THERMAL-REACTION OF 1,2,4-TRIAZOLIUM N-ALLYLIDES - FORMATION OF MESOMERIC BETAINES, 1,2,4-TRIAZOLO[4,3-A]PYRIDINIUMIDES, VIA BACK-DONATED 1,6-CYCLIZATION

The reaction of 1,2,4-triazolium salt (7) with polarized olefins (2, 3 a,b) in the presence of K2CO3 in CHCl3-EtOH gave the corresponding tri azolium N-allylides (8a-c). Thermolyses of the N-allylides (8a,c) affo rded the mesomeric betaine (9a) and the 8-amino-1,2,4-triazolo[4,3-a]p yridine derivative (10). Similar treatment of the salt (7) with polari zed olefins (3c,d, 4a) directly yielded mesomeric betaines (9c-e), whi le the reaction of the salt (7) with polarized olefin (4b) gave the py rrolo[1,2-d]-1,2,4-triazine derivative (11). The formation of mesomeri c betaines is suggested to proceed via back-donated 1,6-cyclization.