THERMAL REACTION OF 1,2,4-TRIAZOLIUM N-ALLYLIDES: FORMATION OF MESOMERIC BETAINES 1,2,4-TRIAZOLOPYRIDINIUMIDES, VIA BACK-DONATED 1,6-CYCLIZATION

Article abstract of DOI:10.3987/COM-94-6950

The reaction of 1,2,4-triazolium salt (7) with polarized olefins (2,3a,b) in the presence of K2CO3 in CHCl3-EtOH gave the corresponding triazolium N-allylides (8a-c).Thermolyses of N-allylides (8a,c) afforded the mesomeric betaine (9a) and the 8-amino-1,2,4-triazolo<4,3-a>pyridine derivative (10).Similar treatment of the salt (7) with polarized olefins (3c,d,4a) directly yielded mesomeric betaines (9c-e), while the reaction of the salt (7) with polarized olefin (4b) gave the pyrrolo<1,2-d>-1,2,4-triazine derivative (11).The formation of mesomeric betaines is suggested to proceed via back-donated 1,6-cyclization.