Aryl, from aromatic compounds

Dickerman, S.C., Weiss, K. (1957) Arylation of aromatic compounds by the Meerwein reaction. Evidence for aryl radicals from orientation studies. J. Org. Chem. 22, 1070. 

Diaryl tellurium dichlorides, obtainable from aromatic compounds and tellurium tetrachloride, react with excess bromine or iodine in refluxing DMF or acetonitrile in the presence of a metal fluoride to give aryl halides in low yields. The reactions with chlorinating agents are very sluggish. The reaction of bromine and bis[4-methoxyphenyl] tellurium dichloride formed 2,4-dibromomethoxybenzene in 76% yield. Reactions of these tellurium dichlorides with copper(I) cyanide in DMF produced aryl cyanides in yields of less than 8%3. 

Intermolecular reductive couplings between aromatic rings mostly involve either reactive aryl cr-radicals, for example, derived from aromatic halides by cleavage of the radical anions, or relatively stable 7r-radical anions derived from aromatic compounds activated by electron-withdrawing substituents. 

Reaction of electron-rich aromatic compounds with TTFA leads to intermolecular oxidative coupling to form the corresponding biaryls without aromatic thallation. The reaction proceeds through one-electron transfer from aromatic compounds to Tl(III) to give an aromatic radical cation which leads to biaryls (Schemes 9.52 and 9.53 [52]). Intramolecular aryl coupling also occurs (Schemes 9.54 [53] and 9.55 [54]) and, further, when the carboxylic acid moiety is present, intramolecular as well as intermolecular lactonization occurs (Schemes 9.56 [55] and 9.57 [56]). 

Since Grignard reagents can easily be obtained from aryl halides, they are of special value in the s nthesis of many aromatic compounds, particularly as, for reasons already stated (pp. 270, 276), aromatic compounds cannot generally be prepared by means of ethyl acetoacetate and ethyl malonate. 

Unsymmetrical diaryls may be prepared by treating an aryl diazonium salt solution with sodium hydroxide or sodium acetate in the presence of a liquid aromatic compound. Thus 2-chlorodiphenyl is readily formed from o-chloro phenyl diazonium chloride and sodium hydroxide solution (or sodium acetate solution) in the presence of benzene ... 

This last result bears also on the mode of conversion of the adduct to the final substitution product. As written in Eq. (10), a hydrogen atom is eliminated from the adduct, but it is more likely that it is abstracted from the adduct by a second radical. In dilute solutions of the radical-producing species, this second radical may be the adduct itself, as in Eq. (12) but when more concentrated solutions of dibenzoyl peroxide are employed, the hydrogen atom is removed by a benzoyloxy radical, for in the arylation of deuterated aromatic compounds the deuterium lost from the aromatic nucleus appears as deuterated benzoic acid, Eq. (13).The over-all reaction for the phenylation of benzene by dibenzoyl peroxide may therefore be written as in Eq, (14). 

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. 

In Figure 13.2, the intensity of the ion at m/z 170 represents a molecular ion of an aromatic compound. The characteristic losses from the molecular ion (M - 1, M - 28, and M - 29) suggest an aromatic aldehyde, phenol, or aryl ether. The molecular formula of Ci2H 0O is suggested by the molecular ion at m/z 170, which can be either a biphenyl ether or a phenylphenol. The simplest test to confirm the structure is to prepare a TMS derivative, even though m/z 11 strongly indicates the diaryl ether. 

Other MOCVD compounds are the aryls, which are formed from aromatic hydrocarbons, that is compounds that have six-member rings with three carbon double bonds, such as phenyl shown below ... 

Diaryl sulfones can be formed by treatment of aromatic compounds with aryl sulfonyl chlorides and a Friedel-Crafts catalyst. This reaction is analogous to Friedel-Crafts acylation with carboxylic acid halides (11-14). In a better procedure, the aromatic compound is treated with an aryl sulfonic acid and P2O5 in polypho-sphoric acid. Still another method uses an arylsulfonic trifluoromethanesulfonic anhydride (ArS020S02CF3) (generated in situ from ArS02Br and CF3S03Ag) without a catalyst. ... 

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