Synthesis of Coumarin Substituted Triazolothiadiazine Derivatives via Ring Transformation Reaction

Abstract

A novel ring transformation reaction for the synthesis of 3-(3-aryl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-6-yl)-2H-chromen-2-ones has been described. Reaction of 3-(2-bromoacetyl)coumarins (1) with 5-aryl-1,3,4-oxadiazole-2-thiol (2) gave ketones (4a–h). The in situ formed ketones (4a–h) were reacted with hydrazine hydrate to give 3-(3-aryl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-6-yl)-2H-chromen-2-ones (3a–h) and not 5 or 6. The compounds (3a–h) can also be prepared by the reaction of 3-(2-bromoacetyl)coumarins (1) with 5-aryl-1,3,4-oxadiazole-2-thiol (2) in anhydrous ethanol to give corresponding 3-(2-(5-aryl-1,3,4-oxadiazol-2-ylthio)acetyl)-2H-chromen-2-ones (4a–h). These on reaction with hydrazine hydrate in acetic acid gave corresponding 3-(3-aryl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-6-yl)-2H-chromen-2-ones (3a–h).