Regioselective single and double conjugate additions to substituted cyclohexa-2,5-dienone monoacetals

[reaction: see text]. A series of quinone monoacetals bearing electron-withdrawing groups was treated with diethyl malonate and other bifunctional nucleophiles in the presence of KO-t-Bu in THF. Reactions of ethyl 3-nitropropionate or diethyl malonate resulted in single conjugate addition adducts. When ethyl acetoacetate was used as a nucleophile, bridged bicyclic products were obtained in good yields. The regiochemistry of conjugate addition was dependent on the quinone monoacetal substitution.     

Synthesis of (+/-)-epoxysorbicillinol using a novel cyclohexa-2,5-dienone with synthetic applications to other sorbicillin derivatives

A novel route to epoxysorbicillinol as well as dimers of sorbicillin is reported. The synthesis is-in principle-amenable to enantioselectivity. The key step is an oxidative dearomatization to produce a stable and highly malleable p-quinol intermediate, which undergoes a highly diastereoselective epoxidation.     

Inclusion adducts of 4,4-bis(4'-biphenylyl)cyclohexa-2,5-dienone: a clay mimic organic host

In the lamellar architecture of the title crystal structure mediated by C-H...O hydrogen bonds, 1,2-dimethoxyethane and n-hexane are included in the hydrophobic galleries; isostructurality of these clathrates is a unique case of guest mimicry.     

Electronic structure and kinetic behavior of 4-(cycloheptatrienylidene)cyclohexa-2,5-dienone (or [6.7]Quinaren-9-one) and its derivatives)

The conjugative interaction between the two terminal groups in title quinarenone 2 and its chloro- and methoxy-derivatives were evaluated, proving that the diatropicity of the seven-membered ring is a little larger in 2 than in tropone. Some of these quinarenones are also found to exist in equilibrium with their oligomers and show unexpectedly low barriers of rotation about the intercyclic bond.     

Oxidative dearomatization of resorcinol derivatives: useful conditions leading to valuable cyclohexa-2,5-dienones

The oxidative dearomatization of resorcinol derivatives with various oxidants is examined, as is the reactivity of cyclohexa-2,5-dienone that emerged. The results of these studies are presented herein.     

Gas-phase structure and conformational properties of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane

The geometric structure and conformational properties of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (diacetone diperoxide) have been studied by gas electron diffraction and quantum chemical calculations (MP2 and B3LYP methods with 6-31G(d,p) and 6-311+G(2df,p) basis sets). The molecule possesses a chair conformation with C2h symmetry and the following geometric parameters for the six-membered ring (rh1 values) have been determined: O-O = 1.463(5) A, C-O = 1.432 (4) A, O-C-O = 108.2(7) degrees, C-O-O = 107.7(4) degrees, phi(C-O-O-C) = 63.7(4) degrees, and phi(O-O-C-O) = -63.9(4) degrees. A small contribution of less than 3.5% of a twist conformer with C2 symmetry cannot be excluded. Quantum chemical calculations predict a contribution between 1 and 2%. Additional calculations for the parent compound 1,2,4,5-tetroxane (diformaldehyde diperoxide) demonstrate that methyl substitution at the carbon atoms has a minor effect on the ring geometry but a strong effect on the conformational properties. Methyl substitution reduces the energy difference between twist and chair conformers by more than 5 kcal/mol.     

Conformational analysis and rotational barriers of alkyl- and phenyl-substituted urea derivatives

Potential energy surfaces (PES) for rotation about the N-C(sp(3)) or N-C(aryl) bond and energies of stationary points on PES for rotation about the C(sp(2))-N bond are reported for methylurea, ethylurea, isopropylurea, tert-butylurea, and phenylurea, using the B3LYP/DZVP2 and MP2/aug-cc-pVDZ methods. The analysis of alkylureas reveals cis and (less stable) trans isomers that adopt anti geometries, whereas syn geometries do not correspond to stationary points. In contrast, the analysis of phenylurea reveals that the lowest energy form at the MP2 level is a trans isomer in a syn geometry. The fully optimized geometries are in good agreement with crystal structure data, and PESs are consistent with the experimental dihedral angle distribution. Rotation about the C(sp(2))-N bond in alkylureas and phenylurea is slightly more hindered (8.6-9.4 kcal/mol) than the analogous motion in the unsubstituted molecule (8.2 kcal/mol). At the MP2 level of theory, the maximum barriers to rotation for the methyl, ethyl, isopropyl, tert-butyl, and phenyl groups are predicted to be 0.9, 6.2, 6.0, 4.6, and 2.4 kcal/mol, respectively. The results are used to benchmark the performance of the MMFF94 force field. Systematic discrepancies between MMFF94 and MP2 results were improved by modification of several torsional parameters.     

Characterization of 4-(2,3-diphenylcyclopropenylidene)cyclohexa-2,5-dienone. Highly polarized 6,7-diphenyl[3.6]q́uinaren-3-one

The title quinarenone 2 has a pronounced contribution of the dipolar resonance structure to the ground state, and the three-membered ring of $\text{2}$ is more diatropic than that of diphenylcyclopropenone. The quinarenone 2 exists in equilibrium with its oligomer in solution. The excited state properties of 2 have also been described.     

Effect of benzannelation on the conformational flexibility of the rings in oxo, imino, and methylene derivatives of cyclohexa-1,4-diene

The effect of benzannelation on the equilibrium conformation and flexibility of the dihydrocycle in cyclohexa-1,4-dienone,para-quinone, and their imino and methylene analogs was studied by the semiempirical quantum-chemical AM1 method. The equilibrium conformations of the carbonyl derivatives are planar. In the imino- and methylene-substituted analogs, the dihydrocycle adopts a boat conformation due to repulsions between substituted analogs, the dihydrocycle adopts a boat conformation due to repulsions between the hydrogen atoms at the exocyclic double bond and in theperi positions of the benzene rings. Annelation of cyclohexa-2,5-dien-1-one andpara-quinone with benzene rings at the C=C double bonds causes an increase in the conformational flexibility of the partially hydrogenated ring owing to an increase in the bending strain in the first compound and a decrease in the conjugation between the carbonyl groups and the remaining part of the molecule in the second compound. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 388–390, March, 1998.     

Solvatochromicity of 3-hydroxy-4-(1-(2,4-dihydroxyphenyl)-2-hydroxy-2,2-diphenylethylidene)cyclohexa-2,5-dienone for screening of solvents

The quinonic compound 3-hydroxy-4-(1-(2,4-dihydroxyphenyl)-2-hydroxy-2,2-diphenylethylidene)cyclohexa-2,5-dienone (I) is synthesised by the reaction of benzil with 1,3-dihydroxybenzene in basic medium. Solution of this compound shows visibly distinct colour differences in different solvents. From the different absorption maxima of the compound in visible spectra it can be used as an excellent analytical reagent to screen different solvents.     

A new family of pi-conjugated delocalized biradicals: Electronic structures of 1,4-bis(2,5-diphenylimidazol-4-ylidene)cyclohexa-2,5-diene

A new family of pi-conjugated delocalized biradical compound is developed. The solution of 1,4-bis(2,5-diphenylimidazol-4-ylidene)cyclohexa-2,5-diene shows the ESR signal consisting of a moderately broad unresolved line, Delta H(pp) approximately 1 mT, at room temperature. The presence of the thermal equilibrium between a triplet biradical state and a singlet state is confirmed by the ESR measurements, and the spin concentration is determined as 7.90 x 10(21) spin/mol at 300 K. The spin concentration can also be controlled by modifying the molecular planarity. Moreover, the unrestricted DFT/B3LYP calculations suggest the biradical character of the singlet ground state, and the modulation of the energy gap between the singlet state and the triplet state is investigated from the theoretical point of view. Controlling the equilibrium between a diamagnetic state and a paramagnetic state will provide significant progress in the field of biradical chemistry, and the materials with the biradical character in a ground state will lead to a novel development of molecular-based organic magnets.     

Density functional theory studies of conformational stabilities and rotational barriers of 2- and 3-thiophenecarboxaldehydes

The molecular structures, conformational stabilities, and infrared vibrational wavenumbers of 2-thiophenecarboxaldehyde and 3-thiophenecarboxaldehyde are computed using Becke-3–Lee–Yang–Parr (B3LYP) with the 6-311++G** basis set. From the computations, cis-2-thiophenecarboxaldehyde is found to be more stable than the transfer conformer with an energy difference of 1.22 kcal/mol, while trans-3-thiophenecarboxaldehyde is found to be more stable than the cis conformer by 0.89 kcal/mol. The computed dipole moments, structural parameters, relative stabilities of the conformers and infrared vibrational wavenumbers of the two molecules coherently support the experimental data in the literature. The normal vibrational wavenumbers are characterized in terms of the potential energy distribution using the VEDA4 program. The effect of solvents on the conformational stability of the molecules in nine different solvents is investigated using the polarizable continuum model.     

Density functional theory study of the rotational barriers,conformational preference,and vibrational spectra of 2-formylfuran and 3-formylfuran

The torsional potentials, molecular structures, conformational stability, and vibrational wavenumbers for the rotational isomers of 2-formylfuran and 3-formylfuran are computed using the density functional theory (B3LYP) method with the 6-31+G* basis set. All structures are fully optimized and the optimized geometries, rotational constants, dipole moments, and energies are presented. From the computations, both 2-formylfuran and 3-formylfuran are predicted to exist predominantly in trans conformation with a cis–trans rotational barrier of 11.19 kcal/mol and 8.10 kcal/mol, respectively. The vibrational wavenumbers and the corresponding vibrational assignments of the molecules in the C _s symmetry are examined and the infrared spectra of the molecules are simulated using the wavenumbers and the corresponding intensities obtained from the computations. The effect of solvents on the conformational stability of all the molecules in nine different solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide, and water) is investigated. The integral equation formalism in the polarizable continuum model (IEF-PCM) is used for all solution phase computations.     

Hetarylethylene derivatives of 2,5-diaryloxazoles and 2,5-diarloxadiazoles and their luminescence and scintillation properties

A number of new organic luminophores were synthesized via the Wittig reaction from 2-(4-bromomethylphenyl)-5-phenyloxazole or 2-(4-bromomethylphenyl)-5-phenyl-1,3,4-oxadiazole and various heterocyclic aldehydes containing a thiophene ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1267–1270, September, 1986.     

Gas-phase structures of dithietane derivatives, including an electron diffraction study of 1,3-dithietane 1,1,3,3-tetraoxide

The gas electron diffraction structure of 1,3-dithietane 1,1,3,3-tetraoxide has been determined using the SARACEN method to restrain parameters that otherwise could not be refined. Quantum chemical calculations for this species showed that the potential-energy surface was extremely flat, and this was also observed from the diffraction experiments. The difference in goodness of fit for the diffraction experiment between a planar ring and one puckered by up to 9° was very small. Calculations were also performed for a variety of similar species with different numbers of oxygen atoms attached to the sulphur atoms. Topological analysis of the electron density, and electron localisation function studies of the relevant molecules, have given deeper insight into the nature of their bonding, and suggested how spatial localisation of electron pairs may influence the molecular structure.     

Synthesis and spectral-luminescence properties of hetarylethylene derivatives of 2,5-diphenyloxazole and 2,5-diphenyl-1,3,4-oxadiazole

A number of new organic luminophores was synthesized by PO olefination from 2- (4-bromomethylphenyl)-5-phenyloxazole and -1,3,4-oxadiazole and various heterocyclic aldehydes that contain a furan ring. The absorption and fluorescence spectra of the products in toluene, as well as their scintillation characteristics, were measured. The effect of the electronic nature of the substituents on the spectral-luminescence properties of the luminophores is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 617–621, May, 1982.     

Semiempirical calculations of ground state properties and rotational barriers in conjugated ethylenes

Ground state properties of methyl-2-carbomethoxy-3-dimethylaminoacrylate 4, and methyl-2-carbomethoxy-3-(1-aziridino) acrylate 5 were calculated by semiempirical methods and found to be in good agreement with the experiment. Barriers to rotation about the CC double bond and the C-N single bond were also calculated, allowing for structure relaxation in the transition state. A comparison of the calculated and experimental barriers to rotation shows good agreement for the rotation about the C-N bond and poor agreement for the rotation about the CC bond. This discrepancy is explained in terms of solvent stabilization of the polar transition state.