C–H arylation of unactivated arenes with aryl halides catalyzed by cobalt porphyrin

To, Ching Tat; Chan, Tek Long; Li, Bao Zhu; Hui, Ying Ying; Kwok, Tsz Yiu; Lam, Suet Yu; Chan, Kin Shing

doi:10.1016/j.tetlet.2010.12.092

Cited by 43 publications

(23 citation statements)

References 32 publications

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“…zugefügt wurden. [45][46][47][48][49] Wir schlagen nun vor, dass diese Reaktionen wahrscheinlich metallkatalysierte oder (eher wahrscheinlich) metallinitiierte, Basen-vermittelte HAS-Reaktionen sind.…”

Section: Methodsunclassified

Organokatalyse und C‐H‐Aktivierung treffen auf Radikal‐ und Elektronentransferreaktionen

2011

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Radikal(isch)e Perspektive: Kürzlich publizierte „organokatalytische C‐H‐Aktivierungen“ werden neu als Basen‐vermittelte homolytische Substitutionen interpretiert. Eine Sequenz aus Addition eines Arylradikals an ein Aren, Deprotonierung (siehe Schema) und Elektronentransfer ist ein Teil der Kettenreaktion. Die Arbeiten sind damit keine konzeptionellen Durchbrüche mehr, können aber gleichwohl neue Synthesemöglichkeiten unter Nutzung der Radikal(anionen)chemie eröffnen.

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Section: Methodsunclassified

Organokatalyse und C‐H‐Aktivierung treffen auf Radikal‐ und Elektronentransferreaktionen

2011

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“…[5] Significant progress in cobalt-catalyzed [6] C À H bond functionalizations was, however, recently accomplished by Nakamura, Yoshikai, and co-workers through the elegant development of direct C À H bond alkylations by means of chelation-assisted hydroarylations, [7,8] as well as oxidative CÀH bond functionalizations with nucleophilic Grignard reagents. [9,10,11] In contrast, we recently devised reaction conditions for cobalt-catalyzed direct arylations by challenging C À H/C À O bond cleavages [12] with phenol-derived sulfamates, carbamates, and phosphates as the electrophilic substrates. [13] Aryl chlorides are the most attractive electrophilic aryl halides for biaryl syntheses, since they are cost-effective and widely available.…”

Section: Introductionmentioning

confidence: 99%

Cobalt‐Catalyzed CH Bond Functionalizations with Aryl and Alkyl Chlorides

Punji

Song

Shevchenko

et al. 2013

Chemistry A European J

185

114

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Inexpensive cobalt catalysts derived from N-heterocylic carbenes (NHC) allowed efficient catalytic C-H bond arylations on heteroaryl-substituted arenes with widely available aryl chlorides, which set the stage for the preparation of sterically hindered tri-ortho-substituted biaryls. Likewise, challenging direct alkylations with β-hydrogen-containing primary and even secondary alkyl chlorides proceeded on pyridyl- and pyrimidyl-substituted arenes and heteroarenes. The cobalt-catalyzed C-H bond functionalizations occurred efficiently at ambient reaction temperature with excellent levels of site-selectivities and ample scope. Mechanistic studies highlighted that electron-deficient aryl chlorides reacted preferentially, while the arenes kinetic C-H bond acidity was found to largely govern their reactivity.

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“…Along these lines, several very recent publications are striking in their similarity to the reactions in Scheme 1 and 2, except that metal salts (Fe, Cu, Co, etc) are added. [45][46][47][48][49] We suggest that such reactions might be metal-catalyzed or (perhaps more likely) metal-initiated base-promoted HAS reactions.…”

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confidence: 99%

Organocatalysis and CH Activation Meet Radical‐ and Electron‐Transfer Reactions

2011

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aryl radicals · CÀH activation · homolytic radical substitutions · organocatalysis · radical anionsThe research groups of Shi, [1] Shirakawa/Hayashi, [2] and Kwong/Lei [3] have recently reported independently on the construction of biaryl compounds from unactivated aromatic rings by direct CÀH activation with the aid of organocatalysts.[4] Published in J. Am. Chem. Soc. and Nature Chem., the results were described as "conceptual breakthroughs" [1,3] because no metal catalyst was needed.Here we suggest that these exciting results are not best viewed in terms of C À H activation or organocatalysis, but instead in terms of homolytic radical aromatic substitution (HAS). [5][6][7][8][9] Although the results may not be conceptual breakthroughs from that viewpoint, they could well herald new opportunities for making organic molecules through organic radical and radical anion reactions.Kwong, Lei, and co-workers discovered that heating aryl iodides in benzene at 80 8C with one equivalent of potassium tert-butoxide and 20 mol % N,N'-dimethylethylenediamine (DMEDA, the organocatalyst) gave biaryls in good yields (60-85 %, Scheme 1).[3] The research groups of Shirakawa/ Hayashi [2] and Shi [1] described similar bimolecular reactions in comparable yields, although their organocatalyst was 1,10-phenanthroline (or a substituted analogue) and used at a level of 20 and 40 mol %, respectively. In addition, Shi and co-workers reported an example of a cyclization: heating 2-iodophenyl benzyl ether (1) in mesitylene with potassium tert-butoxide (3 equiv) and 1,10-phenanthroline provided benzochromene 2 in 75 % yield.In 2008, Itami and co-workers reported that potassium tert-butoxide (1.5 equiv) alone effected the addition of aryl iodides and bromides to pyridizine and other electron-poor aromatic rings. [10,11] These results are reminiscent of the Minisci reaction (addition of alkyl and other radicals to electron-poor heterocycles), [12] except that Minisci reactions are usually conducted under acidic conditions rather than basic conditions. The research groups [1,3,4] discovered these transformations through control experiments while trying to develop metal-catalyzed C À H activation reactions. They observed that with certain "ligands" and KOtBu, the metal was not needed at all to effect the conversion of the aryl halide into the biaryl. Extensive control experiments and trace analyses (Shi and co-workers, [1] Itami and co-workers [10] ) were performed to ensure that the conditions were indeed metal-free. Coming from this direction, the processes look like organocatalylic CÀH activation reactions.In all these reports there are suggestions that aryl radicals are intermediates. The scope and conditions of the reactions (large excess of acceptor needed) and the H/D isotope effects are consistent with aryl radicals being involved. The addition of 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO) and other inhibitors blocked the reactions, [1,3,10] and the successful cyclization of 1 to 2 is consistent with an aryl radical intermediate. Final...

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C–H arylation of unactivated arenes with aryl halides catalyzed by cobalt porphyrin

Cited by 43 publications

References 32 publications

Organokatalyse und C‐H‐Aktivierung treffen auf Radikal‐ und Elektronentransferreaktionen

Organokatalyse und C‐H‐Aktivierung treffen auf Radikal‐ und Elektronentransferreaktionen

Cobalt‐Catalyzed CH Bond Functionalizations with Aryl and Alkyl Chlorides

Organocatalysis and CH Activation Meet Radical‐ and Electron‐Transfer Reactions

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