- Electrosynthesis of benzylboronic acids and esters
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A novel preparation of benzylboronic acids and esters is described by using an electrochemical reductive coupling reaction between benzylic halides and borating agents (trialkylborates or pinacolborane). The reaction is carried out at room temperature in DMF or THF with the use of a sacrificial magnesium anode in a single-compartment cell.
- Pintaric,Laza,Olivero,Du?ach
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Read Online
- Catalytic activity of phosphine - Copper complexes for hydroboration of styrene with pinacolborane: Experiment and theory
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We have carried out density functional theory calculations as well as experiments to rationalize the catalytic activity of various phosphine-copper complexes for the hydroboration of styrene with pinacolborane. The experimentally obtained catalytic efficiency was explained on the basis of activation barriers for consecutive reaction mechanism steps as well as by molecular orbitals and charges in the transition state. Bidentate ligands were found to be more efficient than monodentate ligands for catalytic activity. Bidentate ligands make the reactant complexes less stable than monodentate ligands due to steric hindrance. This information could be usefully utilized for new catalysts design. The calculated kinetic data were consistent with the experimental conversion efficiency in a process that was hypothesizd to undergo the addition of Cu - H to styrene as the rate-limiting step. From the electronic distribution of the HOMO and the charge of the copper atom in the transition state, it was found that styrenes substituted with electron withdrawing groups would give higher conversions, and the catalytic efficiency could be increased with properly designed electron-donating ligands for the copper catalyst complex.
- Won, Jiyeon,Noh, Dongwan,Yun, Jaesook,Lee, Jin Yong
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Read Online
- Selective Benzylic CH-Borylations by Tandem Cobalt Catalysis
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Metal-catalyzed C?H activations are environmentally and economically attractive synthetic strategies for the construction of functional molecules as they obviate the need for pre-functionalized substrates and minimize waste generation. Great challenges reside in the control of selectivities, the utilization of unbiased hydrocarbons, and the operation of atom-economical dehydrocoupling mechanisms. An especially mild borylation of benzylic CH bonds was developed with the ligand-free pre-catalyst Co[N(SiMe3)2]2 and the bench-stable and inexpensive borylation reagent B2pin2 that produces H2 as the only by-product. A full set of kinetic, spectroscopic, and preparative mechanistic studies are indicative of a tandem catalysis mechanism of CH-borylation and dehydrocoupling via molecular CoI catalysts.
- Bauer, Matthias,Ghosh, Pradip,Jacobi von Wangelin, Axel,Schoch, Roland
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supporting information
(2021/11/27)
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- Rhodium-Catalyzed Regiodivergent Synthesis of Alkylboronates via Deoxygenative Hydroboration of Aryl Ketones: Mechanism and Origin of Selectivities
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Here, we report an efficient rhodium-catalyzed deoxygenative borylation of ketones to synthesize alkylboronates, in which the regioselectivity can be switched by the choice of the ligand. The linear alkylboronates were obtained exclusively in the presence of P(nBu)3, and PPh2Me favored the formation of branched alkylboronates. The protocol also allows access to 1,1,2-triboronates from the readily available ketones. Mechanistic studies suggest that this Rh-catalyzed deoxygenative borylation of ketones goes through an alkene intermediate, which undergoes regiodivergent hydroboration to afford linear and branched alkylboronates. The different steric effects of PPh2Me and P(nBu)3 were found to be responsible for product selectivity by density functional theory calculations. The alkene intermediate can alternatively undergo sequential dehydrogenative borylation and hydroboration to deliver the triboronates.
- Zhang, Bing,Xu, Xin,Tao, Lei,Lin, Zhenyang,Zhao, Wanxiang
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p. 9495 - 9505
(2021/08/04)
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- Selective electrocatalytic hydroboration of aryl alkenes
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Organoboron compounds are powerful precursors of value-added organic compounds in synthetic chemistry, and transition metal-catalysed borylation has always been dominant. To avoid toxic reagents and costs associated with metal catalysts, simpler, more eco
- Zhang, Yahui,Zhao, Xiangyu,Bi, Ce,Lu, Wenqi,Song, Mengyuan,Wang, Dongdong,Qing, Guangyan
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p. 1691 - 1699
(2021/03/09)
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- Practical Synthesis of Allyl, Allenyl, and Benzyl Boronates through SN1′-Type Borylation under Heterogeneous Gold Catalysis
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Efficient borylation of sp3 C-O bonds by supported Au catalysts is described. Au nanoparticles supported on TiO2 showed high activity under mild conditions employing low catalyst loading conditions without the aid of any additives, such as phosphine and bases. A variety of allyl, propargyl, and benzyl substrates participated in the heterogeneously catalyzed reactions to furnish the corresponding allyl, allenyl, and benzyl boronates in high yields. Besides, Au/TiO2 was also effective for the direct borylation of allylic and benzylic alcohols. A mechanistic investigation based on a Hammett study and control experiments revealed that sp3 C-O bond borylation over supported Au catalysts proceeded through SN1′-type mechanism involving the formation of a carbocationic intermediate. The high activity, reusability, and environmental compatibility of the supported Au catalysts as well as the scalability of the reaction system enable the practical synthesis of valuable organoboron compounds.
- Miura, Hiroki,Hachiya, Yuka,Nishio, Hidenori,Fukuta, Yohei,Toyomasu, Tomoya,Kobayashi, Kosa,Masaki, Yosuke,Shishido, Tetsuya
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p. 758 - 766
(2021/02/03)
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- Manganese-Catalyzed Hydroboration of Terminal Olefins and Metal-Dependent Selectivity in Internal Olefin Isomerization-Hydroboration
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In the past decade, the use of earth-abundant metals in homogeneous catalysis has flourished. In particular, metals such as cobalt and iron have been used extensively in reductive transformations including hydrogenation, hydroboration, and hydrosilylation
- Garhwal, Subhash,Kroeger, Asja A.,Thenarukandiyil, Ranjeesh,Fridman, Natalia,Karton, Amir,De Ruiter, Graham
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supporting information
p. 494 - 504
(2021/01/11)
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- (o-Phenylenediamino)borylstannanes: Efficient Reagents for Borylation of Various Alkyl Radical Precursors
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(o-Phenylenediamino)borylstannanes were newly synthesized to achieve radical boryl substitutions of a variety of alkyl radical precursors. Dehalogenative, deaminative, decharcogenative, and decarboxylative borylations proceeded in the presence of a radica
- Suzuki, Kensuke,Nishimoto, Yoshihiro,Yasuda, Makoto
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supporting information
p. 3968 - 3973
(2020/12/30)
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- Photochemical Radical C–H Halogenation of Benzyl N-Methyliminodiacetyl (MIDA) Boronates: Synthesis of α-Functionalized Alkyl Boronates
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α-Haloboronates are useful organic synthons that can be converted to a diverse array of α-substituted alkyl borons. Methods to α-haloboronates are limiting and often suffer from harsh reaction conditions. Reported herein is a photochemical radical C-H halogenation of benzyl N-methyliminodiacetyl (MIDA) boronates. Fluorination, chlorination, and bromination reactions were effective by using this protocol. Upon reaction with different nucleophiles, the C?Br bond in the brominated product could be readily transformed to a series of C?C, C?O, C?N, C?S, C?P, and C?I bonds, some of which are difficult to forge with α-halo sp2-B boronate esters. An activation effect of B(MIDA) moiety was found.
- Yang, Ling,Tan, Dong-Hang,Fan, Wen-Xin,Liu, Xu-Ge,Wu, Jia-Qiang,Huang, Zhi-Shu,Li, Qingjiang,Wang, Honggen
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supporting information
p. 3454 - 3458
(2020/12/17)
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- Chemoselective Cross-Coupling of gem-Borazirconocene Alkanes with Aryl Halides
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The direct and chemoselective conversion of the carbon-metal bond of gem-dimetallic reagents enables rapid and sequential formation of multiple carbon-carbon and carbon-heteroatom bonds, thus representing a powerful method for efficiently increasing structural complexity. Herein, we report a visible-light-induced, nickel-catalyzed, chemoselective cross-coupling reaction between gem-borazirconocene alkanes and diverse aryl halides, affording a wide range of alkyl Bpin derivatives in high yields with excellent regioselectivity. This practical method features attractively simple reaction conditions and a broad substrate scope. Additionally, we systematically investigated a Bpin-directed chain walking process underlying the regioselectivity of alkylzirconocenes, thus uncovering the mechanism of the remote functionalization of internal olefins achieved with our method. Finally, DFT calculations indicate that the high regioselectivity of this reaction originates from the directing effect of the Bpin group.
- Bai, Songlin,Gao, Yadong,Jiang, Chao,Qi, Xiangbing,Yang, Chao
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supporting information
p. 11506 - 11513
(2020/07/14)
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- Zirconium-Catalyzed Atom-Economical Synthesis of 1,1-Diborylalkanes from Terminal and Internal Alkenes
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A general and atom-economical synthesis of 1,1-diborylalkanes from alkenes and a borane without the need for an additional H2 acceptor is reported for the first time. The key to our success is the use of an earth-abundant zirconium-based catalyst, which allows a balance of self-contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H2 acceptor, which was required in other reported systems. Furthermore, substrates such as simple long-chain aliphatic alkenes that did not react before also underwent 1,1-diboration in our system. Significantly, the unprecedented 1,1-diboration of internal alkenes enabled the preparation of 1,1-diborylalkanes.
- Cui, Xin,Jiao, Haijun,Li, Sida,Wang, Xianjin,Wang, Yue,Wu, Lipeng,Xia, Chungu
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supporting information
p. 13608 - 13612
(2020/06/02)
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- Selective synthesis of secondary alkylboronates: Markovnikov-selective hydroboration of vinylarenes with bis(pinacolato)diboron catalyzed by a nickel pincer complex
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A nickel pincer complex bearing a β-aminoketonato-based O,N,P-tridentate ligand (1a) has been employed for the highly Markovnikov-selective hydroboration of vinylarenes using bis(pinacolato)diboron. This reaction proceeds smoothly under mild reaction conditions and affords the corresponding Markovnikov products in good to high yield.
- Hashimoto, Toru,Shiota, Keisuke,Yamaguchi, Yoshitaka
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supporting information
p. 4033 - 4037
(2020/05/19)
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- 1-D manganese(ii)-terpyridine coordination polymers as precatalysts for hydrofunctionalisation of carbonyl compounds
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Reductive catalysis with earth-abundant metals is currently of increasing importance and shows potential in replacing precious metal catalysis. In this work, we revealed catalytic hydroboration and hydrosilylation of ketones and aldehydes achieved by a structurally defined manganese(ii) coordination polymer (CP) as a precatalyst under mild conditions. The manganese-catalysed methodology can be applied to a range of functionalized aldehydes and ketones with turnover numbers (TON) of up to 990. Preliminary results on the regioselective catalytic hydrofunctionalization of styrenes by the Mn-CP catalyst are also presented.
- Johnson, Jahvon,Li, Sihan,Mo, Zixuan,Neary, Michelle C.,Zeng, Haisu,Zhang, Guoqi,Zheng, Shengping
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supporting information
p. 2610 - 2615
(2020/03/05)
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- Erratum: Markovnikov-selective hydroboration of olefins catalyzed by a copper N-heterocyclic carbene complex (Organometallics (2019) 38:17 (3322-3326) DOI: 10.1021/acs.organomet.9b00394)
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It has come to our attention that some of the products listed in Table 2 of the article and in eq 1 have the incorrect stereochemistry. The reactions of alkynes with HBpin give the linear E-olefin products, not the branched products as were shown. 1H NMR spectra clearly show two doublets with a large J (18 Hz) for the trans-hydrogens of the alkene product. A DEPT-135 spectrum also confirms that CH and not CH2 is present. Corrected eq 1, Table 2, TOC graphic are shown. Note that the alkene addition products are correctly assigned as branched, displaying a doublet and a quartet for the methyl and methane groups, respectively. NMR spectra for all products are included in the revised Supporting Information. We thank Prof. Jaesook Yun for pointing out this error, as her group has worked on related copper borylations for many years.
- DiBenedetto, Tarah A.,Parsons, Astrid M.,Jones, William D.
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supporting information
p. 3768 - 3769
(2020/11/17)
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- Hydroboration of Alkenes Catalysed by a Nickel N-Heterocyclic Carbene Complex: Reaction and Mechanistic Aspects
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The pentamethylcyclopentadienyl N-heterocyclic carbene nickel complex [Ni(η5-C5Me5)Cl(IMes)] (IMes=1,3-dimesitylimidazol-2-ylidene) efficiently catalyses the anti-Markovnikov hydroboration of alkenes with catecholborane in
- Chetcuti, Michael J.,Cornaton, Yann,Djukic, Jean-Pierre,Ritleng, Vincent,Ulm, Franck
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- Single-Site Cobalt-Catalyst Ligated with Pyridylimine-Functionalized Metal-Organic Frameworks for Arene and Benzylic Borylation
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We report a highly active single-site heterogeneous cobalt-catalyst based on a porous and robust pyridylimine-functionalized metal-organic frameworks (pyrim-MOF) for chemoselective borylation of arene and benzylic C-H bonds. The pyrim-MOF having UiO-68 topology, constructed from zirconium-cluster secondary building units and pyridylimine-functionalized dicarboxylate bridging linkers, was metalated with CoCl2 followed by treatment of NaEt3BH to give the cobalt-functionalized MOF-catalyst (pyrim-MOF-Co). Pyrim-MOF-Co has a broad substrate scope, allowing the C-H borylation of halogen-, alkoxy-, alkyl-substituted arenes as well as heterocyclic ring systems using B2pin2 or HBpin (pin = pinacolate) as the borylating agent to afford the corresponding arene- or alkyl-boronate esters in good yields. Pyrim-MOF-Co gave a turnover number (TON) of up to 2500 and could be recycled and reused at least 9 times. Pyrim-MOF-Co was also significantly more robust and active than its homogeneous control, highlighting the beneficial effect of active-site isolation within the MOF framework that prevents intermolecular decomposition. The experimental and computational studies suggested (pyrim?-)CoI(THF) as the active catalytic species within the MOF, which undergoes a mechanistic pathway of oxidative addition, turnover limiting σ-bond metathesis, followed by reductive elimination to afford the boronate ester.
- Akhtar, Naved,Antil, Neha,Balendra,Begum, Wahida,Kumar, Ajay,Manna, Kuntal,Newar, Rajashree,Shukla, Sakshi
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supporting information
p. 10473 - 10481
(2020/08/05)
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- Pyridine-catalyzed desulfonative borylation of benzyl sulfones
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Herein, we report the transition-metal free, pyridine-catalyzed desulfonative borylation of benzyl sulfones with bis(pinacolato)diboron (B2pin2). A variety of benzhydryl- and benzyl boronic esters could be synthesized from readily prepared sulfone derivatives. The borylation of cyclic sulfones accompanied by ring opening also proceeded to afford the corresponding sulfonate, which could be converted into functionalized sulfones and sulfonamides.
- Maekawa, Yuuki,Ariki, Zachary T.,Nambo, Masakazu,Crudden, Cathleen M.
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p. 7300 - 7303
(2019/08/15)
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- Hydroboration of terminal olefins with pinacolborane catalyzed by new 2-iminopyrrolyl iron(ii) complexes
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Four paramagnetic 14-electron tetracoordinated Fe(ii) complexes of 5-substituted-2-iminopyrrolyl ligands of the type [Fe{κ2N,N′-5-R-NC4H2-2-C(H)N(2,6-iPr2-C6H3)}(Py)Cl], with R = 2,6-Me2-C6H3 (1a), 2,4,6-iPr3-C6H2 (1b), 2,4,6-Ph3-C6H3 (1c) and CPh3 (1d), were synthesized in moderate yields by reacting the respective 5-substituted-2-iminopyrrolyl potassium salts KLa-d with FeCl2(Py)4 in toluene. Complexes 1a-d were characterized by 1H NMR, FTIR spectroscopies, elemental analysis and by the Evans method, the corresponding effective magnetic moments showing a high-spin electronic nature. X-ray diffraction studies on complexes 1a and 1c showed distorted tetrahedral coordination geometries. Complexes 1a-c, activated with K(HBEt3), were efficient catalyst systems for the hydroboration of several terminal alkenes with pinacolborane in good to high yields (50-90%). This system mainly yielded the respective anti-Markovnikov addition products, except when styrenes were used. A screening of the hydroboration of styrene catalyzed by complexes 1a-c activated with K(HBEt3) showed that the selectivity in the Markovnikov product increased with increasing steric bulkiness of the R group, exhibiting selectivities up to 91%. Additionally, the stoichiometric reaction of complex 1b with K(HBEt3) over 30 minutes yielded the mixture of hydride species 2 and 22 (mixture I). On the other hand, when reacting the same components over 16 h, the Fe(i) complex 3 was also identified in the mixture, in addition to 2 + 22 (mixture II). These mixtures were characterized in solution by the Evans method and in the solid state by elemental analysis, 57Fe M?ssbauer and FTIR spectroscopies, compounds 22 and 3 being also analyzed by X-ray diffraction. These results suggest that the corresponding catalytic cycle follows the borane oxidative addition route to a Fe(i) species.
- Cruz, Tiago F. C.,Pereira, Laura C. J.,Waerenborgh, Jo?o C.,Veiros, Luís F.,Gomes, Pedro T.
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p. 3347 - 3360
(2019/07/10)
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- A phenalenyl-based nickel catalyst for the hydroboration of olefins under ambient conditions
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In this report, nickel-catalyzed hydroboration of vinylarenes and aliphatic alkenes is investigated. The non-innocent phenalenyl ligand moiety in the nickel complex Ni(PLY)2(THF)2 (1) was utilized as an electron reservoir for the sel
- Vijaykumar, Gonela,Bhunia, Mrinal,Mandal, Swadhin K.
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p. 5779 - 5784
(2019/05/10)
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- Markovnikov-Selective Hydroboration of Olefins Catalyzed by a Copper N-Heterocyclic Carbene Complex
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The efficient and atom-economical hydroboration of alkenes and alkynes using an N-heterocyclic carbene (NHC) copper hydroxide catalyst has been developed. An equimolar combination of substrate and HBpin allows for the selective Markovnikov hydroboration of alkenes and alkynes. A variety of functional groups were tolerated in good to excellent yield. This system features a facile reaction setup, atom economy, high selectivity, and an easily synthesized copper-NHC catalyst.
- Dibenedetto, Tarah A.,Parsons, Astrid M.,Jones, William D.
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supporting information
p. 3322 - 3326
(2019/09/30)
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- Aluminum-Catalyzed Selective Hydroboration of Alkenes and Alkynylsilanes
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An efficient aluminum-catalyzed selective hydroboration of alkenes and alkynylsilanes is reported. A wide variety of alkenes and alkynylsilanes bearing various functional groups and heterocyclic substituents were converted to boronic ester products in goo
- Li, Feng,Bai, Xu,Cai, Yuan,Li, Han,Zhang, Shuo-Qing,Liu, Feng-Hua,Hong, Xin,Xu, Youjun,Shi, Shi-Liang
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supporting information
p. 1703 - 1708
(2019/09/04)
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- Redox switchable catalysis utilizing a fluorescent dye
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This report describes the implementation of a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye into the ligand framework of a Rh-based catalyst. The redox-active nature of the BODIPY dye is utilized to generate a catalyst that is capable of exhibit
- Heiden, Zachariah M.,Simons, Casey R.,Thompson, Brena L.
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supporting information
p. 11430 - 11433
(2019/09/30)
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- STABILIZATION OF ACTIVE METAL CATALYSTS AT METAL-ORGANIC FRAMEWORK NODES FOR HIGHLY EFFICIENT ORGANIC TRANSFORMATIONS
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Metal-organic framework (MOFs) compositions based on post?synthetic metalation of secondary building unit (SBU) terminal or bridging OH or OH2 groups with metal precursors or other post-synthetic manipulations are described. The MOFs provide a versatile family of recyclable and reusable single-site solid catalysts for catalyzing a variety of asymmetric organic transformations, including the regioselective boryiation and siiylation of benzyiic C—H bonds, the hydrogenation of aikenes, imines, carbonyls, nitroarenes, and heterocycles, hydroboration, hydrophosphination, and cyclization reactions. The solid catalysts can also be integrated into a flow reactor or a supercritical fluid reactor.
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- CU-AND NI-CATALYZED DECARBOXYLATIVE BORYLATION REACTIONS
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The invention is directed to methods of converting a carboxylic acid group in a compound, via a redox active ester, to a corresponding boronic ester by treatment with bis(pinacolato)diboron-alkyllithium complex in the presence of a ligand, a Ni(ll) salt or a copper salt, and an Mg(ll) salt, in the presence of an alkyllithium or a lithium hydroxide or alkoxide salt. The product pinacolato boronate ester can be cleaved to provide a boronic acid. The invention is also directed to methods of preparing various compounds of medical value comprising boronic acid groups, and to novel boronic-acid containing compounds of medicinal value, including an atorvastatin boronic acid analog, a vancomycin aglycone boronic acid analog, and boronic acid containing elastase inhibitors mCBK319, mCBK320, mCBK323, and RPX-7009.
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Page/Page column 36-37; 39-40; 74
(2018/10/19)
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- Synthesis of Secondary and Tertiary Alkyl Boronic Esters by gem-Carboborylation: Carbonyl Compounds as Bis(electrophile) Equivalents
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An unprecedent gem-carboborylation of aldehydes and ketones provides access to various secondary and tertiary alkyl boronic esters. The addition of B2pin2 to a carbonyl compound generates α-oxyl-substituted alkyl boron species. Organ
- Shi, Dunfa,Wang, Lu,Xia, Chungu,Liu, Chao
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supporting information
p. 10318 - 10322
(2018/07/31)
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- Cobalt-Catalyzed C-H Borylation of Alkyl Arenes and Heteroarenes Including the First Selective Borylations of Secondary Benzylic C-H Bonds
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A cobalt di-tert-butoxide complex bearing N-heterocyclic carbene (NHC) ligands has been synthesized and characterized. This complex is effective at catalyzing the selective monoborylation of the benzylic position of alkyl arenes using pinacolborane (HBpin) as the boron source. This same cobalt complex enables selective monoborylation of N-methylpyrrole, N-methylpyrazole, and N-methylindole. Catalysis can be achieved with as little as 2-3 mol % of the cobalt precatalyst at 80 °C.
- Jayasundara, Chathurika R. K.,Sabasovs, Dmitrijs,Staples, Richard J.,Oppenheimer, Jossian,Smith, Milton R.,Maleczka, Robert E.
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supporting information
p. 1567 - 1574
(2018/06/04)
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- Palladium-catalyzed regioselective hydroboration of aryl alkenes with B2pin2
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A palladium(ii)-catalyzed hydroboration of aryl alkenes with stable and easy-to-handle (pinacolato)diboron (B2pin2) under mild conditions has been developed. Acetic acid acted as the solvent and the hydrogen source, which has been identified by deuterium experiments. Notably, isomerization-hydroboration of allyl benzene derivatives was observed. As a result, a series of benzyl boronic esters were obtained in moderate to excellent yields with exclusive regioselectivity.
- Huang, Jiuzhong,Yan, Wuxin,Tan, Chaowei,Wu, Wanqing,Jiang, Huanfeng
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supporting information
p. 1770 - 1773
(2018/02/21)
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- Markovnikov-Selective Co(I)-Catalyzed Hydroboration of Vinylarenes and Carbonyl Compounds
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An NHC-supported Co(I) catalyst has been developed for selective Markovnikov hydroboration of vinylarenes under mild reaction conditions. The hydroboration allows highly selective synthesis of a wide range of secondary and tertiary alkyl boronates in exce
- Verma, Piyush Kumar,Sethulekshmi,Geetharani
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supporting information
p. 7840 - 7845
(2019/01/04)
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- Markovnikov-Selective Hydroboration of Vinylarenes Catalyzed by a Cobalt(II) Coordination Polymer
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Highly efficient and practical hydroboration of alkenes has been catalyzed by an inexpensive and air-stable cobalt(II) coordination polymer (CP) in the presence of KOtBu. Complete conversion of alkenes to alkylboronates were performed within just 5 min with low catalyst loading (0.025 mol%), achieving the record high turnover frequencies of up to 47 520 h-1. For a range of vinylarenes, unusual Markovnikov selectivity was observed.
- Zhang, Guoqi,Wu, Jing,Li, Sihan,Cass, Sean,Zheng, Shengping
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supporting information
p. 7893 - 7897
(2019/01/04)
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- Hydroboration of Terminal Olefins with Pinacolborane Catalyzed by New Mono(2-Iminopyrrolyl) Cobalt(II) Complexes
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The 5-substituted 2-aryliminopyrrolyl ligand precursors of the type 5-R-2-[N-(2,6-diisopropylphenyl)formimino]-1H-pyrrole (R = 2,6-Me2-C6H3 (1a), 2,4,6-iPr3-C6H2 (1b), 2,4,6-Phs
- Cruz, Tiago F. C.,Lopes, Patrícia S.,Pereira, Laura C. J.,Veiros, Luís F.,Gomes, Pedro T.
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p. 8146 - 8159
(2018/07/25)
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- Cobalt-Catalyzed Hydroboration of Alkenes, Aldehydes, and Ketones
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An operationally convenient and general method for hydroboration of alkenes, aldehydes, and ketones employing Co(acac)3 as a precatalyst is reported. The hydroboration of alkenes in the presence of HBpin, PPh3, and NaOtBu affords good to excellent yields with high Markovnikov selectivity with up to 97:3 branched/linear selectivity. Moreover, Co(acac)3 could be used effectively to hydroborate aldehydes and ketones in the absence of additives under mild reaction conditions. Inter- and intramolecular chemoselective reduction of the aldehyde group took place over the ketone functional group.
- Tamang, Sem Raj,Bedi, Deepika,Shafiei-Haghighi, Sara,Smith, Cecilia R.,Crawford, Christian,Findlater, Michael
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supporting information
p. 6695 - 6700
(2018/11/21)
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- Decarboxylative borylation
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The widespread use of alkyl boronic acids and esters is frequently hampered by the challenges associated with their preparation.We describe a simple and practical method to rapidly access densely functionalized alkyl boronate esters from abundant carboxylic substituents. This broad-scope nickel-catalyzed reaction uses the same activating principle as amide bond formation to replace a carboxylic acid moiety with a boronate ester. Application to peptides allowed expedient preparations of a-amino boronic acids, often with high stereoselectivity, thereby facilitating synthesis of the alkyl boronic acid drugs Velcade and Ninlaro as well as a boronic acid version of the iconic antibiotic vancomycin. The reaction also enabled the discovery and extensive biological characterization of potent human neutrophil elastase inhibitors, which offer reversible covalent binding properties.
- Li, Chao,Wang, Jie,Barton, Lisa M.,Yu, Shan,Tian, Maoqun,Peters, David S.,Kumar, Manoj,Yu, Antony W.,Johnson, Kristen A.,Chatterjee, Arnab K.,Yan, Ming,Baran, Phil S.
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- Cobalt-catalysed Markovnikov selective hydroboration of vinylarenes
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A bipyridiyl-oxazoline cobalt catalyst tBuBPOCoCl2 has been developed for the Markovnikov selective hydroboration of alkenes using pinacolborane and NaOtBu as the in situ activator with up to >98 : 2 branched : linear selectivity (24 examples, 45-92% isolated yield).
- Peng, Jingying,Docherty, Jamie H.,Dominey, Andrew P.,Thomas, Stephen P.
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supporting information
p. 4726 - 4729
(2017/07/10)
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- Enantiospecific Synthesis of ortho-Substituted Benzylic Boronic Esters by a 1,2-Metalate Rearrangement/1,3-Borotropic Shift Sequence
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Coupling reactions between benzylamines and boronic esters have been investigated. ortho-Lithiated benzylamines react with boronic esters and a N-activator to afford ortho-substituted benzylic boronic esters with formal 1,1′-benzylidene insertion into the C-B bond. The reaction occurs by a SN2′ elimination and 1,2-metalate rearrangement of the N-activated boronate complex to afford a dearomatized intermediate, which undergoes a Lewis-acid catalyzed 1,3-borotropic shift to afford the boronic ester products in high yield and with excellent enantiospecificity. The use of enantioenriched α-substituted benzylamines gave the corresponding secondary boronic esters with high ee.
- Aichhorn, Stefan,Bigler, Raphael,Myers, Eddie L.,Aggarwal, Varinder K.
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supporting information
p. 9519 - 9522
(2017/07/25)
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- Cobalt-Catalyzed Regioselective Hydroboration of Terminal Alkenes
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Cobalt(II) catalysts based on flexible PNP or NNN ligands were explored for the regioselective hydroboration of alkenes. A known CoII–PNP pincer complex was found to efficiently catalyze alkene hydroboration with excellent anti-Markovnikov selectivity, whereas a newly synthesized dinuclear CoII–NNN complex was found to catalyze the hydroboration of a range of aromatic terminal alkenes with good Markovnikov selectivities (up to 98:2, b/l). This represents a rare example of Markovnikov selectivity in the hydroboration of alkenes using an inexpensive, flexible-ligand-supported dinuclear cobalt catalyst.
- Zhang, Guoqi,Wu, Jing,Wang, Man,Zeng, Haisu,Cheng, Jessica,Neary, Michelle C.,Zheng, Shengping
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supporting information
p. 5814 - 5818
(2017/10/23)
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- Iron-Catalyzed, Markovnikov-Selective Hydroboration of Styrenes
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A highly Markovnikov-selective, iron-catalyzed hydroboration of styrenes is reported using available oxazolinylphenyl picolinamide as the ligand to afford the branched hydroboration products with up to >50/1 b/l. This reaction is operationally simple and
- Chen, Xu,Cheng, Zhaoyang,Lu, Zhan
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supporting information
p. 969 - 971
(2017/03/14)
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- Synthesis, Structure, and Reactivity of a Terminal Magnesium Hydride Compound with a Carbatrane Motif, [TismPriBenz]MgH: A Multifunctional Catalyst for Hydrosilylation and Hydroboration
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The tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl)]methyl ligand, [TismPriBenz], has been employed to form the magnesium carbatrane compound, [TismPriBenz]MgH, which possesses a terminal hydride ligand. Speci
- Rauch, Michael,Ruccolo, Serge,Parkin, Gerard
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supporting information
p. 13264 - 13267
(2017/10/05)
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- Markovnikov-Selective, Activator-Free Iron-Catalyzed Vinylarene Hydroboration
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Two series of structurally related alkoxy-tethered NHC iron(II) complexes have been developed as catalysts for the regioselective hydroboration of alkenes. Significantly, Markonikov-selective alkene hydroboration with HBpin has been controllably achieved using an iron catalyst (11 examples, 35-90% isolated yield) with up to 37:1 branched:linear selectivity. anti-Markovnikov-selective alkene hydroboration was also achieved using HBcat and modification of the ligand backbone (6 examples, 44-71% yields). In both cases, ligand design has enabled activator-free low-oxidation-state iron catalysis.
- Macnair, Alistair J.,Millet, Clément R. P.,Nichol, Gary S.,Ironmonger, Alan,Thomas, Stephen P.
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p. 7217 - 7221
(2016/10/14)
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- Transmetallation from CCC-NHC pincer Zr complexes in the synthesis of air-stable CCC-NHC pincer Co(iii) complexes and initial hydroboration trials
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Development of CCC-NHC pincer Co complexes via transmetalation from Zr is reported. Formation of these air-stable Co(iii) complexes was achieved through use of a CoCl2 or Co(acac)3in situ or with a discrete CCC-NHC pincer Zr transmetallating agent. Preliminary activity in the hydroboration of styrene is reported. This facile methodology will further the development of CCC-NHC pincer first-row transition metal complexes.
- Reilly, Sean W.,Webster, Charles Edwin,Hollis, T. Keith,Valle, Henry U.
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supporting information
p. 2823 - 2828
(2016/02/20)
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- Highly Selective Hydroboration of Alkenes, Ketones and Aldehydes Catalyzed by a Well-Defined Manganese Complex
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Well-defined manganese complexes based on inexpensive, readily available ligands, 2,2′:6′,2′′-terpyridine and its derivatives have been prepared and employed for the selective hydroboration of alkenes, ketones and aldehydes. Highly Markovnikov regioselective hydroboration of styrenes as well as excellent chemoselective hydroboration of ketones over alkenes were achieved, for the first time, by an earth-abundant manganese catalyst.
- Zhang, Guoqi,Zeng, Haisu,Wu, Jing,Yin, Zhiwei,Zheng, Shengping,Fettinger, James C.
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supporting information
p. 14369 - 14372
(2016/11/11)
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- Heteroleptic Nickel Complexes for the Markovnikov-Selective Hydroboration of Styrenes
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First-row transition metal catalysis offers a cheaper, more environmentally sustainable alternative to second- and third-row transition metal catalysts. Nickel has shown great promise as a tool for the borylation of unsaturated compounds to yield boronic esters, but Markovnikov-selective hydroborations of simple styrenes have not been well-explored. Herein, we report the synthesis of benzyl boronic esters via nickel-catalyzed hydroboration of styrenes using a heteroleptic N-heterocyclic carbene (NHC)-phosphine nickel complex, IMes(Cy3P)NiCl2. The IMes(Cy3P)NiCl2 complex displays a broad substrate scope and maintains the integrity of yield and regioselectivity when challenged with substrates bearing increased steric hindrance. The heteroleptic complexes also tolerate both electron-withdrawing and -donating groups, in contrast to traditional bis-phosphine and Ni(0) complexes.
- Touney, Eric E.,Van Hoveln, Ryan,Buttke, Carl T.,Freidberg, Michael D.,Guzei, Ilia A.,Schomaker, Jennifer M.
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supporting information
p. 3436 - 3439
(2016/11/06)
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- Boron Lewis Acid-Catalyzed Hydroboration of Alkenes with Pinacolborane: BArF3Does What B(C6F5)3Cannot Do!
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The transition-metal-free hydroboration of various alkenes with pinacolborane (HBpin) initiated by tris[3,5-bis(trifluoromethyl)phenyl]borane (BArF3) is reported. The choice of the boron Lewis acid is crucial as the more prominent boron Lewis acid tris(pentafluorophenyl)borane (B(C6F5)3) is reluctant to react. Unlike B(C6F5)3, BArF3is found to engage in substituent redistribution with HBpin, resulting in the formation of ArFBpin and the electron-deficient diboranes [H2BArF]2and [(ArF)(H)B(μ-H)2BArF2]. These in situ-generated hydroboranes undergo regioselective hydroboration of styrene derivatives as well as aliphatic alkenes with cis diastereoselectivity. Another ligand metathesis of these adducts with HBpin subsequently affords the corresponding HBpin-derived anti-Markovnikov adducts. The reactive hydroboranes are regenerated in this step, thereby closing the catalytic cycle.
- Yin, Qin,Kemper, Sebastian,Klare, Hendrik F. T.,Oestreich, Martin
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supporting information
p. 13840 - 13844
(2016/09/21)
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- Iron-Catalyzed Hydroboration: Unlocking Reactivity through Ligand Modulation
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Iron-catalyzed hydroboration (HB) of alkenes and alkynes is reported. A simple change in ligand structure leads to an extensive change in catalyst activity. Reactions proceed efficiently over a wide range of challenging substrates including activated, unactivated and sterically encumbered motifs. Conditions are mild and do not require the use of reducing agents or other additives. Large excesses of borating reagent are not required, allowing control of chemo- and regioselectivity in the presence of multiple double bonds. Mechanistic insight reveals that the reaction is likely to proceed via a highly reactive iron hydride intermediate.
- Espinal-Viguri, Maialen,Woof, Callum R.,Webster, Ruth L.
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supporting information
p. 11605 - 11608
(2016/08/05)
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- Nickel-Catalyzed Borylation of Aryl- and Benzyltrimethylammonium Salts via C-N Bond Cleavage
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By developing a mild Ni-catalyzed system, a method for direct borylation of sp2 and sp3 C-N bonds has been established. The key to this hightly efficient C-N bond borylative cleavage depends on the appropriate choice of the nickel catalyst Ni(COD)2, ICy·HCl as a ligand, and the use of 2-ethoxyethanol as the cosolvent. This transformation shows good functional group compatibility and can serve as a powerful synthetic tool for gram-scale synthesis and late-stage C-N borylation of complex compounds.
- Hu, Jiefeng,Sun, Heqing,Cai, Wangshui,Pu, Xinghui,Zhang, Yemin,Shi, Zhuangzhi
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- A proton-switchable bifunctional ruthenium complex that catalyzes nitrile hydroboration
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A new bifunctional pincer ligand framework bearing pendent proton-responsive hydroxyl groups was prepared and metalated with Ru(II) and subsequently isolated in four discrete protonation states. Stoichiometric reactions with H2 and HBPin showed facile E-H (E = H or BPin) activation across a Ru(II)-O bond, providing access to unusual Ru-H species with strong interactions with neighboring proton and boron atoms. These complexes were found to promote the catalytic hydroboration of ketones and nitriles under mild conditions, and the activity was highly dependent on the ligand's protonation state. Mechanistic experiments revealed a crucial role of the pendent hydroxyl groups for catalytic activity.
- Geri, Jacob B.,Szymczak, Nathaniel K.
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supporting information
p. 12808 - 12814
(2015/10/28)
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- Nickel-catalyzed borylation of arenes and indoles via C-H bond cleavage
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The first nickel-catalyzed method for the borylation of carbon-hydrogen bonds in arenes and indoles is described. The use of an N-heterocyclic carbene ligand is essential for an efficient reaction, with an N-cyclohexyl-substituted derivative being optimal. This method is readily applied to the gram scale synthesis of 2-borylindole.
- Furukawa, Takayuki,Tobisu, Mamoru,Chatani, Naoto
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supporting information
p. 6508 - 6511
(2015/04/14)
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- High-activity cobalt catalysts for alkene hydroboration with electronically responsive terpyridine and α-diimine ligands
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Cobalt alkyl complexes bearing readily available and redox-active 2,2′:6′,2″-terpyridine and α-diimine ligands have been synthesized, and their electronic structures have been elucidated. In each case, the supporting chelate is reduced to the monoanionic, radical form that is engaged in antiferromagnetic coupling with the cobalt(II) center. Both classes of cobalt alkyls proved to be effective for the isomerization-hydroboration of sterically hindered alkenes. An α-diimine-substituted cobalt allyl complex proved exceptionally active for the reduction of hindered tri-, tetra-, and geminally substituted alkenes, representing one of the most active homogeneous catalysts known for hydroboration. With limonene, formation of an η3-allyl complex with a C-H agostic interaction was identified and accounts for the sluggish reactivity observed with diene substrates. For the terpyridine derivative, unique Markovnikov selectivity with styrene was also observed with HBPin. (Figure Presented).
- Palmer, W. Neil,Diao, Tianning,Pappas, Iraklis,Chirik, Paul J.
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p. 622 - 626
(2015/03/04)
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- Alkene isomerization-hydroboration promoted by phosphine-ligated cobalt catalysts
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Generated in situ from air-stable cobalt precursors or readily synthesized using NaHBEt3, (PPh3)3CoH(N2) was found to be an effective catalyst for the hydroboration of alkenes. Unlike previous base-metal catalysts for alkene isomerization-hydroboration which favor the incorporation of boron at terminal positions, (PPh3)3CoH(N2) promotes boron incorporation adjacent to π-systems even in substrates where the alkene is at a remote position, enabling a unique route to 1,1-diboron compounds from α -dienes.
- Scheuermann, Margaret L.,Johnson, Elizabeth J.,Chirik, Paul J.
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supporting information
p. 2716 - 2719
(2015/06/16)
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- Iron-catalyzed borylation of alkyl electrophiles
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The use of low-cost iron(III) acetoacetate (Fe(acac)3) and tetramethylethylenediamine (TMEDA) enables the direct cross-coupling of alkyl halides with bis(pinacolato)diboron. This approach allows for the borylation of activated or unactivated primary, secondary, and tertiary bromides. Moreover, even the borylation of benzylic or allylic chlorides, tosylates, and mesylates are possible. The reactions proceed under mild conditions at room temperature and show broad functional-group compatibility and "robustness" as measured by a modified Glorius robustness screen.
- Atack, Thomas C.,Lecker, Rachel M.,Cook, Silas P.
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supporting information
p. 9521 - 9523
(2014/07/22)
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- Stereocontrolled synthesis of 1,5-stereogenic centers through three-carbon homologation of boronic esters
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Allylic pinacol boronic esters are stable toward 1,3-borotropic rearrangement. We developed a PdII-mediated isomerization process that gives di- or trisubstituted allylic boronic esters with high E selectivity. The combination of this method with lithiation-borylation enables the synthesis of carbon chains that bear 1,5-stereogenic centers. The utility of this method has been demonstrated in a formal synthesis of (+)-jasplakinolide. Three more: The 3C homologation of chiral pinacol boronic esters gives di- or trisubstituted allylic boronic esters with high yield and E selectivities. The combination of this method with lithiation-borylation enables the synthesis of alkyl chains that bear 1,5-stereogenic centers. The utility of the process was demonstrated in a formal synthesis of (+)-jasplakinolide.
- Unsworth, Phillip J.,Leonori, Daniele,Aggarwal, Varinder K.
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supporting information
p. 9846 - 9850,5
(2014/10/15)
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- Highly selective bis(imino)pyridine iron-catalyzed alkene hydroboration
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Bis(imino)pyridine iron dinitrogen complexes have been shown to promote the anti-Markovnikov catalytic hydroboration of terminal, internal, and geminal alkenes with high activity and selectivity. The isolated iron dinitrogen compounds offer distinct advan
- Obligacion, Jennifer V.,Chirik, Paul J.
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supporting information
p. 2680 - 2683
(2013/07/19)
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