Arenes coupling with diazonium

Arylamines are converted by diazotization with nitrous acid into arenediazonium salts, ArN2+ X-. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. Aryl chlorides, bromides, iodides, and nitriles can be prepared from arenediazonium salts, as can arenes and phenols. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines to give brightly colored azo dyes. 

The presence of amino substituents in the 2- or 5-position activates the oxazole ring (4-aminooxazoles are unknown). Thus 2-amino-3-aryloxazoles yield the derivatives (127 X = Cl or Br) on halogenation, and nitration of 2-dimethylamino-4-phenyloxazole afforded 2-dimethylamino-5-nitro-4-(4-nitrophenyl)oxazole, the sole example of direct nitration of the oxazole ring. 5-Dialkylamino-2-phenyloxazoles react with trifluoroacetic anhydride to form the ketones (128) and they couple with arene diazonium fluoroborates the products (129) readily rearrange to 1,2,4-triazoles (130) in DMSO solution. 

A series of upper rim pyridyl azo calix[M]arenes ( = 4,6,8) have been synthesized by coupling calix[n]arenes with diazonium salts derived from 3-, 4-aminopyridine. In these reactions, the dizonium salt of... 

Potassium acetate, phase-transferred by 18-crown-6 from the solid into nonpolar solvents, catalyses the formation from arene diazonium tetrafluoroborates of aryl radicals (Scheme 53),-which in aromatic solvents couple with the solvent to... 

Azo compounds have the general formula R -N=N-R, where R and R are alkyl or aryl groups. Aromatic azo compounds are generally strongly colored and many are easily prepared via a so-called diazo coupling reaction, in which a diazonium cation is coupled with a relatively active (i.e., highly nucleophilic) arene such as a phenol or aniline. The dye called aniline yellow, for example, is prepared as follows ... 

Gilman reaction dimethyl cuprate undergoes C-C bond coupling with methyliodide in the Gas Phase the preferred mechanism for Cu involves the formation of a T-shaped Cu transition state. Heck reaction key ionic intermediates of the Heck reaction of arene diazonium salts were intercepted and structurally characterized. Baylis-Hillman reaction protonated intermediates in the catalytic cyde of the Baylis-Hillman reaction between an activated alkene and an electrophile were intercepted and characterized, providing dired evidence for the currently accepted mechanism. 

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... 

An analogous regioselective effect of silver ions on an addition reaction of arene-diazonium ions was found by Ignasiak et al. (1975) with cyanide salts. Potassium cyanide yields diazocyanides (Ar— N2 — C = N see Sec. 6.6), i.e., C-coupling products, but with silver cyanide - albeit in low yield (7-9%) - diazoisocyanides (Ar—N2 — N = C) are formed (a better synthesis of diazoisocyanides is described in Sec. 6.4). 

The azo coupling reaction of the calix[4]arene 12.32 shows an unexpected auto-catalytic effect. If the molar ratio of the diazonium ion (X=N02) to the calix[4]arene is 4 1, the yield of the tetra(arylazo)calix[4]arene 12.33 is 99%, but with ratios 3 1, 2 1, and 1 1 the tetra(arylazo) compound is also a major product (70%, 45%, and 22% respectively). If ratios 3 1, 2 1, and 1 1 are used the yields of the tris- and bis(arylazo) products are in the range of only 1.2-3.4%, and the mono(arylazo) compound is formed with a yield of 5.3-6.0%. Using the ratio 4 1 the bis- and mono(arylazo) products are not found at all, and the tris(arylazo) com-... 

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. 

Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group. Coupling reaction of aryldiazonium salts with phenols or arylamines give rise to the formation of azo dyes. 

Scheme 9. Proposed mechanism for the Suzuki cross-coupling reaction of arene diazonium salts with potassium organotrifluoroborates based on ESl-MS investigation, m/z vaiues are given for cationic intermediates observed by ESl(+)-MS.

Azo-coupling reactions of aromatic compounds with arene diazonium salts, which are usually very fast, have been successfully carried out in... 

With the aim of preparing elaborate molecules in the solid phase, chemists are searching for robust and versatile methods to assemble complex carbon frameworks in the insoluble support. One of the predominant sequences for creating carbon-carbon bonds in the solid phase is Pd-catalysed coupling reactions. The Heck reaction, for instance, is a convenient way to diversify activated alkenes (Scheme 5a). This coupling involves an arene with iodide, bromide, triflate or diazonium on one hand, and an alkene (generally electron poor) on the other, in the presence of a catalyst and a base. 

This reaction is the most simple method for synthesis of these structures beside several recent methods based on cross-coupling reactions with different organometallic reagents. The starting materials are very inexpensive and easily available, whereas an excess of arene can be regenerated by distillation of the filtrate after the separation of potassium tetrafluoroborate. This can be also reused as a precipitation reagent for preparation of the parent aryldiazonium tetrafluoroborate from the diazonium chloride... 

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