Thermolyse von 5‐Alkyliden‐1,4‐dihydro‐5 H ‐tetrazolen

Thermolysis of 5‐Alkylidene‐1,4‐dihydro‐5H tetrazoles In benzene solution at 100°C, the isopropylidenedihydrotetrazole 1 a decomposes mainly (80%) into molecular nitrogen and the aziridinimines ( E )‐ and (Z)‐ 2a which are thermally unstable and afford methyl isocyanide and the imine 3a . In addition, the novel spirocyclic tetrahydropyrimidine 7a is formed (18% yield) in a [4 + 2] cycloaddition of 1a and the hypothetical intermediate 1,3‐diazabutadiene 19a generated from 1a through a [1,4] hydrogen shift and loss of molecular nitrogen. The thermolysis of the neopentylidenedihydrotetrazole 1b at 100°C is more complex. Only small amounts of the aziridinimines ( E )‐ and (Z)‐ 2b and their decomposition products 3b and methyl isocyanide are observed. A major product is the spirocyclic tetrahydropyrimidine 7b which exhibits moderate thermal stability. Slow thermolysis of 7b affords the tetrahydropyrimidinimine 8b and methyl azide. The latter reacts with 1b in a [3 + 2] cycloaddition furnishing the spiro compound 5b which partially decomposes into the amino‐1,2,3‐triazole 16 , thus regenerating methyl azide. This catalyzed isomerization 1b → 16 which is initiated through the thermal [3 + 2] cycloreversion of 7b involves a total of 19% of 1b . The structures of the products are elucidated by means of mass spectra and high‐field NMR spectra. The mechanism of formation of the 1,3‐diazabutadienes 19 from 1 is discussed.