- Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N-Heterocyclic Carbene–Copper Complex
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The alkylative carboxylation of allenamide catalyzed by an N-heterocyclic carbene (NHC)–copper(I) complex [(IPr)CuCl] with CO2and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO2(1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)-α,β-dehydro-β-amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ-carbon, and the carboxyl group introduced onto the β-carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO2. A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β-hydrogen atoms, such as Et2Zn or Bu2Zn, also gave the corresponding alkylative carboxylation products without β-hydride elimination. The present methodology provides an easy route to alkyl-substituted α,β-dehydro-β-amino acid ester derivatives under mild reaction conditions with high regio- and stereoselectivtiy.
- Gholap, Sandeep Suryabhan,Takimoto, Masanori,Hou, Zhaomin
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- Nickel-catalyzed: Syn -stereocontrolled ring-opening of oxa- and azabicyclic alkenes with dialkylzinc reagents
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A new nickel-catalyzed syn-stereocontrolled ring-opening of oxa- and azabicyclic alkenes with dialkylzinc reagents was developed, which afforded the corresponding cis-2-alkyl-1,2-dihydronaphthalen-1-ols and 1,2-alkyl amide derivatives in moderate to excellent yields (up to 99% yield) under mild conditions. In this work, we successfully avoided obtaining hydride addition byproducts arising from β-hydride elimination on an ethyl nickel species. Furthermore, a plausible mechanism for the ring-opening reaction was also proposed.
- Deng, Yingying,Yang, Wen,Yao, Yongqi,Yang, Xin,Zuo, Xiongjun,Yang, Dingqiao
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- Synthesis of zinc dialkyls from zinc and alkyl bromides
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Zinc dialkyls with linear radicals were prepared from zinc and alkyl bromides in the presence of stimulating systems based on a transition metal derivative and an organometallic compound capable of reducing the transition metal derivative under the reaction conditions.
- Eremeev,Danov,Sakhipov,Skudin
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- Preparation of Organozinc and Organocadmium Compounds from the Metals and Alkyl Halides in the Presence of Stimulating Systems Based on a Derivative a Transition Metal and an Organometallic Compound
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Full and mixed alkyl derivatives of zinc and cadmium were prepared from these metals and organic halides in the presence of stimulating systems necessarily containing a transition metal derivative and an organometallic compound capable of reducing this derivative under the process conditions. Such stimulating systems make it possible to introduce selectively organic halides (iodides, bromides, chlorides) into the reaction with zinc and cadmium to obtain the corresponding mixed organometallic compounds.
- Eremeev,Danov,Skudin,Sakhipov
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- A Path to More Sustainable Catalysis: The Critical Role of LiBr in Avoiding Catalyst Death and its Impact on Cross-Coupling
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The role that LiBr plays in the lifetime of Pd-NHC complexes has been investigated. A bromide ion is proposed to coordinate to Pd thereby preventing beta hydride elimination (BHE) (to form NHC-H+) of the reductive elimination (RE) intermediate that normally completes with the desired cross-coupling catalytic cycle. Coordinating groups, such as anilines, are able to bind suitably well to Pd to prevent this pathway from occurring, thus reducing the need for the added salt. The metal hydride formed from BHE is very unstable and RE of the hydride to the NHC ligand occurs very rapidly giving rise to the corresponding hydrido-NHC (i.e., NHC-H+). The use of the per deuterated dibutylzinc shows a significant deuterium isotope effect, shutting down catalyst death almost completely. The use of bis-neopentylzinc, now possessing no hydrides, eliminates catalyst death all together leading to a very long-lived catalytic cycle and confirming the untoward role of BHE.
- Eckert, Philip,Organ, Michael G.
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- Hydrogen/deuterium exchange in alkyl-hydride derivatives of ansa-tungstenocene compounds
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The higher n-alkyl hydrides [W{(η-C5H4)CMe 2(η-C5H4)}(R)H](R = {(CH2) nCH3}, n = 1-4) and the isotopically labelled analogues [W(η-C5D4)C(CD
- Green, Malcolm L.H.,Conway, Stephen L.J.,Doerrer, Linda H.
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- Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide
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Alkylative carboxylation of ynamides with CO2 and dialkylzinc reagents using a N-heterocyclic carbene (NHC)-copper catalyst has been developed. A variety of ynamides, both cyclic and acyclic, undergo this transformation under mild conditions to afford the corresponding α,β-unsaturated carboxylic acids, which contain the α,β-dehydroamino acid skeleton. The present alkylative carboxylation formally consists of Cu-catalyzed carbozincation of ynamides with dialkylzinc reagents with the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO2. Dialkylzinc reagents bearing a β-hydrogen atom such as Et2Zn and Bu2Zn still afford the alkylated products despite the potential for β-hydride elimination. This protocol would be a desirable method for the synthesis of highly substituted α,β- dehydroamino acid derivatives due to its high regio- and stereoselectivity, simple one-pot procedure, and its use of CO2 as a starting material. CO2 incorporation with alkylation: Alkylative carboxylation of ynamides with CO2 and a dialkylzinc reagent has been achieved by using a N-heterocyclic carbene (NHC)-copper complex as the catalyst. The reactions proceeded by Cu-catalyzed carbozincation of ynamides with dialkylzinc reagents and the subsequent carboxylation of the resulting alkenylzinc species (see scheme).
- Takimoto, Masanori,Gholap, Sandeep Suryabhan,Hou, Zhaomin
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- Stereoselective and Stereospecific Triflate-Mediated Intramolecular Schmidt Reaction: Ready Access to Alkaloid Skeletons**
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The stereoselectivity and stereospecificity of the triflate-mediated intramolecular Schmidt reaction of substituted 3-(1-azidocyclohexyl)propanol derivatives leading to octahydro-1H-pyrrolo[1,2-a]azepine, the structural skeleton of several important families of alkaloids such as the Stemona alkaloids, has been examined. The reaction involves an initial intramolecular SN2 reaction between the azide moiety and the triflate affording an intermediate spirocyclic aminodiazonoium salt that undergoes the expected 1,2-shift/N2-elimination followed by hydride-mediated iminium salt reduction. Remarkably, chiral alcohols are converted to the azabicyclic derivative with no or limited racemization. The initial asymmetric alcohol center controls the diastereoselectivity of the whole process, leading to the formation of one out of the four possible diastereoisomers of disubstituted octahydro-1H-pyrrolo[1,2-a]azepine. The origin of the stereoselectivity is rationalized based on theoretical calculations. The concise synthesis of (?)-(cis)-3-propylindolizidine and (?)-(cis)-3-butyllehmizidine, two alkaloids found in the venom of workers of the ant Myrmicaria melanogaster, is reported.
- Gn?gi, Lars,Arnold, Remo,Giornal, Florence,Jangra, Harish,Kapat, Ajoy,Nyfeler, Erich,Sch?rer, Robin M.,Zipse, Hendrik,Renaud, Philippe
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- Theoretical and experimental studies on formation of diethylzinc-triphenylphosphine complex
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This work is mainly focused on understanding the complex-forming behavior of diethylzinc with neutral phosphine ligands such as triphenylphosphine (PPh3) to yield [Zn(PPh3)2Et2]. The complex formation in solution is observed in the presence of a large exc
- Sadhana, Venkatesh,Das, Dhrubjyoti,Sravania, Chinduluri,Sivaramakrishna, Akella,Vijayakrishna, Kari,Clayton, Hadley S.
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- Three-Component Difunctionalization of Cyclohexenyl Triflates: Direct Access to Versatile Cyclohexenes via Cyclohexynes
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Difunctionalization of strained cyclic alkynes presents a powerful strategy to build richly functionalized cyclic alkenes in an expedient fashion. Herein we disclose an efficient and flexible approach to achieve carbohalogenation, dicarbofunctionalization, aminohalogenation and aminocarbonation of readily available cyclohexenyl triflates. We have demonstrated the novel use of zincate base/nucleophile system for effective formation of key cyclohexyne intermediates and selective addition of various carbon and nitrogen nucleophiles. Importantly, leveraging the resulting organozincates enables the incorporation of a broad range of electrophilic partners to deliver structurally diverse cyclohexene motifs. The importance and utility of this method is also exemplified by the modularity of this approach and the ease in which even highly complex polycyclic scaffolds can be accessed in one step.
- Cho, Seoyoung,McLaren, E. J.,Wang, Qiu
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supporting information
p. 26332 - 26336
(2021/11/10)
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- The Role of LiBr and ZnBr2 on the Cross-Coupling of Aryl Bromides with Bu2Zn or BuZnBr
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The impact of LiBr and ZnBr2 salts on the Negishi coupling of alkylZnBr and dialkylzinc nucleophiles with both electron-rich and -poor aryl electrophiles has been examined. Focusing only on the more difficult coupling of deactivated (electron-rich) oxidative addition partners, LiBr promotes coupling with BuZnBr, but does not have such an effect with Bu2Zn. The presence of exogenous ZnBr2 shuts down the coupling of both BuZnBr and Bu2Zn, which has been shown before with alkyl electrophiles. Strikingly, the addition of LiBr to Bu2Zn reactions containing exogenous ZnBr2 now fully restores coupling to levels seen without any salt present. This suggests that there is a very important interaction between LiBr and ZnBr2. It is proposed that Lewis acid adducts are forming between ZnBr2 and the electron-rich Pd0 centre and the bromide from LiBr forms inorganic zincates that prevent the catalyst from binding to ZnBr2. This idea has been supported by catalyst design as chlorinating the backbone of the NHC ring of Pd-PEPPSI-IPent to produce Pd-PEPPSI-IPentCl catalyst now gives quantitative conversion, up from a ceiling of only 50 % with the former catalyst.
- Eckert, Philip,Organ, Michael G.
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supporting information
p. 15751 - 15754
(2019/11/16)
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- O2-Mediated Oxidation of Aminoboranes through 1,2-N Migration
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In analogy to the classical reaction of C?B bonds with peroxides, the first oxidative functionalization of aminoboranes through a 1,2-N migration was realized. Readily available aliphatic nitro compounds are thereby transformed into N- and O-functionalized hydroxylamines in a single synthetic operation. Addition of hazardous peroxides is avoided. Instead, the insertion of O2, as the terminal oxidant, into Zn?C bonds provides the necessary peroxides. The required zinc organyls, in turn, are formed through a boron-to-zinc exchange, from an organoboronic ester byproduct of the nitro-to-aminoborane transformation.
- Rauser, Marian,Warzecha, Daniel P.,Niggemann, Meike
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supporting information
p. 5903 - 5907
(2018/05/14)
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- Asymmetric Sulfinylations of N-Methylephedrine-Modified Tri- or Tetraalkyl Zincates by Symmetric Diaryl Sulfoxides
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Diethylzinc was treated with 1 or 2 equiv. of AlkMgCl or PhMgBr (preferably) or with 1 equiv. of nBuLi (less efficiently) for forming species – plausibly zincates – which were sulfinylated by diaryl sulfoxides to give racemic alkyl aryl sulfoxides in yields reaching 100 %. Dialkylzinc reagents were also activated by treatments with 1 or 2 equiv. of an enantiomerically pure alkylmagnesium β-aminoalkoxide. This worked best when the alkoxide stemmed from a dialkylmagnesium reagent and an equimolar amount of N-methyl-(–)-ephedrine. This second activation mode allowed sulfinylations of what was originally the dialkylzinc reagent with diaryl sulfoxides. This generated alkyl aryl sulfoxides with enantiomeric ratios up to 93:7 in up to 100 % yield.
- Ruppenthal, Simon,Brückner, Reinhard
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p. 2518 - 2530
(2018/06/11)
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- Electrophilic Amination with Nitroarenes
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An exceptionally general electrophilic amination, which directly transforms commercially available nitroarenes into alkylated aromatic aminoboranes with zinc organyl compounds was developed. The reaction starts with a two-step partial reduction of the nitro group to a nitrenoid, which is used in situ as the electrophilic amination reagent. To facilitate isolation, the resulting air- and moisture-sensitive aminoboranes were reacted with a range of electrophiles. The method not only represents a direct transformation of nitro compounds into electrophilic amination reagents but also provides an elegant alternative to dehydrocoupling methods for the generation of aminoboranes.
- Rauser, Marian,Ascheberg, Christoph,Niggemann, Meike
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supporting information
p. 11570 - 11574
(2017/09/11)
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- Asymmetric Pentafulvene Carbometalation - Access to Enantiopure Titanocene Dichlorides of Biological Relevance
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Unprecedented asymmetric copper-catalyzed addition of ZnEt2 (ZnBu2) to the exocyclic C=C bond of pentafulvenes C5H4(=CHAr) (Ar=2-MeOPh and related species) results in enantiomerically enriched (up to 93:7 e.r.)
- Cini, Melchior,Bradshaw, Tracey D.,Woodward, Simon,Lewis, William
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supporting information
p. 14179 - 14182
(2016/01/25)
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- SULFONIC ACID DERIVATIVE COMPOUND, PHOTOACID GENERATOR, RESIST COMPOSITION, CATIONIC POLYMERIZATION INITIATOR, AND CATIONIC POLYMERIZABLE COMPOSITION
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PROBLEM TO BE SOLVED: To provide a sulfonic acid derivative compound that shows a large absorption to light at a wavelength of 365 nm, high solubility with an organic solvent, and a favorable acid generation rate, a photoacid generator, a resist composition, a cationic polymerization initiator, and a cationic polymerizable composition. SOLUTION: The sulfonic acid derivative compound is represented by general formula (I). In formula (I), X represents a linear or branched alkyl group having 1 to 14 carbon atoms; R represents an aliphatic hydrocarbon group having 1 to 18 carbon atoms, an aryl group having 6 to 20 carbon atoms, an arylalkyl group having 7 to 20 carbon atoms, an aryl group having 7 to 20 carbon atoms substituted with an acyl group, an alicyclic hydrocarbon group having 3 to 12 carbon atoms, a 10-camphor-yl group, or the like. COPYRIGHT: (C)2015,JPOandINPIT
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Paragraph 0087
(2016/10/08)
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- Reactivities of mixed organozinc and mixed organocopper reagents: 9. Solvent dependence of group transfer selectivity in sp3C coupling and acylation of mixed diorganocuprates and diorganozincs
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The selectivity and/or reactivity of organyl group transfer of mixed diorganocuprates in their alkyl coupling in THF depends on N- or O-donor solvents as cosolvents. Selective n-Bu group transfer is observed in room temperature alkylation of Grignard reagent derived stoichiometric n-BuPhCuMgBr reagent in THF:cosolvent and solvation effects do not change the group transfer ability. However, in the alkylation of catalytic mixed cuprates derived from CuI catalyzed n-BuPh2ZnMgBr and n-Bu2PhZnMgBr, group transfer ability depends on the solvation effect and it can be controlled by using N- or O-donor solvents. In alkylation of CuI catalyzed mixed zincate n-BuPh 2ZnMgBr and also n-Bu2PhZnMgBr in THF at reflux temperature Ph group transfer takes place (n-Bu/Ph transfer ratio is 1:9 and 4:6, respectively) whereas n-Bu transfer increases in THF:NMP (1:1) resulting n-Bu/Ph transfer ratio of 4:6 and 8:2, respectively. Group transfer ability in allylation of n-BuPhZn seems not to be solvent dependent. The solvent effect on the group transfer ability has been found to be dependent also on the R 1 and R2 partnership in room temperature benzoylation of catalytic mixed cuprates, R1R2CuZnI, derived from CuI catalyzed R1R2Zn. These results are briefly discussed in terms of solvation of mixed diorganocuprate and diorganozinc reagents and provide useful information in their atom-economic alkyl, allyl and acyl coupling reactions.
- Erdik, Ender,Ero?lu, Fatma,Kalkan, Melike,Pekel, ?zgen ?mür,?zkan, Duygu,Serdar, Ebru Z.
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p. 235 - 241
(2013/10/01)
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- Lithium organozincate complexes LiRZnX2: Common species in organozinc chemistry
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We have used a combination of electrospray ionization (ESI) mass spectrometry, electrical conductivity measurements, and NMR spectroscopy to investigate the effect of LiCl on solutions of organylzinc halides RZnX (R = Bu, Bn, Ph; X = halogen) and dibutylzinc Bu2Zn in tetrahydrofuran. In the case of RZnX, the addition of LiX (X = Cl) leads to a steep rise of the ESI signal intensities of RZnX2- organozincate anions. At the same time, the electrical conductivities strongly increase and the NMR absorptions of the α-H atoms of BuZnX shift upfield. These results consistently point to the formation of lithium organozincates Li +RZnX2-. As the most common syntheses of RZnX reagents involve stoichiometric amounts of LiX salts, Li+RZnX 2- complexes are supposedly widespread and may hold the key to understanding the marked effects of LiCl on the reactivity of organozinc halides. In contrast, we find Bu2Zn to have a much lower tendency to add LiCl and form ate complexes. This result is in line with the weak effect of LiCl on the reactivity of diorganozinc compounds reported in the literature.
- Fleckenstein, Julia E.,Koszinowski, Konrad
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p. 5018 - 5026
(2011/11/07)
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- METHODS FOR PREPARING DIORGANOZINC COMPOUNDS
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There are provided methods for preparing the diorganozmc compounds of formula R2Zn (I or Ia), where R is a defined organic radical, and the two R groups can be the same or different The starting material is the zinc compound ZnX2 (II) or R2ZnX (IIa), where X is a defined anion and R2 is a defined organic radical. The zinc reagent of type II is combined with a Grignard reagent and also, when X is Cl or Br, with an alkali metal reagent (VI) to form the diorganozinc product (I or Ia). Also provided are methods for preparing the zinc alcoholates of formula Zn(OR1)2 by reaction of ZnX2, where X = Cl or Br, with an alkali metal reagent of the formula MOR1, where M = Na or K, and where R1 is a defined organic radical.
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Page/Page column 17; 19-20
(2009/01/20)
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- Synthesis of dictyopterene A: Optically active tributylstannylcyclopropane as a chiral synthon
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Synthesis of (IS,2R)-1-[(E)-hex-1-en-1-yl]-2-vinylcyclopropane (dictyopterene A), which was isolated from the essential oil of algae of the genus Dictyopteris in Hawaii, has been demonstrated using optically active tributylstannylcyclopropane as a starting chiral synthon.
- Itoh, Toshiyuki,Inoue, Hitomi,Emoto, Sachie
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p. 409 - 416
(2007/10/03)
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