- The site-selectivity and mechanism of Pd-catalyzed C(sp2)-H arylation of simple arenes
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Control over site-selectivity is a critical challenge for practical application of catalytic C-H functionalization reactions in organic synthesis. Despite the seminal breakthrough of the Pd-catalyzed C(sp2)-H arylation of simple arenes via a concerted metalation-deprotonation (CMD) pathway in 2006, understanding the site-selectivity of the reaction still remains elusive. Here, we have comprehensively investigated the scope, site-selectivity, and mechanism of the Pd-catalyzed direct C-H arylation reaction of simple arenes. Counterintuitively, electron-rich arenes preferably undergo meta-arylation without the need for a specifically designed directing group, whereas electron-deficient arenes bearing fluoro or cyano groups exhibit high ortho-selectivity and electron-deficient arenes bearing bulky electron-withdrawing groups favor the meta-product. Comprehensive mechanistic investigations through a combination of kinetic measurements and stoichiometric experiments using arylpalladium complexes have revealed that the Pd-based catalytic system works via a cooperative bimetallic mechanism, not the originally proposed monometallic CMD mechanism, regardless of the presence of a strongly coordinating L-type ligand. Notably, the transmetalation step, which is influenced by a potassium cation, is suggested as the selectivity-determining step.
- Kim, Daeun,Choi, Geunho,Kim, Weonjeong,Kim, Dongwook,Kang, Youn K.,Hong, Soon Hyeok
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p. 363 - 373
(2021/01/14)
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- N-Heterocarbene Palladium Complexes with Dianisole Backbones: Synthesis, Structure, and Catalysis
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A series of palladium N-heterocyclic carbenes (NHCs), complexes C1-C5, bearing dianisole backbones and substituted N-aryl moieties have been synthesized and characterized. The electronic effect as well as the steric environment of the NHC ligands has been assessed. The synthesized palladium complexes were applied for Suzuki-Miyaura cross-coupling reactions under aerobic conditions. The relationship between the catalytic structure and catalytic performance was then extensively investigated. Upon optimizing the reaction conditions, the C4 was found to be highly efficient to catalyze the cross-coupling of (hetero)aryl chlorides with (hetero)arylboronic acids at a 0.1 mol % palladium loading.
- Li, Dong-Hui,He, Xu-Xian,Xu, Chang,Huang, Fei-Dong,Liu, Ning,Shen, Dong-Sheng,Liu, Feng-Shou
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p. 2539 - 2552
(2019/06/17)
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- Synthesis of a class of binaphthyl monophosphine ligands with a naphthofuran skeleton and their applications in Suzuki-Miyaura coupling reactions
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A series of new monophosphine ligands containing a naphthofuran skeleton have been prepared, characterized and evaluated in palladium-catalyzed Suzuki-Miyaura coupling reactions. Using Pd2(dba)3-L6 as the catalyst the reactions were performed with high catalytic activity under mild reaction conditions and the desired coupling products were obtained in good to excellent yields. The new catalyst system also showed broad substrate adaptability and practicality for gram-scale production.
- Zhou, Zihong,Liang, Hao,Xia, Wang,Chen, Huixuan,Zhang, Yaqi,He, Xuefeng,Yu, Sifan,Cao, Rihui,Qiu, Liqin
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p. 5967 - 5971
(2018/04/23)
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- Glutamate (NMDA) receptor antagonists
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Novel naphthyl-substituted α-amino acid derivatives, pharmaceutical compositions containing the same and a method of using the same, for the blockade of aspartate and glutamate receptors, are described. Novel intermediates of the napthyl-substituted α-amino acid derivatives are disclosed.
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- Potent, Orally Active, Competitive N-Methyl-D-aspartate (NMDA) Receptor Antagonists Are Substrates for a Neutral Amino Acid Uptake System in Chinese Hamster Ovary Cells
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A series of enantiomerically pure (phosphonomethyl)-substituted phenylalanine derivatives related to SDZ EAB 515 (1) were prepared as competitive N-methyl-D-aspartate (NMDA) receptor antagonists.Unlike most known competitive NMDA antagonists, analogs in this series with the S-configuration are potent NMDA antagonists whereas analogs with the unnatural R-configuration are weak NMDA antagonists, as determined by receptor binding experiments and their anticonvulsant action in mice.Examination in a previously reported competitive NMDA pharmacophore model revealed that receptor affinity can be explained partially by a cavity that accommodates the biphenyl ring of 1, while the biphenyl ring of the R-enantiomer 2 extends into a disallowed steric region.We proposed that analogs with the natural S-configuration and a large hydrophobic moiety would have an advantage in vivo over analogs with an R-configuration by being able to use a neutral amino acid uptake system to enhance both peripheral adsorption and transport into the brain.Examination in a system L neutral amino acid transport carrier assay shows that 1 competes with L-Phe for transport in an apparent competitive and stereospecific manner (estimated Ki=50 μM).The 1- and 2-naphthyl derivatives 3a,3b were found to be among the most potent, competitive NMDA antagonists yet discovered, being ca. 15-fold more potent than 1 in vitro and in vivo, with a long duration of action.The title compound 3a had potent oral activity in MES (ED50=5.0 mg/kg). 3a also retains its ability to compete, albeit more weakly than 1 (estimated Ki=200 μM), for L-Phe uptake to CHO cells.In this series, analogs with the R-configuration are not substrates for the system L neutral amino acid transport carrier.These results provide evidence that central nervous system active agents can be designed as substrates of a neutral amino acid transporter as a means to enhance penetration of the blood-brain barrier.
- Li, Jia-He,Bigge, Christopher F.,Williamson, Rufus M.,Borosky, Susan A.,Vartanian, Mark G.,Ortwine, Daniel F.
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p. 1955 - 1965
(2007/10/02)
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