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81.
82.
Fabian WM 《The Journal of organic chemistry》2002,67(21):7475-7482
The site of nucleophilic addition to five-membered heterocyclic 2,3-diones (4-iminomethylfuran-2,3-dione A1 and 4-formyl-pyrrole-2,3-dione B1) is studied by density functional theory calculations (B3LYP/6-31G) with water as the nucleophile. Both uncatalyzed and water-assisted 1,2-addition to the lactone (lactam) and the keto carbonyl group, and conjugate addition to C5 of the heterocycle and the heteroatom of the 4-iminomethyl (formyl) moiety are considered. In addition, concerted and stepwise ring fission of the lactone (lactam) ring is also treated. The effect of solvation (aqueous solution) is taken into account by the polarizable continuum model (PCM) and the Poisson-Boltzmann SCRF method (PB-SCRF), as well as explicit water molecules. Only this latter approach yields meaningful activation free energies. Barriers for addition of H2O increase in the order 1,4-addition to C5 < addition to the lactone (lactam) carbonyl < hydration of the 3-keto group. No reaction path for concerted water-assisted ring opening could be found. 相似文献
83.
Nontrivial steady flows have recently been found that capture the main structures of the turbulent buffer layer. We study the effects of polymer addition on these "exact coherent states" (ECS) in plane Couette flow. Despite the simplicity of the ECS flows, these effects closely mirror those observed experimentally: Structures shift to larger length scales, wall-normal fluctuations are suppressed while streamwise ones are enhanced, and drag is reduced. The mechanism underlying these effects is elucidated. These results suggest that the ECS are closely related to buffer layer turbulence. 相似文献
84.
85.
Litvinyuk IV Légaré F Dooley PW Villeneuve DM Corkum PB Zanghellini J Pegarkov A Fabian C Brabec T 《Physical review letters》2005,94(3):033003
Shakeup of a two-electron system is investigated in the strong infrared laser field limit, both theoretically and experimentally. During tunnel ionization the electron shakes up a second electron to an excited bound state. Theoretically, a complete analytical theory of shakeup in intense laser fields is developed. We predict that shakeup produces one excited sigma(u) D(+)(2) state in approximately 10(5) ionization events. Shakeup is measured experimentally by using the molecular clock provided by the internuclear motion. The number of measured events is found to be in excellent agreement with theory. 相似文献
86.
It is proved that a Banach space X is a subspace of a weaklycompactly generated Banach space if and only if, for every >0,X can be covered by a countable collection of bounded closedconvex symmetric sets where the weak* closure in X** of eachof them lies within the distance from X. A new short functional-analyticproof of the known result that a continuous image of an Eberleincompact is Eberlein is given as a corollary. 相似文献
87.
Peter C. Kunz Indre Thiel Anna Louisa Noffke Guido J. Reiß Fabian Mohr Bernhard Spingler 《Journal of organometallic chemistry》2012,697(1):33-40
A variety of piano-stool complexes of cyclopentadienyl ruthenium(II) with imidazole-based PN ligands have been synthesized starting from the precursor complexes [CpRu(C10H8)]PF6, [CpRu(NCMe)3]PF6 and [CpRu(PPh3)2Cl]. PN ligands used are imidazol-2-yl, -4-yl and -5-yl phosphines.Depending on the ligand and precursor different types of coordination modes were observed; in the case of polyimidazolyl PN ligands these were κ1P-monodentate, κ2P,N-, κ2N,N- and κ3N,N,N- chelating and μ-κP:κ2N,N-brigding. The solid-state structures of [CpRu(1a)2Cl ]·H2O (5.H2O) and [{CpRu(μ-κ2-N,N-κ’1-P-2b)}2](C6H5PO3H)2(C6H5PO3H2)2, a hydrolysis product of the as well determined [{CpRu(2b)}2](PF6)2.2CH3CN (7b.2CH3CN) were determined (1a = imidazol-2-yldiphenyl phosphine, 2b = bis(1-methylimidazol-2-yl)phenyl phosphine, 3a = tris(imidazol-2-yl)phosphine). Furthermore, the complexes [CpRu(L)2]PF6 (L = imidazol-2-yl or imidazol-4-yl phosphine) have been screened for their catalytic activity in the hydration of 1-octyne. 相似文献
88.
Manganese‐Catalyzed Dehydrogenative Alkylation or α‐Olefination of Alkyl‐Substituted N‐Heteroarenes with Alcohols
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Dr. Guoying Zhang Dr. Torsten Irrgang Thomas Dietel Fabian Kallmeier Prof. Dr. Rhett Kempe 《Angewandte Chemie (International ed. in English)》2018,57(29):9131-9135
Catalysis with earth‐abundant transition metals is an option to help save our rare noble‐metal resources and is especially interesting when novel reactivity or selectivity patterns are observed. We report here on a novel reaction, namely the dehydrogenative alkylation or α‐olefination of alkyl‐substituted N‐heteroarenes with alcohols. Manganese complexes developed in our laboratory catalyze the reaction with high efficiency whereas iron and cobalt complexes stabilized by the same ligands are essentially inactive. Hydrogen is liberated during the reaction, and bromine and iodine functional groups as well as olefins are tolerated. A variety of alkyl‐substituted N‐heteroarenes can be functionalized, and benzylic and aliphatic alcohols undergo the reaction. 相似文献
89.
90.
Structural features (orientation of the carboxyl group, ring puckering), electronic absorption, and circular dichroism spectra of 4-alkyl- and 4-aryl-dihydropyrimidones 1-5 are calculated by semiempirical (AM1, INDO/S), ab initio (HF/6-31G, CIS/6-31G, RPA/6-31G), and density functional theory (B3LYP/6-31G) methods. These calculations allow an assignment of the absolute configuration by comparison of simulated and experimental CD spectra. Although the ab initio methods greatly overestimate electronic transition energies, the general appearance of the experimental CD spectra is quite nicely reproduced by these calculations. Thus, comparison of experimental with calculated CD spectra is a reliable tool for the assignment of the absolute configuration. For 4-methyl derivatives 1, the first enantiopure DHPM examples with no additional aromatic substituent, the stereochemistry at C4 provided by the theoretical results is confirmed by X-ray structure determination of the diastereomeric salt 6. Additional support is the consistent HPLC elution order found for all investigated DHPMs on a cellulose-derived chiral stationary phase. 相似文献