The synthesis of 1,3,4-thiadiazol-2(3H)-iminium bromides, which are intermediates in the most commonly used synthetic approach to imidazo[2,1-b][1,3,4]thiadiazoles, and a single crystal X-ray diffraction study of one of these iminium bromides are described. Cyclization of the resulting 1,3,4-thiadiazol-2(3H)-iminium bromides under microwave irradiation afforded imidazo[2,1-b][1,3,4]thiadiazoles in 80-100% yields. 3,4]thiadiazoles are an important class of fused heterocyclic compounds that have attracted attention due to their diverse range of biological activities. 1 Indeed, these compounds have been shown to possess crucial effects such as anticancer, 2,3 antibacterial, 4-7 antitubercular, 3,5,8 antifungal, 6,7,9,10 antimicrobial, 3,7,10,11 analgesic, 7,12 anticonvulsant 12 and antihyperlipidemic 13 activities. In addition, anti-inflammatory, 10,14 antisecretory, 15 antiapoptotic, 16 anthelmintic, 17 diuretic, 18 leishmanicidal, 19 cardiotonic, 20 and herbicidal 21 effects have also been reported. Thus, the imidazo[2,1-b][1,3,4]thiadiazoles are thought to have tremendous potential in medicinal chemistry. Recently, a novel method for synthesizing imidazo[2,1-b][1,3,4]thiadiazoles by the reaction of 4,5-disubstituted-N-arylaminoimidazole-2-thiones with isocyanides in the presence of azodicarboxylates has been reported. 22 However, the most commonly used method for the preparation of imidazo[2,1-b][1,3,4]thiadiazole 1 is the one-pot reaction of 5-substituted-2-amino-1,3,4-thiadiazole 2with appropriate !-haloketone 3. Since 1952, beginning with the work of two-step synthesis of 1 by Matsukawa and Ban, 23 numerous studies on the reaction of 2 and 3 have been reported. A plausible mechanism involving a 1,3,4-thiadiazol-2(3H)-iminium bromide 4 for the one-pot synthesis is outlined in
