Biphenyl synthesis

For example, photolysis of a suspension of an arylthallium ditrifluoro-acetate in benzene results in the formation of unsymmetrical biphenyls in high yield (80-90%) and in a high state of purity 152). The results are in full agreement with a free radical pathway which, as suggested above, is initiated by a photochemically induced homolysis of the aryl carbon-thallium bond. Capture of the resulting aryl radical by benzene would lead to the observed unsymmetrical biphenyl, while spontaneous disproportionation of the initially formed Tl(II) species to thallium(I) trifluoroacetate and trifluoroacetoxy radicals, followed by reaction of the latter with aryl radicals, accounts for the very small amounts of aryl trifluoroacetates formed as by-products. This route to unsymmetrical biphenyls thus complements the well-known Wolf and Kharasch procedure involving photolysis of aromatic iodides 171). Since the most versatile route to the latter compounds involves again the intermediacy of arylthallium ditrifluoroacetates (treatment with aqueous potassium iodide) 91), these latter compounds now occupy a central role in controlled biphenyl synthesis. 

Biphenyl synthesis. In the presence of l,4-dichloro-2-butene, aryl Grignard reagents couple to form biphenyls. The coupling involves electron transfer to the... 

During their work on the arylation of aromatic compounds by substitution, Fujiwara, et al. observed biaryl formation when aromatic compounds were placed in the presence of olefin-palladium complexes and silver nitrate.80 Developing this reaction as a method for biphenyl synthesis, these authors showed that the more stable the olefin-palladium complex was, the lower the yield. Ethylene dichloropalladium proved to be the best choice, when used with silver nitrate. However, the reaction required stoichiometric amounts of both catalysts (Scheme 10.47). Benzene derivatives substituted by electron-donating or -withdrawing groups reacted as well, but a mixture of regioisomers was produced, except for nitrobenzene, which only gave m,m -dinitrobiphenyl. 

Due to the relatively slow addition of aryl radicals to substituted benzenes [7], inter-molecular Gomberg-Bachmann type arylations often require favorable reaction conditions in which the substrate arene is used as solvent to be efficient. To achieve good control and selectivity in the addition step, radical biphenyl synthesis can alternatively be conducted in an intramolecular fashion by taking advantage of a removable tether. In the first examples, sulfonamides, sulfonates [130], and azetidinones [131] were employed as linkers between the two aryl moieties. Recently, phosphinates [132] and siloxanes [133] have been used for this purpose (Scheme 25). 

Scheme 25 Biphenyl synthesis via ipso cyclization of phosphinates [132]...

Weber R, Hagenmaier H (1995), Organohalogen Compounds 23 357-362. Mixed chlorinated fluorinated dibenzodioxins, dibenzofurans, biphenyls synthesis, analysis and formation", Eds. Dioxin 95 Secretariat, Edmonton, Kanada ISBN 3-928379-13-5 Zitko V (1985), Chemosphere 14 165. Shorthand numbering of chlorinated dibenzodioxins and dibenzofurans"... 

Gomberg-Bachmann biphenyl synthesis. Reaction of stable arenediazonium tet-rafluoroborates or hexafluorophosphates in an aromatic solvent with potassium acetate (2 equiv.) and a phase-transfer catalyst results in biar Is in high yield. Crown ethers, Aliquat 336, and tetrabutylammonium hydrogen sulfate arc all effective catalysts. The reaction is useful for synthesis of unsymmetrical biaryls. The ortho-isomer predominates in reactions with a monosubstituted benzene. The most selective method is to couple a substituted arenediazonium salt with a symmetrical arene. 

GOMBERG-BACHMANN BIPHENYL SYNTHESIS Phase-transfer catalysts. 

Broutin, P.-E., Cerna, I., Campaniello, M., Leroux, F., Colobert, F. Palladium-Catalyzed Borylation of Phenyl Bromides and Application in One-Pot Suzuki-Miyaura Biphenyl Synthesis. Org. Lett. 2004, 6, 4419-4422. 

Cross couplings. Biphenyl synthesis by cross-coupling can be promoted by Pd complexes in the presence of 1,3-dimesitylimidazolinium chloride. A chiral phosphine ligand enables the selective replacement of one of two triflyloxy groups on an arene nucleus. ... 

Ullmann coupling. This classic reaction is still valuable for biphenyl synthesis. Unsymmetrical biphenyls are obtained by tethering the aryl iodides (e.g., by a salicyl alcohol unit), thus rendering the reaction intramolecular. 

Biphenyl synthesis. Monoat r unctionalization of biphenyl derivt... 

Biphenyl synthesis. Monoarylation of 1,4-dibromobenzene makes further functionalization of biphenyl derivatives possible. 

The Ullmann biphenyl synthesis (4, 5) involves arylcopper intermediates. The coupling is a typical soft-soft interaction. A useful extension to the generation of alkylarenes is by the reaction of dialkylcuprates with haloarenes (6). 

Scheme 1.9 Biphenyl synthesis through an aryne intermediate (Wittig, 1942).

RW (2008) CYP17 inhibitors. Annulations of ad- 2227. ditional rings in methylene imidazole substituted biphenyls synthesis, biological evaluation and molecular modelling. Arch Pharm 341 597-609... 

Bis [6-(methacryloyloxy)hexoxyl]-benzoate -l,T-biphenyl, synthesis, 185 Blending, property modification, 142 Blending of polymers, advantages, 98-99 Block copolymers advantages, 332... 

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