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61.
Electrochemical reduction of a variety of mono- and di-chloro- and bromo- phenols at a palladised titanium electrode afforded phenolate in all cases according to in situ FTIR studies, with the same intermediate species being observed in some cases. 相似文献
62.
Systems incorporating catalyst–substrate non-covalent interactions are emerging as a versatile approach to address site-selectivity challenges in remote functionalization reactions. Given the achievements that have been made in this regard using metals such as iridium, manganese and rhodium, it is surprising that non-covalent catalyst direction has not been utilized in reactions incorporating palladium-catalyzed C–H activation steps, despite palladium being arguably the most versatile metal for C–H activation. Herein, we demonstrate that electrostatically directed, site-selective C–Cl oxidative addition is compatible with a subsequent C–H activation step, proceeding via a concerted metalation deprotonation-type mechanism. This results in site-selective cross-coupling of dichloroarenes with fluoroarenes and fluoroheteroarenes, with selectivity controlled by catalyst structure. This study demonstrates that Pd-catalyzed C–H activation can be used productively in combination with a non-covalently-directed mode of catalysis, with important implications in both fields.Electrostatically-directed oxidative addition is compatible with a subsequent C–H activation step, enabling site-selective coupling of remote chlorides with fluoroarenes and fluoroheteroarenes. 相似文献
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Yasuji Yamada D. Miljkovic P. Wehrli B. Golding P. Lliger R. Keese K. Müller A. Eschenmoser 《Angewandte Chemie (International ed. in English)》1969,8(5):343-348
Work towards a synthesis of vitamin B12 has inspired a new type of corrin synthesis. The key step is a light-induced 1,16-hydrogen transfer leading to an antarafacial (π→σ)-cycloisomerization of a seco-corrinoid metal complex. The construction of the seco-corrinoid ligand system is achieved by coupling monocyclic ring precursors in their enamide or enamine form through the methods of sulfide-contraction via oxidative coupling and of iminoester-enamine condensation. 相似文献
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A decrease in the group velocity of 0.5 GHz phonons at 0.023 K has been observed in fused SiO2. This is attributed to pulse reshaping associated with the saturation of two-level tunneling states in the glass. 相似文献
70.
Dykman MI Golding B McCann LI Smelyanskiy VN Luchinsky DG Mannella R McClintock PV 《Chaos (Woodbury, N.Y.)》2001,11(3):587-594
We discuss activated escape from a metastable state of a system driven by a time-periodic force. We show that the escape probabilities can be changed very strongly even by a comparatively weak force. In a broad parameter range, the activation energy of escape depends linearly on the force amplitude. This dependence is described by the logarithmic susceptibility, which is analyzed theoretically and through analog and digital simulations. A closed-form explicit expression for the escape rate of an overdamped Brownian particle is presented and shown to be in quantitative agreement with the simulations. We also describe experiments on a Brownian particle optically trapped in a double-well potential. A suitable periodic modulation of the optical intensity breaks the spatio-temporal symmetry of an otherwise spatially symmetric system. This has allowed us to localize a particle in one of the symmetric wells. (c) 2001 American Institute of Physics. 相似文献