Nucleophilic substitution reactions in m-nitrobenzylic substrates

Abstract

The reaction of m-nitrobenzyl 2,4,6-trimethylbenzoate (11) with the salt (2) of 2-nitropropane, or the thiolate (16), gives moderate yields of substitution products [e.g.(3) or (17)]. However, the mechanism of formation of these products could not be definitively assigned. The m-nitrobenzyl chloride (12), on the other hand, was clearly demonstrated to undergo S_RN1 substitution reactions with a variety of anions including the anion from the salt (2), thiolate ion from (16), azide from (22), the malononitrile anion from (20), and the malonic ester anion from (21). Inhibition and entrainment effects clearly rule out an alternative radical anion-radical process involving cage collapse. The occurrence of S_RNl reactions in m-nitrobenzylic substrates adds support to a mechanism involving association of radicals with anions, and for dissociation of radical anions, which involves σ* and π* radical anions.