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91.
92.
Alberto Hernn‐Gmez Emma Herd Eva Hevia Alan R. Kennedy Paul Knochel Konrad Koszinowski Sophia M. Manolikakes Robert E. Mulvey Christoph Schnegelsberg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(10):2744-2748
The pivalates RZnOPiv⋅Mg(OPiv)X⋅n LiCl (OPiv=pivalate; R=aryl; X=Cl, Br, I) stand out amongst salt‐supported organometallic reagents, because apart from their effectiveness in Negishi cross‐coupling reactions, they show more resistance to attack by moist air than conventional organometallic compounds. Herein a combination of synthesis, coupling applications, X‐ray crystallographic studies, NMR (including DOSY) studies, and ESI mass spectrometric studies provide details of these pivalate reagents in their own right. A p‐tolyl case system shows that in [D8]THF solution these reagents exist as separated Me(p‐C6H4)ZnCl and Mg(OPiv)2 species. Air exposure tests and X‐ray crystallographic studies indicate that Mg(OPiv)2 enhances the air stability of aryl zinc species by sequestering H2O contaminants. Coupling reactions of Me(p‐C6H4)ZnX (where X=different salts) with 4‐bromoanisole highlight the importance of the presence of Mg(OPiv)2. Insight into the role of LiCl in these multicomponent mixtures is provided by the molecular structure of [(THF)2Li2(Cl)2(OPiv)2Zn]. 相似文献
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94.
Jose Castro‐Perez Nathan Hatcher Nana Kofi Karikari Sheng‐Ping Wang Vivienne Mendoza Henry Shion Alan Millar John Shockcor Mark Towers David McLaren Vinit Shah Stephen Previs Karen Akinsanya Michele Cleary Thomas P. Roddy Douglas G. Johns 《Rapid communications in mass spectrometry : RCM》2014,28(22):2471-2479
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2′5- and 2′R- and S- cephalexin, (5b) and (5c) respectively, both available in six stages from penicillin G, have each been converted to the more useful 2′R-isomer (5a) by a base catalysed epimerization and selective crystallization process involving the N-nitrosoimidazolidinyl derivatives (7). 相似文献
97.
The alkylation of β-dicarbonyl compounds under phase-transfer conditions has been studied in detail and, in virtually all of the reported examples, the C-alkylation products have been found to predominate.1–6 Only when the reaction rate is slow is there any evidence for O-alkylation as, for example, when there is steric hindrance to the approach of the alkylating agent to the carbanionic centre.1,7 There is no record, however, of the corresponding acylation reactions. 相似文献
98.
Two protonated forms of chlorine nitrate, HClONO+ 2 and ClONO2H+, are treated ab initio by the Hartree-Fock and the second order Møller-Plesset perturbation approach with the standard 6–31G* basis set. Both minimum energy structures are planar (C 3 symmetry) and their structural, energy, and vibrational parameters are reported. The computations conclude that the proton attacks the chlorine nitrate at its central, not end, oxygen atom. The protonation causes a considerable elongation of the central ON bond which becomes most probable place of cleavage. The dissociation should yield the neutral HOCl and NO+ 2. These quantum-chemical findings well agree with the previous experimental indications. 相似文献
99.
R. Alan Aitken Bernd Fodi Michael H. Palmer Alexandra M.Z. Slawin Jing Yang 《Tetrahedron》2012,68(29):5845-5851
The structures of pyridazine N-oxide, pyrimidine N-oxide and pyrazine N-oxide have been determined by X-ray diffraction for the first time. Comparison with theoretical predictions of the equilibrium structures using the B3LYP method together with a cc-pVTZ basis set, show close agreement with the structural parameters observed, and experimental dipole moments, which suggests that the charge distribution is realistic. An ‘atoms in molecules’ (AIM) analysis of the computed wave-functions shows total electron densities rather different from the classical picture of a dative bond, whereas the same wave-functions subjected to Mulliken analysis show a more conventional view of the electron distribution. This latter procedure allows a bond dipole analysis of the N-oxide charge distribution. 相似文献
100.