Arenes to Biaryls

Diaryl telluriums refluxed in bis[2-methoxyethyl] ether over Raney-Nickel were converted in high yields to biaryls.  

Because diaryl telluriums can be prepared from aromatic hydrocarbons and tellurium followed by reduction of the diaryl tellurium dichlorides, the overall reaction sequence converts arenes to biaryls. The formation of benzene from diphenyl tellurium and Raney nickel was also reported.  

A palladium(O) catalyzed reaction in acetonitrile converted bis[4-methoxyphenyl] tellurium to 4,4 -dimethoxybiphenyl in quantitative yield.  

Alkyl phenyl telluriums and diaryl telluriums react with Grignard reagents in THF or diethyl ether in the presence of catalytic amounts of nickel- or cobalt-phosphane complexes. Tellurium is precipitated. The organic groups combine to form in most cases all three possible coupling products in ratios determined by reaction conditions . The reaction of ( Z,)-phenylethenyl phenyl tellurium and phenyl magnesium bromide formed almost exclusively ( Zj-stilbene in quantitative yield. ( ZJ-Ethoxycarbonylethenyl phenyl tellurium and phenyl magnesium bromide reacted differently ( Fj-ethoxycarbonyl-(phenyl)-ethene and diphenyl tellurium were produced. Tellurium was not formed.  

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The carboxylates of indium and thallium are obtained by dissolving the oxides in acid. Acetate and trifluoroacetate salts are used extensively as reagents in organic synthesis. Certain other thallium compounds have been used also. The trifluoroacetate, T1(02CCF3)3, will directly thallate aromatic compounds to give arylthal-lium species, for example, C6H5T1(02CCF3)2 (cf. aromatic mercuration, Section 15-15) and oxidize arenes to biaryls. 

Mechanisms of oxidative couplings of arenes to biaryls and polyaryls... 

In the presence of a Pd(0) catalyst, organozinc halides can couple directly with aryl and vinyl halides to form novel arenes or biaryls. 

Dohi T, Ito M, Morimoto K, Wata M, Kita Y (2008) Oxidative cross-coupling of arenes induced by single-electron transfer leading to biaryls by use of organoiodine(III) oxidants. Angew Chem Int Ed 47 1301-1304... 

It is also likely that radical cation formation occurs in reactions of very reactive arenes with Pd(II) (see Section II.B.3.b), which would also lead to biaryl formation. That the reactions of arenes with Pd(II) compounds are far from simple is illustrated by the work of Arzoumanidis and Rauch.573,574 In the reaction of Pd(02CCF3)2 with benzene or naphthalene in TFA, a variety of polynuclear complexes, containing both Pd(I) and Pd(II) and arenes, were isolated574 in addition to the usual biaryls. 

Biaryls (8, 478-479). The details for oxidative dimerization of arenes containing electron-donating groups to biaryls with TTFA have been published. Lead tetraacetate and cobalt(III) fluoride are equally effective reagents.1... 

The [(OEP)Rh]+ scaffold, while efficient at the metalation of arenes, is ill-suited for catalytic biaryl bond formation. The generation of an intermediate bearing two aryl groups cis to each other as a typical precursor to biaryls through reductive elimination is impossible due to the ligand-imposed geometry at the metal center. Nonetheless, other highly electron-deficient Rh(III) complexes can offer suitable entries into catalytic routes for electrophilic arene arylation. This is especially the case if the electrophilic Rh(III) center can be accessed in situ from the oxidative addition of Ar-X to a Rh(I) complex (Scheme 4). 

Biaryls. Homocoupling of substituted arenes to biphenyls occurs on treatment with Hg(II)-Ce(IV) salts, for example, Hg(OAc)2 and Ce(OTf)4. 

Pd-catalyzed aerobic oxidative coupling of arenes provides efficient access to biaryl compounds. The reaction exhibits near-ideal atom economy with water as the sole by-product however, it typically suffers from low regioselectivity and the blaryl products are often susceptible to further oxidation to afford oligomers. 

The reaction is performed by heating the diaroyl peroxide in an excess of arene to be arylated as solvent in an oxygen atmosphere [104], or in the presence of nitrobenzene until the evolution of carbon dioxide ceased [105]. For example, the yield of biphenyl can be increased to almost 80% by the reaction of dibenzoyl peroxide in refluxing benzene, if nitrobenzene or similar oxidant is present. Nitrobenzene efficiently oxidizes transient arylcyclohexadienyl radicals to biaryls, thus preventing several side-... 

Oxidative couplings of simple arenes, whose reactivity is comparable with benzene itself, to biaryls have been performed with stoichiometric palladium salts [2-5], Biphenyl (8) is obtained in high yield from two molecules of benzene by the influence of palladium(II) acetate or mixture of palladium(II) chloride (1 eq.) and sodium acetate (2 eq.). The reaction apparently involves the electrophilic palladation of benzene to give phenylpalladium(ll) acetate (370) which further reacts with the... 

Scheme 17.43 C-H/C-H cross-coupling of arenes to construct unsymmetrical biaryls.

The hydrolyses of tris(o-aryl)chromium compounds are very complex. As discussed in Section IV,C, rearrangements occur to give 77-arene-chromium(O) compounds in addition to arenes and biaryls 117). 

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