Pyridones 2-hydroxypyridines synthesis

The synthesis of cis-1,4 polymers was also tried by e use of monomers with an s-cis conformation. The solid-state photopolymerization of pyridone derivatives, which is a six-membered cyclic diene amide and is a tautomer of 2-hydroxypyridine, was attempted [100]. Pyridones make hydrogen-bonded cocrystals with a carboxylic acid in the crystalline state. Because the cyclic structure fixes its s-cis conformation, if the polymerization proceeds, a cis-2,5 polymer would be obtained. Actually, however, the photopolymerization did not occur, contrary to our expectation, but [4-1-4] photodimerization proceeded when the carbon-to-carbon distance for the dimerization was small (less than 4 A) [101]. A closer stacking distance of the 2-pyridone moieties might be required for the topochemical polymerization of cychc diene monomers. 

The powerful 7V,7V-diethylcarbamate DMG serves admirably for the synthesis of substituted oxygenated pyridines. Thus, metalation of all isomeric pyridyl O-carbamates 317 with sec-BuLi/TMEDA followed by quench with numerous electrophiles affords diversely substituted products 318 in good to excellent yields (Scheme 96) (85JOC5436). Base-induced hydrolysis provides access to pyridones and hydroxypyridines. 

The 2- or 4-hydroxypyridines [(81) and (82)] are tautomeric and in solution exist preferentially in the corresponding pyridone forms. Their synthesis from the corresponding pyrones by a heteroatom exchange reaction is possible. 

A published synthesis of 3,4-diaminopyridine29 204 starts with nitration of 4-hydroxypyridine 207. This is a difficult reaction in spite of the electron-donating OH group because the compound is mostly a pyridone 206. Nevertheless a 74% yield of 208 can be achieved with a mixture of fuming nitric and sulfuric acids. 

Ab initio calculations on hydroxypyridine-pyridone gas-phase equilibria have been carried out the split-valence basis that was used, together with full optimization of geometry, is said to give considerably greater accuracy than previously achievedAn improved synthesis of 2-amino-3-alkoxy-pyridines by phase-transfer-catalysed alkylation of 2-amino-3-hydroxy-pyridines has been reported Irradiation of 4-methyl-2(l// )-pyridone (28) gives the bicyclic lactam (29), which has been transformed into an isomeric mixture of jS-lactams (30) (Scheme 17). ... 

Table 5 Synthesis of 3-pyridones 58, hydroxypyridines 64 (entries 1—4), and pyridine triflates 65 (entries 5—7)...

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