Abstract
The reactions of 1‐azido‐2,4,6‐trimethyl‐ and 1‐azido‐2,6‐dimethylbenzene with hexamethyl‐Dewar‐benzene (HMDB) give rise to the pentamethyl(iminoethyl)‐4__H__‐1,2‐diazepines 4 and 5, respectively. The X‐ray crystal‐structure analysis of 5 unequivocally established these unexpected structures, which motivated us to re‐investigate the thermolysis of the adduct 1a of HMDB and azidobenzene. Previously, the triazonine 2 was reported to be the major product, but this interpretation could not be corroborated now, and, instead, the 1‐aminopyrrole 6 was identified as the true compound. The structure of the analogous compound 7, obtained by thermolysis of the (1‐azido‐4‐nitrobenzene)‐HMDB adduct 1b, was confirmed by X‐ray diffraction. In the original literature investigation, a second product had been isolated, in addition to the alleged 2, by chromatographic purificiation of the thermolysis mixture, and structure 3 had been ascribed to it. It turns out now that this compound is not a valence isomer of the major product, but a hydrolysis product, i.e., the ketone 8. The formation of the rather different compounds 4 and 5 on the one hand, and 6 and 7 on the other hand, can be rationalized straightforwardly by a sequence of pericyclic reactions leading to 3__H__‐1,2‐diazepines 11 as common intermediates, which are converted to either 4 and 5, or 6 and 7, depending on the nature of the aromatic group.