- Nucleophile-assisted cleavage of benzyltrialkylsilane cation radicals
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The cation radicals of benzyltrialkylsilanes have been generated using photoinduced electron transfer and characterized using transient absorption spectroscopy. Absolute rate constants for nucleophile-assisted C-Si bond cleavage have been determined, for different nucleophiles in different solvents and with different substituents on the phenyl ring. The short lifetime (-9 s) of the parent benzyltrimethylsilane cation radical in acetonitrile was unambiguously shown to be due to a rapid nucleophile-assisted bond cleavage, with the solvent acting as the nucleophile. Even in less polar solvents, such as dichloromethane, the lifetime of benzyltrimethylsilane cation radical is quite short (ca. 20 ns) unless trace amounts of water, which acts as an efficient nucleophile, are removed. Consistent with the nucleophile-assisted cleavage mechanism for the benzyltrialkylsilanes, sterically-demanding substituents on silicon decrease the rate constant for cleavage by as much as 4 orders of magnitude, depending upon the nucleophile. Similarly, increasing steric crowding on the nucleophile also decreases the rate constant, although smaller changes in the rate constants are observed. Electron-donating substituents (4-methyl and 4-methoxy) on the phenyl group also lead to a substantial decrease in the rate constant for cleavage of the cation radicals. When measurements are performed in the least nucleophilic solvent and under conditions that minimize contributions from adventitious nucleophiles, the lifetimes of the cation radicals of the benzyltrialkylsilanes can be so long that the rate of pseudofirst-order decay can not be accurately determined. If the cation radicals undergo unimolecular C-Si bond cleavage (i.e., not nucleophile-assisted) under these conditions, the rate constant for this process is estimated to be less than 104 s-1.
- Dockery, Kevin P.,Dinnocenzo, Joseph P.,Farid, Samir,Goodman, Joshua L.,Gould, Ian R.,Todd, William P.
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- Visible-Light-Promoted Iron-Catalyzed C(sp2)–C(sp3) Kumada Cross-Coupling in Flow
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A continuous-flow, visible-light-promoted method has been developed to overcome the limitations of iron-catalyzed Kumada–Corriu cross-coupling reactions. A variety of strongly electron rich aryl chlorides, previously hardly reactive, could be efficiently coupled with aliphatic Grignard reagents at room temperature in high yields and within a few minutes’ residence time, considerably enhancing the applicability of this iron-catalyzed reaction. The robustness of this protocol was demonstrated on a multigram scale, thus providing the potential for future pharmaceutical application.
- Wei, Xiao-Jing,Abdiaj, Irini,Sambiagio, Carlo,Li, Chenfei,Zysman-Colman, Eli,Alcázar, Jesús,No?l, Timothy
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supporting information
p. 13030 - 13034
(2019/07/18)
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- Iron-catalyzed cross coupling of aryl chlorides with alkyl Grignard reagents: Synthetic scope and FeII/FeIV mechanism supported by x-ray absorption spectroscopy and density functional theory calculations
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A combination of iron(III) fluoride and 1,3-bis(2,6-diiso-propylphenyl)imidazolin-2-ylidene (SIPr) catalyzes the high-yielding cross coupling of an electron-rich aryl chloride with an alkyl Grignard reagent, which cannot be attained using other iron catalysts. A variety of alkoxy-or amino-substituted aryl chlorides can be cross-coupled with various alkyl Grignard reagents regardless of the presence or absence of β-hydrogens in the alkyl group. A radical probe experiment using 1-(but-3-enyl)-2-chlorobenzene does not afford the corresponding cyclization product, therefore excluding the intermediacy of radical species. Solution-phase X-ray absorption spectroscopy (XAS) analysis, with the help of density functional theory (DFT) calculations, indicates the formation of a high-spin (S = 2) heteroleptic difluorido organoferrate(II), [MgX][FeIIF2(SIPr)-(Me/alkyl)], in the reaction mixture. DFT calculations also support a feasible reaction pathway, including the formation of a difluorido organoferrate(II) intermediate which undergoes a novel Lewis acid-assisted oxidative addition to form a neutral organoiron(IV) intermediate, which leads to an FeII/FeIV cata-lytic cycle, where the fluorido ligand and the magnesium ion play key roles.
- Agata, Ryosuke,Takaya, Hikaru,Matsuda, Hiroshi,Nakatani, Naoki,Takeuchi, Katsuhiko,Iwamoto, Takahiro,Hatakeyama, Takuji,Nakamura, Masaharu
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supporting information
p. 381 - 390
(2019/02/25)
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- Modular Functionalization of Arenes in a Triply Selective Sequence: Rapid C(sp2) and C(sp3) Coupling of C?Br, C?OTf, and C?Cl Bonds Enabled by a Single Palladium(I) Dimer
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Full control over multiple competing coupling sites would enable straightforward access to densely functionalized compound libraries. Historically, the site selection in Pd0-catalyzed functionalizations of poly(pseudo)halogenated arenes has been unpredictable, being dependent on the employed catalyst, the reaction conditions, and the substrate itself. Building on our previous report of C?Br-selective functionalization in the presence of C?OTf and C?Cl bonds, we herein complete the sequence and demonstrate the first general arylations and alkylations of C?OTf bonds (in I dimer. This allowed the realization of the first general and triply selective sequential C?C coupling (in 2D and 3D space) of C?Br followed by C?OTf and then C?Cl bonds.
- Keaveney, Sinead T.,Kundu, Gourab,Schoenebeck, Franziska
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supporting information
p. 12573 - 12577
(2018/09/18)
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- Oxygen Activated, Palladium Nanoparticle Catalyzed, Ultrafast Cross-Coupling of Organolithium Reagents
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The discovery of an ultrafast cross-coupling of alkyl- and aryllithium reagents with a range of aryl bromides is presented. The essential role of molecular oxygen to form the active palladium catalyst was established; palladium nanoparticles that are highly active in cross-coupling reactions with reaction times ranging from 5 s to 5 min are thus generated in situ. High selectivities were observed for a range of heterocycles and functional groups as well as for an expanded scope of organolithium reagents. The applicability of this method was showcased by the synthesis of the [11C]-labeled PET tracer celecoxib.
- Heijnen, Dorus,Tosi, Filippo,Vila, Carlos,Stuart, Marc C. A.,Elsinga, Philip H.,Szymanski, Wiktor,Feringa, Ben L.
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supporting information
p. 3354 - 3359
(2017/03/17)
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- Direct oxidation of the C(sp2)-C(sp3) bond from benzyltrimethylsilanes to phenols
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A novel pathway for direct conversion of benzylsilanes to phenols by oxidation with Na2S2O8 and oxygen is efficiently developed under mild and neutral conditions. The reaction shows good functional group tolerance to afford phenols in moderate yields. The possible mechanism is proposed based on the isotopic labeling trials.
- Li, Wei,Gao, Guolin,Gao, Yuan,Yang, Chao,Xia, Wujiong
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supporting information
p. 5291 - 5293
(2017/07/10)
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- Palladium-catalyzed C(sp3)-C(sp2) cross-coupling of homoleptic rare-earth metal trialkyl complexes with aryl bromides: Efficient synthesis of functionalized benzyltrimethylsilanes
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The first C(sp3)-C(sp2) cross-coupling of rare-earth metal alkyl complexes with aryl bromides has been developed. This reaction was conducted at low catalyst loading (0.5 mol%) and exhibited a broad substrate scope, thus providing a facile method for the synthesis of benzyltrimethylsilanes with diverse functional groups.
- Cai, Guilong,Huang, Yingda,Du, Tingting,Zhang, Shaowen,Yao, Bo,Li, Xiaofang
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supporting information
p. 5425 - 5427
(2016/05/09)
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- Iron fluoride/N-heterocyclic carbene catalyzed cross coupling between deactivated aryl chlorides and alkyl grignard reagents with or without β-hydrogens
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High-yielding cross-coupling reactions of various combinations of aryl chlorides and alkyl Grignard reagents have been developed by using an iron(III) fluoride/1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIPr) catalyst composite. The iron(III) fluoride/SIPr-catalyzed aryl-alkyl coupling demonstrates unprecedented scope for both aryl chlorides and alkyl Grignard reagents, thus enabling the first efficient coupling of electron-rich (deactivated) aryl chlorides with alkyl Grignard reagents without β-hydrogens. The present reaction is also effective for diverse alkyl Grignard reagents such as (trimethylsilyl)methyl, primary, and secondary alkyl Grignard reagents.
- Agata, Ryosuke,Iwamoto, Takahiro,Nakagawa, Naohisa,Isozaki, Katsuhiro,Hatakeyama, Takuji,Takaya, Hikaru,Nakamura, Masaharu
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p. 1733 - 1740
(2015/06/16)
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- Palladium-catalyzed C(sp 3)-C(sp 2) cross-coupling of (trimethylsilyl)methyllithium with (hetero)aryl halides
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The palladium-catalyzed direct cross-coupling of a range of organic chlorides and bromides with the bifunctional C(sp3)-(trimethylsilyl)methyllithium reagent is reported. The use of Pd-PEPPSI-IPent as the catalyst allows for the preparation of structurally diverse and synthetically versatile benzyl- and allylsilanes in high yields under mild conditions (room temperature) with short reaction times.
- Heijnen, Dorus,Hornillos, Valentín,Corbet, Brian P.,Giannerini, Massimo,Feringa, Ben L.
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supporting information
p. 2262 - 2265
(2015/05/13)
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- Direct catalytic cross-coupling of organolithium compounds
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Catalytic carbon-carbon bond formation based on cross-coupling reactions plays a central role in the production of natural products, pharmaceuticals, agrochemicals and organic materials. Coupling reactions of a variety of organometallic reagents and organic halides have changed the face of modern synthetic chemistry. However, the high reactivity and poor selectivity of common organolithium reagents have largely prohibited their use as a viable partner in direct catalytic cross-coupling. Here we report that in the presence of a Pd-phosphine catalyst, a wide range of alkyl-, aryl- and heteroaryl-lithium reagents undergo selective cross-coupling with aryl- and alkenyl-bromides. The process proceeds quickly under mild conditions (room temperature) and avoids the notorious lithium halogen exchange and homocoupling. The preparation of key alkyl-, aryl- and heterobiaryl intermediates reported here highlights the potential of these cross-coupling reactions for medicinal chemistry and material science.
- Giannerini, Massimo,Fananas-Mastral, Martin,Feringa, Ben L.
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p. 667 - 672
(2013/08/23)
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- Suzuki-miyaura cross-coupling reactions of primary alkyltrifluoroborates with aryl chlorides
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(Chemical Equation Presented) Parallel microscale experimentation was used to develop general conditions for the Suzuki-Miyaura cross-coupling of diversely functionalized primary alkyltrifluoroborates with a variety of aryl chlorides. These conditions wer
- Dreher, Spencer D.,Lim, Siang-Ee,Sandrock, Deidre L.,Molander, Gary A.
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supporting information; experimental part
p. 3626 - 3631
(2009/09/29)
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- Cobalt-catalyzed cross-coupling reactions of aryl bromides with alkyl grignard reagents
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Aryl bromides react with primary alkyl Grignard reagents in the presence of N,N,N′,N′-tetramethyl-1,3-propanediamine and catalytic amounts of cobalt(II) chloride and an N-heterocyclic carbene to yield the corresponding cross-coupling products in high yields. Copyright
- Hamaguchi, Hiroyuki,Uemura, Minoru,Yasui, Hiroto,Yorimitsu, Hideki,Oshima, Koichiro
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experimental part
p. 1178 - 1179
(2011/02/28)
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- Rhodium-catalyzed silylation and intramolecular arylation of nitriles via the silicon-assisted cleavage of carbon-cyano bonds
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A rhodium-catalyzed silylation reaction of carbon - cyano bonds using disilane has been developed. Under these catalytic conditions, carbon-cyano bonds in aryl, alkenyl, allyl, and benzyl cyanides bearing a variety of functional groups can be silylated. The observation of an enamine side product in the silylation of benzyl cyanides and related stoichiometric studies indicate that the carbon-cyano bond cleavage proceeds through the deinsertion of silyl isocyanide from η2-iminoacyl complex B. Knowledge gained from these studies has led to the development of a new intramolecular biaryl coupling reaction in which aryl cyanides and aryl chlorides are cross-coupled.
- Tobisu, Mamoru,Kita, Yusuke,Ano, Yusuke,Chatani, Naoto
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supporting information; experimental part
p. 15982 - 15989
(2009/05/16)
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- Synthesis of functionalized benzylsilanes from arylzinc compounds and (iodomethyl)trimethylsilane by means of a novel Rh catalysis
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The catalytic activity of a Rh complex in cross-coupling between ArZnI and TMSCH2l was examined in which the Rh complex, generated in situ from [RhCl(1,5-cyclooctadiene)]2 and 1,1′-bis(diphenylphosphino)- ferrocene, exhibited excellent catalytic activity for the production of various functionalized benzylsilanes in good yields. From 31P NMR studies of various solutions containing several of the reaction components, confirmation of the rapid and quantitative transfer of aryl groups from ArZnI to the Rh complex to form arylrhodium species was ascertained. A catalytic cycle, commencing with the transmetalation, was thus proposed for the reaction.
- Takahashi, Hideki,Hossain, Kabir M.,Nishihara, Yasushi,Shibata, Takanori,Takagi, Kentaro
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p. 671 - 675
(2007/10/03)
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- TiCl4-Zn induced reductive acylation of ketones with acylsilanes
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Acylsilanes were found to react with ketones in the presence of a low-valent titanium reagent generated from titanium(IV) chloride and zinc, giving the corresponding reductive acylated compounds.
- Sakurai, Hidehiro,Imamoto, Yuka,Hirao, Toshikazu
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- A kinetic evaluation of carbon-hydrogen, carbon-carbon, and carbon-silicon bond activation in benzylic radical cations
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A detailed study of the competition between C-C, C-H, and C-Si bond fragmentation in a series of 4-methoxy-α-substituted toluene radical cations (1.+), involving both product studies and kinetic analysis, is presented. C-C bond fragmentation occurs with several radical cations in acetonitrile. The rate constants for such processes, determined by laser flash photolysis, varied from 2.8 x 104 (1c.+) to 1.53 x 106 (1f.+) s-1. The activation parameters for C-C bond fragmentation are characterized by low activation enthalpies on the order of 30 kJ mol-1 and negative activation entropies in the range -34 to -55 J mol-1 K-1. Deprotonation of the radical cations is always a second-order process induced by nucleophiles [cerium(IV) ammonium nitrate (CAN) or nitrate anion], with second-order rate constants from 7.7 x 107 (1h.+) to 8.8 x 108 (1i.+) M-1 s-1 in neat acetonitrile (CAN assisted) and from 0.4 x 108 (1j.+) to 7.1 x 108 (1i.+) M-1 s-1 in the presence of nitrate anion. The rate constant for nitrate-induced decarboxylation was higher, 13.6 x 108 M-1 s-1 (1d.+). In a few cases C-C (1e.+, 1f.+) and C-Si (1g.+) fragmentations occurred, also as second-order processes induced by nitrate, with rate constants from 4.4 x 108 (1f.+) to 8.2 x 108 (1g.+) M-1 s-1. ΔH and ΔS had opposing influences on C-H and C-C fragmentation, and in the case of 1e.+ a temperature-dependent product distribution was obtained. The activation parameters for the observed C-H, C-C, and C-Si fragmentations have been compared, and suggest a rationale for the mechanisms and selectively of such processes in radical cations.
- Freccero, Mauro,Pratt, Albert,Albini, Angelo,Long, Conor
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p. 284 - 297
(2007/10/03)
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- Allyl, benzyl and propargyl silanes via the Suzuki reaction
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The clean, efficient Pd-catalyzed cross-coupling of vinyl, alkynyl and aryl bromides with the air-stable organoborane, 10-trimethylsilylmethyl-9-oxa-10-borabicyclo[3.3.2]decane (2) gives excellent yields of the corresponding silylmethylated products, proceeding with complete retention of configuration in the first case.
- Soderquist,Santiago,Rivera
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p. 4981 - 4984
(2007/10/02)
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- Reaction of trimethylsilanes with Arenes and Alk-1-enes in the Presence of Lewis Acid: Syntheses of - and (1-Arylthioalk-3-enyl)-trimethylsilanes
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Treatment of equimolar amounts of the trimethylsilanes (2) or (3) and electron-rich arenes with an equimolar amount of Lewis acid (SnCl4 or TiCl4) gave the Friedel-Crafts reaction products, trimethylsilanes (4) or (5), in high yields.Similar treatment of the chlorides (2) or (3) with alk-1-enes gave ene type products, trimethylsilanes (12) or (13), in moderate yields.Some chemical transformations of these products are also described.
- Ishibashi, Hiroyuki,Nakatani, Hiroshi,Umei, Yoshizumi,Yamamoto, Wako,Ikeda, Masazumi
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p. 589 - 594
(2007/10/02)
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- INTRODUCTION OF AN ARYLTHIO(TRIMETHYLSILYL)METHYL GROUP INTO ARENES BY FRIEDEL-CRAFTS REACTION: SYNTHESIS OF ARYLMETHYLTRIMETHYLSILANES
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Friedel-Crafts reactions of trimethylsilanes (1a, b) with arenes gave trimethylsilanes (2a,b), which were converted into arylmethyltrimethylsilanes (3) by reduction with Raney nickel.
- Ishibashi, Hiroyuki,Nakatani, Hiroshi,Umei, Yoshizumi,Ikeda, Masazumi
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p. 4373 - 4374
(2007/10/02)
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- AN ELECTROREDUCTIVE SYNTHESIS OF ALLYLSILANES AND BENZYLSILANES
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The electrochemical reduction of benzyl and allyl halides carried out in the presence of chlorotrimethylsilane afforded the corresponding benzylsilanes and allylsilanes in satisfactory yields.
- Shono, Tatsuya,Matsumura, Yoshihiro,Katoh, Susumu,Kise, Naoki
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p. 463 - 466
(2007/10/02)
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- NICKEL-CATALYZED CROSS-COUPLING OF ARYL PHOSPHATES WITH GRIGNARD AND ORGANOALUMINIUM REAGENTS. SYNTHESIS OF ALKYL-, ALKENYL-, AND ARYLBENZENES FROM PHENOLS
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Aryl phosphates derived from phenols were converted into alkyl-, alkenyl-, and aryl-benzenes in high yields by cross-coupling with various kinds of Grignard and organoaluminium reagents in the presence of nickel(II) catalysts.
- Hayashi, Tamio,Katsuro, Yoshio,Okamoto, Yasuo,Kumada, Makoto
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p. 4449 - 4452
(2007/10/02)
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