3,4-Bis(bromomethyl)thieno[2,3-b]thiophene: Versatile Precursors for Novel Bis(triazolothiadiazines), Bis(quinoxalines), Bis(dihydrooxadiazoles), and Bis(dihydrothiadiazoles)

A synthesis of novel bis(triazolothiadiazines) 11, 12, 13, 14, bis(quinoxalines) 16 and 17, bis(thiadiazoles) 24 and 25, and bis(oxadiazole) 31, which are linked to the thieno[2,3-b]thiophene core via phenoxymethyl group, was reported. Thus, reaction of the bis(α-bromoketones) 6 and 7 with the corresponding 4-amino-3-mercapto-1,2,4-triazole derivatives 8, 9, 10 in ethanol–DMF mixture in the presence of a few drops of triethylamine as a catalyst under reflux afforded the novel bis(5,6-dihydro-s-triazolo[3,4-b]thiadiazines) 11, 12, 13, 14 in 60–72% yields. The bis(quinoxalines) 16 and 17 were also synthesized as a sole product in high yields by the reaction of 6 and 7 with o-phenylenediamine 15 in refluxing acetonitrile in the presence of piperidine as a catalyst. Cyclization of the bis(aldehyde thiosemicarbazones) 20 and 21 with acetic anhydride afforded the corresponding bis(4,5-dihydro-1,3,4-thiadiazolyl) derivatives 24 and 25 in good yield. Bis(5-phenyl-2,3-dihydro-1,3,4-oxadiazole) derivative 31 could be obtained in 67% yield by cyclization of the appropriate bis(N-phenylhydrazone) 29 in refluxing acetic anhydride for 3 h.