Polymerization behaviour of 2,5-dimethylene- 2,5-dihydrofuran

Spontaneous homopolymerization of 2,5-dimethylene-2,5-dihydrofuran (DDF) was studied. The polymerization rates in two different initial monomer concentrations of DDF were analyzed with the first-order and second-order kinetics, and the homopolymerization of DDF was found to obey the first-order kinetics. The Arrhenius plot of the apparent rate constants at 30, 40, 50, and 60° gave an overall activation energy of 68.0 kJ/mol for the polymerization of DDF. From the comparison of the apparent rate constants at –78° and the time (the so-called half-life time) to decrease in half the monomer concentration for DDF with the corresponding values for p-xylylene (QM), DDF was found to be a less reactive monomer than QM. The copolymerizations of DDF with vinyl monomers such as acrylonitrile (AN), α-chloroacrylonitrile (CIAN), diethyl fumarate (DEF), and fumaronitrile (FN) were carried out in chloroform at 50° in the presence of AIBN to obtain the monomer reactivity ratios r₁(DDF) = 30.0 ± 3.0 and r₂ (AN) = 0 for the DDF-AN system, r₁ (DDF) = 1.55 ± 0.2 and r₂(CIAN) = 0 for the DDF-CIAN system, r₁(DDF) = 3.88 ± 0.2 and r₂(DEF) = 0 for the DDF-DEF system, and r₁(DDF) = 2.41 ± 0.1 and r₂ (FN) = 0 for the DDF-FN system, respectively. As the monomer reactivity ratios of r₂ for all systems were zero, Q and e values of DDF were calculated from the combination of two r₁ (DDF) values of any two copolymerization systems to be the 7.64 to 6.63 ×10²¹ range for Q and the –0.70 to –6.31 range for e, indicating that DDF is a highly conjugative and electron-donating monomer. © 1995 John Wiley & Sons, Inc.     

Protolytic cleavage of derivatives of 2,5-dimethoxy-2,5-dihydrofuran

By analysis of the products from the protolytic cleavage of methyl 3-(2,5-dialkoxy-2,5-dihydro-2-furyl)propionate (I) in the presence of mixed nucleophiles and investigation of their mutual transformations the main paths in the dissociation of the protonated molecule of (I), with the formation of both linear cleavage products (derivatives of 1,4-diketones and 4-ketopimelic acid) and furylcarbinol derivatives, were determined.Latvian Institute of Organic Synthesis. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 190–197, February, 1997.     

Gas-phase protonation of unsaturated ethers: Experimental and theoretical study of 2,3-and 2,5-dihydrofuran and related compounds

The protonation of 2,3- and 2,5-dihydrofuran is examined in gas-phase equilibrium proton transfer reactions conducted in an ion cyclotron resonance spectrometer. The thermodynamically favoured site of protonation in the two compounds is seen to be different: whereas the first isomer forms a carbocation upon protonation, the second isomer protonates on the oxygen atom to form an oxonium ion. The results obtained with substituted derivatives and with linear analogues confirm these conclusions. Molecular orbital calculations on the various structures for protonated bases are performed at the 4–31G level with correction for configuration interaction effects and at the 4–31G* level. The latter basis set provides the best results owing to the introduction of d-type orbitals on the oxygen atom. The calculation results substantiate the experimental observations and provide details on the molecular structure of the protonated species.     

Ring-closing metathesis toward the synthesis of 2,5-dihydrofuran and 2,5-dihydropyrrole skeletons from Baylis-Hillman adducts

We have developed an efficient method for the synthesis of 2,5-dihydrofuran and 2,5-dihydropyrrole skeletons from the simply modified Baylis-Hillman adducts via RCM reaction.     

Synthesis of N-substituted pyrrole-3-carbaldehydes by hydroformamination of 2,5-dimethoxy-2,5-dihydrofuran

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, p. 1285, September, 1990.     

Vibrational assignment of acetylacetone

The infrared and Raman spectra of acetylacetone and its deuterated analogues have been analyzed by the aid of ab initio calculations at post Hartree-Fock level and considering the spectral behavior upon deuteration. By deconvolution of the infrared spectra of acetylacetone and d6-acetylacetone at 1600 cm(-1) region a broad and strong band is found and correlated with the strong Raman lines observed for these compounds in this region. The broadness of this infrared band at room temperature and it's splitting at low temperature is attributed to free rotation of methyl group attached to carbonyl group at room temperature. Furthermore it is found that all ring modes in 1200-1600 cm(-1) region more or less are mixed with the OH in plane bending motion.     

1,3-Dipolar cycloaddition between substituted phenyl azide and 2,3-dihydrofuran

A theoretical study was performed on the 1,3-dipolar cycloaddition between 2,3-dihydrofuran and substituted phenyl azide using Density Functional Theory (DFT) in combination with a 6-311++G(d,p) basis set. The optimum geometries for reactant, transition state and product, as well as the kinetic data, rate constants and reaction constant (ρ) were investigated to rationalise the substitution effects and reaction rates of the 1,3-dipolar cycloaddition process in various solvents. The DFT calculation and Frontier Molecular Orbital (FMO) theory as well as the atomic Fukui indices show that the electron-withdrawing substituents enhance the reaction constant (ρ > 0), especially in polar aprotic solvents. Consequently, small changes in the rate constant of the reaction in various solvents and geometric similarity between reactants and transition state structures were suggested as the early transition state mechanism for electron-withdrawing substituents. In addition, the slope of the Hammett plot and susceptibility of the reaction to electron-withdrawing substituents in various solvents confirmed the mechanism.     

Enantio- and regioselective heck-type reaction of arylboronic acids with 2,3-dihydrofuran

Reported herein is a protocol for the enantioselective Pd(II)-catalyzed Heck-type reaction between arylboronic acids and 2,3-dihydrofuran. The highest chemical and optical yields were obtained when a Pd(OAc)2/(R)-MeO(biphenylphosphine) or a Pd(OAc)2/(R)-(2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) catalyst and a Cu(OAc)2 reoxidant were employed.     

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.     

Vibrational spectra and assignment for trans-3,4-dichlorocyclobutene. Revised assignment for the cis isomer

A complete assignment of the vibrational fundamentals of trans-3,4-dichlorocyclobutene has been derived from infrared and Raman spectra. These freq     

Palladium nanoparticles: Chemoselective control for reductive Heck with aryl triflates and 2,3-dihydrofuran

The reductive-Heck reaction offers a unique entry to formal Csp²-Csp³ cross-coupling reactions that proceed in the absence of a main group organometallic coupling partner. Consequently, further development of new variants would be transformative. Unfortunately, controlling the relative rates of the organopalladium intermediates has proven difficult with homogenous, single-site Pd catalysts. This work describes a selective reductive Heck reaction catalyzed by Pd-nanoparticles. The reaction works well with electron-deficient aryl triflates at room temperature in the absence of ligands. This work addresses some of the challenges found in the reductive-Heck literature.     

A novel and facile synthesis of 2,3-dihydrofuran derivatives containing trifluoromethyl group

A series of CF₃-containing 2,3-dihydrofuran derivatives were prepared via the reaction of arsonium bromides 1 with β,β-di(trifluoroacetyl)ethylene derivatives 2 in the presence of K₂CO₃, usually in a stereoselective manner with moderate yields. The structures of these compounds were confirmed by ¹H NMR, ¹³C NMR, IR, MS and HRMS as well.     

Vibrational spectrum and internal rotation in 2,5-dimethylpyrazine

The infrared and Raman spectra of 2,5-dimethylpyrazine have been recorded and assigned on the basis of a C_2h molecular geometry previously determined by MINDO/3. The potential energy function corresponding to the internal rotation of both methyl groups has been used to solve the Schrödinger equation, and to obtain the energy levels of that motion on the basis of a molecular symmetry G₃₆. The rotation of each substituent is found to be almost independent of the other.     

2,5-Dimethoxy-2,5-dihydrofuran chemistry: a new approach to 2(5H)-furanone derivatives

2,5-Dimethoxy-2,5-dihydrofuran is a synthetic equivalent of 2(5H)-furanone or 2-trimethylsilyloxyfuran, useful C₄ synthons in the preparation of 5-substituted-2(5H)-furanone derivatives. The reaction conditions adopted allow to obtain different classes of complex and biologically interesting compounds, in only one step, with high yields.     

Structure of 2,3- and 2,5-dihydroxypyridines

On the basis of an analysis of the UV and IR spectra, it was established that 2,3- and 2,5-dihydroxypyridines exist in different forms in neutral, acid, and alkaline media. The electronic absorption spectra of the neutral forms of the molecules and the distribution of the -electron charges in them were calculated by means of the Pariser—Parr—Pople (PPP) MO method. A comparison of the results of the calculations with the experimental UV spectroscopic data demonstrated that the calculations correctly predict the number of ^* absorption bands in the accessible region of the UV spectra and their positions and relative intensities.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 60–63, January, 1973.     

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.     

Microbiological synthesis of 4-hydroxy-5-isopropyl-5-methoxy-2-oxo-2,5-dihydrofuran

M. V. Lomonosov Moscow State University, Moscow 119899, and Chemistry Section, Leipzig University, 7062 Leipzig, Germany. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 711–712, May, 1994.