4,4 -Disubstituted 2,2 -bipyridines, reaction with

Four 2-substituted pyridines were found to give the expected 6,6 -disubstituted 2,2 -bipyridines in yields corresponding to only about 3% of the amount of 2,2 -bipyridine formed from pyridine itself under comparable conditions. It is also of interest that with three 2-methyl-pyridines the expected 6,6 -dimethyl-2,2 -bipyridines were accompanied by smaller amounts of 2,2 -bipyridines having no methyl groups in the 6,6 -positions. Moreover, a very small amount of 5,5 -dimethyl-2,2 -bipyridine (8) was isolated following reaction with 2,5-lutidine (6) but no 3,3 -dimethyl-2,2 -bipyridine could be detected. The absence of this compound suggests that 3,3, 6,6 -tetramethyl-2,2 -bipyri-dine (9) is not an intermediate, but that the 2-methyl group is lost before the formation of the 2,2 -bipyridine (6—>8). 

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. 

Like all simple triazolopyridines, bitriazolopyridines 76 react with electrophiles to produce 2,2 -bipyridines 118 (Scheme 24). With these reactions a general route to 2,2 -bipyridines has been discovered with a variety of substituents in the 6 and 6 positions (97T8257). These compounds have use in supramolecular chemistry because of their great complexing power for metal ions and, in particular, 2,2 -disubstituted-6,6 -bipyridines are useful building blocks for oligobipyridines, which spontaneously form helical metal complexes (92T8451). 

Reactions of Mn(CO) SCN with a variety of neutral ligands in chloroform yield complexes which are analogous to those prepared from MnfCO Br (4). The mode of the thiocyanato-manganese bonding in these compounds depends on the nature and position of the neutral ligand(s) present. Strong bases such as pyridine, p-toluidine (L) and 2,2 -bipyridine (L-L) give cis-disubstituted thiocyanato-N carbonyl complexes. 

The synthesis of a molecule containing two 5,5 -disubstituted-2,2 -bipyridyl units was achieved by the reaction of two equivalents of 5-bromomethyl-5 -methyl 2,2 -bipyridine (1) [11] with N,N -dimethylethylene diamine (2) in acetonitrile using potassium carbonate as base. Purification by column chromatography on alumina, using CH Cl /MeOH (99 1) as eluent, and recrystallisation from acetonitrile afforded (3) in 43% yield (Scheme 1). Reaction of (3) with dimethyl sulphate at 75 C for 7 days gave a mixture of products that were not fully methylated. Following conversion to the hexafiuorophosphate salts, this mixture was reacted further with methyl iodide in acetonitrile at reflux for 18 days. After this tii e the product was isolated and converted to the hexa-hexafluorophosphate salt to give L in 11% overall yield (Scheme 1). 

Allylic ethers may react with 2,3-disubstituted 1,3-butadienes in an iron-catalyzed process in two different modes depending on the ligand (Scheme 4-312). A [4+4] ene reaction is favored when a bipyridine(diene)iron complex is used as catalyst to form the corresponding vinyl ethers. If l,2-bis(diphenylphosphano)ethane is used as ligand, a 1,4-hydrovinylation of the diene is observed. The active Fe(0) catalysts are synthesized from Fe(ll) or Fe(III) salts by reduction with Grignard or trialkylaluminum reagents. ... 

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