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41.
Formation of ketone acylals bearing trihaloacetoxy groups and their nucleophilic geminal disubstitution by fluoride ions were investigated. Cyclohexanone reacted with trifluoroacetic anhydride without catalyst to give gem-bistrifluoroacetates via a concerted bimolecular reaction. Treatment with hydrogen fluoride under mild conditions efficiently yielded the corresponding gem-difluorides. In this reaction process, trifluoroacetic acid was recovered and converted to trifluoroacetic anhydride using P2O5. Since gem-difluorides were derived from ketones, HF and P2O5, this constitutes a practical synthesis of gem-difluorides. 相似文献
42.
Dr. Nguyet Trang Thanh Chau Maxime Meyer Dr. Shinsuke Komagawa Dr. Floris Chevallier Prof. Yves Fort Prof. Masanobu Uchiyama Prof. Florence Mongin Dr. Philippe C. Gros 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(41):12425-12433
Homoleptic lithium tri‐ and tetraalkyl zincates were reacted with a set of bromopyridines. Efficient and chemoselective bromine–metal exchanges were realized at room temperature with a substoichiometric amount of nBu4ZnLi2?TMEDA reagent (1/3 equiv; TMEDA=N,N,N′,N′‐tetramethylethylenediamine). This reactivity contrasted with that of tBu4ZnLi2?TMEDA, which was inefficient below one equivalent. DFT calculations allowed us to rationalize the formation of N???Li stabilized polypyridyl zincates in the reaction. The one‐pot difunctionalization of dibromopyridines was also realized using the reagent stoichiometrically. The direct creation of C? Zn bonds in bromopyridines enabled us to perform efficient Negishi‐type cross‐couplings. 相似文献
43.
44.
Li M Ishihara S Akada M Liao M Sang L Hill JP Krishnan V Ma Y Ariga K 《Journal of the American Chemical Society》2011,133(19):7348-7351
Electrochemical-coupling layer-by-layer (ECC-LbL) assembly is introduced as a novel fabrication methodology for preparing layered thin films. This method allows us to covalently immobilize functional units (e.g., porphyrin, fullerene, and fluorene) into thin films having desired thicknesses and designable sequences for both homo- and heteroassemblies while ensuring efficient layer-to-layer electronic interactions. Films were prepared using a conventional electrochemical setup by a simple and inexpensive process from which various layering sequences can be obtained, and the photovoltaic functions of a prototype p/n heterojunction device were demonstrated. 相似文献
45.
Ishihara S Hill JP Shundo A Richards GJ Labuta J Ohkubo K Fukuzumi S Sato A Elsegood MR Teat SJ Ariga K 《Journal of the American Chemical Society》2011,133(40):16119-16126
Porphyrin derivatives bearing 2,6-di-tert-butylphenol substituents at their 5,15-positions undergo reversible photoredox switching between porphyrin and porphodimethene states as revealed by UV-vis spectroscopy, fluorescence spectroscopy, and X-ray single-crystal analyses. Photoredox interconversion is accompanied by substantial variations in electronic absorption and fluorescence emission spectra and a change of conformation of the tetrapyrrole macrocycle from planar to roof-shaped. Oxidation proceeds only under photoillumination of a dianionic state prepared through deprotonation using fluoride anions. Conversely, photoreduction occurs in the presence of a sacrificial electron donor. Transient absorption spectroscopy and electron spin resonance spectroscopy were applied to investigate the processes in photochemical reaction, and radical intermediates were characterized. That is, photooxidation initially results in a phenol-substituent-centered radical, while the reduction process occurs via a delocalized radical state involving both the macrocycle and 5,15-substituents. Forward and reverse photochemical processes are governed by different chemical mechanisms, giving the important benefit that conversion reactions are completely isolated, leading to better separation of the end states. Furthermore, energy diagrams based on electrochemical analyses (cyclic voltammetry) were used to account for the processes occurring during the photochemical reactions. Our molecular design indicates a simple and versatile method for producing photoredox macrocyclic compounds, which should lead to a new class of advanced functional materials suitable for application in molecular devices and machines. 相似文献
46.
Ishida Y Shimada T Masui D Tachibana H Inoue H Takagi S 《Journal of the American Chemical Society》2011,133(36):14280-14286
The quantitative excited energy transfer reaction between cationic porphyrins on an anionic clay surface was successfully achieved. The efficiency reached up to ca. 100% owing to the "Size-Matching Rule" as described in the text. It was revealed that the important factors for the efficient energy transfer reaction are (i) suppression of the self-quenching between adjacent dyes, and (ii) suppression of the segregated adsorption structure of two kinds of dyes on the clay surface. By examining many different kinds of porphyrins, we found that tetrakis(1-methylpyridinium-3-yl) porphyrin (m-TMPyP) and tetrakis(1-methylpyridinium-4-yl) porphyrin (p-TMPyP) are the suitable porphyrins to accomplish a quantitative energy transfer reaction. These findings indicate that the clay/porphyrin complexes are promising and prospective candidates to be used for construction of an efficient artificial light-harvesting system. 相似文献
47.
Yamaguchi K Ueki R Nonaka H Sugihara F Matsuda T Sando S 《Journal of the American Chemical Society》2011,133(36):14208-14211
Monoamine oxidase (MAO) A is a flavoenzyme that catalyzes the oxidation of biologically important monoamines and is thought to be associated with psychiatric disorders. Here, we report a strategy for rationally designing a (19)F magnetic resonance imaging probe for the specific detection of human MAO-A (hMAO-A) activity. Our designed (19)F probe was oxidized expeditiously by hMAO-A to produce 2-fluoro-4-nitrophenol via a spontaneous β-elimination mechanism. Concomitant with the structural change of the probe to the product, the (19)F chemical shift changed by 4.2 ppm, which was enough to visualize the probe and enzymatic product separately. Importantly, our probe achieved excellent discrimination of hMAO-A from its isoform hMAO-B. 相似文献
48.
Enantioselective total synthesis of the biologically important indole alkaloids (+)-lysergol, (+)-isolysergol, and (+)-lysergic acid is described. Key features of these total synthesis include (1) a facile synthesis of a chiral 1,3-amino alcohol via the Pd(0)- and In(I)-mediated reductive coupling reaction between L-serine-derived 2-ethynylaziridine and formaldehyde; (2) the Cr(II)/Ni(0)-mediated Nozaki-Hiyama-Kishi (NHK) reaction of an indole-3-acetaldehyde with iodoalkyne; and (3) Pd(0)-catalyzed domino cyclization of an allene bearing amino and bromoindolyl groups. This domino cyclization enabled direct construction of the C/D ring system of the ergot alkaloids skeleton, as well as the creation of the C5 stereogenic center with transfer of the allenic axial chirality to the central chirality. 相似文献
49.
In vivo time-lapse Raman imaging reveals highly dynamic and concerted changes in concentration and distribution of phospholipids and proteins during and after cell division of a single living Schizosaccharomyces pombe cell. 相似文献
50.
Ariga K Ishihara S Izawa H Xia H Hill JP 《Physical chemistry chemical physics : PCCP》2011,13(11):4802-4811
A landmark accomplishment of nanotechnology would be successful fabrication of ultrasmall machines that can work like tweezers, motors, or even computing devices. Now we must consider how operation of micro- and molecular machines might be implemented for a wide range of applications. If these machines function only under limited conditions and/or require specialized apparatus then they are useless for practical applications. Therefore, it is important to carefully consider the access of functionality of the molecular or nanoscale systems by conventional stimuli at the macroscopic level. In this perspective, we will outline the position of micro- and molecular machines in current science and technology. Most of these machines are operated by light irradiation, application of electrical or magnetic fields, chemical reactions, and thermal fluctuations, which cannot always be applied in remote machine operation. We also propose strategies for molecular machine operation using the most conventional of stimuli, that of macroscopic mechanical force, achieved through mechanical operation of molecular machines located at an air-water interface. The crucial roles of the characteristics of an interfacial environment, i.e. connection between macroscopic dimension and nanoscopic function, and contact of media with different dielectric natures, are also described. 相似文献