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251.
Naoki Mori Chiaki Mase Hidenori Watanabe Hirosato Takikawa 《Tetrahedron letters》2018,59(26):2600-2603
Pseudolaric acids A (1) and B (2) are diterpene acids isolated from the root bark of Pseudolarix kaempferi as the main biologically active constituents of tujinpi, a traditional Chinese medicinal herb. Studies toward the total synthesis of 2 are described. The unusual trans-fused [5–7] ring system in the core structure of 2 was successfully synthesized via Dieckmann condensation. 相似文献
252.
Koichi Mikami Kohsuke Aikawa Satoshi Kainuma Yuji Kawakami Takao Saito Noboru Sayo Hidenori Kumobayashi 《Tetrahedron: Asymmetry》2004,15(24):3885-3889
Chiral dicationic SEGPHOS–Pd(II) complex gives high chemical yield, (E)-olefin selectivity, anti-diastereoselectivity, along with high enantioselectivity even with less reactive mono- and 1,2-disubstituted olefins in this much less reactive ketone-ene reactions. The high levels of enantioselectivity not only in carbonyl-ene but also in Friedel–Crafts reactions stem from the effective shielding with diphenyl groups on phosphines caused by the narrow dihedral angle of metal complexes with SEGPHOS. 相似文献
253.
Ueda H Kaneda N Kawanishi K Alves SM Moriyasu M 《Chemical & pharmaceutical bulletin》2002,50(3):403-404
From the 80% EtOH extract of the bark of Ceiba pentandra (L.) Gaertner, a new isoflavone glycoside was isolated along with known isoflavones, vavain and vavain glucoside. The structure was elucidated by spectroscopic analysis as 5-hydroxy-7,4',5'-trimethoxyisoflavone 3'-O-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside. 相似文献
254.
Numerical Hartree-Fock (NHF) calculations have been performed for 332 ground and low-lying excited states of the fifth period atoms Rb through Xe, with our special interest in the states arising from the 5s
24d
m
, 5s
14d
m
+1, and 5s
0 4d
m
+2 configurations of the second row transition metal atoms. Among various properties, orbital energies and mean values ofr of the outermost orbitals of each symmetry are presented as well as total energies. It is discussed in some detail why the second row transition metal atoms have a tendency to prefers
1
d
m
+1 as the ground configuration in contrast to the preferreds
2
d
m
configuration in the first row transition metal atoms. Our systematic NHF computations reported in this and the previous papers conclude that the Hartree-Fock method correctly predicts the experimental ground state of the atoms He through Xe with the sole exception for Zr. 相似文献
255.
Iwamoto T Masuda H Ishida S Kabuto C Kira M 《Journal of the American Chemical Society》2003,125(31):9300-9301
The reactions of stable cyclic dialkylgermylene 2 and dialkylstannylene 3 with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical (2 equiv) gave the corresponding 1:2 adducts 4 and 5, respectively, which were characterized by NMR, MS, and X-ray analyses. The kinetics of the stepwise addition of two TEMPO molecules to germylene 2 revealed that the initial addition of TEMPO to 2 was 1010 times slower than the second TEMPO addition to the resulting germyl radical. The origin of the rate difference was discussed on the basis of the qualitative perturbation theory. In contrast to the reactions of 2 and 3, the reaction of dialkylsilylene 1 with TEMPO gave an interesting 1,3-dioxadisiletane derivative. 相似文献
256.
Masaki Mifune Hidenori Kamiguchi Seigo Kuremoto Ikuko Tsukamoto Youji Kitamura 《Talanta》2007,71(1):456-461
To reveal an enzyme-like catalytic activity of metal-octabromo-tetrakis(sulfophenyl)porphines (M-OBPSs), their peroxidease-like catalytic activity on linoleate hydroperoxide (LOOH) were evaluated on the basis of dye-formation in the coloring reaction between N,N-diethylaniline and 4-aminoantipyrine that yields a quinoid-type dye. Among M-OBPSs tested, Mn3+-OBPS allowed to produce the largest amount of dye. The optimal conditions of the coloring reaction catalyzed by Mn3+-OBPS for the determination of LOOH were determined. A good linear calibration curve was obtained in the concentration range of 0.025-0.4 μmole LOOH with good reproducibility (coefficient of variance = 1.23%), suggesting that Mn3+-OBPS is a good artificial mimesis of the peroxidase for LOOH. In addition, Mn3+-OBPS was highly specific for LOOH even in the presence of cumene hydroxyperoxide or hydrogen peroxide. It was revealed that the peroxidase-like activity of Mn3+-OBTP is attributable to the redox cycle of Mn3+ ↔ Mn4+. 相似文献
257.
[reaction: see text] A diastereoselective total synthesis of securinine in optically pure form was achieved by employing ring-closing metathesis of the corresponding dienyne compound as a key step. 相似文献
258.
Serricornin, the sex pheromone of Lasioderma serricorne F, was synthesised in 7.6% overall yield starting from methyl (R)-3-hydroxypentanoate of microbial origin. Its (4R,6S,7S)-isomer was also synthesised. 相似文献
259.
Toshio Honda Hidenori Namiki Masayuki Watanabe Hirotake Mizutani 《Tetrahedron letters》2004,45(27):5211-5213
The first diastereoselective chiral synthesis of (+)-viroallosecurinine, isolated from Securinega virosa as a cytotoxic alkaloid, was achieved by using a chelation-controlled addition of an alkyne moiety to the corresponding ketone, and a ring-closing metathesis, as key reactions. 相似文献
260.
Toshikatsu Koga Hidenori Aoki J. M. Garcia de la Vega Hiroshi Tatewaki 《Theoretical chemistry accounts》1997,96(4):248-255
Relativistic corrections to ionization potentials (IPs) and electron affinities (EAs) of atoms with an atomic number Z≤54 are examined based on the first-order perturbation theory with an approximate Schr?dinger form of the Dirac-Coulomb-Breit
Hamiltonian. Using a Hartree-Fock (HF) wave function from the numerical HF method as the unperturbed function, both the LS-non-splitting and fine-structure corrections are evaluated together with the normal and specific mass corrections. The LS-non-splitting corrections are found to be important for IPs and EAs of transition metal atoms. The fine-structure corrections
are generally larger in magnitude than the LS-non-splitting corrections for the atoms of groups 13–18 with Z≥31, and can never be neglected. Comparison of the IPs and EAs presented here and experimental IPs and EAs gives an estimation
of the electron correlation correction for these properties. For some light atoms, the estimated values agree with the results
directly obtained from correlated calculations.
Received: 28 January 1997 / Accepted: 4 March 1997 相似文献