Metal‐Free Cross‐Coupling Reactions of Aryl Sulfonates and Phosphates through Photoheterolysis of Aryl–Oxygen Bonds

Carolis, Marco De; Protti, Stefano; Fagnoni, Maurizio; Albini, Angelo

doi:10.1002/ange.200461444

Cited by 28 publications

(12 citation statements)

References 43 publications

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“…A radically different approach for the synthesis of aryl acetylenes is presented here, and is based on the use of phenyl cations. In the last few years we have demonstrated that these intermediates (in the triplet state) are obtained smoothly by photolysis of aryl halides substitued with electron‐donating groups (for example, chlorophenol15 or fluoroanilines16), aryl sulfonates, and aryl phosphates (for example, methoxyphenyl mesylate or N , N ‐dimethylaminophenyl phosphate),17 and add to alkenes to form an arylC bond via a phenonium ion 15a. 18 We surmised that phenyl cations would react with triple bonds to yield β‐phenylvinyl cations, or more probably cyclic vinylenebenzenium ions (Scheme ).…”

Section: Methodsmentioning

confidence: 99%

Photo‐Cross‐Coupling Reaction of Electron‐Rich Aryl Chlorides and Aryl Esters with Alkynes: A Metal‐Free Alkynylation

2005

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Section: Methodsmentioning

confidence: 99%

Photo‐Cross‐Coupling Reaction of Electron‐Rich Aryl Chlorides and Aryl Esters with Alkynes: A Metal‐Free Alkynylation

2005

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“…[27] Another "innocent" anion was PF 6 À , [6b] but the high viscosity of 2 b hampered an efficient arylation reaction. As for the mesylate anion, its coupling with phenyl cation may go undetected, since 4-aminophenylmesylate undergo itself photoheterolysis [28] leading back to the cation. At any rate, no mesylate was detected.…”

Section: ) Photolysis Of 1 Was Effective In Ils Previous Work Hadmentioning

confidence: 96%

Characterizing Ionic Liquids as Reaction Media through a Chemical Probe

Dichiarante

Betti

Fagnoni

et al. 2007

Chemistry A European J

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The triplet N,N-dimethylaminophenyl cation, a highly reactive but chemospecific electrophile, has been used as a probe for characterizing the properties of reaction media for a series of imidazolium ILs. With the N-hexyl-N-methyl imidazolium derivatives (not with the N-butyl analogues), hydrogen transfer leading to the aniline was the main process. Trapping by iodide occurred with an inverse dependence on viscosity. Trapping by pi nucleophiles exhibited a more complex behavior. This was explained by the effect of both the bulk viscosity and the structure of the IL cation on both steps of the reaction, namely, initial electrophilic attack and ensuing cation elimination or nucleophile addition. However, with an excellent nucleophile, such as thiophene, or when the latter step was intramolecular, as with 4-pentenol, the difference was obliterated and trapping became uniform. Incorporation of the probe into the IL cation (through insertion into the C--H bond alpha to the imidazolium ring) was demonstrated, while no addition to the anion tested (including bis(trifluoromethanesulfonimide)) took place.

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“…EPR spectra of the phenyl cation have been obtained by photolysis of some phenyl diazonium ions in EtOH at 77 K, [8] and only recently, the IR spectrum of the phenyl cation was obtained by photolysis of phenyl iodide in an argon matrix at 4 K in which the phenyl radical is formed and gives the cation by ensuing electron transfer. [9] Recently, a class of reactions has emerged in which C À C bond formation has been achieved by the photolysis of electron-donating substituted aryl halides [10] or esters [11] in the presence of carbon nucleophiles, for example, alkenes, alkynes, or (hetero)aromatics, with little competing solvolysis. These reactions have been rationalized in terms of trapping of the triplet phenylium ion (I, Scheme 1), which generates further cationic intermediates, for example, the phenonium ion (the cyclopropanespirocyclohexadienyl cation, II) in the case of alkenes.…”

Section: Abstract: Aryl Cations · Carbo-a C H T U N G T R E N N U N Gmentioning

confidence: 99%

Revealing Phenylium, Phenonium, Vinylenephenonium, and Benzenium Ions in Solution

Manet

Monti

Grabner

et al. 2008

Chemistry A European J

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The 4-methoxyphenylium ion has been generated in the triplet state ((3)An(+)) by photolysis of 4-chloroanisole in polar media and detected by flash photolysis (lambda(max)=400 nm). This is the first detection of a phenylium ion in solution by flash photolysis and the assignment is supported by time-dependent density functional theory (TD-DFT) calculations. In neat solvents, the cation was reduced to anisole, a process initiated by electron transfer from the starting compound ((3)An(+)+AnCl-->An(*)+AnCl(*+), with the radical cation detected at 470 nm, then An(*)-->AnH). Addition of pi nucleophiles to the (3)An(+) cation offers a novel access to a number of other cationic intermediates under mild, nonacidic conditions. Two intermediates are successively formed with alkenes, a diradical cation and the phenonium ion, which are detected at 440 and 320 nm, respectively, by flash photolysis and are in accordance with calculations. Allylanisoles or beta-alkoxyalkylanisoles are the end products, with a small amount of alpha-alkoxyalkylanisoles that arises from a Wagner-Meerwein rearrangement to form benzyl cations. Further intermediates that have been predicted and detected are the phenylvinylium ion, possibly in equilibrium with the vinylenephenonium ion, with 1-hexyne (lambda(max)=340 nm) and the benzenium ion with benzene (lambda(max)=380 nm). The final products were anisylhexyne and methoxybiphenyl (an analogous product and intermediate were detected with thiophene).

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Metal‐Free Cross‐Coupling Reactions of Aryl Sulfonates and Phosphates through Photoheterolysis of Aryl–Oxygen Bonds

Cited by 28 publications

References 43 publications

Photo‐Cross‐Coupling Reaction of Electron‐Rich Aryl Chlorides and Aryl Esters with Alkynes: A Metal‐Free Alkynylation

Photo‐Cross‐Coupling Reaction of Electron‐Rich Aryl Chlorides and Aryl Esters with Alkynes: A Metal‐Free Alkynylation

Characterizing Ionic Liquids as Reaction Media through a Chemical Probe

Revealing Phenylium, Phenonium, Vinylenephenonium, and Benzenium Ions in Solution

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