Sulfur-substituted 2-pyridones

Studies on sulfur-substituted 2-pyridones have shown (99M545) that unsaturated phenylthio ketones 90 can yield aminopyrans 91 with MN 27a, while enaminone (X = NMe2) gives 2-pyridones 92 (Scheme 26). 

Hydroxypyridines undergo a variety of other electrophilic substitution reactions. Sulfonation of 2-pyridone with 10% oleum at 180° gave the 5-sulfonic acid.69 110 A-Methyl-2-pyridone is similarly sulfonated with chlorosulfonic acid. The action of fuming sulfuric acid gave a mixture of the 5-sulfonic acid and the 3,5-disulfonie acid. A nitro group at C-5 is said not to hinder the reaction, sulfonation at the... 

Yamazaki [51] has reviewed a number of stoichiometric cycloaddition reactions at the cobaltacyclopentadiene ring system that lead to a plethora of heterocycles. For example, five- and six-membered heterocycles containing nitrogen, sulfur, selenium, and phosphorus have been made accessible by this route (eq. (20)) [52]. The co-cyclization of substituted alkynes and isocyanates in the presence of a rhodium metallocycle gives 2-pyridones (eq. (21)) [53]. 

The substituted 4-quinolizones 201 and 202 are hydrolyzed by hot 80% sulfuric acid, giving presumably a pyridone (203) which recyclizes to quino-lones 204 and 205.39... 

If 2- and 4-aminopyridines are diazotized in dilute mineral acids, diazonium salts are formed however, the diazonium ions are not stable and they hydrolyze rapidly to the corresponding pyridones. " For example, the diazotization of 2-amino-4-nitropyridine in sulfuric acid yields 85% of 4-nitro-2-pyridone. Diazonium salts of 2-substituted-4-aminopyridines with electron-withdrawing substituents such as COOH, CONH2 and CN are particularly unstable. ... 

The boron trifluoride and hydrogen chloride salts of 2- and 4-pyridyl N,JV -dimethylthiocarbamate rearrange at room temperature. The lower temperature requirement for phenols substituted with electron withdrawing groups supports a mechanism involving nucleophilic attack by sulfur (XII-633 - XU-634). When 4-pyridone is heated with sodium bisulfite a small amount of... 

Alkyl and Aryl Alkyloxy, Aryloxy, and Hydroxy Amino, Substituted Amino, and Imino Carboxylic Acids, Aldehydes, Amides and Esters Nitriles Halo Nitro and Nitroso and Sulfur Containing Pyridinols and Pyridones. 

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