2,2 -Pyridilic acid

The generality of the rearrangement is further illustrated by the reaction of 2,2 -furil with hydroxide ion in dry ether (Table 1). Likewise, 2,2 -pyridil is rearranged in hot methanol solution (40 min) to give the sodium salt of 2,2 -pyridilic acid (86%). Acidification, however, affords bis(2-pyridyl)methanol by decarboxylation since 2,2 -pyridilic acid (16) is structurally similar to a -keto acid. Benzilic rearrangement of 2,2 -pyridil with methanolic nickel(ll) and cobalt(II) acetates results in the formation of metal complexes of 2,2 -pyridilic acid (17 92%). A plausible mechanism is summarized in Scheme 4. Rearrangement is also observed with 2,2 -quinaldil, but benzil, 2,2 -furil or 1-phenyl-2-(2 -pyridyl)ethane-1,2-dione are not susceptible to these metal template reactions. 

Pyridil allowed to react with hydrated Ni-acetate in methanol 2,2 -pyridilic acid Ni-complex. Y almost 100%. - This extremely mild rearrangement is dependent on chelation. Also with cobaltous acetate and limitations s. D. S. C. Black, Chem. Gommun. 1967, 311. 

Cationic bis(oxazoline) and pyridil-bis(oxazoline) Cu(ll) and Zn(ll) Lewis-acid catalysts. A comparative study in catalysis of Diels-Alder and aldol reactions [101]... 

Oxidation of the pyridoins, e.g. with iodine, gives the corresponding a-diketones. The significant electron withdrawal exerted by the 7r-deficient heterocyclic system on carbonyl groups at the a- and y-positions can be demonstrated in the behaviour of the diketones under benzilic acid rearrangement conditions. Whereas 3,3 -pyridil (73) gives a normal... 

A benzilic acid rearrangement can be achieved with 2,2 -pyridil and with the quinoline analogues (75) under mild conditions by using methanolic nickel(II) or cobalt(II) acetates. The product acid is isolated as a metal complex (Scheme 71) (69AJC1439). 

Figure 8-43. In the case of complexes of 2,2 -pyridil, the benzilic acid rearrangement may be followed and complexes of the intermediate may be isolated.

The oxidation of the metal complexes of l,10-phenanthroline-5,6-quinone is thought to proceed in a similar manner, with the first step being a benzilic acid rearrangement. Rearrangements of this type may also be followed directly in nickel(u) and cobalt(m) complexes of 2,2 -pyridil. The first step of the reaction involves nucleophilic attack on an O-bonded carbonyl group to form a hydrate, followed by a benzilic acid rearrangement. In this case, the benzilic acid rearrangement products may be isolated as metal complexes (Fig. 8-43). 

Diaminopyridine has been condensed with glyoxal, benzil, - diacetyl,and the pyridils 4. ° Ethyl oxalate yields the 2,3-dioxo compound. The conditions employed for these condensations can be critical. Thus glyoxal in neutral solution yields an unidentified, insoluble, infusible solid, whereas in the presence of acetic acid the reaction readily provides the parent heterocycle.The preferred method makes use of glyoxal sodium bisulfite. Many symmetrical dicarbonyl compounds have been condensed with a variety of 2,3-diaminopyridines substituted in the pyridine ring by bromo, ° chloro, methyl, " or combinations of these substituents. ... 

Nowadays, the trend appears to be to determine simultaneously iron and other metals or Fe(II) and Fe(III) species. In the first case, some reagents such as l,5-bis(di-2-pyridylmethylene)thiocarbonohydrazide, 2,4,6-tri-(2-pyridil)-l,3,5-triazine are used. In the second case 4,5-dihydroxy-l,3-benzenedisulfonic acid, disodium salt (635 nm), l-(5-bromo-2-pyridyla-zo)-2-naphthol-6-sulfonic acid (765 and 850 nm), azide complexes in tetrahydrofuran (396 nm), etc. are used... 

The pyridils are not especially remarkable. Some examples have been reported to undergo the benzilic acid rearrangement , but others with ethanolic potash give an aldehyde (which subsequently undergoes the Cannizzaro reaction) and a carboxylic acid . Heated with lead oxide, 2,2 -pyridil gives di-(2-pyridyl) ketone . An x-ray crystallographic study of 2,2 -pyridil has been made" . 

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