Highly regioselective synthesis of 4-hydroxy-6-methyl-3-(3-R-sulfanyl-7H- [1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-6-yl)-2H-pyran-2-ones

Abstract

Bicyclic systems based on [1,2,4]triazolo[3,4-b]- [1,3,4]thiadiazine attract interest from the synthetic viewpoint. In particular, [1,2,4]triazolo[3,4-b][1,3,4]- thiadiazine derivatives exhibit various kinds of pharmacological activity, such as bactericidal [1], CNS stimulating [2], and antimicrobial [3]. Several [1,2,4]triazolo[3,4-b][1,3,4]thiadiazines have also attracted a great deal of interest as a new potent chemotype [4] for selective inhibition of phosphodiesterase 4 (PDE4). In continuation of our search for biologically active nitrogen and sulfur heterocycles [5–8], it was decided to synthesize the title compounds.