6-Alkyl-2,2 -bipyridines, reaction with

Relatively few pyridines with substituents other than alkyl groups have so far been examined, and with some of these the reaction has been carried out only in the presence of added solvent. A comparison of the reactivities of these pyridines is therefore difficult. It has, however, been established that the presence of benzoyl groups in the 3- and 4-positions causes a very marked drop in the yields of the corresponding 2,2 -bipyridines. The 3- and 4-benzylpyridines were found to be more reactive but even in the absence of solvent, and in vacuo, 4-benzylpyridine gave only about one-third of the yield of the 2,2 -bipyridine compared with pyridine itself. Ethyl nicotinate in the absence of solvent and under vacuum -- gave a similar yield of biaryl but 4-phenylpyridine was found to be less reactive. 

R = CHj, R = and adenocarpine(16 R = CH=CHPh, R = H) ° are likewise dehydrogenated to 2,3 -bipyridine, and related dehydrogenation reactions afford substituted 2,3 -bipyridines. Ullmann and Grignard reactions have been used to synthesise 2,3 -bipyridine, whereas the Gomberg reaction of 3-pyridinediazonium chloride with pyridine and alkyl pyridines affords 2,3 -bipyridine, along with other isomeric bipyridines, and alkyl substituted 2,3 -bipyridines, respectively. " Photolysis of 3-... 

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,... 

Semi-flexible bipyridine derivatives incorporating alkyl spacer groups between the pyridyl rings have been demonstrated to yield dinuclear palladium(II) species related to those discussed in Section 7.2 of this chapter.Thus, insertion of -CHjCHj- or -CH2(CgF4)CH2- groups between the 4- and 4 -positions in the parent bipyridine ligand leads to the formation of 2 2 (metal ligand) complexes of type 32 on reaction of these extended bipyridine derivatives with dinitro(ethane-... 

The treatment of 2,2 -bipyridine with diiodomethane yields a dipyridoimidazolium salt (98), and a similar reaction with benzylidene chloride gives a 6-phenyl derivative of (98) <63TL95,65AJC1819>. Alkyl substituted 2,2 -bipyridines react in a similar way with these two reagents but other alkylidene halides are inert. 

In 2009, Roelfes and co-workers reported the catalytic AFC alkylation reaction with olefins in water mediated by a DNA-based catalyst. The DNA-based catalyst is self-assembled by combining a Cu" complex with salmon testes DNA (st-DNA), which is inexpensive and readily available. With 4,4 -dimethyl-2,2 -bipyridine (dmbpy) as the ligand, 30 mol% (0.3 mM) of [Cu(dmbpy)(N02)2] (Cu-dmbpy) and 1.4 mg mL of st-DNA (2 mM in base pairs) were found to be the optimal reaction conditions for the AFC reaction of indoles with o,p-unsaturated 2-acyl imidazoles 98. The AFC products 99 were obtained in good yields and enantioselectivity (Table 6.11). Particularly noteworthy was that with 0.15 mol% catalyst, good yields and high ee values (up to 93 /o) were also obtained for various a,p-unsaturated 2-acyl imidazoles 98 and indoles. 

Reaction of 5,5 -bis(bromomethyl)-2,2 -bipyridine (4) [11] with a large excess of 4,4-bipyridine (5) in acetonitrile, followed by conversion of the resultant precipitate to the hexafiuorophosphate salt, gave the dicationic compound (6) in 88% yield (Scheme 2). The reaction of (6) with methyl iodide in nitromethane at reflux for 24h produced an orange precipitate which was collected, dissolved in water and converted to the hexafiuorophosphate salt to afford the tetra-cationic compound (7) in 89% yield (Scheme 2). Alkylation of (7) with dimethyl sulphate in acetonitrile at reflux for 48h gave initially a white precipitate hich was converted to the hexa-cationic hexafiuorophosphate acyclic receptor molecule L in 71% yield (Scheme 2). 

Bipyridine (5) was reacted with two equivalents of 5-bromomethyl-5 -methyl-2,2 -bipyridine (1) to produce, on addition of ammonium hexafiuorophosphate, the dicationic compound (8) in 78% yield (Scheme 3). Exhaustive methylation of (8) was achieved via alkylation reactions with methyl iodide and subsequently dimethyl sulphate followed finally by conversion to the hexafiuorophosphate salt to give the desired hexa-cationic receptor L in 44% overall yield. (Scheme 3). All these new acyclic receptors gave spectroscopic and analytical data in accordance with assigned structures. 

In the absence of an added solvent, 3-alkyIpyridines, 4-alkyl-pyridines, and 3,4-dialkylpyridines all gave yields of substituted 2,2 -bipyridines that were up to three times greater than that of 2,2 -bipyridine from pyridine under similar conditions. With 3-ethyl-4-methylpyridine a marked improvement in yield was ob.served when the reaction was carried out at about 150°C in a vacuum, rather than at the atmospheric boiling point (195°C) of this base. This effect has also been observed with some other bases but the amount of 3,3, 5,5 -tetramethy 1-2,2 -bipyridine from 3,5-lutidine could not be increased in this way, and this pyridine was as unreactive as the 2-substituted pyridines. This finding is undoubtedly related to the reluctance of 3-substituted pyridines to form 3,3 -disubstituted 2,2 -bipyridines. 

Homolytic aromatic substitution often requires high temperatures, high concentrations of initiator, long reaction times and typically occurs in moderate yields.Such reactions are often conducted under reducing conditions with (TMSlsSiH, even though the reactions are not reductions and often finish with oxidative rearomatization. Reaction (68) shows an example where a solution containing silane (2 equiv) and AIBN (2 equiv) is slowly added (8h) in heated pyridine containing 2-bromopyridine (1 equiv) The synthesis of 2,3 -bipyridine 75 presumably occurs via the formation of cyclohexadienyl radicals 74 and its rearomatization by disproportionation with the alkyl radical from AIBN. ... 

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 last decades have witnessed the emergence of new living Vcontrolled polymerizations based on radical chemistry [81, 82]. Two main approaches have been investigated the first involves mediation of the free radical process by stable nitroxyl radicals, such as TEMPO while the second relies upon a Kharash-type reaction mediated by metal complexes such as copper(I) bromide ligated with 2,2 -bipyridine. In the latter case, the polymerization is initiated by alkyl halides or arenesulfonyl halides. Nitroxide-based initiators are efficient for styrene and styrene derivatives, while the metal-mediated polymerization system, the so called ATRP (Atom Transfer Radical Polymerization) seems the most robust since it can be successfully applied to the living Vcontrolled polymerization of styrenes, acrylates, methacrylates, acrylonitrile, and isobutene. Significantly, both TEMPO and metal-mediated polymerization systems allow molec-... 

Three main parameters were used to evaluate the efficiency of the polymerization, namely monomer conversion (Cmma), initiation efficiency of the reaction (/ = Mn theo/3 n,SEc), and polydispcrsity index (PDI). These results are depicted in Fig. 2. It is obvious that the Cu(I)-catalyzed systems are more effective than the Fe(II)-catalyzed systems under the studied conditions. It was concluded that a bipyridine based ligand with a critical length of the substituted alkyl group (e.g., dHbpy) shows the best performance in Cu(I)-mediated systems. Besides, Cu(I) halide-mediated ATRP with 4,5 -Mbpy as the ligand and TsCl as the initiator was better controlled than that with dMbpy as the ligand, and polymers with much lower PDI values were obtained in the former case. 

A few syntheses of specific substituted 3,3 -bipyridines have been reported. 6,6 -Dialkyl-3,3 -bipyridines have been shown to be one of the products of the reaction of l-lithio-2-alkyl-l,2-dihydropyridines with perhalometh-anes, cyanogen bromide, or bromine. In an interesting double... 

There has been considerable interest in diquaternary salts of 2,2 -bipyr-idine. Simple 1,1-dialkyl-2,2 -bipyridinium salts are obtained by reaction of 2,2 -bipyridine with excess of an alkyl halide or dialkyl sulfate and related processes, - " and dialkyl diquaternary salts of substituted 2,2 -bipyridines are obtained likewise. " Bridged diquaternary salts are formed by reaction of 2,2 -bipyridines with 1,2-dibromoethane. Thus the parent compound alfords 6,7-dihydrodipyrido-[l,2-a 2, T-c]pyrazinediium... 

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