5‐Alkyliden‐4,5‐dihydro‐1H‐tetrazole mit Vinyl‐ oder Phenyl‐Substituenten

5-Alkylidene-4,5-dihydro-1H-tetrazoles Substituted by Vinyl or Phenyl Groups. The nitriles 7e–k and 10 are methylated by methyl triflate to afford the N-methylnitrilium triflates 8e–k and 11 which are allowed to react with methyl azide to produce the tetrazolium triflates 9 · F3CSO3 and 12 · F3CSO3. The crystalline hexafluorophosphates 9 · PF6 and 12 · PF6 are obtained after anion exchange with ammonium hexafluorophosphate. Deprotonation of the tetrazolium cations 9c–g,j,k and 16 furnishes the corresponding alkylidenedihydrotetrazoles 3 and 17 as yellow, distillable oils or sublimable, low melting solids which are extremely sensitive towards moisture and oxygen. The parent compound 3c isomerizes readily to the amino-1,2,3-triazol 15. The rearrangement is initiated by traces of moisture inducing formation of methyl azide which acts as a catalyst. Similarily, 17 is cleaved into the amide 19 and phenyl azide which adds to unchanged 17 in a 1,3-dipolar cycloaddition reaction yielding 18. Nuclear Overhauser experiments demonstrate that, of the two splittings 5J of 3d, the larger one stems from the long-range coupling between the protons at the same side of the double bond, suggesting a contribution from a through-space interaction to that coupling. The α-carbon atoms of 3 and 17 resonate at higher field than those of 2-alkylidenetetrahydroimidazoles 20 having the same substitution pattern, and even benzylpotassium (21). Furthermore, the down-field shifts, caused by α-deprotonation of the cations are smallest in the tetrazole series and hence indicative of extraordinary high electron densities at the α-carbon atoms of 3 and 17 which may be interpreted in terms of contributions by dipolar resonance structures.