First Synthesis of the Novel Triazolo[3,4-b][1,3,4]Thiadiazoles and Triazolo[3,4-b][1,3,4]Thiadiazines Linked Chromeno[2,3-b]Pyridine

The novel 3-(4-amino-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-3-yl)-2H-chromeno[2,3-b]pyridine-2,5(1H)-dione (3) was efficiently synthesized from reaction of ethyl 2,5-dioxo-1,5-dihydro-2H-chromeno[2,3-b]pyridine-3-carboxylate (2) with thiocarbohydrazide. Compound 3 was utilize as building block for building a various heterocyclic systems linked chromeno[2,3-b]pyridine-2,5(1H)-dione. Reaction of compound 3 with some heterocyclic aldehydes afforded the condensation products 6 and 7. Treatment of compound 3 with some mono- and bi-electrophilic reagents afforded triazolo[3,4-b][1,3,4]thiadiazoles and triazolo[3,4-b][1,3,4]thiadiazines linked chromeno[2,3-b]pyridine, respectively. Finally, compound 3 reacted with 2,3-dichloroquinoxaline yielding the novel chromeno[2,3-b]pyridine bearing annulated triazolothiadiazinoquinoxaline 18. The obtained products were examined for their antimicrobial effectiveness appearing variable inhibitory action toward the used microorganisms.