Reaction of N-Aminopyridinium Derivatives. III. Synthesis of s-Triazolo [1, 5-α]-pyridine Ring.

Abstract

N-Aminopyridinium salt (I) was reacted with cyanide ion in water at room temperature to give 2-(4-pyridyl)-s-triazolo [1, 5-α] pyridine (IV). In alkaline medium I exists as an equilibrium mixture with the ylide type, N-iminopyridine (II) which was reacted with several nitrile compounds to produce s-triazolo [1, 5-α] pyridine derivatives by 1, 3 dipolarcyclo addition. This novel triazole ring could also be synthesized by ring closure of 1, 2-diaminopyridinium salt with a carboxylic acid, acid chloride or acid anhydride. Reaction of N-methylaminopyridinium salt (XIII) or N-acetamidopyridinium salt (XIV) with cyanide ion did not afford any 1, 3-dipolar cycloaddition products. Explanation for the difference in reactivity among I, XIII and XIV was attempted from each pKa' values.