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311.
Peez Nadine Becker Jochen Ehlers Sonja M. Fritz Melanie Fischer Christian B. Koop Jochen H. E. Winkelmann Carola Imhof Wolfgang 《Analytical and bioanalytical chemistry》2019,411(28):7603-7603
Analytical and Bioanalytical Chemistry - The original version of this article contained a mistake. 相似文献
312.
Matthias Lischka Dr. Renhao Dong Mingchao Wang Dr. Natalia Martsinovich Massimo Fritton Lukas Grossmann Prof. Dr. Wolfgang M. Heckl Prof. Dr. Xinliang Feng Prof. Dr. Markus Lackinger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(8):1975-1983
The interplay between the self-assembly and surface chemistry of 2,3,6,7,10,11-hexaaminotriphenylene (HATP) on Cu(111) was complementarily studied by high-resolution scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) under ultra-high vacuum conditions. To shed light on the competitive metal coordination, comparative experiments were carried out on pristine and nickel-covered Cu(111). Directly after room-temperature deposition of HATP onto pristine Cu(111), self-assembled aggregates were observed by STM, and XPS results indicated still protonated amino groups. Annealing up to 200 °C activated the progressive single deprotonation of all amino groups as indicated by chemical shifts of both the N 1s and C 1s core levels in the XP spectra. This enabled the formation of topologically diverse π–d conjugated coordination networks with intrinsic copper adatoms. The basic motif of these networks was a metal–organic trimer, in which three HATP molecules were coordinated by Cu3 clusters, as corroborated by the accompanying density functional theory (DFT) simulations. Additional deposition of more reactive nickel atoms resulted in both chemical and structural changes with deprotonation and formation of bis(diimino)–Ni bonded networks already at room temperature. Even though fused hexagonal metal-coordinated pores were observed, extended honeycomb networks remained elusive, as tentatively explained by the restricted reversibility of these metal–organic bonds. 相似文献
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315.
Eberhard Reimann Wolfgang Erdle Eugen Hargasser Hermann Lotter 《Monatshefte für Chemie / Chemical Monthly》2002,133(7):1017-1030
Summary. The stereoselective synthesis of cis-ergoline is presented. Starting from rac-N-benzoyl tryptophan methyl ester, the key compound indolinylmethylpyridin-3-one was prepared via a seven-step reaction in good yield. Since its cyclization to the desired ergolinone failed, the key compound was reduced
to yield the two diastereomeric pyridin-3-ols; only one of them cyclized in trifluoromethanesulfonic acid, affording cis-ergoline. Catalytic hydrogenation of the latter gave N,N′-dimethyldihydroergoline, the X-ray crystallography of which revealed both the correct structure and identical relative configurations
at C-5a and C-6a (SS or RR). Hydroboration and subsequent perruthenate oxidation of the Δ9-ergoline provided access to the regioisomeric ergolinols and ergolinones.
Received December 27, 2001. Accepted January 15, 2002 相似文献
316.
Electronic determinants of photoacidity in cyanonaphthols 总被引:2,自引:0,他引:2
We present semiempirical AM1 calculations for the ground and excited state of 2-naphthol and some of its cyano derivatives in the gas phase. Following photoexcitation, the Mulliken electron density on the oxygen diminishes slightly for the acid and more conspicuously for the anionic conjugated base. This agrees with the measured solvatochromic parameters for 2-naphthol. In both electronic states, we find a nice correlation with the measured pK values in water. The electronic charge distribution on the distal ring of the anion agrees with the experimental acidity order in both S(0) and S(1). Upon excitation, it increases predominantly in positions 3, 5, and 8. The ring system of the anion assumes an alternate quinoidal structure in the ground state of the anion, which becomes more symmetric in the relaxed excited state. This suggests that the enhanced aromatic character of a 4n electron system in the excited state allows for better delocalization of the oxygen charge within the ring. 相似文献
317.
Córdova A Watanabe S Tanaka F Notz W Barbas CF 《Journal of the American Chemical Society》2002,124(9):1866-1867
This report describes the unprecedented use of unmodified aldehydes as donors in a catalytic asymmetric Mannich-type reaction. The proline-catalyzed reaction of N-PMP-protected alpha-imino ethyl glyoxylate with unmodified aliphatic aldehydes provided a general and very mild entry to either enantiomer of beta-amino and alpha-amino acids and derivatives in high yield and stereoselectivity. Six of the seven aldehydes studied yielded products with ee values of 99% or greater. The diastereoselectivity of the reaction increased with the bulkiness of the substituents of the aldehyde donor in the order R = Me < Et < i-Pr < n-Pent. In five of the cases studied, excellent syn stereoselectivities were achieved. In addition, the corresponding chiral beta-amino aldehyde adducts can be readily converted to the corresponding amino acid derivatives. Most significantly, this approach provides facile access to substituted beta-lactams. 相似文献
318.
Wolfgang Reischl Harald Bernhard Christoph Kratky Erich Zbiral 《Monatshefte für Chemie / Chemical Monthly》1985,116(6-7):831-839
Epoxidation of vitamin D3 with benzonitrile ¦H2O2¦ KHCO3 (Payne's reagent) yields exclusively the 5,6-mono-oxirane2. Further epoxidation with the same reagent gives the 5,6-7,8-bisepoxide3 a. Its stereochemistry and therefore the stereochemistry of2 was established by single crystal X-ray analysis of thep-Brbenzoate3b. Thereby for the first time a directive effect of a homoallylic hydroxyl group during thePayne-epoxidation was established.
Herrn Prof.Mihailovic (Universität Belgrad) mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
319.
α-Diazo phosphonates with a conjugated 1,3-diene unit are synthesised by the Bamford-Stevens reaction ( →→). They undergo [4+2]-cycloadditions with the dienophile to form the tetrahydrotriazolopyridazines , which possess an unchanged diazo group. In contrast, dimethyl acetylenedicarboxylate () reacts exclusively with the diazo dipole of to yield the 3H-pyrazoles , which rearrange to by sigmatropic PO-shifts and hydrolyse to form . The diazo compound isomerises to the pyrazole when heated in benzene. 相似文献