6-Aryl-2,2 -bipyridines, reaction with

A heterobimetallic BINOL-Ga/Li complex 53 has been developed for the enantioselective ARO of meso-cpoxides (BINOL = l,T-bi(2-naphthol)).278 Using />-methoxyphenol as the nucleophile, this etherification reaction was observed to take place with a high level of asymmetric induction. An improved catalyst 54 has also been reported that exhibits greater stability under the reaction conditions and delivers higher yields and ee s (Equation (78)).279 A simple catalyst derived from Sc(OTf)3 and the chiral bipyridine ligand 52 has been shown to be effective for the ARO of aryl-substituted /// -epoxides with aliphatic alcohols to give high ee s (Equation (79)).280... 

Quaternary salts of 4,4 -bipyridine other than 1-alkyl or 1-aryl quaternary salts have also been synthesized. Thus l,l -dialkoxy diquaternary salts are formed by reaction of 4,4 -bipyridine l,l -dioxide (see next section) with dialkyl sulfates," and 1-alkyl-I -alkoxy diquaternary salts are obtained similarly. l,r-Bis(2,4-dinitrophenoxy)-4,4 -bipyridinium bisffluoro-borate) has been prepared from 4,4 -bipyridine l,l -dioxide by reaction with 2,4-dinitrobenzenediazonium fluoroborate in sulfolane. Interestingly,... 

In the area of organometallic chemistry, we begin with a procedure for the palladium-catalyzed animation of aryl halides and aryl triflates, illustrated by syntheses of N-HEXYL-2-METHYL-4-METHOXYANIUNE and N-METHYL-N-<4-CHLOROPHENYL)-ANILINE. The next procedure describes the synthesis of 1,2,3,4-TETRAHYDROCARBAZOLE by the palladium-catalyzed annulation of ketones with o-iodoaniline. Next, a procedure for the synthesis of 2,7-DIMETHYLNAPHTHALENE via the nickel-catalyzed coupling of aryl O-carbamates with Grignard reagents is presented. The fourth procedure in this section describes the synthesis of 5-METHYL-2,2 -BIPYRIDINE by a Negishi cross-coupling reaction... 

A complex with a palladium-aryl bond [Pd(I)(C6H3Me2-3,5)(bipy)], prepared from [Pd(dba)2l, 2-2 -bipyridine, and 3,5-Me2C6H3l, enters the insertion reaction with dimethylacetylene dicarboxylate and silver tetrafluoroborate in acetone to yield 74 (OOOM2125). In the absence of silver tetrafluoroborate, the insertion reaction leads to 75. It reacts with silver tetrafluoroborate to yield cationic 76 (010M1087). If dimethylacetylene dicarboxylate is taken in excess, then in the presence of silver tetrafluoroborate, 77 is the product. [Pd(I)(C6H3Me2-3,5)(bipy)] also reacts with phenylallene and silver tetrafluoroborate in acetone, and the reaction is accompanied by the insertion of the C = C bond into the palladium-aryl bond to yield palladium allyl 78. 

Additionaly, less reactive atyl triflates react with arylzincs by method A furnishing the biaryls in excellent yields. Once again, the triflate involving reaction was accomplished in the presence of lithium chloride or bromide as mediators. These in situ generate appropriate more reactive aryl bromides or chlorides from the parent triflate, and thus accelerate the cross-coupling reaction with arylzinc. For instance, the reaction of 2-pyridylzinc chloride (145) with 3-methylpyridyl triflate (146) gave 3-methyl-2,2 -bipyridin (147) in 98% yield [51], respectively. Scheme 13. 

In cyclometalation reactions with metal compounds instead of the metal atoms discussed above, ligands such as hetero atom groups (e.g., bipyridines, phosphines, and carboxylates), unsaturated groups (e.g., aryl, allyl, Cp and Cp ), carbonyl groups, halogen atoms (F, Cl, Br, Cl), etc., also act as metal activators. 

Under the same conditions as described before (Sects. 15.3.2.1 and 15.3.2.2), the electroreduction of aryl halides ArX (X= Cl, Br) allows the coupling reaction with vinylic acetates in the presence of stoichiometric amount 2,2 -bipyridine and catalytic amounts of cobalt bromide This new carbon-carbon bond synthesis successfully led to styrene derivatives that are hardly accessible by other methods according to Scheme 15.15 [27j. 

The iridium complex composed of l/2[ Ir(OMe)(cod)2 ] and 4,4 -di-/ r/-butyl-2,2 -bipyridine (dtbpy) shows a high catalytic activity for aromatic G-H silylation of arenes by l,2-di-/z r/-butyl-l,l,2,2,-tetrafluorodisilane.142 The reaction of 1,2-dimethylbenzene with l,2-di-/< r/-butyl-l,l,2,2,-tetrafluorodisilane in the presence of l/2[ Ir(OMe)(cod)2 ] and dtbpy gives 4-silyl-l,2-dimethylbenzene in 99% yield (Equation (103)), which can be utilized for other functionalizations such as arylation and alkylation. 

Biaryl synthesis from aryl halides is a more interesting reaction due to the value of these molecules and their difficult access by chemical methods. The first electrosyntheses were simultaneously done in 1979-80 by three groups [21-23] who used NiCljPPha (1-20%) as catalyst precursor in the presence of excess PPhs. Later, several groups investigated the use of bidentate phosphines like dppe associated with nickel in the synthesis of various biaryls, and notably 2,2 -bipyridine and of 2,2 -biquinoline from respectively 2-chloropyridine and 2-chloroquinoline [24], More recently new nickel complexes with l,2-bis(di-2-alkyl-phosphino)benzene have been studied from both fundamental and synthetic points of view [25]. They have been applied to the coupling of aryl halides. 

The direct borylation of arenes was catalyzed by iridium complexes [61-63]. Iridium complex generated from [lrCl(cod)]2 and 2,2 -bipyridine (bpy) showed the high catalytic activity of the reaction of bis (pinaco la to) diboron (B2Pin2) 138 with benzene 139 to afford phenylborane 140 (Equation 10.36) [61]. Various arenes and heteroarenes are allowed to react with B2Pin2 and pinacolborane (HBpin) in the presence of [lrCl(cod)]2/bipyridne or [lr(OMe)(cod)]2/bipyridine to produce corresponding aryl- and heteroarylboron compounds [62]. The reaction is considered to proceed via the formation of a tris(boryl)iridium(lll) species and its oxidative addition to an aromahc C—H bond. 

Arylzinc species prepared via the sacrificial anode process and from aryl halides in the presence of a nickel 2,2 -bipyridine, as already reported in Section . .1, were found totally unreactive towards common electrophiles such as aldehydes, carboxylic anhydrides or activated alkyl halides. However, they react with some electrophiles when they are activated by the presence of a catalytic amount of copper salts (10 mol% Cul) together with tetramethylethylene diamine (1MEDA) as described by Knochel and Singer on the ArZnX—CuCN metal exchange47 or when the reaction is catalyzed by palladium complex. 

It has been found that the use, as ligands, of electron-poor phosphines, such as 1,1 -bis(diphenylphosphino)ferrocene, enhances yields in the palladium-catalysed reaction of aryl bromides with sodium phenoxides to yield diaryl ethers.87 Palladium-catalysed coupling of ethynylated derivatives of bipyridine or terpyridine with the corresponding bipyridine or terpyridine halides or triflates has been used in the synthesis of preorganized polytopic ligands.88... 

The aiyl sulfides 424 are prepared by the Pd-catalyzed reaction of aryl halides with the mercaptans 423 or thiophenol 425 in DMSO [209]. Pd(OAc)2 BINAP is active for the reaction of aryl triflates in the presence of t-BuONa [209a], The NiBr2 complex of bipyridine is an active catalyst for thioarylation of aryl iodides with the thiophenol 425, to give diaryl thioether 426 [210],... 

Ester, nitrile, or ketone functions are tolerated in the method. Aryl chlorides can be applied with only slightly decreased yields. For 3-bromopropionate the bipyridine ligand was mandatory for the success of the reaction. The involvement of radicals is supported by ring opening occurring when cyclopropylmethyl bromide was used as the substrate (cf. Part 1, Fig. 8). 

Nickel-2,2-bipyridine complexes are also used for the preparation of unsymmetrical biaryls such as 4-methoxy-4 -trifluoromethylbiphenyl by electroreduction of two aryl halides, one of which has electron-donating and the other electron-withdrawing groups in the aromatic ring as shown in equation 110. The reaction was carried out in N-methylpyrrolidinone at constant current in an undivided cell fitted with a sacrificial magnesium anode and excess of 2,2 -bipyridine167. 

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