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91.
Chengshuo Shen Dr. Emmanuel Anger Dr. Monika Srebro Dr. Nicolas Vanthuyne Dr. Loïc Toupet Prof. Christian Roussel Prof. Jochen Autschbach Prof. Régis Réau Dr. Jeanne Crassous 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16722-16728
Homochiral and heterochiral cis‐bis‐cycloplatinated‐[6]helicene derivatives 1 b1, 2 , as representative examples of platina[6]helicenes that share a common platinum center, have been prepared. A diastereo‐ and enantioselective synthesis, which combines CH activation and dynamic isomerization from heterochiral structure 1 b2 into homochiral structure 1 b1 , is also described. Overall, this isomerization process results in the transfer of chiral information from one helicene moiety to the other one. The chiroptical properties of homochiral (P)‐ and (M)‐ 1 b1 were greatly modified upon oxidation into their corresponding (P)‐ and (M)‐diiodo‐PtIV complexes ( 5 ). The changes were also analyzed by performing theoretical calculations. C? H activation in the synthesis of organometallic helicenes is further demonstrated by the preparation of cis‐bis‐cycloplatinated‐[8]helicene 1 c . 相似文献
92.
T. N. Rostovshchikova M. S. Korobov D. A. Pankratov G. Yu. Yurkov S. P. Gubin 《Russian Chemical Bulletin》2005,54(6):1425-1432
Nanosized iron oxides stabilized on the surface of ultradispersed poly(tetrafluoroethylene) (UPTFE) granules were synthesized
by the thermal destruction of iron formate in boiling bed of UPTFE on the surface of heated mineral oil. The particle size
of nanoparticles (∼6 nm) containing 5, 10, and 16 wt.% Fe depends weakly on the temperature of synthesis and iron to polymer
ratio. The metal state is determined by the synthesis conditions. The nanoparticles synthesized at 280 °C consist mainly of
the Fe3O4 and Fe2O3 phases. The samples obtained at 320 °C also contain iron(II) oxide. The catalytic properties of the obtained samples were tested in dichlorobutene isomerization. Unlike isomerization
on the iron oxide nanoparticles supported on silica gel, reaction over the UPTFE supports proceeds without an induction period.
The sample with 10 wt.% Fe containing magnetically ordered γ-Fe2O3 nanoparticles possesses the highest catalytic activity. Fast electron exchange between the iron ions in different oxidation
states and high defectiveness of the nanoparticles contribute, most likely, to the catalytic activity.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1383–1390, June, 2005. 相似文献
93.
Synthesis of Oxacyclic Scaffolds via Dual Ruthenium Hydride/Brønsted Acid‐Catalyzed Isomerization/Cyclization of Allylic Ethers 下载免费PDF全文
Dr. Erhad Ascic Ragnhild G. Ohm Dr. Rico Petersen Dr. Mette R. Hansen Casper L. Hansen Daniel Madsen Prof. Dr. David Tanner Prof. Dr. Thomas E. Nielsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(12):3297-3300
A ruthenium hydride/Brønsted acid‐catalyzed tandem sequence is reported for the synthesis of 1,3,4,9‐tetrahydropyrano[3,4‐b]indoles (THPIs) and related oxacyclic scaffolds. The process was designed on the premise that readily available allylic ethers would undergo sequential isomerization, first to enol ethers (Ru catalysis), then to oxocarbenium ions (Brønsted acid catalysis) amenable to endo cyclization with tethered nucleophiles. This methodology provides not only an attractive alternative to the traditional oxa‐Pictet–Spengler reaction for the synthesis of THPIs, but also convenient access to THPI congeners and other important oxacycles such as acetals. 相似文献
94.
Hengchao Li Hang Chen Yang Zhou Jin Huang Jundan Yi Hongcai Zhao Wei Wang Linhai Jing 《化学:亚洲杂志》2020,15(5):555-559
A photocatalytic E to Z isomerization of alkenes using an iridium photosensitizer under mild reaction conditions is disclosed. This method provides scalable and efficient access to Z‐cinnamyl ether and allylic alcohol derivatives in high yields with excellent stereoselectivity. Importantly, this method also provides a powerful strategy for the selective synthesis of Z‐magnolol and honokiol derivatives possessing potential biological activity. 相似文献
95.
脯氨酸类衍生物结构独特,鲜有报道利用核磁共振(nuclear magnetic resonance,NMR)技术对氨基酸的手性进行鉴别.利用多种NMR技术:1H NMR、1H-1H同核位移相关谱(1H-1H COSY)、1H-1H质子全相关谱(1H-1H TOCSY)、1H-1H核Overhauser效应谱(1H-1H NOESY)、13C NMR、无畸变的极化转移增强法(DEPT135°)、1H-13C检出1H的异核单量子相干(1H-13C HSQC)和1H-13C检出1H的异核多键相关(1H-13C HMBC),对脯氨酸类N-酰胺衍生物两种构象异构体的1H和13C NMR进行了全归属,确定了室温下在二甲基亚砜(DMSO)中L型和D型的顺反异构体以相同的比例同时存在. 相似文献
96.
An Easily Accessed Nickel Nanoparticle Catalyst for Alkene Hydrosilylation with Tertiary Silanes 下载免费PDF全文
Ivan Buslov Dr. Fang Song Prof. Dr. Xile Hu 《Angewandte Chemie (International ed. in English)》2016,55(40):12295-12299
The first efficient and non‐precious nanoparticle catalyst for alkene hydrosilylation with commercially relevant tertiary silanes has been developed. The nickel nanoparticle catalyst was prepared in situ from a simple nickel alkoxide precatalyst Ni(OtBu)2?x KCl. The catalyst exhibits high activity for anti‐Markovnikov hydrosilylation of unactivated terminal alkenes and isomerizing hydrosilylation of internal alkenes. The catalyst can be applied to synthesize a single terminal alkyl silane from a mixture of internal and terminal alkene isomers, and to remotely functionalize an internal alkene derived from a fatty acid. 相似文献
97.
Density functional calculations have been performed to comparatively investigate two possible pathways of Au(I)‐catalyzed Conia‐ene reaction of β‐ketoesters with alkynes. Our studies find that, under the assistance of trifluoromethanesulfonate (TfO), the β‐ketoester is the most likely to undergo Model II to isomerize into its enol form, in which TfO plays a proton transfer role through a 6‐membered ring transition state. The coordination of the Au(I) catalyst to the alkynes triple bond can enhance the eletrophilic capability and reaction activity of the alkynes moiety, which triggers the nucleophilic addition of the enol moiety on the alkynes moiety to give a vinyl‐Au intermediate. This cycloisomerizaion step is exothermal by 21.3 kJ/mol with an energy barrier of 56.0 kJ/mol. In the whole catalytic process, the protonation of vinyl‐Au is almost spontaneous, and the formation of enol is a rate‐limiting step. The generation of enol and the activation of Au(I) catalyst on the alkynes are the key reasons why the Conia‐ene reaction can occur in mild condition. These calculations support that Au(I)‐catalyzed Conia‐ene reactions of β‐ketoesters with alkynes go through the pathway 2 proposed by Toste. 相似文献
98.
A. I. Yarmolenko S. V. Kukharenko L. N. Novikova V. V. Strelets 《Russian Chemical Bulletin》1995,44(7):1300-1305
It has been shown by cyclic voltammetry in THF within the –90 to 40 °C temperature range that fluorenyl (5-9-R-C13H8)Mn(CO)3 complexes (R=But (3) and Ph (4)) undergo two-electron reduction to form allyl type [(3-9-R-C13H8)Mn(CO)3]2– dianions as final products. At low temperatures complexes3 and4 are reduced in two one-electron steps according to the EEC-scheme. The first step is reversible and corresponds to the formation of 19-radical anions 3–. and 4–.. TheE
0 values for redox pairs3
0/–. and4
0/–. are –1.88 and –1.73 V, respectively. The further reduction of radical anions3
–. and4
–. at more negative potentials is accompanied by fast 5 3 haptocoordination of the fluorenyl ligand to form 18-dianions [(3-9-R-C13H8)Mn(CO)3]2–. These dianions obtained by the reduction of complexes3 and4 by the radical anion of pyrene are stable at –80 °C and are characterized by their IR spectra. At room temperature the 5 3 hapticity change is a fast and reversible process occurring at the step of 19-radical anions3
–. and4
–. and leading to the electron deficient 17-species [(3-9-R-C13H8)Mn(CO)3]–., which are reduced easier than the initial complexes. As a result, complexes3 and4 are reduced to the corresponding dianions [(3-9-R-C13H8)Mn(CO)3]2– at room temperature in one reversible two-electron step according to the ECE-scheme. Reactivities of 19e–-species of the isomeric 5- and 6-fluorenylmanganesetricarbonyl complexes are compared.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1347–1353, July, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-05209) and the International Science Foundation (Grant No. REV 000). 相似文献
99.
Chiral 2-oxazolines are valuable building blocks and famous ligands for asymmetric catalysis. The most common synthesis involves the reaction of an amino alcohol with a carboxylic acid. In this paper, an efficient synthesis of 2-oxazolines has been achieved via the stereospecific isomerization of 3-amido-2-phenyl azetidines. The reactions were studied in the presence of both Brønsted and Lewis acids, and Cu(OTf)2 was found to be the most effective. 相似文献
100.
O. A. Luk'yanov I. A. Savost'yanova V. P. Gorelik N. I. Shlykova V. A. Tartakovskii 《Russian Chemical Bulletin》1992,41(8):1395-1399
Silver and mercury salts of nitro compounds react with bromo- or chloroadamantanes with the formation of products of C- and/or O-alkylation, the ratio of which depends on the structure of the initial reactants. The direct experimental evidence of nitronic esters to be isomerized into nitro derivatives and of their role as intermediates in the formation of the nitro derivatives in the alkylation of nitro compounds has been presented for the first time.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiva Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1798–1803, August, 1992. 相似文献