نتایج جستجو برای: asymmetric catalyst

تعداد نتایج: 108514  

2016
Ming-Liang Zhang Deng-Feng Yue Zhen-Hua Wang Yuan Luo Xiao-Ying Xu Xiao-Mei Zhang Wei-Cheng Yuan

For the first time, a catalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones was achieved with a chiral bifunctional amine-thiourea as a catalyst possessing multiple hydrogen-bond donors. With this developed method, a range of 3-hydroxy-3-nitromethyl-1H-pyrrol-2(3H)-ones bearing quaternary stereocenters were obtained in acceptable yield (up to 75%) and enantioselectivity (up to 73% ee).

Journal: :Journal of the American Chemical Society 2013
Chen Zhao Qing-Fu Sun William M Hart-Cooper Antonio G DiPasquale F Dean Toste Robert G Bergman Kenneth N Raymond

The synthesis of a novel supramolecular tetrahedral assembly of K12Ga4L6 stoichiometry is reported. The newly designed chiral ligand exhibits high diastereoselective control during cluster formation, leading exclusively to a single diastereomer of the desired host. This new assembly also exhibits high stability toward oxidation or a low pH environment and is a more robust and efficient catalyst...

Journal: :Chemical communications 2014
Pu-Cha Yan Jian-Hua Xie Xiang-Dong Zhang Kang Chen Yuan-Qiang Li Qi-Lin Zhou Da-Qing Che

A new efficient and highly enantioselective direct asymmetric hydrogenation of α-keto acids employing the Ir/SpiroPAP catalyst under mild reaction conditions has been developed. This method might be feasible for the preparation of a series of chiral α-hydroxy acids on a large scale.

Journal: :Chemical communications 2012
Jie-Ping Wan Charles C J Loh Fangfang Pan Dieter Enders

The asymmetric synthesis of tetrahydropyridin-2-ols from enals and enaminones is described. The organocatalytic domino reaction involves a Michael addition-hemiaminalization sequence using the Jørgensen-Hayashi catalyst. Dehydration or oxidation leads to the corresponding 1,4-dihydro-pyridines or 3,4-dihydropyridin-2-ones in a one-pot fashion.

Journal: :Chemical communications 2012
Hironori Maeda Shinya Yamada Hisanori Itoh Yoji Hori

We have demonstrated that a combination of enantiopure 2-diarylmethylpyrrolidines and heterogeneous Pd/BaSO(4) is an efficient catalytic system for the asymmetric hydrogenation of citral, specifically, a mixture of E-citral and Z-citral in any ratio, and that citronellal is obtained with high enantioselectivity. This dual catalyst system provides a new and more economical route to L-menthol.

2016
Yasuhiro Yamashita Susumu Yoshimoto Mark J Dutton Shū Kobayashi

Highly efficient catalytic asymmetric [3 + 2] cycloadditions using a chiral copper amide are reported. Compared with the chiral CuOTf/Et3N system, the CuHMDS system showed higher reactivity, and the desired reactions proceeded in high yields and high selectivities with catalyst loadings as low as 0.01 mol %.

2015
Shaheen M. Sarkar Md. Eaqub Ali Md. Lutfor Rahman Mashitah Mohd Yusoff

Optically active (−)-ephedrine, (−)-norephedrine, and (−)-prolinol were immobilized onto cubic mesoporousMCM-48 silica.The immobilized amino alcohols served as a heterogeneous chiral catalyst for the asymmetric addition of diethylzinc to aldehydes and transfer hydrogenation to ketones. The developed catalytic process yielded optically enriches secondary aromatic alcohols with 92–99% conversion ...

Journal: :Organic & biomolecular chemistry 2007
Stephen J Connon

Catalytic asymmetric reduction reactions have long been the preserve of the transition metal catalyst. Inspired by the myriad efficient enzyme-catalysed reduction reactions routine in biological systems, chemists have recently begun to design chiral metal-free organocatalysts that employ synthetic dihydropyridine NADH analogues as the hydride source with impressive results. Recent developments ...

Journal: :The Journal of organic chemistry 2006
Belén Rodríguez Carsten Bolm

The proline-catalyzed direct asymmetric Mannich reaction between cyclohexanone, formaldehyde, and various anilines is thermally accelerated. With only 0.5 mol % of catalyst, Mannich products with up to 98% ee have been obtained after a short period of time in reactions performed under microwave irradiation. In situ reduction of the resulting ketones affords N-aryl amino alcohols in up to 86% yi...

Journal: :Organic letters 2003
Wenjun Tang Duan Liu Xumu Zhang

[reaction: see text] The Rh-TangPhos catalyst has been used for asymmetric hydrogenation of itaconic acid and enol acetate derivatives. A variety of chiral 2-substituted succinic acids and chiral acetates have been obtained in excellent ee values (up to 99% ee).

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