bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of the Selective O-Alkylation and Dealkylation of Flavonoids. XXI. A Convenient Method for Synthesizing 3,5,7-Trihydroxy-6,8-dimethoxyflavones and 5,7-Dihydroxy-3,6,8-trimethoxyflavones
Authors: Horie Tokunaru , Kitou Takeshi , Kawamura Yasuhiko , Yamashita Kazuyo 
Published: June 2006

Abstract
The Friedel–Crafts acetylation with boron trifluoride was studied and it was found that 1-(2,4-dihydroxy-3,5,6-trimethoxyphenyl)ethanone was conveniently synthesized from 2,3,5,6-tetramethoxyphenyl acetate in a mixture of acetic anhydride and acetic acid. 1-[2-Hydroxy-3,5,6-trimethoxy-4-(methoxymethoxy)phenyl]ethanone was cyclized to 7-hydroxy-5,6,8-trimethoxyflavone by using the Baker–Venkataraman transformation. The 7-benzyl ether of the flavone was oxidized with dimethyldioxirane and then treated with a small amount of p-toluenesulfonic acid to give 7-benzyloxy-3-hydroxy-5,6,8-trimethoxyflavone, which was converted into the methyl ether and tosylate. The 5-methoxy group in the methyl ether or tosylate was selectively cleaved with anhydrous aluminum bromide in acetonitrile under mild conditions to give the corresponding 5-hydroxyflavones and the latter compound with a 3-tosyloxy group was smoothly converted into the 3,5-dihydroxyflavone by hydrolysis with potassium carbonate in methanol. The hydrogenolysis of the 7-benzyloxy-3,5-dihydroxyflavone and its 3-methyl ether afforded quantitatively 3,5,7-trihydroxy-6,8-dimethoxyflavone and its 3-methyl ether. The process was suitable as a general method for synthesizing 3,5,7-trihydroxy-6,8-dimethoxyflavones and their 3-methyl ethers and the six flavones were synthesized for the clarification of their 1H and 13C NMR, MS, and UV spectral properties.
Mass-Spectrometric Study on Ion–Molecule Reactions of CF3+ with Monosubstituted Benzenes Carrying a Carbonyl Group at Near-Thermal Energies
Authors: Tsuji Masaharu , Aizawa Masato , Nishimura Yukio 
Published: June 2006

Abstract
The gas-phase ion–molecule reactions of CF3+ with five monosubstituted benzenes carrying a carbonyl group (PhCOX: X = H, CH3, C2H5, OCH3, OC2H5) have been studied at near-thermal energies using an ion-beam apparatus. The major product channel for PhCHO, PhCOCH3, and PhCOOCH3 is electrophilic addition to the O-atom leading to initial adduct ions, which are 80.3—95.0% of the total product ions. Although no initial adduct ions are observed for PhCOC2H5 and PhCOOC2H5, major product ions are formed by electrophilic addition to the O-atom followed by dissociation and molecular eliminations. The reaction mechanism is discussed based on product ion distributions and semi-empirical calculations of the energies of intermediates and products. The results obtained are compared with reported ion-cyclotron-resonance data for aliphatic carbonyl compounds.
Activation of C–O and C–N Bonds in Allylic Alcohols and Amines by Palladium Complexes Promoted by CO2. Synthetic Applications to Allylation of Nucleophiles, Carbonylation, and Allylamine Disproportionation
Authors: Sakamoto Masato , Shimizu Isao , Yamamoto Akio 
Published: June 2006

Abstract
The direct activation of the C–O bonds in allylic alcohols catalyzed by palladium complexes has been accelerated by carrying out the reactions under CO2. On reaction with diethylamine, allyl alcohol can be converted into N,N-diethylallylamine in the presence of palladium complexes at room temperature under normal pressure of carbon dioxide. Allylation of various carbon nucleophiles such as β-keto esters and β-diketones can be achieved by using allylic alcohols directly in the presence of palladium complexes and CO2. Direct carbonylation of allylic alcohols into unsaturated carboxylic acids can be catalyzed by palladium complexes under the pressure of CO and CO2. Disproportionation of diallylamine into triallylamine and allylamine is also catalyzed by palladium complexes in the presence of CO2. On the basis of studies on the behavior of η3-allylpalladium hydrogencarbonate complexes with the nucleophiles, mechanisms are proposed to account for the palladium-catalyzed allylation processes influenced by CO2.
NAD(P)+–NAD(P)H Models. 86. Nonsteric Stereochemistry in Hydride-Transfer to Sulfinylpyridinium Ion
Authors: Ohno Atsuyoshi , Yamazaki Norimasa , Okamura Mutsuo , Kawai Yasushi , Tsutsumi Akihiro , Mikata Yuji , Fujii Masayuki 
Published: June 2006

Abstract
The molecular structure of an enantiomer of nicotinamide coenzyme analog 1 has been determined by X-ray crystallography with the absolute configuration being established by the anomalous dispersion effects of all non-hydrogen atoms: (+)-1 exhibits (S)-form sticking the sulfinyl S–O out of the re face. The stereochemistry of the hydride-transfer reaction between the chiral coenzyme analogs, 1 and MenPNPH, was studied. The hydride from (S)- or (R)-MenPNPH, respectively, transfers to (S)- or (R)-1, affording the dihydropyridine compound syn-2 predominantly: That is, the reaction takes place in the face occupied by the sulfinyl oxygen. On the other hand, the transfer to (R)- or (S)-1 mainly takes place so as to afford anti-2. It has been deduced that (S)-1 reacts with (S)-MenPNPH more than twice as fast as (R)-1 does or vice versa. It has also been elucidated that the amide oxygen in MenPNPH points to 1 exclusively at the transition state of the reaction, regardless the configuration of the reagents. The intermolecular arrangement at the transition state of the reaction is discussed.
Peptide Synthesis in Aqueous Solution. V. Properties and Reactivities of (p-Hydroxyphenyl)benzylmethylsulfonium Salts for Direct Benzyl Esterification of N-Acylpeptides
Authors: Nakata Takashi , Nakatani Masaru , Takahashi Masatoshi , Okai Jiro , Kawaoka Yoshiaki , Kouge Katsushige , Okai Hideo 
Published: June 2006

Abstract
Some (p-hydroxyphenyl)benzylmethylsulfonium salts were prepared. These compounds generated a benzyl cation and converted not only N-acylamino acids but also N-acylpeptides into their corresponding benzyl esters without causing the racemization.
Rh(I)-Catalyzed Dehydrogenative Silylation of Divinylsilanes with Dimethylphenylsilane
Authors: Kawanami Yukio , Yamamoto Keiji 
Published: June 2006

Abstract
Rh(I)-catalyzed dehydrogenative silylation was selectively carried out by using divinylsilanes and half an equimolar amount of trialkylsilanes under ambient conditions to give 1,2-disilylethene and ethylvinylsilane derivatives in equimolar amounts. The mechanistic aspects for the dehydrogenative silylation were discussed in terms of the consecutive migratory insertions of the alkene moiety into both Rh–Si and Rh–H bonds which are formed by an oxidative addition of the hydrosilane to the Rh(I) catalyst precursor.
Chromium-Binding Ability of Tannin in Water-Extracts from Withered Oak Leaves
Authors: Arakawa Hirohumi , Watanabe Norimoto 
Published: June 2006

Abstract
Reaction mixtures containing constant amounts of water-extract from withered oak leaves and various concentrations of potassium chromate were incubated, and each reaction mixture was fractionated by a Sephadex G-25 column. The concentrations of the Cr-tannin obtained in the fractions were determined. Then the Cr-binding ability of the tannin was examined by apparent stability constants and Cr-complexing capacities, following construction of a Scatchard plot which adopts a two-site model. The tannin was shown to have two-classes of Cr-binding sites. Based on the Cr-complexing capacities, 1 mg tannin was shown to bind about 0.5 mg of reduced Cr. Moreover, functional groups contributing to the complexation with Cr were investigated by FTIR and pH titration. The relationship between the Cr-complexing ligans in the two sites and the functional groups in the tannin was also investigated. Finally, Cr ion species which emerged during the reaction between chromate and the tannin were determined by EPR. The spectra showed a sharp signal attributable to Cr(V) and a broad one assignable to Cr(III). Thus, it can be speculated that the tannin most probably forms a final Cr(III)–tannin via Cr(V) species.
Mechanism of Chemiluminescence Reaction between Hypobromite and Ammonia or Urea
Authors: Hu Xincheng , Takenaka Norimichi , Kitano Masaru , Bandow Hiroshi , Maeda Yasuaki 
Published: June 2006

Abstract
The reaction kinetics, the chemiluminescence spectra, the products, and the lifetimes of emission species for the chemiluminescence reaction between hypobromite and ammonia or urea in an alkaline aqueous solution were investigated. Results show that the reaction mechanism for ammonia chemiluminescence is different from that for urea. The reaction of ammonia and hypobromite produces NO2 in the gaseous phase and NO2− in solution; however, the reaction of urea and hypobromite does not. For the reaction of ammonia and hypobromite, chemiluminescence intensity obeys 1.5 order kinetics for hypobromite concentration when ammonia is in excess, but the reaction of urea and hypobromite obeys second order kinetics for hypobromite when urea is in excess. The spectrum of the chemiluminescence from the ammonia and urea with hypobromite shows a maximum intensity at 710, and at 510 nm, respectively. The chemiluminescence lifetimes of the emission species were 0.056 and 0.092 s for the reaction of ammonia and the reaction of urea, respectively. The chemiluminescence species of the reaction between hypobromite and ammonia seems to be excited NO2, that for urea seems to be excited N2.
Insertion vs. Abstraction in the Reactions of NH(a1Δ, v = 0, 1) with H2 and D2
Authors: Yunoki Kumi , Tezaki Atsumu , Yokoyama Keiichi , Matsui Hiroyuki 
Published: June 2006

Abstract
Gas-phase reactions of NH(a1Δ, v = 0,1) + H2 (1) and NH(a1Δ, v = 0,1) + D2 (2) were studied in the photolysis of HNCO/H2 (or D2) mixtures. NH(a1Δ) and product H (D) atom were detected by UV and vacuum-UV laser-induced fluorescence. The observed rate constants at room temperature (295 ± 2K) and activation energies in the range of 295 — 407 K were;

in units of 10−12 cm3 molecule−1 s−1 and kJ mol−1. The product branching ratio in reaction 2 was determined to be [D]/[H] = 3.2 ± 0.76, in which no temperature dependence was indicated. These results are consistent with insertion mechanism having a loose entrance transition state structure, which is suggested by ab initio CI calculations. In contrast, the contribution of direct abstraction channel is supposed to be negligibly small.
Anaerobic Solid-Phase Thermal Configurational Transformations of Cobalt(II) Complexes
Authors: El-Behairy Mostafa 
Published: June 2006

Abstract
New examples of thermal tetrahedral-to-octahedral transformation were discovered and studied in the thermal reactions of disodium tetrakis(aryloxo)cobaltate(II) complexes, of the formula Na2[Co(OAr)4(thf)m]·nthf (OAr = o-chloro-, o-bromo-, m-chloro-, p-bromo-, 2,4-dichloro-, 2,4-dimethyl- or 2,6-dichlorophenoxo; m = 2 for all complexes except for 2,4-dimethylphenoxo complex where m = 0; thf: tetrahydrofuran; n = 1—3), in the solid phase. With one exception, the original complexes were all violet colored and have octahedral configurations. The exception is Na2[Co(2,4-Me2C6H3O)4]·thf, which has an intense blue color and its electronic and magnetic data are characteristic of tetrahedral cobalt(II). The aryloxo complexes of 2,6-dichloro-, m-chloro-, and p-bromophenoxo show a two-step thermochromism, violet → blue → rose, upon heating. These steps correspond to structural changes to tetrahedral thf-free complexes and then to aryloxo bridged polymers with octahedral cobalt(II) ions, respectively. o-Chloro- and o-bromophenoxo complexes underwent only thermal desolvation–polymerization, which occurs in one step, changing directly into the rose aryloxo-bridged polymers. 2,4-Dichlorophenoxo complex shows only one-step thermochromism, violet → blue, thus changing from the octahedral to tetrahedral configuration. The remainder complex, of 2,4-dimethylphenoxo, does not show any color changes and retained its tetrahedral configuration until it decomposed. The reverse changes of the thermal products to the original complexes proceed on standing under dry thf atmosphere, for some hours or days.
Kinetics and Thermodynamics of the Racemization of Tris(l-valinato)chromium(III) Complexes in N,N-Dimethylformamide
Authors: Nakata Ryuji , Yano Masatoshi , Ochi Yukari , Hatanaka Naomi , Oki Hisaya 
Published: June 2006

Abstract
Racemization between fac-Λ-(+)546- and fac-Δ-(−)546-[Cr(val)3] (1 and 2) was studied in N,N-dimethylformamide (DMF). These complexes were preferentially converted into bis-type complexes, Λ-(+)546- and Δ-(−)546-[Cr(val)2(val-N)DMF] (4 and 3), and an equilibrium comprising these four species was established. In order to determine the equilibrium constants, rate constants, and activation parameters in a proposed square-network reaction system, the mole fractions of four species with time in reacting solutions at 40, 50, and 60 °C were determined by liquid chromatography. The reaction processes are discussed based on the obtained values.
Synthesis and Structural Characterization of Praseodymium(III) and Neodymium(III) Complexes of Tripodal Tris[2-(salicylideneamino)ethyl]amine
Authors: Kanesato Masatoshi , Yokoyama Toshiro , Itabashi Osamu , Suzuki Toshishige M , Shiro Motoo 
Published: June 2006

Abstract
The preparation and characterization of praseodymium(III) and neodymium(III) complexes of heptadentate (N4O3) ligand trensal, tris[2-(salicylideneamino)ethyl]amine (H3L1), have been studied. These complexes (PrL1 and NdL1) were prepared by the reaction of the praseodymium(III) or neodymium(III) complex of 1,9-bis(2-aminoethyl)-1,4,6,9,12,14-hexaazacyclohexadecane with salicylaldehyde in acetonitrile. Alternatively, the reaction of tris(2-aminoethyl)amine and salicylaldehyde in the presence of praseodymium(III) or neodymium(III) salt in acetonitrile also gave praseodymium(III) and neodymium(III) complexes of trensal. The molecular structures of PrL1 and NdL1 were determined by X-ray structural analysis; these are rare examples of lanthanide heptadentate complexes in which the metal ions are coordinated by the four nitrogen atoms and the three oxygen atoms. The crystals of Pr(C27H27N4O3)·0.5CH3CN and Nd(C27H27N4O3)·0.5CH3CN are both trigonal, space group , a = 13.713(2), c = 8.093(3) Å, U = 1318.0(7) Å3, Z = 2 for [PrL1]·0.5CH3CN, and a = 13.724(3), c = 8.067(3) Å, U = 1315.8(7) Å3, Z = 2 for [NdL1]·0.5CH3CN. The structures were solved by heavy-atom Patterson methods and expanded using Fourier techniques; they were then refined by full-matrix least-squares procedures to R = 0.033 and Rw = 0.043 for 1547 observed reflections with I ≥ 3σ(I), R = 0.028 and Rw = 0.039 for 1923 observed reflections with I ≥ 3σ(I) for [PrL1]·0.5CH3CN and [NdL1]·0.5CH3CN, respectively. The individual metal ions and the apical nitrogen atoms lie on a 3-fold axis in each crystal; the molecules possess a C3 molecular symmetry.
New Xenia Diterpenoids from a Soft Coral, Xenia Species Containing Fatty Acyl Side Chains
Authors: Iwagawa Tetsuo , Amano Yasuhisa , Nakatani Munehiro , Hase Tsunao 
Published: June 2006

Abstract
Seven new diterpenoids with an opened A-ring containing an aliphatic acid, called azamilides A—G (1—7), have been isolated from an acetone extract of Xenia sp. and their structures elucidated on the basis of spectroscopic analysis.
Mass-Spectrometric Study on Ion-Molecule Reactions of CF3+ with Furan and Thiophene at Near-Thermal Energies
Authors: Aizawa Masato , Tsuji Masaharu , Nishimura Yukio 
Published: June 2006

Abstract
The branching ratios of product ions for the reactions of CF3+ with furan and thiophene were determined by using an ion-beam apparatus. The main reaction channels proceed via α- and β-trifluoromethylated intermediates (C-adducts), followed by HF elimination, CO elimination, and CO + HF elimination for furan, and followed by HF elimination for thiophene. Semiempirical MNDO calculations of heats of formation of various intermediates and products were carried out to explore possible mechanisms. It was concluded that the CO and CO + HF eliminations for furan occur through a cleavage of a C–O skeletal bond of the C-adducts. The lack of CO and CO + HF elimination channels for thiophene was explained by the fact that the ring-opening and ring-contraction channels are energetically closed.
Alkylation of 1-[N-(Hydroxymethyl)-N-methylamino]-4-quinolones. An Improved Preparation of Intermediates for Novel Potent Tricyclic Quinolone Antibacterial Agents
Authors: Barrett David , Sasaki Hiroshi , Kinoshita Takayoshi , Tsutsumi Hideo , Sakane Kazuo 
Published: June 2006

Abstract
A new and improved method for the preparation of the key cyclization precursors for novel pyrido[3,2,1-ij]cinnoline antibacterial agents that avoids the use of di-t-butyl methylenemalonate is described. The key process is the alkylation of 1-[N-(hydroxymethyl)-N-methylamino]-4-quinolones with di-t-butyl malonate via the intermediate chloromethyl derivatives. Unexpectedly, this process produced labile pyrazolo[1,5-a]quinoline derivatives that were subsequently shown to undergo ring opening and cyclization to C8 to produce the pyrido[3,2,1-ij]cinnoline key intermediates.
cine-Substitution of 1-Methyl-3,6,8-trinitro-2-quinolone
Authors: Nishiwaki Nagatoshi , Tanaka Aya , Uchida Mitsue , Tohda Yasuo , Ariga Masahiro 
Published: June 2006

Abstract
cine-Substitution of 1-methyl-3,6,8-trinitro-2-quinolone by 1,3-dicarbonyl compounds in the presence of NEt3 occurred efficiently, affording 4-functionalized 6,8-dinitro-2-quinolone derivatives. The addition intermediate was isolated in the reaction with CH2(CO2Et)2 and EtONa. Conversion of the isolated intermediate into the cine-substituted product was performed. These results indicate that the present cine-substitution proceeds by the addition-elimination mechanism.
Synthesis of [Hexafluorovalyl1,1′]gramicidin S
Authors: Arai Toru , Imachi Takashi , Kato Tamaki , Ogawa H Iyehara , Fujimoto Tsutomu , Nishino Norikazu 
Published: June 2006

Abstract
[Hexafluorovalyl1,1′]gramicidin S (8), in which two valine residues in the natural gramicidin S were replaced by l-hexafluorovaline (Hfv) residues, was synthesized by the solid-phase-synthesis and cyclization-cleavage method on benzophenone oxime resin. Though the racemic hexafluorovaline derivative was employed for the peptide synthesis, the desired product was isolated in moderate yield, probably reflecting the stable cyclic structure of 8. CD and 1H NMR spectra indicated that the conformation of 8 is similar to that of gramicidin S. The two β-turn structure and antiparallel β-sheet structure with four intramolecular hydrogen bondings were maintained in spite of introducing the hexafluorovaline residues. The dye-release experiment from lecithin vesicle and antimacrobial activity assay also indicated that 8 showed membrane-disturbing activity like gramicidin S, although the activity of 8 was somewhat weaker than gramicidin S.
Synthesis of Macrocyclic Amides and Their Intermediate 2 : 1 and 3 : 2 Reaction Compounds from Diethyl Oxalate and Ethereal Oxygen-Containing Diamines
Authors: Fukada Naoaki , Ohtsu Tadashi , Miwa Masamichi , Mashino Masayuki , Takeda Yasuyuki 
Published: June 2006

Abstract
The reaction of diethyl oxalate with ethereal oxygen-containing diamines under high-dilution conditions gave 2 : 2 reaction products, 22-, 28-, and 34-membered macrocyclic amides in good yields. From the 2 : 1-mixed reaction between diethyl oxalate and the diamines, acyclic 2 : 1 and 3 : 2 reaction products were isolated at a ratio of ca. 9 : 1. The intermediate 2 : 1 and 3 : 2 reaction products led to the 2 : 2 reaction products mentioned above and the 3 : 3 reaction products, 33-, 42-, and 51-membered macrocyclic amides, respectively, upon reaction with additional corresponding diamines. Also, other macrocyclic amides were synthesized by combining the 2 : 1 reaction products and diamines.
An Acylative C–C Single-Bond Cleavage and a Self-Cyclization of Ethyl 2-(Trimethylsilylmethyl)penta-2,4-dienoate or Its Free Acid under Ritter Condition
Authors: Kuroda Chiaki , Mitsumata Naoko , Tang Chen Ying 
Published: June 2006

Abstract
An acylative C(3)–C(4)-bond cleavage of ethyl 4,5-disubstituted 2-(trimethylsilylmethyl)penta-2,4-dienoate occurred to give an ethyl 2-(2-oxoalkyl)acrylate by treatment with trifluoromethanesulfonic acid in nitriles. A self-cyclization also occurred to give a 5,5-disubstituted 3-methylenetetrahydrofuran-2-one when the reactions were carried out in bulky nitriles. Only self-cyclization proceeded when the corresponding 4,5-disubstituted 2-(trimethylsilylmethyl)penta-2,4-dienoic acid was treated in acetonitrile. The reaction mechanism is described.
Preparation and Properties of Monovalent Anion Permselective Anion Exchange Membranes
Authors: Takata Kuniaki , Hanada Fumio , Kagiyama Yasuhiro , Sata Toshikatu 
Published: June 2006

Abstract
In order to prepare a monovalent permselective anion exchange membrane, the surface of a precursor membrane, which was prepared from a membranous copolymer of chloromethylstyrene (CMS) and divinylbenzene (DVB) in the presence of poly(vinyl chloride), was treated with various amino compounds; the chloromethylphenyl groups in the membrane were then reacted with trimethylamine so as to introduce (trimethylammoniomethyl)phenyl groups. The anion exchange membranes which were modified with tetraethylenepentamine and 4-vinylpyridine showed a chloride anion permselectivity versus that of a sulfate one in electrodialysis. It was thought that the reaction between these amines and the chloromethylphenyl groups formed a higher crosslinking structure on the surface of the membrane.
Kinetics of the Photobromination of Fluoroethane. Estimate of the C–H Bond Dissociation Energies and the Heats of Formation of the CH3CHF and CH2CH2F Radicals
Authors: Miyokawa Kikuo , Ozaki Shigeko , Yano Takayuki 
Published: June 2006

Abstract
The gas-phase photobromination of fluoroethane was investigated in the temperature range 80—150 °C in both the presence and absence of chloroethane as an external competitor. The rate constant for α-hydrogen abstraction in CH3CH2F was redetermined relative to that in CH3CH2Cl, and the abstraction of β-hydrogen was measured in the internal competition. The relative rates were combined with the known rate parameters for the bromination of C2H6 to obtain the absolute rate constants (cm3 mol−1 s−1): k(α) = (6.50 ± 3.58) × 1012 exp [−(10360 ± 370)/RT] and k(β) = (3.42 ± 1.95) × 1012 exp [−(12950 ± 390)/RT].
Using a justifiable approximation concerning the magnitude of the activation-energy difference for the reverse reactions between any two competitors with similar complexity the following thermochemical quantities (kcal mol−1) have been derived: ΔH°f(CH3CHF) = −16.8 ± 2, ΔH°f(CH2CH2F) = −14.2 ± 2, D°(CH3CHF–H) = 98.2 ± 2, D°(CH2FCH2–H) = 100.8 ± 2, and D°(CH2CH2–F) = 45.6 ± 2. The influence of halogen substitution on the rate parameters of hydrogen abstraction from monohaloethanes is discussed.