Tuning Reactivity and Site Selectivity of Simple Arenes in C–H Activation: Ortho-Arylation of Anisoles via Arene–Metal π-Complexation

Ricci, Paolo F.; Krämer, Katrina; Larrosa, Igor

doi:10.1021/ja510260j

Cited by 50 publications

(22 citation statements)

References 70 publications

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“…However, the site-selective functionalization of the C–H bonds in simple arenes lacking a directing group and lacking a series of strongly activating groups remains challenging . Although there have been reports on site-selective functionalizations of simple arenes to form C(aryl)–C(sp 2 ) bonds, , simple arenes have not been reported to undergo site-selective formation of C(aryl)–C(sp 3 ) bonds by reactions with C(sp 3 ) electrophiles . Yet, such reactions would be valuable because the substrate scope and site selectivity would complement those of electrophilic aromatic substitution (Friedel–Crafts reactions) in which electron-rich arenes are more reactive than electron-poor arenes…”

Section: Introductionmentioning

confidence: 99%

Palladium-Catalyzed, Site-Selective Direct Allylation of Aryl C–H Bonds by Silver-Mediated C–H Activation: A Synthetic and Mechanistic Investigation

2016

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We describe a method for the site-selective construction of a C(aryl)–C(sp3) bond by the palladium-catalyzed direct allylation of arenes with allylic pivalates in the presence of AgOPiv to afford the linear (E)-allylated arene with excellent regioselectivity; this reaction occurs with arenes that have not undergone site-selective and stereoselective direct allylation previously, such as monofluorobenzenes and non-fluorinated arenes. Mechanistic studies indicate that AgOPiv ligated by a phosphine reacts with the arene to form an arylsilver(I) species, presumably through a concerted metalation–deprotonation pathway. The activated aryl moiety is then transferred to an allylpalladium(II) intermediate formed by oxidative addition of the allylic pivalate to the Pd(0) complex. Subsequent reductive elimination furnishes the allyl–aryl coupled product. The aforementioned proposed intermediates, including an arylsilver complex, have been isolated, structurally characterized, and determined to be chemically and kinetically competent to undergo the proposed elementary steps of the catalytic cycle.

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Section: Introductionmentioning

confidence: 99%

Palladium-Catalyzed, Site-Selective Direct Allylation of Aryl C–H Bonds by Silver-Mediated C–H Activation: A Synthetic and Mechanistic Investigation

2016

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“…In most cases, functionalities with an α-heteroatom have not been related essentially with the term of cyclopalladation or directed C–H activation, since the supposed 4-membered palladacycles might have a high degree of strain preventing their formation. A series of experimental works have proved that the aromatics, like anisole, chlorobenzene and their derivatives, were commonly inefficient toward C–H activations by the use of catalytic Pd(OAc) 2 or PdCl 2 . However, they displayed moderate-to-high performance under more demanding reaction conditions, especially using excess aromatic substrates, such as 10 to 100 equiv, or even the cosolvents.…”

Section: Introductionmentioning

confidence: 99%

An Explicit Interpretation of the Directing Group Effect for the Pd(OAc)₂-Catalyzed Aromatic C–H Activations

Zhang

Fang

2016

J. Org. Chem.

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A comprehensive DFT investigation has been performed for a series of the Pd(OAc)2-catalyzed C-H activations, updating and extending the understanding of directing group effect. In the beginning, the directed and undirected C-H activation mechanisms, based on 10 model reactions, have been discussed comparatively, which disclosed that directing group can exert a thermodynamic driving force, not necessarily a kinetic promotion, on the C-H activation process. Formation of the open palladation species via the undirected pathway is thermodynamically unspontaneous (ΔG = 4-9 kcal/mol), in sharp contrast to that of the cyclopalladation species via the directed pathway (ΔG < 0). Further calculations revealed that the free-energy barriers of proton-transfer are in fact not so high on the undirected pathway (17-24 kcal/mol), while mediation of some O-center groups in the directed pathway would increase the free-energy barriers of proton-transfer. For pyridine N-oxide systems, the undirected mechanism was estimated to be more plausible than the 4-member-directed one both thermodynamically and kinetically. In addition, the uncommon 7-membered cyclopalladation has been tentatively explored using two current examples, predicting that electron-rich directing groups can help to stabilize the 7-membered palladacycles formed.

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“…We recently reported a Pd-catalyzed methodology for the C–H arylation of electron-deficient (arene)Cr(CO) 3 complexes with iodoarenes as coupling partners (Scheme ). As is common in this type of process, we found that stoichiometric Ag 2 CO 3 was required, nominally to scavenge the iodide formed during the reaction. A typical Pd(0/II)-type catalytic cycle (mechanistic proposal A in Scheme ), as proposed in most C–H arylation methodologies, could account for these results.…”

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confidence: 99%

Ag(I)-Catalyzed C–H Activation: The Role of the Ag(I) Salt in Pd/Ag-Mediated C–H Arylation of Electron-Deficient Arenes

2016

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ABSTRACT:The use of stoichiometric Ag(I)-salts as additives in Pd-catalyzed C-H functionalization reactions is widespread. It is commonly proposed that this additive acts as an oxidant or as a halide scavenger promoting Pd-catalyst turnover. We demonstrate that, contrary to current proposals, phosphine ligated Ag(I)-carboxylates can efficiently carry out C-H activation on electrondeficient arenes. We show through a combination of stoichiometric and kinetic studies that a (PPh 3 )Ag-carboxylate is responsible for the C-H activation step in the Pd-catalyzed arylation of Cr(CO) 3 -complexed fluorobenzene. Furthermore, the reaction rate is controlled by the rate of Ag(I)-C-H activation, leading to an order zero on the Pd-catalyst. H/D scrambling studies indicate that this Ag(I) complex can carry out C-H activation on a variety of aromatic compounds traditionally used in Pd/Ag-mediated C-H functionalization methodologies.

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Tuning Reactivity and Site Selectivity of Simple Arenes in C–H Activation: Ortho-Arylation of Anisoles via Arene–Metal π-Complexation

Cited by 50 publications

References 70 publications

Palladium-Catalyzed, Site-Selective Direct Allylation of Aryl C–H Bonds by Silver-Mediated C–H Activation: A Synthetic and Mechanistic Investigation

Palladium-Catalyzed, Site-Selective Direct Allylation of Aryl C–H Bonds by Silver-Mediated C–H Activation: A Synthetic and Mechanistic Investigation

An Explicit Interpretation of the Directing Group Effect for the Pd(OAc)₂-Catalyzed Aromatic C–H Activations

Ag(I)-Catalyzed C–H Activation: The Role of the Ag(I) Salt in Pd/Ag-Mediated C–H Arylation of Electron-Deficient Arenes

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Tuning Reactivity and Site Selectivity of Simple Arenes in C–H Activation: Ortho-Arylation of Anisoles via Arene–Metal π-Complexation

Cited by 50 publications

References 70 publications

Palladium-Catalyzed, Site-Selective Direct Allylation of Aryl C–H Bonds by Silver-Mediated C–H Activation: A Synthetic and Mechanistic Investigation

Palladium-Catalyzed, Site-Selective Direct Allylation of Aryl C–H Bonds by Silver-Mediated C–H Activation: A Synthetic and Mechanistic Investigation

An Explicit Interpretation of the Directing Group Effect for the Pd(OAc)2-Catalyzed Aromatic C–H Activations

Ag(I)-Catalyzed C–H Activation: The Role of the Ag(I) Salt in Pd/Ag-Mediated C–H Arylation of Electron-Deficient Arenes

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An Explicit Interpretation of the Directing Group Effect for the Pd(OAc)₂-Catalyzed Aromatic C–H Activations