Carbanions. Electron Transfer vs. Proton Capture. 7. Electron-Transfer Oxidation of an Amino Acid Derived Carbanion

Article abstract of DOI:10.1021/jo00316a004

The dimethylamide of phenylalanine, 1, reacts with potassium tert-butoxide and nitrobenzene in tert-butyl alcohol at 50 deg C in argon atmosphere.The products are potassium nitrobenzenide (PhNO2^-*K⁺)and degradative fragments of the amino amide, including ammonia, dimethylamine, potassium benzoate, potassium carbonate, and potassium cyanide.The yields of these isolated degradation products are relatively low when the reaction is run anaerobically but are improved when the reaction is carried out under oxygen.The oxygen-mediated reaction does not produce cyanide or nitrobenzenide but its products are otherwise the same with the addition of oxalate.Conversions are essentially quantitative when the oxygen-mediated reaction is followed by vigorous, acid-catalyzed, hydrolytic workup.The reaction is believed to begin with the one-electron oxidation of the α-amino carbanion, proceeding through a ketimine and/or enamine which is rapidly oxidized to the eventual products.The rate of oxidation of 1 is approximately the same as its ionization rate but the reaction becomes less efficient if the N-pivalyl derivative of 1 is used.Experiments with the dimethylamide of alanine give qualitatively similar results, with potassium formate replacing potassium benzoate in the products.