- Cu-Catalyzed Reductive gem-Difunctionalization of Terminal Alkynes via Hydrosilylation/Hydroamination Cascade: Concise Synthesis of α-Aminosilanes
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A copper-catalyzed reductive gem-difunctionalization of terminal alkynes with hydrosilanes and hydroxylamines has been developed. The reaction proceeds via hydrosilylation/hydroamination cascade, and the readily available and simple terminal alkynes can be transformed into the corresponding α-aminosilanes of medicinal interest in a single operation. Additionally, the use of chiral bisphosphine ligand successfully makes the reaction enantioselective to deliver the optically active α-aminosilanes with good enantiomeric ratios.
- Nishino, Soshi,Hirano, Koji,Miura, Masahiro
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- Strategies for protodesilylation of C-2 trialkylsilyl terminal alkenes
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The mild and high yielding protodesilylation of C-2 trialkylsilyl terminal alkenes can be effected via a hydroboration-Peterson elimination protocol or, in the case of the phenyldimethylsilyl analogues, a one pot procedure using t-BuOK-18-C-6-TBAF can be used. The Royal Society of Chemistry 2000.
- Anderson, James C.,Flaherty, Alice
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- Hydroalkylation of Alkynes: Functionalization of the Alkenyl Copper Intermediate through Single Electron Transfer Chemistry
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We have developed a method for the stereoselective coupling of terminal alkynes and α-bromo carbonyls to generate functionalized E-alkenes. The coupling is accomplished by merging the closed-shell hydrocupration of alkynes with the open-shell single electron transfer (SET) chemistry of the resulting alkenyl copper intermediate. We demonstrate that the reaction is compatible with various functional groups and can be performed in the presence of aryl bromides, alkyl chlorides, alkyl bromides, esters, nitriles, amides, and a wide range of nitrogen-containing heterocyclic compounds. Mechanistic studies provide evidence for SET oxidation of the alkenyl copper intermediate by an α-bromo ester as the key step that enables the cross coupling.
- Hazra, Avijit,Kephart, Jonathan A.,Velian, Alexandra,Lalic, Gojko
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- Palladium-catalyzed tandem isomerization/hydrothiolation of allylarenes
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Herein we report a tandem olefin migration/hydrothiolation of allyl benzenes facilitated by an in situ generated palladium hydride. A catalyst system composed of palladium acetate and bidentate ligand dtbpx (1,2-bis(di-tert-butylphosphinomethyl)benzene in the presence of catalytic amounts of triflic acid led to the tandem transformation, which furnished benzylic thioethers. The reaction exhibits high regioselectivity and can be conducted under mild conditions. The robustness of the catalyst is displayed through reactions with coordinating thiols.
- Kathe, Prasad M.,Fleischer, Ivana
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- Gas-Phase Elimination Kinetics of ω-Phenylalkyl Chlorides. Participation of the Phenyl Ring
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The kinetics of the gas-phase dehydrochlorination of several phenylalkyl chlorides were determined in a static system, seasoned with allyl bromide, and in the presence of the free radical inhibitor propene.The working temperature and pressure ranges were 398.8-480.6 deg C and 66-202 torr, respectively.The reactions are homogeneous, unimolecular, and follow a first-order rate law.The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3-chloro-1-phenylpropane, log k1 (s-1) = (13.99 +/- 0.26) - (238.4 +/- 3.5) kJ*mol-1; for 4-chloro-1-phenylbutane, log k1 (s-1) = (13.07 +/- 0.43) - (220.5 +/- 5.8) kJ*mol-1 (2.303RT)-1; and for 5-chloro-1-phenylpentane, log k1 (s-1) = (13.75 +/- 0.36) - (231.2 +/- 4.9) kJ*mol-1 (2.303RT)-1.When the rates of HCl elimination among each of the phenylalkyl chlorides are compared with those for the coresponding unsubstituted alkyl chloride, participation of the C6H5 group at the 3 position is more favored, while that at the 5 and 6 positions is rather weak.Participation of C6H5 group at the 4 position is apparently absent.
- Chuchani, Gabriel,Rotinov, Alexandra,Martin, Ignacio
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- A palladium-catalyzed methylenation of olefins using halomethylboronate reagents
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Methylenation of electron-rich olefins is a highly challenging reaction, for which we have developed a new methodology exploiting Pd-catalysis and halomethylboronate reagents, the latter replacing diazomethane and zinc carbenoids as methylene donors. Optimization of the reaction for norbornene and extension to several other olefins are reported, with reasonable-to-excellent yields of cyclopropanes in combination with β-H elimination products. Several mechanisms are plausible for this methylenation reaction.
- Hartog, Tim Den,Toro, Juan Manuel Sarria,Chen, Peter
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- Photochemistry of 5-phenyl-1-pentene in the gas phase
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The photochemistry of the title compound has been studied in the gas phase using 254-nm irradiation. In addition to meta cycloadducts analogous to those observed in solution, population of S1vib in the gas phase gives several products, the relative amounts of which depend on quencher gas pressure but not on excitation wavelength. For example, in the absence of butane, the major photoproduct is compound 5. This product is formed by a [1,5] hydrogen shift in the primary photoproduct, compound 4. Compound 4 is an intramolecular meta cycloadduct that is generated in the gas phase with sufficient excess vibrational energy to undergo rearrangement unless quencher gas is present. Likewise, there is evidence that two other meta cycloadducts (2 and 3) are also formed with appreciable vibrational energy in the absence of a quencher gas. A unique intramolecular ortho cycloadduct is also formed from 1 but only within a narrow range of quencher gas pressures. This is a two-photon product, with the initial cycloadduct (11) ring opening to a cyclooctatriene (12) that photochemically closes to 6. The pressure dependence of this ortho cycloaddition may be due to a requirement for vibrational deactivation of 11 (Scheme 5) or a precursor species (Scheme 6). The overall chemistry is outlined in Scheme 7.
- Ho, Chang-Dar D.,Morrison, Harry
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- Synergistic Hydrocobaltation and Borylcobaltation Enable Regioselective Migratory Triborylation of Unactivated Alkenes
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The structural diversity of sp3-triorganometallic reagents enhances their potentiality in the modular construction of molecular complexity in chemical synthesis. Despite significant achievements on the preparation of sp3 1,1,1- and 1,1,2-triorganometallic B,B,B-reagents, catalytic approaches that enable the installation of multiple boryl groups at skipped carbons of unactivated alkenes still remain elusive. Herein, we report a cobalt-catalyzed selective triborylation reaction of unactivated alkenes to access synthetically versatile 1,1,3-triborylalkanes. This triborylation protocol provides a general platform for regioselective trifunctionalization of unactivated alkenes, and its utility is highlighted by the synthesis of various value-added chemicals from readily accessible unactivated alkenes. Mechanistic studies, including deuterium-labelling experiments and evaluation of potential reactive intermediates, provide insight into the experimentally observed chemo- and regioselectivity.
- Ge, Shaozhong,Zhao, Yinsong
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supporting information
(2022/02/19)
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- Access to Trisubstituted Fluoroalkenes by Ruthenium-Catalyzed Cross-Metathesis
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Although the olefin metathesis reaction is a well-known and powerful strategy to get alkenes, this reaction remained highly challenging with fluororalkenes, especially the Cross-Metathesis (CM) process. Our thought was to find an easy accessible, convenient, reactive and post-functionalizable source of fluoroalkene, that we found as the methyl 2-fluoroacrylate. We reported herein the efficient ruthenium-catalyzed CM reaction of various terminal and internal alkenes with methyl 2-fluoroacrylate giving access, for the first time, to trisubstituted fluoroalkenes stereoselectively. Unprecedent TON for CM involving fluoroalkene, up to 175, have been obtained and the reaction proved to be tolerant and effective with a large range of olefin partners giving fair to high yields in metathesis products. (Figure presented.).
- Nouaille, Augustin,Pannecoucke, Xavier,Poisson, Thomas,Couve-Bonnaire, Samuel
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p. 2140 - 2147
(2021/03/06)
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- Mild olefin formationviabio-inspired vitamin B12photocatalysis
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Dehydrohalogenation, or elimination of hydrogen-halide equivalents, remains one of the simplest methods for the installation of the biologically-important olefin functionality. However, this transformation often requires harsh, strongly-basic conditions, rare noble metals, or both, limiting its applicability in the synthesis of complex molecules. Nature has pursued a complementary approach in the novel vitamin B12-dependent photoreceptor CarH, where photolysis of a cobalt-carbon bond leads to selective olefin formation under mild, physiologically-relevant conditions. Herein we report a light-driven B12-based catalytic system that leverages this reactivity to convert alkyl electrophiles to olefins under incredibly mild conditions using only earth abundant elements. Further, this process exhibits a high level of regioselectivity, producing terminal olefins in moderate to excellent yield and exceptional selectivity. Finally, we are able to access a hitherto-unknown transformation, remote elimination, using two cobalt catalysts in tandem to produce subterminal olefins with excellent regioselectivity. Together, we show vitamin B12to be a powerful platform for developing mild olefin-forming reactions.
- Bam, Radha,Pollatos, Alexandros S.,Moser, Austin J.,West, Julian G.
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p. 1736 - 1744
(2021/02/22)
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- Visible Light/Tertiary Amine Promoted Synergistic Hydroxydifluoroacetamidation of Unactivated Alkenes under Air
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An efficient and novel method for regioselective hydroxydifluoroacetamidation of alkenes with bromodifluoroacetamides has been achieved via a tandem radical pathway mediated by photoredox catalysis under metal-free conditions. This transformation proceeded smoothly in the presence of Rhodamine 6G, affording a series of α,α-difluoro-γ-hydroxyacetamides in moderate to excellent yields. The significant advantages of this protocol are the low-cost photocatalyst, readily available starting materials, synthetic convenience, and wide functional group compatibility.
- Huang, Panyi,Jin, Can,Shi, Xiayue,Sun, Bin,Yan, Zhiyang,Yu, Chuanming,Zhu, Rui,Zhuang, Xiaohui
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supporting information
p. 617 - 622
(2021/01/13)
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- CuPd Nanoparticles as a Robust Catalyst for Electrochemical Allylic Alkylation
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An efficient CuPd nanoparticle (NP) catalyst (3 nm CuPd NPs deposited on carbon support) is designed for catalyzing electrochemical allylic alkylation in water/isopropanol (1:1 v/v) and 0.2 m KHCO3 solution at room temperature. The Pd catalysis was Pd/Cu composition-dependent, and CuPd NPs with a Pd/Cu ratio close to one are the most efficient catalyst for the selective cross-coupling of alkyl halides and allylic halides to form C?C hydrocarbons with product yields reaching up to 99 %. This NP-catalyzed electrochemical allylic alkylation expands the synthetic scope of cross-coupling reactions and can be further extended to other organic reaction systems for developing green chemistry electrosynthesis methods.
- Guo, Xuefeng,Lin, Honghong,Muzzio, Michelle,Pang, Huan,Shen, Mengqi,Sun, Shouheng,Wei, Kecheng,Williard, Paul,Yin, Zhouyang,Yu, Chao
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supporting information
p. 15933 - 15936
(2020/07/04)
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- Migratory Hydrogenation of Terminal Alkynes by Base/Cobalt Relay Catalysis
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Migratory functionalization of alkenes has emerged as a powerful strategy to achieve functionalization at a distal position to the original reactive site on a hydrocarbon chain. However, an analogous protocol for alkyne substrates is yet to be developed. Herein, a base and cobalt relay catalytic process for the selective synthesis of (Z)-2-alkenes and conjugated E alkenes by migratory hydrogenation of terminal alkynes is disclosed. Mechanistic studies support a relay catalytic process involving a sequential base-catalyzed isomerization of terminal alkynes and cobalt-catalyzed hydrogenation of either 2-alkynes or conjugated diene intermediates. Notably, this practical non-noble metal catalytic system enables efficient control of the chemo-, regio-, and stereoselectivity of this transformation.
- Liu, Bingxue,Liu, Qiang,Liu, Xufang
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supporting information
p. 6750 - 6755
(2020/03/13)
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- Convergent First Total Synthesis of Melovinone: A Densely Substituted 3-Methoxy-4-quinolone Isolated from Melochia tomentosa L
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The first total synthesis of melovinone, a nonrutaceous 3-methoxy-4-quinolone alkaloid isolated from Melochia tomentosa L., is reported. The target was acquired in a convergent fashion through the Suzuki-Miyaura cross-coupling reaction between an ortho-nitrobenzoic acid acetonyl ester derivative prepared from vanillin and potassium 5-phenyl-1-pentyltrifluoroborate, obtained from β-phenethyl bromide. The coupling was followed by a chemoselective reduction of the nitro group and a microwave-Assisted and AcOH-promoted cyclization with rearrangement of the resulting acetonyl anthranilate. This afforded a pseudane intermediate, which was selectively methylated on the 3-OH. The synthetic pathway enabled to reach the objective in 11 steps and 18% overall yield. The 1 H NMR spectra of the synthetic and natural product were in full agreement.
- Aguilar, Abel A. Arroyo,Kaufman, Teodoro S.,Larghi, Enrique L.,Ledesma, Gabriela N.,Tirloni, Bárbara
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p. 4253 - 4262
(2019/11/14)
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- Controllable Isomerization of Alkenes by Dual Visible-Light-Cobalt Catalysis
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We report herein that thermodynamic and kinetic isomerization of alkenes can be accomplished by the combination of visible light with Co catalysis. Utilizing Xantphos as the ligand, the most stable isomers are obtained, while isomerizing terminal alkenes over one position can be selectively controlled by using DPEphos as the ligand. The presence of the donor–acceptor dye 4CzIPN accelerates the reaction further. Transformation of exocyclic alkenes into the corresponding endocyclic products could be efficiently realized by using 4CzIPN and Co(acac)2 in the absence of any additional ligands. Spectroscopic and spectroelectrochemical investigations indicate CoI being involved in the generation of a Co hydride, which subsequently adds to alkenes initiating the isomerization.
- Meng, Qing-Yuan,Schirmer, Tobias E.,Katou, Kousuke,K?nig, Burkhard
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supporting information
p. 5723 - 5728
(2019/04/03)
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- Aryltrifluoromethylative cyclization of unactivated alkenes by the use of PhICF3Cl under catalyst-free conditions
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A concise and catalyst-free aryltrifluoromethylative cyclization of unactivated alkenes has been developed herein. The use of PhICF3Cl as a powerful trifluoromethylating agent allows easy transformations. A set of trifluoroethylated carbocycles and aza-hereocycles were efficiently synthesized in good yield and selectivity. A broad substrate scope, mild reaction conditions, and easy operation would make this method well-suited for applications.
- Guo, Jia,Xu, Cong,Liu, Xiaowei,Wang, Mang
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supporting information
p. 2162 - 2168
(2019/02/27)
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- Umpolung of Carbonyl Groups as Alkyl Organometallic Reagent Surrogates for Palladium-Catalyzed Allylic Alkylation
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Palladium-catalyzed allylic alkylation of nonstabilized carbon nucleophiles is difficult and remains a major challenge. Reported here is a highly chemo- and regioselective direct palladium-catalyzed C-allylation of hydrazones, generated from carbonyls, as a source of umpolung unstabilized alkyl carbanions and surrogates of alkyl organometallic reagents. Contrary to classical allylation techniques, this umpolung reaction utilizes hydrazones prepared not only from aryl aldehydes but also from alkyl aldehydes and ketones as renewable feedstocks. This strategy complements the palladium-catalyzed coupling of unstabilized nucleophiles with allylic electrophiles by providing an efficient and selective catalytic alternative to the traditional use of highly reactive alkyl organometallic reagents.
- Zhu, Dianhu,Lv, Leiyang,Li, Chen-Chen,Ung, Sosthene,Gao, Jian,Li, Chao-Jun
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supporting information
p. 16520 - 16524
(2018/11/23)
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- Copper-Catalyzed Propargylic Reduction with Diisobutylaluminum Hydride
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A mild and efficient method for the synthesis of allenes through selective copper-catalyzed hydride addition to propargylic chlorides using commercially available diisobutylaluminum hydride has been developed. This transformation, which is promoted by a readily accessible N-heterocyclic carbene-copper complex, provides a wide range of new and versatile functionalized allenes in good to excellent yields with high regio- A nd stereoselectivities.
- Kim, Yuna,Lee, Hanseul,Park, Sunga,Lee, Yunmi
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supporting information
p. 5478 - 5481
(2018/09/13)
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- Multicatalytic Stereoselective Synthesis of Highly Substituted Alkenes by Sequential Isomerization/Cross-Coupling Reactions
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Starting from readily available alkenyl methyl ethers, the stereoselective preparation of highly substituted alkenes by two complementary multicatalytic sequential isomerization/cross-coupling sequences is described. Both elementary steps of these sequences are challenging processes when considered independently. A cationic iridium catalyst was identified for the stereoselective isomerization of allyl methyl ethers and was found to be compatible with a nickel catalyst for the subsequent cross-coupling of the in situ generated methyl vinyl ethers with various Grignard reagents. The method is compatible with sensitive functional groups and a multitude of olefinic substitution patterns to deliver products with high control of the newly generated C=C bond. A highly enantioselective variant of this [Ir/Ni] sequence has been established using a chiral iridium precatalyst. A complementary [Pd/Ni] catalytic sequence has been optimized for alkenyl methyl ethers with a remote C=C bond. The final alkenes were isolated with a lower level of stereocontrol. Upon proper choice of the Grignard reagent, we demonstrated that C(sp2) - C(sp2) and C(sp2) - C(sp3) bonds can be constructed with both systems delivering products that would be difficult to access by conventional methods.
- Romano, Ciro,Mazet, Clément
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p. 4743 - 4750
(2018/04/10)
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- Stereoselective Alkyne Hydrohalogenation by Trapping of Transfer Hydrogenation Intermediates
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A catalytically generated vinylcopper complex, the reactive intermediate of a copper(I)-catalyzed alkyne transfer hydrogenation, can be trapped by commercially available halogen electrophiles. In this manner, internal alkynes can stereoselectively be hydrohalogenated to the corresponding vinyl chlorides, bromides, and iodides.
- Das, Manas,Kaicharla, Trinadh,Teichert, Johannes F.
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supporting information
p. 4926 - 4929
(2018/08/24)
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- Palladium-Catalyzed Electrochemical Allylic Alkylation between Alkyl and Allylic Halides in Aqueous Solution
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A new route for the direct cross-coupling of alkyl and allylic halides using electrochemical technique has been developed in aqueous media under air. Catalyzed by Pd(OAc)2, the Zn-mediated allylic alkylations proceed smoothly between a full range of alkyl halides (primary, secondary, and tertiary) and substituted allylic halides. Protection-deprotection of acidic hydrogen in the substrates is avoided.
- Lai, Yin-Long,Huang, Jing-Mei
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supporting information
p. 2022 - 2025
(2017/04/28)
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- Supported gold nanoparticles catalyzed: Cis -selective semihydrogenation of alkynes using ammonium formate as the reductant
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TiO2 supported gold nanoparticles with low loading (0.5 mol%) are able to semihydrogenate non-fluorinated and gem-difluorinated alkynes to cis-alkenes with high selectivity, using cost-effective and easy-to-handle ammonium formate as the reductant. No over-reduction was observed. The good recyclability of Au/TiO2 allows for "green" semireduction of alkynes. A difluorinated pyran and α,β-unsaturated δ-lactone were easily prepared from the obtained gem-difluoro alkene building blocks.
- Liang, Shengzong,Hammond, Gerald B.,Xu, Bo
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supporting information
p. 6013 - 6016
(2016/05/24)
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- Copper-catalyzed semi-reduction of alkynes
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The semi-reduction of alkynes to form alkenes is one of the most important reactions in organic chemistry. The reactions reach full conversion without any over-reduction of the alkene to the alkane, avoiding the need for careful monitoring of reaction progress. In the case of internal alkynes, the semi-reduction is completely Z-selective and no isomerization is detected. Finally, this transformation can be achieved using commercially available reagents without the need for a glovebox, and the products can be easily isolated by filtration through silica or alumina.
- Cox, Nick,Dang, Hester,Whittaker, Aaron M.,Lalic, Gojko
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- Iron-catalyzed olefin hydrogenation at 1 bar H2 with a FeCl3-LiAlH4 catalyst
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The scope and mechanism of a practical protocol for the iron-catalyzed hydrogenation of alkenes and alkynes at 1 bar H2 pressure were studied. The catalyst is formed from cheap chemicals (5 mol% FeCl3-LiAlH4, THF). A homogeneous mechanism operates at early stages of the reaction while active nanoparticles form upon ageing of the catalyst solution. This journal is
- Gieshoff, Tim N.,Villa, Matteo,Welther, Alice,Plois, Markus,Chakraborty, Uttam,Wolf, Robert,Jacobi Von Wangelin, Axel
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supporting information
p. 1408 - 1413
(2015/03/18)
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- Copper-Catalyzed Cross-Coupling Reaction of Allyl Boron Ester with 1°/2°/3°-Halogenated Alkanes
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The cross-coupling reaction of allyl boron ester with 1°/2°/3°-halogenated alkanes in the presence of copper has been developed for the first time, which provides a mild and efficient method for the construction of saturated C(sp3)-C(sp3) bonds. This protocol shows excellent compatibility with the nonactivated primary, secondary, and even tertiary halogenated alkanes under mild conditions.
- Wang, Guang-Zu,Jiang, Jian,Bu, Xiao-Song,Dai, Jian-Jun,Xu, Jun,Fu, Yao,Xu, Hua-Jian
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supporting information
p. 3682 - 3685
(2015/08/18)
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- CYCLOPROPANATION
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A method of preparing a cyclopropane ring-bearing compound of the formula (I) in which R1 and R2 are independently selected from C1-C10 alky], optionally substituted, or R1 and R2 together with the bonds linking them to the cyclopropane ring, form a monocyclic or bicyciic ring system, which may comprise at least one hetero-atom, comprising the reaction of a compound of formula (II) in which R1 and R2 have the significances hereinabove defined, with a compound of formula (III) in which X is selected a nucieofuge selected from halides and pseudohalides and Y is an electro flige selected from boranes and borates, in the presence of a metal catalyst complex selected from those that a useful for catalytic cyclopropanation and those useful for catalyzing Heck coupling. The method prov ides a particularly easy and non-hazardous method of cyclopropanation.
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Page/Page column 4; 5; 7
(2015/05/26)
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- Z -selective alkene isomerization by high-spin cobalt(II) complexes
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The isomerization of simple terminal alkenes to internal isomers with Z-stereochemistry is rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminate ligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the resting state. β-Hydride elimination and [1,2]-insertion steps are both rapid, as shown by isotopic labeling experiments. A steric model explains the selectivity through a square-planar geometry at cobalt(II) in the transition state for β-hydride elimination. The catalyst works not only with simple alkenes, but also with homoallyl silanes, ketals, and silyl ethers. Isolation of cobalt(I) or cobalt(II) products from reactions with poor substrates suggests that the key catalyst decomposition pathways are bimolecular, and lowering the catalyst concentration often improves the selectivity. In addition to a potentially useful, selective transformation, these studies provide a mechanistic understanding for catalytic alkene isomerization by high-spin cobalt complexes, and demonstrate the effectiveness of steric bulk in controlling the stereoselectivity of alkene formation.
- Chen, Chi,Dugan, Thomas R.,Brennessel, William W.,Weix, Daniel J.,Holland, Patrick L.
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supporting information
p. 945 - 955
(2014/02/14)
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- Copper-catalyzed selective semihydrogenation of terminal alkynes with hypophosphorous acid
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A novel copper-catalyzed selective semihydrogenation of terminal alkynes using hypophosphorous acid as hydrogen donor took place efficiently to afford the corresponding alkenes in high yields. A broad range of substituted terminal aromatic and aliphatic alkenes, including terminal dienes and enynes bearing internal triple bonds, can be efficiently synthesized by this reaction.
- Cao, Huanyang,Chen, Tieqiao,Zhou, Yongbo,Han, Daoqing,Yin, Shuang-Feng,Han, Li-Biao
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p. 765 - 769
(2014/04/03)
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- Iron-catalysed alkene hydrogenation and reductive cross-coupling using a bench-stable iron(II) pre-catalyst
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Operationally simple, iron-catalysed hydrogenation and reductive cross-coupling protocols have been developed using a bench-stable iron(ii) pre-catalyst. The hydrogenation of 18 alkenes (50-99%) and reductive cross-coupling of vinyl halides with aryl- and alkyl Grignard reagents (8 examples, 18-99%) is reported using 3 mol% pre-catalyst and hydrogen as stoichiometric reductant (1-50 bar).
- Frank, Dominik J.,Guiet, Lea,Kaeslin, Alexander,Murphy, Elliot,Thomas, Stephen P.
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p. 25698 - 25701
(2013/12/04)
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- Palladium-catalyzed cross-coupling of n -sulfonylaziridines with boronic acids
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A mild palladium-catalyzed cross-coupling of unsubstituted and 2-alkyl-substituted aziridines with arylboronic acid nucleophiles is presented. The reaction is highly regioselective and compatible with diverse functionality. A catalytic amount of base, a sterically demanding triarylphosphine ligand, and a phenol additive are critical to the success of the reaction. Coupling of a deuterium-labeled substrate established that ring opening of the aziridine occurs with inversion of stereochemistry.
- Duda, Megan L.,Michael, Forrest E.
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supporting information
p. 18347 - 18349
(2014/01/06)
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- Iron-catalysed reduction of olefins using a borohydride reagent
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The iron-catalysed reduction of olefins has been achieved using a simple iron salt and sodium triethylborohydride. A wide range of mono- and trans-1,2-disubstituted alkenes have been reduced (91-100%) using 25 mol% iron(II) triflate, 1 mol% N-methyl-2-pyrrolidinone and 4 equivalents of sodium triethylborohydride. The reduction of alkynes to alkanes is also reported (up to 84%). Significantly, the reduction of trisubstituted alkenes has also been achieved (60-86%). Copyright
- Carter, Tom S.,Guiet, Lea,Frank, Dominik J.,West, James,Thomas, Stephen P.
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supporting information
p. 880 - 884
(2013/05/08)
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- Cross-coupling of alkyl halides with aryl or alkyl Grignards catalyzed by dinuclear Ni(ii) complexes containing functionalized tripodal amine-pyrazolyl ligands
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Structurally distinctive dinuclear Ni(ii) complexes with furan or thiophene tethered amine-pyrazolyl tripodal hybrid ligands have been synthesized and crystallographically characterized. All complexes are catalytically active towards cross-coupling of aryl/alkyl Grignard reagents with β-H containing alkyl halides at room temperature in the presence of N,N,N',N'- tetramethylethylenediamine (TMEDA). The catalytic efficacy of the complexes is dependent on the tether substituent at the central amine. Two species, Ni(ii) TMEDA and Mg(ii) TMEDA complexes, have been isolated from the catalytic reaction mixtures under different conditions. Some ligand-stabilized Ni(ii) and Mg(ii) bimetallic species have also been identified in the ESI-MS spectra.
- Xue, Fei,Zhao, Jin,Hor, T. S. Andy
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p. 5150 - 5158
(2013/04/10)
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- Copper(I)-catalyzed boryl substitution of unactivated alkyl halides
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Borylation of alkyl halides with diboron proceeded in the presence of a copper(I)/Xantphos catalyst and a stoichiometric amount of K(O-t-Bu) base. The boryl substitution proceeded with normal and secondary alkyl chlorides, bromides, and iodides, but alkyl sulfonates did not react. Menthyl halides afforded the corresponding borylation product with excellent diastereoselectivity, whereas (R)-2-bromo-5-phenylpentane gave a racemic product. Reaction with cyclopropylmethyl bromide resulted in ring-opening products, suggesting the reaction involves a radical pathway.
- Ito, Hajime,Kubota, Koji
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scheme or table
p. 890 - 893
(2012/05/05)
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- Gold-catalyzed intramolecular hydroarylation of olefins. Scope evaluation and preliminary mechanistic studies
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We report a gold-catalyzed intramolecular hydroarylation of unactivated olefins using a combination of AuCl3/AgOTf as the catalytic system affording dihydrobenzopyrans, tetralins and tetrahydroquinolines in good yields. For our preliminary mechanistic studies, we have investigated the kinetic isotope effects with deuterated arene compounds and found that this catalytic hydroarylation is consistent with an electrophilic aromatic substitution process.
- Jean, Mickael,Van De Weghe, Pierre
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supporting information; experimental part
p. 3509 - 3513
(2011/07/09)
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- Regio- and enantioselective intermolecular hydroacylation: Substrate-directed addition of salicylaldehydes to homoallylic sulfides
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We report a Rh-catalyzed, regio- and enantioselective intermolecular olefin hydroacylation under mild conditions. Hydroacylations between homoallylic sulfides, containing a substrate-bound directing group, and salicylaldehyde derivatives occur in the presence of a spiro-phosphoramidite ligand, (R)-SIPHOS-PE, to give α-branched ketones in >20:1 selectivity and up to 97% ee. Our conditions are also applicable to the asymmetric intermolecular hydroacylation of 1,2-disubstituted olefins.
- Coulter, Matthew M.,Kou, Kevin G. M.,Galligan, Baye,Dong, Vy M.
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supporting information; experimental part
p. 16330 - 16333
(2011/02/23)
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- Functional group tolerant Kumada-Corriu-Tamao coupling of nonactivated alkyl halides with aryl and heteroaryl nucleophiles: Catalysis by a nickel pincer complex permits the coupling of functionalized Grignard reagents
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A nickel(II) pincer complex [(MeNN2)NiCl] (1) catalyzes Kumada-Corriu-Tamao cross coupling of nonactivated alkyl halides with aryl and heteroaryl Grignard reagents. The coupling of octyl bromide with phenylmagnesium chloride was used as a test reaction. Using 3 mol % of 1 as the precatalyst and THF as the solvent, and in the presence of a catalytic amount of TMEDA, the coupling product was obtained in a high yield. The reaction conditions could be applied to cross coupling of other primary and secondary alkyl bromides and iodides. The coupling is tolerant to a wide range of functional groups. Therefore, alkyl halides containing ester, amide, ether, thioether, alcohol, pyrrole, indole, furan, nitrile, conjugated enone, and aryl halide moieties were coupled to give high isolated yields of products in which these units stay intact. For the coupling of ester-containing substrates, O-TMEDA is a better additive than TMEDA. The reaction protocol proves to be efficient for the coupling of Knochel-type functionalized Grignard reagents. Thus aryl Grignard reagents containing electron-deficient and/or sensitive ester, nitrile, amide, and CF3 substituents could be successfully coupled to nonactivated and functionalized alkyl iodides. The catalysis is also efficient for the coupling of alkyl iodides with functionalized heteroaryl Grignard reagents, giving rise to pyridine-, thiophene-, pyrazole-, furan-containing molecules with additional functionalities. Concerning the mechanism of the catalysis, [(MeNN2)Ni-(hetero)Ar] was identified as an intermediate, and the activation of alkyl halides was found to take place through a radical-rebound process.
- Vechorkin, Oleg,Proust, Valerie,Hu, Xile
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supporting information; experimental part
p. 9756 - 9766
(2011/03/19)
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- A stereospecific palladium-catalyzed route to monoalkyl diazenes for mild allylic reduction
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(Chemical Equation Presented) One step beyond: The first single-step stereospecific transition-metal-catalyzed conversion of allylic electrophiles into monoalkyl diazenes is described. This synthesis of allylic monoalkyl diazenes offers a new strategy for asymmetric synthesis by the reduction of optically active substrates or the use of chiral catalyst systems. Sensitive substrates are reduced in a highly selective manner. Ar = 2-NO2C 6H2.
- Movassaghi, Mohammad,Ahmad, Omar K.
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supporting information; experimental part
p. 8909 - 8912
(2009/05/26)
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- Palladium(II)-catalyzed isomerization of olefins with tributyltin hydride
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(Chemical Equation Presented) A new efficient method for the synthesis of geometrically pure (E)-alkenes from (Z)-alkenes is described. The reaction of aryl- or alkyl-substituted (Z)-alkenes with tributyltin hydride and triethylamine in the presence of a catalytic amount of palladium acetate afforded the corresponding (E)-alkenes in good yields.
- In, Su Kim,Guang, Ri Dong,Young, Hoon Jung
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p. 5424 - 5426
(2008/02/07)
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- Inter- and intramolecular palladium-catalyzed allyl cross-coupling reactions using allylindium generated in situ from allyl acetates, indium, and indium trichloride
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Inter- and intramolecular palladium-catalyzed ally! cross-coupling reactions using allylindium generated in situ by treatment of allyl acetates with indium and indium trichloride in the presence of Pd0 catalyst and nBuNMe2 in DMF were successfully demonstrated. Allylindium species generated in situ by reductive transmetalation of π- allylpalladium(II) complexes, obtained from a variety of allyl acetales in the presence of Pd0 catalyst together with indium and indium trichloride, were found to be capable of acting as effective nucleophilic coupling partners in Pd-catalyzed cross-coupling reactions. A variety of allyl acetates such as but-l-en-3-yl acetate, crotyl acetate, and 2-methylallyl acetate afforded the corresponding allylic compounds in good yields in cross-coupling reactions. Various electrophilic cross-coupling partners such as aryl iodides and vinyl bromides and triflates participate in these reactions. Not only intermolecular but also intramolecular Pd-catalyzed cross-coupling reactions work equally well to produce the desired allylic coupling products in good yields.
- Seomoon, Dong,Lee, Kooyeon,Kim, Hyunseok,Lee, Phil Ho
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p. 5197 - 5206
(2008/02/10)
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- Vinyldimethylphenylsilanes as safety catch silanols in fluoride-free palladium-catalyzed cross-coupling reactions
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A series of five structurally diverse vinyldimethylphenylsilanes have been shown to undergo a fluoride-free one-pot palladium-catalyzed cross-coupling reaction with phenyl iodide to give ipso coupled products in 62-86% yield. The limitations of this present protocol lie in the activation of Si-Ph vs protodesilylation by KOTMS/18-C-6, which seems sensitive to the sterics of cis substituents, but not geminal substituents.
- Anderson, James C.,Munday, Rachel H.
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p. 8971 - 8974
(2007/10/03)
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- Ru(III)-Catalyzed Cyclization of Arene-Alkene Substrates via Intramolecular Electrophilic Hydroarylation
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(Matrix presented) We herein report that RuCl3/AgOTf has proven to be a hydroarylation catalyst with an efficiency and scope superior to previously known methods. This catalyst demonstrated consistent performance with arene-ene substrates of diverse structural features, providing good to excellent yields of cyclization products (chromanes, tetralins, terpenoids, dihydrocoumarins).
- Youn, So Won,Pastine, Stefan J.,Sames, Dalibor
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p. 581 - 584
(2007/10/03)
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- Iron-catalyzed grignard cross-coupling with alkyl halides possessing β-hydrogens
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Tris(acetylacetonato)iron(III) (Fe(acac)3) was found to be an efficient catalyst for the cross-coupling reaction between aryl Grignard reagents and alkyl halides possessing β-hydrogens. The reaction is applicable to secondary alkyl halides as well as primary ones.
- Nagano, Takashi,Hayashi, Tamio
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p. 1297 - 1299
(2007/10/03)
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- Kinetics and mechanisms of the gas-phase elimination of arylethyl N,N-dimethylcarbamates and ω-phenylalkyl N,N-dimethylcarbamates
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The gas-phase elimination kinetics of several arylethyl N,N-dimethylcarbamates and ω-phenylalkyl N,N-dimethylcarbamates were determined in the temperature range 299.6-399.9 °C and pressure range 18-95 Torr. The reactions in a static system, seasoned with allyl bromide, and in the presence of a free radical suppressor are homogeneous and unimolecular and follow a first-order rate law. The rate coefficients are given by the Arrhenius equations: for 4-phenethyl N,N-dimethylcarbamate, log [k1 (s-1)] = (11.32 ± 0.22) - (166.9 ± 2.5) kJ mol-1 (2.303RT)-1; for methylphenethyl N,N-dimethylcarbamate, log[k1 (s-1)] = (12.07 ± 0.36) - (178.6 ± 4.3) kJ mol-1 (2.303RT)-1; for 4-methoxyphenethyl N,N-dimethylcarbamate, log[k1 (s-1)] = (11.03 ± 0.60) - (167.3 ± 7.1) kJ mol-1 (2.303RT)-1; for 4-nitrophenethyl N,N-dimethylcarbamate, log[k1 (s-1)] = (11.31 ± 0.54) - (163.7 ± 6.1) kJ mol-1 (2.303 RT)-1; for 3-(4-methoxyphenyl) propyl N,N-dimethylcarbamate, log [k1 (s-1)] = (13.52 ± 0.54) - (208.4 ± 6.8) kJ mol-1 (2.303 RT)-1; for 4-phenyl-1-butyl N,N-dimethylcarbamate, log [k1 (s-1)] = (12.00 ± 0.34) - (185.2 ± 4.2) kJ mol-1 (2.303 RT)-1; and for 5-phenyl-1-pentyl N,N-dimethyl carbamate, log [k1 (s-1)] = (11.79 ± 0.31) - (182.2 ± 3.9) kJ mol-1 (2.303RT)-1. The results imply the absence of anchimeric assistance of the phenyl group, while the acidity of the benzylic β-hydrogen appears to be responsible for a small but significant rate augmentation in these eliminations. Copyright
- Chuchani, Gabriel,Dominguez, Rosa M.,Rotinov, Alexandra,Herize, Armando
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- Allyl- and propargylchromium reagents generated by a chromium(III) ate-type reagent as a reductant and their reactions with electrophiles
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A chromium ate-type reagent 'Bu5CrLi2' reacts with allylic and propargylic phosphates to generate the corresponding allyl- and propargylchromium (propargyl = prop-2-ynyl) reagents which further react with a variety of electrophiles such as aldehydes, ketones, imines, and isocyanates to afford the corresponding adducts in high yields.
- Hojo,Sakuragi,Okabe,Hosomi
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p. 357 - 358
(2007/10/03)
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- Intramolecular C-H insertion reactions of (η5-Cyclopentadienyl)dicarbonyliron carbene complexes: Scope of the reactions and application to the synthesis of (±)-sterpurene and (±)-pentalenene
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(η5-Cyclopentadienyl)dicarbonyliron carbene complexes, [(η5C5H5) (CO)2Fe=CHR]+BF4-, are generated as reactive intermediates from thioether derivatives, (η5-C5H5)(CO)2FeCH(R)SPh, by S-alkylation with trimethyloxonium tetrafluoroborate and loss of thioanisole. The carbene complexes undergo intramolecular C-H insertion into appropriately situated side chains to form cyclopentane derivatives. The reaction has been developed into a general procedure employing cycloalkanones as scaffolds bearing the iron carbene moieties and the side chains at C(2) and C(3), respectively. The products of the intramolecular insertion reactions are substituted bicyclo[n.3.0]alkanones. The scope and limitations of the reaction are described. The reaction is applied to a total synthesis of sterpurene and to a formal synthesis of pentalenene. Overall, this approach to cyclopentane annulation complements the related metal-catalyzed insertion reactions of diazocarbonyl compounds, which are also believed to occur via metal carbene complexes.
- Ishii,Zhao,Mehta,Knors,Helquist
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p. 3449 - 3458
(2007/10/03)
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- Catalyst for bisalkoxycarbonylation of olefins, and method for production of succinate derivatives
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A catalyst for the bisalkoxycarbonylation of olefins comprising a noble metal compound and a phosphine chalcogenide of the following formula (1): wherein each of R1, R2 and R3 is, independently, an alkyl group or an aryl group each of which may have a substituent, and A is a Group 16 element of the Periodic Table; and R1, R2 or R3 may be combined, directly or through a bridging group, with one another where the groups to be combined may be attached either to an identical phosphorus atom or to different phosphorus atoms. Element A includes oxygen, sulfur and selenium atoms. The noble metal compound includes palladium(II) halides and other palladium compounds. The catalyst may further include a copper(I) halide or other copper compound as a co-catalyst. The use of this catalyst can provide the bisalkoxycarbonylation of olefins with efficiency.
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- Collagen cross-links: Synthesis of pyridinoline, deoxypyridinoline and their analogues
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An efficient chiral synthesis of (S,S)-(-)-3g, a key intermediate for the preparation of collagen cross-links pyridinoline (Pyd, 1) and deoxypyridinoline (Dpd, 2) was achieved from (4S)-5(tert-butoxy)-4-[(tert- butoxycarbonyl)amino]-5-oxopentanoic acid (21b). Quaternization of (S,S)-(- )-3g with iodide (2S, 5R)-(+)-4a followed by hydrolysiS provided a first chiral synthesis of natural (+)-Pyd (1). 1-(2S)-(+)-Pyd (1) was also synthesized from (S,S)-(-)-3g and iodide (2S, 5S)-(+)-4a. Similarly, quaternization of (S,S)-(-)-3g with iodide (2S)-(-)-4b, which was prepared from (2S)-(-)-6-amino-2[(tert-butoxycarbonyl)amino]hexanoic acid (31) in three steps, followed by hydrolysis afforded natural (+)-Dpd (2) in 5.3% overall yield. Also, the synthesis of racemic Dpd [(±)-2] and a variety of its analogues is presented.
- Adamczyk, Maciej,Johnson, Donald D.,Reddy, Rajarathnam E.
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- Dehydration of α-silylalcohols in the reductive conversion of esters and ketones into alkenes
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The conversion of esters and ketones into easily dehydrated α-silylated alcohols, and protodesilylation of the resultant vinylsilanes, gives alkenes under relatively mild acidic conditions.
- Chenede, Alain,Abd.Rahman, Noorsaadah,Fleming, Ian
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p. 2381 - 2382
(2007/10/03)
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- The regiochemistry of the protodesilylation of some cyclopropylmethylsilanes derived from allylsilanes
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Simmons-Smith type methylenation of allylsilanes, followed by protodesilylation, can be used to achieve overall the S(E)2' replacement of the silyl group by a methyl group. The regioselectivity is good for protonation on the methylene carbon of the cyclopropylmethylsilanes 11, 17, 20 and 23, but the low stereoselectivity in the formation of the cyclopropylmethylsilane 26 and its failure to undergo clean protodesilylation make the method of limited use.
- Fleming,Sanderson,Terrett
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- Aromatic annulation with naphtho[1,8-de]-1,3-dithiin carbocations
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The title carbocations have been produced by the reaction of silver trifluoromethanesulfonate with mixed orthothioesters. Intramolecular aromatic electrophilic substitution (annulation) of the cationic intermediates proceeds readily and provides an efficient, chemoselective route for appending six-membered rings to nonactivated aromatic systems.
- Gamage, Swarna A.,Smith, Robin A. J.
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p. 2111 - 2128
(2007/10/02)
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