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121.
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123.
Chemo-, regio-, and enantioselective Pd-catalyzed allylic alkylation of indolocarbazole pro-aglycons
[reaction: see text] Monosubstituted isomerically pure indolopyrrolocarbazole precursors have been prepared via palladium-catalyzed asymmetric allylic alkylation methodology, employing both achiral cyclopentenyl electrophiles and chiral glycal derivatives. Chemoselective allylation of (bis)indole lactam pro-aglycon 3 allows access to N-distally substituted indolopyrrolocarbazole derivatives; glyoxamide precursor 14 provides entry into N-proximally substituted derivatives. 相似文献
124.
Himo F Demko ZP Noodleman L Sharpless KB 《Journal of the American Chemical Society》2002,124(41):12210-12216
It is well-known that azide salts can engage nitriles at elevated temperatures to yield tetrazoles; however, there is continued debate as to the mechanism of the reaction. Density functional theory calculations with the hybrid functional B3LYP have been performed to study different mechanisms of tetrazole formation, including concerted cycloaddition and stepwise addition of neutral or anionic azide species. The calculations presented here suggest a previously unsuspected nitrile activation step en route to an imidoyl azide, which then cyclizes to give the tetrazole. The activation barriers are found to correlate strongly with the electron-withdrawing potential of the substituent on the nitrile. 相似文献
125.
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127.
Enolstannanes serve as nucleophiles towards allylic acetates under the influence of palladium(O) catalyst. 相似文献
128.
Barry Simon 《Journal of Functional Analysis》1973,12(3):335-339
We prove that an ergodic semigroup of positivity preserving self-adjoint operators is positivity improving. We also present a new proof (using Markov techniques) of the ergodicity of semigroups generated by spatially cutoff P(?)2 Hamiltonians. 相似文献
129.
Barry Simon 《Communications in Mathematical Physics》1977,55(3):259-274
Technically simple proofs are given of the HVZ theorem on the bottom of the essential spectrum of multiparticle systems and of Combes' result on completeness below the lowest three body threshold. The first proof is a variant of a proof of Enss and a decendent of Zhislin's original proof. Finally, we apply our methods to the bound state spectrum.On leave from Princeton University. Research support in part by U.S. National Science Foundation under grants MPS-75-11864 and MPS-75-20638 相似文献
130.
We review the properties of supersymmetric quantum mechanics for a class of models proposed by Witten. Using both Hamiltonian and path integral formulations, we give general conditions for which supersymmetry is broken (unbroken) by quantum fluctuations. The spectrum of states is discussed, and a virial theorem is derived for the energy. We also show that the euclidean path integral for supersymmetric quantum mechanics is equivalent to a classical stochastic process when the supersymmetry is unbroken (E0 = 0). By solving a Fokker-Planck equation for the classical probability distribution, we find Pc(y) is identical to |Ψ0(y)|2 in the quantum theory. 相似文献