Sparing the Ortho-position in Nucleophilic Aromatic Substitution-Specific Displacement of the 4-SePh Group in 2,4-Bis(phenylseleno)nitrobenzene

Upon treatment of o- and p- (phenylseleno)nitrobenzenes with sodium methoxide quantitative exchange reactions took place, affording the corresponding methoxynitrobenzenes. Upon reaction between 2,4-bis(phenylseleno) nitrobenzene 2 and sodium methoxide, an unusual regiopure formation of 4-methoxy-2-(phenylseleno)nitrobenzene 3 was observed. This product remained unreactive toward an excess of sodium methoxide, thus preventing the formation of 2,4-dimethoxynitrobenzene 6. The nature of the reactants and of the intermediate Meisenheimer complexes was examined by synthetic investigations, x-ray crystallography, and DFT calculations. We found that the observed selectivity can be understood in terms of traditional resonance considerations.