A new method for the construction of [1,2,4]triazolo[1,5-a]pyridine system

Quaternization of 4-amino-4H-1,2,4-triazole with γ-bromodipnones and 5-(bromomethyl)-2,2,6,6-tetramethylhept-4-en-3-one occurred at the N-1 nitrogen atom, with the formation of quaternary salts that were cyclized in the presence of bases into [1,2,4]triazolo[1,5-a]-pyridine derivatives. Quaternary 4-amino-4H-1,2,4-triazolium salts and aromatic 1-amino-1H-[1,2,4]triazolo[1,5-a]pyridinium salts can be deaminated by treatment with nitrous acid, giving 1-substituted 1,2,4-triazoles and the respective [1,2,4]triazolo[1,5-a]pyridines.