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21.
A salt‐free procedure for the generation of a wide variety of metal(0) particles, including Fe, Co, Ni, and Cu, was achieved using 2,3,5,6‐tetramethyl‐1,4‐bis(trimethylsilyl)‐1,4‐diaza‐2,5‐cyclohexadiene ( 1 ), which reduced the corresponding metal precursors under mild conditions. Notably, Ni particles formed in situ from the treatment of Ni(acac)2 (acac=acetylacetonate) with 1 in toluene exhibited significant catalytic activity for reductive C? C bond‐forming reactions of aryl halides in the presence of excess amounts of 1 . By examination of high‐magnification transmission electron microscopy images and electron diffraction patterns, we concluded that amorphous Ni nanoparticles (Ni aNPs) were essential for the high catalytic activity.  相似文献   
22.
Yayoi Yoshitomi 《Tetrahedron》2008,64(51):11568-11579
The martinelline chiral core 3 and its diastereomer were synthesized by using the asymmetric tandem Michael-aldol reaction as the key step from 4-methoxycarbonylanthranilaldehyde and the α,β-unsaturated aldehyde.  相似文献   
23.
Tanaka S  Mashima K 《Inorganic chemistry》2011,50(22):11384-11393
Four types of square Pt(4) complexes bearing two or more ferrocenecarboxylate ligands--[Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(4)] (6); [Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(3)(μ-ArNCHNAr)], where ArNCHNAr = N,N'-diarylformamidinate) (7); trans-[Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(2)(μ-ArNCHNAr)(2)] (8); and cis-[Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(2)(κ(4)-N(4)-DArBp)(2)], where DArBp = 1,3-bis(benzamidinato)propane (9)--were successfully prepared via reactions of [FeCp(η(5)-C(5)H(4)COOH)] (5) with the corresponding square Pt(4) complexes, which have labile in-plane acetate ligands. The newly prepared Pt(4) complexes (6-9) with ferrocene moieties as pendants were characterized by nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy (MS), combustion analyses, and single-crystal X-ray analysis for 6, some of the trans-Pt(4)Fe(2)8, and the cis-Pt(4)Fe(2) complexes 9. Weak interactions between two ferrocene moieties across the Pt(4) core, providing ΔE(1/2) values and K(c) constants, were revealed electrochemically, using cyclic and differential-pulse voltammetry in dichloromethane containing [(n)Bu(4)N][BAr(F)(4)] (where Ar(F) = C(6)H(3)(CF(3))(2)-3,5), which was a better supporting electrolyte for such an interaction than [(n)Bu(4)N][PF(6)].  相似文献   
24.
Malyngamide X ( 1 ), the first (7R)‐lyngbic acid connected to a new tripeptide backbone, was isolated from the Thai sea hare Bursatella leachii. The gross structure of 1 was established on the basis of 1D and 2D NMR and mass spectroscopic data. Combination of the NMR spectroscopic experiments with α‐methoxy‐α‐(trifluoromethyl)phenylacetic acid esters, 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol chiral solvating agent, and molecular mechanics of 1 and the synthetic molecular fragments allowed us to determine the absolute stereochemistry of all six stereogenic centers without hydrolytic degradation of the compound. Compound 1 displayed moderate cytotoxic, antitubercular, and antimalarial properties.  相似文献   
25.
A semibiological molecular machine with an implemented "AND" logic gate was developed, which was capable of controlling the folding process of proteins in response to ATP and light as input stimuli. The molecular design made use of a genetically engineered chaperonin GroEL bearing, at both entrance parts of its cylindrical cavity, cysteine residues, which were functionalized by an azobenzene derivative to construct photoresponsive mechanical gates (azo-GroEL). This engineered chaperonin trapped denatured green fluorescent protein (GFP(denat)) and prohibited its refolding. However, when hosting azo-GroEL detected ATP (input stimulus 1) and UV light (input stimulus 2) at the same time, it quickly released GFP(denat) to allow its refolding. In contrast, reception of either input stimulus 1 or 2 resulted in only very slow or no substantial refolding of GFP(denat). Implementation of such "AND" logic gate mechanisms in mechanically driven biomolecular systems is an important step toward the design of secured drug delivery systems.  相似文献   
26.
We demonstrate the ability of all-trans DPEN as a suitable ligand for transition metals by DFT computation [B3LYP/6-311+G(2d,p) and BP86 level]. The iron complex Fe(DPEN) is a unique topological isomer of ferrocene.  相似文献   
27.
We have developed a novel oxidant-free direct cross-coupling reaction of 2,6-lutidine and internal alkynes leading to five-membered carbocyclic compounds mediated by nonmetallocene cationic hafnium alkyl complexes. Mechanistic studies of the coupling reaction showed that the reaction begins with C(sp(3))-H bond activation via σ-bond metathesis, after which the coordinatively unsaturated hafnium center mediates further insertion, migration, and β-H elimination reactions to give five-membered carbocycles from readily available substrates.  相似文献   
28.
Kazushi Sato 《Tetrahedron》2007,63(26):5977-6003
A convergent synthesis of the nonacyclic BCDEFGHIJ-ring polyether core of gambieric acids, potent antifungal polycyclic ether marine natural products, has been achieved. The present synthesis involved as key features: (i) convergent union of the BCD- and GHIJ-ring fragments through esterification, (ii) construction of the E-ring as a lactone form via reductive acetylation, (iii) stereoselective allylation to establish the C26 stereocenter, and (iv) ring-closing metathesis reaction to form the nine-membered F-ring.  相似文献   
29.
We apply our previously developed deconvolution method and interpretation to analyze changes in the OH stretching band [ν(OH) band] of low‐concentration (≤0.2 m) aqueous solutions of NaCl and KCl. We treat these simple, monovalent ions as defects in the hydrogen‐bond network of pure water and quantify the changes in the spectra at low defect concentration with an “order parameter”. Order‐parameter analysis of difference spectra of the two solutions leads to hydration numbers of 7.0±1.0 and 5.9±0.3 for K+ and Na+, respectively. Additionally, we find that changes in the ν(OH) band due to low concentrations of ions result from changes in the topology of the hydrogen‐bond network.  相似文献   
30.
A new catalytic transesterification promoted by a tetranuclear zinc cluster was developed. The mild reaction conditions enabled the reactions of various functionalized substrates to proceed in good to high yield. A large-scale reaction under solvent-free conditions proceeded with a low E-factor value (0.66), indicating the high environmental and economical advantage of the present catalysis.  相似文献   
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