New Facile Tandem Route to Oxo- and Thioxo[1,2,4]triazolo[1,5-<i>a</i>]pyridinium Salts

2-Arylsulfanyl- and benzylsulfanylpyridinium N-arylimides (2), easily available from tetrazolo[1,5-b]pyridinium salts (1), participate in 1,3-dipolar cycloaddition with aryl isothiocyanates and aryl isocyanates to result in formation of fused thioxo- and oxo[1,2,4]triazolium salts (5 and 12), respectively. This transformation is interpreted as a regular 1,3-cycloaddition followed by spontaneous elimination of the aryl- or benzylsulfanyl group. Formation of these triazolium salts can be followedunder appropriate reaction conditionsby ring-opening reactions to afford some new triazolyldienes (6). Recognition of the intermediate participation of the thiolate anion along the pathway 1 → 5 allowed elaboration of a simple procedure to 5 implying a tandem reaction sequence.