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991.
Palladium-catalyzed regio- and stereoselective selenoacylation of allenes with selenol esters proceeded to produce functionalized allyl selenides with the acyl moiety at the inner carbon and the SePh group at the terminal carbon in high yields. A mechanism accounting for the observed regio- and stereoselectivities is proposed based on the results of DFT calculations. 相似文献
992.
Treatment of alkyl halides, including tertiary alkyl bromides, with benzylic or allylic Grignard reagent in the presence of a catalytic amount of silver nitrate in ether yielded the corresponding cross-coupling products in high yields. The coupling reactions of tertiary alkyl halides provide efficient access to quaternary carbon centers. 相似文献
993.
Fujiwara H Wang J Zhao L Nagamochi H Akutsu T 《Journal of chemical information and modeling》2008,48(7):1345-1357
The enumeration of chemical graphs satisfying given constraints is one of the fundamental problems in chemoinformatics. In this paper, we consider the problem of enumerating (i.e., listing) all treelike chemical graphs from a given path frequency. We propose an exact algorithm for enumerating all solutions to this problem on the basis of the branch-and-bound method. To further improve the efficiency of the enumeration, we introduce a new variant of the compound enumeration problem by adding a specification on the number of multiple bonds to the input and design another exact enumeration algorithm. The experimental results show that our algorithms can efficiently solve instances with larger sizes that are impossible to solve by the previous methods. In particular, we apply the latter algorithm to the enumeration problem of the special treelike chemical structures-alkane isomers. The theoretical and experimental results show that our algorithm works at least as fast as the state-of-the-art algorithms specially designed for generating alkane isomers, however using much less memory space. 相似文献
994.
Shuo Wang Prof. Igor Larrosa Prof. Dr. Hideki Yorimitsu Dr. Gregory J. P. Perry 《Angewandte Chemie (International ed. in English)》2023,62(14):e202218371
The potassium salts of carboxylic acids are developed as efficient carboxylating agents through CO2 exchange. We describe these carboxylates as dual-function reagents because they function as a combined source of CO2 and base/metalating agent. By using the salt of a commercially available carboxylic acid, this protocol overcomes difficulties when using CO2 gas or organometallic reagents, such as pressurized containers or strictly inert conditions. The reaction proceeds under mild conditions, does not require transition metals or other additives, and shows broad substrate scope. Through the preparation of several biologically important molecules, we show how this strategy provides an opportunity for isotope labeling with low equivalents of labeled CO2. 相似文献
995.
Ranran Huo Lin Liu Chanika Chanthasa Takuya Okazaki Kazuto Sazawa Kazuharu Sugawara Hideki Kuramitz 《Electroanalysis》2023,35(8):e202200528
A simple electroanalytical method for Cd(II) and Pb(II) detection based on differential pulse anodic stripping voltammetry (DPSV) with in situ prepared antimony-modified glassy carbon rotating disk electrode (in situ Sb-GC-RDE) was developed. The electrochemical detection was performed in a microdroplet (50 μL) of 0.01 M hydrochloric acid that is placed between the electrode surface (top) and a Parafilm®-covered glass slide to maintain a hydrophobic surface (bottom). This method includes a preconcentration process using a membrane filter (MF). The target metal ions were complexed with 1-(2-pyridylazo)-2-naphthol (PAN) as a chelating agent, which was accumulated on the MF via filtration. The RDE microdroplet anodic stripping voltammetry was suitable for the elution and determination of metal ions accumulated on the MF. The in situ preparation of antimony-modified electrode allows the use of common GC electrode with high performance. The detection limits for Cd(II) and Pb(II) were 1.4 and 1.1 μg/L, respectively. The proposed method was successfully used in natural water samples for the simultaneous determination of Cd(II) and Pb(II). 相似文献
996.
Yang-Shin Liu Akira Yamaguchi Yue Yang An Niza El Aisnada Sho Uchida Hideki Abe Shigenori Ueda Kenji Yamaguchi Toyokazu Tanabe Masahiro Miyauchi 《Angewandte Chemie (International ed. in English)》2023,62(17):e202300640
An unexplored tin oxide crystal phase (Sn3O4) was experimentally synthesized via a facile hydrothermal method. After tuning the often-neglected parameters for the hydrothermal synthesis, namely the degree of filling of the precursor solution and the gas composition in the reactor head space, an unreported X-ray diffraction pattern was discovered. Through various characterization studies, such as Rietveld analysis, energy dispersive X-ray spectroscopy, and first-principles calculations, this novel material was characterized as orthorhombic mixed-valence tin oxide with the composition SnII2SnIVO4. This orthorhombic tin oxide is a new polymorph of Sn3O4, which differs from the reported conventional monoclinic structure. Computational and experimental analyses showed that orthorhombic Sn3O4 has a smaller band gap (2.0 eV), enabling greater absorption of visible light. This study is expected to improve the accuracy of hydrothermal synthesis and aid the discovery of new oxide materials. 相似文献
997.
Neya S Suzuki M Ode H Hoshino T Furutani Y Kandori H Hori H Imai K Komatsu T 《Inorganic chemistry》2008,47(22):10771-10778
The iron complex of oxypyriporphyrin, a porphyrinoid containing a keto-substituted pyridine, was coupled with apomyoglobin. The reconstituted ferric myoglobin was found to be five-coordinate without iron-bound water molecules. The anionic ligands such as CN (-) and N 3 (-) bound the myoglobin with high affinities, while neutral imidazole did not. The IR observation indicated that the azide complex was pure high-spin, although the corresponding native protein was in the spin-state equilibrium. The reduced myoglobin was five-coordinate but exhibited no measurable affinity for O 2. The affinity for CO was lowered down to 1/2400 as compared with native myoglobin. These anomalies were ascribed to the deformation in the iron coordination core after the replacement of one of the four pyrroles with a larger pyridine ring. The ligand binding analyses for the ferric and ferrous myoglobin suggest that the proximal histidine pulls the iron atom from the deformed core to reduce the interaction between the iron and exogenous ligands. Similarity of the reconstituted myoglobin with guanylate cyclase, a NO-responsive signaling hemoprotein, was pointed out. 相似文献
998.
A novel dimeric diarylheptanoid, (5R,5′R)‐7,7′‐(6,6′‐dihydroxy‐5,5′‐dimethoxy[1,1′‐biphenyl]‐3,3′‐diyl)bis[5‐methoxy‐1‐phenylheptan‐3‐one] ( 1 ), and two new diarylheptanoids, (4E,6R)‐6‐hydroxy‐7‐(4‐hydroxy‐3‐methoxyphenyl)‐1‐phenylhept‐4‐en‐3‐one ( 2 ) and (4E,6R)‐6‐hydroxy‐1,7‐diphenylhept‐4‐en‐3‐one ( 3 ), together with seven known diarylheptanoids, were isolated from the rhizomes of Alpinia officinarum. Their structures were elucidated by application of extensive spectroscopic analyses and the modified Mosher method. 相似文献
999.
Koike T Yokota S Fujiwara H Sugimoto T Noguchi S de Caro D Valade L 《Inorganic chemistry》2008,47(16):7074-7076
Electrochemical oxidation of a bent donor molecule, ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolmethide ( 2), in chlorobenzene (PhCl)/ethanol containing NBu 4FeCl 4 as a supporting electrolyte is performed using an undoped silicon wafer electrode. Black crystals of 2 6.Fe 2OCl 6.2PhCl are obtained that have a different molecular formula from that of 2 2.FeCl 4 crystals obtained previously using a platinum rod electrode. The new crystal has a structure composed of alternately stacked layers of 2 molecules and Fe 2OCl 6 (2-) ions, whose Fe-O-Fe bond is completely linear and for which the geometry around the Fe atom is almost tetrahedral. The electrical resistivity decreases with temperature until ca. 200 K, but below this temperature, it gently increases. The magnetic susceptibility (chi p) observed can be described by the sum of chi p obeying a Curie-Weiss law for the impurity spins and of chi p obeying a dimer model with a spin-exchange integral ( J approximately -180 K) in each Fe 2OCl 6 (2-) ion, which is also weakly coupled to neighboring Fe 2OCl 6 (2-) ions through an additional exchange interaction. 相似文献
1000.
Harada T Muramatsu K Mizunashi K Kitano C Imaoka D Fujiwara T Kataoka H 《The Journal of organic chemistry》2008,73(1):249-258
Atom-economical carbocyclization reactions of omega-iodo-1-alkynes and 1,omega-diiodo-1-alkynes to give products with incorporation of iodine atoms is described. Cycloisomerization of 2-(2-propynyloxy)ethyl iodides is initiated by a catalytic amount of LDA to give 3-(iodomethylene)tetrahydrofurans in high yields. Upon treatment of with a catalytic amount of 1-hexynyllithium, 1,omega-diiodo-1-alkynes efficiently undergo cycloisomerization to give (diiodomethylene)cycloalkanes. The diiodomethylene products are also obtained by iodine atom-transfer-type cyclization of omega-iodo-1-alkynes, using 1-iodo-1-hexyne as an external iodine atom source. Bromine atom-transfer and proton-transfer cyclization proceed as well by employing 1-bromo-1-octyne and 1-octyne, respectively. These reactions are proposed to proceed through a carbenoid-chain process involving exo-cyclization of the lithium acetylide intermediates to give Li,I-alkylidene carbenoids. It is shown that the exo-cyclization proceeded stereospecifically through inversion of the stereochemistry at the electrophilic carbon. 相似文献