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991.
A new, reusable Pd/MgLa mixed oxide catalyst has been applied successfully in the Suzuki-Miyaura carbon-carbon cross-coupling reaction of aryl halides as well as benzylic bromide with boronic acids in ethanol. The catalyst is air stable, can be stored and handled under an ambient atmosphere and after the reaction it can be recovered by simple filtration and reused without significant loss of activity. 相似文献
992.
Pizzonero M Keller L Dumas F Ourevitch M Morgant G Spasojević-de Biré A Bogdanović G Ghermani NE D'Angelo J 《The Journal of organic chemistry》2004,69(13):4336-4350
In connection with a total synthesis of cephalotaxine (1a), we have examined the addition of various nucleophilic reagents to [ABC] subunits 2 and 7 possessing a pyrrolobenzazepine core. In fact, this reaction implicates invariably the carbonyl group of 2. Regarding the reaction of 7 with nucleophiles, the most striking aspect is the complete lack of reactivity of the enaminonitrile moiety. For instance, the condensation of 7 with methylmagnesium bromide involves exclusively the cleavage of the dioxole ring, yielding regioisomers 9 and 10. With the aim of understanding the unexpected reactivity of 2 and 7 toward nucleophiles, crystallographic studies of 2 and 7 and an experimental electron density determination of 7 were carried out. The marked reactivity of the carbonyl group of 2 was interpreted by invoking the weakness of the amide resonance, due to a pronounced delocalization of the N(9) lone pair over the enaminonitrile moiety. The electron density study of 7 reveals this electron delocalization along the enaminonitrile fragment, highlighted and quantified through the bond geometries, topological indicators, and atomic charges, a phenomenon that is responsible for the failure of the addition of nucleophilic species. 相似文献
993.
994.
995.
Juraj ?ernák Fran?ois Gérard Charles Kappenstein Jozef Chomi? 《Monatshefte für Chemie / Chemical Monthly》2004,66(4):1081-1088
Coordination compounds Zn(mal)(H2O)2 (ZMH) (mal=maleate anion (C2H2(CO2)22-)), Cu0.06Zn0.94(mal)(H2O)2 (ZCMH), Cu(mal)(H2O) (CMH), and physical mixtures of CMH and ZMH were used as precursors for calcination experiments in air at 500 and 1000°C lasting 18 hours. The obtained oxides were investigated by X-ray powder diffraction technique. Calcination at 500°C yielded pure zincite phase (ZnO), tenorite phase (CuO), or their mixtures. The calcination of the Zn-rich sample ZCMH at 1000°C lead to zincite phase displaying a slightly lower cell volume than the pure zincite phase obtained from Zn-only containing precursor (ZMH). These results suggest that the assumed solid solution CuxZn1–xO (x=0.01–0.02) exhibits a solubility limit lower than the copper content in the ZCMH precursor (6mol-%). On the other hand, the calcination of the Cu-rich samples at 1000°C, in the presence of Zn(II), yielded tenorite phase exhibiting cell parameters significantly different from those reported for the pure tenorite phase, due to the formation of Zn0.03Cu0.97O solid solutions. All these results are corroborated by intensity analysis of the diffraction peaks. 相似文献
996.
Dueymes C Schönberger A Adamo I Navarro AE Meyer A Lange M Imbach JL Link F Morvan F Vasseur JJ 《Organic letters》2005,7(16):3485-3488
A new solution-phase phosphoramidite approach is reported for oligonucleotide synthesis employing recyclable solid-supported reagents. It uses polyvinyl pyridinium tosylate as the activator of a nucleoside-3'-O-phosphoramidite in the coupling step with a 5'-OH nucleoside or dinucleotide. The resulting phosphite triester was either sulfurized or oxidized using polystyrene-bound trimethylammonium tetrathionate or periodiate. This method avoids complicated purification steps, as excess reagents are easily removed by filtration. [reaction: see text] 相似文献
997.
Couillet I Hughes T Maitland G Candau F Candau SJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(22):9541-9550
The structural and dynamic properties of micellar solutions of erucyl bis(hydroxyethyl)methylammonium chloride blended with 2-propanol, in the presence of KCl, have been investigated by means of light scattering and rheological experiments. In the dilute regime, the micellar growth is larger than expected from mean-field or scaling models. The results obtained in the vicinity of the overlap concentration suggest the presence of large aggregates, with size >100 nm, possibly micellar rings or microgels. In the semidilute regime, the relationship between the zero shear viscosity and the surfactant concentration is described by a power law with an exponent in agreement with the mean-field model of linear micelles. The methods based on the analysis of the temperature dependence of the complex shear modulus to provide a measure of the scission energy are discussed. 相似文献
998.
An unprecedented outcome of the lithium–ammonia reduction of enones: the formation of cyclopropanols
Franoise Dumas Cyrille Thominiaux Christine Miet Jean d'Angelo Didier Desmaële Mohammed Nour Christian Cav Georges Morgant Marie-Elise Tran Huu-Dau 《Tetrahedron letters》2002,43(52):9649-9652
An unusual process takes place during the lithium–ammonia reduction of a variety of cyclic enones bearing an ester group in the γ-position, furnishing cyclopropanols. The reason for this unprecedented outcome has been attributed to the through-space stabilization of a developing cyclopropyl radical by interaction with the neighboring ester substituent. 相似文献
999.
Chiboub-Fellah Abdelghani Meullemeestre Jean Spies Catrin Vierling François Khan Mustayeen A. 《Transition Metal Chemistry》1999,24(2):135-140
Four NiII chloro complexes were identified spectrophotometrically in aprotic media such as DMSO, DMF and propylene carbonate for the first time. An original multiwavelength numerical treatment, based on a Marquardt method, results in the determination of the individual electronic spectra of the mononuclear chloro complexes and of their stability constants, the values of which indicate the presence of rather weak complexes in DMSO and DMF, much stronger in the less solvating propylene carbonate solvent. The overall stability constants calculated for the NiII chloro complexes are: 1=52, 2=140, 3=160, 4=210 in DMSO, 1=60, 2=110, 3=900, 4=15000 in DMF, 1=1.6×109, 2=6.4×1015, 3=2.7×1021, 4= 5.1×1026 in PC.The solvent effect is discussed in terms of the quantitative results obtained from this spectrophotometric study and reveals that the stability of the complexes is an inverse function of the donor properties of the solvent. This result illustrates the general behavior of complex formation in dipolar aprotic solvents, i.e. the substitution of one solvent molecule in the inner coordination sphere by the ligand is easier if the solvation strength of the solvent is lower. The solvent effect is also described in terms of the variation of shifts of the calculated absorption maxima for the individual electronic spectra of the chloro complexes. This result is used to identify clearly at which step of coordination the octahedral configuration of the nickel ion changes to the tetrahedral configuration, by comparison with the well-known structural properties of these complexes in the solid state. 相似文献
1000.
Kinetics of the reaction of 1-tosyl-3-methyl-imidazolium chloride with various amines were measured to examine the nature of sulfonyl transfer in enzymatic reactions. The activation parameters and the value of the brønsted exponent, β = 0.48, are consistent with a small degree of bonding between the entering amine and the sulfur atom in the transition state. Similarities in the nucleophilic behavior of sulfonyl and carbonyl groups are detected. 相似文献