Pyridones weak bases

Like amides, 2- and 4-pyridones are also very weak bases, mnch weaker than amines. Like amides, they actnally protonate on oxygen rather than nitrogen (see Section 4.5.4). This fnrther emphasizes that the nitrogen lone pair is already in nse and not available for protonation. On the other hand, the N-H can readily be deprotonated pyridones are appreciably acidic abont 11). The conjngate base benefits from considerable resonance stabilization, both via... 

Copper-catalyzed (stoichiometric or catalytic) at room temperature and weak base under air Wide scope of substrates alcohols, amides, amines, anilines, azides, hydantoins, hydrazines, imides, imines, nitroso, phenols, pyrazinones, pyridones, purines, pyrimidines, sulfonamides, sulfinates, sulfoximines, thiols, thiourea, ureas, and sulfonylguanidines... 

The amino function in 4-amino-3-halopyridines belraves unexceptionally. Thus 4-amino-3-diloropyridine gives the 3-chloro-4-pyridinediazonium salt dien treated with nitrous acid the diazonium salt decomposes in the presence of potassium iodide to yield 3-chloro-4-iodopyridine. 4-Amino-2,3,5,6-tetrafluoropyridine is a very weak base but it can be diazotized in 80% hydrofluoric acid. The diazonium salt is converted to 4-bromo-2,3,5,6-tetrabromopyridine with cuprous bromide, but its reaction with water or with A, lV-dimethylaniline are complex. 4-Amino-2-chloro-3-nitropyridine is not converted to 2-chloro-3-nitro-4-pyridone (K-97) on diazotization with mineral acids and sodium nitrite or with isoamyl nitrite in glacial acetic acid with the latter reagent 2-chloro-3-nitropyri-dine (K-98) is formed." Nitrous acid reacts with 4-amlno-2-pyridone to give 4-amino-3-nitroso-2-pyridone instead of the diazonium salt. ... 

Hydroxypyridines (776) are both weak acids and bases and can therefore exist as zwitterions (777) (see Section 2.2.5.1). The zwitterions of 2- and 4-hydroxypyridines are known as 2- and 4-pyridones because of their uncharged canonical forms, e.g. (778) and (779). a- and y-Hydroxypyridines exist in aqueous solution very predominantly as the oxo or pyridone form. For a- and y-hydroxy-benzopyridines and -benzazines, the equilibrium favors the benzopyridone form still more, with the exception of 3-hydroxyisoquinoline. The reactivity of the pyridones and azinones is considered in Sections 3.2.3.7.2-4. 

Hydroxypyridines 806 are both weak acids and bases and can therefore exist as zwitterions 807 (see Section 2.2.5.1). The zwitterions of 2- and 4-hydroxypyridines are known as 2- and 4-pyridones because of their uncharged canonical... 

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