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991.
Kaoru Sano Yoshihito Kohari Hiroto Nakano Chigusa Seki Mitsuhiro Takeshita Micho Tokiwa 《合成通讯》2016,46(1):46-54
Synthesis of bicyclic compounds was achieved via a lipase-catalyzed, stereoselective, domino Michael–aldol reaction of 2-methyl-1,3-cycloalkanedione and methyl vinyl ketone. Appropriate reaction conditions, including the type of enzyme, solvent, and temperature, were determined. In addition, the effects of solvent polarity and addtives were investigated. The reaction proceeded in the presence of lipase AS in a solution of 20% acetone in dimethylsulfoxide (DMSO) at 10 °C for 8 days, followed by the addition of p-toluenesulfonic acid (TsOH) to afford bicyclic compounds in 51–83% yields with moderate stereoselectivity. Although this domino Michael–aldol reaction showed only moderate stereoselectivity, even with the acid-supported enhancement of the reaction, these results represent potential new applications for lipase. 相似文献
992.
993.
Two copper(II) complexes, [Cu(L)(N3)2]·MeOH and [Cu(L)(NCS)2]·MeOH, were prepared and characterized by spectroscopic, analytical, and quantum chemical studies, where L is 2,6-bis(1-butylbenzimidazol-2-yl)pyridine. X-ray quality crystals of [Cu(L)(N3)2]·MeOH were obtained by slow evaporation of MeOH solution of the complex. Molecular structure of [Cu(L)(N3)2]·MeOH was determined by X-ray crystallography. The asymmetric unit contains one [Cu(L)(N3)2] and one MeOH molecule. Cu(II) in [Cu(L)(N3)2]·MeOH is five-coordinate, bonded to five nitrogens (three from L and two from two azide anions). Coordination geometry around Cu(II) center is distorted square-pyramidal with τ value of 0.065. Optimized geometries, IR spectra, and non-linear optical properties of the complexes were obtained by computational studies based on density functional theory (DFT) with M062X method. NLO properties of these complexes were investigated computationally and both complexes exhibit better NLO properties than urea. 相似文献
994.
N‐Substituted Dicyanomethylphenyl Radicals: Dynamic Covalent Properties and Formation of Stimuli‐Responsive Cyclophanes by Self‐Assembly 下载免费PDF全文
Toshiyuki Kobashi Dr. Daisuke Sakamaki Prof. Dr. Shu Seki 《Angewandte Chemie (International ed. in English)》2016,55(30):8634-8638
Dynamic covalent bonds and their chemistry have been of particular interest both from a fundamental and materials science aspect. Demonstrated herein is that triphenylamine (TPA) and carbazole (Cz), substituted with a dicyanomethyl radical, are useful motifs for dynamic covalent chemistry as they have the appropriate bond strength between monomer units as well as high stability and synthetic simplicity. TPA and Cz units substituted by two dicyanomethyl radicals formed macrocyclic oligomers classified as novel types of azacyclophanes, and in particular, the TPA‐based diradical gave a cyclic dimer in almost quantitative yield. The cyclic oligomers exhibited thermo‐ and mechanochromic behavior resulting from the generation of radical species by intermonomer C?C bond cleavage. 相似文献
995.
Orhan Altan Osman Serindağ Koray Sayın Duran Karakaş 《Phosphorus, sulfur, and silicon and the related elements》2016,191(7):993-999
Novel phosphine oxides, (((3-methylpyridin-2-yl)amino)methyl)diphenylphosphine oxide (1) and diphenyl((pyrazin-2-ylamino)methyl)phosphine oxide (2), were synthesized and characterized. Phosphines ligands (3 and 4) were obtained by the reduction of 1 and 2 with AlH3, monitored by 31P NMR spectroscopy. Pd(II) complexes of 3 and 4 were synthesized and characterized (5 and 6). The catalytic activity of 5 and 6 was tested on the reaction of styrene with both activated and deactivated aryl bromides in air. The results of the catalytic experiments were discussed through DFT calculations. 相似文献
996.
Md. Shakhawoat Hossain Gül Altınbaş Özpınar Said Nadeem Ayhan S. Demir 《Phosphorus, sulfur, and silicon and the related elements》2016,191(9):1262-1267
Hetero Diels-Alder (HDA) reactions between 2,3-dimethyl-1,3-butadiene and diethyl ester of aroyl phosphonates catalyzed by AlCl3 to afford (3,6-dihydro-2H-pyran-2-yl) phosphonate derivatives were investigated. Aroyl phosphonates with electron-withdrawing groups generally resulted in better isolated chemical yields. A stoichiometric amount of AlCl3 rather than a catalytic amount was necessary to activate the cycloaddition reaction. The amount of AlCl3 catalyst and its effect on LUMO of ethyl ester benzoyl phosphonate were also investigated by performing density functional theory (DFT) (B97D/6-31+G(d,p)) computations in dichloromethane. An increased loading of AlCl3 induced a considerable decrease in the LUMO energy of ethyl ester of benzoyl phosphonate. The computed Gibbs free activation energy is 17.03 kcal/mol in DCM at 0°C using the same computational level. 相似文献
997.
We prove that the kernels of Bernstein, Stancu and Kantorovich operators are proximinal sets, therefore the infimum of Hyers–Ulam constants is also a Hyers–Ulam constant for the above mentioned operators. Moreover, we investigate what happens when the supremum norm is replaced by the L1-norm. 相似文献
998.
Meral Cansiz Aktaş 《International Journal of Mathematical Education in Science & Technology》2016,47(4):583-596
The aim of this study was to investigate the appropriateness of high school students' definitions. The participants in this study were 269 high school students from a public school in Ordu city, which is on the Black Sea coast of Turkey. The participants were asked to write their definitions with no time constraints. In the analysis of the definitions, students' ability to distinguish necessary and sufficient conditions and their ability to use appropriate mathematical terminology were taken into account. The task used in this study enabled us to mirror students' difficulties and inadequacies about their definitions of a parallelogram. The findings indicated that most of the students defined parallelogram inappropriately because they had used incomplete or incorrect statements. On the other hand, for the appropriate definitions, it was found that the number of uneconomical definitions was almost the same as the number of economical ones. At the end of the study, it was suggested that defining activities should be integrated into curriculums explicitly and should be given importance in our mathematic lessons. 相似文献
999.
In this study, catalytic activity of two different cationic O-Carboxymethyl chitosan Schiff base palladium (II) complexes in Suzuki coupling reactions and synthesis of biarlys having different functional groups, and reusability of the catalysts were tested. Chemical structures of the synthesized biaryls were elucidated by GC-MS and 1H-NMR; and no by-products were observed in the spectra. Cationic palladium (II) catalysts high turnover numbers and selectivity were recorded for the reactions. Mercury test demonstrated that the reaction mechanism proceed a homogeneous route. Reusability tests of cationic biocatalysts showed that their catalytic activity were still highly efficient even after six cycles. 相似文献
1000.
An NACE method was developed for the quantitative determination of acrylamide in processed food. The method is premised on the modification of the aqueous acid-base character of acrylamide in an organic solution. Acrylamide, which is a polar molecule in aqueous solution, in a low-pH environment in ACN acquires a proton, and thereby migrates under its own electrophoretic mobility in CE. Thus, nonaqueous separation of acrylamide was achieved by employing 30 mmol/L HClO(4) in ACN as the running electrolyte. The detection limit of the method for acrylamide was found as 0.041 mg/L using UV detection at 200 nm. The run-to-run and day-to-day precisions for the corrected peak areas were calculated as 1.65 and 3.90%, respectively. The applicability of the method has been demonstrated by analyzing acrylamide in the samples of potato chips and French fries. The method is simple, rapid, inexpensive, and widely applicable for the determination of acrylamide in food samples. 相似文献