Preparation and study of some 5- and 7-substituted 4-nitrobenzofurazans and their N-oxides; a retro-Boulton–Katritzky rearrangement

Abstract

7-Anilino-4-nitrobenzofuroxan rearranges on heating to the sterically more hindered 5-anilino-4-nitrobenzofuroxan. This exception to the Boulton–Katritzky rearrangement is explained in terms of hydrogen-bonding. The equilibrium between 7-dimethylamino-4-nitro- and 4-dimethylamino-7-nitro-benzofuroxan is sufficiently slow at 33° for these two isomers to be distinguished from each other by 1H n.m.r. The 1H n.m.r. spectra of some thirty new benzofurazans and twelve new benzofuroxans are recorded together with other physical properties.