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Yang J Cauble DF Berro AJ Bauld NL Krische MJ 《The Journal of organic chemistry》2004,69(23):7979-7984
Exposure of easily reduced aromatic bis(enones) 1a-1e to the methyl Gilman reagent Me(2)CuLi.LiI at 0 degrees C in tetrahydrofuran solvent provides the products of tandem conjugate addition-Michael cyclization, 2a-2e, along with the products of [2 + 2] cycloaddition, 3a-3e. Complete partitioning of the Gilman alkylation and [2 + 2] cycloaddition pathways may be achieved by adjusting the loading of the Gilman reagent, the rate of addition of the Gilman reagent, and the concentration of the reaction mixture. The Gilman alkylation manifold is favored by the rapid addition of excess Gilman reagent at higher substrate concentrations, while the [2 + 2] cycloaddition manifold is favored by slow addition of the same Gilman reagent at lower concentrations and loadings. Notably, [2 + 2] cycloaddition to form 3a-3e is catalytic in Gilman reagent. Kinetic data reveal that the ratio of 2a and 3a changes such that the cycloaddition pathway becomes dominant upon increased consumption of Gilman reagent. These data suggest a concentration-dependent speciation of the Gilman reagent and differential reactivity of the aggregates present at higher and lower concentrations. While the species present at higher concentration induce Gilman alkylation en route to products 2a-2e, the species present at lower concentration provide products of catalytic [2 + 2] cycloaddition, 3a-3e. Moreover, upon electrochemical reduction of the bis(enones) 1a-1e, or chemically induced single-electron transfer from arene anion radicals, the very same [2 + 2] cycloadducts 3a-3e are formed. The collective data suggest that [2 + 2] cycloadducts 3a-3e arising under Gilman conditions may be products of anion radical chain cyclobutanation that derive via electron transfer (ET) from the Me(2)CuLi.LiI aggregate(s) present at low concentration. These observations provide a link between the Gilman alkylation reaction and related ET chemistry and suggest these reaction paths are mechanistically distinct. This analysis is made possible by the recent observation that easily reduced bis(enones) are subject to intramolecular [2 + 2] cycloaddition upon cathodic reduction or chemically induced ET from arene anion radicals, and is herewith showcased as a novel method of testing for the intermediacy of enone anion radicals. 相似文献
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Da Silva L.B. Cauble R. Barbee T.W. Jr. Celliers P. Ciarlo D. Libby S. London R.A. Matthews D. Mrowka S. Moreno J.C. Ress D. Trebes J.E. Wan A.S. Weber F. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(1):31-32
We have developed a soft X-ray interferometer capable of probing large high-density plasmas with micron spatial resolutions. A neon-like yttrium X-ray laser operating at 155 Å was combined with the Mach-Zehnder interferometer to obtain electron density profiles of a laser-produced exploding selenium foil plasma. The plasma was produced with one Nova laser beam using a 120-μm line focus, the same conditions used to create a selenium X-ray laser. The interferogram of the selenium plasma was obtained from an end-on perspective 相似文献
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An expression for the electron thermal conductivity in the two-component strongly coupled plasmas is derived. The new formulation is examined in the context of laser fusion plasmas, using static correlations derived from the hypernetted chain equations. The model yields results in good agreement with molecular dynamics simulations. 相似文献
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A strategy for the enantioselective catalysis of photomediated reactions in solution is described, involving the use of chiral molecular receptors possessing appendant triplet-sensitizing moieties. Energy transfer is selectively directed to bound substrate as a consequence of the distance dependence of triplet-triplet energy transfer. This effect, which is equivalent to a binding-induced rate enhancement, enables substoichiometric chirality transfer from the receptor template to the substrate, as observed in the intramolecular enone-olefin photo[2 + 2]cycloaddition of a quinolone substrate. 相似文献
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Exposure of monoenone monoketones to catecholborane in THF at ambient temperature results in tandem 1,4-reduction-aldol cyclization. For aromatic and heteroaromatic enones, six-membered cyclic aldol products are formed in excellent yield with high levels of syn diastereoselectivity. Five-membered ring formation proceeds less readily, but the yield of cyclized product is improved through introduction of Rh(I) salts. 相似文献
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