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排序方式: 共有1061条查询结果,搜索用时 31 毫秒
1.
Dr. Christopher R. Opie Dr. Hidetoshi Noda Prof. Dr. Masakatsu Shibasaki Dr. Naoya Kumagai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4648-4653
The B3NO2 six-membered heterocycle (1,3-dioxa-5-aza-2,4,6-triborinane=DATB), comprising three different non-carbon period 2 elements, has been recently demonstrated to be a powerful catalyst for dehydrative condensation of carboxylic acids and amines. The tedious synthesis of DATB, however, has significantly diminished its utility as a catalyst, and thus the inherent chemical properties of the ring system have remained virtually unexplored. Here, a general and facile synthetic strategy that harnesses a pyrimidine-containing scaffold for the reliable installation of boron atoms is disclosed, giving rise to a series of Pym-DATBs from inexpensive materials in a modular fashion. The identification of a soluble Pym-DATB derivative allowed for the investigation of the dynamic nature of the B3NO2 ring system, revealing differential ring-closing and -opening behaviors depending on the medium. Readily accessible Pym-DATBs proved their utility as efficient catalysts for dehydrative amidation with broad substrate scope and functional-group tolerance, offering a general and practical catalytic alternative to reagent-driven amidation. 相似文献
2.
Bingxin LiuYoshio Tatamitani Jun ShimadaTeruhiko Ogata 《Journal of Molecular Spectroscopy》2002,211(1):99-106
The microwave spectrum of the 35Cl and 37Cl isotopic species of 1-chloro-1,1,2-trifluoroethane (HCFC-133b) has been investigated in the frequency region 10 to 50 GHz using a Stark modulation microwave spectrometer. A pulsed jet Fourier transform microwave spectrometer was also used for the measurement of hyperfine splittings. A least-squares analysis of the observed b-type Q- and R-branch transition frequencies gave rotational and centrifugal distortion constants and components of the chlorine nuclear quadrupole coupling constant tensors in the principal axes system as follows: A=4625.161 (3) MHz, B=2004.127 (2) MHz, C=1875.813 (2) MHz, ΔJ=0.144 (9) kHz, ΔJK=1.0748 (8) kHz, ΔK=1.57 (1) kHz, δJ=0.01376 (4) kHz, δK=−0.146 (4) kHz, χaa=−57.958 (10) MHz, χbb=21.231 (11) MHz, and χcc=36.727 (11) MHz for 35ClCF2CH2F species, and A=4607.684 (6) MHz, B=1960.565 (2) MHz, C=1834.823 (2) MHz, ΔJ=0.106 (7) kHz, ΔJK=1.022 (3) kHz, ΔK=1.48 (1) kHz, δJ=0.0142 (2) kHz, δK=−0.18 (2) kHz, χaa=−46.268 (11) MHz, χbb=17.319 (13) MHz, and χcc=28.950 (13) MHz for 37ClCF2CH2F species. The structural parameters are calculated from the observed six rotational constants by assuming the partial structure of ab initio calculation. The electronic properties of the C-Cl bond are evaluated from the observed nuclear quadrupole constants of chlorine. These molecular properties are compared with those of other related molecules. 相似文献
3.
The electrode reaction of decamethylferrocene (DMFc) dissolved in a thin layer of a room-temperature molten salt (RTMS), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C8mimC1C1N) or 1-octyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide (C8mimC2C2N), on a self-assembled monolayer-modified gold electrode is coupled with the ion transfer across the interface between the RTMS and the outer aqueous solution (W) to give a voltammogram whose shape resembles a voltammogram of a simple one-electron transfer process. The electroneutrality of the RTMS layer during the oxidation of DMFc to decamethylferricenium ion is maintained by the concomitant dissolution of C8mim+ ion from the RTMS phase to the W phase, and the reduction of decamethylferricenium ion to DMFc is accompanied by the transfer of either C1C1N- or C2C2N- from RTMS to W. The midpoint potential of the voltammogram varies with the concentration of the salt in the aqueous phase, C8mimCl or LiCnCnN (n = 1 or 2), in a Nernstian manner, showing that the phase-boundary potential between the RTMS and the W is controlled by the partition of these ions. Although the phase-boundary potential across the RTMS / W interface is Nernstian with respect to the ions common to both phases at the equilibrium, the polarization at the RTMS / W interface under current flow distorts the shape of the voltammograms, resulting in a wider peak separation in the voltammogram. 相似文献
4.
Rozics and Johnson's formula is examined and its inconsistency is pointed out. 相似文献
5.
Yosihiko Ogata 《Numerische Mathematik》1989,55(2):137-157
Summary A new method for the numerical integration of very high dimensional functions is introduced and implemented based on the Metropolis' Monte Carlo algorithm. The logarithm of the high dimensional integral is reduced to a 1-dimensional integration of a certain statistical function with respect to a scale parameter over the range of the unit interval. The improvement in accuracy is found to be substantial comparing to the conventional crude Monte Carlo integration. Several numerical demonstrations are made, and variability of the estimates are shown. 相似文献
6.
7.
This paper proposes a two step algorithm for solving a large scale semi-definite logit model, which is appreciated as a powerful
model in failure discriminant analysis. This problem has been successfully solved by a cutting plane (outer approximation)
algorithm. However, it requires much more computation time than the corresponding linear logit model. A two step algorithm
to be proposed in this paper is intended to reduce the amount of computation time by eliminating a certain portion of the
data based on the information obtained by solving an associated linear logit model. It will be shown that this algorithm can
generate a solution with almost the same quality as the solution obtained by solving the original large scale semi-definite
model within a fraction of computation time. 相似文献
8.
Tokutaro Ogata 《Tetrahedron letters》2007,48(38):6648-6650
Asymmetric intramolecular cyclization of aminoalkenes was catalyzed by a catalytic amount of n-butyllithium, diisopropylamine, and a newly designed chiral bisoxazoline in toluene to produce kinetically controlled exo-cyclized amines with up to 91% ee quantitatively. 相似文献
9.
Yosihiko Ogata 《Annals of the Institute of Statistical Mathematics》1990,42(3):403-433
This paper describes a method for an objective selection of the optimal prior distribution, or for adjusting its hyper-parameter, among the competing priors for a variety of Bayesian models. In order to implement this method, the integration of very high dimensional functions is required to get the normalizing constants of the posterior and even of the prior distribution. The logarithm of the high dimensional integral is reduced to the one-dimensional integration of a cerain function with respect to the scalar parameter over the range of the unit interval. Having decided the prior, the Bayes estimate or the posterior mean is used mainly here in addition to the posterior mode. All of these are based on the simulation of Gibbs distributions such as Metropolis' Monte Carlo algorithm. The improvement of the integration's accuracy is substantial in comparison with the conventional crude Monte Carlo integration. In the present method, we have essentially no practical restrictions in modeling the prior and the likelihood. Illustrative artificial data of the lattice system are given to show the practicability of the present procedure. 相似文献
10.
Likelihood estimation of soft-core interaction potentials for Gibbsian point patterns 总被引:3,自引:3,他引:0
Yosihiko Ogata Masaharu Tanemura 《Annals of the Institute of Statistical Mathematics》1989,41(3):583-600
The likelihood method is developed for the analysis of socalled regular point patterns. Approximating the normalizing factor of Gibbs canonical distribution, we simultaneously estimate two parameters, one for the scale and the other which measures the softness (or hardness), of repulsive interactions between points. The approximations are useful up to a considerably high density. Some real data are analyzed to illustrate the utility of the parameters for characterizing the regular point pattern. 相似文献