Cobalt‐Catalyzed Direct Arylation of Unactivated Arenes with Aryl Halides

Liu, Wei; Cao, Hao; Xiao, Jie; Jin, Liqun; Lei, Aiwen

doi:10.1002/chem.201002290

Cited by 98 publications

(53 citation statements)

References 110 publications

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“…To confirm this hypothesis, subsequent radical‐trap experiments were carried out on substrates 9 and 10 (Scheme ). Under conditions that involve substrate‐based radicals, these compounds are known to undergo intramolecular 6‐ endo ‐trig cyclization to yield compound 12 as the major product 24a,27a,35. However, upon reaction with our catalytic system, the iodinated substrate 9 did not provide any cyclized adduct 12 but rather the reduced product 11 , albeit in modest yield (28 %).…”

Section: Resultsmentioning

confidence: 99%

Tandem CH Activation/Arylation Catalyzed by Low‐Valent Iron Complexes with Bisiminopyridine Ligands

Salanouve¹,

Bouzemame²,

Blanchard³

et al. 2014

Chemistry A European J

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Tandem C-H activation/arylation between unactivated arenes and aryl halides catalyzed by iron complexes that bear redox-active non-innocent bisiminopyridine ligands is reported. Similar reactions catalyzed by first-row transition metals have been shown to involve substrate-based aryl radicals, whereas our catalytic system likely involves ligand-centered radicals. Preliminary mechanistic investigations based on spectroscopic and reactivity studies, in conjunction with DFT calculations, led us to propose that the reaction could proceed through an inner-sphere C-H activation pathway, which is rarely observed in the case of iron complexes. This bielectronic noble-metal-like behavior could be sustained by the redox-active non-innocent bisiminopyridine ligands.

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Section: Resultsmentioning

confidence: 99%

Tandem CH Activation/Arylation Catalyzed by Low‐Valent Iron Complexes with Bisiminopyridine Ligands

Salanouve¹,

Bouzemame²,

Blanchard³

et al. 2014

Chemistry A European J

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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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“…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.…”

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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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Cobalt‐Catalyzed Direct Arylation of Unactivated Arenes with Aryl Halides

Cited by 98 publications

References 110 publications

Tandem CH Activation/Arylation Catalyzed by Low‐Valent Iron Complexes with Bisiminopyridine Ligands

Tandem CH Activation/Arylation Catalyzed by Low‐Valent Iron Complexes with Bisiminopyridine Ligands

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

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

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