- Suzuki-Miyaura Csp2-Csp2Cross-Couplings Employing Nickel(II) Pincer Precatalysts: Mechanistic Investigations
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This study investigates the mechanism of Suzuki-Miyaura Csp2-Csp2cross-couplings facilitated by PCP-type nickel(II) pincer complexes. By employing a combination of standard experimental and theoretical methods, it is proposed that a nickel(I)/(III) cycle is involved in this reaction and single-electron pathways likely operate in this transformation.
- Ho, Curtis C.,Olding, Angus,Fuller, Rebecca O.,Canty, Allan J.,Lucas, Nigel T.,Bissember, Alex C.
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supporting information
p. 2305 - 2310
(2021/05/06)
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- Diarylation of alkenes by a Cu-catalyzed migratory insertion/cross-coupling cascade
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A strategy for the catalytic diarylation of alkenes is presented. The method involves the migratory insertion of alkenes into an Ar-Cu complex to generate a new C(sp3)-Cu complex, which subsequently undergoes reaction with an aryl iodide to constitute a vicinal diarylation of an alkene. The method provides access to benzofuran- and indoline-containing products. Furthermore, highly diastereoselective examples are presented, allowing access to complex, stereochemically rich structures from simple alkene starting materials.
- You, Wei,Brown, M. Kevin
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p. 14730 - 14733
(2014/12/11)
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- Copper-catalyzed cross-coupling of boronic esters with aryl iodides and application to the carboboration of alkynes and allenes
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Copper-catalyzed Suzuki-Miyaura-type cross-coupling and carboboration processes are reported. The cross-couplings function well with a variety of substituted aryl iodides and aryl boronic esters and allows for orthogonal reactivity compared to palladium-catalyzed processes. The carboboration method includes both alkynes and allenes and provides access to highly substituted and stereodefined vinyl boronic esters. The alkyne carboboration method is highlighted in the simple one-pot synthesis of Tamoxifen. Cross-Cu-pling: The title cross-couplings function well with a variety of substituted aryl iodides and aryl boronic esters and allows for reactivity orthogonal to that of the palladium-catalyzed processes. The title carboboration method includes both alkynes and allenes and provides access to highly substituted and stereodefined vinyl boronic esters. The alkyne carboboration method is highlighted in a simple one-pot synthesis of Tamoxifen.
- Zhou, Yiqing,You, Wei,Smith, Kevin B.,Brown, M. Kevin
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supporting information
p. 3475 - 3479
(2014/04/03)
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- Tributylgermanium hydride as a replacement for tributyltin hydride in radical reactions
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Tributylgermanium hydride (Bu3GeH) can be used as an alternative to tributyltin hydride (Bu3SnH) as a radical generating reagent with a wide range of radical substrates. Tributylgermanium hydride has several practical advantages over tributyltin hydride, e.g. low toxicity, good stability and much easier work-up of reactions. The reagent can be easily prepared in good yield and stored indefinitely. Suitable substrates include iodides, bromides, activated chlorides, phenyl selenides, tert-nitroalkanes, thiocarbonylimidazolides and Barton esters. Alkyl, vinyl and aryl radicals can be generated in radical reactions including reduction and cyclisation processes. Common radical initiators such as ACCN and triethylborane can be used. The slower rate of hydrogen abstraction by carbon-centred radicals from Bu 3GeH as compared to Bu3SnH facilitates improved cyclisation yields. Polarity reversal catalysis (PRC) with phenylthiol can be used in reactions which generate stable radical intermediates which will not abstract hydrogen from Bu3GeH.
- Bowman, W. Russell,Krintel, Sussie L.,Schilling, Mark B.
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p. 585 - 592
(2007/10/03)
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- Triethylsilane-indium(III) chloride system as a radical reagent
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(Chemical Equation Presented) A novel generation method of indium hydride (Cl2InH) was found by the transmetalation of InCl3 with Et3SiH. In the intramolecular cyclization of enynes, the previously reported system (NaBH4-InCl3) has a problem of side reactions with the coexistent borane. In contrast, the problem was solved by the presented system, which affords effective hydroindation of alkynes.
- Hayashi, Naoki,Shibata, Ikuya,Baba, Akio
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p. 4981 - 4983
(2007/10/03)
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- Determination of rate constants for the reaction of aryl radicals with enolate ions
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The rate of ring closure (kC) of o-(ω-alkenyl)aryl radicals by means of an intramolecular attack of the intermediate phenyl-type radical at the tethered double bond was found to be 4.2 × 108 S-1 (for 1?) and 7.6×107 S-1 (for 8?), both being 6-exo-trig processes, and 9.6 × 109 S-1 for the 5-exo-trig process of 3?. The kC rate constant of these radicals was calibrated with respect to a known rate of H-atom abstraction (kH). The photostimulated SRN1 reactions of radical clock precursor 1 with anions PhS- and (EtO)2PO- in Me2SO at 25 °C provided the rates of addition of these nucleophiles (kY) to intermediate 1? (3.2 × 108 and 2.5 × 109 M-1 S-1, respectively). In contrast, the analogous reaction of a ketone enolate ion with precursor 1 did not take the expected SRN1 course; instead an elimination reaction was favoured. Similarly, the reactions of radical clock precursors 3 or 8 with the enolate ion failed. However, investigation of the distribution of 9-anthracenyl (11?) or 1-naphthyl (12?) radicals between two competing reactions, namely combination with a nucleophile and H abstraction from the solvent (Me2SO), was successful and eventually enabled us to find the kY values for the addition of the enolate ion to these two aryl radical intermediates (4.4 × 108 and 2.9 × 109 M-1 S-1, respectively).
- Annunziata, Alfonso,Galli, Carlo,Marinelli, Manuela,Pau, Tullia
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p. 1323 - 1329
(2007/10/03)
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- Formation of Grignard reagents from aryl halides: Effective radical probes hint at a nonparticipation of dianions in the mechanism
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(equation presented) We have prepared highly efficient radical probes 2a-b involving the hex-5-enyl rearrangement. The reaction of 2a-b with active magnesium leads to the cyclized products 4a-b, providing a direct evidence of radical intermediates during the formation of aryl Grignard reagents. The variations of yields for cyclized products 4a-b as a function of structural modifications in 2a-b suggest that the intervention of dianions is not necessary to explain the observed results.
- Bodineau, Nicolas,Mattalia, Jean-Marc,Thimokhin, Vitaliy,Handoo, Kishan,Négrel, Jean-Claude,Chanon, Michel
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p. 2303 - 2306
(2007/10/03)
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- SmI2-PROMOTED ARYL RADICAL CYCLIZATION. A NEW SYNTHETIC ENTRY INTO HETEROCYCLES
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Benzofuran, naphthofuran, and indole frameworks were expediently constructed at ambient temperature from arene bromides with ortho O- and N-substituents containing double or triple bonds via radical cyclization process promoted by SmI2.
- Inanaga, Junji,Ujikawa, Osamu,Yamaguchi, Masaru
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p. 1737 - 1740
(2007/10/02)
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