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41.
Several types of six-armed, metal tris(bipyridine) core dendrimers were synthesized. Bis-4,4'-alkoxy bipyridine dendrons were prepared and employed to make tris(bipyridine) dendrimers. Although the ruthenium-centered and iron-centered dendrimers displayed quasi-reversible cyclic voltammetry, the analogous cobalt-centered complex did not. The synthesis of 4,4'-disubstituted bipyridines containing -CH(2)OR groups proceeded in low yield. The reactions of the dicarbanion of 4,4'-dimethyl bipyridine prepared with LDA and mesylate, triflate, and bromide groups were found to result in no or poor yields of carbon-carbon bond formation. Use of KDA in place of LDA resulted in much higher yields of dendritic bipyridines. 相似文献
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The conversion of 4-vinyl substituted β-lactams into 4-vinyl substituted 1-azetines and their subsequent reaction with diphenylcyclopropenone (DPP) results in the formation of a highly functionalised 7-azabicyclo[4.2.1]nonene. This heterocyclic system is an isomer of the homotropane (9-azabicyclo[4.2.1]nonene) nucleus, which is the core structure of a class of alkaloid natural products that includes anatoxin-a. The key processes involved are two ring expansions, one of which constitutes a formal [3+2] cycloaddition and the other of which is an unusual aza-Cope (amino-Claisen) [3,3]-sigmatropic rearrangement. 相似文献
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Irradiation of acetophenone or benzophenone in the presence of norbornadiene or quadricyclene gives 1: 1-adducts. These arise via reaction of the ketone triplet with the quadricyclene. Similar reactivity is exhibited in an intramolecular sense by 7-phenacylnorbornadiene and the corresponding quadricyclene. Addition of triplet benzophenone to 5-methylene norbornene is regiospecific in contrast to expectations based on a comparison of the reactivities of 2-methylenenorbornane and norbornene. The possibility is raised that, in contrast to the simple olefins and the quadricyclenes, exciplexes formed by reaction of the rigid homoconjugated dienes with the triplet ketone are endo orientated with participation of both double bounds. 相似文献
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Zhang Zhengping Gorman B.P. Dong Hanjiang Orozco-Teran Rosa A. Mueller D.W. Reidy R.F. 《Journal of Sol-Gel Science and Technology》2003,28(2):159-165
Dimethyldiethoxysilane (DMDES) appears to be a very promising modifier to introduce functional groups to a silicate network. The polymerization and cyclization of DMDES under acid-catalyzed conditions (DMDES : Ethanol : water : HCl = 1:4:4:3.68 × 10–4 in molar ratio) were investigated by high resolution liquid 29Si nuclear magnetic resonance (NMR) and Fourier transform infrared spectrometry (FTIR). Time-dependent NMR and FTIR data illustrate that monomers of (CH3)2Si(OC2H5)2, (CH3)2Si(OC2H5)(OH), and (CH3)2Si(OH)2 reach meta-equilibrium in less than 4 minutes. 3-membered rings ((CH3)2SiO)3 appear about half an hour later and 4-membered rings ((CH3)2SiO)4 an hour later, which continue to be formed over 24 hours. The relative concentrations of monomers, linear structures and cyclic structures suggest a modified model for the kinetics of cyclization, where 4-membered rings are formed by dimer-dimer interactions, as opposed to monomer-trimer interactions previously proposed. 相似文献
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Mellot Draznieks C Newsam JM Gorman AM Freeman CM Férey G 《Angewandte Chemie (International ed. in English)》2000,39(13):2270-2275