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排序方式: 共有602条查询结果,搜索用时 15 毫秒
1.
Dr. Christopher R. Opie Dr. Hidetoshi Noda Prof. Dr. Masakatsu Shibasaki Dr. Naoya Kumagai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4648-4653
The B3NO2 six-membered heterocycle (1,3-dioxa-5-aza-2,4,6-triborinane=DATB), comprising three different non-carbon period 2 elements, has been recently demonstrated to be a powerful catalyst for dehydrative condensation of carboxylic acids and amines. The tedious synthesis of DATB, however, has significantly diminished its utility as a catalyst, and thus the inherent chemical properties of the ring system have remained virtually unexplored. Here, a general and facile synthetic strategy that harnesses a pyrimidine-containing scaffold for the reliable installation of boron atoms is disclosed, giving rise to a series of Pym-DATBs from inexpensive materials in a modular fashion. The identification of a soluble Pym-DATB derivative allowed for the investigation of the dynamic nature of the B3NO2 ring system, revealing differential ring-closing and -opening behaviors depending on the medium. Readily accessible Pym-DATBs proved their utility as efficient catalysts for dehydrative amidation with broad substrate scope and functional-group tolerance, offering a general and practical catalytic alternative to reagent-driven amidation. 相似文献
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Nucleophilic and Electrophilic Activation of Non‐Heteroaromatic Amides in Atom‐Economical Asymmetric Catalysis 下载免费PDF全文
Dr. Naoya Kumagai Prof. Dr. Masakatsu Shibasaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15192-15200
Recent advances in catalytic asymmetric carbon–carbon bond‐forming reactions of non‐heteroaromatic amide substrates are highlighted. Among carbonyl compounds, amides have received limited attention in catalytic asymmetric transformations mainly owing to their lower reactivity. Amides are reluctant to form enolates for nucleophilic addition, and α,β‐unsaturated amides exhibit diminished electrophilicity at the β‐carbon. Recent advances in asymmetric catalysis rendered these amides amenable to enantioselective reactions with perfect atom economy, producing synthetically useful chiral building blocks. This Minireview summarizes recent developments in the field. 相似文献
3.
Dr. Xinxin Tang Dr. Hidetoshi Noda Prof. Dr. Masakatsu Shibasaki 《Angewandte Chemie (International ed. in English)》2023,62(51):e202311027
The exponential proliferation of conformers makes it impossible to examine the entire population in most systems. Controlling conformational ensembles is thus pivotal in many areas of chemistry. Rh2(esp)2, a dicarboxylate-derived paddlewheel rhodium complex, is one of the most effective catalysts for nitrene chemistry. Its enormous success has led to preparing many analogous complexes. However, there has been little consideration for the conformational dynamics of the parent catalyst. Herein, we report a new ligand modification principle that prevents conformer interconversion. The resulting complex comprises two isolable conformers, whose structures have been determined by X-ray diffraction. Combined experimental and computational data has revealed similarities and dissimilarities between the conformationally confined and parent complexes. Three model cases have demonstrated the utility of conformational fixation in the development of stereoselective catalysts for nitrene transfer reactions. The design principle described in this study can be combined with other established modification strategies, serving as a springboard for further advancement of the chemistry of paddlewheel metal complexes. 相似文献
4.
Dr. Karin Weidner Zhongdong Sun Dr. Naoya Kumagai Prof. Dr. Masakatsu Shibasaki 《Angewandte Chemie (International ed. in English)》2015,54(21):6236-6240
A direct aldol reaction of an α‐azido 7‐azaindolinylamide, promoted by a Cu‐based cooperative catalyst, is documented. Aromatic aldehydes bearing an ortho substituent exhibited diastereodivergency depending on the nature of the chiral ligands used. Smooth reactions with ynals highlighted the broad substrate scope. A vicinal azido alcohol unit in the product allowed direct access to the corresponding aziridine and facile hydrolysis of the 7‐azaindolinylamide moiety furnished enantioenriched β‐hydroxy‐α‐azido carboxylic acid derivatives. 相似文献
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Hirosato Monobe Shoji Mima Takushi Sugino Yo Shimizu Masakatsu Ukon 《Liquid crystals》2013,40(8):1253-1258
The orientational behaviour of the nematic discotic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene (C8OBT) on substrates coated with a polyimide or cetyltrimethylammonium bromide (CTAB) was investigated by polarizing optical microscopy. The averaged order parameters and directions of the triphenylene core and the carbonyl groups of C8OBT were evaluated by an infrared dichroic method. The discotic nematic (ND) phase of C8OBT exhibits a homeotropic alignment on a polyimide film, a typical nematic schlieren texture on a glass substrate, and a tilted or planar homogeneous alignment on a CTAB-coated substrate. The order parameter of the triphenylene core is higher on a polyimide film (S = 0.6) than on a CTAB-coated substrate (S = 0.2), whereas that of the carbonyl groups remains roughly constant at 0.2 to 0.3 independent of the substrate for the ND phase. 相似文献
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Maria Carmelita Z. Kasuya Xiaonan Wen Kenichi Hatanaka Kageyasu Akashi 《Journal of fluorine chemistry》2011,132(11):978-981
Incubation of mouse melanoma B16 cells in fluorous solvents with low boiling point such as perfluoromethylcyclohexane, 1,1,1,3,3,3-hexafluoro-2-propanol, ethylpentafluoropropionate resulted in cell death. However, cells lived up to 2 days in fluorous alcohols such as 2,2,3,3,4,4,5,5-octafluoro-1-pentanol and 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol with relatively higher fluorine content. Remarkably, cells survived deprived of nutrition up to 4 days when incubated in 2,2,3,3,4,4,5,5,6,6,6-undecafluoro-1-hexanol or in 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanol that have the most number of fluorine atoms (11 and 12, respectively) among the perfluoroalkyl alcohols used, and with boiling points of 128 °C and 169 °C, respectively. 相似文献
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