6-Ethyl -2,2 -bipyridine, 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. 

Interestingly, the Fe2+ ion in the core can be easily removed by base, the complex dissociates and the individual polymer dimers can be analyzed. Block copolymers of 2-ethyl-2-oxazoline with other substituted oxazolines have also been made [121]. Ru2+(4,4 dichloromethyl-2,2 bipyridine)3 has also been used as the multifunctional initiator for the ATRP of styrene at 110°C [122], It is interesting to note that the Cu+ ions necessary for the polymerization reaction are solubilized via complexation with other bipyridine species. 

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. 

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

When internal trans alkenes were subjected to diazoester in the presence of 80 CuOTf, cyclopropane ent-56, formed in high enantioselectivity, was slightly favored over its isomer (56). The use of ethyl diazoacetate improved diastereoselec-tion relative to the bulkier /-Bu ester. Unfortunately, ee values were somewhat lower with the ethyl ester, Eq. 39. Ito and Katsuki (56) propose the model in Fig. 7 to account for this selectivity. Approach of the trans alkene is controlled by the stereocenter on the bipyridines, directing the bulky group cis to the ester moiety. Larger esters lead to an increased steric interaction in this position and the net result is an erosion in reaction diastereoselectivity. 

To complete the section on the synthesis of 4,4 -bipyridines, we summarize the methods reported for the preparation of some substituted 4,4 -bi-pyridines and 4,4 -bipyridinones. These methods are closely analogous to syntheses already discussed for some of the isomeric bipyridines. Thus the Hantzsch reaction using pyridine-4-aldehyde, ethyl acetoacetate, and ammonia gives 3,5-di(ethoxycarbonyl)-1,4-dihydro-2,6-dimethyl-4,4 -bipyridine, which after oxidation, followed by hydrolysis and decarboxylation, afforded 2,6-dimethyl-4,4 -bipyridine. Several related condensations have been reported. Similarly, pyridine-4-aldehyde and excess acetophenone gave l,5-diphenyl-3-(4-pyridyl)pentane-l,5-dione, which with ammonium acetate afforded 2,6-diphenyl-4,4 -bipyridine. Alternatively, 1-phenyl-3-(4-pyridyl)prop-2-enone, A-phenacylpyridinium bromide, and ammonium acetate gave the same diphenyl-4,4 -bipyridine, and extensions of this synthesis have been discribed. Condensation of pyridine-4-aldehyde with malononitrile in the presence of an alcohol and alkaline catalyst produced compounds such as whereas condensations of... 

Recent studies indicate the reaction of platina-/3-diketone with bipyridines via oxidative addition yields the diacyl hydrido Pt(IV) complex. Further ligand abstraction may result in H bond bridged dimer and a double-deck dimer through Pt Pt interaction (Scheme 17). On the other hand, the prototype of unsupported cis- diacyl platinum(II) species was obtained either via nucleophilic addition to cationic acyl carbonyl complexes or CO insertion into a trans acyl alkyl complex (Scheme 18). In the latter process for propionyl methyl or acetyl ethyl complex. 

Morrow and Trogler (109) have studied the hydrolysis of two phosphate diesters by [Cu(bipy)] (bipy = 2,2 -bipyridine) in aqueous solution at 75°C in the pH range 5.8-8.3. For both bis(4-nitrophenyl)phosphate and ethyl-4-nitrophenylphosphate the reaction was proposed to proceed via coordination of the diester to the [Cu(bipy)] moiety followed by attack of a cis coordinated OH ion at the P center. Maximal rate enhancements of 1(P- to- 10 -fold were reported. The reaction was accompanied by incorporation of a single label in the product ethylphosphate when the reaction was conducted in labeled water. Saturation kinetics were observed for the hydrolysis of ENPP (ethyl-4-nitrophenylphosphate). The reaction obeyed Michaelis-Menton kinetics with a for the ENPP ion of... 

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. 

Hydrogenation of ketones proceeds less readily in aqueous systems, and genuine two-phase procedures are much less developed. A rare example is the hydrogenation of various substituted acetophenones with Ir- and Rh-complexes (95) of phosphonate-substituted bipyridines (Scheme 6). These reactions proceed with high 3delds at room temperature under 4 MPa H2, in water-ethyl acetate, water-diethyl ether mixtures, or without an organic solvent especially if a basic aqueous phase is used. The Rh-catalyst was recycled in the aqueous phase with only a small loss in activity. 

Efficient transition metal catalyzed hydration of 1,3-butadiene could replace the use of sulfuric acid in the production of the important industrial chemical 2-butanone (methyl ethyl ketone), thereby eliminating environmental and corrosion problems. In this reaction, a mixture of [Ru(acac)3] and 2,2 -bipyridine or 1,10-phenantroline together with an excess of a Bronsted acid gave promising results (223) (Scheme 42). 

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