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491.
Perrhenate-Catalyzed Rearrangement of Ethinyl-β-ionol The rearrangement of 2-ethinyl-β-ionol ( 1 ) to α,β-unsaturated carbonyl compounds using tetraalkylammonium perrhenate catalysts was studied. It was found that the Rupe-Kambli product, ketone 2 , is the main product (ca. 70%) of this rearrangement. The by-product 4 (ca. 15%) is formed in a ring-closure reaction. 相似文献
492.
Mbaye MD Renaud JL Demerseman B Bruneau C 《Chemical communications (Cambridge, England)》2004,(16):1870-1871
Regio- and enantioselective substitution of cinnamyl chloride by phenols has been achieved with up to 82% enantiomeric excess, using a ruthenium catalyst prepared from [Cp*(CH(3)CN)(3)Ru][PF(6)] and a chiral bisoxazoline ligand. 相似文献
493.
Schroeyers W Vallée R Patra D Hofkens J Habuchi S Vosch T Cotlet M Müllen K Enderlein J De Schryver FC 《Journal of the American Chemical Society》2004,126(44):14310-14311
In this Communication, we report on the fluorescence behavior of an individual first generation multichromophoric dendrimer. The fact that each of the chromophores in time acts as a fluorescent trap is demonstrated by directly probing the dipole orientation of the emitting chromophore by means of defocused wide-field imaging and comparing experimental and calculated emission patterns. It is shown that in such cases the electromagnetic boundary condition effect results in discrete changes in the fluorescence lifetime as a function of time for individual dendrimers. 相似文献
494.
Tomczak N Vallée RA van Dijk EM Kuipers L van Hulst NF Vancso GJ 《Journal of the American Chemical Society》2004,126(15):4748-4749
Single fluorescent molecules (represented by spheres with a volume equal to the actual van der Waals volume of the molecule) has been embedded in a polystyrene matrix (left). Such molecules act as probes for the study of polymer nanoscale (segmental scale) dynamics in thin films deposited on a glass cover slide (right). 相似文献
495.
496.
Emmerson DP Villard R Mugnaini C Batsanov A Howard JA Hems WP Tooze RP Davis BG 《Organic & biomolecular chemistry》2003,1(21):3826-3838
The ready construction of 24 stereochemically and functionally diverse carbohydrate ligand structures from a core D-glucosamine scaffold has allowed the evaluation of broad ranging structure activity relationships in ligand accelerated zincate additions to aldehydes, with variations in deltadeltaG+/+(R-S) of up to 5650 J mol(-1) that create opposing senses of asymmetric induction and that are consistent with models based on several ligand X-ray structures and molecular mechanics analysis. Factorial analysis of enantioselectivity using key dihedral angles and steric volume on N-2 also highlight the potential for the use of factorial design in ligand construction. 相似文献
497.
498.
In the continuum O(3) sigma model in two spatial dimensions, there are topological solitons whose size can be stabilized by adding Skyrme and potential terms. This Letter describes a lattice version, namely a natural way of modifying the 2D Heisenberg model to achieve topological stability on the lattice. 相似文献
499.
500.
Ring substituted α-bromoacetophenones undergo efficient photodecomposition upon ultraviolet irradiation in alcohol solvents. The process involves chain reactions mediated by the ketyl radicals derived by hydrogen abstraction from the alcohols. It is suggested that two chain reactions involving hydrogen and electron transfer may be taking place concurrently. Competitive studies lead to relative rate constants for the reactions of ketyl radicals with ring-substituted α-bromoacetophenones. 相似文献