New nitronate sigma complexes and the mechanism of nucleophilic aromatic photosubstitution para to a nitro group.
[reaction: see text] Photolysis of 4-nitroanisole with aliphatic amines gives mainly N-substituted 4-nitroanilines. Reactions of this type have been widely attributed to a geminate radical mechanism. We questioned this interpretation and have searched for and found by NMR spectroscopy a new class of stable nitronate adducts generated under the reaction conditions. The adducts imply that photosubstitution by amines para to the nitro group occurs by meta sigma complex formation followed by an unprecedented sigmatropic rearrangement.
Department of Chemistry, University of Nebraska at Kearney, Kearney, Nebraska 68849, USA. wubbelsg@unk.edu
Gene G
GG
Wubbels
Kandra M
KM
Johnson