4- Alkoxypyridines, rearrangement

Alkoxypyridines rearrange at elevated temperatures to A -alkyl.4-pyndones. Isomerizations of this kind are catalyzed by acids and alkyl halides. Spinner and White, however, have prepared 4-methoxypyridine from 4-chloropyridine and sodium methoxide in 86% yield through temperature control and by neutralization of the reaction mixture with solid carbon dioxide. 2-(3,5-Dinitro-2-pyridyl)pyridinium chloride (XII-367), formed from 3,5-di-nitro-2-chloropyridine and pyridine in benzene or ether, is readily hydrolyzed in an alkaline medium to 3,5-dinitro-2-pyridone. ... 

Deuterium-labeling and mass spectrometry prove that the mechanism of the thermal O to N rearrangement of 4-alkoxypyridines to N-alkyl-4-pyridones is intermolecular (88CS347). 

Alkoxypyridines such as 110 undergo thermally induced rearrangement to /V-alkylpyridones such as 111 under flash vacuum pyrolysis <2003AJC913> (Equation 75). 2-Methoxy-4-methylquinoline and 1-methoxyisoquinoline also undergo rearrangement in 35% and 70% yield, respectively. 

Allyloxy derivatives from pyridine-1-oxides posed still a further element of uncertainty. This arose from the facile isomerization of 2-alkoxypyridine-l-oxides into the corresponding l-aIkoxy-2-pyri-dones even under the conditions of synthesis. Thus, treatment of 2-chloropyridine-l-oxide with sodium allylalcoholate afforded the 2-allyloxypyridine-l-oxide whereas treatment of the same starting compound with sodium benzyloxide gave l-benzyloxy-2-pyridone. A closer investigation revealed that 2-benzyloxypyridine-l-oxide rearranged readily under the experimental conditions of synthesis.6... 

Many 4-alkoxypyridines, e.g. (410), and their corresponding iV-methyl-4-alkoxypyridinium iodides (411) have been prepared and pyrolysed at temperatures less than 185 °C to give olefins derived from the alkyl moiety. The alkoxypyridines are obtained by reaction of the alkoxide with 4-chloro-pyridine. However, synthetically, the reaction suffers from a lack of stereospecificity and carbonium ion rearrangement products may be obtained. ... 

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