Biphenyls disubstituted

Of particular synthetic importance is the coupling of aryl- and hetarylboronic acids to aryl- and hetaryl halides (or triflates), allowing for a convenient synthesis of biphenyls, even sterically demanding derivatives such as 14, hetaryl phenyls and Zj/ -hetaryls. With appropriately disubstituted aromatic substrates, the Suzuki coupling reaction can be applied in the synthesis of polyphenylene materials. 

Problems arise in the preparation of substituted l//-azepines with (alkoxycarbonyl)nitrenes as nitrene attack on a mono- or disubstituted benzene ring is not generally regioselective, and with toluene, 04 34-136139 144 o- and p-xy ienes,134-139 p-cresoi,134 chlorobenzene104-134 136 and biphenyl,104 136 mixtures of 1//-azepine-1-carboxylates of undetermined composition are produced. 

The present method of preparation of 4,4 -dimethyl-l,l -biphenyl is that described by McKillop, Elsom, and Taylor 15 It has the particular advantages of high yield and manipulative simplicity and is, moreover, applicable to the synthesis of a variety of symmetrically substituted biaryls 3,3 - and 4,4 -Disubstituted and 3,3, 4,4 -tetrasubstituted 1,1 -biphenyls are readily piepared, but the reaction fails when applied to the synthesis of 2,2 -disubstituted-l,T biphenyls The submitters have effected the following conversions by the above procedure (starting aromatic bromide, product biphenyl, % yield) bromobenzene, biphenyl, 85,1 -bromo-4-methoxybenzene, 4,4 -dimethoxy-l, 1 -biphenyl, 99, 1 bromo 3 methylbenzene, 3,3 dimethyl-1,l -biphenyl, 85 4-bromo-l,2-dimethylbenzene, 3,3, 4,4 -tetramethyl-l,l -biphenyl, 76, l-bromo-4-chlorobenzene, 4,4 -dichloro-l,l -biphenyl, 73, l-bromo-4-fluorobenzene, 4,4 -difluoro-l,l -biphenyl, 73... 

R, Thaimattam, D. S. Reddy, F. Xue, T. C. W. Mak, A Nangia, G. R. Desiraju, Interplay of strong and weak hydrogen bonding in molecular complexes of some 4,4 -disubstituted biphenyls with urea, thiourea and water , J. Chem Soc, Perkin Trans. 2,1998,1783-1789. 

The synthesis of 2,7-dinitrodibenzothiophene via cyclization of the biphenyl derivative (38) with bromine, at 200°, could be usefully extended to the synthesis of other deactivated dibenzothiophenes. The 2,7-disubstitution pattern is rare, the only other reference to it being the... 

A triplet state dimer of a benzofused 1,2,3-trithiole dication was postulated. However the occurrence of this high-spin dimer is strongly dependent on the nature of the solvent and the oxidant129. The 2,5-dimethoxy-4-methylphenyl moiety in which the additional charge and the single electron are stabilized in a quinoidal structure after one-electron oxidation has been utilized as a probe for electron delocalization when two of these moieties were connected either by a trimethylene, a 1,4-disubstituted phenylene or a biphenyl bridge130. 

Benzo[c]cinnoline derivatives of different oxidation levels are prepared by N-N bond formations from suitable 2,2 -disubstituted biphenyls as outlined in Scheme 5. 

Copper(I) salts in the presence of a tertiary amine catalyze the oxidation of 2,6-disubstituted phenols by 02 into poly(phenylene oxides) (high amine/copper ratio) or biphenyl-4,4 -quinones (low amine/copper ratio). When R is a bulky substituent (e.g. Bu ), biphenyl-4,4 -quinone is the sole product (equations 270 and 271).599... 

Many intramolecular nitrone cycloadditions have been carried out on substrates containing a cyclic intervening bridge. Perhaps the simplest possibility here is an o-disubstituted aromatic substrate, as, for example, the nitrone derived from aldehyde (42), which cyclizes to the 5,6-fused isoxazolidine (43 Scheme 10).19 There are many additional possibilities the nitrones derived from biphenyl aldehyde... 

Because of the importance of the biphenyl scaffold, as a structure of pharmaceutical and active therapeutic compounds, the mass spectrometric behavior of a series of 6,6-disubstituted dibenzo[r//][l,3]dioxepins 36 has been studied. The electron ionization-induced fragmentation patterns were discussed based on use of labeled compounds, accurate mass measurements, and collisionally induced dissociation experiments using an ion trap <2006JMP577>. 

The thermal intramolecular 2 + 2-cycloaddition of 4,4,-disubstituted-2,2/-bis(phenyl-ethynyl)biphenyls (1) yielded the intermediate l,2-diphenylcyclobuta[l]phenanthrenes (2), which could be trapped with 2,3,4,5-tetraphenylcyclopenta-2,4-dione (3) to produce the Diels-Alder adduct (4). Thermal decarbonylative ring opening of (4) gave 9,10,11,12,13,14-hexaphenylcycloocta[l]phenanthrenes (5) as the final product in 12-23% yield (Scheme l).1... 

Three piperidine alkaloids lythranine (72), lythranidine (73), and ly-thramine (74) belong to this group. All have a piperidine ring disubstituted at two a positions by two aralkyl C4-C6 groups joined by a biphenyl bond. 

Under the same conditions the sterically more demanding 2-chlorotoluene is coupled in 70% yield. However longer reaction times are necessary. Acceptor- as well as donor-substituents are tolerated under these conditions. Tri-tert.-butyl-phosphane is the ligand of choice in Suzuki-couplings [3] as well 2-chlorotoluene reacts with 2-methyl-phenylboronic acid to 2,2 -disubstituted biphenyl in 87% yield [eq. (b)]. 

Scheme 8.2 Synthesis of nonsymmetrically 1,4 -disubstituted biphenyl building blocks and 1,4 -disubstituted p-terphenylene building blocks (R = H or alkyl).

Phenanthridines are obtained from 2,2 -disubstituted biphenyls in which the substituents react intramolecularly to form the heterocyclic ring. The oldest examples of syntheses of this type involve Hofmann65 and Curtius66- 67 reactions on biphenic acid, and have been explained... 

Tetrasubstituted silanes are also sources of silylene. Suginome and coworkers reported that palladium catalyzed the transfer of dimethylsilylene, formed from silylborane 44, to alkynes [equation (7.8)], 60 Exposure of silylborane 48 and alkyne 49 to substoichiometric amounts of palladium and P(7-Bu)2(2-biphenyl) afforded 2,4-disubstituted silole 50. This process tolerates a variety of functionality including silyl ether-, dimethylamino-, and trifluoromethyl groups. In addition to aliphatic terminal acetylenes, arylacetylenes were also competent substrates. For... 

The palladium(0)-catalyzed borylation/Suzuki coupling protocol was developed by Baudoin and co-workers in order to synthesize sterically hindered 2,2 -disubstituted biaryl compounds such as 170 in high yield and in a convenient manner [162,163], Indeed, the catalytic borylation of 2-bromoaniline 167 (R=H) gave the corresponding pinacolboronic ester 168 which was reacted in a one-pot fashion with phenyl iodide 169 in the presence of barium hydroxide to give the functionalized biphenyl 170 in 78% yield. Cleavage of the MOM group and cyclization in the presence... 

The free energy difference between the two rotamers 126a and 126b was estimated to be 0.8 kcal/mol in favor of 126a by temperature-dependent CD curves (40). Free energy differences of derivatives 103,131, and 132 were estimated to be 1.0, 0.7, and 0.2 kcal/mol, respectively. This shows that the important factor in determining the conformational chirality of the biphenyl moiety is the presence of the 2,6-trans disubstituted piperidine ring in the molecule. 

Boamfa et al. investigated macroscopic orientation of disubstituted cyano-biphenyl poly(norbornene) IV-n (n=3,5) using different magnetic fields of up to 20 T. Both the degree of orientation and optical properties were compared with a cyanobiphenyl-substituted acrylate polymer with a spacer of four methylene units [49,50]. 

More recent work by Hoplf and Koulen further broadened the scope of the reaclion by including an aesortment of disubstituted benzenes, and also biphenyl and acenaphthene. Somerville and Spoerri, 1 moreover, have examined the action of istjbutylene oxide and 2,3-epoxybutane oi) benzene in the presence of aluminuiB chloride Mixtures of alcohols and hydrocarbons were isolated, as in prevkras work. 

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