Reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine with phosphorus pentoxide in the presence of nitriles. New method for the generation of aryloxenium ion

A reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine with nitriles RCN (R = Me, Et, Ph) in the presence of P₄O₁₀ in excess amount at 0 °C leads to the formation of 2-R-5-nitro-1,3-benzoxazoles. The reaction presumably takes place through the intermediate (phenoxy)oxodiazonium ion NO₂C₆H₄O-N=N=O]⁺, which eliminates an N₂O molecule to form the aryloxenium ion NO₂C₆H₄O]⁺. The latter reacts with nitriles RCN at the ortho-carbon atom of the phenyl ring giving 2-R-5-nitro-1,3-benzoxazoles.