Oxidative cyclizations. VI. Mechanism of cyclization of N-chloro-2-nitroanilines to benzofuroxans under alkaline conditions

Abstract

An improved synthesis of N-chloro-2-nitroanilines used chlorine in CCl₄ solution to halogenate the 2-nitroaniline. Treatment of these CCl₄ solutions of the N-chloroamines with methanolic lithium methoxide, or potassium t-butoxide in t-butyl alcohol, produced a transient red colour, and quantitative yields of the corresponding benzofuroxan (benzofurazan 1-oxide) were obtained. U.v. and e.s.r. spectra indicated that the red species is the conjugate base of the N-chloroamine. On the basis of rate measurements, it is concluded that this red anion ejects chloride ion irreversibly to yield a singlet ortho-nitrophenylnitrene, which then rapidly cyclizes to the benzofuroxan. The ortho-nitro group does not assist in chloride ion ejection.