Cl-P(+)-Cl. This unexpected reaction is rationalized by a multistep mechanism that involves an initial heterolytic C-O bond cleavage accompanied by a 1,2-hydride shift, and that ultimately yields a resonance-stabilized allyl cation and HOPCl2. The process is estimated to be highly exothermic (AM1 calculations yield delta H = -(33-38) kcal mol(-1) for the ethers mentioned above). However, the adducts formed from most of the unsaturated ethers are unable to undergo hydride shifts and hence cannot react via this pathway. In some of these cases, e.g., for 2,5-dihydrofuran and 2,5-dihydro-3,4-benzofuran, the C-O bond heterolysis is followed by oxygen/chlorine exchange to yield the O=PCl radical and a resonance-stabilized carbocation (AM1 calculations yield delta H = -14 kcal mol(-1) for the reaction of 2,5-dihydro-3,4-benzofuran). Hydride abstraction by Cl-P(+)-Cl also yields an abundant product for these two ethers. On the other hand, the ethers with low ionization energies, such as 2,3-dihydrofuran and 2,3-dihydrobenzofuran, react with Cl-P(+)-Cl by electron transfer. Finally, a unique pathway, addition followed by elimination of HCl, dominates the reaction with furan. The observed reactions are rationalized by thermochemical data obtained from semiempirical molecular orbital calculations.     

Ab initio and experimental study of the K-shell spectra of 2,5-dihydrofuran

The K-shell spectra of gaseous 2,5-dihydrofuran at the carbon and oxygen thresholds are reported for the first time. They have been measured using the inner-shell electron energy loss spectroscopy (ISEELS) method. Ab initio Configuration Interaction calculations have been carried out to assign the observed bands. The O1s spectrum is similar to that of tetrahydrofuran and the assignments of the bands are close to those obtained in the case of furan, excepting the furan first π* band. At the C1s edge, the spectrum differs from the furan case, because of the different chemical environment of one of the non-equivalent carbon atoms: due to the presence of hydrogen atoms out of the carbon–oxygen ring plane, several Rydberg core excited states have an important valence character, leading to large intensities in the experimental spectrum.     

PdI2-catalyzed coupling-cyclization reactions involving two different 2,3-allenols: an efficient synthesis of 4-(1',3'-dien-2'-yl)-2,5-dihydrofuran derivatives

Transition-metal-catalyzed dimeric coupling-cyclization reactions of two different 2,3-allenols afforded 4-(1',3'-dien-2'-yl)-2,5-dihydrofuran derivatives 3. 2-Substituted 2,3-allenols 1 cyclized to form the 2,5-dihydrofuran ring, whereas the 2-unsubstituted 2,3-allenols 2 provided the 1,3-diene unit at the 4-position. The reaction is proposed to proceed through an oxypalladation, insertion, and beta-hydroxide elimination process. The C=C double bond was formed with high E stereoselectivity by beta-hydroxide elimination.     

Vibrational assignment and analysis for 2,3-dihydrofuran and 2,5-dihydrofuran

The vibrational spectra of 2,3-dihydrofuran and 2,5-dihydrofuran have been recorded using IR and Raman spectroscopy for the gas, liquid and solid states. A vibrational assignment consisting of a nearly complete set of vapor phase wavenumbers is proposed for both molecules based on the observed spectra and normal coordinate analyses. The normal coordinate analyses have been made by scaling the AM1 force field for each molecule with scale factors transferred from an analysis of the cyclopentene fundamental vibrations. The predicted a priori vibrational frequencies justify one reassignment of the fundamentals for 2,5-dihydrofuran from that previously reported. The vibrational assignment for 2,3-dihydrofuran is reported for the first time. Thermodynamic functions are computed for each molecule using the experimentally determined vibrational frequencies.     

Synthesis of novel furan and thiophene PAH'S related to acephenanthrylene

The total syntheses of furan and thiophene PAH's related to acephenanthrylene are reported. Cyclobutanones which were obtained by [2 + 2] addition of ketenes with 2,3-dihydrofuran or 2,3-dihydrothiophene regioselectively could be converted into angular PAH skeleton molecules by rearrangements with polyphosphoric acid. 2,3-Dichloro-5,6-dicyanobenzoquinone was applied for aromatization to achieve the formation of PAH's.     

Conversion of 1,4-butanediol to furan compounds on cobalt catalysts in the liquid phase

The transformation of 1,4-butanediol on cobalt catalysts applied to kieselguhr in the liquid phase under periodic and continuous conditions was investigated. When the reaction is carried out under periodic conditions, the principal reaction products are 2,3-dihydrofuran, tetrahydrofuran, and -butyrolactone. An increase in the selectivity of the formation of 2,3-dihydrofuran as the temperature is raised was established. 2,3-Dihydrofuran is obtained in 63–73 mole % yields under optimum conditions. 2,3-Dihydrofuran is converted to tetrahydrofuran when the process is carried out under continuous conditions on a tableted cobalt catalyst.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 448–450, April, 1981.     

Ab initio study of the decomposition of 2,5-dimethylfuran

The initial steps in the thermal decomposition of 2,5-dimethylfuran are identified as scission of the C-H bond in the methyl side chain and formation of β- and α-carbenes via 3,2-H and 2,3-methyl shifts, respectively. A variety of channels are explored which prise the aromatic ring open and lead to a number of intermediates whose basic properties are essentially unknown. Once the furan ring is opened demethylation to yield highly unsaturated species such as allenylketenes appears to be a feature of this chemistry. The energetics of H abstraction by the hydroxyl radical (and other abstracting species) from a number of mono- and disubstituted methyl furans has been studied. H-atom addition to 2,5-dimethylfuran followed by methyl elimination is shown to be the most important route to formation of the less reactive 2-methylfuran. Identification of 2-ethenylfuran as an C(6)H(6)O intermediate in 2,5-dimethylfuran flames is probably not correct and is more likely the isomeric 2,5-dimethylene-2,5-dihydrofuran for which credible formation channels exist.     

Electrolytic methoxylation of 3,4-bis(hydroxymethyl) furan and synthesis of 4,5-bis-(hydroxymethyl) pyridazine

3,4-Bis(hydroxymethyl)furan was electrolytically methoxylated during intense cooling. 4,5-Bis(hydroxymethyl)pyridazine was obtained by reaction of the methoxylation product — 2,5-dimethoxy-3,4-bis (hydroxymethyl)-2,5-dihydrofuran — with hydrazine hydrate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1306–1307, October, 1970.     

Synthesis and cationic polymerization of substituted 2,3-dihydrofurans

Cationic polymerization of substituted 2,3-dihydrofurans has been performed to investigate the substituent effect on the ring-opening polymerization. 2-Phenyl-2,3-dihydrofuran ( III ), 2-methoxy-5-phenyl-2,3-dihydrofuran ( V _a), and 2-ethoxy-5-phenyl-2,3-dihydrofuran ( V _b) were synthesized and polymerized with BF₃ etherate and AlCl₃ as acid catalysts. V _a and V _b ring-opening polymerized well to give the polymers with benzoyl as pendant group which were formed via cationic rearrangement during the ring-opening process, while III polymerized via simple opening of ethylenic double bond to form a polymer with the retention of tetrahydrofuran ring in the main chain. The nature of substituted cyclic vinyl ethers depending on substituents was also discussed.     

Palladium-Catalyzed Arylation and Vinylation of 2,3-Dihydrofuran with Hypervalent Iodonium Salts

The palladium-catalyzed arylation and vinylation of 2,3-dihydrofuran with aryl and alkenyl iodonium salts afforded 2-phenyl- or 2-alkenyl-2,5-dihydrofurans at room temperature in an aqueous medium.     

Synthesis of 2,5-bis{(diethyl-3′-indolyl)methyl}furan and its N,N′-dimetallated complexes (lithium, sodium and potassium): X-ray crystal structures of 2,5-bis{(diethyl-3′-indolyl)methyl}furan and the polymeric tetrahydrofuran adduct of the dilithiated complex

The synthesis of 2,5-bis{(diethyl-3′-indolyl)methyl}furan by the acid catalysed condensation of 2,5-bis(diethylhydroxymethyl)furan with indole is presented. Dilithium, disodium and dipotassium derivatives are prepared by the reaction of the bis(indole) with n-BuLi, NaH and K, respectively, in the presence of various Lewis bases. The X-ray structures of 2,5-bis{(diethyl-3′-indolyl)methyl}furan and the dilithiated derivative (as a polymeric tetrahydrofuran adduct) are reported.     

The interaction of dihydrofurylsilanes with dichlorocarbene under phase-transfer conditions

Dichlorocarbene generated in a two-phase catalytic system reacts with 3-trimethylsilyl-2,5-dihydrofuran to give both possible products of mono-insertion into the CH bond in positions 2 and 5 of the ring, together with a CC bond adduct. Reaction of 2-trimethylsilyl-4,5-dihydrofuran with dichlorocarbene leads to 2,3-dichloro-2-trimethylsilyl-5,6-dihydro-2H-pyran, which is formed via isomerization of the primary bicyclic adduct.     

CNDO calculations of ring puckering potential energy

The ring puckering potential energy functions are calculated for 2,3-dihydrofuran, 2,5-dihydrofuran, cyclopentene and cyclopent-3-enone using the standard CNDO/2 method. The equilibrium conformations are discussed and the ring puckering force constants as well as the dipole moments are evaluated. A more detailed analysis of the influence of angular deformations on the potential function of the cyclopentene molecule is performed.