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991.
Hindered beta-aminoarylphosphines show promise as bidentate ligands for metal centers, but their reported synthesis requires heating at high temperatures for several days. Herein are reported conditions by which the two steps composing this synthesis, Buchwald-Hartwig amination and nucleophilic phosphorylation reactions, may both be completed in less than 3 h using microwave irradiation. The effects of several parameters on the outcome of the amination reaction are discussed, as are some indications of the scope within which each of these microwave protocols is effective. 相似文献
992.
The racemic synthesis of the common propellane core structure found in various hasubanan alkaloids is reported. The successful completion hinged upon the stereocontrolled construction of the cis-substituted heterobicycle as a precursor for the intramolecular Dieckmann condensation. A novel strategy is introduced for the facile hydrolysis of a sterically demanding carboxamide under a mild condition. The 2-nitroanilide obtained by the Goldberg arylation of a carboxamide with 2-iodonitrobenzene was readily converted to the corresponding ester derivative by way of N-acylbenzotriazole. We expect that the reported synthetic route will allow the synthesis of a series of hasubanan alkaloids starting from the correspondingly functionalized 2-tetralone derivatives. 相似文献
993.
The development of a new method for stereoselective glycosylation with glycosyl trichloroacetimidate donors employing cationic palladium(II), Pd(CH(3)CN)(4)(BF(4))(2), is described. This process employs Pd(CH(3)CN)(4)(BF(4))(2) as an efficient activator, providing access to a variety of disaccharides and glycopeptides. This reaction is highly stereoselective and proceeds under mild conditions with low catalyst loading. Interestingly, this palladium catalysis directs beta-glucosylations in the absence of classical neighboring group participation. 相似文献
994.
Jerome Lozada Wen Xuan Lin Rosana M. Cao-Shen Ruyin Astoria Tai Prof. David M. Perrin 《Angewandte Chemie (International ed. in English)》2023,62(16):e202215371
Tetrafluoroborate (BF4−) has long been used as a spectator counter anion. Herein, we report an unprecedented salt metathesis between a variety of BF4− salts and a series of organoboronic acids yielding the corresponding organotrifluoroborates. We identified conditions for fast and efficient fluoridation (<1 h) with minimal workup. Fundamentally, this work discloses the proclivity of BF4− to exchange fluoride atoms with organoboronates, highlighting the lability of BF4−. 相似文献
995.
Huijun Qian Hieu D. Nguyen Prof. Leiyang Lv Prof. Shuming Chen Prof. Zhiping Li 《Angewandte Chemie (International ed. in English)》2023,62(23):e202303271
Defluorinative manipulation of polyfluorinated molecules has shown great promise due to its granting of synthetic versatility to inert C−F bonds. The development of chemo-, stereo- and regioselective strategies to realize highly efficient formation of either the linear/branched or E/Z products from gem-difluorocyclopropanes (gem-F2CPs) is a challenging task. Herein, we have realized palladium/NHC-catalyzed fluoroallylation/annulation of hydrazones with gem-F2CPs that incorporate the hydrazone N2 moiety into the products. The thermodynamically unstable fluorinated E-allylation products with aryl ketone hydrazones were obtained for the first time, while the di-alkyl ketone hydrazones yielded the monofluorinated products with branched selectivity under similar reaction conditions. With aldehyde hydrazones, two kinds of pyrazoles were obtained via a defluorinative allylation/annulation cascade, in which different carbon atoms of gem-F2CPs could be incorporated into the pyrazole rings regiospecifically. DFT calculations revealed that the divergent selectivity was kinetically controlled and the final C−C bond formation proceeded through a 7-membered TS. 相似文献
996.
Tho Duc Khanh Nguyen Stefania Rabasco Alicia A. Lork Andre Du Toit Prof. Andrew G. Ewing 《Angewandte Chemie (International ed. in English)》2023,62(28):e202304098
We used correlative transmission electron microscopy (TEM) and nanoscale secondary ion mass spectrometry (NanoSIMS) imaging to quantify the contents of subvesicular compartments, and to measure the partial release fraction of 13C-dopamine in cellular nanovesicles as a function of size. Three modes of exocytosis comprise full release, kiss-and-run, and partial release. The latter has been subject to scientific debate, despite a growing amount of supporting literature. We tailored culturing procedures to alter vesicle size and definitively show no size correlation with the fraction of partial release. In NanoSIMS images, vesicle content was indicated by the presence of isotopic dopamine, while vesicles which underwent partial release were identified by the presence of an 127I-labelled drug, to which they were exposed during exocytosis allowing entry into the open vesicle prior to its closing again. Demonstration of similar partial release fractions indicates that this mode of exocytosis is predominant across a wide range of vesicle sizes. 相似文献
997.
998.
Chih‐Hung Chou Jyh‐Cheng Chen Chia‐Cheng Tai I‐Wen Sun Jyh‐Myng Zen 《Electroanalysis》2008,20(7):771-775
We report here a nonenzymatic sensor by using a nanoporous platinum electrode to detect glucose directly. The electrode was fabricated by electrochemical deposition and dissolution of PtZn alloy in zinc chloride‐1‐ethyl‐3‐methylimidazolium chloride (ZnCl2‐EMIC) ionic liquid. Both SEM and electrochemical studies showed the evidences for the nanoporous characteristics of the as‐prepared Pt electrodes. Amperometric measurements allow observation of the electrochemical oxidation of glucose at 0.4 V (vs. Ag/AgCl) in pH 7.4 phosphate buffer solution. The sensor also demonstrates significant reproducibility in glucose detection; the higher the roughness factor of the Pt electrode, the lower the detection limit of glucose. The interfering species such as ascorbic acid and p‐acetamidophenol can be avoided by using a Pt electrode with a high roughness factor of 151. Overall, the nanoporous Pt electrode is promising for enzymeless detection of glucose at physiological condition. 相似文献
999.
Backus EH Nguyen PH Botan V Moretto A Crisma M Toniolo C Zerbe O Stock G Hamm P 《The journal of physical chemistry. B》2008,112(48):15487-15492
Applying ultrafast vibrational spectroscopy, we find that vibrational energy transport along a helical peptide changes from inefficient but mostly ballistic below approximately 270 K into diffusive and significantly more efficient above. On the basis of molecular dynamics simulations, we attribute this change to the increasing flexibility of the helix above this temperature, similar to the glass transition in proteins. Structural flexibility enhances intramolecular vibrational energy redistribution, thereby refeeding energy into the few vibrational modes that delocalize over large parts of the structure and therefore transport energy efficiently. The paper outlines concepts how one might regulate vibrational energy transport properties in ultrafast photobiological processes, as well as in molecular electronic devices, by engineering the flexibility of their components. 相似文献
1000.
Nguyen Van Minh 《Proceedings of the American Mathematical Society》2008,136(5):1749-1755
In this paper we present an extension of the Katznelson-Tzafriri Theorem to the asymptotic behavior of individual solutions of evolution equations . The obtained results do not require the uniform continuity of solutions as well as the well-posedness of the equations. The method of study is based on a recently developed approach to the spectral theory of functions that is direct and free of -semigroups.