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

5‐Alkylidene‐4,5‐dihydro‐1 H ‐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 · F 3 CSO 3 and 12 · F 3 CSO 3 . The crystalline hexafluorophosphates 9 · PF 6 and 12 · PF 6 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 5 J   H,CH   3of 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.