An unexpected course of the Meisenheimer reaction : aryl phosphates in the reaction of phosphoryl chloride with 2,3-diphenylquinoxaline-N1-oxide.

Article abstract of DOI:10.1016/S0040-4020(01)90308-4

Contrary to what is observed with other ?-deficient heteroaromatic N-oxides, the reaction of 2,3-diphenylquinoxaline-N₁-oxide with OPCl₃ gives only very poor yields of chlorinated quinoxalines.It is shown that the major product arises from an unprecedented attack by the nucleophilic oxygen atom of the reagent at a carbon atom of the homocycle of the O-phosphorylated N-oxide, leading ultimately to the corresponding mono- (or di-) aryl ester of phosphoric acid.Using a much smaller excess of OPCl₃ and dilution of the medium with an inert solvent strongly increase the yield of chlorination products.It is suggested that, after the initial O-phosphorylation, phosphate formation might be the primary step in all the Meisenheimer reactions.