Reverse-docking as a computational tool for the study of asymmetric organocatalysis

A novel methodology for 'reverse-docking' a cationic peptide-based organocatalyst to a rigid anionic transition state (TS) model for the conjugate addition of azide to alpha,beta-unsaturated carbonyl substrates is described. The resulting docking poses serve as simplified TS models for enantioselective catalysis. Molecular mechanics-based scoring and ranking of the docking poses, followed by clustering and structural analysis, reveal a clear energetic preference for docking to the S-enantiomeric azidation TS model, in agreement with experiment. Clear energetic trends emerged from docking the catalyst to both enantiomers of all six azidation TS models of this study. Structural analysis of the most favorable pose suggests a mechanism for enantioselective catalysis that is consistent with principles of molecular recognition, catalysis, and experimental data.     

锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展,而具有橄榄石结构的LiFePO_4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源,但自身也存在缺点。综述了锂离子电池正极材料LiFePO_4的研究进展。系统地阐述了LiFePO_4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望,并提出了下一步可能的研究趋势。     

L-脯氨酸催化的不对称Aldol缩合反应实验设计

介绍了L-脯氨酸催化的对硝基苯甲醛与丙酮的不对称Aldol反应的实验设计。室温反应2 h后，柱层析得到（R）-4-（4-硝基苯基）-4-羟基-2-丁酮，利用手性高效液相色谱测试得到产物的ee值。学生实验结果显示，收率范围为53%~74%，对映选择性范围为62%~69%。本实验方案将Aldol反应的研究成果设计成综合性实验，不仅强化训练了学生基本的实验技能和操作，同时拓宽了知识面，培养了学生分析问题、解决问题等方面的综合能力。     

Asymmetric intramolecular Friedel–Crafts reaction catalyzed by a spiropyrrolidine organocatalyst: Enantioselective construction of indolizine and azepine frameworks

The asymmetric intramolecular Friedel–Crafts type Michael reaction of α,β-unsaturated aldehyde with pyrrole, catalyzed by a spiropyrrolidine (SP)-type organocatalyst, has been accomplished, which allows the construction of a series of azepine and indolizine frameworks with high to excellent enantioselectivities (up to 98% ee). Moreover, the substrate scope could be extended to generate a quaternary center in indolizine frameworks (up to 96% ee).     

Resorcinarene supramolecular organocatalyst for functionalized 1-tetralone synthesis in aqueous medium

An efficient, straightforward and environmentally benign process has been developed for the synthesis of fluorenone and 1-tetralone derivatives using cyclic 1,3-dione, malononitrile and dialkylacetylenedicarboxylate as starting materials in aqueous medium. The reaction is favoured in presence of resorcin[4]arene which is effective as a reusable organocatalyst. The catalyst has been easily synthesized and characterized by ¹H, ¹³C NMR, IR, XRD and HRMS analyses. Resorcin[4]arene afforded the resulted products in a shorter time and in good yields. The recyclability of the catalyst was established up to 6th cycle by FT-IR and SEM images.     

Highly active polymeric organocatalyst: Chiral ionic polymers prepared from 10,11‐didehydrogenated cinchonidinium salt

Since few examples of 10,11‐didehydrogenated (3‐ethynyl) cinchona alkaloids have been utilized as organocatalysts in asymmetric reaction, we synthesized 10,11‐didehydrogenated cinchonidine. The 3‐vinyl group of cinchonidine was transformed into a 3‐ethynyl functionality. Based on the resulting 10,11‐didehydrogenated cinchonidine, the corresponding quaternary ammonium salt and its dimers were prepared. The ion‐exchange reaction between the quaternary ammonium salt and sodium sulfonate produced the quaternary ammonium sulfonate as a stable ionic compound. Chiral ionic polymers were then synthesized by the ion‐exchange polymerization of the 10,11‐didehydrogenated cinchonidinium salt dimer and a disulfonate. The chiral ionic polymers were found to be capable of efficiently catalyzing the asymmetric alkylation of N‐(diphenylmethylene)glycine tert‐butyl ester. The enantioselectivities obtained with the polymeric catalysts were higher than those obtained with the corresponding monomeric catalyst. Dimers of 10,11‐didehydrogenated cinchonidinium salts were prepared. Treatment of the dimer with disodium disulfonate gave the chiral ionic polymers, which showed high catalytic activity in asymmetric benzylation of N‐(diphenylmethylen)glycine tert‐butyl ester. The polymeric catalysts were reused several times without the loss of catalytic activity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 621–627     

Asymmetric Synthesis of Novel Axially Chiral 2,2'-Bipyridine N,N'-Dioxides Bearing α-Amino Acid Residues and Their Applications in Enantioselective Allylation of Aromatic Aldehydes with Allyltrichlorosilane

A series of novel axially chiral 2,2′‐bipyridine N,N′‐dioxides bearing C₁ or C₂‐symmetry have been synthesized by the use of enantiopure α‐amino acids as chiral sources. The absolute stereochemistry of the axial chirality of these organocatalysts has been clearly assigned by means of CD measurements together with literature protocols. The reactivities and enantioselectivities of these organocatalysts have been examined in the reactions of aromatic aldehydes with allyltrichlorosilane, thus providing the desired products with moderate yields and enantioselectivies.     

TBD-Catalyzed Trifluoromethylation of Carbonyl Compounds with (Trifluoromethyl)trimethylsilane

Trifluoromethylation of carbonyl compounds using (trifluoromethyl) trimethylsilane catalyzed by 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) afforded the corresponding α-trifluoromethyl alcohols in good to excellent yields under mild reaction conditions.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Synthesis of Sulfonylurea Derivatives Used as Oral Antidiabetics by the Selenium-Assisted Carbonylation Using Carbon Monoxide with Sulfur

Sulfonylurea derivatives including useful antidiabetics (Tolbutamide, Chlorpropamide) were synthesized in good yields from benzene-sulfonamides with thiocarbamates in the presence of DBU. Thiocarbamates were prepared by the selenium-assisted carbonylation of primary amines with carbon monoxide, sulfur, and methyl iodide under mild conditions.