Catalytic Friedel–Crafts C−H Borylation of Electron‐Rich Arenes: Dramatic Rate Acceleration by Added Alkenes

Yin, Qin; Klare, Hendrik F. T.; Oestreich, Martin

doi:10.1002/anie.201611536

Cited by 117 publications

(78 citation statements)

References 69 publications

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“…The examples shown were used in recent studies by the groups of Ingleson, Fontaine and Repo et al., respectively. We have now found that borylation of arenes and heteroarenes with replacement of a C−H bond by the respective C−Bcat (or in a few cases C−Bpin) functionalities can very efficiently be carried out under mild conditions using some specific geminal bis‐borane catalysts featuring strongly electrophilic BC 6 F 5 moieties . First representative examples of such metal‐free catalytic heteroarene borylation reactions will be described in this account.…”

Section: Methodsmentioning

confidence: 99%

“…Similarly, the HBcat p ‐borylation of the derivatives 10 b , c catalyzed by 4 gave the products 12 b (78 %) and 12 c (88 %), respectively (see the Supporting Information for their characterization). On the basis of the respective literature precedence, we assume a pathway that involves formation of reactive borenium‐type intermediates by means of hydride transfer to the chelate bis‐borane catalysts. We carried out a similar experiment as described by Oestreich et al.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Metal‐Free Arene and Heteroarene Borylation Catalyzed by Strongly Electrophilic Bis‐boranes

Liu

Kehr

Daniliuc

et al. 2017

Chemistry A European J

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Abstract:The geminal chelate bis-borylalkanes 4 and 5 featuring strongly electrophilicB (C 6 F 5 ) 2 and B(C 6 F 5 )g roups, respectively,s erve as efficient catalysts for the borylation of arenes and heteroarenes. The borylation reactions proceed under mild conditions with liberation of dihydrogen.Aryl-and heteroarylboronates are of great synthetic importance especially in view of their widespreadu tilization as cross-coupling reagents. [1] Various synthetic entries into this class of compounds have been developed, [2] many of which involve metal-catalyzed borylation reactions with CÀHa ctivation. [3][4][5][6] In the recent years, an increasing number of metal-free arene and heteroarene borylation reactions were disclosed. [7][8][9][10] Many made use of strongly electrophilic stoichiometricb oronderived reagents, [7, 8] among them variouss ources of reactive boreniumi ons. [9,10] Lately,f ew examples of catalytic variants of such borylation reactions were reported. Scheme1 shows as mall series of catalysts and catalyst precursors. The examples shownwere used in recent studies by the groupsofIngleson, [11] Fontaine [12] and Repo et al., [8c] respectively.W eh ave now found that borylation of arenes and heteroarenes with replacemento faC ÀHb ond by the respective CÀBcat (or in af ew cases CÀBpin) functionalities can very efficiently be carried out under mild conditions using some specificg eminal bis-borane catalysts featuring strongly electrophilicB C 6 F 5 moieties. [13] First representative examples of such metal-free catalytic heteroarene borylation reactions will be described in this account.The geminal bis-borane 4 is readily preparedb yatwo-fold anti-Markovnikovh ydroboration reaction of 4-phenylbutyne with HB(C 6 F 5 ) 2 in analogy to similard ouble acetylene hydroborations as reported by Piers et al. [14] We had recently described the formationo ft he heterocyclic geminal bis-borane 5 by meanso ft he reaction of cyclopropyla cetylene with the HB(C 6 F 5 ) 2 reagent, ar eaction that proceeded with as elective rearrangement. [15] The geminal bis-borane 5 was used as an effective catalyst for the CÀHa ctivating borylation reaction of Nmethylindole (6a)w ith catecholb orane [HBcat].T he catalytic borylation reactionw as performed under mild conditions (typically at RT,1h, in dichloromethane) with 1mol %o ft he catalyst 5.W ork-up involving crystallization at À35 8Cb yc overing with ap entanel ayer gave the 3-boryl-N-methylindole product 7a in approximately 59 %y ield. The product wasi dentified by the NMR spectra and by X-ray crystal structure analysis (for details see the Supporting Information). In situ investigation of the reaction in CD 2 Cl 2 by NMR spectroscopy revealed that the overall reactionint his case was slightly more complicated.Formationo ft he borylation product 7a was accompanied by as ubstantial amounto ft he boron-free reduction product Nmethylindoline (8a), [4, 6g, 16] formed as its HBcat N/B Lewis pair adduct 8a·HBcat (see the Supporting Information for its characterization). With ...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Metal‐Free Arene and Heteroarene Borylation Catalyzed by Strongly Electrophilic Bis‐boranes

Liu

Kehr

Daniliuc

et al. 2017

Chemistry A European J

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“…Simultaneously, the eliminated proton from the enol form can activate the keto form of 1 a by generating a Lewis acid ( + NH 2 (Me) 2 ). Here, the proton-shuttling [28] action of dimethylamine facilitats the formation of the persistent ketyl radical A and transient a-carbonyl radical B by fac-Ir(ppy) 3 under visiblelight irradiation. As a result, the transient a-carbonyl radical B could be selectively intercepted by alkynes to synthesize 1naphthols 8-1 and the persistent ketyl radical A dimerizes to pinacols 9 a + 9 a'.…”

Section: Photoredox Catalysis Of Aromatic B-ketoesters For In Situ Prmentioning

confidence: 98%

Photoredox Catalysis of Aromatic β‐Ketoesters for in Situ Production of Transient and Persistent Radicals for Organic Transformation

et al. 2020

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Radical formation is the initial step for conventional radical chemistry. Reported herein is a unified strategy to generate radicals in situ from aromatic β‐ketoesters by using a photocatalyst. Under visible‐light irradiation, a small amount of photocatalyst fac‐Ir(ppy)3 generates a transient α‐carbonyl radical and persistent ketyl radical in situ. In contrast to the well‐established approaches, neither stoichiometric external oxidant nor reductant is required for this reaction. The synthetic utility is demonstrated by pinacol coupling of ketyl radicals and benzannulation of α‐carbonyl radicals with alkynes to give a series of highly substituted 1‐naphthols in good to excellent yields. The readily available photocatalyst, mild reaction conditions, broad substrate scope, and high functional‐group tolerance make this reaction a useful synthetic tool.

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“…In a few cases, Friedel-Crafts-type catalysis could be observed for the TM-free catalytic borylation of arenes, in mechanisms that bear little similarity to TM chemistry. 152,154,158,[161][162][163] Similar reactions are typically metal catalyzed, 164,165 often by precious metals such as iridium or palladium, which act in tandem with an internal base.…”

Section: Arene C-h Activationmentioning

confidence: 99%

Metallomimetic Chemistry of Boron

2019

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The study of main-group molecules that behave and react similarly to transition metal (TM) complexes has attracted significant interest in the recent decades. Most notably, the attractive idea of eliminating the all-too-often rare and costly metals from catalysis has motivated efforts to develop main-group-element-mediated reactions. Main-group elements, however, lack the electronic flexibility of many TM complexes that arise from combinations of empty and filled d-orbitals and that seem ideally suited to bind and activate many substrates. In this Review, we look at boron, an element which, despite its non-metal nature, low atomic weight, and relative redox staticity has achieved great milestones in terms of TM-like reactivity. We show how in inter-element cooperative systems, diboron molecules and hypovalent complexes, the fifth element can acquire a truly metallomimetic character. As we discuss, this character is particularly strikingly demonstrated by the reactivity of boron-based molecules with H2, CO, alkynes, alkenes and even with N2.

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Catalytic Friedel–Crafts C−H Borylation of Electron‐Rich Arenes: Dramatic Rate Acceleration by Added Alkenes

Cited by 117 publications

References 69 publications

Metal‐Free Arene and Heteroarene Borylation Catalyzed by Strongly Electrophilic Bis‐boranes

Metal‐Free Arene and Heteroarene Borylation Catalyzed by Strongly Electrophilic Bis‐boranes

Photoredox Catalysis of Aromatic β‐Ketoesters for in Situ Production of Transient and Persistent Radicals for Organic Transformation

Metallomimetic Chemistry of Boron

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