Thermolyse von 1,2,3,4,6,7,8-Heptaazaspiro[4.4]nona-2,7-dienen, [3+2]-Cycloaddukten von Aziden an 5-Alkyliden-4,5-dihydro-1H-tetrazole

Thermolysis of 1,2,3,4,6,7,8–Heptaazaspiro[4.4]nona–2,7–dienes, [3 + 2] Cycloadducts of Azides and 5–Alkylidene–4,5–dihydro–1H-tetrazoles On thermolysis of the title compounds at 20–150°C, three modes of ring cleavage are observed, viz. [3 + 2] cycloreversion of the triazole (path A) or the tetrazole ring (path B) to azide 2 and the corresponding dipolarophile, or extrusion of molecular nitrogen from the triazole ring with concomitant 1,2 shift of a nitrogen atom of afford an iminotetrahydrotetrazine 31 (path C). An equilibrium between [3 + 2] cycloaddition and cycloreversion (path A) is established starting from the heptaazaspiro[4.4]nonadienes 4. Irreversible [3 + 2] cycloreversion of the tetrazole ring (path B) is observed on thermolysis of 6, yielding azide 2 and iminodihydrotriazoles 7. Path A and B compete in the thermolysis of 6e affording, besides methyl azide (2a), 5c and 7e. Because path A is reversible, the former disappears again while the latter extrudes molecular nitrogen to yield the iminoaziridines (E)- and (Z)-12 which decompose to the imine 13 and methyl isocyanide (14). Competition between path A and B is also observed on thermolysis of 15 and, probably, the diphenyl compound 21 as well. The latter affords a complex mixture comprising the iminodihydrotriazole 16, the iminoaziridines 18 and 23, the [2 + 1] cycloreversion products 14 and 19 of 18, and the 2–aminoindole 26 which is formed by isomerization of 18 and/or 23. None of the [3 + 2] cycloreversion reactions, but only extrusion of molecular nitrogen and formation of 31 (path C) are observed on thermolysis of the nitrophenyl spirocycles 29. The course of the thermolyses is mainly governed by the size and the electronic character of the substituent that stems from the azide used in the formation of the title compounds.