4,4 -Dipyridine

Methoxyestra-l,3,5(10),14-tetraen-17-one. A solution of 9.3 g (0.0328 mole) of 3-methoxyestra-l,3,5(10),14-tetraen-17)S-ol in 300 ml of methylene dichloride is added at a rapid dropwise rate to a stirred suspension of 46.5 g (0.18 mole) of the dipyridine-chromium VI complex in 800 ml of methylene dichloride at room temperature. The mixture is stirred 45 min and then filtered. The residue is washed with ethyl acetate and the organic layers are combined. Water is added to the filtrates and sufficient ethyl acetate is added to make the organic layer less dense than water. After the organic layer is washed with water it is dried over sodium sulfate and concentrated to leave... 

It would be expected that the stabilization of the adsorbed species by an extended conjugated system should increase with the number of aromatic rings in the adsorbed azahydrocarbon. However, data suitable for comparison are available only for phenanthridine, benzo-[/]quinoline, and benzo[h] quinoline. The large difference in the yields of biaryl obtained from the last two bases could be caused by steric interaction of the 7,8-benz-ring with the catalyst, which would lower the concentration of the adsorbed species relative to that with benzo[/]quinoline. The failure of phenanthridine to yield any biaryl is also noteworthy since some 5,6-dihydrophenanthridine was formed. This suggests that adsorption on the catalyst via the nitrogen atom is possible, but that steric inhibition to the combination of the activated species is involved. The same effect could be responsible for the exclusive formation of 5,5 -disubstituted 2,2 -dipyridines from 3-substi-tuted pyridines, as well as for the low yields of 3,3, 5,5 -tetramethyl-2,2 -bipyridines obtained from 3,5-lutidine and of 3,3 -dimethyl-2,2 -... 

DPC dipyridine chromium(vi) oxide TFAA trifluoroacedc anhydride... 

Both benzothieno[3,2-b]pyridine 5-oxide (31) and thieno[3,2-b 4,5-b ]dipyridine 5-oxide (32) exhibit competitive loss of oxygen either as an atom or as carbon monoxide after initial skeletal rearrangement, e.g. to sulfenate esters (equation 10)18b. These results together with some data for Y-oxides indicate that the presence of an intense [M — 16] + peak is not diagnostic for the latter only. 

Dipyridiue-chromium(VI) oxide2 was introduced as an oxidant for the conversion of acid-sensitive alcohols to carbonyl compounds by Poos, Arth, Beyler, and Sarett.3 The complex, dispersed in pyridine, smoothly converts secondary alcohols to ketones, but oxidations of primary alcohols to aldehydes are capricious.4 In 1968, Collins, Hess, and Frank found that anhydrous dipyridine-chromium(VI) oxide is moderately soluble in chlorinated hydrocarbons and chose dichloro-methane as the solvent.5 By this modification, primary and secondary alcohols were oxidized to aldehydes and ketones in yields of 87-98%. Subsequently Dauben, Lorber, and Fullerton showed that dichloro-methane solutions of the complex are also useful for accomplishing allylic oxidations.6... 

The chief drawbacks to using the Collins reagent are the nuisance involved in preparing pure dipyridine chromium VI) oxide,6 its hygroscopic nature5 and its propensity to enflame during preparation.2 3 5 The present method avoids these difficulties by simply preparing diehloromethane solutions of the complex directly.7 In... 

Dirheniumheptoxide 2154 is converted by TCS 14, in the presence of 2,2 -dipyri-dine, into the dipyridine complex 2160 [77]. Free ReCls, NbCls, and WCI5 react with HMDSO 7 and 2,2 -bipyridine to form bipyridine oxochloride complexes 2161 and TCS 14, with reversal of the hitherto described reactions of metal oxides with TCS 14. The analogous Mo complex 2162 undergoes silylahon-amination by N-trimethylsilyl-tert-butylamine 2163 to give the bis-imine complex 2164 and HMDSO 7 [77] (Scheme 13.22). 

Under conditions where the dismutation reaction is slow the exchange between Au(III) and Au(I) has been shown to proceed at a measurable rate at 0 °C in 0.09 M HCl, an exchange half-time of about 2 min was observed. The isotopic method ( Au) and a separation method based on the precipitation of dipyridine -chloroaurate(III) was used to obtain data. An acceleration in the exchange rate was observed as the HCl concentration was increased. ... 

A stopped flow technique coupled with spectrophotometric analysis of the iron (II) complex formed has been used to investigate - the reactions of some organic complexes of iron(III) with the ion Fe ". The iron(III) was complexed with 1,10-phenanthroline, various substituted 1,10-phenanthrolines (5-methyl-, 5-nitro-, 5-chloro-, 5-phenyl-, 5,6-dimethyl-, 4,7-diphenyl-, and 3,4,7,8-tetramethyl-) and 2,2 -dipyridine, 4,4 -dimethyl-2,2 -dipyridine, and 2,2, 2"-tripyridine. The wavelengths used for the analysis lay in the region 500-552 m/i. 

Baker et al, have obtained some kinetic data on the exchange reactions between the 1,10-phenanthroline, 2,2 -dipyridine and 2,2, 2"-tripyridine complexes of Co(III) and Co(ll) in both H2O and D2O solution. The isotopic method ( Co) and separations involving either extraction of Co(II) with organic solvents (n-hexanol-ether or saturated sodium acetate in n-hexanol) or precipitation of Co(III) as Co(phen)3(l3)3 were used. For the 1,10-phenanthroline system, a rate law... 

Hinckley, C. C. Paramagnetic shifts in solutions of cholesterol and the dipyridine adduct of trisdipivalomethan atoeuropium(III). A shift reagent. J. 

Electrocatalysis employing Co complexes as catalysts may have the complex in solution, adsorbed onto the electrode surface, or covalently bound to the electrode surface. This is exemplified with some selected examples. Cobalt(I) coordinatively unsaturated complexes of 2,2 -dipyridine promote the electrochemical oxidation of organic halides, the apparent rate constant showing a first order dependence on substrate concentration.1398,1399 Catalytic reduction of dioxygen has been observed on a glassy carbon electrode to which a cobalt(III) macrocycle tetraamine complex has been adsorbed.1400,1401... 

Both the disilver derivative and its precursory dipyridine complex are highly explosive and extremely shock-sensitive when dry. 

A new synthesis of substituted 1,3-dienes by reductive elimination of allylic nitro derivatives has been reported (Eq. 7.134).180 Tertiary allylic nitro compounds, bearing an acetate group in the (3-position, smoothly undergo reductive elimination to give conjugated 1,3-dienes when treated with chromous acetate and 2,2-dipyridine in DMF at 111-120 °C. 

According to an X-ray diffraction study bis-2-spirocyclohexyl-l-boraadamantane dipyridine adduct 65 is a trans-diequatorial isomer. The presence of two molecules of benzene per one complex molecule in the crystal has also been revealed <20040L313> (see Table 1 entries 3 and 4 and Schemes 26 and 29). 

More recently, a new and straightforward one-pot approach was reported by Bu et al. <2003JOC5415>. This reaction involves the cyclocondensation of l,2-dipyridin-2-yl-ethane-l,2-dione 120 and arylaldehydes, in the presence of ammonium acetate. Imidazo[l,5- ]pyridines 121 were obtained in reasonable yields, but competitive formation of imidazoles 122 was observed. The amount of ammonium acetate used in this reaction was also shown to strongly influence the yield of the cyclization (Scheme 38). 

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