Reaction of 4-Amino-1,2,4-triazolium Salts with Polarized Olefins

Abstract

The reaction of 4-amino-l,2,4-triazolium salts (5a,b) with polarized olefins (3a,b,4a) in the presence of K2CO3 in EtOH or DMSO directly yielded the back-donated 1.6-cyclization products, mesomeric betaines (6a-c,7a,b) via Nvinylimino ylides, while the reaction of the salts (5a,b) with polarized olefins (4b.c) gave the 1,s-dipolar cyclization products, pyrazoles (10a.b) and [1,2,41triazolo[4,3-blpyrazole (11).It is well known that heterocyclic salts react with polarized olefins to produce heterocyclic N-allylides (1) and these N-allylides (I), acting as extended dipole are of interest in heterocyclic chemisuy.lRecently we reported a synthesis of mesomeric betaine (2) due to the resonance structure (1') and we proposed a mechanism which involves a hack-donated 1,6-cyclization for this transformation2 (Scheme 1). Scheme 1The purpose of the present investigation is to extend this back-donated 1,6-cyclization to the synthesis of [1,2,4]triazolo[4,3-blpyridaziniumides (6.7) which were prepared by the reaction of 4-amino-]&-' R N-N' HBr kc03 6a,b --N , HBr -