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211.
Copper‐Catalyzed CH Bond Direct Chalcogenation of Aromatic Compounds Leading to Diaryl Sulfides,Selenides, and Diselenides by Using Elemental Sulfur and Selenium as Chalcogen Sources Under Oxidative Conditions 下载免费PDF全文
Prof. Fumitoshi Shibahara Takafumi Kanai Eiji Yamaguchi Akika Kamei Takayuki Yamauchi Prof. Toshiaki Murai 《化学:亚洲杂志》2014,9(1):237-244
The reactions of aromatic compounds and elemental chalcogens catalyzed by a copper salt with molecular oxygen as an oxidant were carried out. The reaction of 3‐substituted imidazo[1,5‐a]pyridines and elemental sulfur in the presence of CuTC (copper(I) thiophenecarboxylate) gave the corresponding bisimidazopyridyl sulfides in good to quantitative yields. The reaction proceeded even under aerobic oxidation conditions. The use of a polar solvent was crucial for the reaction, and DMSO (dimethyl sulfoxide) in particular stimulated the reaction. The reaction could be applied to common aromatic compounds, such as N‐methyl indole and dialkyl anilines. The reaction of indole proceeded at the nucleophilic C3 position rather than at the acidic C2 position. In addition, the reaction of dialkyl anilines proceeded with an ortho, para orientation. The reactions of imidazopyridines and elemental selenium under similar conditions gave the corresponding bisimidazopyridyl diselenides along with bisimidazopyridyl monoselenides. The resulting diselenides were readily converted to the corresponding monoselenides with unreacted imidazopyridines under the same conditions. The reaction could be applied to the copolymerization of bifunctional bisimidazopyridines and elemental sulfur to give oligomeric copolymers in quantitative yield. 相似文献
212.
The catalytic cross‐dehydrogenative coupling (CDC) reaction has received intense attention in recent years. The attractive feature of this coupling process is the formation of a C? C bond from two C? H moieties under oxidative conditions. In this Focus Review, recent advances in the palladium‐catalyzed CDC reactions of C(sp2)? H bond are summarized, with a focus on the period from 2011 to early 2013. 相似文献
213.
214.
Synthesis of Pyrrolophenanthridine Alkaloids Based on C(sp3)H and C(sp2)H Functionalization Reactions 下载免费PDF全文
Dr. Chihiro Tsukano Nobusuke Muto Iderbat Enkhtaivan Prof. Yoshiji Takemoto 《化学:亚洲杂志》2014,9(9):2628-2634
Assoanine, pratosine, hippadine, and dehydroanhydrolycorine belong to the pyrrolophenanthridine family of alkaloids, which are isolated from plants of the Amaryllidaceae species. Structurally, these alkaloids are characterized by a tetracyclic skeleton that contains a biaryl moiety and an indole core, and compounds belonging to this class have received considerable interest from researchers in a number of fields because of their biological properties and the challenges associated with their synthesis. Herein, a strategy for the total synthesis of these alkaloids by using C? H activation chemistry is described. The tetracyclic skeleton was constructed in a stepwise manner by C(sp3)? H functionalization followed by a Catellani reaction, including C(sp2)? H functionalization. A one‐pot reaction involving both C(sp3)? H and C(sp2)? H functionalization was also attempted. This newly developed strategy is suitable for the facile preparation of various analogues because it uses simple starting materials and does not require protecting groups. 相似文献
215.
8-Anilino-1-naphthalenesulfonic acid (ANS) is used as a hydrophobic fluorescence probe due to its high intensity in hydrophobic environments, and also as a microenvironment probe because of its unique ability to exhibit peak shift and intensity change depending on the surrounding solvent environment. The difference in fluorescence can not only be caused by the microenvironment but can also be affected by the binding affinity, which is represented by the binding constant (K). However, the overall binding process considering the binding constant is not fully understood, which requires the ANS fluorescence binding mechanism to be examined. In this study, to reveal the rate-limiting step of the ANS–protein binding process, protein concentration-dependent measurements of the ANS fluorescence of lysozyme and bovine serum albumin were performed, and the binding constants were analyzed. The results suggest that the main factor of the binding process is the microenvironment at the binding site, which restricts the attached ANS molecule, rather than the attractive diffusion-limited association. The molecular mechanism of ANS–protein binding will help us to interpret the molecular motions of ANS molecules at the binding site in detail, especially with respect to an equilibrium perspective. 相似文献
216.
217.
Ayman A. Ghfar Mohammad Magdy El-Metwally Mohamed Shaaban Sami A. Gabr Nada S. Gabr Marwa S. M. Diab Ahmad Aqel Mohamed A. Habila Wahidah H. Al-Qahtani Mohammad Y. Alfaifi Serag Eldin I. Elbehairi Bayan Ahmed AlJumah 《Molecules (Basel, Switzerland)》2021,26(9)
The anticancer activity of terretonin N (1) and butyrolactone I (2), obtained from the thermophilic fungus Aspergillus terreus TM8, was intensively studied against prostate adenocarcinoma (PC-3) and ovary adenocarcinoma (SKOV3) human cell lines. According to this study, both compounds showed potent cytotoxicity towards ovarian adenocarcinoma cells (SKOV3) with IC50 1.2 and 0.6 μg/mL, respectively. With respect to metastatic prostate cells (PC-3), the two compounds 1 and 2 showed a significantly promising cytotoxicity effect with IC50 of 7.4 and 4.5 μg/mL, respectively. The tested fungal metabolites showed higher rates of early and late apoptosis with little or no necrotic apoptotic pathway in all treated prostate adenocarcinoma (PC-3) and ovary adenocarcinoma (SKOV3) human cell lines, respectively. The results reported in this study confirmed the promising biological properties of terretonin N (1) and butyrolactone I (2) as anticancer agents via the induction of cellular apoptosis. However, further studies are needed to elucidate the molecular mechanism by which cellular apoptosis is induced in cancer cells. 相似文献
218.
Substituent effects on the ring‐opening mechanism of gem‐dibromospiropentanes to related allenes: a theoretical study 下载免费PDF全文
Density functional theory computations at B3LYP and X3LYP levels were performed for ring openings of substituted gem‐dibromospiropentanes (R = ―H, ―Cl, ―Br, ―CH3, ―SiH3, ―OH, ―OCH3, ―CF3, ―BF2, and ―SH) to related allenes. The conversion of spiropentanoids 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j to the corresponding allenes 7a , 7b , 7c , 7d , 7e , 7f , 7g , 7h , 7i , 7j can proceed in both concerted and stepwise mechanism except for R = ―H. Both ring‐opening mechanisms have similar activation energy barriers to open the spiropentanylidene ring and generate the structure of allene at all theoretical levels used herein. Generally the π electron‐donating group (―OH or ―SH) decreases the activation barrier for the follow‐up reaction of 1‐bromo‐1‐lithiospiropentanoid and free spiropentanylidene. Hence, both bearing electron‐donating substituents are more reactive than those with electron‐withdrawing group, and the first one to open the ring to the LiBr–allene complex does so more readily than the second. The sEDA index used to measure sigma‐electron excess/deficiency of the cyclopropylidene ring is mutually correlated for the studied systems. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
219.
In this study, a phase-change memory device was fabricated and the origin of device failure mode was examined using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Ge2Sb2Te5 (GST) was used as the active phase-change material in the memory device and the active pore size was designed to be 0.5 m. After the programming signals of more than 2×106 cycles were repeatedly applied to the device, the high-resistance memory state (reset) could not be rewritten and the cell resistance was fixed at the low-resistance state (set). Based on TEM and EDS studies, Sb excess and Ge deficiency in the device operating region had a strong effect on device reliability, especially under endurance-demanding conditions. An abnormal segregation and oxidation of Ge also was observed in the region between the device operating and inactive peripheral regions. To guarantee an data endurability of more than 1×1010 cycles of PRAM, it is very important to develop phase-change materials with more stable compositions and to reduce the current required for programming. 相似文献
220.
In this report, we demonstrate scanning tunneling microscopy and spectroscopy on thin films of lauryl amine (LAM) and octadecane thiol (ODT) protected gold nanoparticles. We show that the zero current in the I-V curves (measure of Coulomb blockade (CB) of the nanoparticles) depends on the properties of the spacer molecule. In both the cases the gap voltage and the tunneling current at which the images are obtained are quite different which is further confirmed from the fitting performed based on the orthodox theory. The values for the capacitance and charging energy obtained from the fitting for ODT capped particles are comparable to the values obtained using spherical capacitor model. In contrast, values of these parameters were found to differ for LAM capped nanoparticles. While imaging, ODT capped nanoparticles were observed to drag along the scan direction leading to ordering of particles. Images of LAM capped gold nanoparticles show local ordering in self-assembly of particles although no evidence of large scale ordering in spatial Fourier transform was seen. These observations suggest that nanoparticles with larger CB would be imaged nonevasively in contrast to small CB systems for which tip induced effects will be dominant. In both the systems the current was found to rise faster than theoretical curves based on the orthodox theory suggesting that mechanism of charge transfer in this case may involve field emission rather than tunneling through a rectangular barrier. An attempt has been made to explain charge transfer based on Fowler-Nordheim (F-N) plots of the I-V curves. 相似文献