Arenediazonium salts generation

Purpose, In this experiment you will learn the process of generating arene-diazonium salts in solution. The arenediazonium salt generated will be used... 

As an alternative to electrochemical or radiolytic initiation, homolytic dediazoniation reaction products can be obtained photolytically. The organic chemistry of such photolyses of arenediazonium salts will be discussed with regard to mechanisms, products, and applications in Section 10.13. In the present section photochemical investigations are only considered from the standpoint that the photolytic generation of aryldiazenyl radicals became the most effective method for investigating the mechanisms of all types of homolytic dediazoniations —thermal and photolytic —in particular for elucidating the structure and the dissociation of the diazenyl radicals. 

Perfluoroalkyl carbanions, generated by reversible nucleophilic addition of a fluoride anion to fluoroalkenes, react with dry benzenediazonium chloride in dimethyl formamide, giving phenylazoperfluoroalkanes in 41-53% yield (Dyatkin et al., 1972). The dianion obtained from 1,2-dinitrobenzene with dipotassium cyclo-octatetraenide reacts in a complex way with arenediazonium salts, forming 4-aryl-azo-2-nitrophenol in 46-58% yield (Todres et al., 1988). 

Apart from imidazol-2-ylidene carbenes, other electron-rich carbenes such as (L27)—generated by deprotonation of a 4,5-dihydroimidazole—have been tested for cross-coupling reactions, but gave much poorer results. The only reported exception is in the cross-coupling of arenediazonium salts with arylboronic acids, in which (L27) (used as hydrochloride) proved to be efficient.369... 

The generation of intermediate azidothiocarbonyl compounds 10 followed by 1,5-electrocyclic reaction leads to 5-substituted 1,2,3,4-thiatriazoles 9. This mechanism has been proposed in reactions of various derivatives of thiohy-drazides 136 with either nitrous acid or arenediazonium salts, and in reactions of thiophosgene (or dithiocarboxylates) 135 (X = C1, SR) with either sodium or trimethylsilyl azide (Scheme 32) <1984CHEC(6)579, 1996CHEC-II(4)691,... 

Heinrich MR (2009) Intermolecular olefin functionalisation involving aryl radicals generated from arenediazonium salts. Chem-Eur J 15 821-833... 

Heinrich MR (2009), Intermolecular Olefin Functionalisation Involving Aryl Radicals Generated from Arenediazonium Salts, Chem Eur J 15 820, Copyright Wiley-VCH Verlag GmbH Co. KGaA. Schemes 11,13 and 16 reproduced with permission... 

Indolines and indoles were prepared by a direct electrochemical reduction of arenediazonium salts. As a result, radical intermediates were generated from which 3,4-disubstituted tetrahydrofuran skeleta were constructed <02OL2735>. A short and stereoselective total synthesis of furano lignans was realized by radical cyclization of epoxides using a transition-metal radical source <02JOC3242>. Other preparations of tetrahydrofurans using radical cyclization include the synthesis of novel amino acids L-bis-... 

Cyanoxyl radicals were generated in situ by an electron-transfer reaction between cyanate anions and p-chlorobenzenediazonium cations arenediazonium salts were previously prepared in water through the diazotization reaction of p-chloroaniline. Copolymerizations were performed using the Step 2 product and acrylamide at 50°C with ClCgPLtNi BF4 /NaOCN as the initiating system. Copolymers were isolated by precipitation in a 10-fold excess of methanol and characterized. 

The first example of an intramolecular homolytic aromatic substitution was published by Pschorr more than a century ago [34], Biaryls were prepared by intramolecular homolytic substitution of arenes by aryl radicals which were generated by treatment of arenediazonium salts with copper(I) ions (Pschorr reaction). Later it has been shown that similar reactions can be conducted under basic conditions or by photochemical or thermal decomposition of the diazonium salts [35]. Electrochemical reduction [36], titanium (III) ions [37], Fe(II)-salts [38], tetrathiafulvalene... 

Azodiazocyclopentadienes 23, the open-chain tautomers of 27/-cyclopenta[/]-l,2,3,4-tetrazines 10, were generated through coupling of arenediazonium salts with diazocyclopentadienes, or via reaction of diazocyclopentadienes... 

In the initial demonstration of this concept, the aryl radical was obtained by the classic tin method (eq 2). Subsequently, by changing the radical precursor from a halogen to a diazonium ion and working in the presence of an appropriate source of electrons, it was possible to carry out the homolytic displacement reaction under stannane-free, nonreductive conditions. The method is based on work from the Beckwith laboratory, in which it was demonstrated that arenediazonium salts in the presence of electron donors, such as iodide and thiolate ions, can generate aryl radicals in a facile, clean reaction. 

Heck-Matsuda reaction. This reaction was first described in 1977 by Tsutomu Matsuda, who pointed out the unique reactivity of the arenediazonium salts in the Heck reaction, allowing a fast and direct generation of cationic aryl-palladium species in the reaction medium. Indeed, the high levels of chemo- and stereocontrol observed in these reactions usually do not depend on the use of halide scavengers (such Ag" or Tl salts), dry solvents, inert atmosphere, or phosphane hgands (Scheme 1) ... 

The Meerwein reaction between phenyl radicals, thermally generated from arenediazonium salts, and alkenes in the presence of copper(l) ions can also be initiated photochemically. Irradiation of the diaz-onium salt in the presence of copper(ll) ions leads to photoelectron transfer and the generation of phenyl radicals. Addition of the radical to an alkene bond becomes a chain reaction mediated by copper ions according to Scheme 5. Quantum yields for the evolution of nitrogen are in the region of 700. ... 

On the other hand, Hartman and Biffar (1977) reported that decomposition of arenediazonium tetrafluoroborates in dichloromethane in the presence of copper metal is catalysed by dicyclohexyl- 18-crown-6. Electron-withdrawing substituents in the aryl ring enhance the rate of the reaction. The main function of the crown ether is probably to solubilize the salt. The effect of the complexation on the rate was not investigated in detail. Similar enhanced solubilization of diazonium salts in apolar solvents was reported and used by Martin and Bloch (1971) in pyrolysis experiments aimed at the generation of the dehydrocyclopentadienyl anion. 

A new synthetically useful procedure for the preparation of arenediazonium tetrafluoroborates from the corresponding amines involves the in situ generation of nitrosyl fluoride (Scheme 53). The diazotization reactions are performed under mild conditions in an anhydrous solvent, preferably methylene chloride. Excess boron trifluoride etherate traps the alcohol and water produced, and the diazonium salts are precipitated from the reaction medium and isolated by simple filtration. 

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