- Elusive transmetalation intermediate in copper-catalyzed conjugate additions: Direct Nmr detection of an ethyl group attached to a binuclear phosphoramidite copper complex
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Copper-catalyzed asymmetric conjugate addition reactions are a very powerful and widely applied method for enantioselective carbon-carbon bond formation. However, structural and mechanistic insight into these famous reactions has been very limited so far. In this article, the first direct experimental detection of transmetalation intermediates in copper-catalyzed reactions is presented. Special combinations of 1H,31P HMBC spectra allow for the identification of complexes with chemical bonds between the alkyl groups and the copper complexes. For the structural characterization of these transmetalation intermediates, a special approach is applied, in which samples using enantiopure ligands are compared with samples using enantiomeric mixtures of ligands. It is experimentally proven, for the first time, that the dimeric copper complex structure is retained upon transmetalation, providing an intermediate with mixed trigonal/tetrahedral coordination on the copper atoms. In addition, monomeric intermediates with one ligand, but no intermediates with two ligands, are detected. These experimental results, in combination with the well-known optimal ligand-to-copper ratio of 2:1 in synthetic applications, allow us to propose that a binuclear transmetalation intermediate is the reactive species in copper-catalyzed asymmetric conjugate addition reactions. This first direct experimental insight into the structure of the transmetalation intermediate is expected to support the mechanistic and theoretical understanding of this important class of reactions and to enable their further synthetic development. In addition, the special NMR approach presented here for the identification and characterization of intermediates below the detection limit of 1H NMR spectra can be applied also to other classes of catalyses.
- Von Rekowski, Felicitas,Koch, Carina,Gschwind, Ruth M.
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- 8.78% Efficient All-Polymer Solar Cells Enabled by Polymer Acceptors Based on a B←N Embedded Electron-Deficient Unit
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In the field of all-polymer solar cells (all-PSCs), all efficient polymer acceptors that exhibit efficiencies beyond 8% are based on either imide or dicyanoethylene. To boost the development of this promising solar cell type, creating novel electron-deficient units to build high-performance polymer acceptors is critical. A novel electron-deficient unit containing B←N bonds, namely, BNIDT, is synthesized. Systematic investigation of BNIDT reveals desirable properties including good coplanarity, favorable single-crystal structure, narrowed bandgap and downshifted energy levels, and extended absorption profiles. By copolymerizing BNIDT with thiophene and 3,4-difluorothiophene, two novel conjugated polymers named BN-T and BN-2fT are developed, respectively. It is shown that these polymers possess wide absorption spectra covering 350–800 nm, low-lying energy levels, and ambipolar film-transistor characteristics. Using PBDB-T as the donor and BN-2fT as the acceptor, all-PSCs afford an encouraging efficiency of 8.78%, which is the highest for all-PSCs excluding the devices based on imide and dicyanoethylene-type acceptors. Considering that the structure of BNIDT is totally different from these classical units, this work opens up a new class of electron-deficient unit for constructing efficient polymer acceptors that can realize efficiencies beyond 8% for the first time.
- Li, Yongchun,Meng, Huifeng,Liu, Tao,Xiao, Yiqun,Tang, Zhonghai,Pang, Bo,Li, Yuqing,Xiang, Ying,Zhang, Guangye,Lu, Xinhui,Yu, Gui,Yan, He,Zhan, Chuanlang,Huang, Jianhua,Yao, Jiannian
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- Complexation of diphenylzinc simple ethers. Crystal structures of the complexes Ph2Zn*glyme and Ph2Zn*diglyme
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The complexation behavior of diphenylzinc with a series of mono-, di- and tri-coordinating ethers has been investigated.Two stable crystalline 1:1 adducts, with ethyleneglycol dimethyl ether (glyme) (1) and diethyleneglycol dimethyl ether (diglyme) (2) were isolated and characterized by an X-ray diffraction study.Complex 1 has a normal tetra-coordinated zinc atom; 2 represents the first example of a complex penta-coordinated diorganozinc compound, and has a rather unusual geometry.
- Markies, Peter R.,Schat, Gerrit,Akkerman, Otto S.,Bickelhaupt, F.,Spek, Anthony L.
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- Nickel-catalyzed multicomponent coupling of alkyne, buta-1,3-diene, and dimethylzinc under carbon dioxide
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A nickel catalyst promoted the coupling of alkynes with buta-1,3-diene and dimethylzinc under carbon dioxide to provide (5E,8Z)-2-vinyldeca-5,8-dienoic acids with high regio- and stereo selectivity. Georg Thieme Verlag Stuttgart. New York.
- Mori, Yasuyuki,Mori, Takamichi,Onodera, Gen,Kimura, Masanari
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- Vinyl Carbocations Generated under Basic Conditions and Their Intramolecular C-H Insertion Reactions
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Here we report the surprising discovery that high-energy vinyl carbocations can be generated under strongly basic conditions, and that they engage in intramolecular sp3 C-H insertion reactions through the catalysis of weakly coordinating anion salts. This approach relies on the unconventional combination of lithium hexamethyldisilazide base and the commercially available catalyst, triphenylmethylium tetrakis(pentafluorophenyl)borate. These reagents form a catalytically active lithium species that enables the application of vinyl cation C-H insertion reactions to heteroatom-containing substrates.
- Wigman, Benjamin,Popov, Stasik,Bagdasarian, Alex L.,Shao, Brian,Benton, Tyler R.,Williams, Chloé G.,Fisher, Steven P.,Lavallo, Vincent,Houk,Nelson, Hosea M.
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- Remarkably Selective Formation of Allenyl and Dienyl Alcohols via Ni-Catalyzed Coupling Reaction of Conjugated Enyne, Aldehyde, and Organozinc Reagents
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A nickel catalyst promotes the multi-component reactions (MCRs) of conjugated enynes, aldehydes, and organozinc reagents to form unsaturated alcohols. Ligand effects dramatically control the regioselectivity in these Ni-catalyzed MCRs, leading to the selective formation of allenyl alcohols and conjugated dienyl alcohols.
- Mori, Yasuyuki,Kawabata, Toshiki,Onodera, Gen,Kimura, Masanari
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- [(μ2-H)(η2-Ge4)ZnPh2]3?, an edge-on protonated E4 cluster establishing the first three-center two-electron Ge-H-Ge bond
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The first example of a protonated and a rare example of a metal complex of the tetrahedral tetrel cluster anion [Ge4]4? was obtained from a solution of K6Rb6Ge17 in liquid ammonia in the presence of ZnPh2 and [18]crown-6. In [K([18]crown-6)][Rb([18]crown-6)]2[HGe4ZnPh2]·8NH3 (1) one ZnPh2 molecule and one H atom are bound to opposite, significantly elongated edges of a distorted Ge4 tetrahedron. DFT calculations confirm the experimentally found interatomic distances and reveal a structural proof of a three-center two-electron Ge-H-Ge bond.
- Henneberger, Thomas,Klein, Wilhelm,Dums, Jasmin V.,F?ssler, Thomas F.
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- Organozinc-Mediated Direct C?C Bond Formation via C?N Bond Cleavage of Ammonium Salts
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We report a direct cross-coupling reaction between diarylzinc (Ar2Zn) and aryltrimethylammonium salts (ArNMe3 +??OTf) in the presence of LiCl, via C?N bond cleavage. The reaction takes place smoothly upon heating in THF without any external catalyst, enabling an efficient and chemoselective formation of biaryl products. Mechanistic studies indicate that the reaction proceeds through a single electron transfer route.
- Wang, Dong-Yu,Morimoto, Koki,Yang, Ze-Kun,Wang, Chao,Uchiyama, Masanobu
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- On the remarkably different role of salt in the cross-coupling of arylzincs from that seen with alkylzincs
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The role of halide salt additives has been investigated in the Negishi reaction involving aryl zinc reagents. Diarylzincs readily transmetallate to Pd in relatively non-polar media (e.g., THF) with zero salt present and coupling proceeds. Arylzinc halides
- McCann, Lucas C.,Organ, Michael G.
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- Reactivity of mixed organozinc and mixed organocopper reagents: 5-A kinetic insight to compare the transfer ability of the same group in copper catalyzed alkylation of mixed and homozincates
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A detailed kinetic investigation and activation parameters are reported for copper catalyzed coupling reaction of mixed zincate, n-BuPh2ZnMgBr and homozincate, Ph3ZnMgBr with n-pentyl bromide in THF at 25-65 °C. An empirical rate law can be expressed as rate = k[zincate]0 [alkyl bromide]1 [CuI]1. The reaction rate of transferable phenyl group in mixed catalytic cuprate, n-BuPhCuMgBr derived from mixed zincate is higher than the rate of catalytic homocuprate Ph2CuMgBr derived from homozincate. A catalytic cycle and the mechanism which accommodates the kinetic data and activation parameters is given. These results show that the reaction rate of transferable group changes depending on the residual group in the reactions of mixed diorganocuprates and also provide a kinetic support for the commonly accepted hypothesis regarding the dependence of the R 1 group transfer ability on the strength of R2-Cu bond in reactions of R1R2CuMgBr reagents.
- Erdik, Ender,Serdar, Ebru Zeynep
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- Alkyl?(Hetero)Aryl Bond Formation via Decarboxylative Cross-Coupling: A Systematic Analysis
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Suzuki, Negishi, and Kumada couplings are some of the most important reactions for the formation of skeletal C?C linkages. Their widespread use to forge bonds between two aromatic rings has enabled every branch of chemical science. The analogous union between alkyl halides and metallated aryl systems has not been as widely employed due to the lack of commercially available halide building blocks. Redox-active esters have recently emerged as useful surrogates for alkyl halides in cross-coupling chemistry. Such esters are easily accessible through reactions between ubiquitous carboxylic acids and coupling agents widely used in amide bond formation. This article features an amalgamation of in-house experience bolstered by approximately 200 systematically designed experiments to accelerate the selection of ideal reaction conditions and activating agents for the cross-coupling of primary, secondary, and tertiary alkyl carboxylic acids with both aryl and heteroaryl organometallic species.
- Sandfort, Frederik,O'Neill, Matthew J.,Cornella, Josep,Wimmer, Laurin,Baran, Phil S.
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- Exploring Electrochemical C(sp3)-H Oxidation for the Late-Stage Methylation of Complex Molecules
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The magic methyl effect, a dramatic boost in the potency of biologically active compounds from the incorporation of a single methyl group, provides a simple yet powerful strategy employed by medicinal chemists in the drug discovery process. Despite significant advances, methodologies that enable the selective C(sp3)-H methylation of structurally complex medicinal agents remain very limited. In this work, we disclose a modular, efficient, and selective strategy for the α-methylation of protected amines (i.e., amides, carbamates, and sulfonamides) by means of electrochemical oxidation. Mechanistic analysis guided our development of an improved electrochemical protocol on the basis of the classic Shono oxidation reaction, which features broad reaction scope, high functional group compatibility, and operational simplicity. Importantly, this reaction system is amenable to the late-stage functionalization of complex targets containing basic nitrogen groups that are prevalent in medicinally active agents. When combined with organozinc-mediated C-C bond formation, our protocol enabled the direct methylation of a myriad of amine derivatives including those that have previously been explored for the magic methyl effect. This synthesis strategy thus circumvents multistep de novo synthesis that is currently necessary to access such compounds and has the potential to accelerate drug discovery efforts.
- Ho, Justin S. K.,Lin, Song,Liu, Kaida,Mao, Kaining,Neurock, Matthew,Novaes, Luiz F. T.,Tanwar, Mayank,Terrett, Jack A.,Villemure, Elisia
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supporting information
p. 1187 - 1197
(2022/02/05)
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- Atom-efficient transition-metal-free arylation ofN,O-acetals using diarylzinc reagents through Zn/Zn cooperativity
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Exploiting the cooperative action of Lewis acid Zn(C6F5)2with diarylzinc reagents, the efficient arylation ofN,O-acetals to access diarylmethylamines is reported. Reactions take place under mild reaction conditions without the need for transtion-metal catalysis. Mechanistic investigations have revealed that Zn(C6F5)2not only acts as a Lewis acid activator, but also enables the regeneration of nucleophilic ZnAr2species, allowing a limiting 50 mol% to be employed.
- Borys, Andryj M.,Gil-Negrete, Jose M.,Hevia, Eva
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supporting information
p. 8905 - 8908
(2021/09/10)
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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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- General C(sp2)-C(sp3) Cross-Electrophile Coupling Reactions Enabled by Overcharge Protection of Homogeneous Electrocatalysts
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Cross-electrophile coupling (XEC) of alkyl and aryl halides promoted by electrochemistry represents an attractive alternative to conventional methods that require stoichiometric quantities of high-energy reductants. Most importantly, electroreduction can readily exceed the reducing potentials of chemical reductants to activate catalysts with improved reactivities and selectivities over conventional systems. This work details the mechanistically-driven development of an electrochemical methodology for XEC that utilizes redox-active shuttles developed by the energy-storage community to protect reactive coupling catalysts from overreduction. The resulting electrocatalytic system is practical, scalable, and broadly applicable to the reductive coupling of a wide range of aryl, heteroaryl, or vinyl bromides with primary or secondary alkyl bromides. The impact of overcharge protection as a strategy for electrosynthetic methodologies is underscored by the dramatic differences in yields from coupling reactions with added redox shuttles (generally >80%) and those without (generally 20%). In addition to excellent yields for a wide range of substrates, reactions protected from overreduction can be performed at high currents and on multigram scales.
- Hamby, Taylor B.,Sevov, Christo S.,Truesdell, Blaise L.
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supporting information
p. 5884 - 5893
(2020/04/10)
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- Chiral Lithium Amido Aryl Zincates: Simple and Efficient Chemo- and Enantio-Selective Aryl Transfer Reagents
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An enantioselective aryl transfer is promoted using chiral tricoordinated lithium amido aryl zincates that are easily accessible reagents and whose chiral appendage is simply recovered for reuse. The arylation reaction is run in good yields (60 % average on twenty substrates) and high enantiomeric excesses (95 % ee average). This occurs whatever the ortho, meta, or para substituent borne by the substrate and a complete chemoselectivity is observed with respect to the aldehyde function. Sensitive groups such as nitriles, esters, ketones, and enolisable substrates resist to the action of the ate reagent, warranting a large scope to this methodology.
- Chaumont-Olive, Pauline,Rouen, Mathieu,Barozzino-Consiglio, Gabriella,Ben Abdeladhim, Amel,Maddaluno, Jacques,Harrison-Marchand, Anne
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supporting information
p. 3193 - 3197
(2019/01/25)
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- Quaternary Centers by Nickel-Catalyzed Cross-Coupling of Tertiary Carboxylic Acids and (Hetero)Aryl Zinc Reagents
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This work bridges a gap in the cross-coupling of aliphatic redox-active esters with aryl zinc reagents. Previously limited to primary, secondary, and specialized tertiary centers, a new protocol has been devised to enable the coupling of general tertiary systems using nickel catalysis. The scope of this operationally simple method is broad, and it can be used to simplify the synthesis of medicinally relevant motifs bearing quaternary centers.
- Chen, Tie-Gen,Zhang, Haolin,Mykhailiuk, Pavel K.,Merchant, Rohan R.,Smith, Courtney A.,Qin, Tian,Baran, Phil S.
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supporting information
p. 2454 - 2458
(2019/02/09)
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- One-pot Negishi cross-coupling reaction of aryldiazonium salts via Ni catalysis induced by visible-light
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Visible-light induced catalysis is of high interest for its mild and environmentally benign properties. Herein, a general Ni catalysis accelerated by visible-light was successfully developed for one-pot Negishi coupling reactions at room temperature in a short reaction time (2Zn generated in situ from Grignard reagents and ZnBr2. This protocol provides a convenient access to C–C bond formation for important biaryl components. It tolerates various functional groups, and Hammett study illuminates the possiblility of Ni(III)/Ni(I) redox catalytic cycle.
- Wang, Lianjun,Liu, Gao
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- Direct Reductive N-Functionalization of Aliphatic Nitro Compounds
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The first general protocol for the direct reductive N-functionalization of aliphatic nitro compounds is presented. The nitro group is partially reduced to a nitrenoid, with a mild and readily available combination of B2pin2 and zinc organyls. Thereby, the formation of an unstable nitroso intermediate is avoided, which has so far severely limited reductive transformations of aliphatic nitro compounds. The reaction is concluded by an electrophilic amination of zinc organyls.
- Rauser, Marian,Ascheberg, Christoph,Niggemann, Meike
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supporting information
p. 3970 - 3974
(2018/02/26)
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- Exploiting Synergistic Effects in Organozinc Chemistry for Direct Stereoselective C-Glycosylation Reactions at Room Temperature
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Pairing a range of bis(aryl) zinc reagents ZnAr2 with the stronger Lewis acidic [(ZnArF2)] (ArF=C6F5), enables highly stereoselective cross-coupling between glycosyl bromides and ZnAr2 without the use of a transition metal. Reactions occur at room temperature with excellent levels of stereoselectivity, where ZnArF2 acts as a non-coupling partner although its presence is crucial for the execution of the C(sp2)–C(sp3) bond formation process. Mechanistic studies have uncovered a unique synergistic partnership between the two zinc reagents, which circumvents the need for transition-metal catalysis or forcing reaction conditions. Key to the success of the coupling is the avoidance of solvents that act as Lewis bases versus diarylzinc compounds (e.g. THF).
- Hernán-Gómez, Alberto,Orr, Samantha A.,Uzelac, Marina,Kennedy, Alan R.,Barroso, Santiago,Jusseau, Xavier,Lemaire, Sébastien,Farina, Vittorio,Hevia, Eva
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supporting information
p. 10630 - 10634
(2018/08/01)
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- Iron-Catalyzed Difluoromethylation of Arylzincs with Difluoromethyl 2-Pyridyl Sulfone
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We report the first iron-catalyzed difluoromethylation of arylzincs with difluoromethyl 2-pyridyl sulfone via selective C-S bond cleavage. This method employs the readily available, bench-stable fluoroalkyl sulfone reagent and inexpensive iron catalyst, allowing facile access to structurally diverse difluoromethylated arenes at low temperatures. The experiment employing a radical clock indicates the involvement of radical species in this iron-catalyzed difluoromethylation process.
- Miao, Wenjun,Zhao, Yanchuan,Ni, Chuanfa,Gao, Bing,Zhang, Wei,Hu, Jinbo
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supporting information
p. 880 - 883
(2018/02/07)
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- Selective Substitution of POCl 3 with Organometallic Reagents: Synthesis of Phosphinates and Phosphonates
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The selectivity of the substitution reaction of phosphoryl chloride with organometallic reagents was investigated using NMR spectroscopy. This led to the discovery that the selectivity of the substitution reaction can be tuned by choosing a proper organometallic reagent. A phosphinate could be obtained by using a Grignard reagent whereas an organozinc reagent provided a phosphonate. Based on these results, one-pot synthetic methods for the preparation of phosphinates and phosphonates using commercially available starting materials were developed. Both methods allow the synthesis of a broad range of either phosphinate or phosphonate derivatives in a straightforward and general procedure. Moreover, using these one-pot procedures, mixed systems substituted with different alkyl/aryl groups can be prepared.
- Verbelen, Bram,Dehaen, Wim,Binnemans, Koen
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p. 2019 - 2026
(2018/04/14)
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- Decarboxylative Negishi Coupling of Redox-Active Aliphatic Esters by Cobalt Catalysis
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A cobalt-catalyzed decarboxylative Negishi coupling reaction of redox-active aliphatic esters with organozinc reagents was developed. The method enabled efficient alkyl–aryl, alkyl–alkenyl, and alkyl–alkynyl coupling reactions under mild reaction conditions with no external ligand or additive needed. The success of an in situ activation protocol and the facile synthesis of the drug molecule (±)-preclamol highlight the synthetic potential of this method. Mechanistic studies indicated that a radical mechanism is involved.
- Liu, Xu-Ge,Zhou, Chu-Jun,Lin,Han, Xiang-Lei,Zhang, Shang-Shi,Li, Qingjiang,Wang, Honggen
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supporting information
p. 13096 - 13100
(2018/09/21)
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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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- A Zinc Catalyzed C(sp3)?C(sp2) Suzuki–Miyaura Cross-Coupling Reaction Mediated by Aryl-Zincates
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The Suzuki–Miyaura (SM) reaction is one of the most important methods for C?C bond formation in chemical synthesis. In this communication, we show for the first time that the low toxicity, inexpensive element zinc is able to catalyze SM reactions. The cross-coupling of benzyl bromides with aryl borates is catalyzed by ZnBr2, in a process that is free from added ligand, and is compatible with a range of functionalized benzyl bromides and arylboronic acid pinacol esters. Initial mechanistic investigations indicate that the selective in situ formation of triaryl zincates is crucial to promote selective cross-coupling reactivity, which is facilitated by employing an arylborate of optimal nucleophilicity.
- Procter, Richard J.,Dunsford, Jay J.,Rushworth, Philip J.,Hulcoop, David G.,Layfield, Richard A.,Ingleson, Michael J.
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p. 15889 - 15893
(2017/10/24)
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- Copper-Catalyzed Negishi Coupling of Diarylzinc Reagents with Aryl Iodides
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We report an efficient copper(I) iodide catalyzed cross-coupling of diarylzinc reagents with aryl iodides. The reaction proceeds under ligand-free conditions at low catalyst loading (5 mol%) and tolerates a variety of functional groups.
- Thapa, Surendra,Vangala, Adarsh S.,Giri, Ramesh
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p. 504 - 511
(2016/02/14)
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- Redox-Active Esters in Fe-Catalyzed C-C Coupling
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Cross-couplings of alkyl halides and organometallic species based on single electron transfer using Ni and Fe catalyst systems have been studied extensively, and separately, for decades. Here we demonstrate the first couplings of redox-active esters (both isolated and derived in situ from carboxylic acids) with organozinc and organomagnesium species using an Fe-based catalyst system originally developed for alkyl halides. This work is placed in context by showing a direct comparison with a Ni catalyst for >40 examples spanning a range of primary, secondary, and tertiary substrates. This new C-C coupling is scalable and sustainable, and it exhibits a number of clear advantages in several cases over its Ni-based counterpart.
- Toriyama, Fumihiko,Cornella, Josep,Wimmer, Laurin,Chen, Tie-Gen,Dixon, Darryl D.,Creech, Gardner,Baran, Phil S.
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supporting information
p. 11132 - 11135
(2016/10/12)
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- Reactivity of mixed organozinc and mixed organocopper reagents: 12. Three component reaction of mixed (n-alkyl)(diaryl)zincates, chloroformates and phosphines for the synthesis of esters
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The reaction of mixed n-butyldiphenylzincate, n-BuPh2ZnMgBr with ethyl chloroformate, ClCOOEt in the presence n-Bu3P in THF takes place with quantitative yield and phenyl group transfer to give PhCOOEt. Ethoxycarbonylation of n-BuPh2ZnMgBr is preferable to the reaction of PhMgBr forming ester and triphenylcarbinol and also to the reaction of triphenylzincate, Ph3ZnMgBr for atom economy. Group selectivity in the phosphine catalyzed C-COOR coupling of n-BuPh2ZnMgBr and n-Bu2PhZnMgBr can be controlled by changing reaction parameters. n-Bu3P catalyzed reaction of n-BuPh2ZnMgBr with ClCOOEt takes place with phenyl selectivity whereas reaction of n-Bu2PhZnMgBr with ClCOOPh results in n-butyl transfer. Catalysis by Ph3P increases n-butyl group:phenyl group transfer ratio in the ethoxycarbonylation of both zincates. Selective transfer of aryl groups in n-Bu3P catalyzed reaction of n-butyl(aryl)2ZnMgBr reagents with ClCOOEt in THF provides a new procedure for the organometallic synthesis of arenecarboxylic acid ethyl esters at room temperature.
- ?zkan, Duygu,Erdik, Ender
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- Iron catalysed Negishi cross-coupling using simple ethyl-monophosphines
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Monophosphines prepared by iron catalysed hydrophosphination have been used as pro-ligands in iron catalysed Negishi cross-coupling of alkyl bromides and diphenyl zinc reagents. The cross-coupling has been investigated with monophosphines with varying electronic properties and we find the simplest, unsubstituted phosphine to offer the optimum reaction conditions (both in terms of yield of diarylmethane product and cost-effectiveness of the phosphine). In situ catalyst generation from monophosphine and FeCl2 was used in catalysis; however, preparation of a discrete homonuclear iron complex was also achieved and this four-coordinate iron-phosphine complex was isolated and used in catalysis.
- Brown, Caleb A.,Nile, Terence A.,Mahon, Mary F.,Webster, Ruth L.
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p. 12189 - 12195
(2016/01/15)
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- Efficient access to 3-substituted-γ-hydroxylactams: The uncatalyzed addition of diorganozinc reagents to cyclic imides with heterocyclic substitution
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A range of 3-substituted-γ-hydroxylactams have been prepared via the uncatalyzed addition of organozinc nucleophiles to cyclic imides. This reactivity is primarily limited to imides containing heterocyclic N-substitution, but proceeds efficiently with a variety of diorganozinc reagents, including those prepared and utilized without purification, as well as organozinc halides. It is hypothesized that the presence of a Lewis basic directing group is required for optimum reactivity.
- Deglopper, Kimberly S.,Dennis, Joseph M.,Johnson, Jeffrey B.
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supporting information
p. 1843 - 1845
(2014/03/21)
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- Nickel-catalyzed direct addition of diorganozinc reagents to phthalimides: Selective formation of gamma-hydroxylactams
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The nickel-catalyzed addition of diorganozinc reagents to phthalimides proceeds with excellent selectivity to provide 3-substituted-3- hydroxyisoindolin-1-one products. These 3-hydroxy-γ-lactams are produced cleanly in high yield with numerous examples of imide substitution and a broad range of diorganozinc reagents that are prepared and utilized without purification. Georg Thieme Verlag Stuttgart · New York.
- Dennis, Joseph M.,Calyore, Catherine M.,Sjoholm, Jessica S.,Lutz, J. Patrick,Gair, Joseph J.,Johnson, Jeffrey B.
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supporting information
p. 2567 - 2570
(2013/12/04)
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- Iron-catalyzed allylic arylation of olefins via C(sp3)-H activation under mild conditions
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An aryl Grignard reagent in the presence of mesityl iodide converts an allylic C-H bond of a cycloalkene or an allylbenzene derivative into a C-C bond in the presence of a catalytic amount of Fe(acac)3 and a diphosphine ligand at 0 C. The stereo- and regioselectivity of the reaction, together with deuterium labeling experiments, suggest that C-H bond activation is the slow step in the catalytic cycle preceding the formation of an allyliron intermediate.
- Sekine, Masaki,Ilies, Laurean,Nakamura, Eiichi
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supporting information
p. 714 - 717
(2013/04/10)
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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 22
(2009/01/20)
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- An unexpected elimination product leads to 4-alkyl-4-deoxy-4-epi-sialic acid derivatives
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A useful, unexpected β,γ-unsaturated-α-keto ester (ethyl (E)-5-acetamido-3,4,5-trideoxy-6,7:8,9-di-O-isopropylidene-D-manno-non-3-en-2- ulosonate 5) was isolated in 91% yield following ozonolysis and chromatographic purification of its enoate ester precursor ethyl 5-acetamido-2,3,4,5-tetradeoxy- 6,7:8,9-di-O-isopropylidene-2-methylene-4-nitro-D-glycero-D-galacto-nononate (6). When the 4R enoate ester (ethyl 5-acetamido-2,3,4,5-tetradeoxy-6,7:8,9-di- O-isopropylidene-2-methylene-4-nitro-D-glycero-D-talo-nononate, 7) was subjected to the same conditions, enone 5 was a minor product (18%) while the major product did not eliminate HNO2 but instead cyclized to form a five-membered ring containing a hemiaminal linkage between C-2 and the amide nitrogen on C-5 (9, 70%). Conjugate addition, to enone 5 opens up the potential to generate 4-substituted sialic acid derivatives, a general route to such compounds that has not been previously reported. In a preliminary investigation of such a route, diethylzinc and dimethylzinc were added to enone 5 resulting in generation of 4-alkyl-substituted cyclic hemiaminal structures 11 and 13, which could be deprotected to form 2,7-anhydrosialic acid analogues 14 and 15. These products could then be converted to peracetylated glycals 16 and 17, the 4-methyl-substituted compound 17 being finally deprotected to give a 4-methyl-substituted analogue of the glycal of sialic acid (5-acetamido-2,6- anhydro-3,4,5-trideoxy-4-methyl-D-glycero-D-talo-non-2-enonic acid 18).
- Hemeon, Ivan,Bennet, Andrew J.
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p. 238 - 247
(2008/09/20)
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- From aryl bromides to enantioenriched benzylic alcohols in a single flask: Catalytic asymmetric arylation of aldehydes
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(Chemical Equation Presented) Stop that achiral catalyst! Chiral Lewis acid catalyzed aryl additions to aldehydes that originate from aryl halides generate products with very low ee values (see scheme, left), because the achiral metal halide by-products are much more efficient catalysts than those derived from chiral amino alcohols. A LiCl-selective inhibitor is introduced that enables a highly enantioselective one-pot arylation of aldehydes that begins with aryl bromides (right).
- Kim, Jeung Gon,Walsh, Patrick J.
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p. 4175 - 4178
(2007/10/03)
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- Copper-Catalyzed Electrophilic Amination of Diorganozinc Reagents
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The copper-catalyzed electrophilic amination of diorganozinc reagents employing O-acyl N,N-dialkyl hydroxylamine derivatives as aminating agents is described. This reaction offers a general method for the preparation of tertiary amines in high yields and is noteworthy for its convenience both in terms of reaction conditions employed (room temperature, ≤1 h) and ease of product isolation (acid/base extractive workup). Copyright
- Berman, Ashley M.,Johnson, Jeffrey S.
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p. 5680 - 5681
(2007/10/03)
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- Rhenium(VII) oxo-alkyl complexes: Reductive and α-elimination reactions
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Alkylation of ReO2(CH2CMe3)2X(py) (X = Cl, Br) with ZnR2 at low temperature gives ReO2(CH2CMe3)2R (R = Me, CH2CMe3, CH2SiMe3, Ph) in high yield. The crystal structure Of ReO2(CH2CMe3)2Ph shows that it has a distorted trigonal bipyramidal structure with the oxo and Ph ligands in the equatorial plane. Photolysis Of ReO2(CH2CMe3)S in pyridine gives neopentane and ReO2(CHCMe3)(CH2CMe3), and ReO2(CHCMe3)(CH2CMe3) reacts with quinuclidine to give ReO2(CHCMe3)(CH2CMe3)(quinuclidine). In the solid state, ReO2-(CHCMe3)(CH2CMe3) has a distorted tetrahedral structure, and ReO2(CHCMe3)(CH2CMe3)-(quinuclidine) is trigonal bipyramidal with the neopentylidene and oxo ligands defining the equatorial plane. The Re-N bond distance is long, suggesting the rhenium-quinuclidine interaction is weak. Thermolysis of ReO2(CH2CMe3)2Ph in pyridine gives ReO2(CH2CMe3)-(py)3 and neopentylbenzene. An X-ray structure of ReO2(CH2CMe3)(py)3 shows that it is octahedral with trans oxo groups. In solution ReO2(CH2CMe3)(Py)3 is unstable in the absence of excess pyridine, and in the solid state it readily loses pyridine. ReO2(CH2CMe3)(Py)3 reacts with MeC≡CMe and PhC≡CH to form ReO2(CH2CMe3)(alkyne) compounds.
- Cai, Shiang,Hoffman, David M.,Wierda, Derk A.
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p. 1023 - 1032
(2008/10/08)
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- The Role of the Substituent Pattern in Determining Selectivity in the Preparation of Tricarbonyl(η5-cyclohexadienyl)iron(1+) Salts by Acid-Catalyzed Demethoxylation
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The factors that determine the selectivity of the acid-catalyzed dealkoxylation of unsymmetrically substituted tricarbonyl(η4-alkoxycyclohexa-1,3-diene)iron(0) complexes have been investigated.Regioselective demethoxylation of complexes with a variety of substitution patterns has indicated that the selectivity arises from differences in the stabilization of the reaction intermediates and transition states by the diene substituents on the ?-bound ligand.The observed regioisomers correspond to the product of the most stabilized intermediate pathway, rather than the product of minimum rearrangement.The reactions have been shown to proceed under kinetic control.
- Stephenson, G. Richard,Owen, David A.,Finch, Harry,Swanson, Stephen
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p. 121 - 134
(2007/10/02)
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- Interaction of Ph2Zn with 1,3-xylyl crown ethers. Crystal structures of three 1:1 Complexes
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The behavior of diphenylzinc toward four 1,3-xylyl crown ethers was investigated. Only "simple" complexation occurred, whereas diphenylmagnesium had previously been shown to lead to halogen-metal exchange, metalation, or rotaxane formation. Three of the 1:1 complexes were obtained as crystalline solids and characterized by X-ray crystal structure determination; 1,3-xylyl 15-crown-4 (1) gave an oily adduct. Crystals of diphenylzinc-2-bromo-1,3-xylyl 15-crown-4 (8) are monoclinic, space group P21/n, with unit cell dimensions a = 9.800 (1) ?, b = 12.887 (1) ?, c = 19.671 (2) ?, β = 95.66 (1)°, and Z = 4. Crystals of diphenylzinc-2-bromo-1,3-xylyl 18-crown-5 (9) are monoclinic, space group P21/n, with unit cell dimensions a = 9.368 (1) ?, b = 10.975 (1) ?, c = 27.051 (2) ?, β = 97.48 (2)°, and Z = 4. Crystals of diphenylzinc-1,3-xylyl 18-crown-5 (10) are monoclinic, space group P21/n, with unit cell dimensions a = 14.775 (3) ?, b = 18.252 (3) ?, c = 20.082 (1) ?, β = 103.29 (1)°, and Z = 8; two independent but chemically equivalent residues are present in the unit cell. The three molecular structures are closely related: the zinc atom is tetrahedrally surrounded by two phenyl groups and by two of the oxygens of the crown ether. These organozinc complexes may serve as (stable!) models for intermediate stages in the above-mentioned reactions of organomagnesium compounds with crown ethers.
- Markies, Peter R.,Schat, Gerrit,Akkerman, Otto S.,Bickelhaupt, Friedrich,Smeets, Wilberth J. J.,Spek, Anthony L.
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p. 3538 - 3544
(2008/10/08)
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- GEMISCHTE ORGANOZINKVERBINDUNGEN DURCH AUSTAUSCHREAKTIONEN VON DIORGANOZINKVERBINDUNGEN
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The exchange of organyl groups between various diorganozinc compounds, R12Zn (R1=CHMe2 (1), CH2(CH2)2Me (2), CH2C(Me)=CH2 (3), CH2CH=CHMe (4)) and R22Zn (R2=Et (5), CH(Me)Et (6), CH2(CH2)3Me (7), CMe3 (8), Menth
- Nehl, Hans,Scheidt, Walter R.
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- Nature of alkyl-hydrogen exchange reactions involving aluminum and zinc. 5. Reactions of diphenylzinc with lithium aluminum hydride in diethyl ether and tetrahydrofuran. Preparation of PhZn2H3
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The reactions of diphenylzinc with lithium aluminum hydride in diethyl ether and THF have been studied in detail. Although ZnH2 as an insoluble solid and LiAlPhnH4-n in solution are formed when the Ph2Zn:LiAlH4 ratio is 2:1, 3:2, 1:1, and 1:2 in ether, no ZnH2 is formed when Ph2Zn is allowed to react with LiAlH4 in THF in ratios varying from 4:1 to 1:2. Instead, PhZn2H3 is formed which is insoluble in THF. This compound is reported for the first time, and its existence is supported by IR, X-ray powder diffraction, and DTA-TGA studies. When ZnH2, prepared by the reaction of Ph2Zn with LiAlH4 in ether, was allowed to react with Ph2Zn and cyclopentadiene independently in THF, the insoluble products PhZn2H3 and CpZn2H3 formed. Reaction of cyclohexanol with ZnH2 is also discussed.
- Ashby,Goel
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p. 1096 - 1101
(2008/10/08)
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