4,4 -Dimethyl-2,2 -bipyridine

Reaction of -picoline over degassed Raney nickel was found to give 5,5 -dimethyl-2,2 -bipyridine (5), the structure of which was established by its synthesis from 2-bromo-5-methylpyridine. Oxidation of this dimethyl-2,2 -bipyridine, and similar oxidation of the diethyl-2,2 -bipyridine derived from 3-ethylpyridinc, gave the corresponding dicarboxylic acid and the same acid was produced by the action of degassed Raney nickel on sodium nicotinate (in water) or on ethyl nicotinate. These transformations established the 5,5 -substitution pattern for three 2,2 -bipyridines derived from 3-substituted pyridines but such evidence is not available for the biaryls... 

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). 

The 2,2 -bipyridine functional monomer M4 can be synthesized using an elimination reaction [13,14]. 5,5 -Dimethyl-2,2 -bipyridine is first lithiated with lithiumdiisopropyl amide (LDA) at one of the methyl groups. This lithium derivative is subsequently reacted with chloromethoxymethane to form the methoxy-ethyl derivative. Finally, the vinyl group is produced by elimination of the methoxy group in basic tetrahydrofuran (THF) at low temperature. 

Recently, we reported the synthesis of a metal-templated trefoil knot using dynamic covalent chemistry of imine bonds. Inspired by the work of Stoddart on the synthesis of Borromean rings and with the aid of DFT calculations, we anticipated that the combination of a 5,5 -dimethyl-2,2 -bipyridine functionalized with para-aminomethyl-phenyl ether (Scheme 17.6) would provide adequate geometry for the bidentate coordination to a Zinc(II) cation. 

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