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■ Activated Manganese Dioxide as an Oxidizing Agent for the Conversion of N-Methylphenanthrolinium Salts to N-Methylphenanthrolones

Martin R. Johnson,* Dwayne Bell, and Lucy Shanaman

*Department of Chemistry, The George Washington University, Washington, DC 20052, U.S.A.

Abstract

Activated manganese dioxide (MnO₂) in dry THF was studied for the transformation of N-alkylpyridinium salts to N-alkyl-2-pyridones. Only cations of fused ring pyridines (1,10-phenanthroline, quinoline, etc.) were investigated. Nearly quantitative conversion to 1-methyl-1,10-phenanthrol-2-one was achieved under optimum conditions. Oxidative cleavage of ring methyl groups when present also led to pyridones, in some cases producing a 4-pyridone. Different counteranions gave mixed results. Overall, activated MnO₂ is an effective alternavie to aqueous ferricyanide for the conversion of fused ring pyridinium salts to the corresponding 2-pyridones.