Tetrazole Compounds. 3. Modification of 1‐Aryl‐1H‐tetrazole‐5‐acetaldehyde Enamines by Acid‐Catalyzed Transamination
The acid‐catalyzed transamination of tetrazole‐5‐acetaldehyde enamines proves to be a useful synthetic method for preparing specially N‐substituted enamines of this series not accessible directly from 3‐chloro‐propeniminium salts 3 and sodium azide. Thus, starting from (E)‐1‐aryl‐5‐(2‐dimethylamino‐vinyl)‐1H‐tetrazoles 5 transamination with dialkylamines yields tertiary enamines of types 6 and 7. Analogously, acid‐catalyzed reaction of 5 with N‐alkylanilines leads to 1‐aryl‐5‐[2‐(N‐alkylanilino)‐vinyl]‐1H‐tetrazoles 8. Bifunctinal secondary amines such as N,N′‐dimethylethylenediamine result in systems of type 9 with two linked tertiary tetrazolyvinylamino groups. All the transaminations with secondary amines proceed with retention of configuration. According to the same reaction scheme transamination of 5 (Ar = Ph) with primary alkyl‐, aralkyl‐, and arylamines affords secondary tetrazolylvinylamines 10; however, here the formation of Z‐configurated products dominates. Bifunctional primary amines like ethylenediamine and 1,2‐phenylenediamine react with 5 to give the N,N′‐linked systems 11 and 12 possessing two secondary tetrazolylvinylamino groups. – Characteristic i.r., u.v., and 1H‐n.m.r. spectroscopic data of the novel tetrazole‐5‐acetaldehyde enamines are reported.