The Thermolysis of the Cycloadducts between Aryl Azides and Hexamethyl‐Dewar‐Benzene Revisited

Abstract

Dedicated to Professor Rolf Huisgen on the occasion of his 85th birthdayThe reactions of 1-azido-2,4,6-trimethyl-and 1-azido-2,6-dimethylbenzene with hexamethyl-Dewarbenzene (HMDB) give rise to the pentamethyl(iminoethyl)-4H-1,2-diazepines 4 and 5, respectively. The Xray 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 3H-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.

Diazo Compounds as Electrophiles To React with 1,4-Dilithio-1,3-dienes: Efficient Synthesis of 1-Imino-pyrrole Derivatives

“…Herein we report our preliminary results on the reaction between the dilithio reagents 1 and diazo compounds, in which diazo compounds acted as electrophiles. Multiply substituted 1-imino-pyrrole and indole derivatives were obtained in good to excellent isolated yields. , Synthetic methods for N -imino pyrrole and indole derivatives are very limited . A mechanistic investigation revealed that two diazo compounds reacted with one dilithio reagent affording the intermediate 2 .…”

Syntheses and Electron Density Determination of Novel Polyimido Sulfur Ylides

“…During this doctoral study 16 molecular structures have been determined by X-ray crystallography as part of the cooperation with other groups. The cooperations with the groups of Dr. Breuning, Prof. Dr. Christl, Prof. Dr. Klingebiel, and Prof. Dr. Kost lead to five already printed publications [289][290][291][292][293] and two additional publications are in preparation or submitted.…”