Thiolate ions add regiospecifically to N-(4-oxopyridin-l -yl)pyridinium salts (2)-(7) to give in good to excellent yields only the 1,4-dihydropyridine adducts (8)-(13), regardless of whether or not the pyridone moiety carries substituents for sterically shielding the 2and 6-positions of the pyridinium ring. The addition is believed to be thermodynamically controlled. Decomposition of the dihydro-adducts under free-radical conditions, or by pyrolysis, gives good yields of pyridin-4-yl thioethers (1 4) and (1 6) though the reaction failed with the 2-methyl adducts ( 9). An improved synthesis of 6-methyl-4-oxopyran-2-carboxylic acid is also described.
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