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1.
Asymmetric Catalysis with Silicon‐Based Cuprates: Enantio‐ and Regioselective Allylic Substitution of Linear Precursors 下载免费PDF全文
Alexander Hensel Prof. Dr. Martin Oestreich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9062-9065
An enantio‐ and regioselective allylic silylation of linear allylic phosphates that makes use of catalytically generated cuprate‐type silicon nucleophiles is reported. The method relies on soft bis(triorganosilyl) zincs as silicon pronucleophiles that are prepared in situ from the corresponding hard lithium reagents by transmetalation with ZnCl2. With a preformed chiral N‐heterocyclic carbene–copper(I) complex as catalyst, exceedingly high enantiomeric excesses are achieved. The new method is superior to existing ones using a silicon–boron reagent as the source of the silicon nucleophile. 相似文献
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Juri Skotnitzki Lukas Spessert Paul Knochel 《Angewandte Chemie (International ed. in English)》2019,58(5):1509-1514
Chiral secondary alkylcopper reagents were prepared from chiral secondary alkyl iodides by a retentive I/Li exchange followed by a retentive transmetalation with CuBr?P(OEt)3. Switching the solvent to THF significantly increased their configurational stability and made these copper reagents suitable for regioselective allylic substitutions. The optically enriched copper species underwent SN2 substitutions with allylic bromides (up to >99 % SN2 regioselectivity). The addition of ZnCl2 and the use of chiral allylic phosphates allowed to switch the regioselectivity towards SN2′ substitution (up to >99 % SN2′ regioselectivity) and to perform highly selective anti‐SN2′ substitutions with absolute control over two adjacent stereocenters. This method was applied in the total synthesis of the three ant pheromones (+)‐lasiol, (+)‐13‐norfaranal, and (+)‐faranal (up to 98:2 dr, 99 % ee). 相似文献
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Heterogeneous versus Homogeneous Copper(II) Catalysis in Enantioselective Conjugate‐Addition Reactions of Boron in Water 下载免费PDF全文
We have developed CuII‐catalyzed enantioselective conjugate‐addition reactions of boron to α,β‐unsaturated carbonyl compounds and α,β,γ,δ‐unsaturated carbonyl compounds in water. In contrast to the previously reported CuI catalysis that required organic solvents, chiral CuII catalysis was found to proceed efficiently in water. Three catalyst systems have been exploited: cat. 1: Cu(OH)2 with chiral ligand L1 ; cat. 2: Cu(OH)2 and acetic acid with ligand L1 ; and cat. 3: Cu(OAc)2 with ligand L1 . Whereas cat. 1 is a heterogeneous system, cat. 2 and cat. 3 are homogeneous systems. We tested 27 α,β‐unsaturated carbonyl compounds and an α,β‐unsaturated nitrile compound, including acyclic and cyclic α,β‐unsaturated ketones, acyclic and cyclic β,β‐disubstituted enones, acyclic and cyclic α,β‐unsaturated esters (including their β,β‐disubstituted forms), and acyclic α,β‐unsaturated amides (including their β,β‐disubstituted forms). We found that cat. 2 and cat. 3 showed high yields and enantioselectivities for almost all substrates. Notably, no catalysts that can tolerate all of these substrates with high yields and high enantioselectivities have been reported for the conjugate addition of boron. Heterogeneous cat. 1 also gave high yields and enantioselectivities with some substrates and also gave the highest TOF (43 200 h?1) for an asymmetric conjugate‐addition reaction of boron. In addition, the catalyst systems were also applicable to the conjugate addition of boron to α,β,γ,δ‐unsaturated carbonyl compounds, although such reactions have previously been very limited in the literature, even in organic solvents. 1,4‐Addition products were obtained in high yields and enantioselectivities in the reactions of acyclic α,β,γ,δ‐unsaturated carbonyl compounds with diboron 2 by using cat. 1, cat. 2, or cat. 3. On the other hand, in the reactions of cyclic α,β,γ,δ‐unsaturated carbonyl compounds with compound 2 , whereas 1,4‐addition products were exclusively obtained by using cat. 2 or cat. 3, 1,6‐addition products were exclusively produced by using cat. 1. Similar unique reactivities and selectivities were also shown in the reactions of cyclic trienones. Finally, the reaction mechanisms of these unique conjugate‐addition reactions in water were investigated and we propose stereochemical models that are supported by X‐ray crystallography and MS (ESI) analysis. Although the role of water has not been completely revealed, water is expected to be effective in the activation of a borylcopper(II) intermediate and a protonation event subsequent to the nucleophilic addition step, thereby leading to overwhelmingly high catalytic turnover. 相似文献
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《Angewandte Chemie (International ed. in English)》2017,56(9):2260-2294
Hydrosilation reactions represent an important class of chemical transformations and there has been considerable recent interest in expanding the scope of these reactions by developing new catalysts. A major theme to emerge from these investigations is the development of catalysts with electrophilic character that transfer electrophilicity to silicon by Si‐H activation. This type of mechanism has been proposed for catalysts ranging from Group 4 transition metals to Group 15 main group species. Additionally, other electrophilic silicon species, such as silylene complexes and η3‐H2SiRR′ complexes, have been identified as intermediates in hydrosilation reactions. In this Review, different types of catalysts are compared to highlight the range of hydrosilation mechanisms that feature electrophilic silicon centers. The importance of these catalysts to the development of new hydrosilation reactions is also discussed. 相似文献
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Copper‐Catalyzed γ‐Selective and Stereospecific Allylic Cross‐Coupling with Secondary Alkylboranes 下载免费PDF全文
Yuto Yasuda Kazunori Nagao Yoshinori Shido Prof. Dr. Seiji Mori Prof. Dr. Hirohisa Ohmiya Prof. Dr. Masaya Sawamura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9666-9670
The scope of the copper‐catalyzed coupling reactions between organoboron compounds and allylic phosphates is expanded significantly by employing triphenylphosphine as a ligand for copper, allowing the use of secondary alkylboron compounds. The reaction proceeds with complete γ‐E‐selectivity and preferential 1,3‐syn stereoselectivity. The reaction of γ‐silicon‐substituted allylic phosphates affords enantioenriched α‐stereogenic allylsilanes. 相似文献
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Fei Ye Dr. Zhan‐Jiang Zheng Wen‐Hui Deng Long‐Sheng Zheng Dr. Yuan Deng Prof. Chun‐Gu Xia Prof. Dr. Li‐Wen Xu 《化学:亚洲杂志》2013,8(9):2242-2253
In this work, we have successfully synthesized a new family of chiral Schiff base–phosphine ligands derived from chiral binaphthol (BINOL) and chiral primary amine. The controllable synthesis of a novel hexadentate and tetradentate N,O,P ligand that contains both axial and sp3‐central chirality from axial BINOL and sp3‐central primary amine led to the establishment of an efficient multifunctional N,O,P ligand for copper‐catalyzed conjugate addition of an organozinc reagent. In the asymmetric conjugate reaction of organozinc reagents to enones, the polymer‐like bimetallic multinuclear Cu? Zn complex constructed in situ was found to be substrate‐selective and a highly excellent catalyst for diethylzinc reagents in terms of enantioselectivity (up to >99 % ee). More importantly, the chirality matching between different chiral sources, C2‐axial binaphthol and sp3‐central chiral phosphine, was crucial to the enantioselective induction in this reaction. The experimental results indicated that our chiral ligand (R,S,S)‐ L1 ‐ and (R,S)‐ L4 ‐based bimetallic complex catalyst system exhibited the highest catalytic performance to date in terms of enantioselectivity and conversion even in the presence of 0.005 mol % of catalyst (S/C=20 000, turnover number (TON)=17 600). We also studied the tandem silylation or acylation of enantiomerically enriched zinc enolates that formed in situ from copper‐ L4 ‐complex‐catalyzed conjugate addition, which resulted in the high‐yield synthesis of chiral silyl enol ethers and enoacetates, respectively. Furthermore, the specialized structure of the present multifunctional N,O,P ligand L1 or L4 , and the corresponding mechanistic study of the copper catalyst system were investigated by 31P NMR spectroscopy, circular dichroism (CD), and UV/Vis absorption. 相似文献
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Intramolecular conjugate reduction‐aldol addition reactions of β′‐oxoalkyl α,β‐unsaturated carboxylates were performed in the presence of copper catalysts generated in situ from copper salts, phosphine ligands and silanes. Moderate to good yields and high diastereoselectivities were obtained in 15 min to 3 h using bis[(2‐diphenylphosphino)phenyl] ether as the ligand. 相似文献
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Jingjing Yao Prof. Dr. Xiaohua Liu Peng He Yin Zhu Xiangjin Lian Dr. Lili Lin Prof. Dr. Xiaoming Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(48):16424-16430
Chiral N,N′‐dioxide/Zn(NTf2)2 complexes were demonstrated to be highly effective in the direct asymmetric conjugate addition of arylacetonitriles to alkylidene malonates under mild conditions. A wide range of substrates were tolerated to afford their corresponding products in moderate‐to‐good yields with high diastereoselectivities (82:18–>99:1 d.r.) and enantioselectivities (81–99 % ee). The reactions performed well, owing to the high Lewis acidity of the metal triflimidate and a ligand‐acceleration effect. The N,N′‐dioxide also benefited the deprotonation process as a Brønsted base. The catalytic reaction could be performed on the gram‐scale with retention of yield, diastereoselectivity, and enantioselectivity. The products that contained functional groups were ready for further manipulation. In addition, a possible catalytic model was proposed to explain the origin of the asymmetric induction. 相似文献
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Hak‐Suk Sim Xinhui Feng Jaesook Yun Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(8):1939-1943
Josi or Mandy? Asymmetric conjugate addition of diboron to acyclic enones catalyzed by copper affords chiral organoboronates that possess a boronate group at the β stereocenter with excellent chemical yields and enantioselectivities (see scheme). This method accommodates the structural variation of acyclic enones and provides access to highly functionalized chiral organoboronates in one step.
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Brown MK Degrado SJ Hoveyda AH 《Angewandte Chemie (International ed. in English)》2005,44(33):5306-5310
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Remarkable Enhancement of Enantioselectivity in the Asymmetric Conjugate Addition of Dimethylzinc to (Z)‐Nitroalkenes with a Catalytic [(MeCN)4Cu]PF6–Hoveyda Ligand Complex 下载免费PDF全文
Dr. Xingzhong Zeng Joe J. Gao Dr. Jinhua J. Song Dr. Shengli Ma Dr. Jean‐Nicolas Desrosiers Dr. Jason A. Mulder Dr. Sonia Rodriguez Dr. Melissa A. Herbage Dr. Nizar Haddad Dr. Bo Qu Dr. Keith R. Fandrick Dr. Nelu Grinberg Dr. Heewon Lee Dr. Xudong Wei Dr. Nathan K. Yee Dr. Chris H. Senanayake 《Angewandte Chemie (International ed. in English)》2014,53(45):12153-12157
An enantioselective copper‐catalyzed asymmetric conjugate addition of Me2Zn to (Z)‐nitroalkenes led to the formation of all‐carbon quaternary stereogenic centers with high stereoselectivity. The key features of the new method are the unprecedented use of [(MeCN)4Cu]PF6 in conjunction with the Hoveyda ligand L1 and the use of (Z)‐nitroalkene substrates so that undesired nitroalkene isomerization is minimized and enantioselectivity is enhanced dramatically. We also describe a novel, practical, and highly (Z)‐selective nitroalkene synthesis. 相似文献
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Catalytic SN2′‐ and Enantioselective Allylic Substitution with a Diborylmethane Reagent and Application in Synthesis 下载免费PDF全文
Ying Shi Prof. Amir H. Hoveyda 《Angewandte Chemie (International ed. in English)》2016,55(10):3455-3458
A catalytic method for the site‐ and enantioselective addition of commercially available di‐B(pin)‐methane to allylic phosphates is introduced (pin=pinacolato). Transformations may be facilitated by an NHC–Cu complex (NHC=N‐heterocyclic carbene) and products obtained in 63–95 % yield, 88:12 to >98:2 SN2′/SN2 selectivity, and 85:15–99:1 enantiomeric ratio. The utility of the approach, entailing the involvement of different catalytic cross‐coupling processes, is highlighted by its application to the formal synthesis of the cytotoxic natural product rhopaloic acid A. 相似文献
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Dr. Ming Zhang Dr. Naoya Kumagai Prof. Dr. Masakatsu Shibasaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(16):5525-5529
Although catalytic asymmetric conjugate addition reactions have remarkably advanced over the last two decades, the application of less electrophilic α,β‐unsaturated carboxylic acid derivatives in this useful reaction manifold remains challenging. Herein, we report that α,β‐unsaturated 7‐azaindoline amides act as reactive electrophiles to participate in catalytic diastereo‐ and enantioselective vinylogous conjugate addition of γ‐butyrolactones in the presence of a cooperative catalyst comprising of a soft Lewis acid and a Brønsted base. Reactions mostly reached completion with as little as 1 mol % of catalyst loading to give the desired conjugate adducts in a highly stereoselective manner. 相似文献
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Silicon‐Directed Rhenium‐Catalyzed Allylic Carbaminations and Oxidative Fragmentations of γ‐Silyl Allylic Alcohols 下载免费PDF全文
Dr. Sanjay W. Chavhan Dr. Matthew J. Cook 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4891-4895
A highly regioselective allylic substitution of β‐silyl allylic alcohols has been achieved that provides the branched isomer as a single product. This high level of regiocontrol is achieved through the use of a vinyl silane group that can perform a Hiyama coupling providing 1,3‐disubstituted allylic amines. An unusual oxidative fragmentation product was also observed at elevated temperature that appears to proceed by a Fleming–Tamao‐type oxidation–elimination pathway. 相似文献