Reactions of Aryldiazonium Ions

Another example is the reaction of aryldiazonium ions with nucleophiles in aqueous solution according to... 

A mechanism at the Sj 2Ar/Sj l boundary was proposed for the nucleophihc substitution reaction of aryldiazonium ions in water [86],... 

The known pentazoles are aryl derivatives which have the structure (3). They are obtained from the reaction of aryldiazonium ions with azide ion (Equation (2)). No alkylpentazoles are known and the reaction of diazomethane with HN3 which gives methyl azide has been shown by N-labelling not to pass through a pentazole intermediate <58HCA1823>. The parent NH-pentazole is unknown. The numbering system shown in (3) will be used in this chapter. 

The reaction of aryldiazonium ions with l-(4 -sulfophenyl)-3-methyl-pyrazolium-5-one (7.70) takes place at the 4-position, and the p factor for the effects of substituents in the aryl ring of the diazo ion is 3.29, similar to that for coupling at the 1-position of 2-hydroxynaphthalene-6-sulfuric acid (69CCC3895). For coupling at the 4-position of l-phenyl-2,3-dimeth-ylpyrazolium-5-one (7.71) the corresponding p factor was 3.60 (69CC3905). 

The Japp-Klingemann coupling of aryldiazonium ions with enolates and other nucleophilic alkenes provides an alternative route to arylhydrazones. The reaction has most frequently been applied to (Vketoesters, in which deacylation follows coupling and the indolization affords an indole-2-carboxylate ester. 

The mechanism classification and the overall transformation classification are orthogonal to each other. For example, substitution reactions can occur by a polar acidic, polar basic, free-radical, pericyclic, or metal-catalyzed mechanism, and a reaction under polar basic conditions can produce an addition, a substitution, an elimination, or a rearrangement. Both classification schemes are important for determining the mechanism of a reaction, because knowing the class of mechanism and the overall transformation rules out certtdn mechanisms and suggests others. For example, under acidic conditions, aromatic substitution reactions take place by either one of two mechanisms electrophilic addition-elimination or SnI substitution of aryldiazonium ions. Under basic conditions, they take place by one of three mechanisms nucleophilic addition-elimination, elimination-addition, or SrnI. If you know the class of the overall transformation and the class of mechanism, your choices are narrowed considerably. 

Scrambling of the nitrogen atoms during decomposition of aryldiazonium ions has been observed a study of the reaction in which secondary deuterium isotope measurements were carried out excluded the possibility of a benzene spirodiazirine similar to 193, and favoured a carbocation with closely associated nitrogen, which can collapse to reform the diazonium ion. 

Being much more stable than their aliphatic counterparts, aryldiazonium ions can undergo addition reactions in which nitrogen is not lost. Reactions of aryldiazonium salts... 

Aryl bromides or iodides react with di- or monochloro(vinyl)silanes or triethoxy(vinyl)silane in the presence of Et3N and palladium catalyst to give /S-arylvinylsilanes in moderate to excellent yields. In contrast to the simple silyl substituent, the presence of the electron-withdrawing group on sihcon is essential to avoid the elimination of the silyl group. No silver ion is necessary in these examples . The palladium-catalyzed reaction of aryldiazonium tetrafluoroborates with vinylsilanes gives a mixture of terminal and internal vinylsilanes together with styrenes. ... 

The crown catalyzed phase transfer of acetate ion into a nonpolar medium followed by reaction with aryldiazonium ion has also been shown to be an effective and mild method for the generation of aryl radicals [21 ]. Radicals thus generated can be reacted with deuteriochloroform or chloroform to yield deuterio- or protio-arenes. Reaction with bromotrichloromethane leads to the bromoarene and the reaction in benzene solution leads to unsymmetrical biphenyls in good yield [22]. These three processes are formulated in equation 15.7. 

Reaction of glycosylmethylamines with aryldiazonium salts gives a class of compounds which, by acid catalysis or unknown factors of enzymic catalysis, generate glycosylmethyldiazonium ions. These, in turn, lose nitrogen, to yield highly electrophilic carbenium ions, as illustrated for the ) -d-galactosyl derivative 38 (see Scheme 8). 

The use of iodoacetic acid as an aryl radical trapping agent has confirmed the intermediacy of aryl radicals in some hydrodediazoniation reactions, whether these are initiated or not.4 Spontaneous hydrodediazoniation of aryldiazonium fluoroborates occurs in warm dimethylformamide (DMF). Detailed study5 of the conversion of the 4-nitro derivative into nitrobenzene indicates a homolytic mechanism in which H-atom abstraction occurs from both sites in DMF with a formyl methyl preference of 3.5 1.0. High yields of mixed perfluorinated biaryls may be obtained by the catalytic dediazoniation of pentafluorobenzenediazonium ions in acetonitrile containing aromatic substrates and small amounts of iodide salts. The catalytic role of iodide and the isomeric product distributions indicate that arylation proceeds through the pentafluorophenyl radical in an efficient homolytic chain process.6... 

Aromatic Diazonium Ions. In contrast to alkyldiazonium ions, aryldiazonium ions are well-studied.469 77 They were known as early as 1894. They are isolable as ionic salts with a variety of counterions such as BIT, PF6, SbCl6, SbF6, AsF6-, and C104. They undergo a variety of nucleophilic reactions and an excellent review is available on the subject.478... 

Aryldiazonium ions and sodium azide react to form aryl azides. We did not mention this reaction in the discussion of the SN reactions of Ar—N2 (Section 5.4) because it belongs, at least in part, to the 1,3-dipolar cycloadditions. 

Although nitriles lack an acyl group, they are considered acid derivatives because they hydrolyze to carboxylic acids. Nitriles are frequently made from carboxylic acids (with the same number of carbons) by conversion to primary amides followed by dehydration. They are also made from primary alkyl halides and tosylates (adding one carbon) by nucleophilic substitution with cyanide ion. Aryl cyanides can be made by the Sandmeyer reaction of an aryldiazonium salt with cuprous cyanide. a-Hydroxynitriles (cyanohydrins) are made by the reaction of ketones and aldehydes with HCN. 

Aromatic fluorination A new method of aromatic fluorination involves treatment of aryltriazenes, readily prepared from aryldiazonium ions and dialkyl-amines, with 70% hydrogen fluoride in pyridine. The yields of product from this reaction are usually higher than those obtained by the reaction of HF-pyridine with a diazonium ion (6, 285) o-methoxy, iodo-, bromo- and nitro-substituted aryltriazenes generally give unsatisfactory yields. This method may be useful for the synthesis of " F-labeled compounds. 

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