共查询到20条相似文献,搜索用时 15 毫秒
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Brinton Seashore‐Ludlow Piret Villo Prof. Peter Somfai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7219-7223
Herein, we present two methods for an asymmetric transfer hydrogenation through the dynamic kinetic resolution of α‐amido‐β‐ketoesters. These procedures yield the corresponding anti‐β‐hydroxy‐α‐amido esters in good yields and with good diastereo‐ and enantioselectivities. First, the scope of the reduction of α‐amido‐β‐ketoesters by using triethylammonium formate azeotrope is examined. Then, an emulsion technology with sodium formate is explored, which allows for broader substrate scope, faster reaction times, and lower catalyst loading. Furthermore, these reactions are operationally simple and can be set up in air. 相似文献
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Lanning Li Bin Chen Yuanyuan Ke Qing Li Yue Zhuang Kun Duan Yichun Huang Dr. Jiyan Pang Prof. Dr. Liqin Qiu 《化学:亚洲杂志》2013,8(9):2167-2174
A valuable class of new heterocyclic and alicyclic prochiral α‐aminomethylacrylates has been conveniently synthesized through a three‐step transformation involving a Baylis–Hillman reaction, O‐acetylation, and a subsequent allylic amination. The corresponding novel β2‐amino acid derivatives were prepared with excellent enantioselectivities and high yields by catalytic asymmetric hydrogenation using the catalyst rhodium(Et‐Duphos) (Et‐Duphos=2′,5′,2′′,5′′‐tetraethyl‐1,2‐bis(phospholanyl)benzene)) under mild reaction conditions (up to 99 % ee and S/C=1000). The influence of the substrate on the enantioselectivity and reactivity is investigated, and the most suitable substrate configuration for the highly efficient enantioselective hydrogenation of β‐substituted α‐aminomethylacrylates under the Rh–Duphos system is reported. The current protocol provides a very practical, facile, and scalable method for the preparation of heterocyclic and alicyclic β2‐amino acids and their derivatives. 相似文献
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Jia‐Qi Li Xu Quan Prof. Dr. Pher G. Andersson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10609-10616
α,β‐Unsaturated esters have been employed as substrates in iridium‐catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic‐ and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. 相似文献
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Yafei Guo Johanan Kootstra Prof. Dr. Syuzanna R. Harutyunyan 《Angewandte Chemie (International ed. in English)》2018,57(41):13547-13550
A method for catalytic asymmetric alkylation of conjugated dienyl amides has been developed and it allows efficient and high‐yielding transformations of a wide range of polyconjugated amides into the corresponding chiral products. Smooth addition of organomagnesium reagents to relatively unreactive dienyl amides with excellent 1,6‐ and 1,4‐selectivities, as well as enantioselectivites above 90 %, is achieved owing to the complementary action of the Lewis acid and a chiral copper‐based catalyst. 相似文献
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Ernest Salomó Dr. Sílvia Orgué Prof. Antoni Riera Prof. Xavier Verdaguer 《Angewandte Chemie (International ed. in English)》2016,55(28):7988-7992
The MaxPHOX–Ir catalyst system provided the highest selectivity ever reported for the reduction of cyclic enamides derived from α‐ and β‐tetralones. This result indicates that iridium catalysts are also proficient in reducing alkenes bearing metal‐coordinating groups. In the present system, selectivity was pressure‐dependent: In most cases, a decrease in the H2 pressure to 3 bar resulted in an increase in enantioselectivity. Moreover, the process can be carried out in environmentally friendly solvents, such as methanol and ethyl acetate, with no loss of selectivity. 相似文献
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Tsukuru Maeda Dr. Kazuishi Makino Masamichi Iwasaki Prof. Yasumasa Hamada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(39):11954-11962
The development of Ir‐catalyzed asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides is described. This reaction proceeds through a dynamic kinetic resolution to produce anti‐β‐hydroxy‐α‐amino acid esters in a high diastereo‐ and enantioselective manner. Mechanistic studies have revealed that this unique asymmetric hydrogenation proceeds through reduction of the ketone moiety via the five‐membered transition state involving the chelation between the oxygen of the ketone and the nitrogen of the amine function. The relationship studies between the hydrogen pressure and the stereoselectivity have disclosed two mechanisms dependent on hydrogen pressure. Under low hydrogen pressure (<15 atm), the reaction rate proportionally increased with the hydrogen pressure. However, under the high hydrogen conditions, the reaction rate exponentially accelerated along with the increasing hydrogen pressure, which suggests the participation of two or more of hydrogen atoms. 相似文献
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《Angewandte Chemie (International ed. in English)》2017,56(49):15723-15727
A novel ynamide preactivation strategy enables the use of otherwise incompatible reagents and allows preparation of α,β‐disubstituted enamides with high regio‐ and stereoselectivity. Mechanistic analysis reveals the intermediacy of a triflate‐bound intermediate as a solution‐stable, effective keteniminium reservoir, whilst still allowing subsequent addition of organometallic reagents. 相似文献
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Shaoquan Lin Dr. Naoya Kumagai Prof. Dr. Masakatsu Shibasaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3296-3299
We report a direct catalytic asymmetric Mannich‐type addition of α,β‐unsaturated γ‐butyrolactam to α‐ethoxycarbonyl ketimines promoted by a soft Lewis acid/Brønsted base cooperative catalyst. A thiophosphinoyl group on the nitrogen of ketimines was crucial for both electrophilic activation and α‐addition of γ‐butyrolactams. The obtained aza‐Morita–Baylis–Hillman‐type products bear an α‐amino acid architecture with a tetra‐substituted stereogenic center. 相似文献
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Hiroyuki Kakei Riichiro Tsuji Dr. Takashi Ohshima Dr. Hiroyuki Morimoto Shigeki Matsunaga Dr. Masakatsu Shibasaki Prof. Dr. 《化学:亚洲杂志》2007,2(2):257-264
The full details of the asymmetric epoxidation of α,β‐unsaturated esters catalyzed by yttrium complexes with biaryldiol ligands are described. An yttrium–biphenyldiol catalyst, generated from Y(OiPr)3–biphenyldiol ligand–triphenylarsine oxide (1:1:1), is suitable for the epoxidation of various α,β‐unsaturated esters. With this catalyst, β‐aryl α,β‐unsaturated esters gave high enantioselectivities and good yields (≤99 % ee). The reactivity of this catalyst is good, and the catalyst loading could be decreased to as little as 0.5–2 mol % (the turnover number was up to 116), while high enantiomeric excesses were maintained. For β‐alkyl α,β‐unsaturated esters, an yttrium–binol catalyst, generated from Y(OiPr)3–binol ligand–triphenylphosphine oxide (1:1:2), gave the best enantioselectivities (≤97 % ee). The utility of the epoxidation reaction was demonstrated in an efficient synthesis of (?)‐ragaglitazar, a potential antidiabetes agent. 相似文献
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Miguel Espinosa Prof. Dr. Gonzalo Blay Prof. Dr. Luz Cardona Prof. Dr. José R. Pedro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14861-14866
The asymmetric conjugate addition of malonate esters to α,β‐unsaturated N‐sulfonyl imines is catalyzed by PyBOX/La(OTf)3 complexes in the presence of 4 Å MS. The reaction gives the corresponding E enamines bearing a stereogenic center at the allylic position with good yields and enantiomeric ratios up to 97:3. This reaction provides a synthetic entry to chiral δ‐aminoesters and piperidones. 相似文献
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Rhodium‐Catalyzed Highly Regio‐ and Enantioselective Hydrogenation of Tetrasubstituted Allenyl Sulfones: An Efficient Access to Chiral Allylic Sulfones 下载免费PDF全文
Jiao Long Liyang Shi Xiong Li Prof. Hui Lv Prof. Xumu Zhang 《Angewandte Chemie (International ed. in English)》2018,57(40):13248-13251
A highly regio‐ and enantioselective hydrogenation of challenging tetrasubstituted allenyl sulfones has been developed, affording chiral allylic sulfones in good yields with excellent regio‐ and enantioselectivities (up to 99 % yield and 99 % ee). This method provides an efficient and concise route to chiral allylic sulfones, thus offering an atom‐economic process with a wide range of potential applications in organic synthesis and medicinal chemistry. 相似文献
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