Biphenyls formation

Biphenyl formation by the ligand coupling of triphenylbismuth is promoted by Pd(OAc) [418],... 

Shi, Y. Wan, P. Charge polarization in photoexcited alkoxy-suhstituted biphenyls formation of biphenyl quinone methides. J. Chem. Soc., Chem. Commun. 1995, 1217-1218. 

Tanaka. F.S., Wien, R.G, and Hoffer. B.L. Biphenyl formation in the photolysis of 3-(4-chlorophenyl)-l,l-dimethylurea in aqueous solution, 7 Agrlc. Food Chem., 29(6) 1153-1158,1981. 

The other, which is similar to the biphenyl-forming reaction, may be initiated by hydride ions produced by biphenyl formation [Reaction (31a, b, c)]. 

Aromatic Ring Cleavage of Phenolic 0-0-4 Substructure Model Compounds by Laccase. When vanillyl alcohol was used as a substrate, only biphenyl formation (C5-C5 linked) occurred and no evidence for the formation of any ring-opened products was obtained (26). Hence, we also examined the effect of laccase on the sterically hindered 4,6-di-<-butylguaiacol substrate 50, as it would be unlikely to undergo such free-radical coupling reactions... 

The data suggest that hydrogen exchange among benzene molecules is much faster than biphenyl formation, and that the process by which benzene molecules undergo exchange leaves them in an activated state for the reaction to form biphenyl. 

The reduction equivalents required for conversion of N2 to NH3 are obtained from the carbanionic phenyl groups bonded to nickel in 14 (biphenyl formation). The Ni atoms, which are still present as Ni(0), i.e., in the form of metallic nickel after hydrolysis, only function as agents for the transfer of electrons from C6H5 to N2. In this respect, the hydrolysis of... 

When the corresponding phenyl complex was irradiated in benzene solution, biphenyl formation was observed but, surprisingly, most of this came from coupling of two solvent molecules and not from the initial phenyl ligand 137). The fate of the latter was not determined but presumably benzene was formed. Irradiation of CpNi(C6H4CH3)(PPh3) gave biphenyl (3%) and 4,4 -dimethylbiphenyl (45%) as the major products, but no production of toluene was detected. The latter observation... 

A more robust process, suitable for the production of a greater scope of heterocycle, was later developed using SEM-protected azoles that could be readily converted to the N-H counterparts under a variety of conditions (Scheme 13a) [27], Palladium complexes containing imidazyl carbene ligands were utilized to improve the stability of palladium throughout the catalytic cycle, modulate reactivity and disfavour biphenyl formation. 

The o-z-propyl group is the most effective, a moderate steric bulkiness being important. Accordingly the small size of F does not allow biphenyl formation with norbornene expulsion. A complex mixture was formed, containing predominantly a difluorinated compound (Eq. 42) [49, 50], which originates in accordance with Scheme 5, Sect. 4.4. 

As mentioned earlier, Pd-catalyzed arene oxygenations have been known for over four decades. However, the vast majority of the early reports are plagued by low TONs and competing biphenyl formation, which often leads to catalyst decomposition [42]. Furthermore, oxygenations of substituted arenes generally afford the desired products as mixtures of olmlp isomers, which decrease the synthetic... 

Scheme 1-51. Biphenyl formation by accidental oxidation of phenyllithium and of the biphenyl/lithium "radical anion" (74).

In order to provide a quantitative description of the product formation from the photolysis of PMPP, the quantum yield of biphenyl formation in methylene chloride was determined. Photolysis of PMPP in methylene chloride was therefore conducted with a medium-pressure mercury lamp using 254 nm band-pass filter. The light intensity was measured with ferrioxalate actinometry and the product yield was determined by gas chromatographic analysis of the samples photolyzed in methylene chloride. The quantum yield for biphenyl formation is ca. 5 x 10 . No change in the quantum yield for biphenyl was noticed in the presence and in absence of molecular oxygen. Since only a trace amounts of benzene and phenol were detected by gas chromatography, their formation quantum yields could not be determined accurately. 

---