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.