Coupling of aryl diazonium salts

Although coupling of aryl diazonium salts at the -position of dienamines yields indazoles on acid-catalysed cyclization, the presence of an electron-donor substituent may render the aromatic ring sufficiently nucleophilic to cyclize onto the iminium group to give cinnolines or 6,7-diazasteroids2,67 (Scheme 40). 

Tricarbonyl monohydrazones (e.g. (252)), prepared by classical Japp-Klingermann coupling of aryl diazonium salts with j8-dicarbonyl compounds, undergo condensation with sulfamide to yield... 

Scheme 16 Cross-coupling of aryl diazonium salts and olefins mediated by in situ generated Pd/NHC system...

Scheme 4.10 Pd-catalyzed carbonylative coupling of aryl diazonium salts...

A reaction of aryl diazonium salts that does not involve loss of nitrogen takes place when they react with phenols and arylamines Aryl diazonium ions are relatively weak elec trophiles but have sufficient reactivity to attack strongly activated aromatic rings The reaction is known as azo coupling two aryl groups are joined together by an azo (—N=N—) function... 

In a basic medium, 5-nitro-5-hydroxymethyltetrahydro-l,3-oxazine derivatives can be coupled with aryl diazonium salts to form aryl-azo derivatives (54) with the elimination of a molecule of formaldehyde. ... 

These pigments are obtained by coupling substituted aryl diazonium salts with ary-lides of 2-hydroxy-3-naphthoic acid (2-hydroxy-3-naphthoic acid anilide = Naph-tol AS). They provide a broad range of colors from yellowish and medium red to bordeaux, carmine, brown, and violet their solvent fastness and migration resistance are only marginal. Naphthol AS pigments are used mainly in printing inks and paints. 

The Gomberg coupling reaction of aryl diazonium salts with arenes is catalysed by quaternary ammonium salts [49], Although yields are variable, they are generally >50% [49, 50]. When aromatic solvents other than benzene are used, the appropriate biaryls are produced, e.g. 4-chlorobenzenediazonium tetrafluoroborate reacts with chlorobenzene to produce the 2,4 -, 3,4 - and 4,4 -dichlorobiphenyls in a ca. 67 18 15 ratio. 

An old reaction patented by Lange [19] involves the coupling of naphthyl-diazonium salts with sodium sulfite to yield azonaphthalene. A more recent study of this reaction indicates that the first step of the reaction is the formation of an aryl-iyn-diazosulfonate which couples with another molecule of a diazonium salt and by a multicentered rearrangement ultimately affords an azo compound [20, 21]. The reaction is represented in Eq. (7). The validity of... 

Semicarbazones of /J-nitrocarbonyl compounds have been coupled with aryl diazonium salts and the resulting hydrazones cyclized by acid to the 3-nitropyrazoles 43 (Scheme 9).36... 

The versatility of the method is founded on the possibility of grafting a variety of functionalised aryl groups. This allows the attachment of a wide spectrum of substances[60]. In 1992, a study by Delamar and co-workers [61] demonstrated that reduction of diazonium salts at carbon surfaces resulted in a strongly attached surface layer. They attributed this to covalent bond formation between the aryl radical and the carbon surface [61,62], One electron reduction of aryl diazonium salts at carbon electrodes leads to grafting of aryl groups to the surface. Acetonitrile is often used as the modification medium. Reduction of the diazonium salt can be achieved by cyclic voltammetry or controlled potential electrolysis. The coupling reaction is favored both by the adsorption of the diazonium prior to its reduction and by the relatively positive potential of the diazonium prior to its reduction[62],... 

The Pd )-catalyzed reaction of aryl diazonium salts with mono-substituted alkenes [1] was found to be an interesting alternative to the well-known Pd - catalyzed arylhalide alkene coupling (Heck type reaction) or the copper mediated reaction of aryl diazonium salts with alkenes (Meerwein arylation) [2], The reaction can be run without isolation of the diazonium salt in presence of only 0.5 to 1 mol% of the Palladium catalyst in a one pot procedure, in high yield and under nuld conditions. The resulting styrene is reduced in a subsequent hydrogenation step with an in situ generated heterogeneous Pd-catalyst. The combination of three reaction steps without isolation of intermediates and the virtually complete recovery of the Pd-metal at the end of the reaction sequence makes this process [4] extremely efficient. 

The Pschorr reaction is the intramolecular coupling of arenes involving aryl radicals generated by the reduction of aryl diazonium salts [68]. The reaction was extensively studied during the last 100 years [69]. This Cu(I)-catalysed reaction proceeds via an aryl diazenyl radical intermediate (Scheme 45) [70]. Non-protic solvents from which competitive hydrogen abstraction is impossible, are to be preferred [71]. 

Belmont, J. A., C. Bureau, M. M. Chehimi, S. Gam-Derouich, and J. Pinson. Patents and industrial applications of aryl diazonium salts and other coupling reagents, in Aryl Diazonium Salts. New Coupling Agents in Polymer and Surface Science. M. M. Chehimi (Ed.), Wiley-VCH, Weinheim, 2012. Chapter 14. 

C]malonate is sufficient to couple with aryl diazonium salts using aqueous sodium acetate as a base. In the presence of a tautomerizable hydrogen, the azo compound initially formed (e.g., 388) isomerizes to the corresponding hydrazone (e.g., 389). Derivatives of this structural class have been used for the preparation of binuclear heteroaromatic systems. Saponification of the ester groups of hydrazone 389. for example, generated... 

When an aqueous solution of a diazonium salt is added to an alkaline solution of a phenol, coupling occurs with formation of an azo-compound (p. 188). If ho vc cr the ntiueous solution of the diazonium salt, t. . ., />-bromohenzene diazonium chloride, is mixed with an excess of an aromatic hydrocarbon, and aqueous sodium hydroxide then added to the vigorously stirred mixture, the diazotate which is formed, e.g., BrC,H N OH, dissolves in the hydrocarbon and there undergoes decomposition with the formation of nitrogen and two free radicals. The aryl free radical then reacts with the hydrocarbon to give a... 

Azo coupling (Section 22 18) Formation of a compound of the type ArN=NAr by reaction of an aryl diazonium salt with an arene The arene must be strongly activated toward... 

---