Oxidative nucleophilic substitution of hydrogen in nitroarenes

Carbanions of 2-phenylpropionitrile were found to add to nitroarenes in liquid ammonia to form sigma(H) adducts, which were oxidized with KMnO4 to yield products of oxidative nucleophilic substitution of hydrogen (ONSH) in the position para to the nitro group. Treatment of the carbanion-nitroarene system with methyl iodide at -70 degrees C indicated that the addition proceeds almost to completion. Thus, for the first time, the persistence of sigma(H) adducts, formed between free anions and mononitroarenes, has been demonstrated. It was also shown that KMnO4 oxidizes sigma(H) adducts to nitrobenzene faster than it does carbanions. This selective ONSH in the pma positions of nitroarenes is a general process. However, some substituents hinder or inhibit the oxidation step.