3,3 -Biquinoline

A solution of n-butyll ithium in hexane was obtained from Aldrich Chemical Company, Inc. Before use the solution is titrated with a 1 M solution of 2-butanol in xylene according to the procedure of Watson and Eastham, [see Gall, M. House, H. 0. Ovg. Synth. 1972, 52, 39] with 2,2 -biquinoline as indicator. 

Biquinolin-4,4 -dicarboxylic (2,2 -bicinchoninic) acid [1245-13-2] M 344.3, m 367 , pKEst(i) 1.5, pl st(2) 4.0. Dissolve in dilute NaOH and ppte with acetic acid, filter, wash well with H2O and dry at 100° in a vacuum oven. Attempts to form a picrate failed. The methyl ester (SOCl2-MeOH) has m 165.6-166°. [J Am Chem Soc 64 1897 1942 68 2705 1946.] Fordi-K salt see entry in Chapter 5. 

Biquinolin-4,4 -dicarboxylic acid dipotassium salt [63451-34-3] M 420.51. Recryst from H2O. The Cu salt has 3. max 3t 562nm. [Anal Biochem 56 4409 1973.]... 

In 1960 Rapoport and his co-workers found that some 2,2 -biquinoline is formed when quinoline w as used as a solvent for dehydrogenations in the presence of palladiuin-on-carbon catalyst, and they showed that several related bases (including pyridine) gave 2,2 -biai yls when refluxed at atmospheric pressure with a 5% pal-ladium-on-carbon catalyst. With a pyridine-to-catalyst ratio of 10 1, 11% conversion of pyridine to 2,2 -bipyridine was observed after heating for 24 hr. 

The three catalysts which have been used for the preparation of 2,2 -bipyridines from pyridines have also been employed for the preparation of 2,2 -biquinolines from quinolines. Tlie results have... 

Most of the reactions with quinolines and degassed Raney nickels have been carried out at the atmospheric boiling point (above 230 C), a condition which is known to favor the formation of by-products. With quinoline and 4-methylquinoline (lepidine), however, the yields of the 2,2 -biquinolines were increased three to four times by heating in vacuo at 150° C, and it seems probable that other quinolines will behave similarly. Table II also shows that the yields of 2,2 -biquino-lines obtained under comparable conditions vary with the position of the methyl group in a fashion reminiscent of the trends observed with the pyridines (Table I). This similarity extends to the behavior of the two 2-methyl substituted quinolines studied, which undergo loss of the 2-methyl group to some extent and form traces of 2,2 -biquinolines. 

Sufficient data are not yet available to allow evaluation of the relative merits of palladium-on-carbon and degassed Raney nickel catalysts. Comparable yields of 2,2 -biquinolines have been obtained by both methods under suitable conditions but the percentage conversions with degassed Raney nickel have been found to be much lower, reflecting the extent of side reactions with this catalyst. However, work in this laboratory has shown that the reaction of quinoline with palladium-on-carbon is not free from complications for example, at least three products in addition to 2,2 -biquinoline have been detected by paper chromatography. 

Rhodium-on-carbon has also been found to bring about the formation of 2,2 -biquinoline from quinoline, the yield and the percentage conversion being similar to that obtained with palladium-on-carbon. On the other hand, rhodium-on-carbon failed to produce 2,2 -bipyridine from pyridine, and it has not yet been tried with other bases. Experiments with carbon-supported catalysts prepared from ruthenium, osmium, iridium, and platinum have shown that none of these metals is capable of bringing about the formation of 2,2 -biquinoline from quinoline under the conditions used with palladium and rhodium. ... 

Amine complexes stabilized with phosphine ligands of the type [AuL(PR3)]+ have been obtained for L = bipy,2310 phen,2310,231 quinoline,23 1 acridine,2311 benzo[h]quinoline,2311 naphthyr-idine (388)2311 2,2 -biquinoline,2311 di-2-pyridyl-ketone,2311 di-2-pyridylamine,2311 2-(2-pyridyl)-benzimidazole, 2311 ferrocenylpyridine, 2-nitroaniline,2312 4-methoxyaniline,2312 NHPh2, 2 NHEt2,2312 NMe3,2312 quinuclidine,2313 NEt3,2314 2-aminothiazoline,2315 histidine,2316... 

The submitters used butyllithium in hexane available from Janssen Chimica and standardized before use by titration against a solution of benzylic alcohol in toluene and cuproine (2,2 -biquinoline). The checkers used butyllithium (1.6 M in hexane) available from Aldrich Chemical Company, Inc., which was standardized before use by titration with diphenylacetic acid in THF. 

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. 

Oppenauer-type oxidation of secondary alcohols can be a convenient procedure for obtaining the corresponding carbonyl compounds. It was found recently [19], that Ir(I)- and Rh(I)-complexes of 2,2 -biquinoline-4,4 -dicarboxylic acid dipotassium salt (BQC) efficiently catalyze the oxidation of secondary alcohols with acetone in water/acetone 2/1 mixtures (Scheme 8.5). The reaction proceeds in the presence of Na2C03 and affords medium to excellent yields of the isolated ketones. The process is much faster in largely aqueous solutions, such as above, than in wet organic solvents in acetone, containing only 0.5 % water, low yields were observed (15 % vs. 76 % in case of cyclohexanol). 

Water-soluble catalysts for Oppenauer-type oxidation of alcohols can be achieved by adding functionalized salts of classical ligands such as dipotassium 2,2 -biquinoline-4,4 -dicarboxylate (BQC) to acetone-water mixtures. In this way, the catalyst system [ Ir(ix-Cl)(cod) 2]/BQC is highly efficient for the selective oxidation of a wide range of alcohols such as benzylic. 

It has already been known for a long time that haloalkylzinc compounds are excellent reagents in cyclopropanation reactions . Such compounds, however, are rather unstable and are usually prepared in situ. It appears that 2,2 -bipyridine and 2,2 -biquinoline stabilize these haloalkylzinc compounds to a large extent . Compounds 110 and 111 (Table 6) are examples of stabilized cyclopropanating reagents that can be stored as solid materials over a longer period of time. 

Different sequences of reduction processes have also been obtained, when the peripheral bpy ligands are replaced by ligands such as 2,2 -biquinoline (biq), whose reduction potential is intermediate between the first and second reduction potentials of the bridging dpp ligands. Details can be found in the original reference 21. 

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