6,6 -Dimethyl-2,2 -bipyridine, 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). 

Several of the methods of synthesis of 2,2 -bipyridines have their counterpart in the preparation of 4,4 -bipyridine. The Ullmann reaction has been used to prepare 4,4 -bipyridine. Thus 4-halogenated pyridines afford 4,4 -bipyridine. Dehalogenation and dimerization of 4-bromopyridine may be accomplished too with hydrazine and alkali at 65°C in the presence of a palladium catalyst, whereas 4-chloropyridine is converted to 4,4 -bipyridine in 46% yield by reaction with alkaline sodium formate in the presence of palladium on charcoal and a surfactant. Several extensions of the Ullmann reaction have recently been reported, especially for the synthesis of substituted 4,4 -bipyridines. Thus 4-iodo-2-methylpyridine gives 2,2 -dimethyl-4,4 -bipyridine, 3-nitro-4-chloropyridine affords 3,3 -dinitro-4,4 -bipyridine, 4-bromo- or 4-iodotetrafluoropyridine gives octafluoro-4,4 -bipyridine, and 4-iodo- or 4-bromotetrachloropyridine gives octachloro-4,4 -bipyridine. Related syntheses have been de-... 

Reduction of ester functionalities with NaBH4 has furnished the corresponding alcohols. The 4- and 4,4 -substituted hydroxymethyl bipyridines have also been synthesized from halomethyl precursors, (23) and (26), respectively, by reaction with NaOAc followed by acetate hydrolysis.113 The 5,5 -dihydroxymethyl bipyridine ligand has been prepared (55%) by converting 5,5 -dimethyl bipyridine to the bis /V-oxide with hydrogen peroxide, followed by reaction with acetic anhydride in acetic acid,114 then hydrolysis with KCN in ethanol.115... 

Reaction of a-picoline with a nickel-alumina catalyst has been reported to give a mixture of four isomeric dimethylbipyridines, one of which has been identified at 6,6 -dimethyl-2,2 -bipyridine.10 With palladium-on-carbon, 2,4-lutidine was found to be more reactive than pyridine,14 and the isolated biaryl has been assigned the structure (2). However, some confusion arises from the statement that this... 

D-A reactions, comprising st-DNA and the Cn " complex of 4,4 -dimethyl bipyridine. Nitromethane and dimethyl malonate, both of which enolize readily, were employed as the nncleophiles. With 100 equivalents of dimethyl malonate, a clean and quantitative conversion into the Michael addnct was observed after 3 days, with an ee of 91%. The addition of nitromethane was slower nsing 1000 equivalents 97% conversion and an ee of 85% were obtained in the same time. The snbstrate scope proved to be broad a series of derivatives of the snbstrate were tested in the Michael reaction and generally gave high conversions (typically > 75%) and ees (86-99% with dimethylmalonate as the nncleophile, and 82-94% with nitromethane as the nncleophile). Only in the case of the Michael addition to the enone with R = Me instead of aryl, did the ee drop to 60%. Again, it was shown that the reaction conld be performed on a preparative scale (1 mmol), and that the catalyst solution conld be recycled withont loss of activity or enanti-oselectivity over at least two rnns. 

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. 

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. 

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