Investigating the mechanism of 1,3,5-cycloheptatriene formation: Condensation of 1-methylethyl 3-oxo-4-(triphenylarsoranylidene)butanoate with 7-methoxy-3,7-dimethyloctanal

Condensation of [3-(1-methylethoxycarbonyl)-2-oxopropyl]triphenylarsonium bromide 8 with 7-methoxy-3,7-dimethyloctanal 10 in the presence of a base gave bis(1-methylethyl) 4,7-dihydroxy-2-(6-methoxy-2,6-dimethylheptyl)-3,5,7-cycloheptatriene-1,3-dicarboxylate 7b. The formation of 7b can be explained by a number of consecutive steps. The mechanism, strongly supported by liquid secondary ion mass spectrometry, suggests that an aldol condensation of the γ-arsonium ylide 2b and the aldehyde 10 takes place as the initiating step and is followed by a Michael addition of the aldol product and the γ-arsonium ylide 2b. Then an intramolecular nucleophilic substitution and elimination of triphenylarsine, followed by base-catalyzed elimination of a second molecule triphenylarsine takes place to produce 7b. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:411–418, 1998     

Bio-inspired hydrogenase models: mixed-valence triion complexes as proton reduction catalysts

Mixed-valence triiron complexes Fe(3)(CO)(7-x)(PPh(3))(x)(μ-edt)(2) (x = 0-2) have been prepared and are shown to act as proton reduction catalysts. Catalysis takes place via an ECEC mechanism with a reduced overpotential of ca. 0.45 V for Fe(3)(CO)(7)(μ-edt)(2) as compared to the corresponding diiron complex.     

3.3]Ferrocenophanes with guanidine bridging units as multisignalling receptor molecules for selective recognition of anions, cations, and amino acids

The synthesis, electrochemical, and optical properties of a new [3.3]ferrocenophane framework in which two ferrocene subunits, with similar electronic environments, are linked through two substituted guanidine moieties, are reported. The receptors 4-7 have been prepared in good yields by the reaction of bis(carbodiimide) 3 with primary amines. This architecture is exceptionally "tunable" because a variety of "legs" may be appended to the basic [3.3]ferrocenophane scaffold to give a wide range of signaling units. These receptors show remarkable ion-sensing properties, due to the presence of a redox active unit (ferrocene), and an amphoteric binding site (guanidine). In this nitrogen-rich structural motif the guanidine bridges act as multipoint binding sites for anions, cations, and amino acids. Sensing of anions takes place both by unprecedented redox-ratiometric measurements (F-, Cl-, AcO-, NO3-, HSO4-, H2PO4-, and HP2O7(3-)), and colorimetric change (F-, AcO-, H2PO4-, and HP2O7(3-)). Sensing and discrimination of amino acids takes place by redox-ratiometric measurements, whereas the recognition of metal cations (Zn2+, Ni2+, and Cd2+) is achieved either by electrochemical or fluorescence measurements. Moreover, the reported receptors display splitting of the oxidation wave of the Fe(II)/Fe(III) redox couple, and form the mixed-valence species 4+* -7+* by electrochemical partial oxidation which, interestingly, show intervalence charge-transfer transitions associated to the appearance of absorption bands in the near infrared spectral region.     

A study of some 1-alkyl-2,3-dihydroimidazo[1,2-a]benzimidazoles

A series of 1-alkyl-7-nitro (and 7-amino)-2,3-dihydroimidazo[1,2-α]benzimidazoles has been prepared. Similarly, a series of 1-alkyl-2,3-dihydroimidazo[1,2-α]benzimidazoles has been prepared. The prototropic tautomerism of this system has been studied. The site of electrophilic attack (alkylation) has been examined. 1-Alkylation takes place under strongly basic conditions and 9-alkylation occurs under neutral conditions.     

Synthesis and antistatic properties of some surface-active perimidine derivatives

Perimidine derivatives containing as substituents high-molecular-weight alkyl, acyl, and perfluoroalkyl groups in positions 1, 2, 4(9) and 6(7) have been synthesized. The sulfonation of perimidines has been performed for the first time using 2-perfluoroalkyl- and 2- undecylperimidines as examples; it takes place exceptionally readily in this series. It has been shown that the best antistatic effect on application to the surface of polymers is given by 2-perfluoroalkyl-perimidine-6(7)-sulfonic acid).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 550–553, April, 1980.     

Die sterischen Bedingungen der Fragmentierungsreaktion I. Teil. Stereoisomere 3-Chlortropane. Fragmentierungsreaktionen, 14. Mitteilung

The steric requirements for the synchronous fragmentation of γ-aminohalides as previously postulated have been confirmed by a study of the solvolysis of stereoisomeric 3β- and 3β-chloro-tropanes and -nortropanes. 3β-chloro-tropanes ( 7 a ) and 3β-chloro-nortropane ( 7 b ), which fulfil the stereoelectronic requirements, undergo quantitative fragmentation in 80 vol.% ethanol. They react 1.35 × 10⁴ and 1.35 × 10³ times, respectively, as fast as the ‘homomorphous’ exo-3-chloro-bicyclo[3.2.1]octane ( 12 a ). Fragmentation therefore takes place by the synchronous mechanism.     

新型层柱微孔材料—钨镓钴杂多阴离子嵌入阴离子粘土的合成、表征及催化研究

新型层柱微孔材料—钨镓钴杂多阴离子嵌入阴离子粘土的合成、表征及催化研究余新武，张继余，张淑云，王恩波（东北师范大学化学系，长春１３００２４）关键词杂多阴离子，嵌入，层柱化合物，催化活性阴离子粘土又称水滑石（ＬａｙｅｒｅｄＤｏｕｂｌｅＨｙｄｒｏｘｉｄｅ...     

Pressurized liquid extraction of isoflavones from soybeans

Isoflavone derivatives from freeze-dried soybeans were extracted by pressurized liquid extraction (PLE) and determined by reverse-phase high performance liquid chromatography (HPLC) with both photo diode array and mass spectrometry (MS) detection. Both real and spiked samples were used in the development of the method.Several extraction solvents (methanol (MeOH) and ethanol (EtOH), 30-80% in water and water), temperatures (60-200 °C), pressures (100-200 atm), as well as the sample size (0.5-0.05 g) and cycle length (5-10 min) were studied for the optimization of the extraction protocol. The optimized extraction conditions for quantitative recoveries were: 0.1 g of sample, 100 °C, three (7 min) static extraction cycles and ethanol 70% as extracting solvent. The stability of the isoflavones during the PLE was also determined. Under PLE conditions, degradation of malonyl glucoside forms of the isoflavones takes place using temperatures higher than 100 °C whereas degradation of glucosides takes place above 150 °C. Using the optimized protocol, isoflavones can be extracted from freeze-dried soybeans without degradation.     

Synthesis and photoinduced energy- and electron-transfer processes of C60-oligothienylenevinylene-C70 dumbbell compounds

Unsymmetric dumbbell molecules based on N-methylpyrrolidine[60]fullerene, oligothienylenevinylenes (nTV; n=2, 4), and N-methylpyrrolidine[70]fullerene, namely, C(60) -nTV-C(70) were synthesized and their photophysical properties were studied. In nonpolar solvents, photoinduced energy-transfer process predominantly takes place from the singlet excited state of nTV to C(60) and C(70) , as was confirmed by time-resolved emission and transient absorption spectroscopy. In polar solvent, charge-separation processes take place instead of energy transfer. The generated charge-separated radical-ion pairs decay to the neutral molecules by a fast charge-recombination process; for n=4, a rate constant of 2×10(7) s(-1) and lifetime of 50 ns were evaluated.     

Synthesis,chemical transformations,and structure of 1,2,3,4-tetrahydrospiro(quinoline-2-cycloalkanes)

The cyclization of 1-(m-toluidino)-1-allylcyclohexane under acid-catalysis conditions gave 4,5- and 4,7-dimethyl-1,2,3,4-tetrahydrospiro(quinoline-2-cyclohexanes). The bromination, nitration, N-acylation, and N-allylation of 4-methyl-1,2,3,4-tetrahydrospiro[quinoline-2-cyclohexane(cyclopentane)] were studied. It was established that nitration takes place In the 6 and 7 positions, while bromination occurs in the 6 and 8 positions. The amino-Claisen rearrangement of N-allyltetrahydroquinolines is accompanied by quantitative allyl-vinyl isomerization. The stereochemistry of the synthesized spiro(tetrahydroquinolinecycloalkanes) was studied by PMR spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 947–952, July, 1991.     

[3.3.2]- and [3.3.3]Propellanes in Reactions with Oxidizing Electrophiles

The structure of [3.3.2]- and [3.3.3]propellanes, their framework analogs, and their radical-cations was investigated by computational methods (BLYP and B3LYP) in the 6-31G* basis set. The reactivity of the propellanes toward model oxidizing electrophiles does not contradict the quantum-chemical calculations. In the case of the tetracyclic framework analog of [3.3.3]propellane the reaction takes place as C—H substitution, whereas in the case of [3.3.2]propellanes it takes place as C—C-oxidative addition.     

1-oxo-2,2,6,6-tetramethyl-4-chloropiperidinium perchlorate. A new facile oxidant for phenol coupling

The title compound (1) oxidizes 2,6-di-tert-butylphenol (2), 2,6-di-tert-butyl-4-methylphenol (3), 2,6-di-tert-butyl-4-(dipnenylmethyl)phenol (4), and p-naphthol (5), to quinones in good yield under mild conditions in acetonitrile. For unsubstituted phenols the reaction takes place in two ways, phenol (6) is oxidized to quinhydrone (7), while the oxidation products of the phenols, α-naphthol, catechol and 2,4-dihydroxyl-naphthol were only polymers.     

Synthesis of new tricyclic phosphines and phosphinites by intramolecular Diels-Alder reactions of trivalent phospholes

Phospholes bearing an allyl-X substituent at phosphorus tend to undergo an intramolecular Diels-Alder cycloaddition (IMDA) leading to the corresponding tricyclic derivative. When X = O or NR, the IMDA easily takes place at room temperature. When X = CH2, the IMDA slowly takes place around 110-140 degrees C, as a function to the substitution pattern of the dienic system. Two tricyclic derivatives (X = O and CH2) have been characterized by X-ray crystal structure analysis of the P-sulfides.     

Regioselective synthesis of (E)-3-[2-(arylmethylene)-1-(arylsulfonyl)hydrazino]-2-propenoates via the reaction of arylsulfonyl hydrazones and alkyl propiolates in the presence of triphenylphosphine

A regioselective method for the synthesis of (E)-3-[2-(arylmethylene)-1-(arylsulfonyl)hydrazino]-2-propenoates is described. The reaction takes place between arylsulfonyl hydrazones and alkyl propiolates in the presence of triphenylphosphine as the catalyst.     

Anion-induced urea deprotonation

The urea-based receptor 1 (1-(7-nitrobenzo[1,2,5]oxadiazol-4-yl)-3-(4-nitrophenyl)urea, L--H), interacts with X- ions in MeCN, according to two consecutive steps: 1) formation of a hydrogen-bond complex [L--H...X]-; 2) deprotonation of L--H to give L- and [HX2]-, as shown by spectrophotometric and 1H NMR titration experiments. Step 2) takes place with more basic anions (fluoride, carboxylates, dihydrogenphosphate), while less basic anions (Cl-, NO2-, NO3-) do not induce proton transfer. On crystallisation from a solution containing L--H and excess Bu4NF, the tetrabutylammonium salt of the deprotonated urea derivative (Bu4N[L]) was isolated and its crystal and molecular structure determined.     

Asymmetric synthesis of succinic semialdehyde derivatives

The nucleophilic Michael addition of 2-(diphenylmethoxymethyl)-1-methyleneamino pyrrolidine 1Dto prochiral aliphatic and aromatic alkylidene malonates 2 takes place in the presence of MgI(2) to afford the corresponding Michael adducts 3 in excellent yields and good selectivities. In the aromatic series, optically pure (de > 98%) major diastereomers (S,S)-3 were isolated in good yields (77-93%) after chromatographic separation. Direct, racemization-free BF(3).OEt(2)-catalyzed thiolysis of compounds 3 afforded dithioacetals 7. These compounds were transformed into malonates 8 and succinic semialdehyde derivatives 9 by Raney Nickel mediated desulfuration or decarboxylation, respectively.     

Thermal and radical polymerization of anthracene acrylates and methacrylates

The thermal and radical-induced polymerizations of 9-anthrylmethyl acrylate ( I ), 9-anthrylmethyl methacrylate ( II ), 1′-(9-anthryl)ethyl acrylate ( III ), and 1′-(9-anthryl)ethyl methacrylate ( IV ) have been studied. It was found that the radical-induced polymerization takes place for the methacrylates only, while thermal polymerization leads to polymers for both types of monomers and takes place by Diels–Alder cycloaddition in the case of acrylates, and by both normal enchainment and Diels–Alder cycloaddition in the case of methacrylates.     

Electronic absorption spectra of the cations and anions formed from pyrrole analogs of the chalcones

The electronic absorption spectra of 29 pyrrole analogs of the chalcones have been studied in solutions of strong acids and alkalies, in which the corresponding cations and anions are formed. It has been shown by means of the IR spectra that the protonation of the pyrrole chalcones takes place at the carbonyl group. Considerations are given of the structure of the organic cations and anions studied and of the characteristic features in the change in their coloration as a function of their chemical structure. Satisfactory correlations have been found between the shift of the absorption frequency of the long-wave band which takes place at the transition from a neutral solution (molecules) to an acid solution (cations) or to an alkaline solution (anions) and Hammett's o constants. Three 3-(4-halophenyl)-1-(2-pyrryl)propenones not previously reported in the literature have been synthesized.     

Electronic absorption spectra of the cations and anions formed from pyrrole analogs of the chalcones

The electronic absorption spectra of 29 pyrrole analogs of the chalcones have been studied in solutions of strong acids and alkalies, in which the corresponding cations and anions are formed. It has been shown by means of the IR spectra that the protonation of the pyrrole chalcones takes place at the carbonyl group. Considerations are given of the structure of the organic cations and anions studied and of the characteristic features in the change in their coloration as a function of their chemical structure. Satisfactory correlations have been found between the shift of the absorption frequency of the long-wave band which takes place at the transition from a neutral solution (molecules) to an acid solution (cations) or to an alkaline solution (anions) and Hammett's o constants. Three 3-(4-halophenyl)-1-(2-pyrryl)propenones not previously reported in the literature have been synthesized.     

Singlet Oxygen-mediated Photobleaching of the Prosthetic Group in Hemoglobins and C-Phycocyanin

Proteins bearing colored prosthetic groups, such as the heme group in hemoglobin or the bilin group in c-phycocyanin, quench singlet oxygen by interactions at the apoprotein and the prosthetic group levels. In both proteins, chemical modification of the chromophore constitutes only a minor reaction pathway. While total deactivation of singlet oxygen takes place with rate constants of 4.0 x 10(9) and 4.2 x 10(8) M-1 s-1 for hemoglobin and phycocyanin, respectively, the bleaching of the chromophore takes place with rate constants of 3.2 x 10(6) and approximately 1 x 10(7) M-1 s-1. Irradiation of phycocyanin with red light bleaches the chromophore with low yields (approximately 0.8 x 10(-4)). Part of this bleaching is mediated by singlet oxygen produced by the irradiation of the bilin group. The low relevance of the singlet oxygen pathway is compatible with a low quantum yield (approximately 10(-3)) of free singlet oxygen production after irradiation of the protein.