Preparation of New Nitrogen-Bridged Heterocycles. XIV. Further Investigation of the Desulfurization and the Rearrangement of Pyrido [1, 2-d] -1, 3, 4-thiadiazine Intermediates

Abstract

The formation of pyrazolo [1, 5-a] pyridine derivatives via the desulfurization and the rearrangement of pyrido [1, 2-d]-1, 3, 4-thiadiazine intermediates having various substituents at the 2-and 4-positions was investigated, and the wide applicability of this approach to the syntheses of pyrazolo [1, 5-a] pyridines was established. The substituent effect in these reactions was also clarified. The possibility of the extension of this reaction to other heterocyclic systems such as pyrido [1, 2-b]-pyridazine and pyrido [2, 1-f]-1, 2, 4-triazine was examined, but only pyridinium 1-aminide and 1, 2, 4-triazolo [1, 5-a] pyridine were obtained instead of the expected heterocyclic compounds.