The normal and the retro-Boulton–Katritzky rearrangement of hydroxy- and nitro-substituted benzofuroxans

Abstract

The demethylation of 7-methoxy-4-nitrobenzofuroxan by aqueous KOH gives rise to 7-hydroxy-4-nitrobenzofuroxan as well as 5-hydroxy-4-nitrobenzofuroxan, the latter being formed via a retro-Boulton–Katritzky rearrangement. The retro rearrangement also occurs on heating the potassium salt of 7-hydroxy-4-nitrobenzofuroxan in the solid state. In basic aqueous solution 5-hydroxy-4-nitrobenzofuroxan undergoes the normal Boulton–Katritzky rearrangement to yield 7-hydroxy-4-nitrobenzofuroxan. These processes are rationalized on the basis of a balance between electrostatic and steric interactions in the reactants and the products of rearrangement.